Does physical fatigue affect performance on the King-Devick test?

Objectives: Sports related concussions have gained increasing awareness over recent years. The diagnosis of sports related concussion is primarily made on the basis of clinical signs and symptoms and can be extremely challenging especially during sporting events when athletes need to be assessed quickly and effectively. There are a number of psychological tests used in the on-field diagnosis of concussion one of which is the King-Devick test. The potentially confounding effect of physical fatigue on the diagnosis of sports related concussion remains poorly understood. The aim of the present study was to assess the effects of physical fatigue on performance on the King-Devick test. Methods: This study included 140 participants equally divided into two groups: a fatigue group and a control group. The fatigue group comprised 40 males and 30 females with a mean age of 34.24 years ± 12.58 years. The control group included 46 males and 24 females with a mean age of 32.01 years ± 11.38 years. Both groups were assessed on the King-Devick test at baseline and then at a reassessment which was conducted 15 minutes later. Subjects in the fatigue group ran on a treadmill for the 15 minutes intervening the baseline and reassessment conditions. To achieve significant and uniform levels of exertion, subjects in the fatigue group were instructed to run at a rate of perceived exertion of 7/10 for the first 12 minutes and 9/10for the final 3 minutes. Subjects in the control group rested from physical activity for the 15 minutes separating the baseline and reassessment conditions. Results: Comparison of baseline and reassessment scores revealed that the control group demonstrated significantly greater improvement between baseline and reassessment than the fatigue group. A significantly greater number of subjects from the fatigue group (31.4%) scored a slower time at reassessment compared to baseline than did subjects from the control group (14.3%). Finally, five subjects in the fatigue group (7.1%) worsened their score by more than 3 seconds at reassessment relative to baseline, whereas no subject in the control group demonstrated a decrement at reassessment compared to baseline of 3 seconds or more. As ignificantly greater number of subjects from the fatigue group (n = 25) met criteria for concussion at reassessment than did the control subjects (n = 11). Conclusion: The results of the current study contrasted previous findings and indicted that physical fatigue had a significant and negative effect on performance on the King-Devick test. Indeed, a significant number of subjects in the fatigue group “failed” the test and met criteria for a diagnosis of concussion. Future studies are required to validate the effects on physical fatigue on the King-Devick test and other concussion assessment instruments.