Should You Bonk During Training?

Ahhh…. Bonking…

If you’ve ever bonked, then you know that feeling. It’s not pleasant.

But when it comes to training, is bonking just reflective that you’ve put in an awesome amount of effort and something to feel smug about?

To bonk or not to bonk… That is the question

Bonking what?

Before we go any further, let’s go over what bonking actually is.

Our muscles and basically all our organs inside our body run on something called glucose, which is a basic carbohydrate. Our body maintains a pretty tight control of glucose in our bloodstream to make sure that our organs are provided with it constantly.

Our body has a store of glucose, as glycogen, in our muscles, and it converts glycogen into glucose to then be used in our cells to create energy.

Now we’ve only got a limited supply of that glycogen and we use it at a faster rate when we exercise. When we get to a critically low threshold of glycogen, we bonk. That’s the term we use for going to such a low level of glycogen that we can’t support exercise at the same intensity, and generally, it feels pretty dreadful.

So that’s bonking in a nutshell - running out of your stored carbohydrates and not being able to fuel your exercise. When it comes to moderate-high intensity exercise, if you’re well topped up to start with you have about 90 minutes worth of glycogen stored up to use.

How does bonking affect performance?

When we bonk we get slower, no two ways about it. Think of it like a car. If you run out of petrol or diesel, or your battery runs out for any of you driving electric vehicles, nothing more is gonna happen. You might be able to make it jolt down the road a bit or go really slowly, but you’re not going anywhere quickly. You’ve got refuel or recharge before you’re ready to go again.

Exactly the same is true for bonking. You’re going get slower and you’re going have to wait a while until your systems are back online.

So bonking is definitely bad for racing and performance, but let’s bring it back to the topic of today’s post and whether it’s worth doing in training.

The answer is that no, it’s not something you should actively try to do. In fact, you should actively try to avoid bonking in your training.

Aim to feel good in your training, not flat and deflated

There are numerous reasons for that.

Firstly let’s talk pure performance. The point of your training sessions is to create stimulus to improve. If you’re trying to hold ‘X’ pace or power, bonking isn’t going to help with that. You’re going to get slower, and so you’re not actually creating the stimulus that you need to or completing your session as planned.

But it’s far more than that too. Our glycogen stores can take anywhere between 24-72 hours to fully replenish once depleted... So if you’re bonking and then have a training session later that day, or even the next day, you’re not going to perform as well as you can for those either. It’s a bit of a viscous circle here - you ruin your first training session, then that impacts your next one and you basically don’t ever catch up or replenish your glycogen stores and as a result your training suffers.

Bonking and mental fatigue

But it’s also important from a mental point of view. If you’ve properly bonked before then you know that feeling that I’m talking about. It genuinely feels awful, and it takes some time to recover from it. So again it’s likely this is going to disrupt your other sessions too, and perhaps even just daily life.

Because of all these reasons, you should make it your goal to stop bonking being the limiting factor for your training.

Instead you should be aiming to complete your sessions as planned, with proper nutrition, proper recovery and make consistent progress.

How to prevent a bonk

So now you know that it’s not good to bonk so lets quickly talk about how to stop it, and there’s 2 main areas to talk about.

The first is to understand your training sessions and fuel appropriately before and during them. If you know you’re going out on a big training ride or long run then have a good meal beforehand full of carbohydrates, and then consume carbohydrates during your workout too. Generally the earlier the better because you’re giving your body a chance to absorb and then use the carbohydrates. For training sessions 40 grams of carbs per hour is probably sufficient, but if it’s higher intensity then you might need to increase that.

A bit of prior planning here goes a heck of a long way so start factoring nutrition into your sessions.

The second thing is to consider your overall diet and intake of carbs. Carbs really are king for performance, so you need a sufficient amount of them in your diet. The exact amount will depend on training intensity and volume, but in general triathletes should be consuming a minimum of 3 grams of carbs per kg of bodyweight per day. That might go up to about 10g/kg during high volume periods.

You need to replenish the carbs that you use up and ensure you're giving yourself the best chance of recovery and then performing again for the next session.

So, fuel up and enjoy your training