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From 50K to 100K: training for a longer ultra
How a 100K differs from a 50K: longer build-ups, more time on your feet, back-to-backs, fuelling over many hours, night running and race-day logistics.
A 100K is far more than two 50Ks back to back. You may be moving for ten hours or more, through changing weather and often into the dark. It usually makes sense after completing at least one 50K comfortably, with a training block of around 20 to 24 weeks.
Build the time gradually
Weekly training rises slowly over months, with lighter weeks every few weeks to absorb the work. Most of it stays easy. One quality session a week, such as a steady threshold run or hill repetitions, keeps you strong without leaving you too tired for the long runs.
Long runs and back-to-backs
Long runs typically build towards four or five hours, often paired with a second long run the next day. Together they prepare your legs, your stomach and your head for many hours on the move. The aim is to finish these weekends tired but able to train normally a couple of days later, not to push yourself into the ground.
Fuelling over many hours
- Eat from the start and keep eating. Over a very long day, small regular amounts work better than large ones.
- Savoury foods often become more appealing later on. Test a mix of sweet and savoury in training.
- Your stomach can be trained: practise race-day fuelling on every long run.
- Plan what you will take at each aid station or drop bag, and have a back-up.
Night running and the course
If your race finishes after dark, practise running with a head torch on familiar routes. Recce sections of the course if you can, especially technical descents and navigation points, and learn the cut-off times.
Pacing and walking
Many experienced ultra runners walk from the very first climb and use a run-walk pattern on long flat sections. Judge your pace by effort. If you feel strong at halfway, that is a sign you have paced it well, not that you should speed up yet.
Listen to niggles
The volume of 100K training makes small problems more likely to grow. Take an extra easy day at the first sign of a persistent ache, and allow a longer recovery after the race than you would after a marathon: several weeks of easy running before any hard training.
This guide is general information, not medical advice. Speak to a doctor before starting a new training programme, especially if you have a health condition or injury, and stop if you feel pain, dizziness or chest discomfort. See our terms of use.