PRINCIPLES OF EXERCISE TESTING
There are many reasons why it may be necessary to assess the
physiological fitness of an individual, whether an athlete in training
or a patient recovering from heart surgery.
An exercise test can provide baseline data against which later
assessments can be measured, for example
• to monitor the effectiveness of a training programme for and
athlete
•to monitor recovery from MI.
The exact form of the exercise test will depend on the physical
condition of the individual and the reasons for conducting the test.
ASSESSMENT OF AEROBIC FITNESS
The aerobic capacity of an individual is largely determined by their ability to use
oxygen, and this depends on the efficiency of their cardiovascular and respiratory
systems in the delivering oxygen to the exercising muscles at the required rate.
A measure of the maximum amount of oxygen that a person can utilise is called the
maximal oxygen uptake or VO2max.The higher the value of the VO2max, the greater
the aerobic fitness of the individual.
This test, which uses sophisticated laboratory apparatus to measure oxygen
consumption and carbon dioxide production, requires the participant to exercise to
exhaustion and is therefore only suitable for evaluating the fitness of competitive
athletes.
VO2 max differences
depending on activity
Graph showing oxygen
consumption against work
intensity, shows a plateau in
consumption despite
Increasing workload.
TYPICAL VALUES FOR VO2max
Group (25-35 years)
VO2max (ml/kg/min)
Men
VO2max (ml/kg/min)
Women
Elite endurance
athletes
70-80
60-70
Highly trained team
games players
55-65
48-60
Active young adults
44-52
38-46
Average for young
adults
40-45
34-39
The tests are usually carried out on treadmills or bicycle ergometers, and work
intensity is gradually increased until there is no further increase in oxygen
consumption despite an increased workload.
As already stated, VO2max testing is not suitable for most individuals and has several
limitations – it requires expensive laboratory equipment, highly trained technical
personnel and medical back-up.
For these reasons, several less complex indirect measures of VO2max have been
developed which require the individual to exercise at much lower intensities. These
predictive tests are known as sub-maximal tests. They are based on the assumption
that there is a direct linear relationship between heart rate, oxygen consumption and
intensity of exercise.
By measuring heard rate and oxygen consumption at several levels of work intensity, it
is possible to predict VO2max by extrapolating to their predicted maximum heart rate
calculated from 220 minus age in years.
There are however some important possible sources of error in this predicted VO2max :
• Heart rate (especially at low levels) can be affected by other factors apart from
exercise, such as emotion, previous meal, temperature, anxiety etc.
• Predicted maximum heart rate may not be accurate for a particular individual.
STEP TESTS
The simplest and most commonly used sub-maximal test is the step test, which uses
steady-state exercise heart rates or recovery heart rates to evaluate the efficiency of
the cardiovascular response to exercise.
There are many different protocols for step tests but all are based on the same
physiological principles.
They involve the subject stepping up and down from a step or bench at a fixed pace for
several minutes (3-5 minutes). The height of the step and the rate of stepping (often
set by a metronome) vary with different protocols.
At the end of the exercise, HR is measured for 15-30 seconds at one minute intervals
for about four minutes after cessation of exercise to measure the rate of recovery.
The fitter the individual, the lower the HR will be immediately after exercise
and the faster it will return to its resting level.
It is also possible to measure heart rate continuously during exercise by
wearing an HR monitor.
An identical test can be repeated at a later stage in order to evaluate any
changes in the aerobic fitness, with lower HRs indicating an improvement
in fitness.
The table on the following page shows the pulse rate of two pupils
before , during and after exercise.
Time (minutes)
Yvonne
Zara
0
70
75
2
72
80
4
76
100
6
85
120
8
100
140
10
90
130
12
80
120
14
70
105
16
70
95
18
70
85
20
70
75
•At what time did the two
pupils started exercising ?
•At what time did the two
pupils finish exercising ?
•Which of the two pupils
recovered more quickly ?
•Is it easy to work out from
the results an exact
recovery time ?
•Can you think of a better
way of showing which girl
recovered more quickly ?
•Your teacher will show you how information shown as a graph makes
it easier to see patterns in information. Look at the following graph
comparing the pulses of three pupils before , during and after exercise
Effects of exercise on heart rate
150
Pupil A
140
The steeper this line the quicker
the persons pulse rate is
increasing and the less fit the
person is
130
Pulse rate/minute
120
110
Pupil B
100
Pupil C
90
80
70
60
0
5
10
15
20
25
Time (minutes)
Exercis
e starts
Exercise
stops
The shorter this line is the less
time the person has taken to
recover from the exercise and the
fitter they are
SHUTTLE TESTS
The 20-metre shuttle run is a commonly used field test of aerobic fitness. However, it is
maximal and exhaustive and is therefore only suitable for moderately fit
individuals.
Participants run between two markers positioned twenty metres apart at a pace
determined by a pre-recorded tape. The test starts at a fairly slow pace which
increases every minute and the individual runs between the two markers until they
cannot keep up with the pace. The level they reach (i.e. the number of completed
shuttles) is recorded and may be used to predict VO2max.
A variation of this test – the shuttle walking test – is more suitable for less fit
individuals.
EXERCISE STRESS TESTS
Often, individuals with chronic CHD will exhibit normal
electrocardiogram (ECG) traces at rest but abnormal ECGs
during exercise. Such individuals undergo stress tests on a
treadmill when workload is increased in an incremental
fashion whilst their ECG is closely monitored.
You can try learning more about EKG’s and practice being a Doctor by clicking here
Some facts about an ECG
• Now called EKG to prevent confusion when doctors write it down
• Starts at Sinoatrial node or pacemaker
• Electical signal passes actross heart muscle causing them
to contract
• Atria contract first , followed by ventricles
• EKG readout shows rhythm of heart
• Abnormal rhythyms indicate damage to the heart
• Structural damage can only be identified by scans.
Sino-atrial Node
ROLE OF EXERCISE IN CARDIAC REHABILITATION
Over the last twenty years there has been a major change in the treatment of patients
who have had a heart attack or who have undergone cardiac surgery.
Before the 1970s, complete bed rest for at least six weeks following a heart attack or
surgery was the standard treatment. This was to allow time for the damaged heart
muscle to form scar tissue.
Now, however, some form of supervised aerobic exercise sessions are included in all
cardiac rehabilitation programmes, which also offer advice on diet, smoking,
alcohol, stress and relaxation.
The exercise programmes are not designed to produce elite athletes, but aim to allow
patients to improve their physical demands of everyday life.
The initial stages of the exercise programme are likely to start within a week of the
heart attack or surgery and will include gentle walking.
Slightly more vigorous activity can start four to six weeks later.