How to run a marathon without hitting the wall

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The wall is real, but it’s not random

If you’ve run a marathon before, you probably know the wall by its other names: the 20-mile cliff, the point where your legs turn to concrete and your pace falls apart for no obvious reason. If you haven’t run one yet, you’ve heard about it from someone with a thousand-yard stare describing mile 22 like it was a near-death experience.

Here’s the thing most people don’t tell you: hitting the wall isn’t bad luck, and it isn’t a sign you’re not “a real runner.” It’s almost always the predictable result of three things — running too fast early, not fuelling properly, or not training your body to use fat as a backup fuel source when glycogen runs low. All three are fixable. None require you to be faster or fitter than you currently are.

This isn’t about turning you into an elite athlete who glides through 26.2 miles without effort. It’s about understanding what’s actually happening physiologically around mile 18-20, and making the boring, unglamorous decisions in the weeks and hours before that stop it from happening to you.

What’s actually happening when you “hit the wall”

Your body stores roughly 90–120 minutes’ worth of usable glycogen (carbohydrate stored in muscles and liver) for running at marathon effort. For most everyday marathoners — those finishing in 4 to 5.5 hours — that store runs low somewhere between mile 16 and mile 20, unless you’ve been actively topping it up as you go.

When glycogen drops, your body has to lean harder on fat for fuel. Fat is abundant, but it’s slow to convert to energy relative to carbohydrate, especially at the paces most of us run a marathon. The result: your pace per kilometre you could hold easily at mile 5 suddenly feels like a different sport at mile 20. That’s the wall. It’s a fuel problem, not a character flaw.

The fix isn’t one trick. It’s three separate systems working together: pacing, fuelling, and training your metabolism to be more efficient. Get one right and ignore the others, and you’ll still hit trouble.

Pace like you mean to finish, not like you mean to start

The single biggest cause of hitting the wall early isn’t fuelling — it’s starting too fast. Race-day adrenaline, a downhill first mile, and a crowd of people around you who went off too quick combine to make 10-15 seconds per km faster than goal pace feel completely normal for the first 5k. It isn’t. That early “free speed” burns disproportionately more glycogen and you pay for it later, usually around the exact point you can least afford to.

A simple rule that works for most goal times: run the first 10km at least 10-15 seconds/km slower than goal race pace. Negative-split if you can — meaning the second half is faster than the first. It sounds counterintuitive when you’re full of energy at the start line, but it’s the single most reliable predictor of a good marathon finish.

If you’re not sure what pace is realistic for you yet, that’s a training question, not a race-day guess — it’s worth working through a structured plan like a 16-week marathon training plan that builds your long runs and pace sense together, rather than figuring it out cold on the day.

Fuel before you’re hungry — not when you feel you need it

The classic mistake is waiting until you feel depleted to take a gel. By the time you feel it, you’re already behind — it takes 10-15 minutes for carbohydrate to get into your bloodstream and start being used. The target for most runners during a marathon is 30-60g of carbohydrate per hour, starting from around 45 minutes in, not waiting until mile 15.

Practical version of that:
– One energy gel (roughly 22-25g carbs) every 30-40 minutes, starting early
– Alternate with sports drink if the race offers it, to spread fluid and carbs
– Practise this exact timing on your long training runs — race day is not the place to test a new gel brand or a new schedule

If gels upset your stomach, that’s usually a gut-training issue, not a sign you can’t tolerate carbs during exercise — your gut adapts to processing fuel while running the same way your legs adapt to distance. Build this up gradually on long runs rather than introducing it all at once, and it’s worth reading into gut health for runners if nausea or cramping has been a recurring issue for you.

The night-before and morning-of matters too — not in a dramatic “carb-loading feast” sense, but a deliberate one. A proper carbohydrate loading protocol in the 36-48 hours before race day can meaningfully increase your glycogen stores before you even start.

Train your long runs to simulate the problem, not avoid it

Most marathon plans include a weekly long run that builds up to 32-35km (20-22 miles). The point of that run isn’t really distance — it’s teaching your body to burn fat more efficiently at speed, so you have more glycogen left in reserve on race day when it matters.

A few long runs that specifically target “wall-proofing”:
– Fasted or low-carb long runs (occasionally, not every week): running a shorter long run, say 90 minutes, without pre-run food improves fat utilisation over time. Don’t do this on your longest runs — save it for mid-length ones.
– Fuel-practice long runs: on your 3-4 longest runs before race day, take gels at the exact interval and dose you’ll use on race day. This is non-negotiable prep, not optional extra.
– Progression long runs: start slow, finish the last 20-30% at goal marathon pace. This teaches your legs what it feels like to speed up on tired legs — exactly what’s needed late in a marathon.

This is also where consistent base building in the months before your formal plan starts pays off — runners who arrive at week 1 of a marathon block with an existing aerobic base tend to handle the long run progression with far less injury risk and far less glycogen-depletion drama.

Don’t underestimate sleep, taper, and the unglamorous stuff

Two weeks before race day, your training volume should drop sharply — a proper taper, not just “a slightly easier week.” Many everyday runners, worried about losing fitness, keep training too hard into the final fortnight and arrive at the start line with legs that are still fatigued rather than fresh. Fatigued muscles store less glycogen and burn through what they have faster. The taper isn’t laziness; it’s the single cheapest performance gain available to you.

Sleep in the final week matters more than most runners think, and it’s one of the few genuinely boring pieces of advice that holds up: the body replenishes glycogen stores and repairs muscle tissue during sleep, and poor sleep in race week measurably affects next-day performance according to general sports science consensus from bodies like the NHS’s guidance on exercise and sleep. You won’t fix years of bad sleep in one week, but prioritising it in the 3-4 nights before race day is worth the effort.

What to do when you feel it coming anyway

Even with good pacing and fuelling, some days the wall still looms — heat, a rough night’s sleep, an off day. Knowing what to do in the moment matters:

• Walk through aid stations deliberately, rather than trying to drink and run. A 20-30 second walk costs you almost nothing over 4+ hours and lets you actually get fluid and fuel in.
• Take a gel immediately, even if you don’t feel hungry — the lag time means you need to act before the crisis, not during it.
• Shorten your mental target. Instead of “10km to go,” think “get to the next kilometre marker.” Marathon fatigue is as much cognitive as physical, and breaking the remaining distance into small chunks genuinely helps.
• Accept a slower pace rather than stopping. Dropping 30-45 seconds/km for a few kilometres while you recover is far better than a dead stop, which is much harder to restart from.

If this is your first time racing the distance, it’s worth reading a first marathon runner’s honest account of what I wish I knew before race day — not for inspiration, but because knowing what actually goes wrong for real people is more useful than any highlight reel.

The Honest Takeaway

• Run your first 10km of the marathon 10-15 seconds/km slower than goal pace — this single change prevents more wall-hitting than any gel or supplement.
• Start fuelling at 45 minutes in, not when you feel depleted — aim for 30-60g of carbohydrate per hour throughout.
• Practise your exact race-day fuelling strategy on your 3-4 longest training runs — race day is not the time to test anything new.
• Taper properly in the final two weeks and prioritise sleep in race week — both are free performance gains most runners skip.
• If the wall hits anyway, walk the aid stations, take fuel immediately, and shorten your mental target to the next kilometre — it’s a recoverable moment, not a race-ending one.

Next read: Get your fuelling right with a carbohydrate loading plan