Napping
Evidence: moderate
A well-timed daytime nap recovers some of a night-time sleep deficit and reliably improves alertness and mood, with smaller gains in physical and cognitive performance that are largest in athletes who are sleep-restricted. The supporting studies are mostly small, but they point the same way. A nap supplements night sleep; it does not replace it, and a long or late nap can erode the coming night.
What naps are for
A nap is the most practical way to recover part of a sleep deficit during the day. Athletes commonly under-sleep, with around 39% reporting under seven hours a night (Walsh, Halson et al. 2021), and that shortfall matters because sleep loss moderately impairs endurance, with a pooled effect around −0.52 that grows for efforts over 30 minutes (Lopes et al. 2023). When the night has been short, a nap claws back some of what was lost.
A nap does a few distinct things. It recovers a night-time deficit: in a systematic review of napping in athletes, the benefits were consistently larger in those who were sleep-restricted than in the well-rested (Lastella et al. 2021). It supports adaptation around heavy training, where extra sleep gives the body more of the consolidation in which training is turned into fitness (Halson 2014). And it gives a pre-competition or post-lunch-dip alertness boost, riding the natural early-afternoon trough in alertness that follows the circadian rhythm.
Length and sleep inertia
Nap length is a trade-off against sleep inertia, the grogginess of waking out of deep sleep. A short nap of about 20 to 30 minutes stays mostly in light sleep and so avoids waking mid-deep-sleep, leaving the runner alert quickly. A longer nap of around 90 minutes spans a full sleep cycle and suits a larger deficit, but is risky if cut short, because waking part-way through the deep portion produces the worst grogginess. Across studies, naps from 20 to 90 minutes improved performance, with the longer durations giving larger gains but carrying more inertia (Lastella et al. 2021). Either commit to a short nap or to a full cycle; the awkward middle is where inertia bites.
Timing
Nap in the early-to-mid afternoon, roughly between 13:00 and 16:00 (Lastella et al. 2021). This window matches the post-lunch dip and is far enough from bedtime that it does not blunt the drive for the coming night’s sleep. Allow about 30 minutes after waking before training or competing, to let any inertia clear (Lastella et al. 2021). When the day demands an afternoon or evening session, fitting the nap earlier protects the night.
What the evidence shows
The clearest gains are in alertness and mood. After a night cut to four hours, a 30-minute post-lunch nap improved alertness, short-term memory and reaction-time accuracy, and cut both 2-metre and 20-metre sprint times (Waterhouse et al. 2007). The systematic review found favourable effects on physical performance, cognitive performance, alertness and mood, again most marked in sleep-restricted athletes, and timed mid-afternoon naps did not degrade the following night’s sleep (Lastella et al. 2021). The trials are mostly small, so treat the size of any single effect with caution while trusting the direction.
The limits
A nap supplements night sleep; it does not fully replace it. Protecting a consistent night-time sleep window remains the higher-return habit and the foundation everything else sits on; see sleep and the basics. A nap that runs too long or too late can also work against you, eating into the homeostatic sleep drive and making the coming night harder, which compounds rather than fixes a deficit. For runners crossing time zones, napping is one tool among several for managing disrupted sleep; see travel and jet lag.