Oxygen Uptake, Muscle High‐Energy Phosphates, and Lactate in Exercise under Acute Hypoxic Conditions in Man

Virtually all differences in physiological response to identical exercise intensities at altitude as compared to normoxia were appropriately adjusted by expressing exercise intensity relative to the respective aerobic power capacities in the two conditions.

Abstract

Abstract The relationships among muscle metabolite concentration, exercise intensity, and oxygen utilization were studied under simulated altitude conditions (decompression chamber, 462 mm Hg b.p.). 5 male subjects exercised in 4 min bouts on a cycle ergometer at a wide range of exercise intensities (range 20–114% altitude max V o2 ). Oxygen uptake was determined throughout exercise and recovery. Muscle biopsies ( vastus lateralis ) and fingertip blood samples were taken at rest and during recovery. Muscle ATP and creatine phosphate concentrations became reduced during exercise at all intensities. Little or no increase in lactate was observed below apprpx. 60% altitude max V o2 . The hypoxic condition caused a decreased acceleration from resting V o2 and an increase in O 2 ‐deficit at each absolute intensity as compared with normoxia. Close relationships were observed between level of high‐energy phosphate depletion and both O 2 ‐deficit and fast component of O 2 ‐debt not different from the same relationships under normoxic conditions. Virtually all differences in physiological response to identical exercise intensities at altitude as compared to normoxia were appropriately adjusted by expressing exercise intensity relative to the respective aerobic power capacities in the two conditions. Physiological responses to this type of exercise appear determined in great part by the availability of oxygen.