Changes in hip bone mineral density and objectively measured physical activity in middle-aged women: a 6-year prospective study.

Abstract Purpose. This study was conducted to determine if physical activity volume (PAv) and intensity (PAi) at baseline influence the likelihood of gaining hip bone mineral density (BMD) over 6 years. Design and Sample. In a prospective study, the sample was limited to 244 female nonsmokers, ages 35 to 45 years, and was approximately 90% white. Setting and Measures. PAv and PAi were measured in daily living conditions using accelerometers at baseline. BMD, measured by dual energy x-ray absorptiometry, and several confounding factors were measured in the lab. Analysis. On the basis of BMD change scores, participants were divided into three categories: BMD loss, minimal change, and BMD gain. Risk ratios were used to show the likelihood of BMD gains over time across different levels of PAv and PAi at baseline. Results. Women with higher PAv were more likely to show improvements in hip BMD from baseline to follow-up than their counterparts, as indicated by the Mantel-Haenszel chi-square (χ2mh  =  6.1, p  = ...