A rehabilitation exercise program to remediate skeletal muscle atrophy in an estrogen-deficient organism may be ineffective.

To determine rehabilitation exercise program effects under hormone deficient (ovariectomy or OVX) and hormone supplemented [OVX + 17-beta estradiol (E2)] conditions. Mature female rats (n = 123) were assigned to OVX or OVX + E2-supplemented groups. OVX and OVX + E2 groups were allocated to one of four conditions: (1) control, (2) hindlimb unweighted (HLU) for 4 weeks to induce muscle atrophy, (3) cage Recovery for 2 weeks after HLU, and (4) Recovery with 2 weeks of rehabilitation exercise program after 4 weeks of HLU. Atrophy following HLU was comparable for OVX and OVX + E2-supplemented rats and was significant in all muscles examined (soleus, tibialis anterior, plantaris, gastrocnemius, quadriceps). Also significant with HLU was the decline in muscle force (P < 0.05) in soleus, plantaris, gastrocnemius and tibialis anterior (quadriceps not tested). There were trends toward return of muscle mass in Recovery OVX and Recovery OVX + E2 groups but only the E2 supplemented OVX rats had return of muscle mass (4/5 muscles studied) with exercise. Peak tetanic tension (Po) returned to control values in the E2 supplemented Exercise rats but not in the unsupplemented Exercise group. For example, gastrocnemius Po for OVX HLU, OVX Recovery and OVX-Exercise groups was 82%*, 82%* and 76%* of control. Gastrocnemius Po for E2 supplemented HLU, Recovery and Exercise groups was 72%*, 95% and 106% of control (*P < 0.05 compared to control). H&E cross-sections from OVX-Exercise rats showed central nuclei. In conclusion, a rehabilitation exercise program to remediate acute atrophy in females appears more effective if E2 is present.