Recovery effects of exposure to normobaric hyperoxia on central and/or peripheral factors in muscle fatigue

Abstract

Purpose of Study : Reported recovery effects of hyeroxia are conflicted. Increased oxygen concentration influences oxygen transport throughout the organism, therefore it would affect not only peripheral factors in fatigue such as metabolic acidosis in the muscle tissue but also central factors such as the activation levels of central neural drive. This study aimed to identify the effects and the mechanisms of normobaric hyperoxia on recovery of local muscle fatigue. Methods : 12 male subjects performed 3×3×greater than 30 seconds of isometric quadriceps exercise at 70% of maximum voluntary isometric contraction (MVIC) separated by two 15-minutes recovery sessions under one of two different oxygen conditions, one in normoxia (NOX; 20.9% O_2) and one in hyperoxia (HOX; 30.0% O_2). To assess the degree of fatigue and recovery, five parameters were used; MVIC, integrated EMG (iEMG) activity, endurance time to exhaustion, blood lactate, and perceived exertion measured by a visual analog scale (VAS). Results : MVIC improved an average by approximately 14% in HOX compared to NOX at the conclusion of the second recovery session. Further, iEMG changes were nearly proportional to MVIC and were significantly greater in HOX than in NOX. Reduction in endurance time, and increases in blood lactate and VAS were similar between HOX and NOX. Conclusions and Practical Applications : Based on our findings, we hypothesized that hyperoxia mainly increases the central motor output to the activated muscle and therefore muscle force output by responding to the biological conditions in peripheral muscles. For quicker recovery, athletes are recommended to use two sets of 15-minutes recovery under 30.0% hyperoxia.