Oral N‐acetylcysteine supplementation does not improve cycling time trial performance

Abstract

Reactive oxidative species (ROS) have been implicated as a mechanism of skeletal muscle fatigue. ROS have been shown to increase with elevated oxygen consumption and an increase in core temperature. Use of antioxidant supplementation during exercise in the heat may be effective at delaying fatigue and improving performance. The aim of this study was to determine whether supplementation with oral N-acetylcysteine (NAC) would improve performance of trained cyclists during a 30-km time trial in temperate (T) and hot (H) environments. We hypothesized that NAC supplementation would result in a faster 30-km time compared to placebo (PL) in both T and H environments and would alter whole blood glutathione status. Nine healthy, male competitive cyclists (32 ± 2 years; VO2max, 62 ± 3 ml·kg−1·min−1) performed a 30-km time trial in T (23° C) and H (37° C) conditions, with oral NAC or PL supplementation. Subjects received 1200 mg oral NAC or PL for 2 days prior to each trial and 1200 mg prior to testing. Whole blood total glutathione (GSH), oxidized glutathione (GSSG), and GSH/GSSG ratio were analyzed to determine blood redox status. Skin and core temperatures were higher (p<0.05) in the H trials. Cycling time was slower (p<0.05) in the H trials but NAC had no effect (p>0.05) on cycling time in T or H (PL-T 50 ± 0.7, PL-H 52 ± 0.9, NAC-T 50 ± 0.8, & NAC-H 53 ± 1.0 min). In addition, there were no differences (p>0.05) in whole blood glutathione status among the treatments at baseline or following the 30-km time trials. Oral NAC did not alter blood redox status in these highly trained subjects nor did it impact performance in T or H. Lack of improvement in performance may be due to an already elevated antioxidant capacity in these highly trained cyclists.