High-intensity weight training promotes bone growth in older men but is less effective for older women, according to a new US study. The researchers, from Oregon State University, compared the effects of a moderate-intensity seated resistance-training programme with those of a high-intensity standing free-weight exercise programme on bone mass and circulating levels of insulin-like growth factors in healthy men and women in their 50s.

Twenty-eight men and 26 women - all the women being postmenopausal but free of hormone replacement therapy - served as their own controls for the first 12 weeks of the study, when they maintained their normal daily routines and eating habits. They were then randomly assigned to either a high-intensity functional standing free-weight programme or a moderate-intensity seated machine-based programme - both programmes designed to activate all major muscle groups. Training sessions lasting 75 minutes were held three times a week for 24 weeks under the close supervision of personal trainers (one to every two subjects).

Bone mineral density (BMD), body composition, muscle strength, hormonal status and anaerobic power were assessed at the beginning, middle and end of the study.

The men in the study experienced significant bone gain at the lumbar spine with high-intensity training and at the greater trochanter (top of the thigh bone) with both types of training. Women gained bone at the greater trochanter with both types of training but did not make significant gains at the lumbar spine with either type.

In women leg lean mass increased significantly in both training groups, but changes were much greater in the high-intensity group (8.1% compared with 3.4%). In men leg lean mass increased to a lesser extent, by 3.2% in the high-intensity group and 1.9% in the moderate intensity group.

Surprisingly, improvements in BMD, lean mass and strength were not accompanied by increases in circulating serum levels of insulin-like growth factors in either men or women, suggesting that highly localised factors were responsible for the changes observed.

For women the biggest disappointment must be the lack of significant bone gain at the spine in response to training. 'The fact that women were primarily early menopausal (within 36 months) likely explains the lack of spine response,' the researchers explain. 'The majority of the women (78%) in the high intensity group were within their first five years past menopause, a time during which there is accelerated bone loss of 2-6.5% per year. In these women training did not offset low reproductive endocrine status.'

However, an interesting related finding was that two women in the study who were more than eight years past menopause showed significant bone gain of 4-5% at the spine in response to high-intensity training. This suggests the need for further research in which women are separated according to their menopausal status.

Meanwhile the researchers conclude that 'resistance training may help offset musculo-skeletal declines associated with aging and is beneficial to both older men and women.'

Calcif Tissue Int (2000) 66:399-404