Using Machine Learning and SHAP to Identify Biomechanical Risk Factors for Increased Achilles Tendon Stress during...

Achilles tendon injuries are common during running in low-temperature environments, but the underlying biomechanical mechanisms remain unclear. This study combines machine learning with Shapley Additive exPlanations (SHAP) to identify key running biomechanics factors contributing to increased Achilles tendon stress during the running-start and steady-state phases in low-temperature conditions, providing insights into injury prevention strategies for recreational runners.

Trunk and lower limb biomechanics were assessed in 126 recreational runners during running-start and steady-state phases under cold conditions. Achilles tendon stress was quantified via OpenSim modeling and ultrasound. Machine learning models-extreme gradient boosting (XGBoost), random forest, and support vector regression-combined with the SHAP framework identified key biomechanical factors influencing Achilles tendon stress.

XGBoost outperformed other models, so the SHAP framework was based on its results. During the running-start phase, increased Achilles tendon stress was associated with (i) ankle dorsiflexion angles less than 12.449°, (ii) anterior ground reaction force (GRF, defined here as the forward propulsive force during running) greater than 7.143 N/kg, or (iii) contralateral pelvic lean angles exceeding 10.998°. In the steady-state phase, key factors included (i) ankle dorsiflexion angles less than 11.816°, (ii) ankle inversion moments greater than 0.187 N·m/kg, and (iii) ankle inversion angles exceeding 2.482°.

The XGBoost-SHAP framework reveals that, under low-temperature conditions, limited ankle dorsiflexion, excessive anterior GRF, and increased pelvic lean contribute to elevated Achilles tendon stress during the running-start phase. In the steady-state phase, reduced ankle dorsiflexion, excessive ankle inversion moments, and greater ankle inversion angles are potentially associated with higher tendon loading. Targeted gait training may reduce these risk factors and prevent Achilles tendon injuries in low-temperature environments.