Physical exercises are intended for body.
Yoga is intended to yoke mind and soul. You should not
practice it for physical benefits.
From yoga and the spiritual life we can derive peace of mind, divine joy, divine love and a sense of true accomplishment.
http://www.srichinmoylibrary.com/meditation-se rvice/442.html
The deep and eternal essence of yoga has been misrepresented and packaged for personal profit by clever people. At the hands of some, yoga has been reduced to the status of just another exercise program available on videotape.
http://www.swamij.com/yoga-meaning.htm