Arterial oxygenation influences central motor output and exercise performance via effects on peripheral locomotor muscle fatigue in humans

Changing arterial oxygen content ( C   aO   2) has a highly sensitive influence on the rate of peripheral locomotor muscle fatigue development. We examined the effects of C   aO   2on exercise performance and its interaction with peripheral quadriceps fatigue. Eight trained males performed four 5 km cycling time trials (power output voluntarily adjustable) at four levels of C   aO   2(17.6–24.4 ml O 2 dl −1 ), induced by variations in inspired O 2 fraction (0.15–1.0). Peripheral quadriceps fatigue was assessed via changes in force output pre‐ versus post‐exercise in response to supra‐maximal magnetic femoral nerve stimulation (Δ Q tw ; 1–100 Hz). Central neural drive during the time trials was estimated via quadriceps electromyogram. Increased C   aO   2from hypoxia to hyperoxia resulted in parallel increases in central neural output (43%) and power output (30%) during cycling and improved time trial performance (12%); however, the magnitude of Δ Q tw (−33 to −35%) induced by the exercise was not different among the four time trials ( P > 0.2). These effects of C   aO   2on time trial performance and Δ Q tw were reproducible (coefficient of variation = 1–6%) over repeated trials at each F   IO   2on separate days. In the same subjects, changing C   aO   2also affected performance time to exhaustion at a fixed work rate, but similarly there was no effect of Δ C   aO   2on peripheral fatigue. Based on these results, we hypothesize that the effect of C   aO   2on locomotor muscle power output and exercise performance time is determined to a significant extent by the regulation of central motor output to the working muscle in order that peripheral muscle fatigue does not exceed a critical threshold.