A surprising new study by released by Canadian Brock University physiologist Dr. Stephen Cheung shows that losing even three per cent of body mass through dehydration has no noticeable effect on cycling performance. This puts it at odds with conventional wisdom, made famous by sports drink Gatorade, that optimal hydration is a key determinant of athletic success.
Cheung shared the results, with Dr. Mikel Zabala, a friend who heads British cyclist Alex Dowsett’s scientific team.
“He and I were batting around the idea over the winter of just how hot do we want to make the track,” Cheung said. “He was obviously worried that Dowsett was going to get really dehydrated. So I shared the data that I had, and perhaps it put his mind at rest.”
Cheung’s study was published in the Scandinavian Journal of Medicine & Science in Sports, getting much media attention yet leaving the world generally confused. Hydration is a modern obsession: We bring water bottles to the gym, strap them on our backs as we run, and sip from them while working.
Conventional wisdom is that by the time we feel thirst, it’s already too late.
So how can the new results be explained?
For one, Cheung’s research is just the latest in a line of studies over the past decade that have changed conventional thinking on the body’s fluid needs.
Rather than obsessively looking to replace every drop that you sweat out, it now appears that a little thirst isn’t nearly as bad as previously thought.
While drinking water during a workout is definitely not a waste of time, it turns out that how much you need depends less on absolute fluid levels in your body than what’s going on in your head.
Studies have found that in activities such as running, where it’s quite difficult to drink on the go, people tend to replace less than half of their sweat losses, far less than conventional wisdom would imply.
“Anyone who has worked in the field with athletes has probably realized years ago that a strict two-per-cent dehydration cut-off just doesn’t work,” says Dr. Trent Stellingwerff, a physiologist at the Canadian Sport Institute in Victoria. Stellingwerff, who works with elite marathoners, aims for 3 to 6 per cent dehydration, depending on weather and individual tolerance. The conventional rule is two percent.
One issues with earlier studies is that they didn’t distinguish between dehydration and thirst.
Authors of the studies deliberately dehydrated their subjects for hours using heat chambers and diuretics, then forced them to exercise without allowing them to drink. Understandably, performance suffered.
“When you drink, you’re also affecting your thirst, your perception, your psychology, your motivation,” Cheung says. The distraction and unpleasantness of wanting to drink without being able to slows you down, rather than an actual lack of fluid in your body.
While drinking lots of water is a great thing for the body and should be encouraged, new research is suggesting that being a little thirsty isn’t as bad as originally thought.
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