Muscle damage during exercise: possible role of free radicals and protective effect of vitamin E.

Damage to skeletal muscle during or following extensive or unaccustomed exercise is a well-recognized phenomenon. It is known to occur in healthy normal subjects and manifests itself as both morphological and biochemical changes indicative of damage. The manner in which the muscle is used appears to be particularly important in determining the extent of damage which may occur for a given work-load. Eccentric exercise appears to be particularly deleterious in this respect (Newham et al. I 983). One of the means by which damage to tissues, including muscle, can be assessed is by monitoring the efflux of intracellular cytoplasmic enzymes. This feature has been widely utilized in examination of the mechanisms of breakdown in tissues such as the heart, but has only been sparsely utilized in the study of skeletal muscle damage. We have used this technique in the study of damage to skeletal muscle both in vitro (Jones et al. 1983) and in vivo (Jackson et al. 1983) and these investigations have provided considerable information on mechanisms by which muscle breakdown can occur in a variety of situations. Interest in the possibility that oxygen-centred free radicals could be involved in the damage which occurs following exercise was prompted by the suggestion that the myopathy of vitamin E deficiency in animals was precipitated by unaccustomed exercise (Allen et al. 1975). Vitamin E is thought to exert its major effect in the body by detoxification of lipid-soluble free radicals (Tappel, 1962) and the inference was therefore drawn that free radical production may be increased by exercise (Brady et al. 1979). There is a large increase in 0, utilization by mitochondria during exercise and Packer and co-workers have hypothesized that this may increase the oxidative stress to the tissues in exercising subjects (Davies et al. 1982; Quintanilha & Packer, 1983). Work examining this area has primarily concentrated in two areas: ( I ) to demonstrate an increased free radical activity in the muscle during exercise in animals and ( 2 ) to determine the effect of variations in body vitamin E status on the response to exercise.