Physical Activity, Sedentary Behavior, and Bone Health in Older Women

Abstract

The objective of this dissertation was to explore relationships among sedentary behavior, physical activity, and bone health in older women. The primary aim of Study 1 was to evaluate the contribution of self-report measures of sedentary behavior and physical activity (PA) to bone mineral density (BMD) and bone mineral content (BMC) at the femoral and spinal regions using surveillance data collected on more than 2,000 females aged 12 years and older. Findings from Study 1 revealed that a minimum of 60 minutes of daily moderate-to-vigorous physical activity (MVPA) was associated with increased BMD and BMC at the femoral neck and lumbar spine of adolescent females and greater amounts of self-reported sedentary behavior were related to lower femoral neck BMD and BMC levels. The focus of Study 2 was to determine if bone health status at the femoral and spinal regions could be predicted from objective measures of sedentary activity and physical activity in 44 healthy, post-menopausal women. Logistic regression analysis demonstrated that daily sedentary time and frequency of breaks in daily sedentary time were significant predictors of BMD at the femoral neck, but were not predictive of lumbar spine BMD. Furthermore, the degree of adherence to health-related PA guidelines was not a significant predictor of BMD at the femoral neck or lumbar spine. In Study 3, the impact of a 4-week, personalized behavioral intervention program designed to replace sedentary behaviors with weight-bearing, light-intensity physical activities (LIPA) was measured in 24 older females. No changes in daily sedentary time, daily frequency of breaks in sedentary time, or LIPA were observed following the intervention, but MVPA was significantly increased in participants who were contacted once a week for 20 minutes rather than twice a week for 10 minutes. In addition, a significant positive correlation was observed between reduction in daily sedentary time and improvement in health-related quality of life. Results from this trio of studies provide support for future research and community-based efforts to more accurately quantify the contribution of sedentary behavior to bone health and further refine and implement behavioral change strategies to reduce sedentary behaviors in older adults and improve related health outcomes.