U

SCHOLAR Study Guide

SQA Advanced Higher Biology
Unit 3b
Physiology, Health and Exercise

Jaquie Burt
Lasswade High School Centre

Lorraine Knight
Heriot-Watt University

Heriot-Watt University
Edinburgh EH14 4AS, United Kingdom.

First published 2001 by Heriot-Watt University.
This edition published in 2010 by Heriot-Watt University SCHOLAR.
Copyright © 2010 Heriot-Watt University.
Members of the SCHOLAR Forum may reproduce this publication in whole or in part for
educational purposes within their establishment providing that no profit accrues at any stage,
Any other use of the materials is governed by the general copyright statement that follows.
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system
or transmitted in any form or by any means, without written permission from the publisher.
Heriot-Watt University accepts no responsibility or liability whatsoever with regard to the
information contained in this study guide.

Distributed by Heriot-Watt University.
SCHOLAR Study Guide Unit 3: Advanced Higher Biology
1. Advanced Higher Biology
ISBN 978-1-906686-10-9
Printed and bound in Great Britain by Graphic and Printing Services, Heriot-Watt University,
Edinburgh.

Acknowledgements
Thanks are due to the members of Heriot-Watt University’s SCHOLAR team who planned and
created these materials, and to the many colleagues who reviewed the content.
We would like to acknowledge the assistance of the education authorities, colleges, teachers
and students who contributed to the SCHOLAR programme and who evaluated these materials.
Grateful acknowledgement is made for permission to use the following material in the
SCHOLAR programme:
The Scottish Qualifications Authority for permission to use Past Papers assessments.
The Scottish Government for financial support.
All brand names, product names, logos and related devices are used for identification purposes
only and are trademarks, registered trademarks or service marks of their respective holders.

i

Contents
1 The cardiovascular system
1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . .
1.2 Structure and function of the cardiovascular system (CVS)
1.3 Pathology of cardiovascular disease . . . . . . . . . . . .
1.4 Essay Question . . . . . . . . . . . . . . . . . . . . . . . .
1.5 Learning Points . . . . . . . . . . . . . . . . . . . . . . . .

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2 Exercise and the cardiovascular system
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . .
2.2 Risk factors and prevention of cardiovascular disease
2.3 Effect of exercise on the CVS . . . . . . . . . . . . . .
2.4 The ’athletic heart’ . . . . . . . . . . . . . . . . . . . .
2.5 Principles of exercise testing . . . . . . . . . . . . . .
2.6 Essay Question . . . . . . . . . . . . . . . . . . . . . .
2.7 Learning Points . . . . . . . . . . . . . . . . . . . . . .

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3 Exercise and metabolism - energy
3.1 Introduction . . . . . . . . . . . . . . . . .
3.2 The need for energy . . . . . . . . . . . .
3.3 Dietary recommendations for health . . .
3.4 Energy expenditure and its measurement
3.5 Essay Question . . . . . . . . . . . . . . .
3.6 Learning Points . . . . . . . . . . . . . . .

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4 Exercise and metabolism - body composition and weight control
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.2 Measurement of body composition . . . . . . . . . . . . . . . . .
4.3 Weight control and obesity . . . . . . . . . . . . . . . . . . . . . .
4.4 Effect of exercise on body composition and weight control . . . .
4.5 Essay Question . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.6 Learning Points . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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5 Osteoporosis and diabetes mellitus
5.1 Introduction . . . . . . . . . . . .
5.2 Osteoporosis and bone growth .
5.3 Diabetes mellitus . . . . . . . . .
5.4 Essay Question . . . . . . . . . .
5.5 Learning Points . . . . . . . . . .

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6 End of Unit 3b Test (NAB)

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ii

CONTENTS

Answers to questions and activities
1
The cardiovascular system . . . . . . . . . . . . . . . . . . . . .
2
Exercise and the cardiovascular system . . . . . . . . . . . . . .
3
Exercise and metabolism - energy . . . . . . . . . . . . . . . . .
4
Exercise and metabolism - body composition and weight control
5
Osteoporosis and diabetes mellitus . . . . . . . . . . . . . . . .

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© H ERIOT-WATT U NIVERSITY

1

Topic 1

The cardiovascular system

Contents
1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2

1.2 Structure and function of the cardiovascular system (CVS) . . . . . . . . . . . .
1.2.1 Structure and function of blood vessels . . . . . . . . . . . . . . . . . .

2
2

1.2.2 Structure and function of the heart . . . . . . . . . . . . . . . . . . . . .
1.2.3 The cardiovascular system . . . . . . . . . . . . . . . . . . . . . . . . .

7
9

1.2.4 The cardiac cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.2.5 Blood pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

10
12

1.2.6 Heart rate, stroke volume and cardiac output . . . . . . . . . . . . . . .
1.2.7 Relationship between heart rate, stroke volume and cardiac output . . .

13
14

1.3 Pathology of cardiovascular disease . . . . . . . . . . . . . . . . . . . . . . . .
1.3.1 Cardiovascular disease . . . . . . . . . . . . . . . . . . . . . . . . . . .

14
14

1.3.2 Incidence of coronary heart disease . . . . . . . . . . . . . . . . . . . .
1.4 Essay Question . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

15
17

1.5 Learning Points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

17

Learning Objectives
After studying this Topic, you should be able to:
• state the components of the cardiovascular system (CVS) and explain their
functions;
• state the normal values for blood pressure, heart rate, stroke volume and cardiac
output;
• describe the pathophysiology of atherosclerosis, thrombosis, angina pectoris,
myocardial infarction (heart attack), hypertension, stroke;
• state the incidence of these diseases in the the UK and other countries.

2

TOPIC 1. THE CARDIOVASCULAR SYSTEM

1.1

Introduction

In this Topic we will study the anatomy (structure) and physiology (function) of the normal
cardiovascular system (the heart and blood vessels) before going on to look at the
physiology of some of the diseases (pathophysiology) of the cardiovascular system.

1.2

Structure and function of the cardiovascular system
(CVS)

Learning Objective



After studying this section, you should be able to:
• state the components of the cardiovascular system (CVS) and explain their
functions;

Æ

• state the normal values for blood pressure, heart rate, stroke volume and cardiac
output.

The components of the cardiovascular system are: the heart which pumps blood
through a system of interconnected blood vessels which carry the blood around the
body. We will look at each in turn.

1.2.1

Structure and function of blood vessels

There are three types of blood vessel: arteries, capillaries and veins.
In the Web version of this Topic, there is a link to a Web page that shows a micrograph
of a cross-section through an artery.
Blood is pumped from the heart into arteries which quickly branch into smaller arteries.
Eventually these branch into tiny, thin-walled vessels called capillaries which permeate
every organ in the body. The capillaries then begin to join up into larger vessels called
veins which carry the blood back to the heart.

How arteries, capillaries and veins are interconnected
5 min

Figure 1.1 shows how arteries, capillaries and veins are interconnected. Use the terms
in the boxes below to complete the flow chart. (You can check your answers on the Web
version of this Topic.)

© H ERIOT-WATT U NIVERSITY



1.2. STRUCTURE AND FUNCTION OF THE CARDIOVASCULAR SYSTEM (CVS)

Figure 1.1: How arteries, capillaries and veins are connected

1.2.1.1 Structure and function of arteries, veins and capillaries
Both arteries and veins consist of the following:
• a central lumen through which blood flows;
• tunica intima - this layer lines the lumen and is made up of endothelium (single
layer of smooth cells). It minimises friction between the blood and the wall of the
vessel;
• tunica media - this middle layer contains smooth muscle, collagen and elastic
fibres;
• tunica externa - this outer layer contains collagen fibres and some elastic fibres.
The function of an artery is to carry blood away from the heart under pressure (from the
heartbeat) while veins carry blood back to the heart. The pressure in veins is much less
than that in arteries. As a result the structure of arteries and veins differ in the following
ways:
• in arteries the tunica media is much thicker and stronger than in veins, containing
many more elastic and muscle fibres. The elastic tissue enables the artery wall to
stretch and recoil under pressure from the heartbeat.
• the lumen in arteries is much smaller than in veins.

© H ERIOT-WATT U NIVERSITY

3

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TOPIC 1. THE CARDIOVASCULAR SYSTEM

Figure 1.2 below shows a transverse section through an artery.

Figure 1.2: Transverse section through an artery
As blood flows along an artery, the elastic wall stretches and then recoils, pushing the
blood on to the next part of the artery. This ’pulse’ of stretching and recoiling passes
along the length of an artery and can be felt in places where an artery is close to the
surface of the skin, for example in the wrist or neck. However as blood passes along the
artery the friction between the blood and the walls of the artery reduces the rate of flow
of blood and therefore reduces blood pressure. Thus the further away from the heart an
artery is, the lower is the blood pressure.
The function of capillaries (see Figure 1.3 below) is to allow the exchange of materials
between the blood and the cells of the body. To enable this to take place efficiently
the walls of capillaries consist only of a single layer of endothelium and have a tiny
diameter, approximately 7 m, which is about the same diameter as a red blood cell.
The walls of the capillaries are permeable as a result of tiny gaps which exist between
the cells of the endothelium. By the time the blood reaches the capillaries from the
arteries the pressure and flow rate have decreased greatly. This is beneficial because
a low pressure reduces fluid loss through the permeable capillary walls while a low flow
rate allows sufficient time for the exchange of materials between the blood and the body
cells.

© H ERIOT-WATT U NIVERSITY

1.2. STRUCTURE AND FUNCTION OF THE CARDIOVASCULAR SYSTEM (CVS)

Figure 1.3: Transverse section through a capillary
We have seen that the function of veins (see Figure 1.4 below) is to carry blood back to
the heart.

Figure 1.4: Transverse section through a vein

© H ERIOT-WATT U NIVERSITY

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TOPIC 1. THE CARDIOVASCULAR SYSTEM

We also know that capillaries join up to form veins. By the time blood has reached a
vein, its pressure is very low. This is why veins have a much thinner tunica media than
arteries. However the problem with veins having such a low blood pressure is how to
get blood back to the heart, especially from those veins in the leg which are furthest
away from the heart and in which blood must flow against the force of gravity. Many
of these veins lie very close to muscles: when the muscles contract, they squeeze the
veins, temporarily increasing the blood pressure. The veins also contain valves which
allow the blood to flow in only one direction, back towards the heart. You can see how
valves help blood to flow in one direction by looking at the activity ’Blood flow in veins’
below.
Q1: From the diagrams shown in Figure 1.2, Figure 1.3 and Figure 1.4 above, name
three differences in structure between an artery and a vein.
Q2: How are these differences in structure related to the functions of arteries and
veins?
Q3: Name two ways in which the structure of capillaries is different from both arteries
and veins.
Q4:

How are these differences in structure related to the function of capillaries?

Structure of artery, vein and capillary
10 min

This activity is only available on the Web version of this Topic. A roll-over activity showing
the functions of the various structures of an artery, vein and capillary is shown.

Blood pressure differences in arteries, capillaries and veins
10 min

The graph in Figure 1.5 below shows how blood pressure varies in different blood
vessels. Use the terms underneath the graph to complete the boxes. (You can check
your answers on the Web version of this Topic.) Then answer the questions which follow.

Figure 1.5: Pressure differences in different blood vessels
© H ERIOT-WATT U NIVERSITY

1.2. STRUCTURE AND FUNCTION OF THE CARDIOVASCULAR SYSTEM (CVS)

7

Q5: Can you explain why the blood pressure oscillates (goes up and down) in the
arteries? (Hint - think about the heartbeat.)

Blood flow in veins
This activity is only available on the Web version of this Topic. An animation showing
how blood flows in veins is shown.

5 min

Summary of arteries, capillaries and veins
The boxes at the bottom of Figure 1.6 contain information about arteries, capillaries and
veins. Use the information to complete the table. (You can check your answers on the
Web version of this Topic.)

Figure 1.6: Summary of arteries, capillaries and veins

1.2.2

Structure and function of the heart

In this section we will look at the internal and external structure of the mammalian heart.

1.2.2.1 Internal structure of the heart
The heart is a muscular pump which keeps blood flowing continuously in one direction
round the body. It starts pumping before we are born and can continue for a short time
after death.
The heart is a muscular bag consisting of four chambers through which blood flows.
The right and left sides of the heart are completely separated from each other by the
© H ERIOT-WATT U NIVERSITY

5 min

8

TOPIC 1. THE CARDIOVASCULAR SYSTEM

septum. The two upper chambers are called atria, while the lower chambers are known
as ventricles. The following activity looks at its structure in more detail.

Internal structure of the heart
30 min

The diagram in Figure 1.7 below shows the internal structure of the heart. Read the
following information carefully then label the heart diagram using the terms in the boxes.
There is an interactive version available on the Web where you can check your answers.
The left atrium receives oxygenated blood (red) from the lungs via two pulmonary
veins. The blood flows into the left ventricle through the bicuspid valve. When the
ventricle contracts the blood is forced out through the semilunar valve into the aorta,
the largest artery in the body. The blood is passed around the body, materials are
exchanged and deoxygenated blood (blue) flows back to the right atrium via two main
veins called the superior and inferior venae cavae. (Superior means ’above’ while
inferior means ’below’.) The blood flows through the tricuspid valve into the right
ventricle and from there into the pulmonary artery which carries it to the lungs.
The bicuspid and tricuspid valves are known as the atrio-ventricular valves. They prevent
the backflow of blood into the atria when the ventricles contract. These valves are
attached to the ventricle walls by tendons called chordae tendinae which prevent the
valves inverting (turning inside-out) when the ventricles contract. The semilunar valves
(found at the entrance to the aorta and pulmonary artery) prevent blood flowing back
into the ventricles when they relax.
The walls of the atria are thinner than those of the ventricles because they only have
to force blood a very small distance into the ventricles. The walls of the ventricles are
thicker because they have to provide enough force to pump the blood further. The wall
of the left ventricle is thicker than that of the right since the right ventricle only needs to
pump blood to the lungs (which are next to the heart) while the left ventricle has to pump
blood all round the body.
Hint when labelling the sides of the heart - the heart in the diagram is a mirror image of
your heart.

© H ERIOT-WATT U NIVERSITY

1.2. STRUCTURE AND FUNCTION OF THE CARDIOVASCULAR SYSTEM (CVS)

Figure 1.7: Internal structure of the heart
Q6: Why are the bicuspid and tricuspid valves also known as atrio-ventricular valves?
Q7: What is the function of valves in the heart?
Q8: What is the function of the chordae tendinae?

1.2.2.2 External structure of the heart
The Web version of this Topic enables you to visit a web-site showing a diagram of the
external structure of the heart.

1.2.3

The cardiovascular system

The cardiovascular system is described as a closed, double circulatory system.
It is described as closed because blood is transported around the body within blood
vessels. (In some animals, for example grasshoppers, the blood bathes the internal
body tissues and is not confined to vessels - this is known as an open circulatory
system.)
The CV system is described as a double circulation because, in one complete
circulation of the body, blood passes through the heart twice, once going to the lungs
(pulmonary circulation) and once to the rest of the body systems (systemic circulation).
The right side of the heart receives deoxygenated blood from the body and passes it to
the lungs to be reoxygenated. The left side receives oxygenated blood from the lungs
and passes this to the rest of the body tissues. Figure 1.8 shows a highly simplified

© H ERIOT-WATT U NIVERSITY

9

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TOPIC 1. THE CARDIOVASCULAR SYSTEM

diagram of the CV system in a mammal. (There is an animated version of this diagram
in the Web version of the activity ’The cardiovascular system’.)

Figure 1.8: The cardiovascular system

The cardiovascular system
20 min

This activity is only available on the Web version of this Topic. An animation of Figure 1.8
above is shown.

1.2.4

The cardiac cycle

The cardiac cycle refers to the pattern of contraction and relaxation of the heart during
one complete heartbeat. Contraction of the heart muscle is known as systole while
relaxation is known as diastole.
Q9: If an individual has a heart rate of 75 beats per minute, what is the average length
of time of one heartbeat?
The atria (upper chambers) contract a fraction of a second before the ventricles contract.
During atrial systole, the two atria contract simultaneously, the atrio-ventricular
valves (bicuspid and tricuspid valves) are open and blood is forced through into the
ventricles. At this point the ventricles are relaxed (in diastole) and the semilunar valves
are closed.
Atrial systole is followed about 0.1 seconds later by ventricular systole. The atrioventricular valves are closed and blood is forced out through the semilunar valves
into the arteries.

