I have been a yoga instructor for approximately five years and my Mantra is What the mind thinks, you become :). I am living proof that yoga works. I had a shoulder injury years ago and I had to go through physical therapy to help movement and healing. At that time, I was going through yoga teacher training and when physical therapy discontinued I got back to my yoga practice, very slowly of course, and over time I was back to doing all my routine I was doing previously to the injury. I work slowly with people that have injuries, or just generally in need of reconditioning from inactivity.
Again, What the mind thinks, you become. Namaste