During exercise, reactive oxygen species are produced as part of the contractions your muscles perform. The production of these radicals is closely associated with fatigue and damage to the contracting elements of the muscle tissue during short-term or immediate responses.
Over the long-term, however, the production of reactive oxygen species is considered an adaptive response that at some level helps the muscle to coordinate and communicate all of the necessary aspects of optimal muscle performance.
N-Acetyl-cysteine is a derivative of the amino acid cysteine that researchers have suggested for some time has an impact on performance and fatigue. A recent study had twelve active men engage in two identical series of exercise tests. In one situation, all of the participants ingested either N-acetyl-cysteine over a six day period while in the second condition all participants ingested a placebo for six days. The participants according to pre-study exercise performance were matched to ensure both groups were equal to each other before the investigation started. The purpose of this study was to determine the impact of oral N-acetyl-cysteine supplementation on intermittent exercise performance.
After loading with their assigned supplement group, all participants completed a series of three exercise sessions; the first was a pre-muscle damage performance assessment, the second was a muscle damaging bout of intermittent exercise and post-exercise performance assessment (that was identical to the pre-exercise test). As expected, performance in both groups decreased, but when N-acetyl-cysteine was administered, exercise performance was satisfactorily preserved whereby the performance deteriorated substantially when placebo was consumed (Cobley 2011).
Supplementation with N-acetyl-cysteine did exhibit some gastrointestinal side effects so it may be important to experiment with dosing and timing to minimize any negative impact from stomach upset. Due to the short-term nature of the study, the authors concluded their results may have particular relevance for any individual or competitive athlete who is competing in short-term competitions, or those athletes with minimal time for recovery. In closing, intense, stressful exercise results in the production of components called reactive oxygen species that when they increased by a great deal can cause negative outcomes such as a decrease in performance and development of fatigue results. A number of competitive situations involve the need to maximally perform and then recovery before performing maximally again. In these situations, supplementation with n-acetyl-cysteine may help to sustain exercise performance in the short term by resisting the development of fatigue.
Cobley, J. N., C. McGlory, et al. "N-Acetylcysteine's attenuation of fatigue after repeated bouts of intermittent exercise: practical implications for tournament situations." International Journal of Sport Nutrition and Exercise Metabolism (2011) 21(6): 451-461.