Effectiveness of Sulfur-Containing Antioxidants in Delaying Skeletal Muscle Fatigue

FERREIRA, L. F., K. S. CAMPBELL, and M. B. REID. Effectiveness of Sulfur-Containing Antioxidants in Delaying Skeletal Muscle Fatigue. Med. Sci. Sports Exerc., Vol. 43, No. 6, pp. 1025-1031, 2011. Reactions involving thiol biochemistry seem to play a crucial role in skeletal muscle fatigue. N-acetylcysteine amide (NACA) and L-ergothioneine (ERGO) are thiol-based antioxidants available for human use that have not been evaluated for effects on muscle fatigue. Purpose: To test the hypothesis that NACA and ERGO delay skeletal muscle fatigue. Methods: We exposed mouse diaphragm fiber bundles to buffer (CTRL), NACA, ERGO, or N-acetylcysteine (NAC; positive control). Treatments were performed in vitro using 10 mM for 60 min at 37 degrees C. After treatment, we determined the muscle force-frequency and fatigue characteristics. Results: The force-frequency relationship was shifted to the left by ERGO and to the right by NACA compared with CTRL and NAC. Maximal tetanic force was similar among groups. The total force-time integral (FTI; N.s.cm(-2)) during the fatigue trial was decreased by NACA (420 +/- 35, P < 0.05), unaffected by ERGO (657 +/- 53), and increased by NAC (P < 0.05) compared with CTRL (581 +/- 54). The rate of contraction (dF/dt(MAX)) during the fatigue trial was not affected by any of the treatments tested. NAC, but not NACA or ERGO, delayed the slowing of muscle relaxation (dF/dt(MIN)) during fatigue. Conclusions: In summary, NACA and ERGO did not delay skeletal muscle fatigue in vitro. We conclude that these antioxidants are unlikely to improve human exercise performance.