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Dehydration during sporting events doesn’t hurt performance: study

shutterstock_215767075.jpgDehydration may not be the threat to sporting performance that athletes have been led to believe, a new study suggests.

May 12, 2015  By Helen Branswell The Canadian Press

For several decades the mantra in sports has been “hydrate, hydrate,
hydrate” – a tenet based on the belief that not replenishing the fluids
and salts sweated out during exercise is both bad for athletes’ health
and their success.

But a novel study conducted at Brock
University in St. Catharines, Ont., found that competitive athletes
performed equally well regardless of whether they were hydrated or
dehydrated, thirsty or not experiencing the sensation of thirst.

Lead author Stephen Cheung said the dehydrated athletes did have higher core temperatures and heart rates, though.

body is more stressed with dehydration. So no questions there. But the
performance was not different. And also none of these competitive elite
athletes were at any (health) danger,” said Cheung, a professor and a
Canada research chair in environmental ergonomics.


The public should not interpret the results to mean that there is no need to rehydrate, Cheung insisted.

“Obviously dehydration is bad at a severe level,” he said.

But the study results do test the notion that people need to constantly top up their fluids while exercising, he said.

is the common message that we are bombarded with. And I’m suggesting
that there are certainly some cases where hydration is not as critical
as it has been made out to be.”

In the 1990s, the American
College of Sports Medicine issued a statement declaring that people
exercising should replace all the fluids they were sweating out. In 2007
that position was modified to suggest people should not allow
themselves to lose more than two per cent of their body weight through
sweat during exercise, Cheung said.

In Cheung’s study, 11 competitive cyclists and triathletes were put through their paces at 35 C.

were hooked up to intravenous fluids. Some received a volume of saline
(salt water) equivalent to what they were sweating out, while for the
others, the IV was not turned on. Neither the cyclists nor the
researchers knew during each trial who was being hydrated and who was
not getting replacement fluids.

As well, some riders were allowed
to rinse their mouths to alleviate the sensation of thirst while others
were not. The idea there was to see whether the sensation of thirst had
an impact on how well the athletes were able to perform.

the course of four different trials – conducted a week apart – the
researchers gathered data on four conditions: hydrated and not thirsty,
hydrated and thirsty, dehydrated and thirsty, and dehydrated and not

In the trials, the athletes cycled for 90 minutes,
during which time their fluid levels were either topped up or not. Those
who did not get replacement fluids had lost between two per cent and
three per cent of their body weight – more than the sports medicine
college recommends.

After a 10-minute break they were put through
a 20-kilometre competitive time trial in which they were told to cycle
as hard as they could. Their performances were measured every two

When it came to performance, there were no statistically significant differences between the four groups.

can, for a short term, tolerate dehydration and still perform very
well,” Cheung said, noting the findings support the practice among elite
marathon runners, who often drink little during a race.

The study is published in the June issue of the Scandinavian Journal of Medicine and Science in Sports.

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