© H ERIOT-WATT U NIVERSITY

1.2. STRUCTURE AND FUNCTION OF THE CARDIOVASCULAR SYSTEM (CVS)

During atrial and ventricular diastole, blood from the pulmonary veins and the venae
cavae fill up the atria. Then the cycle repeats. Figure 1.9, Figure 1.10 and Figure 1.11
describe the cardiac cycle. An animated version of this is available on the Web version
of the activity ’The cardiac cycle’.

Figure 1.9: Atrial systole

Figure 1.10: Ventricular systole

© H ERIOT-WATT U NIVERSITY

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TOPIC 1. THE CARDIOVASCULAR SYSTEM

Figure 1.11: Diastole

The cardiac cycle
15 min

This activity is only available on the Web version of this Topic.
Figure 1.9, Figure 1.10 and Figure 1.11 is shown.

An animation of

Q10: What is meant by the terms systole and diastole?
Q11: During atrial systole which heart valves are open and which are closed?
Q12: During which process, ventricular systole or diastole, is the pressure greater in
the ventricles? Give a reason for your answer.

1.2.5

Blood pressure

We have seen that the cardiac cycle describes the pumping of the heart, with each
heartbeat consisting of one contraction (systole) and relaxation (diastole) of the heart
(cardiac) muscle. The heartbeat is rhythmical, with the heart beating more than 2.5 x
109 times during a person’s life. The cardiac cycle has a characteristic "lub-dub" sound
that can be heard through a stethoscope. This sound is caused by the valves in the
heart opening and closing as the blood passes through the heart.
Blood pressure describes the pressure in the aorta (the main artery out of the heart).
It can be measured in the large artery in the arm by using an instrument called a
sphygmomanometer and a stethoscope. Two types of blood pressure are measured:
• systolic blood pressure: pressure in the arteries during systole (when the heart
contracts).
• diastolic blood pressure: pressure in the arteries during diastole (when the heart
relaxes).
Systolic blood pressure changes during exercise and can increase to 200 mm Hg, but
the diastolic blood pressure usually remains constant.
© H ERIOT-WATT U NIVERSITY

1.2. STRUCTURE AND FUNCTION OF THE CARDIOVASCULAR SYSTEM (CVS)

13

Conventionally a blood pressure measurement is given as a ratio in the form of systolic
pressure/diastolic pressure. For example, the normal value for an adult would be 120/80,
but this can be higher in older people and lower in younger people.
The blood pressure increases when the heart is overworking, placing a strain on the
circulatory system. It is important to maintain the blood pressure within the normal
limits as high and low blood pressure can be detrimental to health. For example, low
blood pressure can cause kidney problems and high blood pressure can result in a heart
attack.

Measuring blood pressure
This activity is only available on the Web version of this Topic. A simple demonstration
of measuring blood pressure is shown.

1.2.6

Heart rate, stroke volume and cardiac output

Blood does not flow into the arteries continuously, instead every time the heart beats it
pumps blood into the arteries. As the blood is forced into the arteries they expand due
to the elastic fibres in their walls and then recoil. This action can be felt as a pulse.
The pulse rate indicates the heart rate because the arteries pulse every time the heart
contracts. Therefore, the heart rate can be measured by taking the pulse.
The pulse can be measured anywhere that the arteries are close to the surface of the
skin. The most common places are the radial artery in the wrist and the carotid artery
in the neck (Figure 1.12). The pulse is measured when a person is sitting or standing
still by gently placing two fingers over the pulse and counting the number of pulses in a
certain period of time. The pulse is usually counted for 10 - 15 seconds and then used
to calculate the number of beats per minute. It is important not to press too hard as
this constricts the artery and can slow the pulse rate. The thumb also contains a strong
pulse and can be confusing (gently press your thumb and forefinger together and you
should be able to feel a pulse).

Figure 1.12: Measuring the pulse

© H ERIOT-WATT U NIVERSITY

10 min

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TOPIC 1. THE CARDIOVASCULAR SYSTEM

Your pulse rate when you are doing nothing is described as your resting pulse rate. On
average resting pulse rates are between 60 - 100 beats per minute. Generally the fitter
a person is the lower their resting pulse rate is; very fit athletes may have resting pulse
rates as low as 30 - 40 beats per minute. However, resting pulse rates also decrease
with age.

1.2.7

Relationship between heart rate, stroke volume and cardiac output

Cardiac output is the volume of blood pumped out of the heart every minute. It is usually
measured in litres/minute. The stroke volume is the volume of blood pumped out of the
heart with each heartbeat. An individual’s cardiac output can therefore be worked out
by multiplying the heart rate by the stroke volume. This relationship can be written as:
Cardiac output (CO) = heart rate (HR) x stroke volume (SV)
Q13: When resting, an individual’s pulse rate is 64 beats/minute and their stroke volume
is 75 ml. What is their cardiac output?
Q14: If an individual’s cardiac output is 12.7 l/min and their stroke volume is 110 ml,
what is their pulse rate (to the nearest whole number)?

1.3

Pathology of cardiovascular disease

Learning Objective



After studying this section, you should be able to:
• describe the pathophysiology of atherosclerosis, thrombosis, angina pectoris,
myocardial infarction (heart attack), hypertension, stroke;

Æ

• state the incidence of these diseases in the the UK and other countries.

1.3.1

Cardiovascular disease

Cardiovascular disease (CVD) is the general name given to diseases which affect the
heart and blood vessels. Coronary heart disease (CHD) refers to diseases affecting the
heart and coronary blood vessels. The main processes involved in cardiovascular and
coronary heart disease are atherosclerosis and hypertension.
Atherosclerosis is the name given to the build up of plaque (a substance containing
fats and cholesterol) on the inner layers of artery walls. Instead of being smooth and
elastic, the layers become thickened and irregular with the lumen of the artery becoming
narrower. This in turn reduces the circulation of blood and can lead to an increase in
blood pressure.
Hypertension is said to occur when the blood pressure is greater than 160/95 mm Hg
(remember normal blood pressure is about 120/80 mm Hg). Just as atherosclerosis
can lead to an increase in blood pressure, hypertension can accelerate atherosclerosis
in arteries. Nearly 20% of the adult population in the UK suffer from hypertension

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1.3. PATHOLOGY OF CARDIOVASCULAR DISEASE

15

(high blood pressure) which often goes undetected until a heart attack or stroke occurs.
Therefore, it is important to have blood pressure checked on a regular basis and to adopt
a healthy lifestyle to prevent hypertension.
When someone has a stroke or a heart attack (properly known as a myocardial infarction
or MI), it can appear to happen ’out of the blue’. However the damage leading up to it
may have been building up, sometimes for many years, as a result of atherosclerosis
or hypertension. We saw above that during atherosclerosis the inner layers of arteries
become thickened with a build up of plaque. This can cause a blood clot (or thrombus)
to form inside the artery, which restricts the flow of blood. If the clot leads to a complete
blockage of the blood vessel, it is known as a thrombosis. If this happens in a coronary
artery, which supplies the heart muscle, it causes a coronary thrombosis. The part of
the heart muscle supplied by this artery will not receive oxygen and will die - this is a
heart attack. The severity of the heart attack (or myocardial infarction) depends on how
much of the heart muscle is affected.
Sometimes part of a blood clot will break off from the main thrombus and travel to other
blood vessels. If it reaches a narrower artery it may cause a blockage at that point.
This is known as an embolism. If the embolism occurs in a coronary artery, a heart
attack results as above. If the embolism occurs in an artery in the brain a stroke results.
Again the damage caused depends on the area of the brain which has been deprived of
oxygen.
Sometimes the atherosclerosis present in heart arteries is not sufficient to restrict blood
flow when a person is at rest. However during exercise the heart muscle’s demand
for oxygen increases. Due to the narrowing of the arteries blood flow cannot increase
sufficiently to meet the needs of the heart and the result is severe chest pain which
disappears again within minutes of stopping the exercise. This condition is known as
angina pectoris. An angina attack may also be brought on by emotional stress if it
makes the heart beat faster.

Atherosclerosis
This activity is only available on the Web version of this Topic. A short animation showing
the process of atherosclerosis is presented.

1.3.2

Incidence of coronary heart disease

The prevalence of coronary heart disease (CHD) differs in countries throughout the
world. The UK has one of the highest rates of heart disease in the world, mainly as a
result of lifestyle factors. In countries where the diet is low in saturated fats (such as
Japan where fish, rather than meat, is a major dietary component), smoking rates are
low and people lead active lives the incidence of heart disease is lower. CHD is generally
associated with affluence and used to affect only those in developed countries; it is now
becoming increasingly common in developing countries.
Coronary heart disease is increasing in prevalence due to changing life-styles and
people living longer. In the past infectious diseases accounted for most deaths and
relatively few people reached old age, so degenerative diseases were less common. In
developing countries where standards of living are rising and health care is improving,
degenerative diseases, such as CHD, are becoming more common.

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10 min

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TOPIC 1. THE CARDIOVASCULAR SYSTEM

Although the death rate from CHD has fallen over the past 20 years in the UK it still has
one of the highest incidences of coronary heart disease in the world. It was responsible
for over 140 000 deaths in 1997, making CHD one of the most common causes of death
in the UK. CHD usually occurs in people over 65 but is becoming increasingly common
in younger people, for example over 4000 men aged 45-54 died from CHD in 1997.
Scotland, Northern Ireland and the north of England have the highest rates of CHD in
the UK. The disease is also more common among men, the poor and certain ethnic
groups.

Death rates from CHD
10 min

Figure 1.13 shows the number of deaths from coronary heart disease in different
countries around the world. Study the graph and then use it to answer the questions
below.

Figure 1.13: Global incidence of coronary heart disease
Q15: In which sex is coronary heart disease most prevalent?
a) Males
b) Females
Q16: Which of the following countries has the highest death rate from CHD?
a)
b)
c)
d)

Italy
UK
Ireland
Germany

Q17: In the Russian Federation three times as many men die from CHD as women.
a) True
b) False

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1.4. ESSAY QUESTION

1.4

Essay Question

This is an essay question similar to the style you will encounter in the SQA Advanced
Higher Examination. A total of 15 marks is available. You should hand your completed
essay to your tutor for marking.

Essay: Structure and function of blood vessels
Question
The cardiovascular system consists of the heart and blood vessels. Give an account of
the structure and function of the different types of blood vessel. (15 marks)

1.5

Learning Points

• The components of the cardiovascular system are the heart and blood vessels.
• There are three types of blood vessel: arteries, capillaries and veins.
• Arteries carry blood away from the heart and must be able to withstand the
pressure caused by the heartbeat. They have thick, elastic walls which can stretch
and recoil in response to the heartbeat. Blood pressure decreases as blood moves
along arteries away from the heart.
• Capillaries allow the exchange of materials to take place between the blood and
body cells. Their walls are only one cell thick and have a tiny diameter just wide
enough to enable red blood cells to pass through them. Blood pressure is less
than in arteries.
• Veins carry blood back to the heart. Blood pressure is very low in veins so that
they have much thinner, less elastic walls than arteries. They also contain valves
which prevents blood flowing backwards. Blood is pushed towards the heart when
the veins are squeezed as the muscles around them contract.
• Arteries have a smaller lumen than veins.
• The mammalian heart consists of two atria (upper chambers) and two ventricles
(lower chambers).
• The left and right sides of the heart are completely separated from each other by
the septum.
• The right atrium receives deoxygenated blood from the body via the venae cavae
and passes it to the right ventricle through the tricuspid valve. The right ventricle
pumps the blood out into the pulmonary artery which carries it to the lungs to be
reoxygenated.
• Oxygenated blood from the lungs is carried back to the left atrium of the heart via
the pulmonary vein. The left atrium passes the blood to the left ventricle through
the bicuspid valve. The left ventricle then pumps the blood out into the aorta which
carries it round the body.
• The bicuspid and tricuspid valves are known as atrio-ventricular (AV) valves.
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TOPIC 1. THE CARDIOVASCULAR SYSTEM

Semilunar valves are found at the entrance to the aorta and pulmonary artery.
Their function is to prevent the backflow of blood.
• The atrio-ventricular valves are attached to the walls of the ventricles by tendons
called chordae tendinae which prevent the valves inverting when the ventricles
contract.
• The atria have thinner walls than the ventricles because they only need to generate
enough pressure to push the blood down into the ventricles.
• The left ventricle is much thicker than the right because the left ventricle has to
pump blood all around the body while the right ventricle has only to pump blood to
the lungs, which are situated next to the heart.
• The mammalian circulatory system is a closed double circulation. It is said to be
closed because blood is carried round the body enclosed in vessels. It is a double
circulation because, in one complete circulation of the body, blood passes through
the heart twice, once going to the lungs (pulmonary circulation) and once to the
rest of the body systems (systemic circulation).
• The cardiac cycle refers to the pattern of contraction and relaxation of the heart
muscle which occurs during one complete heartbeat. Contraction of the heart
muscle is known as systole, while relaxation is called diastole.
• The pulse rate corresponds to the heart rate and can be measured by gently
placing the fingers over the pulse and counting. The heart rate increases directly
in proportion to the amount of work done.
• Normal resting heart rates are 60-100 bpm, but are lower in fitter people.
• The stroke volume is the volume of blood pumped out of the heart with each
heartbeat.
• Cardiac output is the volume of blood pumped out of the heart every minute. It is
usually measured in litres/minute.
• An individual’s cardiac output is be worked out by multiplying the heart rate by the
stroke volume.
• Blood pressure describes the pressure in the aorta and is measured using a
sphygmomanometer and stethoscope. Blood pressure in measured in mm Hg.
• Sytolic blood pressure is the pressure in the arteries when the heart contracts
(systole).
• Diastolic blood pressure is the pressure in the arteries when the heart relaxes
(diastole).
• Blood pressure is written as systolic/diastolic. Normal blood pressure for an adult
is 120/180 mm Hg.
• People with blood pressures over 160/95 mm Hg have high blood pressure and are
hypertensive. Hypertension is one of the main causes of cardiovascular disease
(CVD).

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1.5. LEARNING POINTS

19

• Atherosclerosis is another disease process which leads to CVD. It results from a
build up of plaque on the inner lining of arteries, which reduces the flow of blood
through the artery.
• Examples of CVD are: thrombosis, angina pectoris, myocardial infarction (heart
attack), stroke.
• A thrombosis occurs when a blood clot forms in a artery, completing blocking the
flow of blood. If this happens in one of the coronary arteries in the heart it causes
a heart attack or myocardial infarction. If it occurs in an artery in the brain it causes
a stroke.
• Angina pectoris occurs when the blood vessels in the heart are partially blocked
due to atherosclerosis. During exercise blood flow cannot increase to meet the
needs of the heart muscle and chest pain results. The pain disappears when the
exercise stops.
• Coronary heart disease (CHD) is more common in countries with high fat
diets, high smoking rates and sedentary lifestyles (such as the UK). Developing
countries tend to have lower incidences of CHD but numbers there are increasing.

End of Topic test
An online assessment is provided to help you review this topic.
30 min

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TOPIC 1. THE CARDIOVASCULAR SYSTEM

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21

Topic 2

Exercise and the cardiovascular
system

Contents
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . .
2.2 Risk factors and prevention of cardiovascular disease .
2.2.1 Modifiable risk factors . . . . . . . . . . . . . . .
2.2.2 Non-modifiable risk factors . . . . . . . . . . . .
2.3 Effect of exercise on the CVS . . . . . . . . . . . . . . .
2.3.1 Effect on heart rate and recovery time . . . . . .
2.3.2 Effect on blood pressure and cardiac output . . .
2.3.3 Distribution of blood to tissues . . . . . . . . . .
2.4 The ’athletic heart’ . . . . . . . . . . . . . . . . . . . . .
2.5 Principles of exercise testing . . . . . . . . . . . . . . .
2.5.1 Measuring fitness . . . . . . . . . . . . . . . . .
2.5.2 Stress testing and cardiac patients’ rehabilitation
2.6 Essay Question . . . . . . . . . . . . . . . . . . . . . . .
2.7 Learning Points . . . . . . . . . . . . . . . . . . . . . . .

