The purpose of this study was to examine the effects of walking characteristics in relation to BMD. Several previous studies have reported a link between physical performance and bone loss among the elderly, ^12.14-19） but these studies have utilized physical activity questionnaires or multiple methods to measure performance or strenuous exercise programs. This study was conceived on the premise that the easy and simple walker's test parameters, especially the 10-m walking speed, total step, mean stride length during the 10-m walk, and maximal step length were significantly decreased with the risk of osteoporosis in elderly women. These results suggest that fast walking speed and long stride length have a protective effect on femoral bone mineral density. Furthermore, our results suggest that osteoporosis and osteopenia do not increase the risk of poor balance and body sway. To the best of our knowledge, studies of brisk walk ability and osteoporosis in women aged 70 years and older are extremely rare. In their study, Dargent et al. ^12） demonstrated that low gait speed increased the risk of hip fracture (relative risk = 1.4 for 1 SD, 95% confidence interval = 1.1-1.6). Brooke-Wavell et al. ^20） demonstrated that, in postmenopausal women, brisk walking could decrease bone loss in the lumbar spine and heel.

Ringsberg et al. ^21） showed, in a study of an activity group and urban control groups (aged 60±7 and 64±11) that BMD was related to walking speed.

Aoyagi et al. ^22） reported, in a study of healthy men and women aged 60 and older, that those with slower rapid walking speed tended to have low bone mineral density. They also found that poor physical performance was a risk factor for low BMD to compound the risk of fracture. According to these studies, elderly women with poor physical activity in daily living, especially slow walking speed, are at high risk factor for developing osteoporosis. This hypothesis is in agreement with our findings.

Walking has traditionally been viewed as a moderate-intensity activity. However the present study clearly indicates that using the adjective "brisk" when prescribing walking evokes a more vigorous intensity of exercise. When asked to walk briskly, recent studies reported the walking speed as 1.78 ± 0.19 m/s ^23） or 1.79 ± 0.19 m/s ^24）. Duncan et al. ^25） investigated the training effects of walking at 1.78 m/s, corresponding to 67 % HRmax, and found that, while similar improvements in HDL cholesterol were seen in all groups, aerobic power increased in a dose-dependent manner according to walking speed. Thorsen et al. ^26） reported that one bout of brisk walking in postmenopausal women had a significant effect upon markers of collagen metabolism, and their findings also support the fact that serum levels of PTH as well as those of osteocalcin are associated with total body BMD in elderly, postmenopausal women.

　

　

a: 40-cm step test, b: maximal step length (cm), c: 10-m rapid walking time (sec)

　

　

( ) : indicates confidence interval.

　

　

Interestingly, the finding of this study is that brisk walking speed is related to BMD. Women with a mean time of, 5.1 - 5.6 secs over 10 m (1.96 m/sec -1.78 m/sec) have higher BMD than those with a mean time of 6.1 secs or more over 10 m (1.78-1.63 m/sec) or lower (Fig 2 ). In general, walking has traditionally been viewed as a moderate-intensity activity. However, recent studies clearly indicate that using the adjective "brisk" when prescribing walking evokes a more vigorous intensity of exercise ^23,24）. Accordingly, our findings suggest that brisk walking (1.78 m/sec or faster) in elderly women had a positive effect upon their BMD.

Heinonen, et al. ^27） demonstrated that improvements in muscular performance and dynamic balance in pre-menopausal women decreased the risk of osteoporotic fractures in later life, but they did not find any association between balance function and BMD. Similarly, this study found no association between osteoporosis, onelegged balance at total locus length and postural sway as predictive factors of injurious falls in community-dwelling elderly women. Balance is probably influenced by other factors such as neuromuscular impairment, visual impairment, and functional disorders. In conclusion, our results suggest that maximal step length, 10-m walking speed, total step and mean stride length over a 10-m walk are impaired with lower BMD in elderly women. Femoral neck BMD and OSI are correlated with the simple walker's test parameters. Thus, this simple test of mobility could be a useful instrument in diagnosis of osteoporotic women. Moreover, "brisk" walking may be prescribed as a more intense activity for optimal bone fitness benefit.