Cutaneous reflex modulation of the peroneus longus during rhythmic side-stepping in subjects with and without chronic ankle instability.

Previous studies have found that people with chronic ankle instability (CAI) experience altered cutaneous reflex patterns in lower leg muscles during gait. The purpose of this study was to investigate whether cutaneous reflex alterations persist as people with and without CAI ambulate using rhythmic side-stepping. Twenty-seven subjects (15 Control; 12 CAI) were separated into groups based on IDFAI scores (CAI ≥ 11; Control = 0). Peroneus Longus (PL) reflex amplitudes were measured via surface electromyography following non-noxious sural nerve stimulation at time-normalized swing intervals as subjects side-stepped on a treadmill at 4 km/h. The net middle-latency reflex amplitudes were extracted from the ipsilateral limb across three separate phases of swing. Two-way mixed factor ANOVAs found a statistically significant interaction between the group and phase on PL reflex amplitude (F(1.3,31.4) = 7.35, p = .007, η2 = 0.227). Although both groups had similar average PL reflex amplitudes across the three phases (Control M = 15.7 ± 4.1, CAI M = 21.5 ± 4.6, p > .05), the reflex modulation patterns of the PL varied between groups. These findings demonstrate evidence of abnormal neural control mechanisms in the swing phase of side-stepping as CAI subjects are preparing to transition back into stance.