Effects of Exercise Training on Exercise Capacity and Free Radical Metabolism in Different Muscle Fibers in Rats

Objective To investigate the influence of exercise training on the exercise capacity,the free radical content and the antioxidant enzyme activity in different muscle fibers in rats.Methods Male Sprague-Dawley rats were divided into three groups: sedentary,untrained and trained groups.The trained rats run on a treadmill(15~20 m/min,60 min/d,6 d/wk) for 8 weeks and were subjected to the exericse test before and 24 h after exercise training.The untrained rats,used as the control of the trained group,moved freely within a cage except for being subjected to the exercise test at the corresponding time point.The sedentary rats moved freely within a cage without any intervention.24 hours after exercise test the malondialdehyde(MDA) content,total antioxidant capacity(T-AOC)and superoxide diasmutase(SOD) activity were measured in three types of skeletal muscle fibers(Ⅰ,Ⅱa,Ⅱb).Results(1) Compared with the untrained group and before-exercise session,the maximal running distance and duration were significantly higher in the trained group(P0.01).(2) MDA content of red muscle(Ⅰ,Ⅱa) was higher than that in white muscle(Ⅱb) whithin a control group(P0.05).MDA levels ofⅡa and Ⅱb fibers in the untrained group and of Ⅱb fiber alone in the trained group were higher than those of the sedentary group(P0.05).(3) Compared with that of the control group,T-AOC of the I and Ⅱa fibers in the trained group increased significantly,but had no difference in Ⅱb fiber.However,T-AOC of the Ⅱb fiber in the untrained rats was lower than that in control group(P0.05).(4) Compared with that of the sedentary group,SOD activity of I and Ⅱa fibers in the trained group increased significantly,but had no difference in Ⅱb fiber.SOD activity was unchanged in three types of fibers in the untrained group.Conclusion Exercise training selectively increases SOD activity and T-AOC in I and Ⅱa fibers and enhances free radical degradation,which is responsible for training-induced augmentation of the exercise capacity in the skeletal muscle.