Altered energy dissipation patterns and increased ground reaction force in patients with chronic ankle instability...

The purpose of this study was to investigate whether the interaction between chronic ankle instability (CAI) and fatigue alters energy absorption strategies and ground reaction force (GRF) during landing. This cross-sectional study was conducted in a laboratory setting and included 20 patients with CAI, 20 copers, and 20 healthy controls. All participants performed single-leg drop landing before and after the fatigue protocol. The fatigue protocol consisted of repeated cycles of multidirectional running, hopping, and jumping tasks. Heart rate (HR) and rating of perceived exertion (RPE) were monitored after each cycle, and the protocol was repeated until participants reached ≥ 85% of maximal heart rate and RPE ≥ 17. Lower-extremity angles and power, relative joint contribution to shock absorption, and GRF were measured from initial foot contact to 200 ms after landing. The interaction effect of group and fatigue was analyzed using functional ANOVA and two-way repeated measures ANOVA. Interaction effects showed that after fatiguing exercises, patients with CAI exhibited (1) less sagittal hip excursion, (2) more eccentric power patterns in the hip and knee joints, (3) a greater contribution of the hip and knee to total lower-extremity energy dissipation, and (4) greater vertical GRF during the initial phase of landing compared to copers and/or controls. Under fatigue, patients with CAI demonstrated altered proximal kinetic strategies with greater GRF. Despite these adaptations, patients with CAI exhibited higher GRF after fatigue. This highlights the need for interventions aimed at optimizing neuromuscular control to more efficiently distribute impact forces across the lower-extremity.