Effects of Cognitive Load on Stride-to-Stride Variability During Walking Among Participants With and Without Functional Ankle Instability

BackgroundStudying the dynamics of nonlinear systems under dual-task conditions in people with functional ankle instability (FAI) can provide additional information about the variability of the structure of the system. However, how the cognitive load affects the stride-to-stride variability in the lower extremities throughout walking in those with and without FAI using nonlinear evaluation tools is unknown.MethodsEighteen volunteers with FAI and 19 healthy individuals were recruited for this study. The participants walked on a motor-driven treadmill at their preferred speed, with or without completing a cognitive task involving an auditory Stroop test. A passive retroreflective marker motion-capture system recorded the lower extremity gait kinematics in the sagittal, frontal, and transverse planes. The largest Lyapunov exponent (LyE) characterizes the variability of the temporal structure in walking patterns. Cognitive task performance was analyzed using error ratio and average reaction time in walking and sitting conditions.ResultsDuring walking with cognitive load, the group with FAI exhibited lower values for the LyE in knee kinematics in the sagittal plane than the normal walking (95% confidence interval [CI]: 0.44-0.92, P < .001). During normal walking (single task), participants with FAI demonstrated higher knee flexion-extension LyE (95% CI: 0.52-0.93, P = .04) than healthy people. The 2 groups had no significant differences regarding the LyE values for other kinematic variables (P > .05). Regarding cognitive performance, both FAI and healthy groups had remarkably longer reaction times (P < .001) while walking (mean ± SD: 0.92 ± 0.06) compared with the sitting condition (mean ± SD: 0.77 ± 0.03).ConclusionThe reduced variability observed in the walking patterns of individuals with FAI during walking with an added cognitive load suggests a compensatory mechanism due to sensorimotor constraints, highlighting the altered motor control strategies. Dual task and cognitive training may help correct these patterns and improve responses.Levels of Evidence:Level II.