Roughly three in four finishers of two big mountain ultras napped on course. Most naps ran under 30 minutes. That’s the headline from the largest sleep survey of ultra runners so far, and it’s more useful than the usual “just push through” advice.
One catch first. These 1,154 runners didn’t race 100 miles. They finished the Diagonale des Fous (165 km, about 102 miles, 882 runners) or the Trail de Bourbon (111 km, about 69 miles, 272 runners) on Réunion Island. Only the first one is true 100-mile length. It’s a self-reported survey, filled out after the race. Treat it as a map, not a prescription.
How many runners slept, and how much
The longer race had more sleepers and more sleep. Average finish times were about 50 hours at 165 km and about 34 hours at 111 km. Translation: the long race has you awake through two nights. The shorter one has you awake through one.
| 165 km Diagonale des Fous | 111 km Trail de Bourbon | |
|---|---|---|
| Runners in the survey | 882 | 272 |
| Approx. distance | 102 mi | 69 mi |
| Mean finish time | ~50 h | ~34 h |
| Nights on course | 2 | 1 |
| Took at least one nap | 84% | 53% |
| Mean total sleep | 76 min | 27 min |
Seventy-six minutes sounds like nothing. Spread across two nights, it’s a few short naps. In short: the typical finisher didn’t sleep much, and almost nobody slept in big blocks.
From 50 miles to 100: why sleep suddenly matters
A 50-miler is usually over before your body clock notices. A 100-miler isn’t. Somewhere around hour 18 to 22, the clock stops being a number and becomes an opponent.
Your 50-mile habits don’t carry over. At 50 miles, you can push through a bad hour on gels and willpower. At 100, the same trick runs into the dark hours, when your brain wants to shut down no matter how fit your legs are. In short: fitness gets you to the night. Sleep planning gets you through it.
When and how long runners napped
Of the naps, 82% lasted under 30 minutes. About 80% of nappers slept at night and about 15% by day (secondary summary, so hold those loosely).
Why short? Think of your brain as a phone on 3% battery. A nap is a quick charge, not a full overnight. Plug in for ten minutes and you get usable juice. Plug in for 40 and you may boot up groggy.
That grogginess has a name: sleep inertia. It’s the foggy, slow stretch right after waking from deeper sleep.
| Nap length | What to expect | Best use |
|---|---|---|
| 10 min | Best alertness boost in one lab test | Default nap |
| 20 min | Between the two; the lab test didn’t single it out | If you can’t wake at 10 |
| 30+ min | Higher sleep inertia risk | Avoid if you can |
| ~90 min | General sleep science: one full cycle, often an easier wake-up | Last resort, with crew |
The 10-minute result comes from a lab test of afternoon naps after a short night. It wasn’t done on a mountain at 3 am. It’s a good starting point, not a guarantee. The 90-minute row isn’t from the survey or that lab test. It’s a general sleep-science idea, and few runners can spare the time.
Does napping slow you down?
Nobody knows. The survey shows how runners slept and what they felt. It can’t show that naps speed you up or slow you down. Someone who sleeps 90 minutes spent longer on the course, and slower runners always spend longer on the course.
Correlation isn’t a pacing plan.
Here’s what the survey does support. About 80% of runners reported at least one symptom they blamed on sleep loss. Reduced alertness and hallucinations were the most common. Falls were also reported. Normal wakefulness came back in about two days. In short: almost everyone gets a little strange out there, and it passes.
Pre-race sleep banking
Runners showed up with a debt. They averaged 7.5 hours of habitual sleep against 8 hours desired, and about 50 minutes of sleep debt in race week. A little over half (54.9%, or 633 of 1,154) slept longer the week before. Runners who slept longer before the race reported fewer sleep-loss falls.
Outside ultras, a Stanford basketball study pushed players toward 10 hours a night for 5 to 7 weeks. Sleep rose by about 111 minutes a night, and sprint times improved. It was small and uncontrolled, so don’t oversell it. But the direction is clear.
Start the race with a full tank. Don’t start it with a loan.
Caffeine and the 2 to 6 am low
Two points here come from general physiology, not from this survey. First, most people hit their sleepiest stretch between roughly 2 and 6 am. Second, caffeine at about 200 to 300 mg helped vigilance in military sleep-deprivation trials. No ultra-specific caffeine trial turned up in our research. So this is extrapolation.
A reasonable use of it: hold caffeine through the evening. Take it when the low arrives, and pair it with a short nap if your eyes won’t stay open. Test it in training first. Your stomach gets a vote.
When and how long to sleep in a 100-mile race: build your plan
Here’s a trick that costs nothing. If your race starts at 6 am, the 2 to 6 am low lands at hours 20 to 24 of the race, every time. Your projected finish time decides how many hours of darkness you spend awake.
| Projected finish (6 am start) | Where the low hits | Nights awake on course |
|---|---|---|
| 24 h | Final 4 hours | 1 |
| 28 h | Hours 20 to 24, with 4 hours to go | 1 |
| 32 h | Hours 20 to 24, with 8 hours to go | 1 |
| 44 h+ | Hours 20 to 24, then again at hours 44 to 48 | 2 |
Finish between 33 and 43 hours and you still cross the first low, then spend a second night moving toward the finish before the next one arrives. This is an illustrative template, not study data. The idea is simple: pace, then clock time, then sleep.
A hypothetical runner
Take a runner I’ll call Dana: 41, building toward her first 100-miler, with a projected finish of 30 hours. She’s made up, and so are her numbers. They show the method.
Before: in her last 50-miler she had no sleep plan. She slept 6.5 hours a night in race week, ran through her low, and her pace slid from 12:30 per mile to 15:45 per mile in the final 10 miles. She lost about 15 minutes weaving between aid tables.
After: for the 100, she starts at 6 am Saturday, so her low lands around 2 to 6 am Sunday, and she finishes at noon. She sleeps 8 hours a night for the 7 days before. She holds caffeine until the low arrives. Around 2:30 am, at about hour 20, she takes a 10-minute nap at an aid station, with her pacer set to wake her. She budgets 10 to 20 minutes of total sleep, not 76. In this made-up race, her pace holds within about 90 seconds per mile through the low, and she saves the 15 minutes.
AthleteOS builds the pacing plan and projected finish time for a goal race, and its race readiness check looks at your recovery before the start. Pair that finish time with the clock and you can place your nap. You can start a plan here. For the training that comes first, see how Zone 2 builds the aerobic base, what aerobic decoupling says about your endurance, and how fitness, fatigue and form track training load.
Crew and pacer wake-up protocol
Your crew is your alarm clock, and you won’t be a good judge at 3 am. Brief them before the start, not at the aid station.
- Set a hard cap: nap alarm at 10 minutes, with a 20-minute limit if you asked for it. No snoozes.
- Give your pacer one job at wake-up: say your name, hand you water, and walk you out of the chair.
- Pre-pack the nap kit: warm layer, eye cover, a chair or cot, and your next fuel in hand.
- Walk the first few minutes after waking. Fog lifts faster when you move.
- Treat hallucinations as a signal, not a failure. Eat, sit down safely, then reassess.
- If you fall, stop and check yourself before you carry on.
What if you can’t fall asleep in 10 minutes?
It happens a lot. Adrenaline, noise, and a pounding heart all fight sleep. Don’t treat it as a failed nap.
Lie still with your eyes closed for the full 10 minutes. Quiet rest still gives you a short break. Then eat something, drink, and walk. If the sleepy wave comes back within the hour, try again. Don’t stretch a nap past 30 minutes just to feel you’ve “won” it. That raises your sleep inertia risk.
Plan the nap before the night plans it for you.