Abstract

The study was designed to investigate the influences of exogenous testosterone administration for weight and functional profiles of slow (soleus: SOL) and fast (extensor digitorum longus: EDL) skeletal muscles in exercise trained rats. 28 male Wistar rats were divided into 4 groups; control (C), testosterone administered control (TC), sprint trained testosterone administered (TS), and endurance trained testosterone administered (TE). TS and TE groups were trained using motor-driven treadmill from 4 wks old. TC, TS, and TE groups were administered testosterone dissolved in corn-oil daily (20 mg/kg BW) from 4 wks old. At the age of 17 wks, SOL and EDL muscles were isolated, and weight and functional profiles were measured. Relative muscle weight of TC, TS, and TE groups were significantly higher than that of C group in both SOL and EDL muscles. Time to peak tension of twitch contraction in TS and TE groups were significantly shorter than that of C group in EDL muscle. Half relaxation times of TC, TS, and TE groups were significantly shorter than that of the C group in SOL muscle. FG fiber composition of TS group was significantly higher than those of the C and TC groups. Phosphofructokinase activity of TC and TS groups were significantly higher 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 with the highest impact on sprint trained EDL muscle. Verf.-Ref.