Histochemical study on the changes in muscle fibers in relation to the effects of aging on recovery from muscular atrophy caused by disuse in rats.

To investigate the effects of aging on the degree of muscular atrophy caused by disuse and its recovery, we evaluated the recovery from muscular atrophy induced in both young and old rats under the same conditions. The soleus was atrophied by immobilization of the foot joint in a hindlimb and unweighting of the bilateral hindlimbs for 2 weeks, and measurement of the wet weight of muscles and biochemical examination were performed 2, 4, and 6 weeks after the removal of unweighting and fixation during the recovery period of 6 weeks. There was no difference in the degree of atrophy in the fixed soleus between the young and old rats. The recovery from atrophy was delayed in the older rats compared to the young rats. In the unfixed hindlimb, the degree of atrophy was low in both the old and young rats, and the recovery was rapid. Because the recovery from disuse muscular atrophy is delayed with aging, it is necessary to avoid unweighting and immobilization, or to reduce the period spent under such conditions.