What Is Bonking? Here’s Your Complete Guide

If you find yourself feeling totally tapped out on rides and struggling to make it to the end - A.K.A. bonking - you need this guide to maintaining energy.


If you’ve ever gone just a little too long without eating or drinking on the bike and found yourself feeling flat, unable to put out power or continue to pedal hard, you’ve experienced the dreaded bonk. Bonking isn’t a weird piece of slang that the kids are using these days. Bonking happens when your muscles and brain are depleted of the fuel they need to do the work you’re asking of them.

Pro racer and cycling coach Tyler Williams has dealt with athletes who bonk and has been an athlete who has bonked himself many, many times. It’s nothing to be ashamed of, especially if you come from a more old-school cycling background. Even a decade ago, cyclists like Williams were taught to fuel minimally, encouraged to do fasted rides, and generally followed the idea that pushing through a bonk is a sign of strength. Spoiler alert: It’s not. Bonking leads to worse results, lower power outputs, and a general feeling of hating the ride.

Here, Williams and Stevie Lyn Smith, sports dietitian, share their best tips for catching a bonk early and hopefully avoiding it in the future.

What is bonking?

“A true bonk is when the muscles have inadequate glycogen on-board and we see a reduction in muscle contractions with an increase in fatigue,” says Smith. This leads to an inability to perform on the bike, and it makes you feel terrible.

Glycogen is the fuel your legs and your brain need in order to function. We can only store so much in our muscles, which is why we need to take in fuel on longer, harder rides as those stores become depleted. Bonking is your body’s way of warning you that your glycogen stores are depleted—and that it’s past time to either refuel or stop.

To put it a little more simply: “I’ve had clients describe it as the lights going out,” says Williams. “Or they say it’s like their gas tank is empty.”

“[Bonking] will also include nausea, dizziness, cognitive impairment, lack of coordination, and physical weakness.”

You’ll recognise symptoms of bonking beyond heavy legs and feeling like you just can’t go any farther. “[Bonking] will also include nausea, dizziness, cognitive impairment, lack of coordination, and physical weakness,” says Smith.

If you start to feel lightheaded, or you’re suddenly struggling on a climb that’s normally easy, think back: When was the last time you ate something?

How do you avoid bonking?

1. Don’t start your ride depleted

If you start a ride properly fueled, you’re in a better position even if you accidentally wait a little too long to start snacking. That means you should eat a meal within two hours of your ride. “This is highly individual but if you’re having breakfast a couple of hours preride, a great place to start is aiming for 2 grams of carbohydrate per kilogram of bodyweight, plus a moderate amount of protein—around 15 to 20 grams—to keep you satiated,” says Smith. For example, this could look like a bowl of oats with a spoonful of peanut butter and some berries, or some toast with two eggs.

2.Fuel and hydrate early and often

“The thing is, if you’re not fueling, then you’re digging a hole,” says Williams. “You want to be focused on fueling and have a plan from the start of your ride, rather than starting to fuel after a couple hours.”

Proper fueling practices will help you avoid bonking. For rides under an hour, just water is fine as long as you start the ride well-fueled. Anything longer means it’s time to start taking in carbs. Keep it simple: Aim to take in between 30 to 60 grams (120 to 240 calories) of carbohydrates per hour in the form of bars, gels, sports drinks, or gummies.

3. Carefully increase your carb intake to find your optimal fueling strategy

“I try to get most of my athletes, who are typically doing longer Gran Fondo-style racing, up to 80 to 100 grams of carbohydrates per hour for events like that,” Williams says. “But that takes practice, so I’m always working with the athletes to fuel like that on their longer weekend rides so they know if 100 grams per hour feels better or is more doable than 80.”

Start slow if you want to up your carb intake: Williams has his athletes add 10 grams per hour to what they’ve been doing, tests that for a few rides, then adds another 10 if they’re feeling good. The goal is to find your sweet spot where you feel fueled and strong: Too little, and you bonk. But too much, and you’ll deal with digestive issues like cramping, gas, and bloating.

One caveat: Everyone is individual and has different energy needs. That’s why the range of hourly carbohydrate intake is so big. You may find that you need 400 calories per hour to feel good when you’re doing a really long, hard effort, while someone else needs 200. Your riding partner may not need to eat as much as you to avoid bonking, so don’t base your fueling strategy off of what your buddy is doing, stick to your plan.

4. Stay hydrated

While dehydration isn’t the same as bonking, staying properly hydrated both avoids symptoms of dehydration (that can feel similar to a bonk) and helps you digest your food. Imagine your gut like a sink drain: If you add in only food, it clogs the drain and doesn’t go anywhere. Your gut needs water to help it break down those carbohydrates into usable fuel for your muscles.

