Why do I always bonk out on the bike?

Wednesday, April 17th, 2024

Marine LENEHAN, Sports Nutritionist, Massage Therapist & Yoga Teacher

Cycling friends, I am guessing you have already heard the word “bonking out”. In the cycling world, bonking out is not a nice feeling at all. It literally feels like hitting a wall, a point of no return, impossible to carry on. This can simply be avoided with proper nutrition and fuelling. If you are planning to do some long cycle rides (over 90 minutes) or participate in an event or race, it is essential that you learn about bonking as it is best avoided at all costs.

What is bonking out exactly?

Bonking is a common word for hypoglycemia, meaning that you haven’t taken in enough sugar and have used up all your body’s glycogen stores, leaving you with abnormally low blood glucose levels. Your body can only store enough glucose (in the form of glycogen in your muscles and liver ) to last you for about 90 minutes of moderate exercise. Anything longer than this and you will need to take in some more fuel for your body to function correctly. That fuel is nothing else than carbohydrates.

What does bonking out feel like?

You know that feeling of seeing stars, pushing hard on the pedals and not getting anywhere? Well, that is bonking out. Although symptoms may vary, on the physical side you will generally feel extremely weak and tired and you may shake, sweat a lot and feel dizzy or light-headed. You may also have heart palpitations and will probably be very hungry. Bonking can also affect your awareness as the brain burns glucose to function and you may feel anxious, and emotional and find it very hard to focus and concentrate.

What to do when I bonk out?

Bonking out is running out of fuel. Just like if your car runs out of petrol on the side of the road, you need to top it up again. The body’s fuel is sugar meaning you need to ingest some simple carbs that your body can quickly absorb to raise your blood glucose levels again. Simple carbohydrates include food such as energy gels, jelly beans, fruits, honey, jam, white bread. More complex carbs, such as carb bars, take much longer for the body to process into glucose and so are best avoided at this point in time. If you identify that you are about to bonk and manage to catch it early, you should be able to carry on cycling at medium intensity while ingesting your simple carbs. However, if you have missed this window and are showing more serious symptoms, you must get off your bike and give yourself a bit more of a chance to recover because bonking out is usually a point of no return. 

What happens after a bonk?

It can take the body up to 24-48 hours to replenish your glycogen levels. After a bonk, you have to be mindful of your carbohydrate intake. After topping up on simple carbohydrates to bring you to the finish line or back home, you should focus on complex carbohydrates to replenish your glycogen stores. 

How to prevent bonking out?

Eat more carbs! Carbohydrates are often pictured as the bad guys out there but they are not. They are your best friend if consumed accordingly. Having a correct nutritional plan is the best solution to avoid bonking out. This means having a sufficient pre-ride breakfast snack and getting the correct amount of carbohydrates per hour on the bike. For bike rides more than 90 minutes long, you should be eating a minimum of 30g carbs per hour. That said, this is an average number and the body can need anything from 20 to 120g of carbs per hour depending on your metabolism, training session or event. What you eat on the bike matters, but what you eat off the bike matters even more. 

If you bonk out regularly on your bike or you often feel empty at the end of your training sessions, this is probably a sign that your diet is not suited to your training load and you are not benefiting from your training adaptations. The type, the quality and the quantity of food you put into your body can have a strong impact on your performance. 

Fed up, of not being able to perform at your very best? Book your personalized nutrition here : https://www.vivifysports.com/nutritionalcoaching