ORIGINAL ARTICLE Association of unipedal standing time and bone mineral density in community-dwelling Japanese women A. Sakai & N. Toba & M. Takeda & M. Suzuki & Y. Abe & K. Aoyagi & T. Nakamura Received: 6 June 2008 / Accepted: 21 July 2008 / Published online: 2 September 2008 # International Osteoporosis Foundation and National Osteoporosis Foundation 2008 Abstract Summary Bone mineral density (BMD) and physical per- formance of the lower extremities decrease with age. In community-dwelling Japanese women, unipedal standing time, timed up and go test, and age are associated with BMD while in women aged 70 years and over, unipedal standing time is associated with BMD. Introduction The aim of this study was to clarify whether unipedal standing time is significantly associated with BMD in community-dwelling women. Methods The subjects were 90 community-dwelling Japanese women aged 54.7 years. BMD of the second metacarpal bone was measured by computed X-ray densitometry. We measured unipedal standing time as well as timed up and go test to assess physical performance of the lower extremities. Results Unipedal standing time decreased with increased age. Timed up and go test significantly correlated with age. Low BMD was significantly associated with old age, short unipedal standing time, and long timed up and go test. Stepwise regression analysis revealed that age, unipedal standing time, and timed up and go test were significant factors associated with BMD. In 21 participants aged 70 years and over, body weight and unipedal standing time, but not age, were significantly associated with BMD. Conclusion BMD and physical performance of the lower extremities decrease with older age. Unipedal standing time, timed up and go test, and age are associated with BMD in community-dwelling Japanese women. In women aged 70 years and over, unipedal standing time is significantly associated with BMD. Keywords Bone mineral density . Lower extremity . Physical performance . Timed up and go test . Unipedal standing Introduction Physical activity is necessary to maintain bone mass and bone strength. The lack of mechanical loading on bone induces disuse osteoporosis, which is characterized by bone fragility due to decreased bone mass and disruption of normal bone architecture [1–4]. Adequate physical perfor- mance of the lower extremities is needed to keep activity of daily living unlimited. Thus, we postulated that physical performance of the lower extremities is an important factor that associates with bone mineral density (BMD) in an age- dependent or age-independent manner in community- dwelling women. Aoyagi and colleagues [5] reported previously that women with poor physical performance, as assessed by grip strength, chair stand time, walking speed, and functional reach, tend to have low calcaneus BMD even after adjustment for age, body mass index (BMI), and physical activity. Taaffe et al. [6] reported that chair stand time is related to BMD at the femoral neck, and knee extensor strength, chair stand time, and standing balance are related to BMD at the trochanter in white women. Other studies showed that usual walking speed is associated with Osteoporos Int (2009) 20:731–736 DOI 10.1007/s00198-008-0726-8 A. Sakai (*) : N. Toba : M. Takeda : M. Suzuki : T. Nakamura Department of Orthopaedic Surgery, School of Medicine, University of Occupational and Environmental Health, 1-1 Iseigaoka, Yahatanishi-ku, Kitakyushu 807-8555, Japan e-mail: a-sakai@med.uoeh-u.ac.jp Y. Abe : K. Aoyagi Department of Public Health, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki 852-8523, Japan