We are often told we need to drink more water, but less often told why. I’ll keep this short and to the point. Basically, we’re made of the stuff, it accounts for approx. 60% of our body weight. Our blood is made up of approx. 50% water, and our brain and heart are over 70% water!
Every day we lose water, some of this loss is pretty obvious, like going to the toilet and sweating. But some water loss is a lot less obvious. The average adult will lose 250-350ml of water just through breathing every day, this is without exercise. We’ll lose a further 350ml (approx.) per day through our skin, and that’s WITHOUT any visible signs of sweating. Of course, as soon as you start training those numbers are going to go through the roof, once you start sweating and breathing heavily, you can quite easily lose 1 litre per hour.
The majority of the water in the blood is in the blood plasma (which is over 90% water), so as we lose water, blood plasma reduces and our blood becomes more concentrated/thicker. This causes the overall volume of blood to be lower and therefore blood pressure reduces. To try and maintain blood pressure our blood vessels constrict and our heart has to work over-time. I’m not trying to scare you, the human body is pretty awesome, and as long as you rehydrate, it will sort itself out. However, I’m sure you can appreciate that during a training session, event, or race, none of this stuff is ideal! Even very mild dehydration will therefore certainly reduce performance.
We also lose electrolytes through sweating, these are essential minerals that are involved in transmitting electrical impulses through our bodies to do things like contract our muscles and make our heart beat.
So it’s really important that we are replacing this loss of fluids and electrolytes during and after training. I encourage all of my riders to drink regularly when on the bike and aim for roughly 500ml per hour, and more if they’re thirsty. This is especially important during the winter months when we feel less thirsty because of the cold weather. When riding in really hot weather you could quite easily double this. When I was out in Mallorca earlier this year I drank over 5 litres during a 5-hour ride and would have drank much more had it been available to me.
You are probably very familiar with the electrolyte replacement sports drinks that are available, and if you’re riding in hot temperatures and for multiple hours these can be extremely useful. However, if just training for a 1 hour session, they’re just not needed, providing you drink water and eat a healthy balanced diet, you will get all the electrolytes you need from your food.
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Dan Small, Mountain Goat Coaching
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