Exercise for prevention of osteoporotic fracture

Exercise is increasingly recognized as a means of reducing the risk of osteoporotic fracture and for managing the condition of osteoporosis even in old age. However the right choices must be made since not all forms of exercise are suitable, indeed some physical activities would increase the risk of fracture. Active lifestyles, as assessed in surveys, are associated with a halving of hip fracture risk [1]. Analysis of the data in these surveys to find optimal forms of exercise has been un-rewarding. This is not surprising since animal evidence suggests that a variety of brief bouts of unusual physical activity is osteogenic. However, those who report that their normal walking speed is brisk and those who regularly climb stairs emerge as having higher bone mineral density and lower fracture risks than their more sedentary peers. Exercise has an influence on fracture risk through several pathways. It can improve postural stability and muscle strength and so reduce the prevalence of injurious falls, as well as increasing bone mineral density (BMD) and by implication bone strength. Indeed the large reduction in fracture risk compared with the modest gains in BMD suggest that the increase in bone strength may exceed the increase in density. Moderate forms of exercise such as walking have been disappointing. Interventions based on increasing walking duration and speed have not been successful for improving BMD except at the calcaneum which is not a bone which fractures [2]. In a cross-sectional study in American women, those who walked less than one mile per week were found to have lower BMD than those who walked more, but further increases conferred no further benefit [3]. One mile per week amounts to little more than 3 minutes per day so the significant difference was between an almost completely sedentary lifestyle and normal levels of inactivity. There is therefore no justification for recommending more than a brisk 5 minute walk daily but the frail elderly and their carers should be encouraged in this. Physical activities which are not weight-bearing such as swimming and cycling are likewise ineffective for improving BMD presumably because there is not enough gravitational load on the skeleton. In water the body floats and in cycling most of the body weight rests on the saddle. More vigorous activities such as exercise to music classes where there is a variety of fully weight-bearing exercise and perhaps a small amount of high impact activity have been successful [4–6]. The variety is probably important but makes it impossible to pin point which elements if any are critical. For young women high impact exercise such as running [7] and jumping will increase BMD despite the supposedly ‘peak bone mass’ status of this age group. Daily jumping for 60 seconds was found to increase BMD in the hip by nearly 4% after five months in premenopausal women [8]. This intervention was based on successful animal experiments [9]; fifty jumps a day provides a hundred rapid strain reversals of high magnitude to the femur. The ground reactions and the compressive strain in the bone are about five times body weight. The exercise is feasible even for busy individuals because it takes so little time; the jumps were modest at about 8 cm. By analogy, skipping and sport such as netball or hockey, and dance such as Tap or Scottish, which provide similar impact should be osteogenic. Regular exposure is obviously important, most studies have required participants to exercise three times a week, but prolonged activity such as a 20 minute run may be more than is needed. Running or jogging provides a strain reversal of high magnitude each time the body lands and takes off again. Foot-falls occur at about one a second providing more than 1000 strain reversals for each hip in 20 minutes of running. The study of jumping was repeated in postmenopausal women using an identical protocol but it was not successful. No significant changes could be attributed to the exercise, there was not even a trend [10]. It appears that older women need a more prolonged protocol than a minute or so of jumping. They are certainly able to respond to appropriate boneloading regimens, indeed many of the successful studies have been in post-menopausal women who, despite their low oestrogen status, often improve as much if not more than younger women. For example, an intervention, in post-menopausal women with a history of osteoporosis, Age and Ageing 2001; 30-S4: 29–31 # 2001, British Geriatrics Society