For many of them, and the rest of us who exercise outdoors, late summer heat and humidity are the toughest preseason opponents. Doctors at UT Southwestern Medical Center at Dallas don't recommend exercising outdoors during the hottest part of the day. One reason is that it's not as effective. You can't exercise as hard in the heat, so your muscles don't get as much conditioning as they might during a harder workout. Exercising in the heat also boosts your risk of injury because overheated tissues can be damaged during exercise.
Dehydration is another risk of hot weather exercise.
During exercise, you should drink about eight ounces of water every 15 minutes. It's also best to drink plenty of fluids before beginning your workout. UT Southwestern exercise experts suggest you plan your workouts so that you avoid or minimize exercising in direct sunlight on hot, humid days. Exercise in the morning or later in the evening, or find a place to exercise indoors. Also, drink plenty of water during your workout in order to prevent dehydration.