Relationship of chronic ankle instability to muscle activation patterns during the transition from double-leg to single-leg stance

Background: Impaired muscle activation may predispose subjects to develop chronic ankle instability. It has been suggested that impairments are found not only in structures around the injured ankle but also around the more proximal joint complexes. Hypothesis: Subjects with chronic ankle instability were expected to show later onset times for lower limb and trunk muscle activation when compared with control subjects. They were expected to show less variability in muscle activation patterns compared with the control group. Study Design: Controlled laboratory study. Methods: Thirty control subjects and 10 subjects with chronic ankle instability participated in the study. The onset of muscle activity of 14 muscles of the lower limb and trunk was measured during the transition from a double-leg stance position to a single-leg stance position in eyes-open and eyes-closed test conditions. Results: Subjects with chronic ankle instability showed significantly later onset times for the ankle, hip, and hamstring muscles compared with control subjects. They used a similar muscle activation pattern in both test conditions, whereas control subjects adjusted their activation pattern according to the condition. Conclusions: Differences in muscle activation patterns between subjects with chronic ankle instability and control subjects occur not only around the ankle but also around other joints. Subjects with chronic ankle instability show less variability in muscle activation patterns between test conditions. Clinical Relevance: Knowledge of muscle activation patterns in the whole lower limb and trunk in noninjured subjects and the differences found in chronic ankle instability subjects broadens the physical therapy approach to the treatment of chronic ankle instability.