During physical exercise, cells produce a high level of ROS. While this actually serves a biological role that positively affects skeletal muscle adaptations and force production, in vitro and animal studies suggest that excessively high levels of ROS can contribute to impaired muscle function and muscle fatiguing.[1][2][3]
NAC has been explored as a potential ergogenic due to its antioxidant effects, but research supporting its use is limited. A 2017 meta-analysis was unable to find any evidence of a performance benefit with NAC supplementation, but the analysis included studies using vastly different dosages, exercise regimens, and study populations (e.g., elite athletes, untrained individuals).[4] NAC seems to display the most consistent benefit when exercise is being performed in a fatigued state,[5][6][7] but it may negatively affect muscle adaptations to training.[8] Ultimately, further research is needed to determine if NAC supplementation is beneficial in this context, and if so, in what setting and dosage.