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23
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31
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34

Learning Objectives
After studying this Topic, you should be able to:
• describe modifiable risk factors such as: diet, smoking, activity and obesity and
explain their roles in cardiovascular disease;
• describe non-modifiable risk factors such as: age, gender, heredity and race and
explain their roles in cardiovascular disease;
• describe the effect of exercise on heart rate, systolic and diastolic blood pressure,
cardiac output and recovery time;
• describe the distribution of blood to tissues during exercise;
• describe cardiac hypertrophy as a fundamental adaptation to increased workload
imposed by exercise training;
• explain the difference in stroke volume of the heart of an endurance athlete and
an untrained individual;

22

TOPIC 2. EXERCISE AND THE CARDIOVASCULAR SYSTEM

• describe the protective effects of exercise to include: improved myocardial
circulation, enhancing contractile properties of myocardium, improving blood lipid
profile, lowering heart rate and blood pressure, decreasing body fat;
• explain maximal and sub-maximal testing used to measure fitness;
• describe stress testing and cardiac patients’ rehabilitation.

© H ERIOT-WATT U NIVERSITY

2.1. INTRODUCTION

2.1

23

Introduction

In this Topic we will examine the risk factors involved in cardiovascular disease and how
they can be minimised. We will study the short term and long term effects which regular
exercise has on the heart and the rest of the body. Finally we will take a short look
at how cardiac patients can use exercise as a form of rehabilitation to increase their
recovery and survival chances.

2.2

Risk factors and prevention of cardiovascular disease

Learning Objective



After studying this section, you should be able to:
• describe modifiable risk factors such as: diet, smoking, activity and obesity and
explain their roles in cardiovascular disease;
• describe the protective effects of exercise to include: improved myocardial
circulation, enhancing contractile properties of myocardium, improving blood
lipid profile, lowering heart rate and blood pressure, decreasing body fat;

Æ

• describe non-modifiable risk factors such as: age, gender, heredity and race
and explain their roles in cardiovascular disease.

There are many factors which can contribute to cardiovascular disease. Some of these
factors can be decreased by lifestyle changes: these are known as modifiable risk
factors and include diet, smoking, activity and obesity. Those factors which cannot be
decreased by lifestyle changes are known as non-modifiable risk factors and include
age, gender, heredity (genetics) and race (ethnicity).

2.2.1

Modifiable risk factors

Diet
A person’s diet has a huge influence over their health. It is important to have a healthy,
balanced diet that is low in saturated fat and cholesterol. This limits the amount of fat
that is deposited in the arteries as well as having many other health benefits.
You may be aware of the need for many people to lower their cholesterol levels, but why
is this? Cholesterol is produced in the liver and is also consumed in the diet. It is a type
of lipid which plays important roles in the body. For example cholesterol is an important
component of cell membranes and some hormones. However it is only required in small
amounts and when very high levels are present in the blood the likelihood of developing
atherosclerosis increases. It is transported around the body by high and low density
lipoproteins (HDL and LDL, respectively). HDL are good for you because they remove
cholesterol from the tissues, transporting it to the liver where it is disposed of. LDL are
harmful when they are present at high levels since they promote the deposition of fat in
the blood vessels.
Saturated fats increase the amount of cholesterol that is produced by the liver and

© H ERIOT-WATT U NIVERSITY



24

TOPIC 2. EXERCISE AND THE CARDIOVASCULAR SYSTEM

passed into the blood, so by reducing the intake of saturated fats cholesterol levels
can be lowered. Butter, margarine, dairy products, chips, meat, cakes and biscuits all
contain high levels of saturated fats and are all abundant in the British diet. Saturated
fats should be minimised in the diet and replaced with unsaturated fats such as olive oil
whenever possible.
Although a small amount of alcohol is thought to be good for the health, excessive
drinking is not. Drinking too much alcohol raises the blood pressure and places a strain
on the heart and contributes to weight gain. Alcohol helps to increase the levels of
HDL cholesterol in the body, but this can also be achieved through exercise or weight
loss. Some components of alcoholic drinks are also thought to prevent blood clots from
forming, thereby reducing the risk of heart attacks and strokes. It has been found that
moderate drinkers (one drink a day for women and two for men) are at a lower risk of
coronary heart disease than heavy or non-drinkers. It is not recommended that nondrinkers start drinking to reduce the risk of heart diseases as the benefits may not be
due to the alcohol but to other lifestyle factors.
Recent research has indicated the importance of vitamins A, C and E in protecting
the body against coronary heart disease. These vitamins contain antioxidants that may
help to protect the HDL which removes cholesterol from the blood. These vitamins are
obtained by eating fruit and vegetables.
The fatty acids found in oily fish, such as salmon, make the blood less likely to clot by
thinning it. It is recommended that at least one serving of oily fish is eaten each week.
Fibre is also important as it reduces the amount of cholesterol that is absorbed from the
digested food in the intestine, thereby decreasing blood cholesterol levels.
Smoking
As soon as smoke is inhaled from a cigarette it has an effect on the body. Two
components of tobacco smoke have a major effect on the cardiovascular system:
• Nicotine increases the blood pressure by constricting the blood vessels.
• Carbon monoxide reduces the amount of oxygen that is carried by the blood as
it binds to haemoglobin more effectively than oxygen.
Both of these substances increase the heart rate as the heart has to work harder to
meet the energy demands of the body. A smoker’s heart rate may increase by as much
as 30 % when they are smoking.
Q1: A woman measured her pulse before and after smoking a cigarette. Her pulse
rates are shown in the table below. Use the data to calculate the percentage increase in
her heart rate after she had smoked. (Give your answer to the nearest whole number.)

Q2:

resting pulse

pulse (bpm)

before smoking

72

after smoking

92

Explain why the woman’s heart rate increased.

Some of the substances in smoke can damage the internal lining of arteries, thus
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2.2. RISK FACTORS AND PREVENTION OF CARDIOVASCULAR DISEASE

25

causing or accelerating atherosclerosis. Smoking also causes blood to clot more
readily, thus increasing the chances of a stroke or myocardial infarction (heart attack).
Furthermore smoking reduces the proportion of beneficial high density lipoproteins
(HDL) to harmful low density lipoproteins (LDL) which may lead to an increase in
cholesterol levels in the blood and in the deposition of fat in blood vessels.

What’s in a cigarette?
This activity is only available on the Web version of this Topic. A roll-over activity showing
some of the chemicals present in a cigarette is presented.

10 min

Activity
Everybody knows that exercise is good for you, but what are the actual benefits of
regular exercise? There are many different benefits of exercising on a regular basis
and improving your level of fitness.
Being physically fit reduces the risk of cardiovascular disease, with people who do not
exercise being twice as likely to develop heart disease. Regular exercise:
• strengthens the heart muscle (myocardium) so that it can pump more blood with
each beat - this lowers the resting heart rate;
• improves blood lipid profile by decreasing LDL and increasing HDL levels;
• lowers blood pressure by maintaining the elasticity of the arteries;
• helps weight loss by decreasing body fat.
Even a small amount of moderate exercise, such as walking, can improve the quality of
life and increase life expectancy.
Q3: Suggest three ways in which exercise prevents heart disease.

Benefits of exercise
This activity is only available on the Web version of this Topic. A roll-over activity showing
some benefits of exercise is presented.
Obesity
Obesity is an increasingly common problem in both adults and children. Although
obesity is more widespread in Europe, North America and Australia, it is becoming
more common in developing countries where Western lifestyles are being adopted
(Figure 2.1).

© H ERIOT-WATT U NIVERSITY

5 min

26

TOPIC 2. EXERCISE AND THE CARDIOVASCULAR SYSTEM

Figure 2.1: Prevalence of obesity around the world
Obesity is caused by overnutrition. If more energy is consumed than is used then the
excess is stored as fat by the body, resulting in weight gain. Being slightly overweight
does not pose any health risks, but if more weight is put on and a person becomes
obese then there may be serious health consequences. Obese people are at a higher
risk of developing cardiovascular diseases, including coronary heart disease, high blood
pressure, atherosclerosis, angina and stroke.
The health risks caused by being obese are drastically reduced when the excess weight
is lost. However, being obese makes it difficult to exercise which adds to the health
problems and makes it harder to lose weight.
It is currently estimated that 45 % of men and 34 % of women in Britain are overweight.
Although more men are overweight, more women are obese, with 16 % of men and 18
% of women being obese. In other words 1/3 of the overweight men are obese and 1/2
of the overweight women are obese.
Obesity is a multifactorial disease. British people are leading more and more sedentary
lives with few people doing physical jobs or exercising regularly. Large quantities of high
fat foods are consumed which, coupled with a lack of activity causes weight gain. Eating
a well balanced diet and not exceeding your energy needs prevents weight gain and
obesity.

2.2.2

Non-modifiable risk factors

Age
As you age the risk of developing CVD increases. This is because the arteries become
less elastic and blood pressure tends to increase. Also atherosclerosis is a normal part
of the aging process. Both high blood pressure and atherosclerosis are risk factors
in developing CVD. Men over the age of 45 and women over the age of 55 are at an
increased risk of cardiovascular disease. However the natural effects of aging can be
slowed by controlling your weight, having a healthy diet and taking regular exercise.

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2.2. RISK FACTORS AND PREVENTION OF CARDIOVASCULAR DISEASE

27

Gender
Men are at greater risk from CVD than women. Before the menopause men are
much more likely than women to suffer from CVD; after the menopause, although men
at still at greater risk, the difference in risk level decreases. On average a woman
develops coronary artery disease about 10 years later in life than men. The reasons
for these differences are not known, although the female hormone oestrogen may have
a protective role against heart disease. After the menopause oestrogen levels decrease,
while the woman’s risk of CVD increases.
Heredity
If your parents or siblings (brothers or sisters) had early CVD (before 55 years of age
for men, before 65 for women) then your risk of developing CVD is greater than that for
someone who has no family history of the disease. The greatest genetic risk seems to
be a mutation which leads to a predisposition to dangerously high levels of cholesterol.
Other possible genetic factors include a tendency to obesity and high blood pressure
(hypertension), both of which are risk factors for CVD. If a person is at greater risk
because of inherited factors, they should have their blood pressure and cholesterol
levels checked regularly. If they are too high they can be treated with medication. Also
such an individual can reduce their total risk by controlling the modifiable risk factors
mentioned previously.
Race (Ethnicity)
Studies have been done relating ethnicity to a greater risk of CVD which show that in
Britain, mortality rates amongst people from a South Asian background are around 40%
greater than among the white population and that early onset of the disease can be
two to three times higher. Similar results have been found in South Asian communities
living in different parts of the world. Although the reasons for these links are not known,
and research is ongoing, it has been found that people from a South Asian background
also have an increased rate of insulin resistance, a condition known to be a risk factor
in Type 2 diabetes. (This condition is discussed in more detail in Topic 5.) Diabetes
is also known to be a risk factor in the development of CVD. The risk can be reduced
by monitoring susceptible individuals for insulin resistance and diabetes so that these
conditions can be discovered early and treated. Also, as above, an individual can reduce
their total risk by controlling the modifiable risk factors mentioned above.

CVD risk factors
Some of the risk factors for CVD are shown below the table in Figure 2.2 below.
Write the risk factors into the correct columns in the table. (You can check your answers
on the Web version of this Topic.)

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5 min

28

TOPIC 2. EXERCISE AND THE CARDIOVASCULAR SYSTEM

Figure 2.2: CHD risk factors

2.3



Effect of exercise on the CVS

Learning Objective
After studying this section, you should be able to:
• describe the effect of exercise on heart rate, systolic and diastolic blood
pressure, cardiac output and recovery time;

Æ

• describe the distribution of blood to tissues during exercise.

2.3.1

Effect on heart rate and recovery time

The heart rate increases directly in proportion to the amount of work done, so the harder
you exercise the higher your heart rate will be. If you walk a mile your heart rate will
increase slightly but if you run the same distance your heart rate will increase a lot more
and you will probably feel short of breath and tired. Even though you have travelled the
same distance you worked harder when you were running.
The Web version presents an animation showing the differences in heart rate between
walking and running one mile.
Your heart rate increases when you exercise because the heart has to work harder to
meet the body’s demands. The muscles require more oxygen and energy and more

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2.3. EFFECT OF EXERCISE ON THE CVS

29

waste carbon dioxide is produced, therefore the blood needs to be pumped around the
body faster.
Recovery time is the length of time it takes your heart rate to return to normal once the
exercise is finished. The fitter a person is the faster is the recovery time.

Heart rate experiment
Two students carried out a heart rate test. One person performed the test while the
other acted as the time keeper.
Before doing any exercise student A’s pulse rate (while standing) was measured for
15 seconds. The student then did star jumps at a regular pace for 1 minute. The
pulse rate was measured for 15 seconds immediately after stopping exercising, then for
15 seconds every minute until it returned to normal. The student remained standing
throughout the experiment. The experiment was repeated for student B.
The results for the two students are shown in Figure 2.3. Use the data to plot the graph
(plot the graph for student A first and then the graph for student B).

Figure 2.3: Heart rate experiment graph
Q4: Which of the students is fitter?
a) Student A
b) Student B
Q5: Explain your answer to question 1.
Q6: Explain why the students remained standing throughout the experiment.

© H ERIOT-WATT U NIVERSITY

15 min

30

TOPIC 2. EXERCISE AND THE CARDIOVASCULAR SYSTEM

Try performing this experiment yourself. You can perform different exercises such as
running on the spot and step ups. Try to ensure that each person performs the activity
at the same pace. For example, if you are doing step ups try to complete each cycle in
a set period of time i.e. two seconds - you may find it useful to use a metronome to do
this.
Q7:

Why should each person perform the activity at the same rate?

2.3.2

Effect on blood pressure and cardiac output

During exercise a person’s systolic blood pressure usually increases but the diastolic
pressure remains fairly constant. Remember the systolic pressure is a measure of how
hard the ventricles are pushing blood out of the heart when they contract, while the
diastolic pressure is a measure of the pressure in the aorta when the heart muscle
relaxes. Systolic pressure can increase from 120 to 200 mm Hg, showing that the walls
of the ventricles are working much harder than normal.
Remember that a person’s cardiac output is the heart rate multiplied by the stroke
volume. We have seen that the systolic pressure increases during exercise as a result
of the muscles of the ventricles contracting more vigorously. The result of this is that the
volume of blood pushed out of the heart with every beat (the stroke volume) increases.
In fact the stroke volume can increase from 70 ml to120 ml per beat.
Since heart rate and stroke volume both increase during exercise, it follows that cardiac
output is also greatly increased.
Q8: Work out the percentage increase in cardiac output in an individual whose pulse
rate rises from 75 to 120 beats per minute and whose stroke volume increases from 80
ml to 100 ml per beat.

2.3.3

Distribution of blood to tissues

Every tissue in the body requires a constant blood supply to supply the cells with oxygen
and nutrients. During exercise muscles have a much greater requirement for oxygen
and glucose and therefore need a larger blood supply to meet these extra requirements.
Since there is only a finite volume of blood in the body, if some tissues receive an
increased blood supply it follows that others must receive a smaller blood supply during
exercise.
This change in distribution of blood is brought about by the widening of arterioles
(vasodilation) increasing the blood supply to the active tissues (eg muscles) and the
narrowing of arterioles (vasoconstriction) decreasing the supply to those tissues which
are not actively involved in exercise (eg the abdominal organs).
Tissue

Blood flow at rest
(ml/min)

Blood flow during exercise
(ml/min)

Brain
Heart
Muscle
Skin
Abdominal organs

750
250
1200
500
2400

750
750
12000
1900
1200

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2.4. THE ’ATHLETIC HEART’

31

Q9: The brain’s activity does not increase during exercise. Why does the blood supply
to the brain remain constant while that to the abdominal organs decreases?
Q10: What is the percentage decrease in the supply to the abdominal organs during
exercise?
Q11: What is the percentage increase in the supply to the muscles during exercise?
Q12: Why do you think blood flow to the skin increases during exercise?

2.4



The ’athletic heart’

Learning Objective
After studying this section, you should be able to:
• describe cardiac hypertrophy as a fundamental adaptation to increased
workload imposed by exercise training;

Æ

• explain the difference in stroke volume of the heart of an endurance athlete and
an untrained individual.

