The latest endurance booster might give you a headache. A new study published in the journal Medicine & Science in Sports & Exercise found that runners who drank a ten-ounce slushie (made of blended ice and sugar water) were able to run 19 percent longer before exhaustion in 93-degree heat than a control group drinking the same ice-cold beverage in liquid form. Because a slushie is mostly bits of ice suspended in syrupy water, it can stay fluid below 32 degrees and drop your core temperature by half a degree more than 33-degree sugar water without ice. "While that doesn't sound like much, half a degree will make a big difference in terms of your performance, especially at the elite level," says study co-author Paul Laursen. To make your own pre-workout slushie, puree ice in a blender with just enough syrup (like Torani; $8; torani.com) and sports drink to make it go down easy. Drink about eight ounces 30 minutes before the event--and be prepared for the brain freeze.