To prevent chronic ankle instability (CAI) and understand why outcomes vary among patients with a lateral ankle sprain, it is important to examine the differences in movement patterns between copers without recurrent ankle sprain and those who develop CAI. The differences in coordination between both groups are unclear, even though abnormal movements of the rearfoot may affect the forefoot through coupling. Therefore, the purpose of this study was to investigate the coordination between the rearfoot and forefoot of CAI, coper groups. Twelve individuals with CAI, 12 copers, and 12 controls ran on a treadmill at a fixed speed of 2.5 m/s. Kinematic data of the rearfoot and forefoot were measured using a three-dimensional motion analysis system. The coupling angle between the rearfoot and forefoot was calculated using the modified vector coding technique and was classified into four coordination patterns. During early stance, the coper group showed a significantly greater proportion of anti-phase with distal dominancy than the CAI group (p<0.05), and in-phase with distal dominancy approached to decrease than the CAI group (p=0.052). During midstance, the CAI group approached to increase proportion of anti-phase with distal dominancy than the control group (p=0.053). During late stance, the coper group showed a significantly decreased proportion of anti-phase with distal dominancy than the control group (p<0.05). This study may provide in-depth knowledge of motor-behavioral characteristics of coper and CAI.
