The hundred miler. Find races and get a periodized training plan.
The hundred miler is the ultimate test of endurance. Training spans 24-36 weeks with peak volumes of 100-130km per week. You'll run through two nights, manage sleep deprivation, and push through multiple physical and mental crises.
Build to 100+ km/week gradually. The rule: increase weekly volume by no more than 10%. Include at least one 50K+ training run and several back-to-back weekends of 60+ km total.
You'll be awake for 24-36+ hours. Practice staying up through one full night during training. Consider planned micro-naps of 10-20 minutes at aid stations during the race.
You need 250-350 calories per hour for 24+ hours. That's 6000-8000 calories during the race. Practice eating a variety of foods while running: gels, real food, broth, potatoes, PB&J.
Start 20-30% slower than you think you should. You're running for 24-36 hours. If you feel great at mile 30, you're going too fast. The race starts at mile 60.
24-36 hours for most finishers. Sub-24 is a major achievement. Cutoffs range from 30-48 hours depending on the race.
Sleep deprivation and stomach issues, not fitness. Most DNFs happen because of GI problems or the inability to eat, not because of tired legs.