Impact-Related Ground Reaction Forces Are More Strongly Associated With Some Running Injuries Than Others

Background: Inconsistent associations have been reported for impact-related ground reaction force variables and running injuries when grouping all injuries together. However, previous work has shown more consistent associations when focusing on specific injuries. Purpose: To compare ground reaction force variables between healthy and injured runners as a group and within specific common injuries. Study Design: Controlled laboratory study. Methods: A total of 125 runners presenting with patellofemoral pain, tibial bone stress injury, plantar fasciitis, Achilles tendinopathy, or iliotibial band syndrome and 65 healthy controls completed an instrumented treadmill assessment at a self-selected speed. Impact-related ground reaction force variables included vertical average (VALR) and instantaneous (VILR) load rates, posterior and medial/lateral instantaneous load rates, and vertical stiffness at initial loading (VSIL). Mean comparisons were made between the general and specific injury and control groups (alpha = .05). Cutoff thresholds were established and evaluated using several criteria. Results: VALR (+17.5%;P< .01), VILR (+15.8%;P< .01), and VSIL (+19.7%;P< .01) were significantly higher in the overall injured versus control groups. For individual injuries, VALR, VILR, and VSIL were significantly higher for patellofemoral pain (+23.4%-26.4%;P< .01) and plantar fasciitis (+17.5%-29.0%;P< .01), as well as VSIL for Achilles tendinopathy (+29.4%;P< .01). Cutoff thresholds showed better diagnostic criteria for individual versus grouped injuries. Conclusion: Impact variables (VALR, VILR, and VSIL) were significantly higher when assessing the injured group as a whole. However, these findings were driven by specific injury groups, highlighting the importance of taking an injury-specific approach to biomechanical risk factors for running injury.