Key takeaways
A first 50K needs about 16 weeks if you can already run a half marathon, built on easy volume, one long run and one back-to-back weekend
In ultras, durability (how well your fitness holds up after hours of running) and fatigue resistance matter as much as VO2max
For 100K and 100 miles, train time on feet, vertical gain, power hiking and race fuelling, and accept that the long run will be capped well short of race distance
An ultra marathon is any race longer than the marathon's 42.2 km. The step from 50K to 100 miles is huge, but the training rests on the same few ideas: a lot of easy running, a long run that grows slowly, practice at eating and hiking, and enough recovery to absorb it all. This guide gives a full 16-week 50K plan, a 12-week shortcut, and the principles that scale up to 100K and 100 miles.
What matters in an ultra: VO2max or durability?
VO2max sets your aerobic ceiling, and in shorter ultras it still predicts performance. But ultras are run far below that ceiling, and what decides most races is how well your physiology holds up after hours of work. Maunder et al. (2021, Sports Medicine) called this durability: the time of onset and the size of the deterioration in physiological characteristics such as running economy, heart rate and threshold during prolonged exercise. Two runners with the same fresh VO2max and lactate threshold can differ widely in how much these drift after three hours.
Mountain ultras also cause severe muscle fatigue. In Millet et al. (2011, PLoS One), runners finishing a 166 km mountain race with about 9,500 m of climbing and descending had lost 35% of maximal knee-extensor force and 39% of plantar-flexor force, with a large central (nervous system) component, and force had returned to baseline within about two weeks. The practical lesson: an ultra plan should build tissue resilience, economy at slow speeds and eating on the move, not just a bigger engine.
Volume is a consistent predictor. In a study of 448 finishers of mountain ultra-endurance races, Belinchón-deMiguel et al. (2021) found training intensity and volume were key predictors for races of 45 to 90 km, while experience and more demanding training mattered more for races over 90 km.
50K training plan for beginners (16 weeks)
This plan assumes you can run a half marathon, are running about 30 km a week, and have a comfortable 15 km long run. "Easy" means conversational, roughly zone 2 (see zone 2 training and the heart rate zone calculator). Run long runs on terrain similar to your race.
| Week | Weekly km | Long run (Sat) | Sun | Key midweek session |
|---|---|---|---|---|
| 1 | 32 | 15 km | 5 km easy | 6 × 20 s strides |
| 2 | 35 | 16 km | 6 km easy | 30 min hills, easy effort |
| 3 | 38 | 18 km | 6 km easy | 3 × 8 min steady |
| 4 (down) | 30 | 13 km | rest | strides |
| 5 | 42 | 20 km | 8 km easy | 6 × 2 min hill repeats |
| 6 | 45 | 22 km | 8 km easy | 20 min tempo |
| 7 | 48 | 24 km | 10 km easy | hilly run with power hiking |
| 8 (down) | 36 | 16 km | rest | strides |
| 9 | 52 | 26 km | 10 km easy | 8 × 2 min hills |
| 10 | 55 | 28 km | 12 km easy | 2 × 15 min steady |
| 11 | 58 | 24 km | 16 km (back-to-back) | hilly run, test race kit |
| 12 (down) | 42 | 18 km | rest | strides |
| 13 | 62 | 30 to 32 km | 12 km easy | dress rehearsal fuelling |
| 14 | 58 | 26 km | 16 km (back-to-back) | 20 min steady |
| 15 (taper) | 42 | 18 km | 6 km easy | short strides |
| 16 (race) | 20 + race | 50K race | rest | 2 short easy runs |
Notes: add two strength sessions a week through week 13 (see strength training for runners), keep long runs easy (see long run pace), and walk the steep climbs in long runs just as you will in the race. If a week goes badly, repeat it rather than pushing on.
50K training plan in 12 weeks
A 12-week plan works only if you start fitter: roughly 40 km or more a week and a recent long run of about 20 km, such as after a marathon block (see marathon training). Start at week 5 of the table above. Do not compress the down weeks or the taper. If you are starting from a lower base, take the full 16 weeks or choose a later race.
Ultra marathon training plan for 100K and 100 miles
The 50K plan above is a foundation. For longer races, the main changes are:
| Principle | 50K | 100K | 100 miles |
|---|---|---|---|
| Typical plan length | 16 weeks | 20 to 24 weeks | 24+ weeks, after a 50K or 100K |
| Peak weekly volume | 55 to 65 km | 70 to 100 km or 10 to 12 h | 80 to 120 km or 12 to 15 h |
| Longest single run | 30 to 32 km | 40 to 50 km | 50 to 65 km |
| Back-to-back weekend | optional | 30 + 20 km | 40 + 25 km or longer |
| Night running | not needed | useful | essential |
Back-to-back long runs. Two long runs on consecutive days give a large training stimulus on tired legs while limiting the recovery cost of a single huge run. This targets durability directly.
