Enzyme adaptations in rat skeletal muscle after two intensities of treadmill training

The effects of high intensity, short duration chronic exercise (HSD, N = 9) and low intensity, long duration chronic exercise (LLD, N = 9) on the selected enzyme activities of three muscles of rats were studied. After 12 wk of treadmill training, the LLD group showed 15-23% decreases in lactate dehydrogenase activity in all muscles (P less than 0.05), while succinic oxidase activity increased in the soleus (49%) and the vastus lateralis profundus (42%) (P less than 0.05). No change in creatine kinase activity was found in either group. The HSD group showed no change in lactate dehydrogenase activity; however, phosphofructokinase activity increased (greater than 50%) in both of the fast-twitch muscles (P less than 0.01), while only the vastus lateralis superficialis showed increased succinic oxidase activity (30-40%) (P less than 0.05). Following training no difference was observed in mean heart weights; however, the mean body weight of the sedentary control group (SC, N = 9) was greater than both exercise groups (P less than 0.05). No difference was observed between the exercise groups. The mean heart weight/body weight ratios were significantly different between all groups (P less than 0.01). These results indicated that the HSD group selectively increased its glycolytic power, while the LLD group increased only its oxidative ability. Furthermore, both exercise groups exhibited less gains in body weight than the non-exercise group. This change was independent of any work performed.