Effect of spontaneous recovery or retraining after hindlimb suspension on aerobic capacity

The purpose of this study was to compare the effects of spontaneous recovery or recovery by treadmill training (180 min/day, 5 days/wk, 30 m/min for 8 wk) on maximal O2 uptake (VO2max), histochemical and biochemical muscular properties (soleus), of rats subsequent to 5 wk of hindlimb suspension. Spontaneous recovery reversed the 15% reduction in VO2max, whereas training posthypokinesia induced a 20% increase over control values. In the spontaneous recovery group, both citrate synthase and 3-hydroxyacyl-CoA dehydrogenase activities, decreased by hypokinesia (-40%), increased but remained 20% below the control level. In the training posthypokinesia group, an increase of these activities over control occurred (+50 and +20%, respectively). Recovery or training led to a 100% type I distribution in soleus muscle and to a recovery of all fibers' cross-sectional areas. In the spontaneous recovery group, capillaries per fiber, decreased by 46%, returned to the normal range. In the training posthypokinesia group, training induced an increase in capillaries per fiber above their control values (+23%). These results point to the plasticity of the muscle and indicate the necessity of a posthypokinesia training program for recovery of the total oxidative enzyme capacity.