Time on feet, not just distance. A mountain 100-miler can take 24 to 36 hours. Plan in hours on trail, and treat 6 to 8 hour days as rehearsals for kit, fuel and pacing.
Vertical gain. Match climbing in training to the race's gain per km. Downhill running causes muscle damage, but a prior bout protects against later damage (the repeated bout effect), so include regular descents. Details in the trail running training plan and hill repeats.
Power hiking. On steep ground, walking is cheaper than running. Giovanelli et al. (2016) found walking was more economical than running at inclines of about 15.8 degrees and above. Practise fast hiking with hands on thighs or poles.
Gut training. Practising race fuelling in training improves tolerance (Jeukendrup, 2017). Ultra-specific guidance from the International Society of Sports Nutrition (Tiller et al., 2019) suggests about 150 to 400 kcal an hour, including 30 to 50 g of carbohydrate per hour, with many runners tolerating more after training. See marathon and ultra fueling and runner's stomach.
Intensity distribution. Most training should be easy, in line with polarised 80/20 training. A weekly hill or threshold session keeps your VO2max and threshold from fading. Use the VO2max running calculator for road paces, but on trails go by effort and heart rate.
Recovery, taper and injury risk
Ultrarunners get hurt often. In the ULTRA study of 1,212 ultramarathon runners, Hoffman and Krishnan (2014) reported that 64.6% had an exercise-related injury that cost training days in the previous year, most often at the knee. Protect yourself with down weeks every third or fourth week, sleep, enough energy intake, and a two to three week taper. Watch for overtraining signs such as a rising resting heart rate and persistent fatigue.
Safety: if you have a heart condition or symptoms such as chest pain, fainting or unusual breathlessness, see a doctor before starting. In races, carry required kit, drink to thirst rather than to a fixed schedule, and stop if you become confused or unwell.
Frequently asked questions
What is a good 50k training plan for beginners?
Start from a base of about 30 km a week and a comfortable 15 km long run. Over 16 weeks build to 55 to 65 km a week, with a longest run of about 30 to 32 km or a back-to-back weekend of similar total distance, then taper for two weeks.
Can I follow a 50k training plan in 12 weeks?
Yes, if you have recently trained for a marathon or already run 40 km or more a week with a long run near 20 km. Start at week 5 of the 16-week plan and keep the down weeks and the two-week taper.
How is an ultra marathon training plan for 100 miles different?
It takes longer, often 6 months or more on top of previous ultras, and focuses on back-to-back long runs, total time on feet, climbing, power hiking, night running and eating roughly 150 to 400 kcal an hour on the move. The longest single run is usually 50 to 65 km, not 100 miles.
How long should an ultra marathon training plan be?
Plan on about 16 weeks for a first 50K from a half-marathon base, 20 to 24 weeks for a 100K, and 24 weeks or more for a first 100 miles, ideally after completing a 50K or 100K first.
Sources
- Maunder E, Seiler S, Mildenhall MJ, Kilding AE, Plews DJ. The importance of 'durability' in the physiological profiling of endurance athletes. Sports Med, 2021.
- Millet GY, Tomazin K, Verges S, et al. Neuromuscular consequences of an extreme mountain ultra-marathon. PLoS One, 2011.
- Belinchón-deMiguel P, et al. Predictors of athlete's performance in ultra-endurance mountain races. Int J Environ Res Public Health, 2021.
- Giovanelli N, Ortiz ALR, Henninger K, Kram R. Energetics of vertical kilometer foot races; is steeper cheaper? J Appl Physiol, 2016.
- Bontemps B, Vercruyssen F, Gruet M, Louis J. Downhill running: what are the effects and how can we adapt? A narrative review. Sports Med, 2020.
- Tiller NB, et al. International Society of Sports Nutrition position stand: nutritional considerations for single-stage ultra-marathon training and racing. J Int Soc Sports Nutr, 2019.
- Jeukendrup AE. Training the gut for athletes. Sports Med, 2017.
- Hoffman MD, Krishnan E. Health and exercise-related medical issues among 1,212 ultramarathon runners: baseline findings from the ULTRA study. PLoS One, 2014.