Oxidative stress contributes to muscular fatigue. GSH is the major intracellular antioxidant, the biosynthesis of which is dependent on cysteine availability. We hypothesized that supplementation with a whey-based cysteine donor [Immunocal (HMS90)] designed to augment intracellular GSH would enhance performance. Twenty healthy young adults (10 men, 10 women) were studied presupplementation and 3 mo postsupplementation with either Immunocal (20 g/day) or casein placebo. Muscular performance was assessed by whole leg isokinetic cycle testing, measuring peak power and 30-s work capacity. Lymphocyte GSH was used as a marker of tissue GSH. There were no baseline differences (age, ht, wt, %ideal wt, peak power, 30-s work capacity). Follow-up data on 18 subjects (9 Immunocal, 9 placebo) were analyzed. Both peak power [13 ± 3.5 (SE) %,P < 0.02] and 30-s work capacity (13 ± 3.7%, P < 0.03) increased significantly in the Immunocal group, with no change (2 ± 9.0 and 1 ± 9.3%) in the placebo group. Lymphocyte GSH also increased significantly in the Immunocal group (35.5 ± 11.04%,P < 0.02), with no change in the placebo group (−0.9 ± 9.6%). This is the first study to demonstrate that prolonged supplementation with a product designed to augment antioxidant defenses resulted in improved volitional performance.
Note that this was done with whey protein; also note that no exercise training was involved – the subjects developed more power from whey protein alone. N-acetylcysteine is also a cysteine donor and one may speculate that the results from that might be as good.