You’re pedaling along, feeling good, when all of a sudden you’re dropped from the back of the pack. You try to recover, but you’ve got nothing left. You can’t turn the pedals even one stroke more, and even the slowest of speeds feels like pure torture. Your legs turn to cement, concentration becomes difficult and full-body fatigue takes over.
This is the bonk. The good news is, with a little planning, you can avoid this complete disaster on the bike. Here’s how it’s done.
The Bonk Explained
Scientifically speaking, a bonk happens when you deplete all glycogen stores from the body. During long rides or those of a high intensity, your body rapidly burns glycogen and depletes all of your reserves.
Research commonly agrees that the body can store about 300–400 grams of glycogen in the muscles and about 120 grams in the liver. During your ride, this translates to about 1,200 calories of energy. If you don’t replenish this on the bike, you’ll deplete your reserves fairly quickly; at a moderate intensity, most cyclists will burn about 800 calories an hour.
If you aren’t consuming carbs on a ride, you’ll burn through your glycogen in about an hour and a half. After that, you’ll use fat for energy instead — and since the body doesn’t convert fat to fuel as efficiently, you won’t likely have the energy required to pedal.
What You Can Do
While it makes sense that to maintain glycogen stores all you’ll need to do is eat, unfortunately, it’s not quite that simple. This is because the amount of carbs your body can absorb is limited to around 60 grams per hour — meaning that eventually, depending on distance and intensity, it’s going to get harder to keep up.
To avoid the bonk for the duration of your ride, you’ll need to focus on three things:
- Fueling on the bike
- Topping off your reserves before a ride
As a general rule, you should either ride long and slow or short and hard. Extending yourself beyond what you’re capable of in the beginning of a race or long training ride is setting yourself up for failure as the miles start to add up.
To avoid bonking, pace yourself by riding at a low intensity during efforts lasting longer than two hours. If you’re going to ride at a high intensity, keep the effort to two hours or less.
On the Bike
Your body can process 60 grams of carbohydrates per hour. Anything more than this and digestion will become more difficult, which can cause cramping and force the body to use even more energy to process what you’re putting in.
What this means in practice is one sports drink and one energy bar per hour. Packing a variety of food is usually a good idea, and energy gels are another great option. Depending on the brand, two energy gels will usually equal one energy bar. Gels are generally helpful when you need to get glycogen into your system quickly because they’re easier to digest and process into energy. For this reason, it’s also a good idea to save your gels for when you increase the intensity, such as when you head up a particularly tough climb, and use the energy bars when the intensity is lower.
Also keep in mind that while you’ll only need one sports drink per hour for energy, you’ll still need to drink plain water to satisfy your hydration needs — which can range from two to four 500 ml bottles per hour in hot weather.
If you begin a ride with your glycogen stores at a deficit, you’re increasing your chances of bonking. When you prepare for a century ride or other long-distance event, carb loading might be something to consider, and it should be done two days prior to your event.
For regular training rides, a pre-ride meal of complex carbohydrates consisting of about 200–400 calories should be sufficient to top off your liver glycogen storage before you ride. Ideally, you’ll also want to give yourself about three hours to process the meal before you head out the door. Anything more than this, and you’ll be overstuffing yourself for no reason since you won’t be able to change your muscle glycogen storage a few hours before a ride.
If your ride or race is really early in the morning and eating three hours before the event isn’t feasible, top off liver glycogen (what you’ll use as energy first) by consuming a sports drink or gel about 10 minutes prior to the start. This will top off your storage and provide enough fuel for at least the first hour of your ride. After that, you’ll use muscle glycogen and the carbs you consume on the bike.