Fig. 2.

Physical activity-related mechanical loading during youth conferred lifelong benefits in cortical bone size and estimated strength but not in cortical bone mass. (A) Peripheral QCT images of the midshaft humerus in representative former throwers show increased medullary expansion and cortex trabecularization (arrows) in the throwing arm with increasing years of detraining but maintenance of loading effects on overall bone cross-sectional size. (B–I) Graphs show the maintenance of the effects of physical activity during youth on cortical volumetric bone mineral density (B); cortical bone mineral content (C); trabecular/subcortical bone mineral content (D); total cross-sectional area (E); cortical cross-sectional area (F); medullary cross-sectional area (G); cortical thickness (H); and density-weighted polar moment of inertia (I). Data show the mean difference and 95% CI between the throwing and nonthrowing arms in former throwers normalized to the differences between the dominant and nondominant arms in controls. CIs greater or less than 0% indicate differences between the throwing and nonthrowing arms in throwers that are greater or less, respectively, than the differences between the dominant and nondominant arms in controls (*P < 0.05, ^†P < 0.01 and ^‡P < 0.001, unpaired t test). Source data are provided in Table S3.