So far in this topic we have studied the effects of exercise and other factors in helping
to reduce the risk of CVD. However athletes are people who are fitter than most people
because they undergo a regime of training. Training involves exercising at more extreme
levels and for greater periods of time than most people can maintain. Athletes achieve
the benefits of exercise that we have discussed previously.
However as a result of the increased workload imposed by exercise training an athlete’s
heart actually gets bigger. This adaptation is known as cardiac hypertrophy and is the
result of an increase in protein synthesis in the muscle fibres of the heart causing them
to increase in size. The increase in size of the cardiac muscles enables them to contract
more forcibly, leading to an overall increase in the stroke volume of an athlete’s heart.
The following table compares cardiac output in a trained athlete and an untrained
person both at rest and during moderate exercise.
Moderate
exercise

At rest

Athlete
Untrained

HR
SV (ml)
(beats/min)

CO
(l/min)

40
70

5
4.9

125
70

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HR
(beats/min) SV (ml)
100
140

160
110

CO
(l/min)
16
12.4



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TOPIC 2. EXERCISE AND THE CARDIOVASCULAR SYSTEM

2.5



Principles of exercise testing

Learning Objective
After studying this section, you should be able to:
• explain maximal and sub-maximal testing used to measure fitness;

Æ

• describe stress testing and cardiac patients’ rehabilitation.

There are many reasons why people may wish to measure their fitness. For example
someone who begins a training regime will want to know how much their fitness has
improved, or someone recovering after suffering a heart attack must be sure that they
do not undertake too vigorous an exercise programme. Exercise testing can provide an
assessment of the fitness of an individual at the beginning of an exercise programme
and can also be used to assess progress during it.

2.5.1

Measuring fitness

One way to determine aerobic fitness is to measure the maximum rate at which the body
is able to take up and use oxygen (maximal testing). This is known as the V O2 max
and is usually measured in cm 3 kg-1 min-1 . To establish the VO2 max a person runs on
a treadmill whilst breathing in a measured gas supply. As the intensity of exercise is
increased (by increasing the speed and gradient of the treadmill) more oxygen is taken in
until it reaches a level that does not change even if the intensity of exercise is increased.
The greater the V O2 max the fitter is the individual.
The VO2 max can be difficult to measure as a treadmill and measureable air supply are
required. This test also requires the individual to exercise to exhaustion and so is not
suitable for most people.
A less extreme form of testing, called the sub-maximal test, relies on two assumptions:
1. that there is a linear correlation between V O2 max, heart rate and intensity of
exercise, and
2. that an individual’s maximum heart rate = 220 - age.
Using this method an individual’s pulse rate and oxygen uptake are measured at various
levels of activity. These results are used to construct a graph of pulse rate against
oxygen uptake. A straight line is drawn through the points on the graph and extrapolated
to the maximum heart rate. (For example the maximum heart rate for a 20 year old would
be 220-20 = 200 beats/minute. The V O2 max can then be predicted from the graph.
Sub-maximal testing is not as accurate as the V O2 max test because:
1. heart rate can be affected by factors other than exercise, for example temperature,
anxiety;
2. using 220-age gives only an average value for maximum heart rate - this may not
be accurate for a particular individual.
To increase aerobic fitness the body needs to be worked harder than it does during
normal daily activities. Aerobic exercise is performed over a long period of time but at
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2.5. PRINCIPLES OF EXERCISE TESTING

a low intensity. In order to benefit from an aerobic activity and improve your fitness it
is recommended that you exercise at least three times a week. When exercising your
heart rate should be raised to and maintained at 70 % of its maximum for 20 minutes or
more (this is roughly 50 % of the VO2 max). Remember maximum heart rate = 220 - age.
By exercising more frequently and for longer periods of time the benefits of exercising
can be seen more quickly. However, it is important not to over do it as this can be
detrimental so a maximum of four or five periods of exercise a week is recommended.
The most important thing is to continue to exercise, the benefits are lost if you stop
exercising. There is no point in exercising intensively for a couple of weeks and then
doing nothing for several months. It is much better to follow a less intense but sustainable
exercise plan and increase the intensity as your level of fitness increases.
Aerobic activities are continuous and rhythmical. Some examples include:
• walking;
• jogging;
• cycling;
• swimming.

Q13: Simon is 25. At what rate does he need to maintain his heart rate in order to
increase his fitness?
Q14: Julie is 56. At what rate does she need to maintain her heart rate in order to
increase her fitness?

2.5.2

Stress testing and cardiac patients’ rehabilitation

Sometimes individuals with coronary heart disease show a normal ECG
(electrocardiograph) at rest but abnormalities show up during exercise. Also some heart
rhythm abnormalities are triggered by exercise. It is important that these abnormalities
are detected so that appropriate treatment can be provided.
A stress test (or exercise ECG test) records an individual’s ECG traces before, during
and after exercise, normally while walking on a treadmill or pedalling on a stationary
bike. The exercise is started at a very relaxed pace, then every few minutes the speed
and incline of the treadmill (or the resistance on the bike) are increased so that the
workload is increased and the heart beats faster. The exercise is continued until the
individual is too tired to go on or until symptoms such as chest pain or breathlessness
are experienced.
The results of the test are used to establish exercise limits and to develop a fitness
programme for the rehabilitation of cardiac patients. It used to be thought that bed
rest was the appropriate treatment for cardiac patients, but it has been found that
a programme of medically supervised exercise leads to better recovery and survival
rates. Fitness programmes are tailored to the individual, but generally they encourage
gradually increasing aerobic exercise and some muscle strengthening exercises. The
stress test is repeated periodically to monitor the individual’s progress.

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34

TOPIC 2. EXERCISE AND THE CARDIOVASCULAR SYSTEM

2.6

Essay Question

This is an essay question similar to the style you will encounter in the SQA Advanced
Higher Examination. A total of 15 marks is available. You should hand your completed
essay to your tutor for marking.

Essay: Risk factors for cardiovascular disease
Question
There are many risk factors which increase the likelihood of cardiovascular disease
(CVD), some modifiable and other non-modifiable. Explain what is meant by the terms
’modifiable’ and ’non-modifiable’ and, using two named examples of each, explain their
roles in CVD. (15 marks)

2.7

Learning Points

• Modifiable risk factors in CVD are those which can be decreased by lifestyle
changes. They include: diet, smoking, activity and obesity.
• Non-modifiable risk factors cannot be decreased by lifestyle changes.
include: age, gender, heredity and race (ethnicity).

They

• Exercise increases heart rate and cardiac output.
• During exercise systolic blood pressure increases but diastolic blood pressure
remains constant.
• Regular exercise improves recovery time.
• During exercise more blood is distributed to skeletal muscles and the skin, while
less blood is distributed to abdominal organs. The distribution of blood to the brain
remains constant both before and during exercise.
• Cardiac hypertrophy is a fundamental adaptation to increased workload imposed
by exercise training. It involves the muscle fibres of the heart becoming larger as a
result of increased protein synthesis. This increase in size of the cardiac muscles
enables them to contract more forcibly.
• The stroke volume of the heart of an endurance athlete is much greater than that
of an untrained individual as a result of cardiac hypertrophy.
• Protective effects of exercise include: improved myocardial circulation, enhanced
contractile properties of myocardium, improved blood lipid profile, lowered heart
rate and blood pressure, decreased body fat.
• Maximal testing involves measuring the maximum rate at which the body is able
to take up and use oxygen (V O2 max). The greater the V O2 max the fitter is the
individual.
• Sub-maximal testing
– involves measuring heart rate and oxygen consumption at lower intensity
exercise levels than that used in maximal testing;
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2.7. LEARNING POINTS

35

– assumes that there is a linear relationship between heart rate, oxygen
consumption and level of exercise;
– is less accurate than maximal testing because heart rate can be affected by
factors other than exercise.
• A stress test records an individual’s ECG traces before, during and after exercise
• The results of a stress test are used to establish exercise limits and to develop a
fitness programme for the rehabilitation of cardiac patients.

End of Topic test
An online assessment is provided to help you review this topic.
30 min

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TOPIC 2. EXERCISE AND THE CARDIOVASCULAR SYSTEM

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37

Topic 3

Exercise and metabolism - energy

Contents
3.1
3.2
3.3
3.4

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The need for energy . . . . . . . . . . . . . . . . . . . . . . . . . . .
Dietary recommendations for health . . . . . . . . . . . . . . . . . .
Energy expenditure and its measurement . . . . . . . . . . . . . . .
3.4.1 Basal metabolic rate (BMR) . . . . . . . . . . . . . . . . . . .
3.4.2 Effect of physical activity on energy expenditure . . . . . . .
3.4.3 Effect of diet-induced thermogenesis on energy expenditure .
3.4.4 Factors affecting total energy expenditure . . . . . . . . . . .
3.4.5 Methods of measuring energy expenditure . . . . . . . . . .
3.5 Essay Question . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.6 Learning Points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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38
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51

Learning Objectives
After studying this Topic, you should be able to:
• explain that food energy comes from carbohydrates, lipids and proteins;
• explain how the potential energy in food is used to synthesise ATP;
• state that energy is measured in kilojoules (kJ);
• state that energy balance is considered as: energy in - energy out = change in
energy stores;
• explain the link between diet, coronary heart disease and obesity;
• describe basal metabolic rate (BMR) and its measurement;
• describe how physical activity and dietary-induced thermogenesis can affect
energy expenditure;
• describe factors affecting total energy expenditure to include: body size and
composition, age, sex, nutritional status, pregnancy and lactation;
• describe methods of measuring energy expenditure to include: direct calorimetry,
indirect calorimetry, heart rate recording.

38

TOPIC 3. EXERCISE AND METABOLISM - ENERGY

3.1

Introduction

This Topic deals with the balance between energy intake from food and energy output.
We will look at the energy content of different food types, at the importance of energy
balance (energy in = energy out) and at what factors influence the amount of energy we
expend. Finally we will look at different methods of measuring energy expenditure.

3.2



The need for energy

Learning Objective
After studying this section, you should be able to:
• explain that food energy comes from carbohydrates, lipids and proteins;
• explain how the potential energy in food is used to synthesise ATP;
• state that energy is measured in kilojoules (kJ);

Æ

• state that energy balance is considered as: energy in - energy out = change in
energy stores.

We need energy for growth and repair, for contraction of muscles, to produce heat and
to drive metabolic reactions. This energy comes from the food we eat, in particular
from carbohydrates, proteins and fats (lipids). The energy in food is stored as potential
energy, which is released during respiration and used to synthesise ATP (adenosine
triphosphate), sometimes known as the energy currency in cells.
The energy content of food can be measured in either kilojoules (kJ) or kilocalories
(kcal).
1 kcal = 4.184 kJ
1kJ = 0.239kcal
1 MJ = 1000kJ = 239 kcal
The energy contents of some dietary components are shown in Table 3.1.
Table 3.1: Energy content of nutrients
energy content
(kJ/g)

energy content
(kcal/g)

carbohydrate

16

3.8

protein

17
37
29

4
9
7

nutrient

fat
alcohol

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3.3. DIETARY RECOMMENDATIONS FOR HEALTH

39

An individual is said to be in energy balance when the energy they obtain from food over
a period of time is equal to the energy they expend over the same period. If the energy
taken in is greater than the energy expended, the person will gain weight. Conversely if
the energy taken in is less than the energy expended, the person will lose weight.
This relationship can be shown by the following equation:
energy in - energy out = change in energy stores
When energy in - energy out = 0, the individual is in energy balance.

3.3



Dietary recommendations for health

Learning Objective
After studying this section, you should be able to:

Æ

• explain the link between diet, coronary heart disease and obesity.

We saw in the previous Topic that levels of obesity in this country are increasing. It
appears to be caused by two main reasons, namely more inactive lifestyles and an
increase in energy intake from fat. We also saw that an increase in saturated fat in the
diet is thought to be linked to coronary heart disease by causing increased cholesterol
levels which in turn may lead to an increase in the rate of formation of atherosclerosis
with all the consequences that this has. Exercise (or increased activity) is thought
to decrease the risk of coronary heart disease because it has the opposite effect:
decreasing cholesterol levels and blood pressure.



In order to try to reduce the levels of obesity and cardiovascular disease, the UK
government has recommended that we should get about 30% of our daily energy intake
from fat, about 20% from protein and about 50% from carbohydrate. Table 3.2 compares
these recommendations with the actual figures from 1943 (during the Second World
War) and 1995.
Table 3.2: Comparisons of energy intake with current recommendations

Current recommendations
1943
1995

Fat
(%)

Protein
(%)

30

20

50

34
38

14
15

52
47

Carbohydrate
(%)

Energy intake
The following tables show a day’s diet for two different students, showing the total energy
intake and the proportion of energy intake from fat, protein and carbohydrate. Table 3.3
is for Student A who is a 16 year old male while Table 3.4 is for Student B who is an 18
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15 min

40

TOPIC 3. EXERCISE AND METABOLISM - ENERGY

year old female.
The estimated average daily energy requirement for males aged 15-18 years is 11510
kJ (2755 kcal), while for females in the same age range it is 8830 kJ (2110 kcal).
Study the tables then answer the questions which follow.
Table 3.3: Student A (male, 16 years old)
Breakfast

Lunch

2 cheeseburgers
2 bacon rolls
with butter; can with chips; bottle
of orange juice
of Coke
Energy intake
(kcal)

525

Total energy
intake (kcal)

2915

Total energy
from fat (kcal)

1150

Total energy from
protein (kcal)

430

Total energy from
carbohydrate
(kcal)

1335

870

Dinner

chilli and rice;
glass of milk

800

Snacks
small bottle of
lemonade; 4
chocolate
biscuits; 2
packets of
crisps
720

Table 3.4: Student B (female, 18 years old)
Breakfast

Lunch

2 slices of toast
chicken salad;
and marmalade;
apple; bottle of
glass of orange
water
juice
Energy intake
(kcal)

305

Total energy
intake (kcal)

2110

Energy from fat
(kcal)

650

Energy from
protein (kcal)

390

Energy from
carbohydrate
(kcal)

1070

430

Dinner
chilli and rice;
glass of milk

710

Snacks
2 handfuls of
hazelnuts;
carton of
apple juice; 2
bananas
665

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3.4. ENERGY EXPENDITURE AND ITS MEASUREMENT

41

Q1: Work out the percentage energy intake from fat, protein and carbohydrate for
Student A. Give your answers to one decimal point.
Q2: Work out the percentage energy intake from fat, protein and carbohydrate for
Student B. Give your answers to one decimal point.
Q3: Which of the students is likely to be, or to become, obese? Give a reason for your
answer.

3.4



Energy expenditure and its measurement

Learning Objective
After studying this section, you should be able to:
• describe basal metabolic rate (BMR) and its measurement;
• describe how physical activity and dietary-induced thermogenesis can affect
energy expenditure;
• describe factors affecting total energy expenditure to include: body size and
composition, age, sex, nutritional status, pregnancy and lactation;

Æ

• describe methods of measuring energy expenditure to include:
calorimetry, indirect calorimetry, heart rate recording.

3.4.1

direct

Basal metabolic rate (BMR)

The basal metabolic rate (BMR) is the minimum amount of energy required to maintain
essential metabolic processes (such as breathing, keeping the heart beating and other
organ systems functioning) during a given period of time when at rest. It is usually
measured in MJ/day or kcal/day.
In order to be accurate, an individual’s BMR should be measured several hours after
exercise and digestion, and when the individual is in a comfortable resting position. The
surroundings should be neither too hot nor too cold and the individual should be at rest,
both physically and mentally.
For most people it is very difficult to achieve the above conditions, not to mention the
apparatus required! However it is possible to estimate one’s BMR using equations which
have been adjusted to take age, sex and weight into account. An example of such
equations is shown in Table 3.5 below.

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42

TOPIC 3. EXERCISE AND METABOLISM - ENERGY

Table 3.5: Estimates of BMR
Sex

Age (years)

Estimated BMR (kcal/day)

male

10-17

BMR = 17.5 x body weight (kg) + 651

male

18-30

BMR = 15.3 x body weight (kg) + 679

male

31-60

BMR = 11.6 x body weight (kg) + 879

female

10-17

BMR = 12.2 x body weight (kg) + 746

female

18-30

BMR = 14.7 x body weight (kg) + 496

female

31-60

BMR = 8.7 x body weight (kg) + 829

Q4:

Work out the estimated BMR for a 19 year old male weighing 65 kg.

Q5:

Calculate the estimated BMR for a 16 year old female weighing 45 kg.

