INFLUENCE OF RECREATIONAL ACTIVITY AND MUSCLE STRENGTH ON ULNAR BENDING STIFFNESS IN MEN

Bone bending stiffness (modulus of elasticity [E] x moment of inertia [I]), a measure of bone strength, is related to its mineral content (B MC) and geometry and may be influenced by exercise. We evaluated the r elationship of habitual recreational exercise and muscle strength to u lnar EI, width, and BMC in 51 healthy men, 28-61 yr of age. BMC and wi dth were measured by single photon absorptiometry and EI by mechanical resistance tissue analysis. Maximum biceps strength was determined dy namically (1-RM) and grip strength isometrically. Subjects were classi fied as sedentary (S) (N = 13), moderately (M) (N = 18), or highly act ive (H) (N = 20) and exercised 0.2 +/- 0.2; 2.2 +/- 1.3; and 6.8 +/- 2 .3 h . wk-1 (P < 0.001). H had greater biceps (P < 0.0005) and grip st rength (P < 0.05), ulnar BMC (P < 0.05), and ulnar EI (P = 0.01) than M or S, who were similar. Amount of activity correlated with grip and biceps strength (r = 0.47 and 0.49; P < 0.001), but not with bone meas urements, whereas muscle strength correlated with both EI and BMC (r = 0.40-0.52, P < 0.005). EI also correlated significantly with both BMC and ulnar width (P < 0.0001). Ulnar width and biceps strength were th e only independent predictors of EI (r2 = 0.67, P < 0.0001). We conclu de that levels of physical activity sufficient to increase arm strengt h influence ulnar bending stiffness.