It is recommended that adults over the age 35, who never have exercised before, obtain medical clearance. This is necessary for the protection of the individual?s health and from any fitness professional?s legal perspective. Also, the questionnaire consent/waiver form in Appendix A should be completed for further legal protection and for the medical doctor's perusal.
VALUE OF A STRESS TEST
A stress test should be completed by all mature adults and individuals age 35 or older who are sedentary. Individuals who possess one or several coronary risk factors, such as high HDLs, a smoker, high BP, or if the individual has not seen a physician within the last 5 years should undertake a stress test.
A stress test becomes even more crucial for those over 65 as it is difficult to determine the over 65's tolerance for activity. It also is necessary to determine presence or absence of myocardial ischemia (a temporary deficiency of blood supply to the heart caused by an obstruction), either prior to an exercise program, while in relatively good health, or as a post-coronary test to indicate damage levels and a therapeutic program. A stress test is not a substitute for complete history and yearly physical examinations, but it is a viable test that can pick up on problems that would preclude a person's participation in an exercise program or indicate required modification of a program in accordance with physical problems.
Fitness professionals or physicians should explain in advance to the individual to be tested what is involved. This helps to increase motivation and for the individual to exercise for longer and with less anxiety. The individual will need to:
-Wear proper clothing (tracksuit) and comfortable running or walking shoes.
-Refrain from eating for 2-3 hours prior to the test, so that digestion does not interfere with optimal blood flow.
-Refrain from smoking for at least 1-2 hours, since smoking can impair cardiovascular capaci! ty.
< p>WHAT OCCURS
The stress test conducted by the physician can be performed with a motorized treadmill, bicycle or arm ergometer. Often if the individual suffers from lower body maladies, or if a return to work after an illness involves strenuous upper body activity, the arm ergometer may be used to produce a more accurate test.
The stress test is designed to challenge the body to a safe but necessary level to reveal irregularities that are unlikely to show when at rest. Usually an undiagnosed heart disease appears only during vigorous exercise. The narrowed coronary arteries may supply enough blood to the resting individual, but, as oxygen needs rise, electrocardiographic abnormalities indicate a problem. The physician will look for evidence of ischemia and its effects in rhythm disturbances (tachyarrhythmias or bradyarrhythmias), aortic and mitral valve disease, significant hypertension, and myocardial disease.
The stress test usually will not take more than 10 minutes. Exercise for longer will measure endurance rather than aerobic capacity (VO2max). During any physical activity, the body responds as follows:
-Heart rate increases
-Systolic BP increases
-Diastolic BP remains the same or decreases
-Cardiac output increases
-Systemic vascular resistance decreases
-Coronary blood flow increases
-Myocardial O2 demand increases
The client is tested at 85-90% of predicted maximal heart rate, although some doctors do not advance the test this far as they feel it is unnecessary to do so ? usually as a safety precaution. Doctors even may stop the test once the client reaches his or her target heart rate. There is one serious drawback to this approach. There is variability in maximal heart rate of individuals within each specific age group. For example, the predicted heart rate of a 60-year old at 85% maximum heart rate is approximately 132 bpm. Because there is a standard deviation, some individuals being in b! etter he alth and others in worse health for any age group, or at least less tolerant to exercise strain, it is possible that some people may have a maximal heart rate well above or below 132 bpm. If an individual's heart rate is above or below the age-specific level, the result will be unreliable in that it is difficult to determine the safety or severity of the test. The strain may not be enough, or too much. Therefore, it is necessary for the physician to motivate the client safely to his or her limits to determine the proposed intensity of the exercise program, and for the client, or the client?s personal trainer, to know at what level the body was stressed sufficiently.
VO2max is another important consideration of the stress test and this correlates well with physical fitness at least in a cardiorespiratory and cardiovascular sense. The amount of oxygen consumed by the myocardium is dependent on oxygen demand: heart rate, contractility, and wall tension. The individual will exercise until the oxygen demand by the myocardial cells exceeds the ability of the stenotic coronary artery to deliver oxygen. In other words, exercise continues until the coronary reserve has been exhausted. At this point, ischemia is induced and exercise must be terminated. During the exercise test, if the individual experiences pectoral angina, intense dyspnea or unusual changes on the electrocardiogram, or significant rhythm change due to a heart block or ventricular disturbance, an unsupervised exercise program may be contraindicated.
The test may be stopped for reasons other than reaching a VO2max upper threshold or having chest discomfort; fatigue, dyspnea, and musculoskeletal problems may cause the mature adult to discontinue exercise. The test also will be terminated if the blood pressure drops as the work increases. Blood pressure is recorded before the test, at an exercise peak, and at recovery. Diastolic BP should remain constant, but could increase slightly because of ! anxiety. It then could decrease once the test begins. Systolic BP usually increases by 60+/-25 mm Hg in males 50-64 years of age, and by 40+/-20 mm Hg in women in the same age group. For example, if the systolic BP fails to increase, or initially increases then drops by more than 20 mm Hg during exercise, then it may indicate severe left ventricular dysfunction. Should the systolic blood pressure fall more than 30mm Hg, then an unsupervised exercise program may be contraindicated.
Sometimes the stress test shows heart complications when, in fact, extrinsic factors are responsible, and this will cause a false-positive result. These include:
-Hypertension
-Fasting
-Drug use (e.g., antidepressants) - the physician will take into account the effects of any medication the individual may be taking
-Malfunctioning ECG recording equipment
-And a host of other minor heart complications that should not stop an individual from participating in an exercise program.
It will be up to the physician to remove the causative agent and re-test the patient. This especially is necessary to discover if the patient is asymptomatic or has the potential for a high exercise capacity. A false-negative test resulting from an extrinsic factor is even more disturbing as this would indicate failure to diagnose the presence of abnormal coronary arteries. It then is up to the physician to rely on other test procedures and for the individual or the fitness professional to monitor progress carefully and to supply the physician with any information in regard to physical difficulty during exercise.
If the test is performed properly, and there is a negative ECG response to exercise, the test does not indicate coronary disease necessarily. Rather, it implies a risk factor that must be taken into consideration when an exercise program is created, and that there must be close monitoring of the individual?s health and fitness level.
CONTRAINDICATIONS FOR A STRESS! TEST
-Acute myocardial infarction (heart attack)
-Uncontrolled congestive heart failure
-Acute inflammatory cardiac disease, e.g., active rheumatic heart disease, myocarditis
-Acute asthma or pneumonia
-Blood pressure greater than 240/120 mm Hg and uncontrolled
-Acute renal (kidney) disease
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Brian D. Johnston is the Director of Education and President of the I.A.R.T. fitness certification and education institute. He has written over 12 books and is a contributing author to the Merck Medical Manual. An international lecturer, Mr. Johnston wears many hats in the fitness and health industries, and can be reached at info@ExerciseCertification.com.
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