Effect of hyperoxia on aerobic and anaerobic performances and muscle metabolism during maximal cycling exercise

The hyperoxia-improved tolerance to maximal aerobic performance was studied in relation to exercising muscle metabolic state. Five students were submi tted to four different tests on a cycle ergometer, each being conducted und er normoxia and hyperoxia (60% FiO2) on separate days: Test 1, a progressiv e exercise until exhaustion to determine the maximal work load ((W) over do t (max)) which was unchanged by hyperoxia; Test 2, an exercise at (W) over dot(max) (287 +/- 12 W) until exhaustion to determine the performance time (t(exh)) which was elevated by 38% under hyperoxia but exhaustion occurred at the same arterial proton and lactate concentrations; Test 3 (S-Exercise test) consisted of cycling at (W) over dot(max) for 90% normoxic-t(exh) (4. 8 +/- 0.5 min under both O-2 conditions) then followed by a 10-s sprint bou t during which the total work output ((W) over dot(tot)) was determined; (W ) over dot(tot) was elevated by 15% when exercising under hyperoxia; Test 4 (M-Exercise test) consisted also of cycling at (W) over dot(max) for 4.8 /- 0.5 min with blood and muscle samples' taken at rest and at the end of t he exercise to compare the level of different metabolites. During hyperoxic M-Exercise test, glycogen was twice more depleted whereas glucose-6-phosph ate and lactate were less accumulated when compared with normoxia. No signi ficant differences were observed for pyruvate, phosphocreatine and muscle/b lood lactate ratio between the two conditions. Conversely to normoxia, leve ls of ATP, ADP and total NADH were maintained at their resting level under 60% FiO2. These data lead us to suppose a higher oxidation rate for pyruvat e and NADH in mitochondria, thereby lowering the metabolic acidosis and all owing a better functioning of the glycolytic and contractile processes to d elay the time to exhaustion.