Association of Physical Activity with Trabecular Microstructure and Cortical Bone at Distal Tibia and Radius in Young Adult Men

Context: The relationship between physical activity, trabecular microstructure, and cortical geometry in weight-bearing and non-weight-bearing bone has not previously been studied in men. Objective: The aim of this study was to investigate whether present (type and amount) and previous duration of physical activity were associated with trabecular microstructure and cortical cross-sectional area (CSA) in weight-bearing bone in young men. Design and Setting: This was a cross-sectional, population-based study. Participants: Participants included a cohort of 829 Swedish men between 22.8 and 25.7 yr old (24.1 +/- 0.6 yr, mean +/- SD). Main Outcome Measures: Several microstructural trabecular and cortical traits were assessed with high-resolution three-dimensional peripheral quantitative computed tomography at distal tibia and radius. A standardized questionnaire was used to collect information about physical activity amount (hours per year), duration (years), and type (strain score 0-3, based on ground reaction forces). Results: Men with the highest physical activity strain score had higher tibial trabecular bone volume fraction (13.9 Delta%) and trabecular number (12.7%) than men with the lowest strain score (P < 0.001). Men in the group with the longest duration of physical activity had higher tibial cortical CSA (16.1%) than the sedentary men (P < 0.001). Inclusion of all physical activity variables in a linear regression model revealed that strain score independently predicted trabecular bone volume fraction, and trabecular number (P < 0.001) and that duration of previous physical activity independently predicted cortical CSA (P < 0.001) of the tibia. Conclusions: In this large cohort of young men, the degree of mechanical loading due to type of physical activity was predominantly associated with trabecular microstructure, whereas duration of previous physical activity was mainly related to parameters reflecting cortical bone size in weight-bearing bone. (J Clin Endocrinol Metab 95: 2917-2926, 2010)