Drink It or Pour It?

Picture by richseow from Flickr

You've often seen the elite athletes pour water over their heads to cool themselves while racing. So is it really better to pour the water over your head on a really hot day or is it better to drink it?

Picture by richseow from Flickr

Well, here are some numbers obtained in the paper referenced below. In the article, kilojoules and calories are a measure of the energy dissipated as heat. The heat is produced as a by product of muscular exertion, which is powered by the energy from food.

Drinking a 250 mL cup of water at just above freezing ( 1 degree Celsius or 34 degress Fahrenheit) helps you get rid of 39 kJ of heat (about 9 calories).

If you drink a slushie that is half water and half ice, it's better as the ice can melt inside your body. A 250 mL slushie will get rid of 81 kJ of heat (or 19 calories).

Pouring a 250 mL cup of water on your head will get rid of 607 kJ (145 calories) if the water can be spread around your body surface so it all evaporates rather than dripping to the ground. Yes, evaporation is a great way of dissipating heat.

But, that's a very big "if" in my opinion as it's hard to pour a bottle over your head without spilling any water. although the authors suggested that even if you spill 85 percent of the water you still get more heat loss from pouring than from drinking the slushie.

Do take note that the water you pour over yourself has to evaporate. If it's a hot and super humid day like it always is in Singapore where your sweat is dripping like there's no tomorrow you won't have the water evaporating. Pouring cold water over your head probably makes your feel cooler (and hopefully better) for a while.

It works best when the weather is dry and breezy so that your sweat can evaporate. (Local runners who race overseas take note).

My suggestion would be to drink when you need and pour some cold water over your head and neck too to cool off if you don't mind your running shoes getting a little wet.

Best to be sure it is water and not a sports drink that you pour over yourself. Yes, I've accidentally poured 100 Plus over myself before when I was racing, so beware.


Reference

Morris N and Jay O (2016). To Drink Or To Pour: How Should Athletes Use Water To Cool Themselves? Temperature. 3(2): 191-194. DOI: 10.1080/23328940.1185206.