Women’s collegiate gymnastics and cross-country running are sports that differ in impact loading characteristics while sharing high rates of stress fracture and an emphasis on leanness, which can impact eating behavior, energy availability, and menstrual function. Thus, skeletal sites that commonly fracture in both groups should be examined to determine the effect of sport on bone quality and adaptation over time.

PURPOSE:​ To compare bone structure, density, and estimated strength of the distal tibia between NCAA Division I gymnasts and cross-country runners to appreciate differences at baseline and tibial adaptations to sport specific training.

METHODS:​ Geometry, microarchitecture, volumetric bone mineral density (vBMD) and estimated strength were assessed via high resolution peripheral quantitative computed tomography (HRpQCT) and areal bone mineral density (aBMD) of the total body, total hip, femoral neck, and lumbar spine was assessed via dual-energy x-ray absorptiometry (DXA) in forty-five women (XC = 22, GYM = 23) before the start of their competitive season. Surrogates of energy availability and history of menstrual irregularity were assessed via questionnaire. Independent samples t-tests were used to compare bone characteristics at baseline and lean mass was used in an analysis of covariance to adjust for body size. A two-way repeated measures analysis of variance was used on a small subset (XC = 5, GYM = 6) of healthy athletes to compare bone adaptation over time.

RESULTS:​ After controlling for lean mass, trabecular separation at the tibial metaphysis was lower in gymnasts than in cross-country runners. Despite a greater frequency of delayed menarche, behaviors potentially associated with disordered eating, and perceptions of body dissatisfaction reported in gymnasts than cross-country runners, baseline differences in tibial bone characteristics were similar between athlete groups after adjusting for lean mass. In the subset of health athletes over time, vBMD increased in both groups at the metaphysis and increased in gymnasts at the diaphysis while decreasing in the runners.

CONCLUSION:​ Lower trabecular separation at the distal tibial metaphysis between competitive female gymnasts and cross-country runners suggests a sport-specific adaptation. Pilot data on a small number of healthy athletes indicates increases in tibial vBMD following a competitive season and further research is required to corroborate these findings.