The experiment was design to investigate the influences of exogenous testosterone administration for the weight and functional profiles of slow (soleus: SOL) and fast (extensor digitorum longus: EDL) skeletal muscles in exercise trained rats. Twenty-eight male Wistar strain rats were divided into four groups (n=7, each group); control (C), testosterone administered control (TC), sprint trained with testosterone administered (TS), and endurance trained with testosterone administered (TE). TS and TE groups were trained using motor-driven treadmill from 4 weeks old. TC, TS, and TE groups were administered the testosterone dissolved in corn-oil every day (20 mg/Kg body weight) from 4 weeks old. At the age of 17 weeks old, SOL and EDL muscles were isolated, and weight and functional profiles were measured. Relative muscle weight of TC, TE, and TE groups were significantly higher (p<0.01) than that of control group in both SOL and EDL muscles. Time to peak tension of twitch contraction in TS and TE groups were significantly shorter (P<0.05) than that of the control group in EDL muscle. The half relaxation time of TC, TS, and TE groups were significantly shorter (TC and TE: p<0.05,TS: p<0.01) than that of the control group in SOL muscle. FG fiber composition of TS group was significantly higher (p<0.01) than those of the control and TC groups. Phosphofructokinase activity of TC and TS groups were significantly higher (TC: p<0.05, TS: p<0.01) than that of TC group in SOL muscle. These results suggest that the exogenous testosterone administration influences weight and functional profiles in slow- and fast-twitch skeletal muscle fibers of exercise trained rats differently. Furthermore these influences appeared remakably in sprint trained rat EDL muscle.
