CORRELATION OF BONE-DENSITY TO STRENGTH AND PHYSICAL-ACTIVITY IN YOUNG MEN WITH A LOW OR MODERATE LEVEL OF PHYSICAL-ACTIVITY

The objective of this study was to evaluate the relationship among bon e mineral density (BMD), physical activity, muscle strength, and body constitution, in young men with a low or moderate level of physical ex ercise. Another aim was to investigate whether the head is unaffected by physical activity. The subjects consisted of 33 Caucasian healthy m en, mean age 24.8 +/- 2.3 years. BMDs of the total body, lumbar spine (L2-L4), femoral neck, Ward's triangle and trochanter, humerus, and he ad were measured using dual-energy-X-ray absorptiometry (DXA). Bivaria te correlations were measured among the different BMD sites and age, w eight, height, body mass index (BMI), fat mass, lean body mass, amount of physical activity (hours/week), hamstrings strength, and quadricep s strength. Significant predictors were found for all BMD sites except the head. Using all these variables. only 6% of the variation in BMD of the head could be explained, whereas 46% (total body), 31% (humerus ), 17% (lumbar spine), 38% (femoral neck, Ward's), and 41% could be ex plained for the trochanter. Physical activity and muscle strength were found to be independent significant predictors of BMD of the total bo dy and the sites at the proximal femur. These results suggest that at the time of peak bone mass attainment, physical activity is an importa nt predictor of the clinically relevant proximal femur in young men wi th a low or moderate level of physical activity. Furthermore, since he ad BMD was not related to the level of physical activity, we suggest t hat head BMD may be used as an internal standard, to control for selec tion bias, in studies investigating the effect of physical activity on bone mass.