Quantification of exercise capability and evaluation of physical capacity in man

Abstract

1. (1) Every type of exercise is in a sense a unique situation. However, all forms of muscular work do increase the metabolic rate and therefore it is of particular interest to analyse the involvement of the oxygen transport system. The oxygen uptake gives an accurate measure of the aerobic power, and it is highly related to the cardiac output. The V̇O 2 max is under standardized conditions a highly reproducible characteristic of the individual's aerobic fitness. It is, however, subject to variations under certain conditions (i.e., after prolonged inactivity, after training, as a consequence of cardiac diseases). The main factor behind such variations in V̇O 2 max is proportional changes in the stroke volume. Therefore a recording of the heart rate during exercise at a given oxygen uptake will reflect these variations in longitudinal studies. Generally speaking, a high heart rate is usually associated with a low stroke volume. However, from this information it is not possible to tell whether this (poor) exercise response was caused by genetic factors, lack of training, impaired heart function, or other factors. 2. (2) Data have been presented suggesting that the maximal transport of oxygen (cardiac output X oxygen content of arterial blood) is limited by the central circulation rather than by the tissues' ability to utilize the oxygen. 3. (3) A multi-stage exercise test on a treadmill or bicycle ergometer will provide a measurement of the rate of work an individual is able to tolerate without symptoms or electro-cardiographic abnormalities. 4. (4) For a prediction of the subject's ability to move his body the maximal oxygen uptake per kilogram body weight should be calculated. However, an evaluation of the cardiac performance should be based on the total oxygen transport (liter V̇O 2/min), for that is correlated to the cardiac output, the myocardial oxygen consumption and blood flow. Variation in the body-fat content is not followed by similar changes in the dimensions of muscles, heart, blood volume etc., and demands for local blood flow. In other words, in a heterogenous group of individuals the V̇O 2 X kg −1 X min −1 value is unrelated to the actual load on their hearts. One good measure of the cardiac performance is the ratio of oxygen uptake/heart rate. 5. (5) There is not one test protocol ideal for all situations. It is recommended that one adapts the initial rate of work and the increment in work intensity to the assumed maximal power of the tested person. The work time on each stage should if possible be at least 3 min; the larger the increments in rate of work, the longer the work time on each stage. If the main purpose of the exercise test is to establish the V̇O 2 max or symptom-limited work tolerance one can apply a nonsteady-state protocol with 1–2 min on each stage. 6. (6) For the investigator who is willing to accept the small but definite risk involved, a multi-stage test carried to symptom-limited or maximal power will provide the clearest results, particularly for a differentiation between normals and coronary heart disease patients. 7. (7) It is an alternative to terminate the multistage exercise test at a heart rate close to 195 minus the age (years) of the subject. For most individuals that means a submaximal test. The third alternative is to simulate on a bicycle ergometer or treadmill the metabolic rate of the subject's job and recreational activities. Repeated single-stage or multi-stage tests give excellent measures of variations in physical conditioning (changes in body weight must be considered in a treadmill test).