Hitting the wall in a marathon: why it happens and how to avoid it

Hitting the wall in a marathon is the late-race collapse where your pace falls off a cliff, your legs turn to concrete and your brain starts negotiating with you about walking. It usually shows up after mile 20, and it usually starts much earlier: with a first half that was too fast and fuel that was too little. That's the good news. Both of those are under your control.

Below: what's actually happening when you hit the wall, how common it is, who it hits most, and the pacing and fueling plan that keeps you off it. Plan it by hand, or with a running app that also coaches lifting, so the long runs where you practice all this don't collide with leg day.

What is hitting the wall in a marathon?

In the largest analysis of the problem so far, Smyth (2021) describes hitting the wall as a significant slowing of pace late in the race, typically after the 20-mile mark, and usually because of a depletion of the body's energy stores. Using pacing data from more than 4 million race records, the study defined it as a sustained period of slowing in the latter stages of the marathon.

The energy store in question is glycogen: carbohydrate stored in your muscles and liver. You burn a mix of fat and carbohydrate while running, and at marathon pace, carbohydrate is a big part of the mix. Run out of it and your body is forced to slow down to a pace fat can support. You don't decide to slow down. You just do.

The plan that keeps you off the wall is built across a whole block, not on race morning. That's what a marathon training plan is for: long runs that grow gradually, fueling practice built into them, and a goal pace that matches your actual fitness. For the full training picture, start with how to train to run a marathon.

How common is hitting the wall?

More common than your race-photo optimism suggests.

• ›Smyth (2021): 28% of male and 17% of female recreational marathoners hit the wall, by the study's pacing-based definition (Smyth, 2021).
• ›Rapoport (2010): a computational study estimated that more than two-fifths of marathon starters experience severe, performance-limiting depletion of carbohydrate reserves (Rapoport, 2010).

Different methods, different numbers. Same message: a big chunk of every start line will slow dramatically in the last 10K.

Who hits the wall most?

Smyth's data has a few patterns worth knowing (Smyth, 2021):

• ›Men more than women. And when men hit it, they slowed slightly more and for slightly longer, though the study notes the size of those differences was small.
• ›Runners chasing a PB. Wall hits were more frequent in the three years around a recent personal best: 36% of runners hit the wall in the three years before a recent PB, compared with 23% in earlier years (Smyth, 2021). Ambition is expensive.
• ›Faster runners lose more minutes when it happens, because there's more pace to fall from.

The PB finding is the one to tape to your fridge. Chasing a time is exactly when you're most tempted to bank minutes early.

Why marathon runners hit the wall

1. Pacing too fast early

The first half of a marathon feels easy. That's the trap. Every minute you run faster than your fitness supports burns carbohydrate faster than you can afford. Rapoport (2010) modeled the distance at which runners exhaust their glycogen, and found it depends on running intensity alongside things like muscle mass and glycogen stores. Translation: pace is a fuel decision.

2. Not taking enough carbs during the race

The joint position stand from the ACSM, the Academy of Nutrition and Dietetics and Dietitians of Canada gives 30 to 60 g of carbohydrate per hour for exercise lasting 1 to 2.5 hours, and up to 90 g per hour beyond about 2.5 to 3 hours (Thomas, Erdman and Burke, 2016). Most marathoners are out there long enough for the higher range to apply. Many take a gel or two, if they remember.

3. Starting with low tanks

Carb loading isn't pasta-party folklore. The same position stand gives 10 to 12 g of carbohydrate per kilogram per day for 36 to 48 hours before events longer than 90 minutes (Thomas, Erdman and Burke, 2016). Glycogen is stored with water, so expect the scale to go up a bit that week. That's the point, not a problem, and it's the same reason behind most of a guide to marathon training weight gain.

4. Not enough long-run training

If your longest run was 12 miles, miles 20 to 26 are uncharted. Most plans build the long run to around 18 to 20 miles about three weeks out, and that takes months, which is why more on how long to train for a marathon matters more than any race-day trick. People who try it on little preparation are the extreme version of this: the honest answer to can you run a marathon without training involves a lot of walking after halfway.

