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 VO 2max.The higher the value of the VO 2max, 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.

Graph showing oxygen consumption against work intensity, shows a plateau in consumption despite Increasing workload. VO2 max differences depending on activity

TYPICAL VALUES FOR VO 2max 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. Group (25-35 years)VO 2max (ml/kg/min) Men VO 2max (ml/kg/min) Women Elite endurance athletes Highly trained team games players Active young adults Average for young adults

As already stated, VO 2max 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 VO 2max 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 VO 2max 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 VO 2max : 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 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)YvonneZara 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 ?

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 Pupil A Pupil B Pupil C The steeper this line the quicker the persons pulse rate is increasing and the less fit the person is

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 VO 2max. 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 herehere

Sino-atrial Node 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.

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. ROLE OF EXERCISE IN CARDIAC REHABILITATION