How to Avoid Bonking While Working Out
Blowing up. Hitting the wall. Bonking. Simply defined, it’s when you run out of glycogen— a carbohydrate supply stored in your liver and muscles — in the middle of a hard effort. To fix it, you need to get fast-absorbing carbohydrates into your system, ASAP!
Most committed exercisers know the feeling (and don’t need to ask “what is bonking?”). It’s like this: Your workout is going great. Then, suddenly, every step, stroke, rep, and jump becomes an epic challenge. If this is a race, you’ve lost. (But, good news: Bonking is not a sign that your cardiovascular endurance is lacking.)
Bonking is usually avoidable, so once you learn what it is, you can identify your own “hitting the wall” symptoms and strategize ways to prevent it from ruining your next big workout or event.
What Is Bonking?
Simply put, bonking is when your body runs out of fuel during a hard effort.
Your body’s sole energy source is a molecule called adenosine triphosphate, or ATP. Your body creates ATP in a number of ways. Because it’s in short supply, you constantly need to produce it. When you’re exercising, the demand obviously increases.
There are three primary raw materials for creating ATP.
- Glucose (blood sugar) and glycogen can be converted quickly. If your stores are topped off, the average person has about 90 minutes (1,400 to 1,800 calories worth) of these carbohydrates.
- Body fat converts to ATP much more slowly. You have fat in your muscles as intracellular triglycerides and almost everywhere else as adipose tissue. Even thin people have a huge supply of fat from an exercise perspective.
- Muscle protein can also be used for fuel. However, it is your body’s least-preferred fuel source. You can minimize using it by eating adequate calories, particularly carbs.
The harder you work, the faster you need ATP, so your body is going to favor glucose and glycogen.
When you ease off, your body switches to fat-burning mode because you don’t need ATP as quickly.
When you put in a hard effort (racing, high-intensity training, etc.) for longer than 90 minutes, and you’re not able to consume carbohydrates fast enough to refuel your glycogen stores, you run out and your body shifts to burning fat. But because fat can’t change to ATP as quickly, you are also forced to slow down. A lot.
This is bonking.
Some authorities say “hitting the wall” means running out of muscle glycogen while “bonking” means you’re out of both muscle and liver glycogen. But, from your point of view, they’re both pretty rotten — and your recovery and prevention plan are the same.
The Side Effects of Bonking
Bonking is temporary, and so are its unpleasant side effects and symptoms. When you bonk and continue to exercise, your body considers it an emergency, so it also breaks down muscle protein to give you as much fuel as possible. (But, slow down, weight-loss seekers. It’s not that easy.)
- It’s tough on your body. You can’t exercise as hard in a glycogen-depleted state. Put those two factors together, and it’s clear that you’re breaking yourself down more than you’re building yourself up, so it’s not doing you any good.
- Bonking causes serious physiological stress, which can put your immune system on high alert and result in inflammation.
- Your brain uses glucose as fuel. This means you can be mentally impaired when you bonk, which is especially dangerous when you’re on two wheels or in the middle of the woods during a trail race.
Bonking is training without glycogen. It is not the same as fasted-state training, during which you deplete glycogen stores.
Many endurance athletes like to train with low glycogen in hopes of forcing their body to better utilize fat stores. Although a potentially fruitful strategy, it’s different from trying to push through a bonk without feeding because you still have glycogen on reserve.
Bonking: Not Just for Athletes
Bonking happens to pro athletes and regular gym goers alike. The 90-minute glycogen countdown isn’t set in stone. There are times when your body may go way longer on existing stores and times when you’re lucky to make it past 30 minutes.
Causes of Bonking
What can cause you to bonk? Low blood sugar (hypoglycemia) is the culprit, but there’s more to it.
Common causes of bonking include:
- your diet
- how well-adapted your body is to burning fat
- the state of your glycogen stores
- how much glucose you have circulating in your blood
- the size of your muscles
You don’t flip a switch between glycogen and fat. (It’s more like a dimmer switch.) Even when you perceive yourself as exercising full-tilt, your body still taps fat stores to produce ATP, albeit not to the extent that it uses glycogen.
The 90-minute rule assumes your glycogen stores are 100% topped off, which is highly unlikely for both endurance athletes (who live in a chronic state of low glycogen due to their high volume of training ) and non-athletes (who also regularly short-shrift their glycogen).