3.4.2

Effect of physical activity on energy expenditure

The BMR is a measure of the energy consumed at rest. Any activity, however gentle,
uses energy in addition to the BMR. The more strenuous the activity, the more energy
is used up.
The amount of energy expended by an individual in a given period of time can be
calculated if the following information is available:
1. the individual’s BMR;
2. the energy cost of each activity;
3. the length of time each activity lasts.
The energy cost of an activity is often expressed as a multiple of BMR. This value is
known as the Physical Activity Ratio or PAR. For example, playing badminton has an
average PAR of 5. This means that when someone is playing badminton they are using
up 5 times more energy than they would be at rest.
It is important, in order to maintain an energy balance, that exercise is taken on a regular
basis. For example it is better, from an energy expenditure point of view, to exercise
moderately for 30-40 minutes 3-5 times a week than to exercise intensely once a week
for 2 hours. There are two main reasons for this:
1. When you stop exercising (or performing any activity) your metabolic rate does not
return to the BMR immediately. This extra energy is needed to enable the body to
replenish its glycogen stores used up during the exercise. Although the amount of
energy needed may be small, up to about 24 kcals, the cumulative effect resulting
from an active lifestyle can be quite large.
2. Several studies have shown that exercise can actually increase an individual’s
BMR for several hours after exercise. This increase is only temporary, however, so
that in order to maintain it, regular exercise (or a generally more active lifestyle) is
required.

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3.4. ENERGY EXPENDITURE AND ITS MEASUREMENT

43

Calculating daily energy expenditure
Table 3.6 shows the average PARs for various activities.
Table 3.6: Average PARs for various activities
Activity

Average PAR

Sleeping

1.0

Personal activities (washing, dressing, eating)

1.4

Quiet sitting activities (reading, watching TV)

1.2

Active sitting activities (studying)

1.6

Slow moving activities (cleaning and tidying up)

2.1

Cycling

5

The energy expended (EE) for each activity is calculated as follows:
EE = PAR x BMR (kcal/hour) x duration of activity (hours)
Table 3.7 shows the activity of Angela, who is 17 years old and weighs 50 kg, over a 24
hour period.
Q6: Using the information in Table 3.5, estimate Angela’s BMR in kcal/hour.
Complete Table 3.7 for the PARs and energy expended for each activity. For the energy
expended, calculate each answer to the nearest whole number. (There is an interactive
version of this activity on the Web where you can check your answers.)

© H ERIOT-WATT U NIVERSITY

20 min

44

TOPIC 3. EXERCISE AND METABOLISM - ENERGY

Table 3.7: Energy expenditure
Activity

Time
00.00 08.00
08.00 09.00
09.00 12.00
12.00 13.00
13.00 16.00
16.00 17.00
17.00 17.30
17.30 19.30
19.30 23.00
23.00 24.00

Q7:

3.4.3

PAR

Energy expended
(kcal)

Sleeping
Getting washed, dressed and
eating breakfast
Cycling trip with friends
Lunch
Cycling home
Tidying bedroom
Eating dinner
Studying for exams
Watching TV and reading
Sleeping

Calculate the total energy expenditure over the 24 hour period.

Effect of diet-induced thermogenesis on energy expenditure

Thermogenesis literally means heat production. Every time you eat, some energy is
used up in digesting, absorbing, metabolising and storing the food. This energy is
eventually converted to heat.
However different types of food have different thermic effects. Protein exerts the highest
thermic effect: in a high protein meal up to 17% of the energy contained in it can
be burned off as heat. Carbohydrates have a milder effect - about 10% in a high
carbohydrate meal is used to produce heat. Fats have the least thermic effect of all,
only about 3%.
Thus eating carbohydrate and protein rich foods increases energy expenditure much
more than eating high fat foods. Apart from the other health reasons previously
discussed in Topics 1 and 2, this is another good reason to keep your intake of fat
low.
Thermogenesis can also be increased by eating several small meals a day rather than
two or three larger ones. Every time you eat, thermogenesis increases, therefore
increasing the number of times you eat, without increasing the daily calory intake, will
increase the amount of energy used to digest and metabolise the food.

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3.4. ENERGY EXPENDITURE AND ITS MEASUREMENT

3.4.4

45

Factors affecting total energy expenditure

There are many factors which affect the total energy expenditure of an individual,
including body size and composition, age and sex, nutritional status, pregnancy and
lactation. We will look at each of these in turn.

3.4.4.1 Body size and composition
Energy expenditure increases as body size (and therefore body weight) increases. The
more tissue an individual has, the more energy is used up.
As well as the actual mass, or weight, of body tissue, the kind of tissue is important in
energy expenditure. Muscle tissue uses up much more energy than fat (adipose) tissue.
Therefore the greater the ratio of muscle to fat, the greater is the energy expended.
This is another reason why exercising is important in weight control. When you exercise
you increase your muscle to fat ratio, so your BMR will increase. This will increase the
rate at which energy is expended and so in turn will increase the rate of fat (and weight)
loss.

3.4.4.2 Age and sex (gender)
Generally males have higher energy requirements than females and teenagers need the
most energy due to their accelerated growth rate.
Figure 3.1 shows the energy requirements of males and females at different ages.

580 -1165 kcal

1600 kcal

2100 kcal

1950 kcal

1900 kcal

620 - 1230 kcal

1800 kcal

2700 kcal

2550 kcal

2400 kcal

Figure 3.1: Energy requirements for males and females at different ages
© H ERIOT-WATT U NIVERSITY

46

TOPIC 3. EXERCISE AND METABOLISM - ENERGY

Energy requirements
15 min

Use the data in Table 3.8 to plot a bar chart (Figure 3.2) for male and female energy
requirements at different ages. Remember to use different colours for the different
sexes. (An interactive version of this activity is available on the Web.)
The data in Table 3.8 is given in kcal. Remember that:
1 kcal = 4.184 kJ
1MJ = 239 kcal
Table 3.8: Average energy requirements of different groups
age

male (kcal/day)

female (kcal/day)

0-6 months
7-12 months
1-3 years

620
875
1230

580
815
1165

4-6 years

1715

1545

7-10 years

1970

1740

11-14 years

2220

1845

15-18 years

2755

2110

19-50 years

2550

1940

51-74 years
75+ years

2420
2100

1900
1810

Figure 3.2: Graph showing average energy requirements of different groups
© H ERIOT-WATT U NIVERSITY

3.4. ENERGY EXPENDITURE AND ITS MEASUREMENT

Q8: When does a male have the highest energy requirements?
a)
b)
c)
d)

As a child
As a teenager
As an adult
As a pensioner

Q9: When does a female have the highest energy requirements?
a)
b)
c)
d)

As a child
As a teenager
As an adult
During pregnancy

Q10: Why do both males and females require more energy during adolesence than
adulthood?
Q11: Calculate how many kJ of energy a 4-6 year old girl requires each day. Enter your
answer to one decimal place.
Q12: Calculate how many MJ of energy a 51-74 year old man requires each day. Enter
your answer to one decimal place.

3.4.4.3 Nutritional status
Fasting, or strict dieting, which drastically reduces energy intake causes the body to
go into ’famine’ mode. This causes the body to use up lean muscle tissue as well as
fat tissue to meet the body’s energy requirements. Since muscle tissue uses up more
energy, losing some of it lowers the BMR.
This is the body’s way of coping with restricted calories which has evolved over hundreds
of thousands of years to enable humans to survive times when food was scarce.
Unfortunately some people use very low calorie diets to try to lose weight only to find
themselves having to reduce their calories more and more as a result of the reduction in
their BMR. When they increase their food intake they may find that their weight increases
rapidly. This so-called yo-yo dieting usually leads to an increase in weight in the long
run.
Being active, even moderately so, along with a small decrease in calory intake can
achieve a slow, but permanent weight loss.

3.4.4.4 Pregnancy and lactation
During pregnancy a woman needs to consume about 837 kJ (200 kcal) a day more
than normal during the last three months of pregnancy because she has to supply
nutrients to the foetus as well as to herself. A woman also has higher nutrient and
energy requirements when she is breast feeding (lactating).
Q13: During the last three months of pregnancy the average energy requirements for a
woman increases by 200 kcal a day. Using the information in Table 3.8 (see Activity
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’Energy requirements’), calculate how much energy a 33 year old pregnant woman
would require each day at this time.

3.4.5

Methods of measuring energy expenditure

There are several methods which can be used to measure energy expenditure including
direct calorimetry, indirect calorimetry and heart rate recording. We will look at each of
these in turn.

3.4.5.1 Direct calorimetry
All energy is eventually converted to heat energy. This applies to the energy produced
as a result of metabolism. The total energy expended by an individual can be measured
directly by measuring the heat energy produced. This is known as direct calorimetry
and involves placing the individual inside an insulated chamber and directly measuring
the temperature rise of a known mass of water.
A calorie is defined as the amount of energy required to raise the temperature of 1g of
water by 1Æ C, therefore
energy (calories) = mass of water (g) x temperature change ( Æ C).
Although this is an extremely accurate method of measuring energy expenditure, it is
very expensive and difficult to operate. It is therefore not a very suitable method for
most people.

3.4.5.2 Indirect calorimetry
Since oxygen is usually required to release energy during respiration, it can be assumed
that there is a relationship between oxygen consumption and energy expenditure. In
fact about 4.8 kcal (20 kJ) of energy are released for every litre of oxygen used by an
individual.
Therefore an individual’s energy expenditure can be indirectly estimated if the volume of
oxygen taken in over a given period of time is known. In order to measure an individual’s
oxygen consumption we need to know the volume of air they have breathed in (inspired
air), which is equal to the volume of air breathed out (expired air), and the proportion of
oxygen in the air breathed in and out.
The volume of air is measured using a spirometer, a large bag which collects the air
breathed out over a given time period.
The composition of oxygen in the inspired and expired air is measured. The percentage
of oxygen absorbed by the individual is equal to the percentage of oxygen in the inspired
air (usually 20%) minus the percentage of oxygen in the expired air.
The following example may illustrate the process more clearly:
An individual walking on a treadmill breathes out 200 litres of air in 10 minutes. The
inspired air contained 20% oxygen, while the expired air contained 16 % oxygen.

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3.4. ENERGY EXPENDITURE AND ITS MEASUREMENT

The volume of oxygen in inspired air = 20% x 200 = 40 l;
the volume of oxygen in expired air = 16% x 200 = 32 l;
the volume of oxygen absorbed in 10 minutes = 40 - 32 = 8 l.
Remember that about 4.8 kcal of energy are released for every litre of oxygen used by
an individual. Therefore during the 10 minute period above, the individual used up 8 x
4.8 = 38.4 kcal.
Although this method is not as accurate as direct calorimetry, it is still fairly accurate and
is much cheaper and easier to carry out.

3.4.5.3 Heart rate recording
This method is related to Indirect calorimetry. We saw in Topic 2 of this Unit that there
is a linear relationship between heart rate and oxygen consumption. As the heart rate
increases the rate of oxygen consumption increases. This relationship can be shown by
calculating and graphing the oxygen consumption (l/min) and heart rate (beats/min) of
an individual during different activities.
Once the graph of the relationship has been drawn, an individual can carry out a
particular activity and use a heart rate monitor to record their heart rate during a given
period of time. If they find their average heart rate in beats/min, they can read their
oxygen consumption (l/min) from the graph. The total oxygen consumption for the
duration of the activity can then be calculated.
We know from the previous section that about 4.8 kcal of energy are produced from
every litre of oxygen used, therefore the energy expenditure can be estimated. Again
a worked example may help. Figure 3.3 shows the relationship between heart rate and
oxygen consumption for an individual.

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Figure 3.3: Relationship between heart rate and oxygen consumption in an individual
Q14: If this individual ran for 10 minutes and, using a heart rate monitor, it was found
that their heart rate averaged 160 beats/minute, work out the energy expended by this
individual during the activity.
As with indirect calorimetry, estimating energy expenditure using heart rate monitoring
is not as accurate as direct calorimetry. However if:
1. the relationship between heart rate and oxygen consumption and
2. the monitoring of the heart rate during a period of time
are accurate, then this is a fairly accurate and easy way to estimate energy expenditure.

3.5

Essay Question

This is an essay question similar to the style you will encounter in the SQA Advanced
Higher Examination. A total of 15 marks is available. You should hand your completed
essay to your tutor for marking.

Essay: Measuring energy expenditure
Question
Energy expenditure can be measured by direct calorimetry, indirect calorimetry
and heart rate recording. Describe each method, including their advantages and
disadvantages. (15 marks)
© H ERIOT-WATT U NIVERSITY

3.6. LEARNING POINTS

3.6

Learning Points

• Food energy comes from carbohydrates, lipids and proteins.
• The energy in food is stored as potential energy, which is released during
respiration and used to synthesise ATP.
• Energy is measured in kilojoules (kJ).
• Energy balance is considered as: energy in - energy out = change in energy
stores. When the change in energy is zero, a person is said to be in energy
balance. A positive energy balance will lead to an increase in weight over time,
while a negative energy balance will lead to a decrease in weight.
• Fat contains 9 kcal of energy per gram, protein 4 kcal per gram and carbohydrates
3.8 kcal per gram. A diet rich in high fat foods will lead to a positive energy balance
which can lead to overweight and obesity.
• High fat diets have also been linked to coronary heart disease by causing
increased cholesterol levels which in turn may lead to an increase in the rate of
formation of atherlosclerosis.
• The basal metabolic rate (BMR) is the minimum amount of energy required to
maintain essential metabolic processes during a given period of time when at rest.
It is usually measured in MJ/day or kcal/day.
• Physical activity uses energy in addition to the BMR. The more strenuous the
activity, the more energy is expended.
• Every time you eat, some energy is used up in digesting, absorbing, metabolising
and storing the food. This energy is eventually converted to heat. The process is
known as dietary-induced thermogenesis. About 17% of energy in protein, 10% in
carbohydrate and 3% in fat is burned off as heat energy.
• Increasing body size increases total energy expenditure. The greater the
proportion of muscle to fat, the more energy is expended, since muscle burns
more energy per gram than does fat.
• Males tend to expend more energy than females of the same age and body
size. Energy requirements increase with age up to late teens, when it begins
to decrease.
• Fasting, or strict dieting, causes the body to use up lean muscle tissue as well as
fat tissue to meet the body’s energy requirements. Since muscle tissue uses a lot
of energy, losing some of it lowers the total energy expended.
• During pregnancy a woman needs to consume about 837 kJ (200 kcal) a day more
than normal during the last three months of pregnancy. A woman also has higher
nutrient and energy requirements when she is breast feeding (lactating).
• Energy expenditure can be measured in various ways, including direct calorimetry,
indirect calorimetry and heart rate recording.
• Direct calorimetry measures the amount of heat energy given out by an individual.

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• Indirect calorimetry depends on the assumption that there is a relationship
between oxygen consumption and energy expended. If oxygen consumption can
be measured, energy expended can be estimated (but not measured directly).
• Heart rate monitoring depends on the assumption that there is a linear relationship
(which can be graphed) between heart rate and oxygen consumption. Heart
rate can be measured, oxygen consumption read off from the graph and energy
expended estimated (but again not measured directly).

End of Topic test
An online assessment is provided to help you review this topic.
30 min

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53

Topic 4

Exercise and metabolism - body
composition and weight control

Contents
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . .
4.2 Measurement of body composition . . . . . . . . . . . . .
4.2.1 Densitometry . . . . . . . . . . . . . . . . . . . . .
4.2.2 Skinfold thicknesses . . . . . . . . . . . . . . . . .
4.2.3 Bioelectrical impedance analysis . . . . . . . . . .
4.2.4 Body mass index (BMI) . . . . . . . . . . . . . . .
4.2.5 Waist/hip ratio . . . . . . . . . . . . . . . . . . . .
4.3 Weight control and obesity . . . . . . . . . . . . . . . . . .
4.4 Effect of exercise on body composition and weight control
4.5 Essay Question . . . . . . . . . . . . . . . . . . . . . . . .
4.6 Learning Points . . . . . . . . . . . . . . . . . . . . . . . .

