There’s good and bad news about running in the heat. First, the bad news: When the temperature rises about 55 degrees F (10 degrees C), you’re going to run more slowly and feel worse than you will at lower temperatures. But by gradually preparing yourself for increased temperatures and taking action from the beginning of hot weather runs, you’ll get a welcome dose of the good news. You’ll learn how to hydrate yourself, what to wear, and when and how much your body can take in hot weather, all of which will help you recover faster and run better than others of your ability on hot days. While even the most heat-adapted runners won’t run as fast on hot days as they can on cold ones, they won’t slow down as much nor will they feel as much discomfort.
Until the temperature rises to about 65 degrees F, most runners don’t notice much heat buildup, even though it is already putting extra burdens on the system. It takes most folks about 30 to 45 minutes of running (with or without walk breaks) to feel warm. But soon after that, if the temperature is above about 62 degrees F, you’re suddenly hot and sweating. On runs and especially races under those conditions, most runners have to force themselves to slow down. It’s just too easy to start faster than you should when the temperature is between 60 and 69 degrees F because it feels cool at first.
As the mercury rises about 65 degrees F, your body can’t get rid of the heat building up. This causes a rise in core body temperature and an early depletion of fluids through sweating. The internal temperature rise also triggers the rapid dispersion of blood into the capillaries of the skin, reducing the amount of that vital fluid that is available to the exercising muscles. Just when those workhorses are being pushed to capacity, they are receiving less oxygen and nutrients. What used to be a river becomes a creek and can’t remove the waste products of exercise (such as lactic acid). As these accumulate, your muscles slow down.
The best time for hot weather running is before sunrise. The more you can run before sunrise, the cooler you will feel, compared with how you’ll feel later in the day. The second best time to run, by the way, is right after sunrise, unless the temperature cools off dramatically at sunset, which would make that time more favorable. In humid areas, however, it usually doesn’t cool down much after sunset.
Some tips on how to say cool at 55 degrees F or above
• Slow down early – The later you wait to slow down, the more dramatically you’ll slow down at the end and the longer it will take to recover from the run. Walk breaks, early and often, help you lower the exertion level, which conserves resources for the end and reduces heat buildup.
• Wear lighter garments – Loose-fitting clothes allow heat to escape. Don’t wear cotton clothing. Sweat soaks into cotton, causing it to cling to your skin, increasing heat buildup. Several materials will wick the perspiration away from your skin: Coolmax, polypro, etc. As moisture leaves your skin, you receive a cooling effect, and these types of materials are designed for this.
• Pour water over yourself – Up to 70 percent of the heat you can lose goes out through the top of your head so regularly pour water over your hair (even if, like me, you are hair challenged). Regularly pouring water on a light, polypro (or a similar material) singlet or tank top will keep you cooler.
• Drink cold water – Not only does cold water leave the stomach of a runner quicker than any type of fluid, it produces a slight physiological cooling effect – and an even greater psychological cooling effect. But don’t drink too much either. Most of us do well with between 6 and 10 ounces an hour during warm weather. Drink until you hear sloshing in your stomach, then stop. When the sloshing sound goes away, resume drinking.
From Marathon You Can Do It by Jeff Galloway (Shelter Publications, 2010) pp. 171-173