A one-year exercise intervention program in pre-pubertal girls does not influence hip structure

Fifty-three girls aged 7 – 9 years were included in a curriculum-based exercise intervention program comprising 40 minutes of general physical activity per school day (200 minutes/week). Fifty healthy age-matched girls who participated in the general Swedish physical education curriculum (60 minutes/week) served as controls. The hip was scanned by dual X-ray absorptiometry (DXA) and the hip structural analysis (HSA) software was applied to evaluate bone mineral content (BMC), areal bone mineral density (aBMD), periosteal and endosteal diameter, cortical thickness, cross-sectional moment of inertia (CSMI), section modulus (Z) and cross-sectional area (CSA) of the femoral neck (FN). Annual changes were compared. Group comparisons were done by independent student's t-test between means and analyses of covariance (ANCOVA). Pearson's correlation test was used to evaluate associations between activity level and annual changes in FN. All children remained at Tanner stage 1 throughout the study.No between-group differences were found during the 12 months study period for changes in the FN variables. The total duration of exercise during the year was not correlated with the changes in the FN traits.Evaluated by the DXA technique and the HSA software, a general one-year school-based exercise program for 7–9-year-old pre-pubertal girls seems not to influence the structure of the hip.Physical activity during growth is associated with benefits in bone mineral accrual and possibly bone structure [1-4], a clinically relevant notion, as both traits independently improve bone strength [5]. But, most prospective controlled exercise intervention trials have predominantly focused on the accrual of bone mineral [6-9], a study design that could underestimate the skeletal effects of exercise, as the effect on bone structure is then neglected. That is, also the three-dimensional structure ought to be assessed when evaluating bone strength [10,11]. As a result, the Hip Structural Analysis (