It is a low-impact exercise because it is slow, even pressure on the muscle and joint. In aerobic exercise, you might move your arms up and down. In isometric exercise, the arm is just held straight out. The isometric pressure on the muscle and joints strengthens without the pounding of aerobic exercise. Tai chi also improves flexibility and balance.
People are surprised to find their legs shaking and sweat on their brow during tai chi.
This gentle method of exercise is very popular with seniors who may find other forms of exercise too exhausting or jarring. The meditative and breathing aspects of tai chi make it an excellent way to fight stress, which is one of the reasons Jeff Zwier turned to tai chi. The movements in tai chi are just sophisticated enough that you can't think about anything else. The recent popularity of tai chi has brought some imitators. Barnett cautioned people interested in pursuing tai chi to check on the qualifications of the instructor.