How to Avoid Hitting the Wall in a Marathon

Somewhere after mile 20, a runner who felt fine suddenly cannot lift their legs, their pace falls off a cliff, and every step becomes a negotiation. That is the wall, and it feels like a failure of character. It is not. It is a fuel problem with a fuel solution. Your body stores only a limited amount of the fast carbohydrate that fast running relies on, and when that tank runs dry, you slow down whether you like it or not. The good news is that this is one of the most predictable and preventable events in endurance sport. Get three things right, before and during the race, and the wall stops being your problem.

The short version

The wall is your body running out of stored carbohydrate, not running out of willpower. It hits when muscle glycogen empties, usually around 32 kilometres, or mile 20.
Your muscles and liver hold only about 1,800 to 2,000 calories of carbohydrate, and a marathon can burn more than that.
Carb load in the two to three days before the race, aiming for 8 to 12 grams of carbohydrate per kilogram of body weight per day.
During the race, take in 30 to 60 grams of carbohydrate per hour, and up to 90 grams per hour on longer efforts using mixed glucose and fructose fuels.
Pacing protects your fuel. Start too fast and you burn through glycogen early, which is the single most common cause of a late-race collapse.

What the wall actually is

Your body runs on two main fuels: carbohydrate and fat. Fat is almost unlimited, even in lean runners, but it burns slowly. Carbohydrate burns fast and clean, which is exactly what you need to hold marathon pace. The problem is that you store very little of it. Carbohydrate is kept as glycogen in your muscles and liver, and the total tank holds only around 1,800 to 2,000 calories in a trained runner.

A marathon can burn well over 2,000 calories, and a large share of that comes from carbohydrate. When the glycogen runs low, your body is forced to lean harder on fat, which cannot supply energy fast enough to keep you at speed. Your pace drops, often by about 30 percent, and it feels like your legs have been unplugged. That sudden shift is the wall. It is a metabolic event, not a moral one.

~2,000kcal

Carbohydrate your body can store as glycogen

Rapoport, PLoS Comput Biol 2010

32km

Where the wall typically hits (mile 20)

Marathon metabolism modelling

~40%

Of marathoners report hitting the wall

Rapoport, PLoS Comput Biol 2010

The fuel math, made simple

You do not need a spreadsheet, but seeing the arithmetic makes the wall obvious. A runner burns roughly 60 calories of energy per kilometre, and a big chunk of that is carbohydrate. Multiply across 42 kilometres and your carbohydrate demand outstrips what you can store. The gap is exactly what fuelling during the race is designed to close.

Fuel source	Roughly how much you carry	How fast it burns
Muscle and liver glycogen	1,800 to 2,000 kcal	Fast, ideal for pace
Body fat	Tens of thousands of kcal	Slow, cannot hold race pace alone
Carbohydrate taken during the race	As much as your gut tolerates	Fast, tops up the tank on the move

The one idea to hold onto

You cannot store enough carbohydrate to cover a whole marathon at pace. So you do two things: start the race with the tank as full as possible, and keep topping it up while you run. Fuelling is not optional for the marathon distance, it is part of the race plan.

Start full: carb loading that works

Carb loading is not a single giant pasta dinner the night before. It is a deliberate two to three day increase in carbohydrate while you taper your training, so your muscles pack in as much glycogen as they can hold. The evidence-based target from sports nutrition guidelines is 8 to 12 grams of carbohydrate per kilogram of body weight per day in the final 24 to 48 hours before a long event.

For a 70 kilogram runner that is roughly 560 to 840 grams of carbohydrate a day, which is a lot more than it sounds once you cut back on fat and fibre to make room. The classic mistake is eating your normal diet plus extra, feeling stuffed, and never actually raising the carbohydrate. Load the carbohydrate, ease off heavy and very high-fibre foods, and keep portions frequent rather than enormous.

Build meals around starchy carbohydrate. Rice, pasta, potatoes, bread, oats, and fruit. Plant-based runners are well served here, since most loading staples are already plant foods.
Trim fat and fibre in the final day. They fill you up and can upset your gut on race morning. Choose lower-fibre versions such as white rice or peeled potato close to the race.
Keep drinking to stay hydrated. Stored glycogen holds water with it, so a small bump on the scale before race day is normal and expected.
Eat a familiar breakfast 2 to 4 hours before. Aim for 1 to 4 grams of carbohydrate per kilogram, something you have tested in training, never a new food on race day.

Top up on the move: carbs per hour

A full tank still is not enough for the full distance, so you refuel while running. Sports nutrition guidance is to take in 30 to 60 grams of carbohydrate per hour for efforts lasting up to about two and a half hours. For runners out there longer, or anyone chasing a fast time over three hours plus, intake can rise toward 90 grams per hour.

