Effects of periodic weight support on medial gastrocnemius fibers of suspended rats

The effects of seven-day-long hindlimb suspension (HS) and HS plus daily periodic weight support activity on the size and metabolic properties of individual fibers in the medial gastrocnemius (MG) of rats were examined. Sections of muscle tissue removed after seven day suspension were stained quantitatively for succinate dehydrogenase and alpha-glycerophosphate dehydrogenase, and qualitatively for myosin ATPase. It was found that short intermittent periods of weight support had a beneficial effect in maintaining the size and metabolic properties of both dark and light ATPase fibers in the deep regions (i.e., close to the bone) and of dark ATPase fibers in the superficial regions of the MG. The effect was greater in the deep regions.