Effect of supplementation with a cysteine donor on muscular performance

Oxidative stress contributes to muscular fatigue. GSH is the major intracel lular antioxidant, the biosynthesis of which is dependent on cysteine avail ability. We hypothesized that supplementation with a whey-based cysteine do nor [Immunocal (HMS90)] designed to augment intracellular GSH would enhance performance. Twenty healthy young adults (10 men, 10 women) were studied p resupplementation and 3 mo postsupplementation with either Immunocal (20 g/ day) or casein placebo. Muscular performance was assessed by whole leg isok inetic cycle testing, measuring peak power and 30-s work capacity. Lymphocy te GSH was used as a marker of tissue GSH. There were no baseline differenc es (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) i ncreased significantly in the Immunocal group, with no change (2 +/- 9.0 an d 1 +/- 9.3%) in the placebo group. Lymphocyte GSH also increased significa ntly 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 t hat prolonged supplementation with a product designed to augment antioxidan t defenses resulted in improved volitional performance.