After a normal night, an afternoon nap lowered perceived exertion during exercise (SMD 1.62) and after it (1.11), fatigue (0.91) and mood disturbance (0.61) and raised perceived recovery (1.66) against no nap, but did not significantly change sleepiness, muscle soreness, exercise heart rate or temperature, in a meta-analysis of 35 small crossover studies (489 athletes and active people, nearly all male); certainty moderate only for exertion, low to very low elsewhere, and the exertion effect sat in team-sport studies, not individual sports
Main caveat: The authors': high heterogeneity; meta-regression and subgroup results are observational; several outcomes could not be pooled.
Boukhris and colleagues pooled studies that gave athletes or physically active people an afternoon nap and compared them with the same people kept awake after the same night, either a normal night or a night of partial sleep deprivation, and measured perceptual and physiological responses.
They searched nine databases to June 2024 and included 35 studies with 489 participants (7-27 per study, mean ages 15-35, women in only two studies).
After a normal night, napping reduced the total mood-disturbance score, fatigue and perceived exertion during and straight after exercise, and improved perceived recovery; sleepiness, muscle soreness, heart rate during exercise and body temperature did not change significantly although their effect sizes were moderate to large.
After partial sleep deprivation, napping did not significantly change sleepiness or fatigue. Longer naps went with larger exertion effects, and the exertion benefit appeared in athletes and team sports but not in physically active people or individual sports. Risk of bias was mostly "some concerns", and certainty was moderate only for perceived exertion.
The authors conclude that naps help fatigue, mood, exertion and recovery after a normal night and that the low certainty calls for better studies.
Participants
35 studies, 489 participants; the largest study had 27, the smallest 7; mean ages 15-35 years.
Women only in two studies; all others male.
7 studies of moderately trained, physically active people (150-300 min of moderate or 75-150 min of vigorous activity a week) and 27 of trained athletes (training at least three times a week to compete); the sports are listed in the supplement.
Protocol
Search: nine databases (PubMed/MEDLINE, Embase, Scopus, Web of Science, SPORTDiscus, PsycInfo, Cochrane Library, ProQuest Central, SciELO), inception to 23 June 2024, plus reference lists, Google Scholar citations and hand-searched journals; 25 studies from databases, 10 from other sources.
Comparison: a daytime nap vs no nap after the same night, normal (7-9 h) or partially deprived; Ramadan studies excluded.
Outcomes: perceptual (mood, fatigue, sleepiness, RPE, perceived recovery, soreness) and physiological (heart rate, temperature and others); meta-analysis only where enough studies existed.
Analysis: three-level random-effects model (metafor), SMD with positive values favouring the nap; subgroups (level, activity type, time of day, exercise type, scale) and meta-regression (age, nap duration, time from waking to testing); outlier diagnostics; Begg and multilevel Egger tests.
Quality: RoB 2 (a protocol deviation from the registered QUALSYST tool) and GRADE starting at low for these designs.
Key Results
| Outcome, nap vs no nap | SMD (positive favours nap) | p | GRADE |
|---|---|---|---|
| After normal sleep | |||
| RPE during exercise (lower) | 1.62 | 0.008 | moderate |
| RPE after exercise (lower) | 1.11 | 0.007 | moderate |
| Perceived recovery (higher) | 1.66 | 0.009 | low |
| Fatigue (lower) | 0.91 | 0.01 | low |
| Total mood disturbance, POMS (lower) | 0.61 | 0.008 | very low |
| Sleepiness | 1.09 | 0.10, not significant | low |
| Muscle soreness | 1.57 | 0.06, not significant | low |
| Heart rate during exercise | 0.62 | 0.11, not significant | very low |
| Body temperature | 0.66 | 0.23, not significant | very low |
| After partial sleep deprivation | |||
| Sleepiness | 1.03 | 0.11, not significant | low |
| Fatigue | 0.79 | 0.07, not significant | very low |
Confidence intervals are in the forest plots, not in the text. Heterogeneity was significant for every outcome except mood (sleepiness I² 96.6%).
Nap duration (meta-regression): each extra minute raised the RPE effect by 0.01 during exercise (p = 0.005) and 0.026 after (p = 0.003).
Who benefited, RPE during exercise: athletes ES 2.09 (p = 0.003) vs physically active 0.18 (p = 0.23); team sports 2.09 vs individual sports 0.18 (the same two values, our reading: probably the same studies split two ways). RPE after exercise: team sports 1.62 (p < 0.001) vs individual sports 0.02 (p = 0.93).
Fatigue: physically active people ES 2.28 vs athletes 0.39 (p < 0.001 for the difference).
Sleepiness by scale: Stanford Sleepiness Scale ES 3.16 vs Epworth −1.43.
Publication bias detected for RPE during and after, perceived recovery and soreness after normal sleep, and for sleepiness after deprivation.
Not pooled (too few studies): mood subscales, lactate, muscle-damage and inflammation markers, HRV, blood pressure; single studies pointed both ways.
Practical Application
After a normal night, an afternoon nap before training mainly makes the session feel easier and the athlete feel more recovered: exertion during and after exercise fell (SMD 1.62 and 1.11, the only outcomes of moderate certainty), fatigue and mood disturbance fell and perceived recovery rose; heart rate and temperature did not change significantly. This is a perception benefit; this review measured no performance outcome.
For cyclists, runners and triathletes the exertion benefit is not shown: it appeared in team-sport studies (ES 2.09 during, 1.62 after) and not in individual sports (0.18 and 0.02, not significant). Inference, not tested here: a nap may still help an endurance athlete's fatigue and recovery ratings, which were pooled across sports.
Agrees with [SYNTH-07]'s nap window: the studies scheduled naps in the afternoon and the authors suggest 25-90 min between 13:00 and 16:00 (their reading of the literature, not a tested moderator), close to the guide's 20-90 min before 16:00; longer naps went with larger exertion effects.The studies left 30-270 min between waking and testing; the guide's 30 min awake before training is at the short end of that range, and the authors suggest at least an hour before testing in future studies.
After a short night the evidence is thinner than the guide's trigger implies: SYNTH-07 makes a short night a reason to nap (its own practice); here, after partial deprivation, napping did not significantly reduce sleepiness (SMD 1.03, p = 0.11) or fatigue (0.79, p = 0.07) in few studies — large point estimates, not shown, not disproved.
Limitations
The authors': high heterogeneity; meta-regression and subgroup results are observational; several outcomes could not be pooled; most studies estimated nap duration or used actigraphy rather than polysomnography; sleep inertia and testing time varied; habitual napping and chronotype were not assessed.
Certainty: 86% some concerns and 14% high risk of bias; GRADE low to very low for everything except exertion, and publication bias was detected for the exertion outcomes that carry the moderate rating.
Small, male samples: 7-27 per study, two studies with women; crossover designs only.
Author overlap: several included studies are by members of the review team (Boukhris, Suppiah), as listed in the text.
Reporting: the discussion lists muscle soreness among outcomes napping improved, but its pooled effect was not significant (p = 0.06); the "athlete" and "team sport" subgroup results for exertion during exercise carry identical values and test statistics.
No funding; no conflicts of interest declared.
How this entry was checked and changed
Why this level
risk of bias and certainty read in the full text: 86% of studies some concerns and 14% high risk, GRADE moderate only for perceived exertion and low to very low for every other outcome, significant heterogeneity in most outcomes, and publication bias detected for exertion, recovery and soreness; that is serious enough to hold it at A- at most