Key points

  • A drop in weight of just 2% (from water loss) can lead to a 20% drop in performance
  • For a 70kg (11st) person that is approximately 1.4kg
  • We typically lose 1-1.5 litres of water per day via breathing and perspiration (1-1.5kg water) without exercise
  • Hydration is more than just water

If you lose just 2% bodyweight through water loss, you can get seriously fatigued and lose up to 20% in mental or physical performance as well as a drop in mood. That’s how important water is.

Hydration in perspective

For someone weighing 70kg (11st) that equates to roughly 1.4kg of water loss in a day. We typically lose somewhere between 1-1.5 kg of water a day just through breathing, perspiration and other bodily functions (and assuming no exercise and a reasonable climate). 

Or to put it another way; losing that 2% is an everyday occurrence for most people. We tend not to notice it because we top up by eating and drinking during the day. But it’s important to realise just how easy it is to become dehydrated without realising. We are continually losing water so we need to be sure we’re taking it in regularly (ideally every hour). Not all of it has to come from drinks and hydration is about much more than just water; but it’s a good starting point.

Your body as regulator

Your body continually monitors your hydration levels by checking water and sodium levels in your blood; as you lose water your blood volume decreases and it becomes more ‘salty’. Your body responds by making your kidneys filter more water back into your bloodstream (which is why urine gets darker the more dehydrated you are) and triggering a feeling of being thirsty. You drink water, your blood volume goes up, your blood gets less ‘salty’ and everything returns to normal. 

Like most bodily functions, this happens all the time on a kind of loop called ‘homeostasis’. But be careful; fluid loss, especially sweating, can also produce loss of electrolytes (sodium and potassium) and that can bring its own problems, even more so if you just take in water and dilute your electrolyte levels too much. 

Achieve peak performance

Popular advice says we should drink “8 glasses of water per day”; but as with all generic nutrition advice, it’s oversimplified and not that useful. Equally; just waiting until you feel thirsty doesn’t always work. It’s very easy to supress that feeling when you’re focused on something. 

So here’s a plan

  • A few hours before training eat a decent meal (we’ll discuss that more in future posts) and just before training drink enough water to feel you don’t want any more right now. That may be a small glass or whole bottle, whatever works for you. 
  • On an indoor training session of just a couple of hours you can get away with just drinking water during your training and having a decent meal afterwards. 
  • If you’re out for the day doing some big sends; use isotonic drinks (like Lucozade sport or sports gels and add a small amount of protein every 2-3 hours to maintain optimal performance.

Proper hydration is crucial and easy to get wrong; so next time you’re feeling fatigued, hit that mid-afternoon crash or you’re struggling to send a problem – stop and have a drink. Your body will thank you for it.

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