Respiratory gas exchange ratio and prediction of aerobic power.

The Issekutz procedure for the prediction of maximum oxygen intake from the respiratory exchange ratio (R) has been evaluated on a diverse group of 308 subjects, including "whites" and Eskimos, men and women ranging in age from 16 to 65 yr. When applied to young white men performing 12 min of progressive step or treadmill exercise, the prediction procedure has a coefficient of variation of less than 10%, without systematic error. Unfortunately, the standard equation lacks generality, and erroneous predictions can arise from a change of test protocol, the use of a different exercise modality, or application to older subjects. If a brief exercise format is used, low R values may be reported during an early phase of relative hypoventilation. At a given metabolic loading, bicycle ergometry yields a higher respiratory minute volume than other modes of exercise. A heavy loading of one muscle group seems responsible, and the results is a high R value in submaximum effort. Aging is associated with a lowering of maximum blood lactate levels and thus maximum figures for R.