How to Recognize and Treat the BONK

Out on a foggy, rainy trail this week, I found myself thinking about one of the toughest experiences a runner can have: bonking.

If you've ever hit the wall mid-run and felt like your body was shutting down, you already know how rough it can be.

But what exactly is bonking, what causes it, and how can you avoid it? Let’s break it down.

What Is a Bonk?

Bonking refers to the moment your body runs out of fuel during a workout especially during long runs.

Symptoms usually begin with a headache, heavy legs, or overwhelming fatigue.

In more serious cases, it can lead to dizziness or even disorientation, especially on trails or during ultramarathons. If it gets bad enough, continuing safely becomes impossible.

5 Common Causes of Bonking

1. Your Long Run Is Too Long

If you’re increasing distance too quickly or attempting a two-hour run before your body’s ready, you’re likely to crash.

Stick to gradual progress about 10% more mileage per week is a safe rule of thumb.

2. Your Training Week Is Too Demanding

Sometimes the issue isn’t the long run itself, but what led up to it.

A sudden jump in weekly mileage can leave you depleted before the long run even starts.

Overtraining can leave you without enough glycogen to power through.

3. You’re Running Too Hard

Joining a group that’s faster than your usual pace? It might push you over the edge. Running at a higher intensity than you're used to means your energy burns faster, and bonking hits sooner.

Stay in your lane even during group sessions.

4. Insufficient Recovery From Previous Workouts

Doing speed work or a tough session the day before your long run can sneak up on you. If your legs aren't fully recovered, you're entering the run already low on resources.

5. You Didn’t Fuel Properly

Ultimately, bonking comes down to depleted energy stores.

If you don’t eat enough beforehand or fail to take in calories during the run your body simply runs out of usable energy. That’s when things get rough.

How to Prevent a Bonk

• Fuel the Day Before: Make sure you’ve had enough food leading up to your run, especially complex carbs.
• Start With a Full Tank: Eat a balanced pre-run meal with carbs and a bit of protein a few hours before you head out.
• Bring Fuel With You: Gels, energy chews, a banana, or even a spoonful of maple syrup can make a huge difference mid-run.
• Hydrate with Electrolytes: Don’t just drink water your body also needs sodium and other minerals to function during endurance efforts.

What to Do If You Start Bonking

If you feel the early signs dizziness, fogginess, or extreme fatigue don’t ignore them.S

low down.

Take in quick-digesting carbs and electrolytes right away. And if things don’t improve, it’s okay to end the run early.

Call for help or walk it in. There’s no shame in listening to your body.

Final Thoughts

Bonking happens to almost every serious runner at some point. It’s not a failure it’s a lesson.

The key is understanding what went wrong so you can adjust and improve for next time. Long runs are where your training gains are made, but they have to be done smart.

Fuel up, pace yourself, and don’t be afraid to call it a day if things go south.