There are different styles of tai chi, but all involve slow, flowing movements performed while standing upright. While the body never stops moving, you also never get going very fast. According to the Chinese, tai chi helps guide the body's flow of energy, and according to recent medical research, the flowing exercises help lower blood pressure—a welcome benefit on a scorching day. Search for a local martial arts center or YMCA that offers classes.
DIY and Stay Cool: If you can't find a class or practice group in your area, check out a DVD like master tai chi instructor David Dorian-Ross' T'ai Chi Beginning Practice (Gaiam) to get the moves down. The Crane Spreads Wings exercise shows how these gentle, relaxed movements could seem more appealing on a hot day than a back bend or a headstand.