Effects of hyperoxia and hypoxia on dynamic and sustained static performance of the human quadriceps muscle.

The influence of variations in inspired PO2 on dynamic and static muscle performance of the left quadriceps muscle was studied. Eight subjects performed (1) 60 maximal consecutive dynamic contractions and (2) one sustained exhaustive static contraction at 27% of maximal voluntary contraction (MVC). Breathing mixtures containing 11%, 21% or 99% O2, were administered. Peak torque as an average of the 60 knee extensions was higher (p less than 0.01) during hyperoxia (mean +/- SE = 104 +/- 4 Nm) than during normoxia (98 +/- 4 Nm), but did not differ significantly between hypoxia (95 +/- 5 Nm) and normoxia. Peak torque of individual extensions declined more rapidly during hypoxia than during normoxia, differing in the final 12 extensions by 11% from normoxic values. Static endurance time was reduced (p less than 0.02) during hypoxia (152 +/- 12 s) as compared to normoxia (189 +/- 13 s) and hyperoxia (169 +/- 11 s). No significant difference in endurance time was demonstrated between hyperoxia and normoxia. Thus, hypoxia impaired muscle performance in both dynamic and sustained static exercise, whereas acute hyperoxia improved dynamic but not static muscle performance. The results are interpreted in terms of differences in rate of intramuscular H+ accumulation.