There is a catch at the high end. Your gut can only absorb about 60 grams per hour of a single type of carbohydrate, such as glucose, because it saturates one transport route. To go higher you need a mix of glucose and fructose, which travel through separate doorways in the gut wall and so add up rather than compete. That is why endurance gels, drinks, and chews aimed at long events use blended sugars, often around a 2 to 1 ratio.

Race duration	Carbohydrate target	What that looks like
Up to 2.5 hours	30 to 60 g/hr	One gel every 30 to 45 min, or a carb drink
2.5 to 3 hours plus	Up to 90 g/hr	Mixed glucose and fructose fuels, spaced regularly
Any duration	Practice in training	Never trial a new fuel on race day

Train your gut, not just your legs

Taking 60 to 90 grams of carbohydrate an hour while running hard is a skill your stomach has to learn. Practise your exact race fuel on your long runs for weeks beforehand. A gut that has never handled race-day fuelling will rebel at the worst moment. Whole-food options such as bananas, dates, and dried fruit work too, and are naturally plant-based, as long as you have tested how they sit.

Pace and training that spare your fuel

Fuelling gets the headlines, but pacing is the other half of avoiding the wall. The faster you run, the larger the share of energy that comes from carbohydrate rather than fat. Go out too fast in the excitement of the start and you quietly burn through your glycogen early, guaranteeing an empty tank later. A steady or slightly negative split, where the second half is no slower than the first, is the pattern that protects your fuel.

Training matters too. Consistent endurance training teaches your body to burn a higher proportion of fat at any given pace, which stretches your limited carbohydrate further. Your long runs also rehearse the whole system: pace discipline, fuelling on the move, and the mental practice of staying calm when it gets hard. This is why the marathon rewards months of preparation, not last-minute heroics.

The simple version

Start slightly slower than feels right, hold it steady, and fuel from early rather than waiting until you feel empty. By the time you feel the wall coming, it is often too late to fully fix it, so eat before you are desperate, and pace like the race is won in the last 10 kilometres.

A race-day plan you can trust

Pull it together into a plan you have rehearsed. Nothing here should be new on the day.

Load carbohydrate for two to three days. 8 to 12 g/kg per day, easing off fat and fibre near the end.
Eat a tested breakfast 2 to 4 hours out. Familiar, carbohydrate-rich, easy on your stomach.
Start controlled. Run the first few kilometres a touch slower than goal pace to bank fuel and nerves.
Fuel from around 45 minutes in. Hit your 30 to 90 grams per hour on a schedule, with fluid, before you feel low.
Hold your line late. If you paced and fuelled well, the last 10 kilometres are where your plan pays off and others fade.

Questions people ask

What exactly does hitting the wall feel like?

Most runners describe a sudden, dramatic drop in energy and pace, usually after mile 20, where the legs feel heavy and unresponsive and even a slow jog becomes a struggle. It comes on faster than normal fatigue because it reflects your fast fuel, carbohydrate, running low rather than gradual tiredness.

Can I avoid the wall by just eating a huge pasta dinner the night before?

Not reliably. One big meal cannot fully top up your glycogen stores and often just leaves you bloated. Effective carb loading is a two to three day increase in carbohydrate, around 8 to 12 grams per kilogram per day, paired with a taper in training so your muscles actually store the extra fuel.

How many gels do I actually need in a marathon?

It depends on your pace and the gel, but many runners take one gel of about 20 to 30 grams of carbohydrate every 30 to 45 minutes, which lands in the 30 to 60 grams per hour range. Faster runners chasing 90 grams per hour use mixed glucose and fructose products. Practise your exact plan in training first.

Do fat-adapted or low-carb runners still hit the wall?

Training can raise how much fat you burn at a given pace, which helps spare carbohydrate. But at true marathon race pace, carbohydrate still matters, and most competitive runners perform better fuelling with carbohydrate during the race rather than relying on fat alone. There is no single approach that works for everyone, so test in training.

References

Rapoport BI. PLoS Computational Biology. Metabolic Factors Limiting Performance in Marathon Runners. 2010. doi.org/10.1371/journal.pcbi.1000960
Thomas DT, Erdman KA, Burke LM. Medicine and Science in Sports and Exercise. Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. 2016. pubmed.ncbi.nlm.nih.gov/26891166
Jeukendrup A. Sports Medicine. A Step Towards Personalized Sports Nutrition: Carbohydrate Intake During Exercise. 2014. doi.org/10.1007/s40279-014-0148-z

Last reviewed 18 July 2026. We check health-condition articles against current guidelines and update the date above when we do.