Aim for at least one bottle of water or sports drink per hour of riding, more if it’s hot or you’re a heavy sweater.

What are common reasons people tend to bonk?

1. Focusing on weight loss

Many cyclists find cycling because they’re trying to lose weight. But trying to lose weight by cutting calories is a recipe for disaster both on and off the bike. “You can’t do hard training and try to cut weight simultaneously,” says Williams. “Trying to cut 20 pounds and also perform at a high level is nearly impossible. And if you cut calories during your ride, you’ll be a less effective rider, you’ll hurt your recovery, and you’ll likely end up overeating later because you’ll be hungry.”

In fact, fueling well during a ride is the best way to ensure that you’re able to focus on healthy eating off the bike. “If you’ve fueled your ride well, you’re generally less hungry after, so you’re going to make better decisions postride and have less weird cravings generally,” says Williams. “You’ll be better equipped to make healthy choices.”

2. Training fasted

The whole “no breakfast” movement has picked up steam in recent years under the banner of fasted cardio. If you’re on this bandwagon, there is a way to train in the morning without bonking, but it’s not going to be easy, and needs to be done carefully.

“Fasted rides should be done really methodically, and usually with coach supervision and advice,” says Williams. “They only make sense at certain points in your training.”

If you are training fasted, keep it short and easy. “If you deplete yourself by pushing past your endurance pace, you’re no longer burning fat, you’re burning whatever glycogen is left in your muscles, which will cause you to bonk,” Williams adds. “Stay in that easy zone, because if you start pushing the pace, you’re going to bonk or you’re going to finish the ride starving.”

3. Simply forgetting to eat

Most bonks happen accidentally. It’s easy to skip a gel or two if you’re highly focused and working hard in a race, on a technical mountain bike ride that requires full focus, or you simply didn’t pack enough snacks because you thought your ride would be shorter. You may need to reconsider your fueling strategy if you find yourself constantly bonking accidentally.

This might mean switching from gels and bars to sports drink in a race so that you can take in calories as you hydrate. On the mountain bike, it could mean swapping bottles for a hydration pack with sports drink so it’s easier to take quick sips even while riding on rocky single track. And if you’re someone who constantly forgets to pack enough, get a large bar bag or saddle bag and stuff them with extra snacks that come with you on every ride.

How do you come back from bonking?

If you miscalculated on your fueling and you’re starting to feel those flat legs, that drifty feeling in your brain, and a bit of a wobble to your pedal stroke, you may be heading toward a serious bonk. Can you come out of it?

Unfortunately, not fully, says Williams. “But you can start to feel a bit better [by eating something] and finish your ride,” he says. (Bonking in a race, though, means it’s very unlikely that you’ll get the result you were hoping for.)

Much like avoiding a bonk, coming back from one starts with fueling. “Eat and hydrate,” says Smith. “Bonking is clear feedback from your body that you’re depleted. Start to get some carbs, electrolytes, and fluids on board ASAP.”

If you’re riding outside and your bonk symptoms include any kind of cognitive impairment, don’t fuel while riding. Pull over and have a snack, and give your body a break. Otherwise, you’re at risk of crashing.

You also may need to cut your ride short or drop from doing intervals to pedaling at an easy pace if you’re not feeling better quickly. Don’t try to push the pace right away. “Always proceed with caution and pedal at an easy pace for a while, because depending on how depleted you are, just eating a gel or a bar might not get you fully ready to finish your workout,” says Smith. “It takes time for your body to process the carbs you’re taking in. Luckily, you should start to feel better within a few minutes.”

What are the downsides of continuously bonking?

A bonk used to be almost a badge of honour amongst old-school cyclists. It indicated that you went as hard as you could and you were finishing the ride with the tank empty. This is not something to celebrate, though.

“Bonking was such a frequent occurrence when I was first starting to ride,” says Williams. “Back then, I would just ride until I bonked, and that was considered good training. We thought that was finding our limit, but it turns out, you don’t really hit that limit if you fuel correctly.”

A bonk doesn’t just hurt you on that day. Continually running out of energy and depleting yourself on rides will delay recovery and make it hard for you to see improvements in your cycling. “Fueling your ride helps to keep from dipping too deep into your body’s glycogen stores and promotes a quicker recovery postride,” Smith adds.

Finally, bonking frequently can increase your risk of Relative Energy Deficiency in Sport (RED-S), which happens when you’re not meeting your body’s energy demands. If you’re constantly finishing rides under-fueled, it can be hard to make up that deficit, especially if you lead a busy life. RED-S can make it impossible for you to train or race at the level you want to be at, and can cause long-term health damages, including lowering your immunity, and increasing your risk of injury.

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