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

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Abstract
The hyperoxia‐improved tolerance to maximal aerobic performance was studied in relation to exercising muscle metabolic state. Five students were submitted to four different tests on a cycle ergometer, each being conducted under normoxia and hyperoxia (60% FiO2) on separate days: Test 1, a progressive exercise until exhaustion to determine the maximal work load (W˙max) which was unchanged by hyperoxia; Test 2, an exercise at W˙max (287 ± 12 W) until exhaustion to determine the performance time (texh) 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˙max for 90% normoxic‐texh (4.8 ± 0.5 min under both O2 conditions) then followed by a 10‐s sprint bout during which the total work output (W˙tot) was determined; W˙tot was elevated by 15% when exercising under hyperoxia; Test 4 (M‐Exercise test) consisted also of cycling at W˙max for 4.8 ± 0.5 min with blood and muscle samples taken at rest and at the end of the exercise to compare the level of different metabolites. During hyperoxic M‐Exercise test, glycogen was twice more depleted whereas glucose‐6‐phosphate and lactate were less accumulated when compared with normoxia. No significant differences were observed for pyruvate, phosphocreatine and muscle/blood lactate ratio between the two conditions. Conversely to normoxia, levels 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 pyruvate and NADH in mitochondria, thereby lowering the metabolic acidosis and allowing a better functioning of the glycolytic and contractile processes to delay the time to exhaustion.

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