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Sports Hydration: When should you drink?


Posted by Cags R under Nutrition on 21 April 2012 at 8:00 AM

This week Sam Murphy wrote an article for The Guardian titled How much water should you drink during a marathon? 

The article addresses the necessity of runners planning their water intake to a prescribed measure compared with drinking when you are thirsty.

Too often we look for an exact science when it comes to sport, the fact is each athlete is different and environmental conditions can change the amount of water you need to drink.

The thirst feedback loop is initiated when the sodium levels in the blood rise as water is lost through sweat. You can roughly measure how much you sweat by weighing yourself before and after exercise; this 'sweat test' can give you a rough guide of how much water you have lost during exercise.

Where the misunderstanding seems to have taken place is that people assume if they sweat that much in the hour of exercise they will have to drink an equal amount to rehydrate themselves within that hour. Water should be taken on board to rehydrate yourself but it is not necessary for it to be an hourly 'water-lost-through-sweat/water-taken-on' ratio.

If you look at pro-runners at a marathon you'll find that they won't be stopping at every water station and certainly won't be gulping down 500ml in one go:

"A race winner will typically lose three to four kilograms in a marathon, and they hardly drink at all - you'll see they sip water or sports drink every few kilometres, but that's it. There's none of this 'one litre per hour' doctrine that others are following."

Dr Ross Tucker

For years 2% dehydration has been quoted as a dangerous level, thus athletes were encouraged to drink before they feel thirsty in order to maintain their hydration levels. This theory has been filtered down from elite to beginner athletes and has lead to some going over-board on staying on top of their thirst.

The danger of this is it may cause Hyponatremia - a condition caused when the blood is too dilute and sodium levels are too low. Read more about Hyponatremia here.

I spoke to Julian Goater - author of The Art of Running Faster - on the subject of overhydration in athletes, he agrees with the 'drink when you're thirsty' method: 

"For endurance-event  athletes, worrying about hydration is like driving with a full tank of petrol all the time - the car can run just fine with a half tank! In fact if you start a race full of water it can be very uncomfortable, sloshing around as you run."

Julian advised making use of water aid stations on long runs but only sipping the water and avoiding gulping down too much. Every runner is different but listen to your body, if your mouth is dry, drink, if you don't want to drink then you probably don't need to.

So Tribesports, do you drink when you're thirsty or follow a planned out drinking schedule?