Effects of oral N-acetylcysteine on fatigue, critical power, and W' in exercising humans

Respir Physiol Neurobiol. 2011 Sep 15;178(2):261-8. doi: 10.1016/j.resp.2011.06.020. Epub 2011 Jun 29.


The accumulation of reactive oxygen species (ROS) is associated with muscular fatigue. The antioxidant N-acetylcysteine (NAC) can extend time to fatigue (TTF), but the effect appears to be exercise intensity dependent. The purpose of this study was to determine the effects of an acute oral dose of NAC on time to fatigue (TTF), critical power (CP), W' (curvature constant), V(O2) kinetics and muscle EMG during cycling exercise. Male (n=7) subjects performed four tests at power outputs corresponding to 80, 90, 100, and 110% of the peak power output achieved during the incremental test (Pmax) under NAC and placebo (PLA) conditions. TTF was increased only in the 80% Pmax trial (p=0.033). CP was higher with NAC (NAC: 232±28 W versus PLA: 226±31 W; p=0.032), but W' tended to decrease (NAC: 15.5±3.8 kJ versus W': 16.4±4.5 kJ; p=0.10). The change in W' was negatively related to the change in CP (r = -0.96). MdPF and RMS of EMG tended to change less with NAC. There were no significant differences in V(O2) kinetics. These results demonstrate that oral NAC was successful in extending time to fatigue at 80% Pmax but not at higher work rates.

Publication types

  • Comparative Study
  • Randomized Controlled Trial

MeSH terms

  • Acetylcysteine / administration & dosage*
  • Administration, Oral
  • Antioxidants / administration & dosage
  • Cross-Over Studies
  • Double-Blind Method
  • Exercise / physiology*
  • Exercise Tolerance / drug effects*
  • Exercise Tolerance / physiology*
  • Humans
  • Male
  • Muscle Fatigue / drug effects*
  • Muscle Fatigue / physiology*
  • Young Adult


  • Antioxidants
  • Acetylcysteine