The ability of bone to respond to mechanical stimuli is well-known; however, the BMD response to exercise is traditionally modest. The effect can be attributed in part to historically inappropriate exercise prescription, but is compounded by the inability of areal BMD to detect changes in bone morphology. Subtle adaptations in bone geometry will substantially modify structural strength and may be highly clinically meaningful. The recent development of 3D Hip software (DMS Group, France) for the MedixDR DXA (Medilink, France) permits the detection of morphological adaptation at the proximal femur (PF).
The aim of the current pilot study was to determine the influence of a bone-targeted exercise program on parameters of femoral neck (FN) geometry in postmenopausal women with low bone mass.
Postmenopausal women with FN BMD T-score <-1.0 (screened for conditions and medications that influence bone and function), were recruited from the community. Participants were randomized to 8 months of twice-weekly, 30-minute, supervised high intensity progressive resistance training (HiPRT) or home-based, low intensity exercise (CON). Traditional DXA hip scans were re-analysed using 3D Hip software to derive a range of parameters of bone geometry. Treatment effects were examined with repeated measures ANCOVA (intention-to-treat), controlling for initial values.
Twenty-eight women (64.2±4.2yrs, 160.4±6.4cm, 62.6±9.1kg, T-score -2.12±0.64) were examined. Despite a lack of difference in vBMD change, HiPRT (n=13) increased FN total cortical thickness and specifically FN lateral cortical thickness compared with CON (17.7±20.7% vs 4.1±11.4%; p<0.006 and 29.5±35.7% vs 2.3±28.2%; p<0.001, respectively). No other geometric differences were detected.
Findings indicate that while bone-targeted exercise may not increase FN BMD in postmenopausal women with low bone mass, bone strength benefits may be conferred by enhanced geometry of the superior cortex of the FN. 3D analysis should be considered when evaluating the effects of exercise interventions at the proximal femur.