Restoration of voluntary muscle strength after 3 weeks of cast immobilization is suppressed in women compared with men

OBJECTIVE: To investigate sex-related differences in the loss and recovery of voluntary muscle strength after immobilization. DESIGN: Longitudinal, repeated measures. SETTING: Research laboratory. PARTICIPANTS: Healthy men (n=5) and healthy women (n=5). INTERVENTION: Three weeks of forearm immobilization. MAIN OUTCOME MEASURES: Voluntary wrist flexion muscle strength was assessed at baseline and weekly during the immobilization protocol and 1 week after cast removal. Central activation was assessed before and after immobilization and after 1 week of recovery to determine what percentage of the muscle could be activated voluntarily. RESULTS: Men and women lost voluntary strength at a similar rate during immobilization. However, after 1 week of recovery voluntary strength had returned to within 1% of baseline in the men, but remained approximately 30% less than baseline in the women (P=0.03). Both sexes displayed reduced central activation after immobilization (P=0.02), but the decrease was similar in both sexes (P=0.82). CONCLUSIONS: These findings suggest sex-dependent adaptations to and recovery from limb immobilization, with voluntary strength recovering slower in women. As such, sex-specific rehabilitation protocols may be warranted, with women requiring additional or more intensive rehabilitation programs after periods of disuse. Future work is needed to determine the extent and mechanisms of these differences.