Why Runners Hit the Wall at Mile 20 (And How to Stop It)

Everyone hits the wall at some point.

In training. In a race. Sometimes both.

It's not a badge of honour, and it's not bad luck either.

So why do runners hit the wall around mile 20? Most people will tell you it's because you ran out of fuel, and that's part of it, but there's more going on than that. A recent study highlighted in this piece from VDOT shows the wall is a mix of things all catching up with you at once: pacing, fuelling, tired legs, and your brain deciding it's had enough.

The good news is you can do something about every one of them.

You went off too fast

This is the big one.

Run even a few seconds per mile quicker than your actual fitness and your body burns through its fuel much faster, and you pay for it later, usually right around mile 20. Race the fitness you've got, not the time you're hoping for, and learn what the right pace feels like, because heat, wind and hills will all change the number on your watch.

You didn't feed it

You've only got roughly 90 minutes to two hours of stored fuel at marathon effort. After that you're running on whatever you put in.

The guidance is around 60 to 90g of carbohydrate an hour, depending on what your stomach can handle.

But here's the bit people skip.

Practise it.

On your long runs. Not on race day.

Your legs gave up

You can have plenty of fuel and still grind to a halt if your legs can't take the pounding anymore. Hilly courses batter your quads, flat ones hammer the same muscles over and over. Train for the course you're actually racing, and get your strength work in, it's the bit that keeps your legs working when everything else is tired.

You never practised being tired

If you've never run marathon pace on tired legs, mile 20 comes as a shock. Long sessions that mix marathon pace with some harder threshold efforts teach your body and your head what that feels like before the day it matters.

What I've learned

Read the guidance.

Feed your body what it needs.

Practise it early.

Getting that sorted well before race day really sets you apart.

Because the goal isn't just to finish.

It's to actually enjoy the race. Cross the line fit and healthy. Recover well. And go on to the next event.

That's how you get a long running life out of this, rather than one painful marathon you never want to repeat.

If you want help pacing, fuelling and building your marathon properly, have a look at running coaching.

Andy