What Is the Toughest Part of a Marathon?

Most people think the toughest part of a marathon is the last few miles. You’re tired, your legs are heavy, and the finish line feels like it’s moving away. But that’s not where the real battle starts. The toughest part of a marathon isn’t physical-it’s the moment your brain stops listening to your body and starts screaming at you to stop. It’s not at mile 20, or mile 25. It’s usually between mile 18 and 22, when your body is running on fumes and your mind is begging you to walk.

The Wall Isn’t Just a Myth

Every runner hears about "the wall." It’s that point where your glycogen stores run dry, and your muscles start burning with lactic acid. But here’s the thing: the wall doesn’t hit everyone the same way. Some runners feel it at mile 16. Others don’t feel it until mile 24. What’s consistent is this: when the wall hits, your legs don’t stop working-you just stop believing they can keep going.

Studies from the University of Birmingham tracked over 1,200 marathon finishers and found that 73% of runners experienced severe mental fatigue between miles 18 and 22. That’s not because their muscles gave out. It’s because their brain decided it was time to quit. The body can keep going. The mind? Not so much.

Why Your Mind Gives Up Before Your Legs Do

Your body is built to survive. It’s wired to conserve energy. When you run 26.2 miles, your brain is constantly running calculations: How much fuel do I have left? How long until I can rest? Is this worth it? Around mile 18, those calculations start tipping toward "no." That’s when your internal alarm system goes off. It doesn’t care about your goals. It doesn’t care about your training. It just wants you to stop before you damage something.

Think of it like a car running on empty. The engine might still turn, but the dashboard light is flashing. Your brain is that light. It’s not lying. Your energy is low. But here’s the catch: you still have enough left to finish. You just have to ignore the warning.

Training Doesn’t Prepare You for This

You can do 20-mile long runs. You can do speed workouts. You can even do back-to-back weekends of 16-mile runs. But none of that fully prepares you for the mental collapse that happens in the middle of a race.

Why? Because training is controlled. You know when you’ll stop. You have water, music, a route you’ve mapped out. Race day? Everything changes. The crowd noise, the pace, the weather, the people around you-all of it adds pressure. Your brain goes from "I’m training" to "I’m in a fight for survival."

One runner I spoke to in Melbourne, Lisa, ran her first marathon in 2025. She’d trained for six months. She hit every long run. But at mile 20, she sat down on the curb and cried. "I didn’t think my brain could betray me like that," she said. "I didn’t know the pain wasn’t in my legs. It was in my head."

What Actually Helps When the Wall Hits

There’s no magic trick. But there are habits that make a difference.

• Break the race into chunks. Don’t think about 6.2 miles left. Think about getting to the next water station. Then the next. Then the next. Small wins keep your brain engaged.
• Use a mantra. Something short, repetitive, and personal. "Strong legs. Steady breath." "One step. Then another." It doesn’t matter what it is. What matters is that you say it out loud or in your head, over and over.
• Focus on form. When your mind is screaming, your body starts to collapse. Tighten your core. Relax your shoulders. Swing your arms. It tricks your brain into thinking you’re still in control.
• Find one person to follow. Pick someone just ahead of you. Stay with them for a mile. Then pick another. It’s not drafting-it’s distraction.

These aren’t fancy tactics. They’re simple, repeatable, and proven by elite runners and weekend warriors alike. The difference between finishing and quitting often comes down to whether you’ve practiced these mental moves before race day.

What Most Runners Get Wrong

Too many runners think the toughest part is the physical pain. So they focus on fueling, shoe choice, or hydration. All of that matters. But if your mind breaks, none of it helps.

Runners who train only their bodies, not their minds, are the ones who collapse at mile 22. They didn’t run out of energy. They ran out of belief.

There’s a reason elite runners do mental rehearsal. They visualize hitting the wall. They visualize pushing through it. They rehearse the moment they want to quit-and then they imagine themselves taking one more step. That’s not optional. It’s part of the training.

The Real Finish Line

The marathon doesn’t end at the timing mat. It ends when you stop listening to your brain’s lies.

The toughest part isn’t the distance. It’s not the soreness. It’s not even the heat or the wind. It’s the quiet, relentless voice inside your head that says, "You’ve done enough. Just stop."

And the only thing that beats that voice? The one you’ve trained to say back: "Not yet."