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54
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57
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60

Learning Objectives
After studying this Topic, you should be able to:
• describe various methods to measure body composition to include: densitometry,
skinfold thicknesses, bioelectrical impedance analysis, body mass index (BMI),
waist/hip ratio;
• describe the limitations of the above methods;
• explain the importance of differentiating between ’overweight’ related to large
muscle mass or bone mass and that due to excess fat;
• describe the problem of rising incidence of obesity in the UK;
• describe possible causes and possible treatments of obesity;
• explain the place of exercise in increased energy expenditure as part of weightcontrol programmes;
• describe the effect of frequency, intensity, duration and type of exercise on body
composition and weight control.

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TOPIC 4. EXERCISE AND METABOLISM - BODY COMPOSITION AND WEIGHT
CONTROL

4.1

Introduction

In this Topic we will examine various methods used to measure body composition, before
going on to look at the increasing incidence in obesity and the effect that regular exercise
can have in weight-control programmes.

4.2

Measurement of body composition

Learning Objective



After studying this section, you should be able to:
• describe various methods to measure body composition to include:
densitometry, skinfold thicknesses, bioelectrical impedance analysis, body
mass index (BMI), waist/hip ratio, mid-upper arm circumference;
• describe the limitations of the above methods.

Æ

• explain the importance of differentiating between ’overweight’ related to large
muscle mass or bone mass and that due to excess fat.

Many people who are trying to slim often weigh themselves to determine their progress.
However your weight doesn’t tell you much about the size and composition of your body.
For example someone who has a lot of body fat can weigh exactly the same as a person
who has less fat but more muscle.
In order to determine how healthy a shape your body is in, it is more important to
determine the ratio of fat to lean tissue (muscle, bone etc) rather than just weight. This
ratio of fat to lean tissue is known as body composition.
It is probably useful at this stage to point out that some fat is essential for good health.
Fat is needed for the formation of cell membranes, the formation of some hormones,
insulation etc. The problem is that many of us have too much! The percentage body fat
associated with the least health risk is 18-25% for women and 13-18% for men.
There are several ways to measure or estimate body composition, some of which we
will look at next.

4.2.1

Densitometry

This method of determining body composition depends on the fact that fat is less dense
than lean tissue. A person’s density (g/cm3 ) is calculated by measuring their weight and
body volume. Weight is easily measured, but volume is a bit more complicated. Usually
it involves submerging the person completely in water and measuring the volume of
water displaced. (According to Archimedes Principle, an object submerged in water will
displace a volume of water equal to its own volume.)
Once the density has been determined, the percentage of body fat is calculated using
the following mathematical formula:
% fat = 495/density (g/cm 3 ) - 450
© H ERIOT-WATT U NIVERSITY



4.2. MEASUREMENT OF BODY COMPOSITION

The following example will illustrate how two people weighing the same can have
different percentages of body fat:
Persons A and B both weigh 60kg. On submerging them, person A displaced 56.9 litres
of water while person B displaced 58.3 litres.
Q1: Calculate the densities of both people in g/cm 3 . Give your answer to 4 decimal
places.
Q2: Calculate the % body fat for both people.
Q3: Which person is overweight?
Although this method is an accurate one, the specialised equipment involved makes it
unsuitable for most people. Also the individual needs to be confident about being under
water.

4.2.2

Skinfold thicknesses

This method involves measuring the layer of fat under the skin at various places on the
body. A piece of apparatus called a skinfold caliper measures the thickness of the skin
in millimetres in three to seven specific sites. The most common sites are: on the front
and back of the upper arm (the biceps and triceps muscles), below the shoulder blade
and just above the hip.
These measurements can then be used to estimate the amount of fat in the whole body.
The advantages of this method are that it is quick, cheap and relatively accurate once
the skill has been mastered. Also you don’t need to work out your % body fat all the
time. If you use it the first time to give you a baseline to work from, then all you need
to do is to use the calipers regularly and compare the measurements with the original
ones. If your weight increases but the caliper measurements stay the same, then your
weight gain is not due to fat gain - it could be muscle gain or temporary water retention.
The disadvantages of using the skinfold caliper are:
• that it takes practice to develop accurate measuring skills;
• it assumes that everyone has the same distribution of fat over their body. This is
not the case as very lean people tend to have a different fat distribution from very
obese people.

4.2.3

Bioelectrical impedance analysis

This method relies on the fact that fat is an insulator of electricity while lean tissue
(like muscle) is a good conductor. A conductor allows an electric current to flow easily
through it, offering little resistance. An insulator, on the other hand, does not allow
the current to flow through it easily: it offers resistance (or impedance) to the current.
A small electrical current is passed through the body and the electrical resistance (or
impedance) is measured. The greater the resistance, the greater is the percentage body
fat.
The advantages of this method are that it is quick, the equipment is portable and
very easy to use. The disadvantage is that it is not as accurate as other methods.
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CONTROL
For example changes in hydration (water) levels and skin temperature will affect the
conduction of the current and therefore the percentage body fat calculation. Also it
tends to overestimate the percentage body fat of lean people and underestimate the
percentage of overweight people by about 2-5%.

4.2.4

Body mass index (BMI)

It is possible to tell if someone is overweight by calculating the Body Mass Index (BMI).
This is calculated in terms of a person’s height and weight, as follows:
BMI (kg m-2 ) = weight (kg) / height (m)2
(Table 4.1) shows how the BMI is used to describe different categories of weight.
Table 4.1: BMI
BMI (kg m-2 )

category
underweight

under 20

ideal weight

20 - 25

overweight

25 - 30
over 30

obese

BMI measurements can be used to assess a person’s risk of developing conditions such
as coronary heart disease, high blood pressure and Type 2 diabetes. A BMI of 20-25
is associated with the lowest health risk, people with a BMI of 25-30 are at moderate
risk, while a BMI of more than 30 is considered to confer a greater risk with the risk
increasing as the BMI increases.
The advantage of using this method is that it is extremely easy to calculate. However
the disadvantage is that someone may be classified as overweight or obese when the
additional weight is not fat but muscle or bone mass. For example body builders build
up a much greater muscle mass than most people and could have a higher BMI than
someone else of the same height; they may even be classified as overweight or obese.
However in this case the excess weight is made up mainly of lean muscle tissue. It is
important therefore to differentiate between ’overweight’ which is related to large muscle
mass or bone mass and that due to excess fat.
The following activity shows how to calculate the BMI.

Body Mass Index (BMI)
Try calculating your BMI using the following equation:
15 min

BMI (kg m-2 ) = weight (kg) / height (m)2
then refer to Table 4.1 to see which weight category you fall into.
Q4:

Kate is 150 cm tall and weighs 65 kg. What is her BMI?

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4.2. MEASUREMENT OF BODY COMPOSITION

Q5: What weight catergory does Kate fall into?
a)
b)
c)
d)

Underweight
Normal
Overweight
Obese

Q6: How much weight does Kate need to lose in order for her BMI to be within the
normal range?
Q7: Frank is 187 cm tall and weighs 79 kg. What is his BMI?
Q8: What weight catergory does Frank fall into?
a)
b)
c)
d)

Underweight
Normal
Overweight
Obese

Q9: Julie is 1.7 m tall and weighed 69 kg, she recently lost 15 kg on a diet. Explain
how her BMI has changed and what could happen if she continues to lose weight.
Q10: Which of the following best defines obesity?
a)
b)
c)
d)

The body mass index is greater than 20.
The body mass index is less than 20.
The body mass index is greater than 30.
The body mass index is less than 30.

4.2.5

Waist/hip ratio

When people gain enough weight to be classified as overweight or obese, there are two
distinct patterns to the distribution of fat. Those people who tend to distribute fat on their
abdomen (a ’pot-belly’) are said to be ’apple-shaped’ while those who distribute excess
fat on their hips and thighs are said to be ’pear-shaped’.
The distribution of fat can be calculated using a simple ratio: the waist : hip ratio. This is
calculated by dividing the waist measurement by the hip measurement (the units, either
centimetres or inches, must be the same in both cases).
For women, because they tend to have proportionately larger hips than men, a waist:hip
ratio of 0.8 or less indicates a pear shape, while a ratio above 0.8 indicates an apple
shape. For men a ratio of 1 or less indicates a pear shape, while apple shapes will have
a ratio greater than 1.
Research has shown that those people who are overweight and apple-shaped (ie have
excess abdominal fat) have a higher risk of developing coronary heart disease, high
blood pressure, Type 2 diabetes than those who are ’pears’.

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4.3



Weight control and obesity

Learning Objective
After studying this section, you should be able to:
• describe the problem of rising incidence of obesity in the UK;

Æ

• describe possible causes and possible treatments of obesity.

We have seen already that the incidence of obesity is rising in the UK. It is estimated
that 16 % of men and 18 % of women are obese, that is with a BMI of greater than 30. In
Scotland it is estimated that more than 20% of the population is obese and the trend is
rapidly rising among children. In a recent study 8% of boys and 7% of girls were classed
as obese.
Being slightly overweight does not pose any health risks, however obesity can have
serious health consequences. Obese people are at a higher risk of developing
cardiovascular diseases, including coronary heart disease and high blood pressure;
Type 2 diabetes and osteoarthritis. In fact Type 2 diabetes, which has traditionally been
seen as a disease of people over 40 years old, is now being found in children as young
as 13.
The consequences of such health risks include time off work due to illness and reduced
life expectancy. Studies have shown that the life expectancy of people who have obesity
related illnesses is shortened by several years.
The causes of obesity seem to be complex, involving genetic, psychological and dietary
factors. However strictly speaking a person will become obese if they remain in a positive
energy balance. In other words if a person constantly consumes more calories than they
expend, they will eventually become obese.
The rapid increase in obesity in recent years is mainly due to two factors: a more
sedentary lifestyle reducing the amount of physical activity undertaken, and an increase
in the intake of high fat foods. Remember that fat contains more than twice as much
energy per gram than either carbohydrate or protein.
Given the above reasons for the possible causes of obesity, it follows that treatments for
it must include reducing energy intake and increasing energy expenditure.

© H ERIOT-WATT U NIVERSITY



4.4. EFFECT OF EXERCISE ON BODY COMPOSITION AND WEIGHT CONTROL

4.4

Effect of exercise on body composition and weight
control

Learning Objective

59



After studying this section, you should be able to:
• explain the place of exercise in increased energy expenditure as part of weightcontrol programmes;

Æ

• describe the effect of frequency, intensity, duration and type of exercise on body
composition and weight control.

We saw in the last section that treatments for obesity involve reducing energy intake
and increasing energy expenditure. In fact recent studies have found that weight loss
is more likely to be permanent if a weight reduction regime contains a combination of
increasing activity and reducing energy intake.
Any kind of physical activity increases energy expenditure but it is important in a weightcontrol programme that the activity is regular and strenuous enough to make you breathe
more heavily than normal. Examples of such exercise include brisk walking, jogging,
swimming, dancing.
Most health experts suggest that we should try to include up to 30 minutes of aerobic
exercise most days, strenuous enough to increase the heart rate to between 55% and
70% of the maximum heart rate. Remember the maximum heart rate is 220 - age.
Some of the benefits regular exercise has on body composition and weight control
include:
• increased muscle:fat ratio;
• increased BMR (basal metabolic rate);
• increased energy expenditure.
It is important to remember however that exercise must be taken regularly in order to
maintain the benefits.

4.5

Essay Question

This is an essay question similar to the style you will encounter in the SQA Advanced
Higher Examination. A total of 15 marks is available. You should hand your completed
essay to your tutor for marking.

Essay: Measuring body composition
Question
Describe how densitometry, skinfold thicknesses and bioelectrical impedance analysis
can be used to measure body composition, giving one advantage and one disadvantage
© H ERIOT-WATT U NIVERSITY



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TOPIC 4. EXERCISE AND METABOLISM - BODY COMPOSITION AND WEIGHT
CONTROL
for each method. (15 marks)

4.6

Learning Points

• The ratio of fat to lean tissue is known as body composition.
• Determining body composition by densitometry depends on the fact that fat is less
dense than lean tissue. Density = mass (g) / volume cm 3 . Volume is measured
by submerging the person in water and measuring the volume of water displaced.
Percentage body fat can then be calculated. Advantage - it is an accurate method;
disadvantages - it requires specialist equipment, individual needs to be confident
in water.
• A skinfold caliper is used to measure the layer of fat (in mm) under the skin at
various places on the body. These measurements are used to estimate total body
fat. Advantages - it is quick, cheap and fairly accurate; disadvantages - it takes
practice to master the accurate use of the calipers, and it wrongly assumes that
body fat is distributed in the same way in everyone.
• Bioelectrical impedance analysis depends on the following facts:
– that an electrical conductor allows electricity to pass through it easily, offering
little resistance, but that an insulator offers resistance (or impedance) to the
flow of electricity;
– that lean tissue, like muscle, is a good conductor while fat is an insulator.
A small electric current is passed through the body and the electrical resistance
measured. The greater the resistance, the greater the body fat percentage.
Advantages - it is quick, the equipment is portable and easy to use: disadvantage
- not as accurate as other methods - changes in hydration levels and skin
temperature will affect electrical conduction and therefore the estimation of body
fat.
• Body Mass Index (BMI) is a calculation which is used to determine whether
someone is a normal weight or overweight for their height. BMI (kg m -2 ) =
weight (kg) / height (m)2 . A BMI of less than 20 is classed as underweight, 2025 is classed as ideal weight, 25-30 is overweight and more that 30 is obese.
Advantage - it is very easy to calculate: disadvantage- someone may be classified
as overweight or obese when the additional weight is not fat but muscle or bone
mass.
• If a person is overweight their waist:hip ratio can be used to determine whether
they are an ’apple’ or ’pear’ shape. Apple shaped people have more fat laid
down in their abdominal area and have a higher risk of developing coronary heart
disease, high blood pressure, Type 2 diabetes than those who are ’pears’.
• The incidence of obesity is rising in the UK. Obese people are at a higher risk of
developing cardiovascular diseases, including coronary heart disease, and high
blood pressure; Type 2 diabetes and osteoarthritis. The consequences of such
health risks include time off work due to illness and reduced life expectancy.
© H ERIOT-WATT U NIVERSITY

4.6. LEARNING POINTS

61

• A person will become obese if they remain in a positive energy balance. The rapid
increase in obesity in recent years is mainly due to a more sedentary lifestyle and
an increase in the intake of high fat foods. Treatments for obesity include reducing
energy intake and increasing energy expenditure.
• Exercise is important as part of a weight-control programme because it increases
energy expenditure.
• Exercise should be regular, about 30 minutes of aerobic exercise most days, and
strenuous enough to increase the heart rate to between 55% and 70% of the
maximum heart rate (220 - age). Examples of such exercise include brisk walking,
jogging, swimming and dancing.
• Some of the benefits regular exercise has on body composition and weight control
include:
– increased muscle:fat ratio;
– increased BMR;
– increased energy expenditure.

End of Topic test
An online assessment is provided to help you review this topic.
30 min

© H ERIOT-WATT U NIVERSITY

62

TOPIC 4. EXERCISE AND METABOLISM - BODY COMPOSITION AND WEIGHT
CONTROL

© H ERIOT-WATT U NIVERSITY

63

Topic 5

Osteoporosis and diabetes mellitus

Contents
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

64

5.2 Osteoporosis and bone growth . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.2.1 Cause of osteoporosis . . . . . . . . . . . . . . . . . . . . . . . . . . . .

64
64

5.2.2 Risk factors for osteoporosis . . . . . . . . . . . . . . . . . . . . . . . .
5.2.3 Effects of exercise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

64
66

5.3 Diabetes mellitus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.3.1 Controlling blood glucose levels . . . . . . . . . . . . . . . . . . . . . . .

66
66

5.3.2 Insulin dependent and non-insulin dependent diabetes mellitus . . . . .
5.3.3 Effect of exercise on people with NIDDM . . . . . . . . . . . . . . . . . .

68
71

5.4 Essay Question . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.5 Learning Points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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72

Learning Objectives
After studying this Topic, you should be able to:
• describe the cause of osteoporosis;
• state that osteoporosis affects men, women and children but is most common in
post-menopausal women;
• describe the effects of exercise on bone mass and osteoporosis;
• explain the role of insulin and glucagon in the control of blood glucose levels;
• state that non-insulin dependent diabetes mellitus (NIDDM) is generally
associated with obesity;
• describe how cells become resistant to the effects of insulin in NIDDM;
• describe the effect of exercise on blood glucose levels in subjects with NIDDM.

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5.1

Introduction

In this Topic we will look at the causes of osteoporosis and non-insulin dependent
diabetes mellitus and at the effect of exercise on the prevention and treatment of these
diseases.

