The maximum oxygen intake. An international reference standard of cardiorespiratory fitness

Lack of cardiorespiratory fitness may well contribute to the increasing prevalence of degenerative cardiovascular disease throughout the world. As a first step towards co-ordinated and internationally comparable investigation of this problem, methods of measuring the reference standard of cardiorespiratory fitness-the maximum oxygen intake, (Vo(2))(max)-were compared by an international working party that met in Toronto in the summer of 1967.Repeated testing of 24 subjects showed that the (Vo(2))(max) was greatest on the treadmill, 3.4% smaller in a stepping test, and 6.6% smaller during use of a bicycle ergometer. There were also parallel differences in cardiac stroke volume. Uphill treadmill running was recommended for the laboratory measurement of (Vo(2))(max), and stepping or bicycle exercise for field studies. A discontinuous series of maximum tests caused some improvement in the fitness of subjects, and a "continuous" test (with small increases in load at 2-min intervals) was preferred.

Standardization of submaximal exercise tests

It is often impossible to measure the reference standard of cardiorespiratory fitness (the maximum oxygen intake) directly, and there is thus a need for subsidiary standard procedures based on body responses to submaximal exercise. In order to reach agreement on such procedures, a recent international working party has compared a variety of possible tests involving step, bicycle, and treadmill exercise; criteria of comparison included the extent of habituation and learning with each procedure, the physiological responses, and practical considerations. There was little to commend submaximal exercise on the treadmill. Anxiety and learning were least on the bicycle ergometer, but significant anaerobic metabolism developed at loads of more than 55% of aerobic power; the main role of the bicycle was thus in laboratory tests requiring arm immobilization. The step test was cheap and portable, subjects showed relatively little anxiety or learning, and good-quality electrocardiograms were obtained: it thus seemed the procedure of choice for field tests. The results of all forms of submaximal test should be extrapolated to maximum oxygen intake in order to overcome difficulties arising from differences in the age and fitness of subjects. Four common extrapolation procedures, based respectively on one to four measurements of oxygen consumption and pulse rate, yielded similar predictions of maximum oxygen intake. A single progressive test, in which the exercise load was increased at the end of every third minute, gave an identical prediction of maximum oxygen intake to that obtained from a series of 4 discontinuous tests. The progressive test was thus the preferred procedure; however, in subjects with some circulatory delay, it might be necessary to replace the four 3-min loads by three 4-min loads.

A survey of enteric infections among Alaskan Indians

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