Alterations in Center of Pressure and Ground Reaction Forces Across Transition and Progression Conditions of Stair Negotiation in Adults with Chronic Ankle Instability: A Cross-Sectional Study

Chronic ankle instability (CAI) is associated with recurrent ankle sprains, episodes of giving way, and functional limitations. Stair negotiation is a mechanically demanding daily activity, but whether CAI-related alterations differ between the transition and progression conditions of stair negotiation remains unclear. This cross-sectional study (IRB No. 1044396-202505-HR-068-01) compared center of pressure (COP) and ground reaction force (GRF) responses between 13 adults with CAI and 12 healthy adults across four stair negotiation conditions. COP and GRF were measured using a force plate and analyzed using a 2 × 4 mixed repeated-measures analysis of variance. Significant group × condition interactions were observed for COP path length (p = 0.015), COP velocity (p = 0.007), anterior force at push-off (p = 0.036), and vertical force at push-off (p = 0.030). The healthy group demonstrated greater COP path length and velocity during the transition from level walking to stair ascent, whereas the CAI group demonstrated greater anterior force at push-off during the transition and progression conditions of stair descent and greater vertical force at push-off during stair-ascent progression. These findings suggest that CAI may be associated with condition-dependent alterations in COP and GRF responses related to dynamic balance and force regulation during stair negotiation.