Age-sex differences in the hip abductor muscle properties

Aim: Elderly women are reported to have worse postural balance in the mediolateral direction than elderly men, which may be related to hip lateral muscle properties. The purpose of this study was to investigate the effects of sex, age and their interactions on hip abductor muscle properties. Methods: Thirty elderly and 30 young healthy subjects were recruited in this study. Subjects were instructed to abduct their leg as forcefully and quickly as possible under isometric condition, in response to audible beeps. Electromyogram was measured on the gluteus medius muscle and abduction torque was measured. Investigated muscle properties included torque amplitudes and muscle contraction timings. Muscle contraction timings were designated as premotor time, electromechanical delay and total reaction time. The effects of sex, age and their interactions on muscle properties were analyzed. Results: Women showed smaller torque amplitudes, longer electromechanical delay and longer total reaction time than men (P < 0.01), whereas no sex difference was observed in association with premotor time (P = 0.15). Age-sex interaction was significant in torque amplitudes and in electromechanical delay (P < 0.01). Post-hoc test revealed that torque amplitude differed between sexes only in the young (P < 0.001). In contrast, the electromechanical delay differed between sexes only in the elderly and the age-related elongation of electromechanical delay was significant only in women (P < 0.001). Conclusion: Both a sex difference and a sex difference of age-related change in hip abductor muscle properties were demonstrated. These sex differences may contribute to the sex difference in lateral balance performance. Geriatr Gerontol Int 2011; 11: 333-340.