Carbohydrates are the main source of energy for cyclists. The body converts all carbohydrates to glucose and then releases it into the bloodstream. The lack (or absence) of glucose will severely impact your endurance performance, leading to bonking.
What is bonking?
Bonking is a term cyclists use to describe the situation where the body depletes all its glycogen stores. Sometimes it’s also referred to as hitting the wall.
Bonking usually happens on longer rides when you didn’t replenish your glycogen stores during the ride. Our body burns about 600 to 800 calories an hour on moderate-intensity rides. The actual figure varies individually and depends on time, intensity, and body weight.
Your body metabolizes glucose (vs fat) at a higher rate as intensity increases. The harder you ride, the faster your glycogen stores are depleted. If you aren’t consuming carbs on high-intensity rides that last more than 2 hours, you’ll run out of glycogen in your muscles and bloodstream, and your chances of bonking increase every minute.
If you ride at low to moderate intensity (50 to 60% FTP, recovery rides), your body metabolizes approximately 50% glucose and 50% fat. This allows you to go on longer rides (2 to 2.5 hours) before deploying your glycogen stores.
What does bonking feel like?
All experienced cyclists can relate to a ride where they bonked badly. Bonking is an experience you will never forget and never want to happen again.
Bonking comes without any warning signs. You can be okay one minute and feel like you can barely turn the pedals the very next minute. Depending on the individual, it can be a combination of many feelings such as feeling anxious, confused, dizzy, extremely hungry, having heart palpitations, or irritable.
You’ll know it when you bonked.
The longer this goes on, the worse it becomes. If you continue riding on, it could lead to headache, nausea, shaking hands and legs, and loss of focus, which is a danger to yourself and the group you’re riding.
It’s not uncommon to see that even pro cyclists bonked. Chris Froome was on the verge of bonking with 5km to go in Stage 18 of the 2013 Tour de France that his teammate Richie Porte had to get a gel from the team car for him. This move outside the feeding zone cost Froome a 20 seconds time penalty and a 200 Swiss franc fine.
Matthew van der Poel famously bonked 13km to go in the 2019 Road World Championships. It was due to a combination of a long, hard race in cold and wet weather.
How to prevent bonking
The easiest way to prevent bonking is to ensure your glycogen stores are full before the ride and constantly replenished throughout the ride. It’s often easier said than done, as experienced by many cyclists before.
When you’re on the bike, eating and drinking is not the first thing you have on your mind. Plus, eating while pedaling is a skill that needs practicing.
Figure out how much carbs you need
Everyone is different, and you need to find out what your body needs and can handle. Use your training rides to experiment with fueling schedules (time intervals, amount of carbs, hydration) and observe how you felt.
This will be an ongoing process as your body adapts. The more you know about your body, the lower the chances of bonking.
Prepare your fuels
Place the bars, gels, and snacks in your jersey back pockets or handlebar bag. Make the snacks easily accessible by cutting open the top of the wrapper. You don’t want to be messing around with the wrapper while riding at 25mph.
Simple carbohydrates are the best for mid-ride refueling. The more complex the carbs, the longer it takes for the body to digest. Glucose and fructose, found in energy gels, can be fully digested within 15 minutes of consumption.
Our body can digest 60 to 90g of carbs every hour with a 2:1 glucose to fructose ratio. The glucose goes directly into the bloodstream, while fructose goes to the liver and is converted to glucose. Ingesting glucose and fructose together will lower the chances of experiencing GI distress.
Load up the carbs before a big ride
Cyclists often refer to this as carbo-loading. It’s a process that starts 2 to 3 days before a big ride where you stock up your glycogen stores in your liver and muscles. The aim is to eat conventional foods in your usual way to minimize GI distress.
It’s not uncommon that many cyclists often overload themselves with more carbs than they need. Carbo-loading is not a reason for you to overeat, believing that you will burn them off during the ride and prevent bonking.
Focus on nutrient-rich foods high in carbohydrates such as pasta, rice, potatoes, fruits, and vegetables.
“Every day, you need about 7-10g of carbohydrate per kilogram of body weight to keep glycogen fully topped up.”
Dr Karen Reid, PerformanceFood.co.uk
Plan your refueling ahead of time
Most cyclists plan their riding routes but often overlook their refueling plan, which is one of the main reasons for bonking.
Take a close look at the route and terrain and pinpoint the locations and/or time you’ll need to start refueling. It can be a roadside refuel while waiting for the bunch to regroup, a mid-ride cafe stop, or refueling while on the move.
If it’s a hilly terrain that requires more effort, plan to refuel earlier. If it’s flat terrain, you might get away with refueling later.
Stick to the refueling plan
Now that you have the plan, it’s time to execute it. It’s easy to forget about refueling when riding, especially when the pace is high. All we focus on is the wheel in front.
Set reminders on your route, or have an elapsed time field on your bike computer to remind you to refuel.
Never skip a refuel even if you aren’t feeling hungry. Bonking often happens without any signs, and it’ll be too late when it happens.