1. The time-course of the age-related decline in specific muscle force (maximum voluntary force per cross-sectional area) in men and women was determined by measuring the maximum voluntary force and cross-sectional area of the adductor pollicis muscle in 273 subjects aged 17-90 years (176 men, 30 premenopausal women and 67 peri- or post-menopausal women who were not receiving hormone replacement therapy). 2. To determine whether the loss of specific muscle force is hormone-dependent in women, we studied a further 25 women, aged 42-72 years, who were receiving hormone replacement therapy. 3. There was no significant difference in specific force between young men and pre-menopausal women. Around the time of the menopause there was a dramatic decline in specific force in women which was prevented by the use of hormone replacement therapy. In men the weakness started later (around the age of 60 years) and the decline in specific force was more gradual, reaching the level seen in post-menopausal women after the age of 75 years. 4. The protective effect of hormone replacement therapy on muscle strength is likely to be an important contributory factor to its proven action in preventing osteoporotic fractures. The dramatic peri-menopausal decline in muscle strength is a likely explanation for the known increases in falls and Colles' fractures around the time of the menopause.

1. Muscle strength of the adductor pollicis (AP) was studied throughout the menstrual cycle to determine whether any variation in force is similar to the known cyclical changes in ovarian hormones. Three groups of young women were studied: trained regularly menstruating athletes (trained), untrained regularly menstruating (untrained) and trained oral contraceptive pill users (OCU). In addition a group of untrained young men was studied as controls. 2. Maximum voluntary force (MVF) of AP was measured over a maximum period of 6 months.Ovulation was detected by luteinizing hormone measurements or change in basal body temperature. There was a significant increase in MVF (about 10%) during the follicular phase of the menstrual cycle when oestrogen levels are rising, in both the trained and untrained groups. This was followed by a similar drop in MVF around the time of ovulation. Neither the OCU nor the male subjects showed cyclical changes in MVF.We have shown previously that the maximum voluntary force (MVF) which can be exerted by the adductor pollicis muscle (AP) relative to its cross-sectional area (CSA) is 28 % lower in old than in young people (Phillips, Rook, Siddle, Bruce & Woledge, 1993b). In women this decline in MVF/CSA occurs at the time of the menopause, i.e. at the time when ovarian failure leads to a permanent decline in sex hormone secretion. In postmenopausal women using hormone replacement therapy MVF/CSA is greater than in age-matched controls and not less than that of young women (Phillips et al. 1993b). These facts suggest that oestrogen may have a muscle-strengthening action. If this is correct, and if the action is exerted within a few days, then we could expect to see changes in MVF during the menstrual cycle. It is well recognized that, during the follicular phase of the menstrual cycle, oestrogen levels rise to a peak and then fall during the day or two before ovulation, while during the luteal phase the oestrogen levels remain relatively stable but at a higher level than that at the start of the cycle. In contrast, progesterone levels are negligible during the follicular phase but, after ovulation, rise to a peak during the luteal phase (Moghissi, Syner & Evans, 1972). Therefore, it would be predicted from the hypothesis of oestrogen increasing muscle strength, that a rise in MVF would be seen during the follicular phase of the cycle followed by a fall near the time of ovulation. Moreover, if the action of oestrogen was not opposed by that of progesterone, MVF would remain higher during the luteal phase than at the start of the cycle. This paper reports the results of experiments carried out to test these predictions. We compared highly trained athletes, during their training season, with non-training subjects for two reasons: (1) the highly physically active subjects may have developed oligomenorrhoea or amenorrhoea giving anovulatory cycles with little change in cyclical hormones or force; and (2) physical activity itself may saturate any force effect caused by changes in the levels of s...

Maximum voluntary force and cross-sectional area (MVF and CSA) of the human adductor pollicis muscle were compared in groups of young (19-55 years, mean = 28, n = 53) and elderly (74-90 years, mean = 80, n = 39) subjects, of both sexes. Despite the elderly subjects being in good health and active outdoors, they were considerably weaker than the young subjects, their MVF/CSA being 26 +/- 3% (mean +/- SEM) lower. It was found that both young and elderly subjects could fully activate their muscles. Therefore the muscle weakness of old age does not appear to be due to reduced activation and must be caused by another mechanism, possibly biochemical in nature.

A randomized open trial of hormone replacement therapy was used to assess changes in adductor pollicis muscle strength during 6-12 months of treatment with Prempak C 0.625(R) in comparison with an untreated control group. Muscle strength (maximal voluntary force; MVF), muscle cross-sectional area and bone mineral density were measured. Women entering the trial had oestrogen levels below 150 pmol.l-1, confirming their post-menopausal hormonal status. In the treated group, MVF increased by 12.4+/-1.0% (mean+/-S.E.M.) of initial MVF over the duration of treatment, while it declined slightly (2.9+/-0.9%) in the control group. This increase in strength could not be explained by an increase in muscle bulk, there being no significant increase in cross-sectional area during the study. Those subjects who were weakest at enrolment showed the greatest increases in muscle strength after treatment. Bone mineral density in total hip, Ward's triangle and total spine increased in the treated group, in agreement with previous studies. There was no correlation between the individual increases in bone mineral density and those in MVF.

SUMMARY1. The contractile force was compared in isolated soleus muscles from young (2-5-8 months old) and aged (28-31 months old) mice. Force was measured at 25 'C during isometric tetanic contractions during isovelocity stretching and shortening contractions.2. The normalized isometric force was lower by 13-3 % in muscles from aged mice. Muscles from young and aged mice produced 0-951 +0-031 N mg-1 (n = 12) and 0-824+0-048 N mg-' (n = 9) respectively. The relaxation time, from 90 to 10% of the tetanic force, of muscles from aged mice was 102-1+ 3-7 ms (n = 6), which was longer than that for muscles from young mice, 84-4 + 3-8 ms (n = 6) (means + S.E.M.).3. The force during shortening was also reduced in muscles from aged animals by the same proportion as the isometric force. Therefore the force during shortening relative to the isometric force was the same in muscles from young and aged mice.4. During rapid stretching soleus muscles from aged mice produced a similar force to those from young mice. Therefore stretch can remove the weakness in muscles of aged mice.5. These changes in muscles from aged mice are similar to those produced when inorganic phosphate (Pi) levels are raised, in skinned rabbit psoas fibres, or during fatigue or with low intracellular pH (pHi), in frog muscle. It is possible therefore that the force loss due to ageing may be due to a higher Pi level or a lower pHi.