A 48-hour race is a continuous timed event: the clock keeps running while you decide when to run, walk, eat, change gear, rest, and possibly sleep. That freedom is the appeal—and the reason a flexible plan matters more than a single pace or mileage target. This explainer covers the format; the 48-hour race guide collects training, sleep, nutrition, and the event calendar in one place.
The Format
A 48-hour race is scored on distance: everyone is ranked by how far they have gone when 48 hours expire. Courses on our calendar range from the 400 m track at Loutraki in Greece and the 443 m indoor track at Six Days in the Dome in Milwaukee to a 2.27 km (1.42-mile) loop at Across the Years in Arizona. Chip timing counts every lap. Some races measure the final partial lap when the horn sounds; others count only complete laps.
At Across the Years, for example, one aid tent is open around the clock, crews work from runners' own tents, tables or RVs beside the loop, and a shared napping tent has cots and a three-hour limit. Before you plan, check the organizer's rules on partial-lap credit, direction changes, crew access and leaving the course.
At the 48 heures de Royan in October 2025, the median of 38 results was 201.1 km and the middle half ran 161.4–222.0 km. At Across the Years in December 2025 the median of 53 results was 161.2 km, just past 100 miles. We recommend 160 km as a first target and 200 km as the stretch; the records and more fields are in the 48-hour race guide.
| Question | 24-hour | 48-hour |
|---|---|---|
| Our first-race target | 100 km for anyone who has finished a marathon or 50K; 130–160 km with a 100-mile finish behind you | 160 km (100 miles), with 200 km as the stretch |
| Average speed for that target, stops included | 4.2 km/h for 100 km | 3.3 km/h for 160 km |
| 2025 field medians | 164.4 km at the London 24-hour | 201.1 km at Royan, 161.2 km at Across the Years |
| Nights | One | Two; the second is usually the hardest |
| Our sleep default | No planned sleep; a 10–20 minute nap if you get drowsy | 1–3 hours in total: a 20-minute nap on night one if drowsy, about 90 minutes on night two |
| Our training plan | 12 weeks from a marathon or 50K finish | 16 weeks, after a 24-hour race or 100 km finish |
Stopped time comes off the clock. For 200 km, four stopped hours leave 44 moving hours and need 13:12 per km while moving; six stopped hours leave 42 and need 12:36 per km. For 160 km with six hours stopped, 15:45 per km is enough, which is an ordinary walking pace.
Compare the 48-hour calendar with the 24-hour calendar. Use the pace calculator for your own scenarios and the training guide for preparation.
What Changes After One Day
- Sleep pressure accumulates. Sleep loss can impair endurance performance, mood, vigilance, reaction time, and judgment.
- Small problems have longer to grow. Hot spots, chafing, cold stress, heat stress, and GI symptoms deserve early attention instead of an automatic gear or medication response.
- Food preference can change. Familiar alternatives in different flavors, textures, and temperatures make adaptation easier.
- Decision quality matters. A written plan and an observant crew member can catch unsafe changes that the runner misses.
How Much to Sleep
Our default for a first 48-hour race is 1–3 hours of sleep in total. Sleep sooner and longer if you start weaving or nodding off:
- Night one: a 20-minute nap (alarm at 25 minutes) if you get drowsy, in a warm rest space with a wake-up plan ready.
- Night two: one longer sleep of about 90 minutes in the small hours, plus 20-minute naps as needed.
- Every stop: allow settling and wake-up time, use reliable alarms or crew support, and assess alertness before restarting.
Deep sleep usually begins about 30 minutes after you fall asleep, and waking from it brings the worst grogginess, so we avoid naps of 30–60 minutes. Even after a short nap at night, expect to feel groggy for up to 15–30 minutes: walk the first lap and let your crew check you before you run again. Sleep well in the week before the race; it does not let you skip sleep during it. The evidence and rest planning for other formats are in the sleep strategy guide.
Fuel and Fluid Over Two Days
Our default is about 50 g of carbohydrate an hour, the top of the ISSN's 30–50 g range, dropping to about 30 g on bad-stomach hours rather than stopping. For sodium, our default is the ISSN's 500–700 mg per litre of fluid, or about 300–600 mg an hour in hot or humid conditions. Over two days, sweet products wear thin: bring savory solids, warm soup, rice and potatoes, and one liquid carbohydrate you know you tolerate for when chewing stops appealing.
