Variability of motion in individuals with mechanical or functional ankle instability during a stop jump maneuver

BackgroundMovement variability may influence episodes of instability following lateral ankle sprain.MethodsSixty-three recreational athletes with a history of moderate-severe ankle sprain were recruited. Mechanically and functionally unstable ankle groups had ⩾2 episodes of instability in the last year. Mechanically unstable had clinically lax lateral ankle ligaments; functionally unstable and copers did not. Copers had a history of sprain but no residual instability. Lower extremity 3-dimensional kinematics and ground reaction forces were measured during a 2-legged stop jump. Average ensemble curves of eight trials normalized to 100% of stance phase were created. The coefficient of variation and average standard deviation of the ensemble curves of each variable were identified. A loge (ln) transformation was performed on the data. One-way ANOVAs with Tukey post hoc testing were utilized with α = 0.05.FindingsThe functionally unstable group demonstrated greater mean (standard deviation) ln coefficient of variation ankle inversion/eversion 3.56 (1.19) than the mechanically unstable 2.77 (0.95) and copers 2.74 (1.05) (P = 0.05 and P = 0.04; ηp2 = 0.12), and greater ln standard deviation ankle inversion/eversion 1.07 (0.78) than copers 0.61 (0.31) (ηp2 = 0.13). The mechanically unstable group demonstrated greater ln coefficient of variation anterior–posterior ground reaction force 3.69 (0.27) than functionally unstable 3.43 (0.25) (P = 0.02; ηp2 = 0.13).InterpretationFunctionally unstable individuals demonstrated greater ankle frontal plane movement variability during a stop jump, which may increase risk of instability. Mechanically unstable participants demonstrated greater anterior–posterior ground reaction force variability, which may indicate difficulty mitigating landing forces with lax ligaments. Movement variability may influence episodes of ankle instability.