Habitual levels of high, but not moderate or low, impact activity, are positively related to hip BMD and geometry: Results from a population-based study of adolescents

Whether a certain level of impact needs to be exceeded for physical activity (PA) to benefit bone accrual is currently unclear. To examine this question, we performed a cross-sectional analysis between PA and hip BMD in 724 adolescents (292 boys, mean 17.7 years) from the Avon Longitudinal Study of Parents and Children (ALSPAC), partitioning outputs from a Newtest accelerometer into six different impact bands. Counts within 2.1-3.1g, 3.1-4.2g, 4.2-5.1g and >5.1 g bands were positively related to femoral neck (FN) BMD, in boys and girls combined, in our minimally adjusted model including age, height and sex (0.5-1.1g: beta = -0.007, p = 0.8; 1.1-2.1g: beta = 0.003, p = 0.9; 2.1-3.1g: beta = 0.042, p = 0.08; 3.1-4.2g: beta = 0.058, p = 0.009; 4.2-5.1g: beta = 0.070, p = 0.001; >5.1g: beta = 0.080, p 4.2g) were positively related to FN BMD, whereas if anything, moderate (2.1-4.2g) and low impacts (0.5-2.1g) were inversely related (low: beta = -0.052, p = 0.2; medium: beta = -0.058, p = 0.2; high: beta = 0.137, p 4.2g, such as jumping and running (which further studies suggested requires speeds >10km/hour) is positively related to hip BMD and structure in adolescents, whereas moderate impact activity (e.g. jogging) is of little benefit. Hence, PA may only strengthen lower limb bones in adolescents, and possibly adults, if this comprises high impact activity.