The relationships between multiaxial loading history and tibial strains during load carriage.

OBJECTIVES To determine if a history of exercise involving multiaxial loading, through soccer participation, influences tibial stains during incremented load carriage. DESIGN Cross-sectional study. METHODS 20 female soccer players (20±1 yr) and 20 mass- and height-matched healthy women (21±1 yr) participated in walking tasks with 0kg, 10kg, 20kg, and 30kg loads on a force instrumented treadmill at 1.67m/s. Subject-specific tibial CT models were combined with subject-specific musculoskeletal models for forward-dynamic simulations and finite element analyses. Strains from the middle third of the tibial shaft were analyzed. A mixed model repeated measures analysis of variance (ANOVA) and one-way ANOVAs were run with a Bonferroni correction setting significance at 0.0009. RESULTS Significant differences in tibial characteristics were found among loading conditions and between groups (all p<0.0001). Tensile strains were 19.6%, 22.2%, 44.1%, and 20.7% lower in soccer players at 0kg, 10kg, 20kg, and 30kg of load carriage, respectively. Strain rates were 20.4%, 29.9%, 43.4%, and 18.9% lower, respectively, in soccer players. Lower compressive and shear strain magnitudes and rates were also observed in soccer players, with the only exception at the 30kg loading condition in which controls had 2.4% lower strain magnitudes in compression, on average, compared to soccer players. CONCLUSIONS A history of activity involving multiaxial loading was associated with generally lower estimated tibial strains during load carriage. Lower strain levels during repetitive physical activity may be protective from stress fracture. These findings suggest that physical training, such as participating in soccer, may be effective for preconditioning prior to entering military or endurance training.