Exercise effect on contractile properties of skeletal muscle in mouse muscular dystrophy.

The purpose of this study was to determine the effect of a high repetitive exercise program, treadmill running, on the tetanic tension and rate of tension development of the slow twitch soleus muscle of normal plus dystrophic mice and their littermates. The exercise program used would be considered to be of mild intensity since it failed to produce any detectable histochemical or biochemical changes. In the noninvolved normal and littermate mice, there was no difference in maximum tetanic tension between the exercised and nonexercised control groups. In the normal mice (eight weeks of age), there was a significant decrease in rate of tension development for those exercised for five weeks compared to nonexercised controls. In littermate mice (seven weeks old) exercised for a four-week period, there was also a significantly lower rate of tension development compared to their nonexercised controls. In dystrophic mice (seven weeks old) exercised for only one to two weeks, there was significantly lower tension as well as rate of tension developed for the exercised mice when compared to nonexercised dystrophic mice. In dystrophic mice (six weeks old) exercised for one to two weeks, there was no difference in tension or rate of tension development when compared to nonexercised controls. In both six and seven-week-old littermate mice, also exercised for one to two weeks, this reduction in tension and rate of tension development did not occur. The average life span for the dystrophic mice used in this study is about 30 weeks. Of the nine exercised dystrophic mice scheduled for study at eight weeks, only one survived, suggesting that even the mild exercise used might have shortened their life expectancy.