Relationships between bone mineral density, body composition, and isokinetic strength in postmenopausal women

Objectives: The increase in body fat mass (BFM) and the loss of lean body mass (LBM) or muscle strength with age affects bone mineral (BMD). These factors increase the prevalence and incidence of obesity and sarcopenia, which have unclear effects on bone mineral density. The purpose of this study was to determine how the above selected factors affect BMD. Methods: A cross-sectional study was conducted involving 58 women (aged 62.1 +/- 4.8 years). Total body, left proximal femur, lumbar spine BMD, and body composition parameters were measured with dual-energy x-ray absorptiometry. Isokinetic flexion and extension strength of the dominant leg were measured at 60 deg./s. Grip strength was measured with the dominant upper extremity. To determine the volume of physical activity (PA), the PA level was monitored for seven consecutive days using an ActiGraph model GT1M accelerometer. Results: BFM was positively associated with BMD of the proximal femur (beta = 0.31; P < 0.05), whereas LBM or appendicular lean mass (ALM) did not relate to BMD at any sites. Dominant isokinetic strength also did not relate to BMD at any site. A/G (android/gynoid) fat ratio shows positive association with lumbar spine BMD after adjusting for YSM (years since menopause), height, smoking status, and steps per day. Conclusion: We observed a positive association between proximal femur BMD and BFM, but not between LBM, ALM or isokinetic strength. A/G ratio and BMI showed a positive association with lumbar spine BMD or proximal femur BMD, respectively.