Napping is an important fatigue management strategy for shift workers, especially for nightshift workers as nightshifts are synonymous with fatigue. Night shifts are associated with increased sleepiness, performance impairment, and risk of workplace injury and errors. Studies have shown 30 minute naps cause sleep inertia lasting between 5-35 minutes and that 10 min naps immediately improve performance, with this improvement lasting at least 35min after waking. While the methodology and operational settings of nap related research is quite varied across the industry, most studies have observed benefits to performance and subjective alertness following naps during nightshift. However these studies have not included 10 minute naps in their methodology nor have they tested for sleep inertia and its effect delaying or preventing this performance improvement post nap. This study aims to inform recommendations for napping on nightshift.
This study was conducted by Cassie J. Hilditch et al. at the Centre for Sleep Research, University of South Australia. They recruited 31 healthy adults, aged between 21-35 years of age to participate in the study which ran over three days. The protocol involved one night of normal sleep from 10pm to 7am, and then one experimental night where the participants were randomly assigned to one of three groups: the No-Nap, the 30 min Nap or the 10min nap group. All naps finished at 4am, and the participants completed one performance assessment pre Nap, and four assessments performed after the Nap at regular intervals over a 45 minute time period. The performance was assessed with two tasks; one a cognition based assessment, the other a reflex based assessment.
The participants did sleep (TST – total sleep time) for the majority of the nap periods, however 80% of participants in the 10 minute nap group woke from stage 2 sleep (normal sleep), and 80% of participants in the 30 minute nap group woke from Slow Wave Sleep (very deep sleep). Waking from SWS is thought to increase sleep inertia.
No-nap group: Performance was reduced for 45 minutes post Nap for both tasks, potentially highlighting the expected cognitive decline due to sleepiness and fatigue.
Nap group: No significant change in performance was noted for both tasks, indicating both an absence of sleep inertia and potential to prevent cognitive decline.
30 minute Nap group: performance declined in the Response Speed performance assessment for the entire 45 mins post nap, with no significant decline in cognitive performance.
Self-rated performance improved post nap in all groups.
Key message: a 10-min nap at night is not as effective as during the day; a 30-min nap at night can result in sleep inertia lasting nearly an hour; and workers may not be aware of their own performance impairment following a nap at night.
Citation: Hilditch CJ, Centofanti SA, Dorrian J, Banks S. A 30-minute, but not a 10-minute nighttime nap is associated with sleep inertia. SLEEP
2016;39(3):675–685.
