Treadmill exercise training increases the oxidative capacity of chicken iliotibialis muscle

The number of fibers staining for the oxidative enzyme succinic dehydrogenase (SDH) was measured in the iliotibialis lateralis caudalis muscle of the domestic fowl before treadmill training and after 6 wk and 15 wk of training, respectively. This leg muscle contains exclusively fast-twitch or type II fibers, and before exercise training approximately 40% of these stained intensely for SDH. After 6 and 15 wk training this proportion rose to approximately 50 and 60%, respectively. Most of these highly oxidative fibers also stained weakly for the glycolytic enzyme alpha-glycerophosphate dehydrogenase (alpha-GPDH) and belonged to the fast-twitch oxidative category. Most of the poorly oxidative fibers stained strongly for alpha-GPDH and therefore belonged to the fast-twitch glycolytic category. It is concluded that exercise training in birds can bring about adaptive changes in the oxidative capacity of skeletal muscle similar to those that have been observed in man and other mammals.