Relationships Between Body Composition, Muscular Strength, and Bone Mineral Density in Estrogen-Deficient Postmenopausal Women

Abstract 

The purpose of this study was to examine relationships between muscular strength, body composition, and bone mineral density (BMD) in untrained postmenopausal women who are not on hormone replacement therapy (HRT). Fifty-five women (age: 63.3±0.6yr) completed menstrual history, physical activity, and calcium intake questionnaires. Total and regional body composition and total body, anteroposterior lumbar spine, nondominant forearm, and right proximal femur BMD were measured using dual-energy X-ray absorptiometry (DXA) (GE Lunar Prodigy, Prodigy enCORE software version 10.50.086, Madison, WI). Participants performed strength tests for 3 upper body and 5 lower body resistance exercises. Women with a relative skeletal muscle mass index (RSMI) value less than 5.45kg/m² were defined as a sarcopenia group (SAR). SAR had significantly (p<0.05) lower total body and forearm BMD compared with those who were not sarcopenic. BMD sites were significantly correlated with upper body strength (UBS) and lower body strength (LBS) (r=0.28–0.50, p<0.01), with the strength of relationship being site specific. Strength and fat mass (FM) significantly predicted total body BMD (R²=0.232–0.241, p<0.05), FM variables predicted spine BMD (R²=0.109–0.140, p<0.05), and LBS and RSMI predicted hip BMD sites (R²=0.073–0.237, p<0.05). Body composition variables failed to significantly predict LBS. In conclusion, the contribution of body composition and strength variables to BMD varied by site as FM was more important for total body, forearm and spine BMD, and LBS exerted greater influence on the hip sites.

Key Words: Bone free lean body mass, fat mass, relative skeletal muscle index, sarcopenia