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Primary Publication
DeMers MS, Hicks JL, Delp SL. Preparatory co-activation of the ankle muscles may prevent ankle inversion injuries. Journal of Biomechanics. (accepted) (2016)

Ankle inversion sprains are the most frequent acute musculoskeletal injuries occurring in physical activity. Interventions that retrain muscle coordination have helped rehabilitate injured ankles, but it is unclear which muscle coordination strategies, if any, can prevent ankle sprains. The purpose of this study was to determine whether coordinated activity of the ankle muscles could prevent excessive ankle inversion during a simulated landing on a 30 degree incline. We used musculoskeletal simulation to evaluate the efficacy of two strategies for coordinating the ankle evertor and invertor muscles during simulated landing scenarios: planned co-activation and stretch reflex activation with physiologic latency (60-millisecond delay). We developed a full-body musculoskeletal model and used it to generate simulations of a subject dropping and landing on an inclined surface with either coordination condition, systematically varying the intensity of evertor and invertor co-activity or stretch reflexes. Our simulations revealed that strong preparatory co-activation of the ankle evertors and invertors prior to ground contact prevented ankle inversion from exceeding injury thresholds by rapidly generating eversion moments after initial contact. Conversely, stretch reflexes were too slow to generate eversion moments before the simulations reached the threshold for inversion injury. These results suggest that training interventions to protect the ankle should focus on stiffening the ankle with muscle co-activation instead of increasing the speed or intensity of the evertor reflexes. The musculoskeletal models, controllers, software, and simulation results are freely available online, enabling others to reproduce the results and explore new injury scenarios and interventions.