Relationships between Body Composition, Strength and Bone Density in Postmenopausal Women

Abstract

Osteoporosis is a major concern for aging women, especially after menopause. It is important to understand the role of body composition and strength in the maintenance of bone health. PURPOSE: The purpose of this study was to examine relationships between strength, body composition, and bone mineral density (BMD) in sedentary postmenopausal women who are not on hormone replacement therapy (HRT). METHODS: Sixty-one women (63.38 ± 4.64 yrs) filled out a Menstrual History, PASE, and Calcium Intake questionnaires. Blood samples were collected by venepuncture to determine the bone formation marker, bone-specific alkaline phosphatase (BAP). Body composition and BMD (total body, AP spine, left femur, forearm) were measured using Dual Energy X-ray Absorptiometry (DXA GE Lunar Prodigy). Participants performed 1RM tests for 3 upper body and 5 lower body exercises. Zero order Pearson correlation coefficients were used to determine relationships between strength, body composition, BAP and BMD variables. Stepwise multiple regression was used to test for predictors of BMD. RESULTS: Body mass index (BMI) showed low positive correlations (r .27- .46, p<0.05) with all BMD sites. Fat mass was positively related to spine, trochanter and total body BMD, while lean tissue mass was related to total hip, forearm, and total body BMD. Lower body strength (leg press, hip adduction, hip extension) was related to trochanter and total hip BMD. Similar results were determined from the regression analyses as fat mass was found to be a significant predictor (p<0.05) of total body and spine BMD, accounting for about 10–19% of the variance. Age and fat mass were found to be significant predictors of L2-L4 BMD (R2=0.134). Lean tissue mass predicted trochanter and total hip BMD. BAP and calcium intake were not correlated with BMD variables. CONCLUSION: The contribution of body composition and strength variables to BMD varied by site as fat mass was more important for total body and spine BMD and lean mass and lower body strength exerted greater influences on the hip sites.