Match your workout to the weather by slowing down during exercise and seeking shade afterward. Check out these tips to beat the heat:
Pick sunrise or sunset. Your best bet on a hot day is to head out in the early morning or evening, when your shadow is twice as long as you are tall. According to The Weather Network, exposure to direct sunlight can increase how hot it feels by as many as 15 degrees.
Mind the 90-degree line. When the mercury is above 90 — the temperature of the surface of your skin — you'll gain heat from the air around you, and your body heat will have nowhere to go. At that tipping point, you'll sweat more and your body temperature will rise rapidly, making you more susceptible to heat-related illness. Go easy or go inside.
Bottom's up! Stay well hydrated throughout the day by drinking at least eight cups of water, then make sure to have eight to 12 ounces about 15 minutes prior to your run. Sip three to eight ounces every 15 or 20 minutes as you run, and don't forget to drink after your workout.
Field the heat. Rule number one before you run: Check the heat index — a combination of air temperature and humidity — rather than your thermometer to get a better idea of the real feel outside. (At 70 percent humidity, an 29-degree day can feel as if it's 32.) Also, the more humid it becomes, the less your sweat evaporates from your skin, meaning your body's key cooling mechanism is disabled. To run sun smart, determine the day's heat index (see the Weather Network), then follow the guidelines below.
Higher than 40 degrees: No-brainer: Move it indoors, because you're at severe risk of heat-related illness, including heatstroke. (A 38-degree day with just 40 percent humidity will feel like 43 degrees.)
Between 33 and 39 degrees: Exercise early in the morning, when it's coolest, and keep your workout superlight.
Between 27 and 32 degrees: Keep workouts shorter than usual and moderate.