King-Devick test performance declines following fatigue independent of concussion history: a cross-sectional case-control study

Objectives: Exertional fatigue impairs athletic performance and has been linked to an increased injury risk. Yet, its role in concussion remains unclear. Fatigue may disrupt vestibulo-ocular function, mimicking concussion-related vestibulo-ocular deficits. These effects may be pronounced in athletes with a previous history. The King-Devick (KD) test offers an objective tool to assess eye movements; however, its sensitivity to fatigue is unknown. The purpose of this study was to examine the effect of fatigue on KD test performance in males with and without a history of concussionMethods: This was a cross-sectional quasi-experimental mixed repeated measures cohort study. Subjects included 16 males with a history of concussion and 16 age-matched controls. Vestibulo-ocular function was assessed by the KD test before and after an exhaustive treadmill protocol. A 2×2 mixed analysis of variance analyzed KD test performance across fatigue and concussion history with ηp² calculated for effect size.Results: There was a significant main effect for KD test time pre- and post-fatigue (p=0.002, ηp²=0.28). Both groups recorded an approximately 2.5-second increase post-fatigue. There were no significant group or interaction effects.Conclusions: Fatigue-induced declines in KD performance highlight vestibulo-ocular deterioration independent of concussion history. These changes may limit the KD test’s independent utility in fatigued athletes when athletes are exposed to worsened vestibular function. Future research is needed to determine if and how fatigue-induced vestibulocular deficits contribute to concussion risk. Clinicians should be cautious when interpreting KD test scores in fatigued athletes.