Structural and biomechanical analysis of the whole tibia by pQCT in trained long-distance runners.

SARA FELDMAN; RICARDO FRANCISCO CAPOZZA; PABLO ANDRÉS MORTARINO; IVAN YELIN; MARÍA ROSA ULLA; JOERN RITTWEGER; JOSÉ LUIS FERRETTI; GUSTAVO ROBERTO COINTRY

Denver (CO)

Congreso; XXXI ANNUAL MEETING, American Society for Bone & Mineral Research (ASBMR); 2009

Structural and Biomechanical Analysis of the Whole Tibia By pQCT In Trained Long-Distance Runners. Authors: S. Feldman, R. Capozza, P. Mortarino, I. Yelin, P. Reina, M. Ulla, J. Rittweger, J. Ferretti, G. CointryS. Feldman, R. Capozza, P. Mortarino, I. Yelin, P. Reina, M. Ulla, J. Rittweger, J. Ferretti, G. Cointry Aiming to study the impact of a chronic, low-intensity, long-volume mechanical stimulation of the leg on tibia structure, pQCT scans were taken at regular intervals (5% of whole bone length each, 19 scans/leg) in 15 trained long-distance runners (9 males) aged 20-40yr, otherwise normal. Indicators of bone mass (cortical area, total & cortical BMC, ToA, ToC, CtC), diaphyseal design (periosteal & endocortical perimeters, PeriC, EndoC; cortical thickness, CtTh; bending & torsion moments of inertia, MI) and material "quality" (cortical vBMD, vCtD), and muscle mass (area, MA) were determined in each scan and compared with similar data obtained in 10/10 male/female age-matched sedentary individuals. Correlations between MIs(y) and CtA (distribution/mass curves) or vCtD (distribution/quality curves) were calculated for each group. All CtA, ToC, PeriC, CtTh, MIs and MA values were significantly larger in males than females. Despite their high-volume physical activity, long-distance runners did not show larger MA than controls. Instead, runners had larger CtC and MIs than controls, either in absolute values or adjusted to a same MA value (p<0.001), especially close to the middiaphyses. However, the vCtD, always higher in females than males, was reduced in both groups of runners (p<0.01). Nevertheless, d/m and d/q curves showed always larger MIs’ values for runners for the same CtC or vCtD values, respectively (p<0.001). Results suggest that bone mass and structure are achieved as a function of the intensity and volume of the mechanical use of the regional muscles, rather than their mass. However, when the volume of that activity is exaggerated, the intrinsic stiffness of cortical bone (proportional to vCtD) can be impaired by microdamage caused by excessive remodeling. Nevertheless, the architectural distribution of cortical tissue would be sensitive to exercise volume, perhaps to compensate for the reduction of bone material quality in the runners. Long-distance runners would tend to show both a reduced "quality" and a better architectural distribution of cortical bone in their tibiae. As a result, runners’ tibiae tend to be more robust than those of their sedentary controls for a similar cortical mass or quality, or for the same calf muscle mass, perhaps as a function of the volume of mechanical use of the legs. This mechanism would improve bone design, but not necessarily bone strength, as long as runners’ tibiae may tend to suffer fatigue fractures.