RELATIONSHIP AMONG RUNNING MILEAGE, BONE-DENSITY, AND SERUM TESTOSTERONE IN MALE RUNNERS

Our purpose was to investigate the relationship between running volume and bone mineral mass in adult male runners. Whole body and regional bone mineral density were determined by dual-photon absorptiometry in 22 sedentary controls and 53 runners who were selected according to their running mileage to fall into a 5- to 10-, 15- to 20-, 25- to 30-, 40- to 55-, or 60- to 75-mile/wk group. All groups were of similar age (20-45 yr) and nutritional status, as determined by 7-day food records. Regional sites for bone density measurements included the trunk, spine, pelvis, thighs, and lower legs. In addition, serum total testosterone was determined in each subject and computed tomography scans were made of the lower legs in 34 subjects to assess bone cross-sectional area. No significant differences were detected for bone density measurements with the exception of the lower legs where it was significantly (P < 0.05) greater for the 15- to 20 mile/wk group than for the control and 5- to 10-mile/wk groups. With mileage >20 miles/wk, bone density of the lower legs showed no further increase and, in fact, tended to decrease, so that for the 60- to 75-mile/wk group it was similar to that of the controls. Cross-sectional area of the tibia and fibula when normalized to body weight tended to be greater as weekly mileage increased and was significantly greater in the 40- to 55 mile/wk runners than in the control group. Serum testosterone concentration was similar for all groups and thus did not appear to have affected bone density. The data suggest that running volume may affect bone density and bone thickness in certain load-bearing bones, but the mechanism is unknown.