Circadian Variation In Reaction Time Performance

Abstract

Circadian rhythms in cognitive and athletic performance have been demonstrated. However, to our knowledge, no study has directly compared the characteristics of these rhythms. PURPOSE: We aimed to compare the circadian rhythm of reaction time performance with the circadian rhythm of swim performance. METHODS: Twenty-five participants were assessed for 50-55 consecutive hr in the laboratory. Throughout the duration of the laboratory protocol, all participants adhered to a 3-hr "ultra-short" sleep/wake cycle, a known chronobiological technique consisting of repeated 3-hr cycles of 2 hr of wakefulness in dim light followed by 1 hr of sleep in darkness. Beginning with the initial wake period and every third wake period thereafter (i.e., every 9 hr), participants performed a 5-min psychomotor vigilance task (PVT), with median reaction time as the outcome measure. In the wake period subsequent to PVT assessment, participants performed a maximal-effort 200-m freestyle swim. Overall, each participant performed 6 PVT assessments and 6 swim trials at randomly assigned times across the 24-hr day. A cosine fit of intra-aural temperature, measured three times each wake period, was used to establish the body temperature minimum (Tmin). PVT and swim performances were z-transformed (based on individual performance), expressed relative to Tmin, and subsequently placed into 2-hr bins relative to Tmin. RESULTS: ANOVA revealed significant (p<0.001) circadian patterns in PVT and swim performance. PVT performance was best between 9 and 7 hr before the Tmin (~2100 hr), and was worst from 1 to 3 hr after Tmin (~0700 hr). In contrast, swim performance peaked between 5 and 7 hr before the Tmin (~2300 hr) and was worst between 1 hr before to 1 hr after the Tmin (~0500 hr). Cosinor analysis revealed an earlier acrophase (i.e., fitted time of peak performance) for PVT performance (1738 hr) relative to swim performance (1803 hr). CONCLUSIONS: Although PVT and swim performance both demonstrated circadian patterns, their acrophases differed slightly, with swim performance slightly phasedelayed in relation to PVT performance. This study was supported by a Gatorade Sports Science Institute Student Grant, NIH grant HL71560, and a VA VISN-7 Career Development Award.