I have a senior student that was working with a bad knee. After a few months his condition required knee replacement surgery. He needed Physical Therapy afterward. He remarked to me over a recent lunch that ALL of his physical therapists were surprised by his level of strength and flexibility. because of his Tai Chi, his rehabilitation will be much shorter than the patients who didn't. 

Another friend/student returned after being in a car accident. The accident was horrible and could have killed him but it didn't. He is a little stiff and sore but he is up and around and back to practice. He credits his quick recovery to his tai chi practice.