ADAPTATIONS IN RAT SKELETAL-MUSCLE FOLLOWING LONG-TERM RESISTANCE EXERCISE TRAINING

The purpose of this investigation was to determine whether long-term, heavy resistance training would cause adaptations in rat skeletal musc le structure and function. Ten male Wistar rats (3 weeks old) were tra ined to climb a 40-cm vertical ladder (4 days/week) while carrying pro gressively heavier loads secured to their tails. After 26 weeks of tra ining the rats were capable of lifting up to 800 g or 140% of their in dividual body mass for four sets of 12-15 repetitions per session. No difference in body mass was observed between the trained rats and age- matched sedentary control rats. Absolute and relative heart mass were greater in trained rats than control rats. When expressed relative to body mass, the mass of the extensor digitorum longus (EDL) and soleus muscles was greater in trained rats than control rats. No difference i n absolute muscle mass or maximum force-producing capacity was evident in either the EDL or soleus muscles after training, although both mus cles exhibited an increased resistance to fatigue. Individual fibre hy pertrophy was evident in all four skeletal muscles investigated, i.e. EDL, soleus, plantaris and rectus femoris muscles of trained rats, but muscle fibre type proportions within each of the muscles tested remai ned unchanged. Despite an increased ability of the rats to lift progre ssively heavier loads, this heavy resistance training model did not in duce gross muscle hypertrophy nor did it increase the force-producing capacity of the EDL or soleus muscles.