5. Your head

A small, older study of 66 London Marathon finishers (Stevinson and Biddle, 1998) found the runners who hit the wall used more "internal dissociation", basically zoning out from their body's signals. Focusing heavily on physical symptoms was linked to an earlier onset, while paying attention to the race around you was linked to a later one. It's one study, but the practical version is sensible: stay engaged with pace, fuel and the course, without obsessing over every twinge.

Hitting the wall vs other late-race problems

Not every bad mile 22 is the wall.

A side stitch when running is annoying but usually passes when you ease off. The wall doesn't pass by itself. If you feel dizzy, confused or unwell in a way that isn't just tired, stop and get help from race medical staff.

How to avoid hitting the wall in a marathon

Train for it

• ›Build the long run gradually to 18 to 20 miles, peaking about three weeks out.
• ›Run long runs mostly easy, with some marathon-pace miles late in the build. That's where you find out if your goal pace is real.
• ›Keep your strength work, but protect the long run. A long run started on legs wrecked by yesterday's squats teaches you nothing about race day. Lifting during a marathon block is mostly about scheduling it away from those long runs.

Practice fueling like it's a workout

• ›Take carbs on every long run over about 90 minutes. Start at the low end of the range and build up over weeks.
• ›Use the same gels or drink the race will serve, or carry your own.
• ›Rehearse race morning: same breakfast, same timing, same start time if you can.

Pick an honest goal

Set your goal from a recent half marathon and your long-run paces, not a number you like the sound of. If you're not sure what's realistic, look at what counts as a good half marathon time and full marathon time for runners like you, then be a little conservative.

Race-day plan

1. ›First 10K slower than goal pace. It should feel almost silly.
2. ›Settle into goal pace from 10K to 30K. Use course markers, not just your watch.
3. ›Fuel on a schedule, from early. Every 20 to 30 minutes, starting well before you feel you need it.
4. ›Hold at 30K. If there's something left at 35K, use it then.
5. ›Keep race week boring. A shakeout run before marathon day is a short, very easy jog, not a fitness test. Nothing new.

What to do if you hit the wall mid-race

It happens to well-prepared runners too. Damage control:

• ›Take carbohydrate immediately. A gel, sports drink, whatever the aid station has.
• ›Slow down on purpose before your body does it for you. A controlled slower pace beats an uncontrolled shuffle.
• ›Use walk breaks. Walk the aid stations, run between them. Many people get some pace back after fueling.
• ›Break it into pieces. Next mile marker, next aid station, next corner.

Then, after the race, be honest about which of the five causes above got you.

How exrsz handles this

exrsz builds a periodized marathon plan from your goal, schedule, level and equipment, with running and lifting in one plan, so your long runs and fueling practice get the fresh legs they need. It adapts each week to how your training actually went and reshuffles missed sessions so the build still lands on race day.

FAQ

What does hitting the wall in a marathon feel like?

A sudden, sustained drop in pace late in the race, usually after mile 20, with heavy legs and a strong urge to walk. Smyth (2021) links it to depleted energy stores and defines it as a sustained period of late-race slowing.

How many marathon runners hit the wall?

In an analysis of millions of race records, 28% of male and 17% of female recreational runners hit the wall (Smyth, 2021). Other estimates are higher, depending on how the wall is defined.

At what mile do you hit the wall in a marathon?

Typically after the 20-mile mark (Smyth, 2021). It can come earlier if you start much too fast or skip fueling.

How many gels do I need to avoid hitting the wall?

It depends on the gel and your finish time. The ACSM, Academy of Nutrition and Dietetics and Dietitians of Canada position stand gives up to 90 g of carbohydrate per hour beyond about 2.5 to 3 hours, so check the grams on the packet and build up gradually in training (Thomas, Erdman and Burke, 2016).

Can you recover after hitting the wall in a marathon?

Partly. Taking carbohydrate, slowing down on purpose and using walk breaks often brings some pace back. Most runners won't get back to their original pace, which is why prevention matters more.