Influence of exercise and fiber type on antioxidant enzyme activity in rat skeletal muscle SCOTT K. POWERS, DAVID CRISWELL, JOHN LAWLER, LI LI JI, DANIEL MARTIN, ROBERT A. HERB, AND GARY DUDLEY Center for Exercise Science, Departments of Exercise and Sport Sciences and Physiology, University of Florida, Gainesville, Florida 32611; University of Wisconsin, Madison, Wisconsin 53706; and University of Georgia, Athens, Georgia 30601 Powers, Scott I(,, David Criswell, John Lawler, Li Li Ji, Daniel Martin, Robert A. Herb, and Gary Dudley. Influence of exercise and fiber type on antioxidant enzyme activity in rat skeletal muscle. Am. J. Physiol. 266 (Regzdatory Integrative Comp. Physiol. 35): R375-R380, 1994.-These experiments examined the influence of exercise intensity and duration on antioxidant enzyme activity in locomotor muscles differing in fiber type composition. Nine groups of female Sprague-Dawley rats (age 120 days) exercised 4 days/wk on a motor-driven treadmill for 10 wk. The impact of three levels of exercise intensity (low, moderate, and high: - 55, - 65, and - 75% of maximal oxygen consumption, respectively) and exercise duration (30, 60, and 90 min/day) was assessed. Sedentary animals served as controls. Oxidative capacity in the soleus and white and red gastrocnemius was assessed by measurement of citrate synthase (CS) activity, and antioxi- dant capacity was evaluated by assay of total superoxide dismutase, catalase, and total glutathione peroxidase (GPX) activities. In all muscles, CS activity increased as a function of exercise duration. Furthermore, in the soleus and white gastrocnemius, the magnitude of the training-induced in- crease in CS activity was directly related to exercise intensity. In contrast, the peak increase in CS activity in the red gastrocnemius was relatively independent of exercise inten- sity. Catalase activity was not increased (P > 0.05) in any muscle with training. Training-induced changes in superoxide dismutase and GPX activities were muscle specific; specifi- cally, exercise training significantly (P < 0.05) increased superoxide dismutase activity in the soleus as a function of exercise duration up to 60 min/day. Conversely, training- induced significant (P < 0.05) increases in GPX activity occurred in red gastrocnemius only; the magnitude of the GPX increase was directly related to exercise duration but relatively independent of intensity. These data demonstrate that exer- cise training-induced changes in muscle antioxidant enzymes are muscle specific. free radicals; superoxide dismutase; catalase; glutathione per- oxidase FREE RADICALS are highly reactive atoms or molecules that have an unpaired electron in their outer orbital and that may be formed during normal oxidative metabolism (i.e., in the electron transport chain) in aerobic organ- isms. Evidence exists to implicate cytotoxic reactive oxygen species as an underlying etiology in exercise- induced muscle fatigue and bioenergetic enzyme down- regulation (13, 20). Given the potential role of these reactive speciesin mediating muscular dysfunction, it is not surprising that cells contain several naturally occur- ring defense mechanisms to prevent oxidative injury. These protective mechanisms include the enzymes super- oxide dismutase (SOD), catalase, and glutathione peroxi- dase (GPX). SOD catalyzes the dismutation of superox- ide to 02 and H,O,; HZOBcan be converted to water and 02 by catalase. GPX acting with reduced glutathione can reduce hydroperoxides to form glutathione and alcohol or water. It seems plausible that increased cellular activity of one or more of these antioxidant enzymes will reduce the risk of cellular injury from free radicals (7). Therefore it is of obvious interest to examine methods of increasing cellular levels of antioxidant enzymes. It is generally accepted that exercise results in in- creased free radical production in skeletal muscle (5, 17). Because of the relationship between free radical production and exercise, some investigators have hypoth- esized that endurance exercise will result in elevated antioxidant enzyme activities in skeletal muscle (8, 11, 13, 16). To date, the question of whether endurance exercise increases antioxidant enzyme activity in skel- etal muscle remains controversial. For example, al- though evidence exists that exercise training upregu- lates catalase activity in skeletal muscle (19), other investigations do not report an exercise effect on skeletal muscle catalase (2, 16). Similarly, controversy exists concerning the effects of exercise training on the upregu- lation of SOD activity in skeletal muscle. It seems possible that these equivocal results are related to interstudy differences in the exercise training protocol used to train the animals and/or differences in the muscle fiber types studied. For instance, those investiga- tors that report training-induced increases in muscle antioxidant enzymes have generally employed rigorous exercise training programs (i.e., high intensity and duration of exercise). This observation suggests that rigorous exercise training programs may be required to promote antioxidant enzyme activity in skeletal muscle. Furthermore, a survey of training studies reveals that exercise induction of antioxidant enzymes may be fiber type specific, with highly oxidative muscles being most responsive (8, 12, 16). Clearly, additional experiments are required to clarify these issues. Therefore the pre- sent experiments were designed to test the following hypotheses: 1) rigorous exercise training (i.e., high intensity or long duration) is required to promote antioxidant enzyme activity in skeletal muscle and 2) exercise training-induced increases in skeletal muscle antioxidant enzyme activity are fiber type specific, with highly oxidative muscles fibers being most responsive. To test these hypotheses, we examined the influence of exercise intensity and duration on antioxidant enzyme activity in skeletal muscle differing in fiber type compo- sition. 0363-6119/94 $3.00 Copyright o 1994 the American Physiological Society R375