Site and Sex Effects on Tibia Structure in Distance Runners and Untrained People

SARA FELDMAN; RICARDO FRANCISCO CAPOZZA; PABLO ANDRÉS MORTARINO; PAOLA REINA; JOSÉ LUIS FERRETTI; JOERN RITTWEGER; GUSTAVO ROBERTO COINTRY

MEDICINE AND SCIENCE IN SPORTS AND EXERCISE

LIPPINCOTT WILLIAMS & WILKINS

Año: 2012 vol. 44 p. 1580 - 1588

0195-9131

PURPOSE: Study the relationship between mechanical environment and bone structure by comparing the tibia in people with different physical activity. MATERIAL & METHODS: Indicators of bone mass (bone mineral content, BMC), bone material "quality" (cortical volumetric mineral density, vBMD) and diaphyseal design (endocortical and periosteal perimeters, EcPm; PoPm; cortical thickness, CtTh; circularity, Circ; bending and torsion cross-sectional moments of inertia, CSMIs) were determined in serial pQCT scans taken at 5%-steps of the tibia in 40 voluntary men and women aged 25-40 yr who were either physically inactive or experienced distance runners (n=10-12/group). RESULTS: Bone mass and design indicators were higher in runner than in non-runner men, with variable effect size along the tibia. In the distal tibia, runners had enhanced BMC and CtTh (resistance to compression), but EcPm, PoPm, Circ, or CSMI were unaffected. In the midshaft, CSMIs (resistance to bending/torsion) were enhanced in runners, whilst bone mass was unaffected. In the proximal third, effects were observed for CtTh, EoPm and PoPm. In female runners, these benefits were restricted to CSMIs only. Cortical vBMD, naturally lower in men than in women, was reduced in runners of either sex. DISCUSSION: Results are coherent with previous findings in physically inactive people and with Frost´s Mechanostat Theory. The observed group differences in cortical vBMD could reflect an increase in intra-cortical porosity (enhanced remodeling for damage repair), eventually compensated biomechanically by CSMIs improvements. The sex-specificity of exercise effects may suggest the interference by the endocrine environment. Results confirm that the mechanical environment is a strong determinant of regional tibia structure, and suggest that the endocrine environment may reduce the effects of physical interventions on bone health in fertile women.