Abstract
1323 The purpose of this study was to investigate the effects of hindlimb suspension and a prior 10-wk endurance training on muscle energy metabolism. Male Wistar rats were divided into exercise+hindlimb suspension (EX-HS), suspension only (HS) and control (CON) groups. The rats in the EX-HS group underwent training on a treadmill for 1.5h·d-1 at 40m·min-1 before the suspension period. After a 4-wk suspension period, measurements of phosphorus nuclear magnetic resonance spectroscopy(31P NMR) were performed and then the medial gastrocnemius (MG) and soleus muscles (SOL) were removed for histochemical and biochemical analysis. Although significant reductions in the ratio of muscle mass to body weight were found after suspension (P<0.05), the EX-HS group showed a higher ratio than the HS group. Training had no effect on the changes in fiber composition in both muscles. The phosphocreatine(PCr)/(PCr+inorganic phosphate) ratio during the steady-state electrical stimulation were lower in EX-HS and HS groups than that in the CON group (P<0.05). The time constant of PCr recovery after stimulation was also prolonged after suspension (P<0.05). There was no difference in these metabolic responses to stimulation between the EX-HS and HS groups. The citrate synthase (CS) activity increased significantly after training in both muscles (P<0.01). Although the CS activity decreased significantly during suspension in MG (P<0.01), but not in SOL, the EX-HS group showed a higher activity than the HS group(P<0.01). These results suggest that the prior endurance training contributes to the maintenance of higher muscle mass and CS activity, but does not inhibit the suspension-induced decline of oxidative capacity determined by31 P NMR.
Published Version
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