WEIGHT-BEARING EFFECTS ON SKELETAL-MUSCLE DURING AND AFTER SIMULATED BED REST

The detrimental consequences of bed rest include a rapid loss of muscl e mass and strength. Yet, the utility of treatment to offset the effec ts of bed rest has not been well established, It was the purpose of th is study to examine the effects of therapeutic intervention on simulat ed bed rest in rats, Simulated bed rest was accomplished by unweightin g the hindlimbs of rats for 2 weeks via a suspension apparatus attache d to the fail and midriff. Weight-bearing (eg, standing, walking) effe cts on hindlimb unweighting (HLU) were investigated under three condit ions: (1) 1 hour of weight bearing per day during HLU; (2) a week of n atural cage recovery after HLU; and (3) a combination of 1 hour of wei ght bearing per day during HLU and a week of recovery after HLU, Muscl e contractile function and fiber atrophy were examined in the soleus ( SOL), a postural muscle, and the extensor digitorum longus (EDL), a no npostural muscle, The unweighted SOL showed a 37% loss in wet weight a nd a 61% decline in peak tetanic tension (P-0). The SOL in rats allowe d 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 i n a SOL wet weight that was 26% less and P-0 that was 42% less than co ntrols. Animals that received the combination of 1 hour of weight bear ing 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 affect ed by HLU than the SOL, Results strongly support early intervention, p articularly weight bearing, during a period of bed rest to modify the decline in strength and muscle mass in postural muscles such as the SO L. Further, results suggest that simply sending a patient home from th e hospital to recover from bed rest delays return of strength unnecess arily.