The lateral ankle sprain is the most common athletic injury, and many people who suffer an ankle sprain develop chronic ankle instability (CAI). The purpose of this study was to examine the ground reaction force during a simulated lateral ankle sprain among participants with no history of ankle injury and those with CAI. Twelve participants, which included six with CAI, and six with no history of ankle sprain performed 14 repetitions of a vertical drop down off a 27 cm box, landing on an AMTI force platform. Seven trials were completed with a fulcrum outer sole strapped to the bottom of the participant’s shoe, which caused 25° of inversion upon landing, and seven trials were performed with a flat outer sole. Outer sole assignment was randomized. Peak vertical, anterior/posterior, and medial/lateral ground reaction force, normalized to multiples of body weight (BW), were measured for each participant. Results revealed that the no injury group landed with significantly greater (P< .05) peak vertical and peak anterior/posterior force than the CAI group. These differences in force between the two groups may be an attempt by the CAI participants to change loading of the unstable ankle, and the altered landing kinetics potentially increase future risk of injury.

Context: Previous research has reported that while barefoot, individuals with chronic ankle instability (CAI) demonstrate altered gait kinematics compared to healthy controls. However, no studies have evaluated the effect of CAI on gait kinematics while shod. Objective: To determine if there are sagittal and frontal plane ankle kinematic differences during shod walking and jogging between subjects with and without CAI. Methods: Fifteen subjects with self-reported CAI and 13 healthy subjects walked and jogged on a treadmill with embedded force plates while lower extremity kinematics were captured. Each stride of the gait cycle was normalized to 100 frames. Sagittal and frontal plane angles were calculated in each frame. Means and associated 95% confidence intervals (CIs) were calculated across the entire gait cycle. To identify significant differences, increments where the CI bands for the two groups did not cross each other were identified. Results: While walking, the CAI group was significantly less dorsiflexed from 44% to 48% of the gait cycle (mean difference=5.0±0.2°). In the frontal plane, there were no increments where the CIs between the two groups did not overlap. While jogging, there were no increments where the CI did not overlap. Conclusions: During shod walking, the CAI group was significantly less dorsiflexed compared to the healthy group near the time of peak dorsiflexion. Significant differences between groups were not found in frontal plane motion during walking or in either the frontal or sagittal planes during jogging indicating that shoes may stimulate CAI subjects differently than they do healthy.