Night Running for Ultras

Before the race

Do at least one run through the night in the build for a race that has one, at the pace and with the light, food and caffeine you plan to race with. It is where you find out whether your light lasts, what you can eat at 3 a.m. and how sleepy you get, and it costs nothing on race day. Treat it as a very long day and keep the days after it easy. See the guide on race-specific preparation.

Go in rested. A race that runs through the night starts from whatever sleep you bring to it, so protect the week before. See the guide on sleep.

Pacing the night

Plan to slow after dark, and expect the low between midnight and the early morning. A 2020 study followed one 100-mile race with splits every five miles. The 9 finishers, of 21 starters, averaged 13.7 minutes per mile before sunset and slowed by 35.9% after it. Their slowest five miles came around 3:30 a.m., at 20.8 minutes per mile, and pace returned to their average at the next sunrise¹. It is one race, so read it as an example and not a rule.

The same stretch shows up in a survey of 1,154 finishers of two mountain races, where 79.5% of naps were taken between midnight and 5 a.m.². Plan your crew, your pacer and your food around the stretch from midnight to sunrise, and see the guide on crewing and pacing.

Seeing and being seen

Carry a second light and spare batteries, and check your light's runtime on the setting you plan to use, not the setting on the box.

On roads, put retroreflective material on your moving joints, such as ankles, knees and wrists, and not only on a vest. A 2023 review of road studies found that drivers recognize a person at much longer distances when the material is on the joints than when it is on the torso³. In a 2021 test, young drivers judged a pedestrian's walking direction from 135 m on a closed-road circuit at night, and were right 80% of the time with retroreflective material on the joints, 53% with it on the torso only and 33% in black clothing alone⁴. Those tests used walking pedestrians.

What sleepiness looks like

Expect to feel it, and tell your crew and pacer before the race so they can spot it. In a survey of 1,154 finishers of two mountain races (165 km and 111 km), 77% slept at some point and 80% reported at least one symptom they attributed to sleep deprivation. Decreased alertness was reported by 54.0%, hallucinations by 34.0% and a fall by 14.6%. The symptoms were self-reported, and 30.4% of eligible runners responded².

Seeing things is a known effect of sleep deprivation. A 2026 review of 14 studies found sleep deprivation the most consistent contributor to unusual perceptual experiences in ultra-endurance sport, followed by exhaustion and low light. They typically began after 24 hours or more of exertion, especially in darkness, and appeared transient and non-pathologic, with no long-term psychiatric effects reported⁵. Treat them as a sign you need sleep, as the safety note below says.

Caffeine

Caffeine helps alertness, and it does not replace sleep. A 2021 position stand of the International Society of Sports Nutrition says caffeine consistently improved exercise performance at 3 to 6 mg per kg of body mass (225 to 450 mg for a 75 kg runner), that the minimal effective dose may be as low as 2 mg per kg, and that very high doses (for example 9 mg per kg) bring a high incidence of side effects without being needed. It says caffeine improves attention and vigilance in most people and may improve cognitive and physical performance under sleep deprivation, that responses differ, and that habitual intake may play a role. The most common timing is 60 minutes before exercise⁶.

In a 2020 laboratory study, 23 adults kept awake for three nights took 200 mg of caffeine or placebo at the start of each 2-hour test block from 01:00 to 09:00. Caffeine kept vigilance and a complex motor task better than placebo, but its longer lapses stayed worse than at baseline. The authors concluded caffeine does not restore normal functioning during sleep deprivation and cannot replace sleep⁷.

Try your caffeine plan on your night run in training, with the dose and the timing you will race with, and see the guide on sleep for how late caffeine costs the sleep that follows.

Short naps

When you are too sleepy to run safely, a short nap is the tool. In 52 finishers at the Ultra-Trail du Mont-Blanc, runners chose at three checkpoints between a 20-minute sleep opportunity and staying awake. Nap decisions followed how sleepy runners felt more than their measured reaction times. Sleepiness fell right after a 20-minute nap, and reaction times were faster only at later checkpoints. The authors concluded brief naps reduced perceived drowsiness and gave partial protection against late-race decline without compromising finish times⁸. Runners chose whether to nap, so that comparison is not randomized.

Keep a nap to 10 to 20 minutes. In a 2006 laboratory trial, 24 adults napped in the afternoon after sleep restricted to about 5 hours. A 10-minute nap improved sleepiness, fatigue, vigor and cognitive performance straight away, a 20-minute nap helped from 35 minutes after waking, and a 30-minute nap left a period of impaired alertness and performance right after waking before the benefits arrived⁹.

After the race

Expect broken sleep for several nights. In 18 athletes who ran a 64 km ultra-trail race that started at 03:30, sleep efficiency fell and waking rose for up to four nights afterward¹⁰. In the survey of 1,154 finishers, runners reported recovering a normal state of wakefulness within two days². Plan easy days after the race and do not drive when drowsy.