5.2



Osteoporosis and bone growth

Learning Objective
After studying this section, you should be able to:
• describe the cause of osteoporosis;
• state that osteoporosis affects men, women and children but is most common
in post-menopausal women;

Æ

• describe the effects of exercise on bone mass and osteoporosis.

Osteoporosis literally means ’porous bones’. It is a fairly common disease in older
people; it is estimated that 1 in 3 women and 1 in 12 men in the UK will develop it.

5.2.1

Cause of osteoporosis

Bone is living tissue which consists of a honeycomb mesh of collagen fibres which is
hardened by minerals such as calcium salts. Bone is dynamic tissue; in other words
old bone is constantly being broken down and new bone made. It has been estimated
that the bones in our body are entirely renewed every 10 years. As long as the rate
of bone formation exceeds the rate of breakdown, bone gets denser and stronger.
This happens during childhood, adolescence and young adulthood, reaching a peak
of maximum density (known as peak bone density) between 25 and 35 years of age.
After this, as a normal part of aging, calcium and other minerals are removed more
quickly from bone than can be added. As this process continues the bones become
more porous and brittle which increases the risk of fractures.
Osteoporosis can affect men, women and children but is more common in menopausal
women.

5.2.2

Risk factors for osteoporosis

There are many factors which increase the risk of developing osteoporosis in later
life including: age, sex, menopause, diet, family history, smoking, excessive alcohol
consumption, lack of exercise and excessive exercise (in women). We will look at each
of these in turn.
Age
We saw earlier that peak bone density occurs between 25 and 35 years of age, after
which mineral loss from bone increases as a natural consequence of aging.

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Sex
Men tend to have denser, stronger bones than women and so have a higher peak bone
density. It therefore takes men longer to reach the level of bone loss which will make
their bones brittle and liable to fracture. Also men tend to lose bone at a slower rate than
women: while women tend to lose bone at a rate of 1% per year before the menopause
and 2-3% per year after the menopause, men tend to lose bone at about 0.4% per year.
Menopause
In women, between puberty and the menopause, high levels of oestrogen contribute
to bone density by promoting the absorption of calcium from the digestive system
and preventing its removal from bone. After the menopause oestrogen levels drop,
causing more calcium to be lost from bone. An early menopause, before 45 years
of age, is associated with an increased risk of osteoporosis. Hormone replacement
therapy is sometimes advised, particularly for those women who have a family history of
osteoporosis, since it maintains levels of oestrogen.
Diet
A diet lacking sufficient calcium and vitamin D is a risk factor in developing osteoporosis.
Calcium from the diet is laid down in bones and teeth, making them strong and hard. An
adequate intake of calcium ensures that bones are as strong as possible. Vitamin D is
needed for the absorption of calcium from the digestive system. Vitamin D can be made
by skin when it is exposed to sunlight, but is also found in fish liver oils and oily fish like
sardines, salmon and tuna.
Family history
Having a family history of osteoporosis, particularly if several family members have been
affected, is associated with a greater risk of an individual developing osteoporosis at a
younger age.
Smoking and excessive alcohol consumption
Both of these activities increase the rate of bone loss and so increase the risk of
osteoporosis.
Exercise
Both insufficient and excessive exercise can increase the risk of osteoporosis. Bone
strength is increased by weight bearing exercises, such as brisk walking, jogging,
dancing etc. It is important therefore to include such exercise on a regular basis,
particularly for women in their teens, twenties and early thirties, in order to maximise
their peak bone density before bone loss begins.
On the other hand, in women, excessive exercise coupled with a restricted diet can
decrease bone density by reducing their body fat to such a level that they stop
menstruating. This causes oestrogen levels to drop which, as we saw earlier, causes an
increase in bone loss as a result of increased loss of calcium from bones. Although this
may happen in adolescence or young adulthood, it increases the risk of osteoporosis
later in life.

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5.2.3

Effects of exercise

We saw in the previous section that lack of exercise and excessive exercise in women
can increase the risk of developing osteoporosis. However regular exercise throughout
life is important both in promoting bone density and in reducing or slowing down the rate
of bone loss later in life.
Bone becomes stronger and denser when it is subjected to mechanical stress. This
happens during weight bearing activities such as brisk walking, jogging, playing
badminton and dancing. Non-weight bearing activities, like swimming, although useful
as aerobic exercise, are thought to have little effect on increasing bone density. In order
to reduce the risk of osteoporosis, it is important at all ages to carry out some weight
bearing exercise on a regular basis. This is particularly important, however, during
adolescence and young adulthood, so that peak bone density is maximised.

5.3



Diabetes mellitus

Learning Objective
After studying this section, you should be able to:
• explain the role of insulin and glucagon in the control of blood glucose levels;
• state that non-insulin dependent diabetes mellitus (NIDDM) is generally
associated with obesity;
• describe how cells become resistant to the effects of insulin in NIDDM;

Æ

• describe the effect of exercise on blood glucose levels in subjects with NIDDM.

Diabetes mellitus is a disease in which the body cannot control the levels of blood
glucose. Before looking at this condition in more detail it is important to examine the
normal mechanisms of control.

5.3.1

Controlling blood glucose levels

The sugar glucose is an important source of energy for the body. Carbohydrates are
digested to glucose, which is absorbed into the blood stream and carried to the liver
before being distributed to body cells.
If there is too much glucose in the blood it is converted to glycogen and stored in the
liver until it is needed (it may also be stored as fat). If glucose levels are low, glycogen
is converted back to glucose which can then be used by the body.
The receptor cells that monitor the changes in blood sugar levels are found in the islets
of Langerhans. These are specialised cells in the pancreas that secrete two different
hormones, insulin and glucagon, in response to changes in concentration of glucose in
the blood (Figure 5.1). Insulin is secreted by  cells while glucagon is secreted by 
cells.
• Insulin is secreted when the blood glucose level is high. This hormone causes
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the conversion of glucose to glycogen in the liver. As a result the blood glucose
level falls.
• Glucagon is secreted when the blood glucose level is low. This hormone
catalyses the conversion of glycogen to glucose in the liver. As a result the
blood glucose level rises.

Figure 5.1: Insulin and glucagon

Blood glucose levels
The control of blood glucose is an example of homeostasis, the name given to various
processes by which the body maintains a constant internal environment. It is also an
example of negative feedback control. These processes are discussed in more detail in
Higher Biology, Unit 3, Topic 7.
Figure 5.2 is a flow diagram showing the homeostatic control of blood glucose levels.

Figure 5.2: Changes in blood glucose levels

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5.3.2

Insulin dependent and non-insulin dependent diabetes mellitus

Some people are unable to make enough (or any) insulin to regulate their blood sugar
levels. This is a common disorder (Figure 5.3) known as diabetes mellitus (or diabetes).

Figure 5.3: Incidence of diabetes
There are two types of diabetes mellitus:
1. Type 1 or insulin dependent diabetes is caused by the destruction of some (or
all) of the  cells in the islets of Langerhans, resulting in too little insulin production.
This type of diabetes accounts for 5-10% of all cases of diabetes mellitus. It usually
occurs in childhood and used to be called early-onset diabetes. The treatment for
Type 1 diabetes is daily insulin injections.
2. Type 2 or non-insulin dependent diabetes (NIDDM) used to be called late-onset
diabetes because it is more common in adults over 40 years of age. (However
type 2 diabetes is becoming more common in younger people with some children
as young as 13 being diagnosed with this type of diabetes.) It is found mainly
in people who are overweight or obese; more than 80% of people with Type 2
diabetes are or were overweight. In fact, obesity appears to be the greatest
risk factor for NIDDM, although heredity is also thought to play a part since the
disease tends to run in families.
People with this type of diabetes have normal (or above normal) levels of insulin,
but the target cells have become less sensitive to its effects.
Insulin works by binding to specific receptors in the cell membranes of its target
cells. As well as liver cells, insulin targets skeletal muscle cells and fat cells. As
a result of insulin binding to the receptors, the cell membranes allow glucose to
pass through into the cells more easily. When someone is obese, it is thought
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that the number of insulin receptors decreases. This reduced number of receptors
makes the cells less sensitive to insulin and there is a reduced uptake of glucose
by them. This condition is known as insulin resistance and is often a precursor to
non-insulin dependent diabetes mellitus.
The pancreas tries to compensate for the cells’ resistance by producing more
insulin. Eventually the  cells stop functioning effectively and insulin production
decreases. As a result blood glucose levels rise and diabetes develops.
Many sufferers of NIDDM can control their blood sugar levels by regular exercise
and a carefully controlled diet. If it continues to get out of control, however, insulin
injections may be necessary.

Q1: Insulin has to be delivered by injection; it cannot be given orally. Why not?
We have seen that diabetics have higher than normal levels of glucose in their blood.
This excess glucose is excreted in the urine and can be detected by a simple glucose
test (Clinistix). This is one of the first tests used in the diagnosis of diabetes. Other
symptoms include: rapid weight loss, dehydration and frequent urination. Diabetes is
very dangerous and can result in a sufferer falling into a coma and dying if it is left
untreated.

Glucose tolerance test
Glucose tolerance tests are performed on people who are suspected of having diabetes
mellitus. The patient must fast (not eat) for at least eight hours before taking the test,
then they are given a glucose drink (with a known volume of glucose in it). Blood
samples are then taken at regular time intervals and the glucose concentration in the
blood measured to monitor how the body is processing the glucose.
Normal blood glucose levels are between 4 - 8 mmol / L, low blood glucose levels are
below 4 mmol / L and high blood glucose levels are above 8 mmol / L. A person is
considered a diabetic if their blood glucose levels are over 10 mmol / L.
Table 5.1 shows the blood glucose levels for two adults during a glucose tolerance test.
Table 5.1: Blood glucose levels for two adults
time (hours)

0

0.5

1

2

3

patient A

6.2

9.1

7.2

6.5

6.0

patient B

10.1

15.7

18.5

19.6

17.2

Use the data in Table 5.1 to plot graphs in Figure 5.4 showing the change in blood
glucose levels for each patient.

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TOPIC 5. OSTEOPOROSIS AND DIABETES MELLITUS

Figure 5.4: Glucose tolerance test results
Q2:

Which patient is diabetic?

a) A
b) B
Q3:

Why do the patients have to fast before taking the glucose tolerance test?

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Blood glucose levels - a problem solving exercise
Blood glucose levels can be measured in two different ways. The British system
measures blood glucose in mmol / L and the American system uses mg / dL. Remember
that normal blood glucose levels are between 4 - 8 mmol / L, low blood glucose levels
are below 4 mmol / L and high blood glucose levels are above 8 mmol / L.
Sam is a diabetic. On a recent holiday to America his luggage was lost at the airport.
Unfortunately, his blood glucose monitoring kit was in his suitcase. Sam bought a new
one at a pharmacy in America, but, when he came to use it he found that the units it
measured blood glucose levels in was different.
This information will help you to answer the questions:
Number of moles per litre = mass per litre / molecular weight
Molecular weight of glucose = 132 g / mol
1 d / L = 1/10 L
Q4: Calculate Sam’s blood glucose level in mmol / L when the monitor showed a
reading of 95 mg / dL.
Q5: Is Sam’s blood glucose level normal?
a) Yes
b) No
Q6: Calculate Sam’s blood glucose level in mmol / L when the monitor showed a
reading of 159 mg / dL.
Q7: Is Sam’s blood glucose level normal?
a) Yes
b) No
Q8: What are the consequences of getting the calculation wrong?

5.3.3

Effect of exercise on people with NIDDM

As well as the benefits of exercise mentioned in Topics 2 and 4, physical activity has
additional benefits for sufferers of insulin resistance or non-insulin dependent diabetes
mellitus.
Exercise improves the uptake of glucose in people with NIDDM. This is thought to be
due to an increase in the sensitivity of and an increase in the number of insulin receptors
on the cell membranes of target cells, particularly skeletal muscle cells. This means that
individuals are able to control their blood sugar levels more effectively with increased
physical activity. This, combined with a carefully controlled diet, can reduce or even
remove the need for insulin injections.
Any kind of increased physical activity is beneficial, but again the general advice of
about 30 minutes of moderate exercise most days which is given by most health experts
applies to sufferers of NIDDM.

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5.4

Essay Question

This is an essay question similar to the style you will encounter in the SQA Advanced
Higher Examination. A total of 15 marks is available. You should hand your completed
essay to your tutor for marking.

Essay: Controlling blood glucose levels
Question
Describe the roles of insulin and glucagon in controlling blood sugar levels; why and
how non-insulin dependent diabetes (NIDDM) arises; the effects of exercise in people
with NIDDM. (15 marks)

5.5

Learning Points

• Osteoporosis occurs when calcium and other minerals are removed more quickly
from bone than can be added. The bones become more porous and brittle with an
increased risk of fractures.
• Osteoporosis affects men, women and children but is most common in postmenopausal women.
• Risk factors for osteoporosis include increasing age, being female, being postmenopausal, a diet inadequate in calcium and vitamin D, family history of
osteoporosis, smoking, excessive alcohol consumption, lack of exercise and
excessive exercise (in women).
• Bone becomes stronger and denser as a result of weight bearing activities such
as brisk walking, jogging, playing badminton and dancing.
• Non-weight bearing activities, like swimming, are thought to have little effect on
increasing bone density.
• Insulin and glucagon are hormones produced in the islets of Langerhans in the
pancreas. Insulin is produced by  cells while glucagon is produced by  cells.
• When blood sugar levels are high, insulin is released into the blood and causes
glucose to be converted to glycogen in the liver, thus returning blood glucose levels
to normal.
• When blood sugar levels are low, glucagon is released causing glycogen in the
liver to be converted to glucose. Again the blood glucose level returns to normal.
• Non-insulin dependent diabetes mellitus (NIDDM), or Type 2 diabetes, is linked to
obesity. More than 80% of people with NIDDM are or have been overweight.
• Heredity is also thought to be a factor in the development of the NIDDM since the
disease tends to run in families.
• Insulin works by binding to specific insulin receptors in the cell membranes of its
target cells (liver cells, skeletal muscle cells and fat cells).
• As a result of insulin binding to the receptors, the cell membranes allow glucose
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73

to pass through into the cells more easily.
• People with NIDDM have normal (or above normal) levels of insulin, but the target
cells have become less sensitive to its effects.
• When someone is obese the number of insulin receptors decreases. This reduced
number of receptors makes the cells less sensitive to insulin and there is a reduced
uptake of glucose by them.
• Exercise improves the uptake of glucose in people with NIDDM. This is thought to
be due to an increase in the sensitivity of and an increase in the number of insulin
receptors on the cell membranes of target cells, particularly skeletal muscle cells.

End of Topic test
An online assessment is provided to help you review this topic.
30 min

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Topic 6

End of Unit 3b Test (NAB)

Contents

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TOPIC 6. END OF UNIT 3B TEST (NAB)

Online there is an end-of-unit test.

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ANSWERS: TOPIC 1

Answers to questions and activities
1 The cardiovascular system
Answers from page 6.
Q1: The vein has a larger lumen than the artery, but the artery has a thicker tunica
media and tunica externa with more muscle and elastic fibres than the vein.
Q2: Arteries must have thick, muscular and elastic walls in order to withstand the
pressure of blood being pumped out by the heart. The pressure in veins is less than
in arteries so they do not need as many muscle or elastic fibres.
Q3: The walls of the capillaries are only one cell thick, while their diameter is very
small.
Q4: Because the walls are only one cell thick, materials can be exchanged rapidly
between the blood and body tissues; because the diameter of capillaries is so small
they can permeate all the body tissues so that every cell is in close proximity to the
blood.

Blood pressure differences in arteries, capillaries and veins (page 6)
Q5: When the heart contracts the blood pressure increases, forcing blood into the
arteries. Then the heart relaxes before the next heartbeat so the pressure drops.

Internal structure of the heart (page 8)
Q6: Because they are found between the atria and ventricles in the heart.
Q7: To prevent backflow of blood.
Q8: They prevent the atrio-ventricular valves from being inverted when the ventricles
contract.

