Use the two-minute rule. It takes about two weeks for your body to get used to warmer temps, so take a two-minute walk break for every five to eight minutes of running. As the summer wears on, your body will gradually become better at cooling itself and youll be able to get back up to speed.
Protect yourself. Keep cool with light-colored, loose-fitting running gear made of a noncotton technical fabric like Coolmax that allows sweat to evaporate. For sun protection, wear a mesh cap or visor and sunglasses that block UVA and UVB rays. Slather on some waterproof sunscreen (SPF 15 or higher) 20 minutes before heading out.
Time it right. Avoid running between noon and 3 p.m., when heat and humidity are worst.
Breathe easy. If theres a heat or air-quality alert for the day, stick to the treadmill. (Sign up to have air-quality updates sent to your computer or cell phone.) And stay hydrated no matter where you run. For workouts shorter than 45 minutes, drink 8 ounces of water 15 minutes pre- and postrun. For longer bouts, sip 6 ounces of sports drink every 15 to 20 minutes during your run to replace the electrolytes you lose through sweat.