Slushies: the new weapon for exercising in heat

THANK YOU FOR VISITING SWEATSCIENCE.COM!

My new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Also check out my new book, THE EXPLORER'S GENE: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map, published in March 2025.

- Alex Hutchinson (@sweatscience)

***

Reading up on Australian sports research for an upcoming magazine story, I came across this little nugget about dealing with competition in hot conditions. The Aussies have been leaders in research on “pre-cooling” to lower body temperature before starting extended exercise in the heat. They introduced ice vests at the 1996 Olympics (which have since become widely used commercial products), and in 2004 brought big bathtubs full of ice-water to the Athens Olympic venues, actually immersing their endurance athletes shortly before their competitions.

I can’t imagine the pre-race ice bath becoming a really widespread phenomenon, for many reasons including logistical ones. But for the Beijing Olympics in 2008, the Aussies unveiled a new idea: slushies! As Louise Burke, head of sports nutrition at the Australian Institute of Sport, explained at a conference in Switzerland last fall, ingesting crushed-ice drinks cools the athletes internally — not just with the coolness of the ice, but with the energy of the phase transition as it melts. In tests, the Aussies found their athletes lowered their body temperature by about one degree Celsius by drinking the slushies (which were filled with “a mix of carbohydrates, electrolytes, and ice with other secret ingredients“). So the Australian Olympic team brought seven slushie machines to Beijing.

Other interesting points from Burke’s talk in Switzerland: The ice baths actually lowered body temperature more than the slushies, but this turned out to be a negative. In cycling time-trial tests, the athletes felt so good after the ice baths that their internal pace regulation was messed up, so they started too fast and paid for it late in the race. The slushie-fed athletes, on the other hand, started a little slower but ultimately performed better.

And the other reason the Aussies introduced slushies in 2008? They wanted to have something new, Burke says, to elicit a placebo response in their athletes.