Answers from page 10.
Q9: 0.8 seconds (60 seconds / 75)

The cardiac cycle (page 12)
Q10: Systole is contraction of the heart muscle while diastole is relaxation of the heart
muscle.
Q11: The atrio-ventricular (bicuspid and tricuspid) valves are open and the semilunar
valves are closed.
Q12: The pressure is greater during ventricular systole because the ventricle walls have
contracted thus putting the blood under increased pressure. This forces the blood out
into the arteries.
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ANSWERS: TOPIC 1

Answers from page 14.
Q13: 4.8 l/min (Remember you have to convert the 75 ml to 0.075 l.)
Q14: 115 beats/min

Death rates from CHD (page 16)
Q15: a) Males
Q16: c) Ireland
Q17: a) True

Essay: Structure and function of blood vessels (page 17)
blood vessels are arteries, veins and capillaries (1);
Arteries (maximum 5 marks)
1. carry blood away from the heart (1);
2. at high pressure (1);
3. contain a central lumen (through which blood flows) (1);
4. inner layer (tunica intima) lines the lumen / is made up of endothelium (single layer
of smooth cells) (1);
5. this layer minimises friction between the blood and the wall of the vessel (1);
6. middle layer (tunica media) contains smooth muscle, collagen and elastic fibres
(1);
7. outer layer (tunica externa) contains collagen fibres and some elastic fibres (1);
8. elastic tissue enables arteries to stretch and recoil with each heartbeat (1);
9. the stretch and recoil can be felt as a pulse in arteries (eg in the wrist and neck)
(1);
Capillaries (maximum 4 marks)
1. allow exchange of materials between blood and body tissues (1);
2. lower blood pressure than in arteries (1);
3. walls consist of a single layer of endothelium (1);
4. walls are permeable as a result of tiny gaps between cells of endothelium (1);
5. tiny diameter (7 m) (1);
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ANSWERS: TOPIC 1

6. permeate through all tissues of the body (1).
Veins (maximum 5 marks)
1. carry blood back to the heart (1);
2. blood pressure lower (in veins than in arteries or capillaries) (1);
3. have thinner layers (tunica interna, media and externa) than arteries (1);
4. less elastic tissue than arteries (1);
5. larger lumen than arteries (1);
6. blood flow in one direction maintained by contraction of muscles (squeezing the
veins) (1);
7. and by the presence of valves (1).

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2 Exercise and the cardiovascular system
Answers from page 24.
Q1:

22

Q2: When she smoked the cigarette the nicotine caused her arteries to constrict and
the carbon monoxide reduced the amount of oxygen in her blood. As a result her heart
had to pump faster to supply her body with enough oxygen.

Answers from page 25.
Q3:

Any three of the following:

• strengthens the heart muscle so that it can pump more blood with each beat, this
reduces the resting heart rate.
• improves blood lipid profile by decreasing LDL and increasing HDL levels.
• lowers blood pressure by maintaining the elasticity of the arteries.
• helps weight loss by decreasing body fat.

Heart rate experiment (page 29)
Q4:

a) Student A

Q5: Student A is fitter because their pulse returned to its resting rate faster than
Student B. Student A also has a lower resting pulse than Student B.
Q6: The heart rate differs slightly when a person is sitting and standing as the heart
has to work slightly harder to pump blood around the body when a person is standing.
By always taking their pulse when they were standing the students ensured that the
change in heart rate was due to them recovering from exercise and not from sitting
down. This makes the results of their experiment more reliable.
Q7:

This makes the results more reliable and comparable.

Let’s say person A did 25 starjumps and it took 2 minutes to restore their resting pulse
but person B did 45 starjumps and took 3 minutes to return to their resting pulse person
B. Person A is not necessarily fitter because person B worked harder.

Answers from page 30.
Q8: 100% increase. (Initial CO = HR x SV = 75 x 80 = 6000 ml/min = 6l/min. Final CO
= 120 x 100 = 12000 ml/min = 12l/min. Increase in CO = 6l/min. Percentage increase =
increase/initial CO x 100 = 6/6 x 100 = 100%.)

Answers from page 30.
Q9: The brain requires a constant supply of glucose and oxygen. It could not survive
for long with a smaller blood supply. Therefore during exercise its blood supply must
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ANSWERS: TOPIC 2

be maintained. The abdominal organs can survive with a smaller blood supply during
exercise.
Q10: 50% (The decrease is 2400 - 1200 = 1200 ml/min. Percentage decrease =
decrease/original supply x 100 = 1200/2400 x 100 = 50%.)
Q11: 900% (The increase is 12000 - 1200 = 10800 ml/min. Percentage increase =
increase/original supply x 100 = 10800/1200 x 100 = 900%.)
Q12: As muscle work harder during exercise heat is produced. Increasing blood flow to
the skin means that this heat can be lost to the air thus cooling the body down.

Answers from page 33.
Q13: 136.5 beats/minute
Q14: 114.8 beats/minute

Essay: Risk factors for cardiovascular disease (page 34)
1. modifiable risks can be reduced by lifestyle changes, non-modifiable risks cannot
(1);
2. modifiable risks - any two from diet, smoking, activity (exercise), obesity (1);
3. non-modifiable - any two from age, gender, heredity (genetic), race (ethnicity) (1);
Modifiable risks (maximum 6 marks - 3 for each risk)
diet
1. reduce saturated fats (1);
2. reduce cholesterol (1);
3. lower alcohol intake (1);
4. include vitamins A, C and E (1);
5. include one portion of oily fish / salmon per week (1);
6. increase fibre intake (1).
smoking
1. nicotine increases blood pressure / constricts blood vessels (1);
2. carbon monoxide reduces amount of oxygen carried by the blood / binds to
haemoglobin more effectively than oxygen (1);
3. smoking increases heart rate / makes heart work harder (1);
4. smoking can cause / accelerate atherosclerosis / damages internal lining of
arteries (1);
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ANSWERS: TOPIC 2

5. smoking causes blood to clot more easily / increases risk of stroke / heart attack
(1);
6. smoking lowers HDL:LDL / leads to increased cholesterol levels / deposition of fat
in blood vessels (1).
activity
1. strengthens the heart muscle (myocardium) / heart can pump more blood with
each beat (1);
2. lowers the resting heart rate (1);
3. improves blood lipid profile / decreases LDL and increases HDL levels (1);
4. lowers blood pressure / maintains the elasticity of the arteries (1);
5. helps weight loss / decreases body fat (1).
obesity
1. overeating / energy in is greater than energy out (1);
2. sedentary livestyles / too little physical activity (1);
3. consuming high fat foods (1).
Non-modifiable risks (maximum 6 marks - 3 for each risk)
age
1. increasing age increases risk of CVD (1);
2. arteries become less elastic / blood pressure increases with age (1);
3. atherosclerosis increases with age (1);
4. men over 45 and women over 55 at increased risk (1).
gender
1. men at greater risk than women (1);
2. women develop CVD (on average) 10 years later than men (1);
3. after the menopause women’s risk is greater (1);
4. oestrogen may have a protective role against heart disease (1).
heredity
1. having close family members with CVD increases risk (1);
2. risk greater if CVD before 55 years in men / 65 in women (1);
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ANSWERS: TOPIC 2

3. genetic mutation leads to predisposition to very high cholesterol levels (1);
4. other possible genetic factors: tendency to obesity (1) and high blood pressure
(1).
race (ethnicity)
1. people of S. Asian background have greater risk than white people (1);
2. mortality from CVD 40% greater among S.A. ethnic group (1);
3. early onset of CVD 2 to 3 times higher among S.A. ethnic group (1);
4. people of S.A. background have higher incidence of insulin resistance (1);
5. insulin resistance is risk factor for diabetes, which is a risk factor for CVD (1).

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ANSWERS: TOPIC 3

3 Exercise and metabolism - energy
Energy intake (page 39)
Q1:

fat - 39.5%, protein - 14.8%, carbohydrate - 45.8%.

Q2:

fat - 30.8%, protein - 18.5%, carbohydrate - 50.7%.

Q3: Student A, because he has an energy surplus of 160 kcal per day (2915 kcal in 2755 kcal out = 160 kcal surplus), while student B is in energy balance.

Answers from page 42.
Q4:

1673.5 kcal/day

Q5:

1295 kcal/day

Calculating daily energy expenditure (page 43)
Q6: 56.5 kcal/hour. (BMR = 12.2 x 50 + 746 = 1356 kcal/day = 1356/24 = 56.5
kcal/hour)
Q7:

2940 kcal

Energy requirements (page 46)
Q8:

b) As a teenager

Q9:

b) As a teenager

Q10: A lot of growth occurs in a relatively short period of time during adolesence. This
requires a lot of energy. As a child the growth rate is less rapid and as an adult little or
no growth occurs.
Q11: 6464.3 kJ
Q12: 10.1 MJ

Answers from page 47.
Q13: 2140 kcal

Answers from page 50.
Q14: 96 kcals
(At a heart rate of 160 beats/min, this individual is using 2 l of oxygen/min. During 10
minutes they will use 2 x 10 = 20 litres of oxygen. 4.8 kcal of energy are released for
every litre of oxygen used. Therefore the energy released = 4.8 x 20 = 96 kcal.)
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ANSWERS: TOPIC 3

Essay: Measuring energy expenditure (page 50)
Direct calorimetry (maximum 5 marks)
1. depends on the fact that all energy is eventually expended as heat (1);
2. heat energy produced is measured by placing individual inside an insulated
chamber (1);
3. then measuring the temperature rise of a known mass of water (1);
4. energy (cal) = mass of water (g) x rise in temp (Æ C) (1);
5. advantage - extremely accurate method (1);
6. disadvantage - very expensive / difficult to operate (1)
Indirect calorimetry (maximum 5 marks)
1. based on the assumption that there is a relationship between oxygen consumption
and energy expended (1);
2. about 4.8 kcal (20 kJ) of energy are released for every litre of oxygen used (1);
3. information needed are volume of air expired and percentage oxygen in inspired
and expired air (1);
4. energy expended (kcal) = 4.8 x volume of oxygen (litres) (1);
5. advantage - cheap / easy to carry out (1);
6. disadvantage - not as accurate as direct calorimetry (1)
Heart rate recording (maximum 5 marks)
1. depends on the assumption that there is a linear relationship between heart rate
and oxygen consumption (1);
2. the relationship for an individual must be graphed (for a given individual) (1);
3. need to know length of time of activity and average heart rate during the activity
(1);
4. when average heart rate for activity is known, oxygen consumption can be read off
the graph (1);
5. total oxygen consumption = oxygen consumption (l/min) x time (min) (1);
6. energy expenditure (kcal) = 4.8 x oxygen consumption (litres) (1);
7. advantage - easy to carry out if relationship is known for a given individual (1);
8. disadvantage - not as accurate as direct calorimetry (1)

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ANSWERS: TOPIC 4

4 Exercise and metabolism - body composition and weight control
Answers from page 55.
Q1:

Person A - 1.0545 gcm/ 3 , person B - 1.0292 g/cm 3 .

Q2:

Person A has 19.4% fat, while person B has 30.1% fat.

Q3:

Person B.

Body Mass Index (BMI) (page 56)
Q4:

28.9 kg m-2

Q5:

c) Overweight

Q6:

9 kg

Q7:

22.6 kg m-2

Q8:

b) Normal

Q9: Julie used to have a BMI of 23.8 and was of normal weight. By dieting she has
reduced her BMI to 18.7 and is now underweight. If she continues to lose weight Julie
will be seriously underweight which will have a negative effect on her health.
Q10: c) The body mass index is greater than 30.

Essay: Measuring body composition (page 59)
Densitrometry (maximum 5 marks)
1. depends on the fact that fat is less dense than lean tissue (1);
2. density = mass (weight) / volume (1);
3. mass (weight) measured in g, volume measured in (cm 3 ) (1);
4. volume measured by immersion in water and measuring volume of water displaced
(1);
5. percentage body fat is calculated using the formula:% fat = 495/density (g/cm 3 ) 450 (1);
6. advantage - it is an accurate method (1);
7. disadvantage - needs specialist equipment / person needs to be confidant in water
(1).
Skinfold thicknesses (maximum 5 marks)
1. involves measuring the layer of fat under the skin at various places on the body
(1);
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ANSWERS: TOPIC 4

2. using a skinfold caliper (1);
3. most common sites to be measured are: front and back of the upper arm / the
biceps and triceps muscles, below the shoulder blade and (just) above the hip (1);
4. these measurements are used to estimate the amount of (total) body fat (1);
5. advantage - any one of quick, cheap and relatively accurate (1);
6. disadvantage - takes practice to develop accurate measuring skills/ assumes
everyone has the same distribution of body fat (over their body) (1).
Bioelectrical impedance analysis (maximum 5 marks)
1. a conductor allows electricity to pass through it / offers little resistance to the flow
of electricity (1);
2. an insulator does not allow electricity to pass through easily / offers resistance
(impedance) to the flow of electricity (1);
3. fat is an insulator, while lean tissue/ muscle is a conductor (1);
4. a (small) electric current is passed through the body and the resistance/
impedance measured (1);
5. the greater the resistance the greater the (percentage) body fat (1);
6. advantage - any one from: it is quick, equipment is portable, equipment is easy to
use (1);
7. disadvantage - any one from: not as accurate as other methods, changes
in hydration/ skin temperature will affect conduction (and therefore body fat
calculation), tends to overestimate % body fat of lean people/underestimate the
% body fat in overweight people (by about 2-5%.

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ANSWERS: TOPIC 5

5 Osteoporosis and diabetes mellitus
Answers from page 69.
Q1: Insulin is a protein, like all hormones. If given orally, it would be digested before
being absorbed into the blood stream.

Glucose tolerance test (page 69)
Q2:

b) B

Q3: This ensures that the glucose present in the patient’s blood is from the glucose
drink they have been given. This makes it easier to monitor how well the body is
processing the glucose. If the patient had eaten before taking the test their glucose
levels would be higher due to the food they had eaten and not necessarily due to a lack
of insulin.

Blood glucose levels - a problem solving exercise (page 71)
Q4:

7.2

A common problem with this type of calculation is to forget the importance of units. The
correct way to perform the calculations is as follows:
95 mg/dL = 950 mg/L = 950 x 10 -3 g/L
Number of moles per litre = mass per litre / molecular weight = 950 x 10 -3 g/L
g/mol = 7.2 x 10-3 mols/L

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7.2 x 10-3 mols/L = 7.2 mmol / L
In these calculations it is possible to arrive at the correct answers without converting
everything into grams. However you should be aware that this is not always the case
and that following the correct procedure will prevent problems later on.
Q5:

a) Yes

Q6:

12.0

Q7:

b) No

Q8: If the calculation is done incorrectly an inaccurate value for the blood glucose
level could be obtained. This could be very dangerous because the diabetic may give
themselves too much or too little insulin.
For example, 175 mg / dL is the equivalent of 13.25 mmol / L (high blood glucose).
However, if the calculation was performed incorrectly it may be thought that it is 1.325
mmol / L (low blood glucose).

Essay: Controlling blood glucose levels (page 72)
(a) roles of insulin and glucagon (maximum 8 marks)
1. insulin and glucagon produced in islets of Langerhans / pancreas (1);
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2. insulin produced by  cells, glucagon by  cells (1);
3. high blood sugar levels detected by pancreas / islets of Langerhans /  cells (1);
4. insulin is produced (1);
5. causes glucose to be converted to glycogen (1);
6. in liver (1);
7. low blood sugar levels detected by pancreas / islets of Langerhans /  cells (1);
8. glucagon produced (1);
9. causes glycogen to be converted to glucose (1);
10. in both cases glucose levels return to normal (1);
11. (control of blood glucose) is an example of homeostasis / negative feedback (1)
(b) why and how NIDDM arises (maximum 5 marks)
1. obesity / being overweight is the main risk factor / NIDDM associated with obesity
/ being overweight (1);
2. more than 80% of people with NIDDM are or were overweight (1);
3. heredity is also a risk factor (1);
4. insulin levels are normal / above normal (1);
5. (target) cells / muscle cells / fat cells are less sensitive to the effects of insulin (1);
6. (this is thought to be because) there is a decrease in the number of insulin
receptors on the cell membrane (1);
7. which results in a reduced uptake of glucose into the cells (1);
8. therefore blood sugar levels rise (1)
(c) effects of exercise (maximum 2 marks)
1. exercise improves uptake of glucose (in people with NIDDM) (1);
2. (thought to be) due to an increase in the sensitivity of the (insulin) receptors (on
the cell membrane) (1);
3. and an increase in the number of (insulin) receptors (1)

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