Drink to thirst. The ISSN's planning range is 450–750 mL an hour, and smaller or slower runners on cool nights may need less. The exercise-associated hyponatremia consensus identifies sustained overdrinking as the principal preventable risk and warns that sodium-containing drinks cannot make excess fluid safe. See the timed-race food planning guide and the hydration and sodium guide for practical guardrails.
Manage the Second Night Safely
The second overnight period combines the body-clock low with about 40 hours of accumulated fatigue after a morning start, and for most runners 02:00–05:00 is the hardest stretch of the race. Prepare the environment before dark: working lights and backups, warm and dry layers, an accessible rest space, familiar food, and written check-in rules.
Our caffeine default: none in the first 10 hours, then about 50 mg an hour overnight, for example one 1–2 mg/kg dose every two hours. The ISSN advises saving caffeine for the later stages and the night, in small repeated doses of 1–2 mg/kg (70–140 mg at 70 kg) rather than large ones, and calls 50 mg an hour likely well tolerated; the 10-hour wait and the two-hour spacing are our own rules. Stop at least three hours before the planned longer sleep, earlier after large doses, and skip caffeine if you are sensitive to it. Count coffee, cola, gels and tablets in the total. Caffeine does not replace sleep, and it is never a reason to keep going through the warning signs below.
Is the Format a Good Fit?
A 48-hour race may fit if you can answer these questions clearly:
- Have you built an appropriate endurance base without a current injury or unresolved illness?
- Have you practiced easy pacing, walking, fueling, foot care, darkness, and weather-specific gear?
- Do you know the event's medical, crew, sleep-area, and withdrawal procedures?
- Can you name the signs that will make you stop, rest, or seek help?
- Do you have safe transport and recovery plans after the event?
We recommend a 24-hour race or a 100 km finish first: it shows you can manage pacing, food and feet through one night before you add a second. Discuss major health concerns and medications with a clinician familiar with your history, and build the race plan with the 48-hour training guide and sleep strategy guide.
Sources
- Global Organization of Multi-Day Ultramarathoners — multiday race information and championship formats.
- Guilherme, L.Q. et al. (2026) — The Role of Sleep on Physical and Cognitive Performance of Ultra-Endurance Athletes: A Systematic Review. Journal of Clinical Medicine, 15(4), 1398.
- Lopes, T.R. et al. (2023) — How much does sleep deprivation impair endurance performance? A systematic review and meta-analysis. European Journal of Sport Science, 23(7), 1279–1292.
- Kishi, A. et al. (2024) — Sleep and Ultramarathon: Exploring Patterns, Strategies, and Repercussions of 1,154 Mountain Ultramarathons Finishers. Sports Medicine - Open, 10(1), 34.
- Tiller, N.B. et al. (2019) — International Society of Sports Nutrition Position Stand: nutritional considerations for single-stage ultra-marathon training and racing. Journal of the International Society of Sports Nutrition, 16(1), 50. Source of the carbohydrate, sodium, fluid and caffeine ranges.
- Hew-Butler, T. et al. (2015) — Third International Exercise-Associated Hyponatremia Consensus Statement.
- Hilditch, C.J. & McHill, A.W. (2019) — Sleep inertia: current insights. Nature and Science of Sleep, 11, 155–165.
Frequently Asked Questions
What pace do you need for 160 km in 48 hours?
An average of 3.3 km/h over the full 48 hours, including every stop. With 3 hours of sleep and 3 hours of other stops, that is 3.8 km/h while moving, or 15:45 per kilometre: a steady walk. 200 km needs 4.2 km/h overall.
What is the hardest part of a 48-hour race?
For most runners it is the second night, roughly 02:00 to 05:00 after a morning start, when the body-clock low lands on top of about 40 hours of effort and little sleep. Our default plan puts the one longer sleep there, but take it earlier if you start weaving or nodding off.
Should I try a 48-hour race before a 6-day race?
Yes. Our six-day training plan assumes a 48-hour finish, or at least 150 km in a 24-hour race. A 48-hour race tests the second-night routine, sleep stops, foot care and crew handoffs that a six-day race repeats night after night, in a much shorter event.