People do yoga for many reasons. It is a practice that is for people of all temperaments and constitutions. There is a yoga practice for everyone, from the paraplegic to the tri-athlete. No matter what ails you or how active you are, you can do yoga. Most yoga taught today comes from the physical fitness angle. This is not bad. It is important to have a physically demanding practice of some sort to keep the body in shape. If you are using yoga as such a practice, great, but don't sell yourself short and neglect the other, more subtle beneficial aspects of yoga.