100K Training: What Changes When You Go Beyond 50K

Is a 50K enough base for a 100K?

The short answer is: it depends on how you ran it, how long ago, and what your training looked like in between. A 50K finish is a good signal that your body can handle sustained effort. But a 100K is a fundamentally different race and requires a training block that reflects that.

Before I agree to coach an athlete towards a 100K, I want to understand their recent training history, not just their race history. Someone who finished a 50K eight months ago and has barely run since is in a very different position to someone who has been training consistently and has recent long runs in the bank. I also look at how they handled the 50K mentally and physically. If they crossed the line completely broken and took weeks to recover, we probably need another 50K before we step up. If they finished strongly and recovered well, we have something to build on. As a rule, I like at least six months of solid, consistent training between a first 50K and starting a 100K build.

The key differences between a 50K and a 100K

The obvious answer is that a 100K is twice as far. But that doesn't begin to capture what the distance actually demands. At 50K, most athletes are on their feet for somewhere between four and nine hours. At 100K, that becomes ten to twenty hours, sometimes more. Everything compounds over that time: fatigue, fueling difficulty, foot problems, and mental load all escalate in ways that training for a 50K won't have prepared you for.

The thing that surprises athletes most when they make this jump is usually the mental side of the night. Many 100K races extend into darkness and running through the early hours of the morning is a genuinely strange experience. Your body wants to sleep. Your brain starts playing tricks. The emotional swings get more extreme. Athletes who have done a night run in training handle this much better than those who haven't.

Fueling also becomes significantly more complex. Appetite suppression, flavour fatigue with sweet products, and GI issues that didn't appear at 50K can all emerge in the back half of a 100K. Preparing for this is as important as any long run in the training block.

How training volume changes

The increase in training load from 50K to 100K prep should be gradual and deliberate. The goal is to increase time on feet, not just distance, and to build fatigue resistance through the training block.

A 100K training block typically needs 16 to 20 weeks to do properly. I structure it in phases: a base phase focused on building aerobic volume and strength, a build phase where the key sessions get longer and more specific, and a peak phase with the biggest training weeks before the taper begins. Peak weekly volume varies by athlete, but I'm generally looking for athletes to have several weeks where they're running eight to twelve hours across the week, with the key sessions being longer and more demanding than anything in a 50K block.

The important distinction is that more hours doesn't mean more intensity. Most of the additional volume should be easy, aerobic running. The quality sessions are still there, but they're less frequent because the recovery demand from the volume alone is significant. Getting this balance wrong is one of the most common mistakes in 100K preparation, and it usually shows up as fatigue, illness, or injury in the final four weeks before the race.

Time on feet vs pace

At 100K, pacing by feel and effort, rather than kilometre splits, becomes even more important. Terrain, elevation, and conditions matter far more than pace. Training your brain to let go of the watch is part of the preparation.

I coach almost entirely through RPE and heart rate rather than pace for 100K athletes. Pace is essentially meaningless on technical terrain or on a climb, and athletes who chase pace targets in the early stages of a long race almost always pay for it later. What I want to know is how an athlete is feeling relative to their effort, and whether that effort is sustainable. I'll often use heart rate as a ceiling rather than a target: keep your heart rate below a certain number for the first third of the race regardless of what your pace looks like. For athletes who struggle to let go of the watch, I'll sometimes ask them to cover the screen entirely on long training runs. Learning to run by feel is a skill that takes time, but it's an essential one for this distance.

Running through the night

Many 100K races extend into darkness. Running through the night is a different physical and psychological experience from anything most athletes have done before. It needs to be practised.

Yes, I include night running in 100K training blocks. Usually two or three sessions across the build and peak phases, starting with something simple like a two-hour evening run that extends into the dark, and progressing to a longer night run of three to four hours if the race demands it. What athletes struggle with most is the sleepiness that sets in between about midnight and 4am. The body is fighting its circadian rhythm and it takes real effort to keep moving. The other thing they find hard is the isolation. It's quieter, darker, and the mental challenge is different to daytime running. Practising it means that on race day, when it arrives, it's familiar rather than terrifying.

In my own racing I've found the hour just before dawn to be the hardest of any long event. There's something about that particular darkness, when the night has gone on for hours but the light hasn't come yet, that tests you in a way nothing else does. Getting through it is one of the most satisfying things in ultra running.

Fueling at 100K: what changes

Everything you learned about fueling at 50K applies, and then some. At 100K, appetite suppression, flavour fatigue, and GI distress all become more likely the longer you are out there.

The biggest shift in fueling strategy between a 50K and a 100K is the emphasis on real food and savoury options in the back half. After eight or ten hours, most athletes can't face another gel. I prepare athletes for this by building a wider range of race-day foods into their training nutrition and specifically by practising eating when they don't feel like it. I'll ask athletes to eat on long runs even when they're not hungry, to train the habit rather than waiting until hunger arrives.

I also build in specific conversations about what happens when eating feels genuinely impossible. The answer is almost always to slow down, walk, and eat something small regardless of taste. Appetite usually returns once effort comes down slightly. If an athlete has gone more than 90 minutes without eating in a race, that's a problem that needs addressing immediately.

Managing the low patches

Every 100K has multiple low patches. Unlike a 50K, where there might be one, a 100K will almost certainly have several. The key is knowing they will come and having a plan for each one.

Before race day, I walk athletes through a mental map of the course and talk through where the likely hard sections are. We identify what the trigger for a low patch might be (night, a big climb, a long flat section, hunger) and we agree in advance what the response will be. This pre-commitment matters because when you're exhausted and low, your decision-making is compromised. Having a plan removes the need to think clearly in a moment when clear thinking is difficult.

The consistent message I give is that low patches are temporary. Every athlete who has come through one and carried on will tell you that things changed, often within 20 to 30 minutes. The danger is making a permanent decision (quitting) based on a temporary feeling. I've seen athletes who were ready to pull out at an aid station finish the race feeling strong an hour later, simply because they kept moving and let the low pass.

Recovery within the training block

The demands of 100K training are significant. Recovery is not an afterthought. It is part of the programme. Athletes who try to cram 100K preparation into the same timeline as a 50K block often break down before race day.

Within a 100K block I build in deliberate recovery weeks every three to four weeks, where volume drops significantly before building again. These aren't easy weeks because the athlete is flagging. They're planned reductions that allow the body to absorb the previous weeks' work and come back stronger. Athletes who resist these weeks and try to keep pushing through are the ones who tend to get injured or sick in the final phase of the block when they can least afford it.

For athletes who want to push through when the schedule says rest, my response is consistent: the training is already done. Rest is not falling behind. Skipping the recovery week is what will cost you the race. I've had that conversation more times than I can count, and the athletes who listened are the ones who arrived at the start line in the best shape.