We examined the effect of hindlimb suspension on muscle function, and the effects of two kinds of intensities of running training on atrophied muscle induced by suspension in young and aged Wistar male rats. A significant decrease in the whole muscle wet weight of the soleus followed by hindlimb suspension for 2 weeks was observed in 10 -week (young) and 50 -week (aged) rats. There was no change in the wet weight of extensor digitorum longus (EDL) muscle in young and aged rats following suspension. The responses of the percentage of slow-twitch fibers, maximal isometric tension, and Ca²⁺ sensitivity in soleus and EDL muscles in aged rats to suspension differed from those in young rats.
　A relatively light intensity of running exercise induced the recovery of muscle function in the suspended muscles, compared with the high intensity of running exercise and non-exercise in both young and aged rats. In aged rats, a high intensity of running exercise apparently prevented the recovery of Ca²⁺ sensitivity and maximal tension, but not in young rats. In the non-exercise group, the altered muscle function of young rats during simulated weightlessness re-covered to the control level in the same period as that for hindlimb suspension. These results show that the capacity of protein synthesis of skeletal muscle was decreased during aging, and the intensity of exercise to advance the recovery of muscle function is dependent on the age level. Moderate exercise applied to the aged and/or atrophied muscle has an effect of facilitating recovery in the atrophied muscle function and maintains muscle function during aging.

DESCENTE SPORTS SCIENCE Vol.16/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE