Gait Termination Control Strategies Are Altered in Chronic Ankle Instability Subjects

Despite the high incidence of chronic ankle instability (CAI), the underlying neurophysiologic mechanism is unknown. Evidence suggests that both feed-forward and feedback mechanisms may play a role. However, no investigation has examined both control mechanisms during the same movement task in the same cohort of CAI patients. To determine the neuromuscular and biomechanical control alterations present in CAI patients during planned (feed-forward) and unplanned (feedback) gait termination. Twenty subjects with CAI and 20 uninjured controls completed planned and unplanned gait termination protocols. Both tasks began with subjects walking at a self-selected speed across a 12-m walkway. Unplanned gait termination required subjects to stop during randomly selected trials on two adjacent force plates when cued. Planned gait termination required purposeful stopping on the force places. Propulsive and braking force magnitude and the dynamic postural stability index were calculated from the resulting ground reaction forces. In addition, muscle activity from the soleus, tibialis anterior, and gluteus medius was collected bilaterally. Both maximum propulsive (CAI = 99.8 +/- 40.8 N, control = 88.6 +/- 33.6 N) and braking (CAI = 207.1 +/- 80.9 N, control = 161.6 +/- 62.2 N) forces were significantly higher in the CAI group. The dynamic postural stability index revealed higher scores in the CAI group (0.24 +/- 0.03) compared with the control group (0.22 +/- 0.03). Muscle activation of the soleus and tibialis anterior differed during unplanned and planned gait termination between groups (P < 0.05) and between the limbs of the CAI group (P < 0.05). Altered biomechanical strategies during both planned and unplanned gait termination indicate that patients with CAI have alterations in feed-forward neuromuscular control and suggest the presence of feedback neuromuscular control deficits.