If you’re eating at a caloric deficit or eating a low-carb diet, for example, it’s easy to bonk in far less than 90 minutes. So if you’re on a restrictive eating plan, take regular bonking as a signal to increase your daily calorie intake.
How Do I Know I’m Bonking?
You’ll know. When you bonk, you just feel done. It’s a feeling that, once you experience, you’ll never forget.
Symptoms of Bonking
Since your brain lacks glucose, bonking can leave you feeling anything from foggy and sleepy to disoriented and completely goofy. Here are some other signs and symptoms of the dreaded bonk:
- You feel weak, tired, heavy, or empty.
- You feel clumsy or uncoordinated.
- You shake, sweat, or tremble.
- You feel really emotional (think: anxious, irrational, or angry).
- You feel ravenous (but sometimes you’re not at all hungry).
- You’re doing something you know that you’re normally quite capable of — but it becomes inexplicably difficult.
Sometimes a bonk isn’t a bonk. Usually, when you bonk, you think you’re okay and then suddenly you crash. But, if you start your workout feeling meh, and it just goes from bad to worse, a lack of glycogen can certainly be a factor. You could also be tired, over-trained, stressed out, or having a bad day.
How Do I Prevent Bonking?
You eat. Bonking happens due to a lack of fuel, so the solution is to fuel up before you work out. How to do this depends on your situation.
If you’re preparing for a big event like a marathon, triathlon, or gravel grinder, your best bet is to increase food intake, especially carbs, for three days beforehand to top off your glycogen.
Chow down on bread, pasta, and burritos for a few days and then have a solid breakfast two to three hours before your event. (Check out “How to Eat Leading up to Your Big Endurance Event” for a more detailed discussion of carb loading.)
During-event feeding is also a good idea if you’ll be hitting it hard for more than an hour. Unfortunately, the human body can’t absorb as many carbs hourly as it can burn, so trying to replace what you’re burning as you’re burning it is a tricky business. (Here’s an article outlining the best way to go about it.)
If you bonk on a regular basis during training, try eating 50 to 100 calories of fast-absorbing carbs (e.g., a banana) about 10 minutes before you work out. That should boost your blood sugar enough to push you a bit further.
If bonking is a reoccurring issue, take it seriously. Perpetually low glycogen is bad news. In fact, there’s a theory called the glycogen hypothesis that claims remaining in this state can lead to overtraining syndrome, which is basically the serious exerciser’s version of chronic fatigue syndrome.
But fixing perpetually low glycogen is easy: Eat more carbs throughout the day (not just before exercise).
You may also want to consider adding a pre-workout supplement with beta-alanine for muscular endurance to your routine.
What Do I Do Once I’ve Bonked (and How Do I Stop Bonking)?
During a bonk, you’re just grinding your gears and running on fumes, so call it a day as soon as you can.
Unfortunately, it’s rare that bonking happens conveniently. You’re typically a couple of hours into a race, ride, run, or other activity that requires at least a couple more hours to get to a stopping point.
And let’s be real: If you’re 20.5 miles into your 26.2-mile marathon, you’re not gonna let 5.7 miles of senseless agony get between you and a finisher’s medal.
In these situations, the solution is simple:
- Consume fast-absorbing carbs ASAP. Given that you’re burning fuel as fast, if not faster, than you’re consuming it, this is one of those rare times when big sugar hits are a good thing.
- Keep consuming those carbs. Odds are that this bonk is going to hound you for the rest of your event. You might suck down a sports gel and suddenly feel restored, but you’re going to blow through those 100 calories pretty quickly, so don’t be so quick to burn that match.
- Slow down. Bonking doesn’t mean you have to quit, but you might not win this one. Soldier on at a reduced pace in hopes that you can modulate between fat and carbs before re-bonking.
- Force those calories down. Your glucose-deprived brain might suddenly find your fuel choices repugnant. But you need the carbs, so choke them down anyway, unless you have the luxury of choosing what you want to eat or drink.
- Eat or drink whatever you can (if that’s an option). Smart nutritional choices can take a backseat to surviving the next few hours. An electrolyte-balanced sports drink might be ideal, but many a bonk-savvy cyclist acknowledges the sugar, caffeine, and water trifecta of an ice-cold Coke as “survival in a can.”
Like it or not, bonking happens. And when it does, it’s awful. But as long as you manage it correctly, you’ll get through it.
Just think of it as good lesson on your body’s relationship with carbohydrates —and a great story to tell over linguine arrabbiata the next time you’re carbing up with teammates before for your next big event.