IMPACT OF SUBJECTS?? INITIAL CHARACTERISTICS AND EXERCISE TYPE INTERVENTION ON BMD CHANGES IN POSTMENOPAUSAL WOMEN

Abstract

Despite a reduced skeletal response to mechanical stimulus, older women present a greater skeletal response variability when compared with young women. PURPOSE This study was designed to determine the influence of subject's individual characteristics and exercise type on bone mineral density change (ΔBMD) in the femoral neck and lumbar spine. METHODS Subjects were 36 women, 53–78 yrs, at least 1 yr postmenopausal, not taking any medication affecting bone. Subjects were randomly assigned to a hydro-gymnastics (HG, n = 20) and step aerobics (SG, n = 16) groups during 18 months, 2 or 3 sessions/wk, respectively. Ground reaction forces of SG program were between 1.6–1.7 of body weight. Assessment of BMD, fat mass and fat-free mass was performed with DXA. Upper and lower body muscle strength was evaluated with a hand dynamometer and an isometric leg press test. Calcium and magnesium on the plasma were measured by atomic absorption spectrophotometry. Calcium and magnesium intake were evaluated with 3-d food records. Stepwise regression was used to analyze the contribution of initial subjects characteristics on ΔBMD. Predictors selected by regression were then used as covariates to analyze group differences on ΔBMD. RESULTS Age explained 16.4% of the ΔBMD variance on femoral neck (β = 0.405, p = 0.021). Initial lumbar spine BMD (β = −0.367, p = 0.028) and fat-free mass (β = −0.351, p = 0.035) explained 27.3% of the ΔBMD variance on spine. Using these predictors as covariates, ANCOVA showed ΔBMD group differences on spine (HG 2.8 ± 0.6% vs. SG 0.4 ± 0.8%, p < 0.001) but not on femoral neck (HG −0.7 ± 0.9% vs. SG – 0.6 ± 1.0%, p = 0.801). CONCLUSION The efficacy magnitude of a specific exercise intervention for bone seems to be dependent of some subject characteristics. After adjusting for other predictors, the HG program induced a higher ΔBMD on lumbar spine of postmenopausal women while femoral neck ΔBMD was not impacted by either program. Supported by the Portuguese Foundation for Science (Sapiens 358007/99)