Influence of habitual physical activity on bone mass of postmenopausal women
A new self-administered bone-specific physical activity questionnaire (bsPAQ) aimed at older Scottish women was developed in order to examine the influence of habitual physical activity (PA) on bone mineral density (BMD). The ability of the Aberdeen bsPAQ to estimate both the metabolic and mechanical component of self-reported PA was tested amongst 127 women (mean age (SD): 61.4 (6.0) y) from the Aberdeen area. The estimated metabolic and mechanical component was compared to total and vertical acceleration, respectively, from a triaxial accelerometer (RT3, Stayhealthy, Inc.). the agreement between the bsPAQ and the objective measure of physical activity used in this investigation ranged from fair to moderate for the different self-reported physical activity variables, making the Aberdeen bsPAQ a useful tool for accessing PA in older women with musculoskeletal diseases. The Aberdeen bsPAQ was used to examine the effect of lifestyle PA on BMD amongst Scottish postmenopausal women who had taken part in a large population-based screening study [North of Scotland Osteoporosis Study (NOSOS)]. BMD was measured using dual X-ray absorptiometry (LUNAR PRODIGYTM X-ray scanner, Lunar Corporation, GE Medical Systems) at the lumbar spine and left and right hip. One thousand two hundred and fifty-four (n=1254) postmenopausal women (mean age (SD): 69.3 ± 5.5y) from the Aberdeen and Inverness area completed the bsPAQ (overall return rate 68.7%). Classification of women according to self-reported PA revealed that those in the highest tertiles had a greater BMD than those in the lowest tertiles and this remained significant for the majority of the self-reported PA outcome variables after adjusting for a variety of confounding factors. The observed differences were biologically significant if maintained through life, as they could substantially reduce the relative risk of hop fractures in this group of older postmenopausal women. Current levels of physical activity had a small but significant independent effect of current BMD especially at the total hip site. The mechanical component explained more of the BMD variation (1.3% of the left hip and 0.6% of the right hip) than the metabolic component (0.2% of the left and right hip). The addition of simple self-assessed anthopometric measurements into the regression model improved the prediction model. Significant interactions were identified between dietary calcium and the mechanical (but not the metabolic) component of PA, with the presence of the mechanical component of PA being more important at low and medium intakes of dietary calcium. Finally, an association was also found between past PA and current BMD.