No abstract

ObjectivesTo determine if running biomechanics and bone mineral density (BMD) were independently associated with bone stress injury (BSI) in a cohort of National Collegiate Athletic Association Division I cross country runners.MethodsThis was a prospective, observational study of 54 healthy collegiate cross country runners over three consecutive seasons. Whole body kinematics, ground reaction forces (GRFs) and BMD measures were collected during the preseason over 3 years via motion capture on an instrumented treadmill and total body densitometer scans. All medically diagnosed BSIs up to 12 months following preseason data collection were recorded. Generalised estimating equations were used to identify independent risk factors of BSI.ResultsUnivariably, step rate, centre of mass vertical excursion, peak vertical GRF and vertical GRF impulse were associated with BSI incidence. After adjusting for history of BSI and sex in a multivariable model, a higher step rate was independently associated with a decreased risk of BSI. BSI risk decreased by 5% (relative risk (RR): 0.95; 95% CI 0.91 to 0.98) with each one step/min increase in step rate. BMD z-score was not a statistically significant risk predictor in the final multivariable model (RR: 0.93, 95% CI 0.85 to 1.03). No other biomechanical variables were found to be associated with BSI risk.ConclusionLow step rate is an important risk factor for BSI among collegiate cross country runners and should be considered when developing comprehensive programmes to mitigate BSI risk in distance runners.

Vertical loading rates are typically found to be lower in forefoot compared to rearfoot strikers, promoting the idea that forefoot striking is desirable and may reduce running injury risk. However, prior work using linear models has shown that foot inclination angle at initial contact (FIA) is a poor predictor of vertical loading rate, suggesting a more complex association exists. PURPOSE: To determine if a non-linear model superiorly describes the relationship between FIA and average vertical loading rate (AVLR). Secondary analyses assessed the influence of sex and sport on the association between FIA and AVLR. METHODS: Whole body kinematics and vertical ground reaction forces were collected for 170 healthy NCAA Division I athletes (97 males; 81 cross country runners) during treadmill running at 2.68, 3.35, and 4.47 m/s. FIA and AVLR were calculated for 15 strides and averaged across strides for each limb. Polynomial mixed effects models assessed linear and non-linear trends in the relationship between FIA and AVLR across the entire sample and accounting for sex and sport participation. RESULTS: AVLR was lowest at the extremes of FIA (i.e.,-15°, 20°), while greater AVLRs were observed between 5-10°. The cubic model resulted in a significantly better fit than the linear model (p < 0.001). AVLR was also more variable among FIA associated with rear-and midfoot strike than forefoot strike. Adding sex to the model did not influence model fit; though, controlling for sport minimally improved model fit. CONCLUSIONS: The relationship between FIA and AVLR is best represented by a cubic model. Consequently, FIA should be treated as a continuous variable. Reducing FIA into categories may misrepresent the relationship between FIA and other gait variables.