Racing 6 min
How do I stop hitting the wall in a marathon?
Hitting the wall — the sudden, severe fatigue that strikes many marathon runners around mile 18 to 22 — is almost always glycogen depletion combined with going out too fast. You prevent it with three things done consistently: even pacing, enough carbohydrate during the race, and long runs that train your body to burn fat alongside stored sugar. None of it is complicated, but all three have to be in place together.
What actually causes the wall?
Your muscles run mainly on glycogen (stored carbohydrate) during hard effort, and the average trained runner carries roughly 90–120 minutes of it. A marathon takes most people well beyond that. Once glycogen stores empty, your body has to lean harder on fat for fuel, which can't be converted to energy fast enough to hold marathon pace — legs feel suddenly heavy, pace collapses, and the final miles become a grind. Starting too fast burns through glycogen faster and brings the wall forward; under-fuelling during the race does the same.
How does pacing prevent it?
The single biggest lever is running an even, or slightly negative, split. Going out even 10–15 seconds per mile faster than goal pace in the first few miles — which feels easy on fresh legs — burns disproportionately more glycogen and brings the wall on earlier and harder. Aim to run the first 10 miles at or slightly slower than goal pace, hold steady through the middle, and only push if you have something left after mile 20.
How much should you eat and drink during the race?
- Start taking in carbohydrate early — from around 45 minutes in, not when you first feel tired
- Most runners tolerate 30–60g of carbohydrate per hour from gels, chews or sports drink
- Practise your exact race-day fuelling plan on long training runs first — the marathon is not the day to try something new
- Drink to thirst rather than on a fixed schedule; both over- and under-hydrating can cause problems
- Pair carbohydrate with fluid where you can, since concentrated gels absorb faster with water
Can training make the wall less likely?
Yes. Long runs of 16–20 miles teach your body to spare glycogen and use fat more efficiently at a given pace — a genuine physiological adaptation, not just mental toughening. A handful of long runs where the final few miles are run at or near goal marathon pace are particularly effective, because they rehearse exactly the fatigue you'll face late in the race while your glycogen stores are already low.
What should you do if it happens anyway?
If you do hit the wall, easing off pace immediately does far less damage than trying to fight through it at goal pace — a short walk through an aid station to get carbohydrate and fluid in is often enough to steady things. Treat it as information for next time: it usually points to either too fast an early pace or too little fuel taken on board, and both are fixable with the next training block.
Where does training structure fit in?
Pacing discipline and fuelling only work if the weeks beforehand built the endurance to support them. RunV builds marathon plans around progressive long runs and goal-pace practice, and adjusts the following week automatically if a session gets missed, so the long-run work that prevents the wall doesn't quietly fall away when life gets in the way.
FAQ
- At what mile does the wall usually hit?
- Most commonly between mile 18 and 22, though it can arrive earlier if pacing was too aggressive at the start or fuelling was inadequate. Well-paced, well-fuelled runners often avoid it altogether.
- Does carb-loading before the race stop the wall on its own?
- It helps but isn't enough by itself. Carb-loading tops up glycogen stores before the start, but if you go out too fast or skip fuelling during the race, you can still deplete those stores and hit the wall regardless.
- Is hitting the wall just about fitness level?
- No. Well-trained runners hit the wall too if they pace poorly or under-fuel during the race. Fitness raises how much effort you can sustain, but pacing and fuelling decide whether you actually run out of fuel before the finish.
Train smarter
RunV turns this thinking into your plan — adaptive coaching that rebuilds after every run.
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