Commencing, continuing and stopping brisk walking: effects on bone mineral density, quantitative ultrasound of bone and markers of bone metabolism in postmenopausal women.

Regular walking is associated with reduced risk of fracture and, in our recent randomized trial, reduced calcaneal bone loss relative to controls. The present follow-up study compared the effects on dual-energy X-ray absorptiometry, ultrasound and biochemical indices of bone density and metabolism of (i) taking up (ii) continuing with and (iii) ceasing brisk walking for exercise. Subjects were 68 postmenopausal women aged 60-70 years. Twenty previously sedentary women remained sedentary (Sed/Sed) whilst 17 took up brisk walking (Sed/Walk). Fifteen women who had been walking regularly for 1 year returned to their former sedentary lifestyle (Walk/Sed), whilst 16 continued brisk walking over a second year (Walk/Walk). Bone mineral density (BMD), broadband ultrasonic attenuation (BUA), and biochemical markers of bone formation (serum osteocalcin, C-terminal propeptide of type I collagen and bone alkaline phosphatase) and resorption (urinary deoxypyridinoline) were assessed at baseline and 12 months. Women in the Sed/Walk and Walk/Walk groups completed a mean (SEM) of 16.9 (0.7) and 20.8 (1.2) min of brisk walking per day, respectively. Changes in BMD did not differ significantly between groups. Calcaneal BMD decreased significantly in Walk/Sed women [by 2.7 (1.4)%; p = 0.01] whilst changes in other groups were not significant. Calcaneal BUA increased significantly (p = 0.02) in Sed/Walk women [by 7.4 (3.3)%] relative to other groups. Urinary deoxypyridinoline increased over the year in the Sed/Sed group but there were no significant changes in biochemical markers in other groups. Women taking up brisk walking for exercise showed no change in BMD but a significant increase in calcaneal BUA. There was no significant effect on BMD or BUA of continuing brisk walking but calcaneal BMD declined on ceasing brisk walking. Bone resorption increased in sedentary women but not exercisers, suggesting the effect on exercise on bone in postmenopausal women could be through amelioration of this increased turnover.