EXERCISE AND HYPOXIC EFFECTS ON FATIGUE MANIFESTATIONS IN HUMAN SKELETAL MUSCLE

Abstract

To determine the role of exercise, as modified by hypoxia, on fatigue development and recovery, 8 untrained volunteers (age = 20.1 ± 0.66 yr; x ± SE) performed knee extension isometric exercise for 60 min followed by 30 min of recovery during both normoxia (N) and hypoxia (H; FI 02 = 0.14). The exercise was performed at 50% of maximal voluntary contraction (MVC) and 50% duty cycle (5 s contraction and 5 s recovery). Fatigue was assessed both by changes in MVC and at different frequencies of transclutaneous electrical stimulation. Repetitive activity resulted in both a time dependent loss of MVC and 100 Hz torque. For 10 Hz, an initial increase in torque was observed at 5 min of exercise followed by progressive decreases. No further changes in force were observed during the recovery period regardless of the property assessed. During H both MVC and 100 Hz torque were persistently lower than H regardless of time. E = exercise; R = recovery These results demonstrate that hypoxia impairs force production but only at high force outputs, an effect that occurs prior to exercise and which persists throughout exercise and recovery. Supported by NSERC (Canada)Table