Effects of Acute Lateral Ankle Sprain on Spinal Reflex Excitability and Time-to-Boundary Postural Control in...

Background/Objectives: Acute lateral ankle sprain (ALAS) affects balance, often assessed by changes in traditional center of pressure (COP) parameters. Spatiotemporal measures of COP and time-to-boundary (TTB) analysis may offer improved sensitivity in detecting postural deviations associated with ALAS. However, the neurophysiological mechanism underlying these changes remains unknown. This study aimed to explore the effects of ALAS on spinal reflex excitability in the fibularis longus (FL) during single-leg balance and TTB parameters following ALAS. Methods: Fourteen participants with and without ALAS were recruited within 14 days from the onset of the injury. We assessed FL spinal reflex excitability and postural control during a single-leg stance. The primary outcomes included the H/M ratio, H-latency, and TTB parameters. For H-reflex testing, the peripheral electrical stimulation was delivered at the sciatic nerve before bifurcating into the tibial and common fibular nerve while participants maintained a single-leg balance position with the involved side of the limb. The TTB parameters of the medial-lateral (ML) and anterior-posterior (AP) directions of the mean, SD, and minimum were assessed, which indicate postural correction and strategies. Results: Patients with ALAS had a significantly lower AP-TTB minimum compared with healthy uninjured controls, with a moderate effect size (p = 0.039; d = -0.83). However, there was no significant difference in the H/M ratio (ALAS: 0.29 ± 0.16 vs. CON: 0.24 ± 0.10; p = 0.258) and H-reflex latency (ALAS: 34.6 ± 1.92 vs. CON: 33.8 ± 1.75 ms; p = 0.277); Conclusions: These results indicate that reflex control at the spinal level may have a minimal role in response to balance deficits following ALAS.