Why Do Runners Hit 'The Wall' at Mile 20? The Science Explained

In this reel

Mile 20 of a marathon and your legs just... stop. Here's the brutal science behind why it happens to almost every runner. 🏃

Transcript

Mile 20 — and suddenly nothing works. Glycogen — stored carbs — is your engine fuel. After roughly 90 minutes, those stores run out. So your body switches — burning fat instead. That switch is brutal. And your brain needs glucose too — so focus crumbles. Carb-loading the night before can delay it — but rarely stops it. Long slow training runs teach your body to burn fat more efficiently. Follow for more sports science like this.