Background The retrospective studies have reported altered spinal reflex excitability of the lower leg muscles in patients with acute lateral ankle sprain (LAS); however, these authors relied on data without a pre-injury assessment. Prospective examination of the longitudinal changes in neural excitability from pre-injury characteristics would provide a more comprehensive view of the underlying neuromuscular impairments. This study aimed to prospectively examine spinal reflex excitability of the fibularis longus and perceived ankle instability following acute LAS in collegiate basketball players. Methods Using a prospective cohort study design, this study included 9 collegiate male basketball players who sprained their ankle during a competitive season and 26 those who were free from LAS during the season. All athletic patients were tested to assess spinal reflex excitability bilaterally of the fibularis longus and completed the Cumberland Ankle Instability Tool (CAIT) prior to the beginning of the season (pre-injury), as well as at 24-hour, one-week, and one-month post-injury. Spinal reflex excitability was assessed by eliciting Hoffman reflex (H-reflex) and motor responses. The Hmax:Mmax ratio was calculated using the averaged values of maximum H-reflex and motor responses from the three recordings. Results There were no significantly differences in the pre-injury Hmax:Mmax ratio of the fibularis longus between athletes who sustained LAS and those who did not (P > 0.05). A receiver operating characteristic curve analysis revealed poor diagnostic utility of the Hmax:Mmax ratio for predicting LAS (area under curve = 0.52, 95% CI: 0.33-0.70, P = 0.88). Additionally, no significant changes were observed in Hmax:Mmax ratios between baseline and post-injury time points (P > 0.05). However, a trend toward decreased spinal reflex excitability was observed on the injured side at 24 h post-injury compared to pre-injury levels. While this overall trend change did not reach statistical significance, the decreases observed in some individuals exceeded the established minimal detectable change (MDC) (0.03) for the Hmax:Mmax ratio of the fibularis longus. A significant time main effect was found for the CAIT scores (P = 0.03). Post-hoc analyses revealed significantly lower CAIT scores at 24 h (P = 0.03) and one week (P = 0.02) post-injury compared to baseline. Conclusions These findings suggest that the pre-injury Hmax:Mmax ratio of the fibularis longus may be not a reliable predictor for LAS in collegiate basketball players and is not consistently altered following acute injury. However, some individuals demonstrated a decrease in the post-injury Hmax:Mmax ratio of the fibularis longus exceeding the MDC, suggesting clinically meaningful changes. Additionally, basketball players reported significantly lower CAIT scores within the first week post-injury, indicating early perceived ankle instability. These findings highlight the importance of considering both group and individual-level responses in the assessment of LAS. Future prospective studies with larger sample sizes are warranted to explore longitudinal changes in spinal reflex excitability and their potential role in injury recovery and prevention.
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