Several different ones from two main systems.
It is the most effective way to learn the internal form-work and then put it into IMA. Without it, you increase your training-time unnecessarily. It is also quite common that the real power in a style comes from a qigong or neigong-set that fuels the MA part.
Haoran, if you want a more detailed answer, please make the question more precise. Right now it´s a bit like asking a group of painters whether they use paint.
Edited: also on the same line as Dave comments above. Having just IMA will often create tension in you and close your system down a bit. Ideally, you need some kind of stable qigong/neigong to open your system up, balance it, and balance your mind outside a martial framework. This will make the process of the IMA itself go faster and deeper, safer.
D.
Sarcasm. Oh yeah, like that´ll work.