Myosin ATPase activity after strengthening exercise.

Alteration in the histochemical activity of myosin ATPase has been demonstrated in the soleus of adult rats after brief (A) and prolonged (B) intensive weight lifting exercises. The former represented 'high intensity-short duration' and the latter 'high intensity-prolonged duration' exercise. The data revealed a significant muscle hypertrophy (23-26%) in both the exercising groups. Whereas group A muscles showed a relative increase in the number of type II (FOG) fibres, accompanied by a hypertrophy of the type I or slow twitch-oxidative (SO) fibres, the soleus muscles in group B showed a significant decrease (P less than 0.01) in the number of type II (FOG) fibres, presumably owing to a conversion of type II (FOG) to type I (SO) fibres. It is hypothesized that strengthening exercise may enhance the activity of the 'fast type' of myosin ATPase in brief or static work, and the 'slow type' in prolonged or more dynamic high intensity work.