Ankle kinematics, center of pressure progression, and lower extremity muscle activity during a side-cutting task in participants with and without chronic ankle instability.

This study assessed ankle kinematics, surface electromyography, and center-of-pressure (COP) progression relative to the medial border of the foot during a side-cutting task in individuals with and without chronic ankle instability (CAI). Thirty participants (CAI = 15; Controls = 15) performed a side-cutting task on a force platform while 3-dimentional ankle kinematics, COP position, and surface electromyography from the tibialis anterior, medial gastrocnemius, fibularis longus, fibularis brevis, vastus medialis, and semitendinosus were recorded on the testing leg. Ankle kinematics, root-mean-square muscle activity and COP position relative to the medial boarder of the foot were compared between CAI and healthy controls (p < 0.05). Significantly greater ankle internal rotation from 35-54% of the stance phase (p = 0.032) was found for the CAI group compared to controls. Furthermore, significantly greater tibialis anterior muscle activity from 86-94% of the stance phase (p = 0.022) and a more medial COP position from 81-100% (p < 0.05) and of the stance phase was also observed in the CAI group. Less lateral COP progression and increased tibialis anterior activation in the CAI group could reflect a protective movement strategy during anticipated side-cutting to avoid recurrent injury. However, greater ankle internal rotation during mid-stance highlights a potential 'giving way' mechanism in individuals with CAI.