THE EFFECT OF INDUCED HYPOXIA ON OXYGEN UPTAKE DURING MUSCULAR EXERCISE IN NORMAL SUBJECTS

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Abstract
During the moderate exercise of treadmill walking, steady-state oxygen uptake bears a linear relationship to the work performed (i.e. to the slope of the treadmill), when the speed of walking is kept constant. Four normal male subjects were studied on the treadmill at several levels of exercise while they were breathing air and again while breathing a mixture of approximately 11% oxygen in nitrogen. An alteration in the linear relationship between oxygen uptake and work, established with the subjects breathing air, was observed when the subjects were restudied breathing 11% oxygen. In each case, this alteration indicated that the subject took up less oxygen while breathing a low-oxygen mixture despite the accomplishment of similar work loads. That this phenomenon is explicable on the basis of slower attainment of the steady state was excluded by prolonging each exercise period in two subjects. Another possible explanation, i.e. that the subjects effect greater utilization of anaerobic metabolic sources while hypoxic, was excluded by direct measurement of the oxygen debt after each period of exercise. It is concluded that exercising normal subjects exhibit an adaptive mechanism under conditions of induced hypoxia permitting reduced oxygen uptake for a given work load.