太极拳 is good for the balance of old men and women whose equilibrium are progressively worsening as the age advances. Although does not do the muscle builder job, it certainly will help to regain the better balance function and to a some extent, help the cardiovascular system. Is this 健身 also? Nothing is surreality, any exercise will be as good as designed 健身 exercise so long as you can take it.
Funny though, how about those exercises in bed ? Is that a study of that?