Muscle Force Generation and Age: The Role of Sex Hormones

Abstract

The effect of oestrogen deficiency on active stretch force production was determined to establish whether weakness after the menopause in women is the same as that seen in old age. A mouse model of oestrogen deficiency was also tested. The maximum isometric force and active stretch force was measured; soleus muscles of young mice were compared in ovariectomised and control animals, and the adductor pollicis muscles of young control and post-menopausal human subjects were compared. The isometric force per cross-sectional area (CSA) was significantly reduced in post-menopausal women and ovariectomised mice as compared to controls. In contrast, active stretch force/CSA was not different. Therefore stretch can remove the weakness in oestrogen deficient muscle. This resulted in as increased stretch/isometric force ratio in the oestrogen deficient muscle. This suggests isometric muscle weakness is due to a reduction in force per acto-myosin cross-bridge. These changes are similar to those seen in old age. Thus, the mechanism of muscle weakness is the same in muscle from old animals, ovariectomised mice and post-menopausal women.