Particular adaptation of the human fibula to long-term exercise.

LAURA NOCCIOLINO; GUSTAVO ROBERTO COINTRY; ALEX IRELAND; SERGIO LUSCHER; JOSÉ LUIS FERRETTI; JOERN RITTWEGER; RICARDO FRANCISCO CAPOZZA

Denver (CO)

Congreso; XXXIX ANNUAL MEETING, American Society for Bone & Mineral Research; 2017

American Society for Bone & Mineral Research

PARTICULAR ADAPTATION OF THE HUMAN FIBULA TO LONG-TERM EXERCISE.1Laura M Nocciolino; 1Gustavo R Cointry; 2Alex Ireland; 1Sergio H Lüscher, 1José L Ferretti*; 3Joern Rittweger; 1Ricardo F Capozza.1Center of P-Ca Metabolism Studies (CEMFoC), National University of Rosario, Rosario, Argentina2School of Healthcare Science, Manchester Metropolitan University, Manchester, UK3Division of Space Physiology, Institute of Aerospace Medicine, German Aerospace Center, Cologne, Germany.INTRODUCTIONWe have shown that cortical structure of human tibia and fibula respond differently to disuse [Ireland et al, OPInt 2017], and fibula is adapted to resist bending/torsion rather than compression [Cointry et al, Bone 2016]. Now we analyze the fibula response to long-term exercise. MATERIALS AND METHODSIn a cross-sectional study, 26 healthy men and women (13/13) aged 20-40 years who were either sedentary (13/13) or chronically trained in long-distance running (13/13) were analyzed. Serial scans of the fibula were taken at 5% increments along the tibia length measured between the tibio-tarsal joint line and the proximal articular surface of the tibia (From S5 -heel- to S95 -knee-, excluding the central bone site (18 scans per individual, Fig 1). The following indicators were determined in every scan and plotted by bone site for each group studied: - Cortical mass indicators: cortical BMC, cortical area - Bone tissue mineralization: cortical vBMD - Bone design indicators: Periosteal and endocortical perimeters, cortical thickness, moments of inertia for A-P and lateral bending (xMI, yMI) and torsion (polar MI, pMI), buckling ratio (cortical thickness / bone diameter, BR), ?shape index? (independent of body size and height) = yMI/xMI. - Bone strength indicators: Bone Strength Indices for A-P and lateral bending and torsion (xBSI, yBSI, pSSI), Buckling Resistance Index, BRI = 1/BR. RESULTSProximally, runners? fibula cross-sections were smaller (Fig 1), more elliptically shaped and more sagittally oriented, with lower total and cortical BMC and cortical area than controls (Figs 5-6). Distally, the sections were smaller in runners than in controls, with smaller endocortical perimeters and thicker cortices and slightly higher area and BMC (Figs 2-6), especially in men. Cortical vBMD of runners? bones was slightly but significantly lower proximally and higher distally than in controls (Fig 7). The yMI and yBSI were lower in runners than in their controls throughout the bone (Figs 9 & 12). Both xMI and pMI were lower in runners than controls only in the distal half (Figs 8 & 10). Adjustment of MIs? values to bone length and/or body mass did not affect these results. The size-independent ?shape index? (yMI/xMI ? Invertir la gráfica) was lower in runners than in controls throughout the bones (Fig 11).While the percent differences between runners and controls in xMI, yMI, xBSI and yBSI values decayed progressively toward the distal end of the bone (congruent with the smaller bone size), the BRI values showed a specular increase of bone resistance to buckling (congruent with the thicker cortices) (Fig 12).These results strongly contrast with those previously reported for the adjacent tibia in the same individuals [Feldman et al, Med Sci Sport Exerc 2012].INTERPRETATIONWithin the limitations of its cross-sectional design, this study shows a particular response of the human fibula to its mechanical environment, which seems to comprise a striking compliance to lateral bending or torsion after a chronic training in long-distance running. Those changes would have enhanced the fibula?s contribution to fast-running optimization (elastic energy storage for muscles, tibio-talar joint widening), in spite of a general weakening of the bone in bending/torsion. However, bone resistance to failure in buckling would have been conveniently improved at its ultra-distal end (the region most prone to fracture). This suggests that, in the studied conditions, the usage-derived strains may induce different changes in structural stiffness or strength in different regions of the fibula as a response to the same method of mechanical stimulation of the bones.