Comparison of lower extremity peak muscle forces and force-generating capacities during the functional side hop test in male collegiate football players with and without chronic ankle instability

Chronic ankle instability (CAI) alters lower extremity kinematics and neuromuscular function during dynamic tasks, yet potential compensatory mechanisms in muscle forces and force-generating capacity remain unexplored during repeated lateral movements. This study examined muscle force and force-generating capacity as primary outcome measures, with kinematics and performance as secondary measures, during the side-hop test (SHT) in athletes with and without CAI. Thirteen male football players with CAI and thirteen healthy (CON) players performed the SHT with maximum effort, during which motion capture, force platform, and electromyography (EMG) data were recorded. Individual peak muscle forces and force-generating capacities were estimated using a scaled, generic lower-limb musculoskeletal model in OpenSim, driven by joint kinematics and ground reaction forces via static optimisation, verified against EMG signals. Players with CAI demonstrated significantly greater peak force of the peroneus longus (CAI: 0.14 ± 0.05 N/kg vs. CON: 0.08 ± 0.02 N/kg; p = 0.001) and vastii muscles (CAI: 5.34 ± 2.25 N/kg vs. CON: 2.52 ± 1.32 N/kg; p < 0.001) during the lateral hop contact (LHC), alongside elevated vastii force-generating capacity during the medial hop contact (MHC) (CAI: 0.86 ± 0.07 vs. CON: 0.73 ± 0.12; p = 0.005). Additionally, athletes with CAI exhibited significantly increased sagittal ankle ROM, prolonged ground contact time and slower completion times in the SHT ( p < 0.05). These findings suggest that CAI athletes exhibited compensatory adaptations in muscle force and force-generating capacity, which may be associated with an ankle functional deficit and reflected in altered lower-extremity kinematics and reduced SHT performance.