The three common mind-body exercises are Tai-chi, Yoga and Pilates. Each has its own special strengths and weaknesses, and practitioners of each can get some insight and benefit by having some understanding of the principles of the other two.
Pilates primarily works with core-strength. Essentially the body is viewed as a working mechanistic system, with the power of movement generated from the core abdominal muscles. The training objectives are therefore, firstly, build up the core strength, and secondly, build up the transmission mechanism whereby movement of the peripherals (like the limbs) are directed by the core with a smooth diminishing gradient of strength. Resulting from achieving the first objective, the structure of the human body as whole will be strengthened. And resulting from the achievement of the second objective, a practitioner's body movement will become graceful together with strength that seems to flow smoothly.
The primarily objective of chi-kung is to quickly build up chi in the body. With ample chi, a good body structure together with targeted clearance of chi-channels can be achieved, with further practice. By chi-kung here, I specifically refer to my practice of zhan zhuang, tai-chi and Taoist meditation. Chi-kung is too broad a term to encompass everything, like some practitioners say it can cure cancer, which I beg to disagree. In general there are two essential criteria for a good chi-kung style or master, firstly, chi can be generated quickly, and secondly, chi thus generated can be managed and guided by the practitioner (rather than running wild - which can result from some "aggressive" styles or masters).
Today's physiotherapists commonly make use of Pilates techniques, rather than chi-kung techniques for their patients. For example, to loosen one's frozen shoulder, typically a patient will be seated with a straight back with the affected arm straightened at 90 degree and being pulled up through a pulley system using the good arm. Fixing the torso, plus assisted movements at defined angles are the hallmark of good Pilates practice.
In comparison, in the practice of zhan zhuang, the natural stance of the practitioner will be taken as a given. With the body and mind being relaxed, chi will be generated to activate a practitioner's "sleeping muscles" to move one's "natural" (often time not well balanced) stance to a better, ever improving balanced stance. A "perfect" stance is to be avoided in the beginning, as it can impede the speedy generation of chi, and its subsequent smooth flow.
One can see that the philosophies of chi-kung and Pilates are quite different. But can practitioner of one learn from that of the other? Certainly yes, and below is such a perspective from the angle of a chi-kung practitioner, using zhan zhuang and tai-chi as examples.
Both chi-kung and Pilates can alleviate the problem of frozen shoulders. In both cases, patients are not seeking for a perfect final structure. In Pilates, essentially a patient will have to stop somewhere (where a physiotherapist will say "completed") because going further will need to open subtler or inner muscles and tendons that can't be achieved without enough chi going into the inner parts). And for zhan zhuang, chi will go so far as enabling a patient to feel no pain (actually comfortable!) as well as able to use one's affected arm again in daily routine. Stay natural becomes the defining objective. The question is: how can a practitioner of zhan zhuang improves further if one chooses to? Learn from Pilates.
And it is quite simple. The only thing a zhan zhuang practitioner should do is to do zhan zhuang with his back lightly resting against a wall. As discussed above, too early to do so can impede chi-flow, however, with more practice, lightly resting against a wall can enable chi to be generated stronger, and can "force" this stronger chi to flow along more "blocked" channels, that otherwise will be by-passed in normal more "natural" zhan zhuang stance. When a practitioner understand the logic and can feel the difference, he can further practice in the following way. This time, instead of resting the back, he can rest his palms (in more than one direction) on a wall! For the same beneficial results. For more advanced practitioners, the fixation of the torso can also be applied in tai-chi rooting practice as well as in pushing hands, for building up a still better structure as well as strength, after all tai-chi is a form of martial art!