How to train for your first ultramarathon

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You’ve run a marathon, or maybe a few halfs, and somewhere along the way someone mentioned ultras. Now it’s sitting in your head like a splinter. Could you actually do it?

The answer, for most consistent runners, is probably yes — but not by just running more of what you’re already doing. An ultramarathon (anything beyond 26.2 miles, typically 50K, 50 miles, or 100K for first-timers) demands a genuinely different approach to training: more time on your feet, serious attention to nutrition, and a mental gear you’ve likely never had to use before. This article will walk you through what that actually looks like for a real runner with a job, a life, and no altitude tent in the spare bedroom.

What follows isn’t a single training plan — it’s a framework. Your first ultra will probably be a 50K (31 miles), and that’s what most of this is built around. If you’re eyeing something longer, the same principles apply, just scaled up with more lead time.

Are you ready to start ultra training?

Before you do anything else, be honest about where your running is right now. Jumping from your first half marathon into ultra training is a recipe for injury or burnout. As a rough benchmark, you should be able to:

• Run at least 4 days a week consistently
• Complete a long run of 18–20 miles (or comfortably run back-to-back long runs of 10–12 miles)
• Have at least one marathon under your belt, or 6–12 months of structured training at high volume

If you’re not there yet, spend time building your aerobic base before committing to a race. Signing up for a 50K in four months when your long run is currently 10 miles is the most common mistake first-time ultra runners make — and it usually ends with a DNF or an injury.

How long does ultra training take?

For a 50K, most runners coming from a solid marathon background need 16–24 weeks of dedicated training. If you’ve never run a marathon, add another 16 weeks of marathon prep first.

Be realistic about where you sit. Most people overestimate their readiness because they’re excited. That excitement is good — just don’t let it override judgement.

What your weekly training should look like

Ultra training isn’t just about one big long run a week. The key shift from marathon training is time on feet, not pace. You’re training your body to keep moving when it’s tired, not to run 6:00/km forever.

A typical week during the build phase (weeks 8–16 of a 20-week plan) might look like:

• Monday: Rest or easy 45-minute recovery run at conversational pace
• Tuesday: Medium run, 60–90 minutes with some hills or trail terrain
• Wednesday: Cross-training (cycling, swimming, hiking) or 45-minute easy run
• Thursday: Midweek long run, 75–90 minutes at easy effort
• Friday: Rest
• Saturday: Long run, 20–26 miles at a genuinely easy effort — aim for 6:30–8:00/km depending on terrain
• Sunday: Back-to-back run, 8–12 miles. Tired legs are the point.

Weekly mileage during peak training typically sits between 50–70 miles for a 50K, but this varies enormously. If you’re running 35 miles a week consistently before you start, building to 55–60 miles is reasonable. Don’t copy someone else’s peak mileage — match it to your history.

The back-to-back long run on Saturday/Sunday is probably the single most important ultra-specific training tool. It teaches your body to run on fatigue, which is exactly what you’ll face in the second half of your race.

Pace: slower than you think

This needs its own section because it’s where most first-time ultra runners go wrong.

Your long runs — especially anything over 3 hours — should feel genuinely comfortable. If you can’t hold a conversation, you’re going too fast. In ultra training, “easy” often means 60–90 seconds per kilometre slower than your marathon easy pace. On hilly or technical trail, it might mean walking entirely.

Walking is not failure in an ultra. It’s strategy. Most experienced ultra runners walk all significant uphills, even in races. Practice this in training. If your route has a climb that takes 8 minutes to run and 10 to walk, the walking version is often better — it saves your legs for what comes after.

If you’re used to training for road marathons, the mental adjustment to slowing down (a lot) is real. Let it happen. Your pace in a 50K will likely be 45–90 seconds/km slower than your marathon pace, and that’s completely normal.

Nutrition and fuelling for long efforts

Marathon fuelling — a gel every 45 minutes — doesn’t cut it for ultras. You need to practise eating real food while moving.

During training runs over 2.5 hours, experiment with:
– Boiled salty potatoes
– Peanut butter and banana sandwiches cut into quarters
– Rice cakes
– Dates and nuts
– Energy chews and gels as backup, not the primary strategy

You’re looking for 200–300 calories per hour on efforts over 90 minutes, rising toward the higher end for very long days. Aim for a mix of carbohydrates and some sodium — sweat loss over 6–8 hours is significant and low sodium is a common cause of late-race nausea and cramps. Research from the British Journal of Sports Medicine consistently shows that sodium intake matters far more in events over 4 hours than in shorter races.

Practice your nutrition strategy on your long runs, not for the first time on race day. Your gut needs training too.

Hydration matters just as much. Carry your own water — most ultras require you to. A soft flask vest (1.5–2L capacity) is the standard choice.

Kit you’ll actually need

You don’t need to spend £800. But some kit genuinely matters for ultras:

Check your specific race’s mandatory kit list — it varies by event and conditions. Many trail and mountain ultras require a full emergency kit.

Injury prevention during high-volume training

Training for an ultra means more miles, more terrain, and more load. Injury risk rises accordingly. A few things that genuinely help:

Increase mileage gradually. The 10% rule is often quoted — don’t increase your weekly total by more than 10% from one week to the next. In practice, build for 3 weeks, then drop back 20–30% for a recovery week.

Strength work matters. Single-leg squats, glute bridges, calf raises and hip strengthening exercises three times a week will do more for your injury resilience than almost anything else. The American College of Sports Medicine emphasises resistance training as central to endurance injury prevention — not an optional add-on.

Listen to niggles early. A sore Achilles or tight IT band that you train through for three weeks becomes a 6-week layoff. If something feels wrong two days running, take a day off. If it persists five days, see a physio.

Recovery between sessions is non-negotiable at this volume. This isn’t just sleep — it’s the easy days being genuinely easy, not sneaking in extra miles because you feel good.

Race day: what your first ultra actually feels like

There’s a point in almost every ultra — usually somewhere between miles 20 and 30 in a 50K — where you’ll wonder why you signed up. Everything hurts, you’re tired in a way that feels different from any marathon, and the finish still feels impossibly far away.

This is normal. It’s not a sign you’re failing. It’s the part of ultras that makes finishing one mean something.

What helps:
– Break the race into sections between aid stations. Don’t think about the finish; think about the next checkpoint, 4 miles away.
– Eat something even when you don’t feel hungry. Nausea in the later miles is often low blood sugar, not a reason to stop eating.
– Slow down before you blow up. If you feel yourself struggling at mile 18, ease off now — not at mile 25 when it’s too late.
– Talk to people. Ultras are uniquely sociable. Other runners are going through the same thing and most will talk.

The honest takeaway

1. Don’t rush the base. A solid year of consistent running — including at least one marathon — is better preparation than 16 weeks of frantic mileage increases. The injury maths are simple: under-prepared runners don’t finish.

2. Slow your long runs down significantly. Run by time and perceived effort, not by pace. Anything over 3 hours should feel conversational for most of it. Walk the hills — in training and on race day.

3. Back-to-back long runs are your biggest training asset. One 22-mile Saturday and one 10-mile Sunday on tired legs is more specific ultra preparation than a single 26-mile run.

4. Sort your nutrition before race day. Practise eating real food on every run over 2.5 hours. Know exactly what works for your stomach and what doesn’t. The aid station is not the place to experiment.

5. Finishing your first ultra is the goal. Time targets are for your second one. Get to the finish line in one piece, learn what you can, and decide from there.

Next read: Base building for runners: what it is and why it matters