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Cellular damage caused by free radical reactions may play a role in the aging process. A bout of exercise can increase free radical concentration with damage to mitochondria in muscle (Davies et al., 1982). This study was undertaken to determine if muscle adapts to exercise training with an enhancement of enzymatic defenses against free radical damage. A program of running that induced two-fold increases in mitochondrial enzymes in leg muscles of rats resulted in no increase in catalase or cytoplasmic superoxide dismutase (SOD) activities. Mitochondrial SOD activity was increased 37% in fast-twitch red and slow-twitch red types of muscle and 14% in white muscle. Thus, despite an increase in mitochondrial SOD, the ratio of SOD to mitochondrial citrate cycle and respiratory chain enzymes was decreased. It seems unlikely that increased capacity for enzymatic scavenging of superoxide radical is a major protective adaptation against free radical damage in exercise-trained muscle.
Higuchi et al. (Wed,) studied this question.