As summer approaches, running in the heat can become grueling as your endurance drops while the temperature rises. New research out of Australia proposes a simple method for increasing workout endurance on a hot day: drink a slushie first.
The main factor thought to decrease endurance in the heat is the faster rise in core body temperature. Once your core temperature reaches a certain point, your body protects against heat stroke, shutting down your exercise capacity. Precooling is a good way to extend the time it takes to reach such core temperatures, thus prolonging exercise.
Cold water or sports drinks are obviously good ways to hydrate and keep cool before exercise. The researchers tested the effects of drinking either cold water or an ice slurry, also known as a slushie, before running in hot conditions. The runners who had the slushie were able to run 10 minutes more than those who drank cold water (50 and 40 minutes, respectively). Slushie drinkers also had lower core temperatures, both before exercise and through about 40 minutes after starting.
Why might a slushie be better than cold water? Two reasons. First, the ice made the slushies about 30-31 degrees F, lower than the 39-40 degree temperatures attained by drinks in your fridge. Second, as opposed to a cold drink with ice cubes, a slushie involves actually ingesting the ice. The phase change of ice (solid) to water (liquid) requires a lot of energy. When this phase change happens in your stomach, it diverts that energy, or heat, into the stomach and away from your muscles. This further pre-cools your muscles before exercise.
So next time you go for a run on a really hot day, consider having a slushie or plain water with lots of finely-crushed ice about 30 minutes beforehand. And if the heat does get to you, always be safe- take a break and cool down before starting up again.