BENEFICIAL-EFFECTS OF VOLUNTARY WHEEL RUNNING ON THE PROPERTIES OF DYSTROPHIC MOUSE MUSCLE

Effects of voluntary exercise on the isometric contractile fatigue, an d histochemical properties of hindlimb dystrophic (mdx and 129ReJ dy/d y) skeletal muscles were investigated. Mice were allowed free access t o a voluntary running wheel at 4 wk of age for a duration of 16 (mdx) or 5 (dy/dy) wk. Running performance of mdx mice (similar to 4 km/day at 1.6 km/h) was inferior to normal mice (similar to 6.5 km/day at 2.1 km/h). However, exercise improved the force output (similar to 15%) a nd the fatigue resistance of both C57BL/10 and mdx soleus muscles. The se changes coincided with increased proportions of smaller type I fibe rs and decreased proportions of larger type IIa fibers in the mdx sole us. The extensor digitorum longus of mdx, but not of normal, mice also exhibited improved resistance to fatigue and conversion towards oxida tive fiber types. The dy/dy animals were capable of exercising, yet ra n significantly less than normal animals (similar to 0.5 km/day). Desp ite this, running increased the force output of the plantaris muscle ( similar to 50%). Taken together, the results showed that exercise. can have beneficial effects on dystrophic skeletal muscles.