Abstract
This study was undertaken to investigate contractile responses of the soleus muscle to hindlimb suspension (HS) and the effects of isometric exercise during HS in the adult (4 months old) and old (20 months old) rats. In adult and old rats, soleus wet weight decreased by 39% and 41% and maximum tetanic tension decreased by 70% and 75% during 3 weeks of HS. Isometric exercise (stational support on a grid at 80° with a load equal to 30% of body weight attached to the tail for 30min per day, 6 days per week) counteracted the decreases in the soleus wet weight and maximum tetanic tension by HS but was less effective in old rats than in adult rats. These results indicate that isometric exercise can counteract loss of force-generating capacity by reduced use. Moreover, although the ageing process did not seem to affect the degree of the soleus muscle atrophy caused by reduced use, it did influence the effects of isometric exercise on the soleus muscle atrophy.
