- Stay hydrated! I rarely carry a bottle when I run, only runs over about 90 minutes when the temperature is above 80F. Of course, I can only remember two times in the last four years when I ran over an hour when it was over 95F. Both times turned into painful lessons of dehydration and orientation. (For the record I'm thinking of that Saturday from TZ's parents house in Denver in 2008 and a long run last summer on the Heritage Trail.) However, since most of my bicycle rides are about two hours and take place in the afternoon I always drink during bicycle rides. Also, if you have the chance drink an electrolyte drink instead of water while you are exercising in the heat. You could use some salts in addition to the water to keep the sweat processing through your body.
- Exercise in the morning. The coolest part of the day is right around sunrise. Plus, the sun comes up earlier in the summer so you can still exercise in the light. In the winter it can be quite hard to get up at 5AM and go for a run, shower and go to work all before the sun comes up. It is much easier in the summer.
- Take it off! I have been told that wearing a shirt would allow the sweat to evaporate and cool you down more than running without that shirt. Well, I got an A in Heat Transfer (ES 3003) and I can tell you that with one exception that is not true. (Similarly the naked-in-your-sleeping-bag-is-warmer is not true either.) Sweat evaporating directly off of your skin is cooler than wearing a shirt. The one exception is extremely hot temperatures, somewhere around 120F+. In that case you want to protect your skin from the sun because the radiation from the sun and the surrounding sand is so high that your body can not sweat fast enough to maintain exercising. The requirement for the clothing then is light colored (white) and very loose fitting so that you do not build up any heat in the trapped air next to your skin.
- If you must exercise in the heat do two things. First, exercise for a shorter than normal duration of time. Perhaps three quarters or half as long as you would otherwise exercise. Second, exercise at a lower intensity than you would normally, perhaps 80-95% of your normal pace depending on the conditions. The heat will raise your metabolism so you body must work harder to achieve the same feat of a cooler day.
Hopefully this keeps you safe out there as we delve into the hottest month of the year.