Bone Bending Stiffness And Mineral Density In Endurance Cyclists, Runners And Untrained Men

Mechanical Tissue Response Analysis (MRTA) is a novel technique that may be used to non-invasively measure bone bending stiffness or EI (E is the modulus of elasticity and I, the bending moment of inertia), a measure of bone strength. PURPOSE: To examine the effects of running and cycling exercise in athletes on measurements of bone bending stiffness and bone mineral density (BMD). METHODS: Volunteers were 22 athletes (11 NCAA division II runners and 12 road race cyclists) for comparison with 12 untrained men (CON) of similar age (24.3±5.4 vs. 22.4±2.1 yrs). Left Ulnar and tibial bone bending stiffness (EI) were measured with the MRTA. A Peripheral Instantaneous X-ray Imager (PIXI, GE Lunar) was used to determine BMD of the left heel and wrist. All measured EI and BMD variables between the two athletic groups (ATH) were similar, except the heel BMD. The runners have higher heel BMD than the cyclists (0.6329±0.088 vs. 0.6651±0.078 g/cm2, p < .05). Thus, descriptive, MRTA and PIXI data were combined for the ATH compared to the CON. The means were subjected to a 2-tailed t-test for all measured variables with equal variances. RESULTS: The ATH were lighter in weight and in BMI than the CON (70.1±9.1 kg and 22.6±2.0 kg/m2 vs. 78.5±11.6 kg and 25.4±3.6 kg/m2, respectively, both p<0.05). The ATH have higher ulna EI (60.8±19.6 vs. 44.1±9.7 Nm2, p<0.01) and heel BMD than CON (.647±0.08 vs. 0.578±0.06 g/cm2, p<0.01). The ATH have almost similar tibial EI (322±101 vs. 274±74 Nm2) and wrist BMD values relative to the CON (0.553±0.065 vs. 0.526±0.062 g/cm2). The small sample size precluded detecting differences in the tibial EI and the wrist BMD measurements between the two athletic groups. CONCLUSION: The results show similar values for ulnar and tibial EI as well as wrist BMD in athletes engaged in different types of sports. Their ulna strength and heel BMD values were greater than values in the untrained controls. (Partially supported by -NASA grant No. SAA2-401535).