Bonking and cycling don't mix

Andy Henderson describes a potentially dangerous condition you might encounter, what to do about it and ways to prevent it.

In cycling we talk about 'bonking', in running they talk about 'hitting the wall', the medical term is Hypoglycaemia. Your body runs out of readily usable fuel. You are close to fainting on the bike, with all the dangers that could result. It's a condition that usually happens on rides that are demanding because of length, hilliness, weather, or maybe all three. Or, maybe, you just ride too long without stopping.

When you get close to bonking there are a number of symptoms. The main one is extreme weariness. You might be pedalling on the flat but you feel like you're going up a steep hill. Any effort is difficult - even just turning the pedals. I get a nasty feeling in my stomach - a lot like nausea. You feel like you can't carry on. The feeling is hard to explain but, once encountered, it is unmistakeable. It can come on suddenly without warning. Although I've not encountered them, sites also list symptoms including:

  • Loss of focus
  • Loss of vision or impairment
  • Cold flashes throughout the body
  • Shaking
  • Sweating
  • Heart palpitations

Please take action...

... if you see someone weaving for no reason and they're complaining of extreme tiredness, maybe they're even incoherent. They might be about to faint.

The problem needs to be tackled, and the rider might not be in a good state to recognise what is happening.

You need to stop and get off the road as soon as it is safe to do so. Ideally, someone should stay with you. This is not a good time to be on your own.

When you bonk, your body has got very low on glycogen. It has little left to run on - and wants to shut down. You need some quickly-absorbed carbohydrate. I carry fruit pastilles (not the sugar-free kind). Energy gels will also help (but I can't stand them). A can of coke will also work. Basically anything with easily-absorbed sugar. If you’re lucky enough to bonk within a stone's throw of a café then that’s another option.

Obviously you shouldn't try to get going again until you've given your body time to get some glucose into your bloodstream. When you do get going, keep another rider behind you (if possible) looking out for a recurrence. Take it very easy. If you are a long way out, consider finding a railway station or calling for a pick-up. Otherwise, go straight home.

Avoiding the condition

If you Google "cycling bonking" you'll find plenty of good advice some of which does not apply to the type of cycling we do. The basics are simple:

  • Fuel up before you start the ride
  • Top up your energy as you go
  • Drink plenty

Giving blood...

... can result in similar symptoms to bonking. Although blood plasma is quickly regenerated, your red blood cells (which carry oxygen around the body) take longer. And that time increases with age. In effect it is reverse EPO. It's not the same condition as Hypoglycaemia, but it has similar effects.

Have a decent breakfast that includes slow and fast release carbohydrates. Starting a demanding ride on an empty stomach is asking for trouble. Many use porridge with sugar or syrup. If it's a long ride you'll need to have a decent lunch (not a lot of fatty food, however, that can slow glucose absorption). I know some riders have a pint of coke (virtually liquid sugar).

Take something with you to top up your energy as you go. And take every opportunity to drink - small, frequent sips are best - gulps of water tend to trigger the 'pee response'.

Some use energy gels. I use this stuff added to my water bottles. That's a triple whammy:

  • Hydration
  • Energy supplement
  • Replacement of electrolytes (lost through sweat)

In summary

Please don't let any of the above put you off distance riding. As long as you are comfortable on your bike and you are aware of your body's needs, bonking won't be an issue for you.

Take care of your fellow riders and be on the look-out for problems they might be having.

And enjoy the ride.