Bonking – and how to avoid it

'Bonking' can really spoil a great day out on the bike, but what exactly is bonking and how do you avoid it?

Refuelling during cycling to avoid the bonk

Er, this is NOT what they mean when they say 'refuelling' ... Photo: Yun Huang Yong

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What is bonking?

This term 'bonking' refers to extreme fatigue that’s triggered by hitting the wall or the ‘bonk’.

It's a condition that hits even the best cyclists at one time or another – Chris Froome was famously penalised during 2013 Tour de France after Richie Porte picked up some energy gels for him inside the last 5km of Alpe d'Huez. Risking a penalty was worth 'avoiding the bonk'.

Bonking is primarily caused by the total depletion of stored glycogen in your body. Once you reach this state, in medical terms known as hypoglycaemia, you will experience many detrimental physical and psychological effects, which may include:

  • Loss of muscle strength/power
  • Loss of co-ordination
  • Muscle tremors and/or cramping
  • Dizziness
  • Visual or auditory hallucinations

It would be bad enough if you experienced these symptoms just walking around but when you experience them on a bike, the danger is multiplied.

How do you know when it is happening to you?

While bonking most commonly affects road cyclists, it can also happen to leisure and touring cyclists who have headed out on long rides without taking enough food or water with them, or who haven't factored local restaurant or boulangerie closing times into their French itinerary (we rode for what seemed like HOURS to find a solitary tarte au citron after we left one lunch run too late on our Velo Francette ride). 

See here for suggestions to help you eat well on the road in France.

Usually the first sign that you're in trouble is that you are not producing power for the effort you're putting in, and every movement just seems to be more difficult than it usually is.

You may also feel light-headed, have reduced peripheral vision, experience some degree of temporary hearing loss, see spots or colours, or just generally feel a lot weaker than you should.

This is different from merely being tired or fatigued from exercise. When you have that experience, it doesn't feel bad in the same way that bonking does. Once the bonk sets in, you won't really feel like yourself.

Yet bonking is actually a voluntary condition; it's just that most people are unaware of it or downplay the possibility until it actually happens to them.

Preventing the ‘bonk’ is not necessarily a difficult task as just by being aware of the danger of it, you are already past the first major hurdle. Because the bonk is caused by glycogen depletion, the key to preventing it lies in managing your glycogen stores. How you do that depends a bit on what you'll be doing.

How to prevent bonking

If you are just training, and not too intensely, then the best prevention strategy is to make sure you are taking in a decent amount of carbohydrates during the ride.

If, however, you are preparing for serious competition, then glycogen loading is recommended. You can do this by really loading up on carbs during the 2 to 3 days preceding the event, and then of course you also need to be taking in plenty of carbs, electrolytes and water during the actual competition.

While out on the road, sports energy drinks with glucose or sugar, plus electrolytes are also a good idea. Energy bars and gels are generally the foods of choice for road cyclists as they are easy to carry and handle. In fact, for a long hot ride, they can be as important an accessory as your spare inner tube, pump and tyre levers. When deciding on which bars, make sure you don't choose low-carb versions.

Muesli bars, cakes and dried fruit can also make great on-road nibbles. (See here for more suggestions on how to eat well while cycling in France).

Beating the bonk with an energy bar

Alexi Ueltzen captioned this photo on Flickr: 'Happiness is a warm Powerbar.'

In the case of both training and competition, it is also a good idea to consume a high carbohydrate intake 20 to 30 minutes before participating.

Bonking can be a scary sensation, but it is preventable if you anticipate it and plan for it, and maintain a steady carbohydrate intake during your ride.

If you find this article or anything else on Freewheeling France useful, please tell your cyclist friends about us (I say 'us' but it's usually just 'me').

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