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Woman cycling on road with tired expression

How to Prevent Bonking on Longer Bike Rides

Coach Darryl was riding the Davis Double Century, one of his favorite spring rides. Nearing the end of the race for his eighth year in a row, finishing should have been no problem. But something was wrong. 

With only 12 miles to go, he was cruising along at 14 miles an hour when a sudden fatigue came over his body and mind. How long would it take to get to the end? He tried to do the simple math in his head, but it wouldn’t compute. It was then he knew he had to stop or risk hurting himself. 

“I stopped, got into one of the sag vehicles and drove back,” he recalls. “Because I knew that if I’m not smart enough to do that in my brain, then I’m not smart enough to be on the road.”

What happened to Darryl is not uncommon in cycling, but many cyclists don’t know enough about it to realize the dangers. It’s called “bonking.” It’s a serious problem, and every cyclist should know the signs of and how to prevent bonking on longer bike rides.

What Is Bonking?

Biologically speaking, bonking is what happens when your body exhausts its energy stores for a high-intensity workout. Essentially, you’ve run out of glycogen in your muscles and glucose in your bloodstream, and these are the essential fuel your body and mind need to keep going.

In a low- or moderate-intensity workout — with your heart rate around 120 bpm, your body can sustain the pace much longer because it’s burning fat. When you’re working out at a high level of intensity — a heart rate closer to 160 — for a prolonged period, your body is burning glycogen stores from your muscles. These stores burn much more quickly than fat, and when they’re gone, it’s truly like running out of gas.

This is a concern for distance cyclists or any endurance athletes who often work out for more than 90 minutes at a time. That’s the point at which your body burns up the available stores of glycogen that it has made from the food you ate earlier.

What Does Bonking Feel Like?

Those who have experienced it would describe bonking as simply “hitting a wall.” One moment, you’re riding hard and fully alert, the next you are overcome by a cloud of fatigue.

“It’s not like a dimmer switch. It is going to happen in a matter of seconds,” Coach Darryl says. “Your muscles will not go at any speed, you can barely turn the pedals, and you’re not smart enough to be able to make decisions on your own. You’re not safe to be by yourself.” 

You’ll feel extremely weak and may experience shakes, extreme sweating and dizziness. You’ll probably feel extremely hungry and very confused. You might even experience heart palpitations. 

Once you’ve bonked, your cycling day is over. In reality, you’re looking at 24 hours of fatigue, and your body is demanding replenishment. 

Why Is Bonking Dangerous?

In reality, bonking while cycling can be incredibly dangerous—not just for you, but also for those around you. The idea that this makes you unsafe may sound surprising, but that’s how all-encompassing the bodily shutdown is. Your brain needs glycogen for fuel as well, so when your stores run out, you can be cognitively impaired. You may not even be able to tell the difference between a red and green traffic light — something that could obviously be dangerous.

On one ride, Darryl was passing another cyclist and, as he often does, asked him how he was doing. When the response was “Terrible!” Darryl decided to investigate. The rider was lost in an unfamiliar area of town and clearly out of it. Because he knew the signs and dangers of bonking, Darryl coached the rider off the road to rehydrate and refuel.

“You rarely have the opportunity to save the life of another person,” Darryl says. “But if that person is incapacitated on the road, you are his brains.” That’s why he regularly greets other cyclists and asks them how they’re doing as he passes. 

If you think someone has bonked, give them a simple math quiz. If they can’t answer some basic multiplication questions, that’s a pretty good sign they’ve hit the wall.

How Do You Prevent Bonking?

Your body makes glycogen from glucose, which it creates from carbohydrates — the essential energy source for your body. This process takes time, so you have to plan ahead. Once you’ve bonked, it’s already too late.

Here are three basic rules on how to prevent bonking while cycling:

  1. Eat lots of carbs before the race. You need plenty of fuel for a long, high-intensity workout. This isn’t the time to eat a bunch of protein. Fill up on bread, rice, potatoes, or pasta so your body has plenty of stores to burn through.
  2. Bring an energy drink on long rides. If you’re going to ride longer than 90 minutes, bring an energy drink, not just water. On those longer rides, start drinking the energy drinks early in the ride so your body has time to process it. Your body is burning through carbohydrate stores from the food you ate 90 minutes earlier. Keep eating and drinking carbs throughout the ride to prevent bonking while on the road or trail.
  3. Slow down if you have to. Again, at lower intensity levels, your body burns fat instead of glycogen. So, if you don’t have an energy drink, you can ride slower to prevent bonking.

If you do bonk on a ride — or you see another cyclist who has — you have to realize there is no quick fix. Eating or drinking a lot of simple sugars will help, but your body really needs time to recover. If it happens, stop and seek help. 

The best plan, though, is prevention. If you give your body the fuel it needs well ahead of time, you can tackle those extreme rides with strong legs and a clear head. 


You can find more insights from Coach Darryl over at his website.