The average human body is 60 to 70 percent water, that's about 37 to 45 litres. As your body heats up, you start to sweat. "Generally males can lose about one to two-and-a-half litres of sweat per hour. For females it's generally a little bit less than that," says Cathryn Pruscino, a sports scientist from the Victorian Institute of Sport.
Studies have shown that one percent dehydration can cause major changes in body temperature, while two percent dehydration will drop your performance levels by a third! So to operate efficiently it's crucial we keep our fluids up. But what is best for fluid replacement? Plain old water or sports drinks?
The test
Let's see if sports drinks can help us retain more fluid than water.
Vaughn and Gerard are hard-core runners, both in their 20s and super-fit. Steve is a former English county cricketer now living in Australia and, like Michael, he's left his 20s well and truly behind. All three men plus Michael weighed-in so they could work out how much fluid they lost after they exercised.
In order to test the difference between the drinks, Cathryn wanted them to lose two percent of their body weight during their exercise period. "Then we'll get them to re-hydrate using either sports drinks or water. After the re-hydration period we'll collect all of the urine they excrete and have a look at who's retained the most amount of fluid," says Cathryn.
Steve and Michael were put on the bikes, doing a medium-intensity workout as befits men of their age. Meanwhile the young blokes, Vaughan and Gerard, were on the treadmill doing a high-intensity workout.
Vaughn and Michael replaced what they sweated out with water while Gerard and Steve chugged back sports drinks to make good their liquid losses.
After exercising for 40 minutes, Michael and Steve continue for another 10 because they're only doing moderate exercise, even though the sweat is dripping off them.
Sports dietitian Lisa Sutherland took all the men's pre- and post-workout weights and calculated that they all sweated out two percent of their body weight. "It's a great idea to weigh yourself before and after exercise because the weight you lose is the equivalent to the amount of fluid in litres that you lose. So if you lose a kilo of weight during exercise it means you've lost one litre of fluid," says Lisa.
The boys re-hydrated with one-and-a-half times the fluid they lost:
- Michael drank 1.5 litres of water
- Steve drank two litres of sports drink
- Vaughn 1.7 litres of water
- Gerard 1.9 litres of water
And as we all know, what goes in must come out. So it's also time for a urine sample to help Cathryn determine the results.
The results
Now, we're not looking for a big result here, in fact, the less urine the boys pass the better, because it means the fluid's stayed in their bodies, where it's needed most.
Steve was doing moderate exercise like Michael. After his sports drink he passed 240ml. Michael was on the water and he passed 255ml, so only slightly more than if he had also drunk a sports drink.
Which means that for a low intensity work out, water and sports drinks pretty much do the same job.
But if we look at the high intensity runners, Gerard, who was on sports drinks, produced 100ml. While Vaughn, who was on the water, passed 600mls! By drinking water he lost six times more body fluid than he would have had he chose the sports drink instead.
So for endurance or high intensity workouts, sports drinks are a winner. But why do sports drinks work so well? They contain important extras like carbohydrates and electrolytes to promote hydration because they're specifically designed for athletes.
But here's a warning — if you're drinking them as part of your everyday routine you'll end up putting on weight. "In the case of any sorts of drinks that have got carbohydrates or nutrients in them, if you're having too much of any of those sorts of drinks and you're not active then that can affect your weight and your body fat levels," says Lisa.
Hydration tips
- Make sure you're well-hydrated before you exercise — start drinking about two hours before.
- Top up your fluids during exercising
- Weigh yourself before and after. Losing a kilo is the equivalent of a litre of fluid, and you need to drink one-a-half times that to replace it.
If you're exercising hard and looking for peak performance then sports drinks are the go for you. But if like most of us you're into the moderate exercise, then water will hydrate you just fine and there's a little bonus with that — it's free!
Read more
- Sports drinks: the real facts
- Do our bodies need eight glasses of water a day?
- Can you overdo exercise?
- Diet versus exercise: which is better for weight loss?
- Common exercise mistakes
- Hassle-free exercise: get in shape the easy way
- Does exercise make you hungry?
- How much exercise should you do before burning fat?
- More exercise tips
Fast facts
- Can drinking water make you more resistant to a heart attack? A study published in the American Journal of Epidemiology found that women who drink more than five glasses of water a day are 41 percent less likely to die from a heart attack. For men, that figure jumps to 55 percent.
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