Effects of N-acetylcysteine on respiratory muscle fatigue during heavy exercise

Respiratory muscle fatigue (RMF) occurs during heavy exercise in humans. N-acetylcysteine (NAC) infusion has been shown to reduce RMF, suggesting that oxidative stress is a contributing factor. The purpose of the present study was to determine the effect of an acute oral dose of NAC on RMF during heavy exercise. Subjects (n = 8) were given either placebo (PLA) or NAC (1800 mg) 45 min prior to a 30 min constant load (85V˙O2peak), discontinuous exercise test. Maximum respiratory pressures (inspiratory, PImax; expiratory, PEmax) and venous blood samples were made prior to and following each 5 min of exercise. There was no difference (p > 0.05) in PImax between NAC (127.9 ± 34.1 cmH2O) or PLA (134.1 ± 28.1 cmH2O) at rest. During exercise, PImax was significantly lower with PLA (∼14%) compared to NAC at 25 and 30 min suggesting less RMF with NAC. There were no differences (p > 0.05) between groups in PEmax, V˙O2, V˙E, or heart rate at rest or throughout exercise. These results suggest that an acute dose of NAC reduces RMF during heavy exercise.