Ankle Kinematics and Neuromuscular Activity During the Stair-to-Ground Transition in Individuals With Acute Ankle Sprain: A Cross-Sectional Study.

BACKGROUND: Evidence regarding the biomechanics of stair-to-ground transitions after acute ankle sprain (AAS) remains limited. This study examined ankle kinematics, center-of-mass (COM) displacement, muscle activation, and intermuscular coherence during this transition. METHODS: Thirty individuals with AAS and 30 healthy controls completed the task while motion-capture, force-plate, and surface electromyography data were collected. Ankle kinematics were derived from motion capture, and COM displacement was obtained using a participant-scaled OpenSim model. Trial-level outcomes were averaged within each participant. RESULTS: At initial contact, the AAS group showed an ankle position that was 1.622° more plantarflexed and 2.661° more internally rotated than that of the control group. Transverse-plane COM displacement was 0.004 m lower in the AAS group (p = 0.011), whereas ankle range of motion did not differ between groups. Mean biceps femoris activation was lower, whereas mean medial gastrocnemius and tibialis anterior activation and peak tibialis anterior and soleus activation were higher in the AAS group (p < 0.05). In the AAS group, global efficiency, clustering coefficient, and network density were higher in the 0-25 Hz band than in the 25-50 Hz band (p < 0.05). CONCLUSIONS: AAS was associated with altered ankle posture at initial contact, a smaller transverse-plane COM displacement amplitude, and differences in selected muscle-activation outcomes during the stair-to-ground transition.