With advancing age there is a progressive muscle atrophy that results in a loss of strength and power. Aged muscle has also been reported to be less able to produce steady force contractions than younger muscle (Tracy & Enoka, 2001). The mechanisms could include altered muscle control and may be linked to the increased susceptibility to falling and loss of performance of functional activities with increasing age. The decline in strength follows a different time course in men and women. In men there is a gradual decline from the fifth decade onwards, whereas in women there is a faster decline around the menopause (Samson et al. 2000). The latter is believed to be due to reduced oestrogen levels and the effect is lessened by hormone replacement therapy (HRT) (Skelton et al. 1999). This study aimed to investigate whether HRT can also affect the decline in steadiness of quadriceps force in women.

The quadriceps were tested for isometric strength. Steadiness of contraction force at 10, 25, 50 and 100 % of the maximum voluntary isometric force (MVC) using the force coefficient of variation (CoV). Three groups of subjects were studied: 1) 15 elderly women (68.1 ± 5.3 years (mean ± S.D.)) taking HRT, 2) 14 elderly women who had never taken HRT (70.5 ± 5.8 years), and 3) 16 young females (27.4 ± 5.6 years). Local ethical approval was obtained for the study, which was carried out in accordance with the Declaration of Helsinki. Results were tested for significance using ANOVA.

There was a tendency for all groups to be most steady during maximal, compared to sub-maximal contractions. There were no significant differences in steadiness between the three groups at any of the contraction levels (e.g. CoV at 50% MVC; 1.61 ± 0.13%, 1.58 ± 0.13 and 1.95 ± 0.15 for groups 1, 2 and 3 respectively). The young were stronger (297.5±13N) than the elderly group not on HRT (241.3 ± 12.7N) P < 0.05, but of similar strength to the group on HRT (255.4 ± 10.0).

These findings suggest that the steadiness of force generation in the quadriceps is unaffected by HRT and that the loss of this aspect of motor control is not a universal finding in older people.

This work was supported by The Guy’s and St.Thomas’ Charitable Foundation.