Reduced physical activity corresponds with greater bone loss at the trabecular than the cortical bone sites in men

Previous research has been inconclusive as to whether high peak bone mineral density (BMD, g/cm2) resulting from previous physical activity is retained with reduced activity later in life. The aim of this 12-year longitudinal study was to investigate the association between BMD loss and reduced physical activity (h/wk) at trabecular and cortical bone sites in men. Three groups with a mean age of 17 years at baseline were investigated: i) 51 athletes who discontinued their active careers during the follow-up period (former athletes), ii) 16 athletes who were active throughout the follow-up period (active athletes), and iii) 25 controls. BMD loss at the hip, spine, and pelvis (mainly trabecular bone) was compared to BMD loss at femur, humerus, and legs (mainly cortical bone) during a 12-year follow-up period. Across the total follow-up period in the total cohort, reduced physical activity was more strongly associated with changes at trabecular BMD sites, i.e. hip, spine, and pelvis (B = 0.008–0.005 g/cm2 per weekly hour physical activity (h), p < 0.001), than at cortical bone sites, i.e. humerus, legs (B = 0.002–0.003 g/cm2/h, p < 0.05), and femur (p > 0.05). At the final follow-up, former athletes showed higher BMD than controls only at the cortical bone sites of the humerus, legs, and femur (difference 0.05–0.10 g/cm2, p < 0.05). In conclusion, this study indicates that predominantly trabecular bone is lost with reduced physical activity levels in young men. Benefits were still evident at the more cortical sites eight years after the discontinuation of an active sports career.