The role of sural nerve reflexes during drop-landing in subjects with and without chronic ankle instability

The purpose of this study was to investigate the functional role of cutaneous reflexes during a single-leg drop-landing task among healthy, neurologically intact adults, and to identify whether individuals with chronic ankle instability (CAI) demonstrate altered reflexes and subsequent ankle kinematics. All subjects were physically active adults and were categorized as control (n = 10, Male = 6, Female = 4) or CAI (n = 9, Male = 4, Female = 5) depending on whether they scored a 0 or ≥ 11 on the Identification of Functional Ankle Instability questionnaire, respectively. Subjects performed 30-40 single-leg drop-landing trials from a platform set to the height of their tibial tuberosity. Muscle activity of four lower leg muscles was collected via surface electromyography, while ankle kinematics were recorded via an electrogoniometer. Non-noxious stimulations were elicited randomly to the ipsilateral sural nerve at two unique phases of the drop-landing task (takeoff and landing). Unstimulated and stimulated trials were used to calculate middle latency reflex amplitudes (80-120 ms) and net ankle kinematics (140-220 ms) post-stimulation. Mixed-factor ANOVAs were used to identify significant reflexes within groups and differences in reflex amplitudes between groups. Unlike the CAI group, the control group experienced significant facilitation of the Peroneus Longus (PL) and inhibition of the Lateral Gastrocnemius (LG) when stimulated at takeoff, resulting in eversion immediately prior to landing. When stimulated at landing, the control group experienced significantly more inhibition of the PL compared to the CAI group (p = 0.019). These results suggest lower neural excitability for individuals with CAI, which may predispose them to recurrent injury during similar functional tasks.