Objectives The aim of this study was to quantify changes in peak bending moments at the distal tibia, peak patellofemoral joint contact forces and peak Achilles tendon forces during a high-intensity run to fatigue at middle-distance speed. Design Observational study. Methods 16 high-level runners (7 female) ran on a treadmill at the final speed achieved during a preceding maximum oxygen uptake test until failure (~ 3min). Three-dimensional kinetics and kinematics were used to derive and compare tibial bending moments, patellofemoral joint contact forces and Achilles tendon forces at the start, 33%, 67% and the end of the run. Results Average running speed was 5.7 (0.4) m·s-1. There was a decrease in peak tibial bending moments (- 6.8%, p=0.004) from the start to the end of the run, driven by a decrease in peak bending moments due to muscular forces (- 6.5%, p=0.001), whilst there was no difference in peak bending moments due to joint reaction forces. There was an increase in peak patellofemoral joint forces (+ 8.9%, p=0.026) from the start to the end of the run, but a decrease in peak Achilles tendon forces (- 9.1%, p<0.001). Conclusions Running at a fixed, high-intensity speed to failure led to reduced tibial bending moments and Achilles tendon forces, and increased patellofemoral joint forces. Thus, the altered neuromechanics of high-intensity running to fatigue may increase patellofemoral joint injury risk, but may not be a mechanism for tibial or Achilles tendon overuse injury development.
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