The effects of sleep inertia following EEG-monitored short and long naps on perceptual, cognitive, and physical performance in recreational athletes

The purpose of this study was to examine the effects of sleep inertia following naps of two durations on cognitive performance (reaction time and decision making), physical performance (countermovement jump (CMJ) and handgrip strength (HG)), and perceptual responses (i.e. sleepiness, fatigue, and readiness to perform). In a randomized, counterbalanced, crossover design, 17 physically active participants (9 males, 8 females, age: 23 ± 2 y) completed three conditions: no-nap (NN), a 25-min nap opportunity (N25), and a 90-min nap opportunity (N90). Naps were conducted in a controlled laboratory setting using a sleep pod. Nighttime sleep prior to each session was tracked using a wrist-worn actigraph, and sleep during naps was assessed using a forehead mounted EEG device. Following each condition, participants completed four 30-min test batteries within the first two post-nap hours (T1: 0-30 min post-nap, T2: 30-60 min post-nap, T3: 60-90 min post-nap, and T4: 90-120 min post-nap), starting at 15:00 h. Each session included assessments of sleepiness, fatigue, readiness to perform, cognitive function (psychomotor vigilance task and Simon task (ST)), and physical performance (HG and CMJ). All performance markers were impaired at T1 compared to the subsequent time points (p < 0.05) for both nap durations, with more pronounced sleep inertia after N90 (p < 0.05) for sleepiness, readiness to perform, HG, and accuracy during ST. However, most performance markers improved after both N25 and N90 at T3 (p < 0.05), with more improvement observed after N90 at T4 compared to NN and N25 in sleepiness, fatigue, reaction time during ST, and HG (p < 0.05). In conclusion, at least one hour is required for sleep inertia to dissipate following N25 and N90, with significant improvements in perceptual, cognitive, and physical performance observed at 1-2 h post napping.