It’s no surprise that it’s hard to exercise on a hot day. You go slower. An easy workout is grueling. You have no endurance.

The reasons are also no surprise. Blood is directed to the skin for cooling, which means it is diverted from working muscles. The hotter it is, and the harder the effort, the harder exercise becomes. Eventually, you slow down or stop, unable to go on. Exercise physiologists debate why. It could be that muscles are starved for blood. It could be that the brain gets too hot. It could be that the heart eventually can’t beat fast enough to satisfy all the demands for blood. But even without knowing why, researchers have found they can delay the time to utter exhaustion by getting people a bit chilled before they start.

So companies sell devices, like cooling vests to wear before exercise, or even portable cold baths for prerace immersion. Researchers have tested methods like having athletes swim for an hour in cold water or sit in a cold room or stand in a cold shower. No matter what the method, companies and researchers report a precooling effect.

The problem is that none of the methods are easy, cheap and practical. But now, a New Zealand endurance athlete and exercise researcher says he has found a method that is. All you have to do is drink an ice slurry, also known as a slushie, before exercising. In a new study, he reports that young male recreational athletes who drank a syrup-flavored ice slurry just before running on a treadmill in hot room could keep going for an average of 50 minutes before they had to stop. When they drank only syrup-flavored cold water, they could run for an average of 40 minutes.