I am currently relearning Taijiquan. After having done some Yang style Taiji years ago I now try to learn Wu style, which is said to have extremely strong healing properties. Several things I notice when doing it:

The body basically knows how the move should go. If I start to divert from the move too much, listening to what is comfortable and what is not usually helps me to nail the move down very quickly. This can be done if you developed some ability to listen to your body or even to learn that. It surely also helps that I am not too flexible and my body will clearly tell me when I am "crossing the limit".

The opening and closing moves of Taiji, when done right (enough), have quite some effect on the joints. In my case I could hear several "trouble joints" crackle and presumably release tension while I was doing the part of the form I am familiar with. The more slowly and consciously I do it, the more this happens.

Taiji is not a "heart-lung workout" in the sense that it makes you run out of breath when starting to work your muscles. Fascinatingly enough it still works the muscles, though. In fact, I could glisten with sweat in no time without the other symptoms we commonly expect of exercise - like heightened breath or pulse rate. Taiji provides motion in the body without an aerobic component. In fact your heartbeat might just as well be lower than normal and still your muscles get a workout. This is especially important for old people and physically unfit people like me.

It's also fun to tackle these complex moves and make them your own.

Oliver