Weight-bearing effects on skeletal muscle during and after simulated bed rest

Abstract

The detrimental consequences of bed rest include a rapid loss of muscle mass and strength. Yet, the utility of treatment to offset the effects of bed rest has not been well established. It was the purpose of this study to examine the effects of therapeutic intervention on simulated bed rest in rats. Simulated bed rest was accomplished by unweighting the hindlimbs of rats for 2 weeks via a suspension apparatus attached to the tail and midriff. Weight-bearing (eg, standing, walking) effects on hindlimb unweighting (HLU) were investigated under three conditions: (1) 1 hour of weight bearing per day during HLU; (2) a week of natural cage recovery after HLU; and (3) a combination of 1 hour of weight bearing per day during HLU and a week of recovery after HLU. Muscle contractile function and fiber atrophy were examined in the soleus (SOL), a postural muscle, and the extensor digitorum longus (EDL), a nonpostural muscle. The unweighted SOL showed a 37% loss in wet weight and a 61% decline in peak tetanic tension (P 0). The SOL in rats allowed 1 hour of weight bearing per day lost 22% of its mass and 38% of its P 0, a 38% attenuation. One week of cage recovery after HLU resulted in a SOL wet weight that was 26% less and P 0 that was 42% less than controls. Animals that received the combination of 1 hour of weight bearing per day and 1 week of cage activity nearly recovered muscle mass, but P 0 still was 19% less than controls. The EDL was much less affected by HLU than the SOL. Results strongly support early intervention, particularly weight bearing, during a period of bed rest to modify the decline in strength and muscle mass in postural muscles such as the SOL. Further, results suggest that simply sending a patient home from the hospital to recover from bed rest delays return of strength unnecessarily.