How long should my longest run be training for an ultramarathon?

Training for ultramarathons often raises one of the most common questions: how long should my longest run be? Many runners believe there is a magic number or a single epic run that guarantees success. The truth is different. Your longest run will depend on many factors, including experience, current fitness, and how well you can tolerate volume. It is not about hitting a specific distance or time in training.

Understanding how to approach your longest run can make the difference between steady progress, burnout or worse injury. Here, I will break down what works for different levels of ultrarunners and provide practical advice to build endurance without risking injury or overtraining.

Running UTS100K by UTMB. In this picture, I was over 80K into the race, running up Mynydd Mawr

Long runs for novice ultrarunners

If you are new to ultrarunning, forget about trying to complete 8- or 10-hour long runs for now. These epic sessions can produce too much stress on the body and be counterproductive. Instead, focus on back-to-back long runs of about 3-3.5 hours each day. This approach helps build:

• Durability (how well your body behaves when fatigued)

• Aerobic efficiency (how efficiently your body uses oxygen)

• Mental resilience

  
  

Back-to-back runs simulate the fatigue and stress of ultramarathons without wrecking your recovery. For example, running 3 hours on Saturday and another 3 hours on Sunday teaches your body to handle sustained effort on tired legs. This method also reduces the risk of injury compared to one very long run.

Building a solid base with consistent, moderate long runs prepares your body for the demands of ultramarathons better than chasing a single longest run - trust me! It also allows you to gradually increase your weekly mileage and improve your endurance safely.

Long runs for experienced ultrarunners

Experienced athletes can tolerate longer sessions, but the key still remains in accumulating volume over weeks, not a single epic run. For seasoned ultrarunners, the focus shifts to consistency and smart progression. Long runs might extend beyond 4 hours, but they should fit into a balanced training plan.

For example, an experienced runner might do a 5-hour long run once a week, combined with other runs and back-to-back sessions. The goal is to maintain a steady build-up of fatigue and recovery cycles. This approach prevents burnout and keeps the body adapting.

Avoid the temptation to do one mega session that leaves you exhausted for days; this won't be efficient. Instead, spread your effort across multiple runs and weeks. This strategy supports sustainable improvement and reduces injury risk.

Using prep races as part of your build-up

Shorter ultras or marathons make excellent preparation races. They offer realistic conditions to test, fuelling strategies, gear choices, and pacing.

Running a shorter ultra or marathon before your main ultramarathon helps you learn what works without the stress of a single isolated long run. These races simulate race-day fatigue and terrain, providing valuable feedback. The key is to choose them well; you want these races to have similar characteristics to your goal races, but be a shorter version of them.

For example, if you plan a 100-mile race, completing a 50-mile to a 100K trail race a few months prior can reveal weaknesses in nutrition or equipment. Adjusting these early improves your chances on race day.

Learning from the pros

Some elite ultrarunners have adopted this strategy. Camille Herron, a world-record holder for crazy ultradistances, rarely trains longer than 3 hours in a single session. Instead, she focuses on total weekly load and back-to-back runs and even double running days. Even Kilian Jornet adopted a similar approach after becoming a father.

This approach highlights that performance comes from the entire training cycle: balancing stress, recovery, adaptation, and progression. It is not about surviving one mega run but building a sustainable base over months and months of training.

Wild70 by UTMB. That year we had a snowstorm, fun race!

Signs your longest run is too long

If your longest run leaves you needing two weeks to recover, it was excessive, not productive. Overdoing long runs can cause unnecessary fatigue accumulation, increased injury risk, mental burnout, non-functional overreaching or worse overtraining. Check your HRV, resting HR, and fatigue levels during your normal runs to ensure that you are not overdoing it.

Aim for runs that challenge you but still allow you to recover. This balance supports steady progress and keeps motivation high.

Practical tips for planning your longest run

• Base your longest run on your current weekly mileage and experience.

• For beginners, keep long runs around 3 hours and do back-to-back sessions.

• For experienced runners, extend long runs gradually but focus on weekly and monthly volume.

• Use prep races to simulate race conditions and test strategies.

• Listen to your body and adjust if recovery takes too long.

• Prioritise consistency over chasing one massive run.

  
  

Final thoughts

There is no one-size-fits-all answer to how long your longest run should be when training for ultramarathons. It depends on your experience, conditioning, how you tolerate volume, and injury history. Focus on building durability through consistent, manageable long runs and back-to-back sessions. Use prep races to test your race-day plans. Learn from pro runners who emphasise total volume rather than a mega session.

Long distances are my speciality, so if you need help preparing for your next ultra, get in touch.