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

Authors


Corresponding author M. Amann: The John Rankin Laboratory of Pulmonary Medicine, 4245 Medical Science Center, 1300 University Avenue, Madison, WI 53706, USA. Email: amann@wisc.edu

Abstract

Changing arterial oxygen content (Cmath formula) has a highly sensitive influence on the rate of peripheral locomotor muscle fatigue development. We examined the effects of Cmath formula on 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 Cmath formula (17.6–24.4 ml O2 dl−1), induced by variations in inspired O2 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 (ΔQtw; 1–100 Hz). Central neural drive during the time trials was estimated via quadriceps electromyogram. Increased Cmath formula from 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 ΔQtw (−33 to −35%) induced by the exercise was not different among the four time trials (P > 0.2). These effects of Cmath formula on time trial performance and ΔQtw were reproducible (coefficient of variation = 1–6%) over repeated trials at each Fmath formula on separate days. In the same subjects, changing Cmath formula also affected performance time to exhaustion at a fixed work rate, but similarly there was no effect of ΔCmath formula on peripheral fatigue. Based on these results, we hypothesize that the effect of Cmath formula on 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.

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