I was very skeptical of Tai Chi -- about 5 or 6 years ago, when I first got into it. However, I soon discovered that it is a surprising good workout, it requires a fair bit of balance, and it does lift the heart rate, and burn calories. All told, I come to believe it an excellent form of exercise -- has very low injury rate, can be done by all ages, and it not competitive.

http://www.dotaichi.com/Articles/TaiChiLowersBP.htm

Besides resperate, I'm now trying to incorporate 10 minutes of Tai chi every day into my routine.
I usually do 5 minutes in my office in the morning, and 5 minutes in the afternoon.