JOURNAL OF APPLIED PHYSIOLOGY, 87: 1381-1385, 1999

The Effect Of Supplementation With A Cysteine Donor On Muscular Performance

LC Lands, MD, PhD*†, VL Grey, PhD†‡, AA Smountas, BSc*

*Division of Respiratory Medicine, † Department of Pediatrics, ‡Department of Biochemistry, McGill University Health Centre-Montreal Children’s Hospital, Montreal, Quebec, Canada

ABSTRACT - Oxidative stress contributes to muscular fatigue. Glutathione (GSH) is the major intracellular antioxidant, whose biosynthesis is dependent upon 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 m) were studied pre- and 3 months post-supplementation with either Immunocal (20 gm/day) or casein placebo. Muscular performance was assessed by whole leg isokinetic cycle testing, measuring Peak Power and 30-sec 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-sec Work Capacity). Follow-up data on 18 subjects (9 Immunocal, 9 placebo) were analyzed. Both Peak Power (mean±se: 13±3.5%, p<0.02) and 30-sec 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.