If we look back to the end of Ming and starting of Qing dynasty, there was no classification of “neijia” and “waijia” at the time. There was a record of something called “nei jia quan”, however, that was a single style as supposed to a broad catagorization. Description of the style can be found in “WangZhengNan tomb record”, and stories of ZhangSongXi in “Ning Buo government records”. Both WangZhengNan and ZhangSongXi are NeiJiaQuan masters, and Wang’s skills is claimed to have descended from Zhang. They both claim that the root of their art is from ZhangSanFeng, and from the principal of taiji. It’s important to know here that Taiji itself is just a theory, and has little to do with Taijiquan itself. The name of the style itself is simply “Nei Jia Quan”, and our earliest record of it is around the same period that Chen Wang Ting came up with Chen Taiji. They are independent however, because Chen Wang Ting founded Chen Taiji in isolation and in his old age.
There is in fact a “Song Xi Nei jia” style in NanChong, SiChuan province in China right now., which claims to be the style ZhangSongXi practiced in the end of Ming dynasty. It was only recently discovered in 1980s, and many of its movements interestingly corresponds with QiJiGuang’s 32 fist methods. Even the names of some of the techniques are the same.
Looking at this style however, it has more in common with Long fist than with Taiji. It’s a style that is uses throws heavily, and excels at close range standup grappling. The training method also focuses heavily in external conditioning as well as body coordination and power generation not unlike taiji, although it’s much more dynamic.
My point is that the classification of “Neijia” and “waijia” for styles is basically meaningless. Any respectable Chinese style contains similar power generation, body coordination and conditioning methods. “External” styles such baji, pigua/tongbei, or long fist have very “internal” power generation methods. And “internal” styles like bagua, chen taiji have very rigorous and difficult external conditioning methods.
The label “internal” and “external” is simple the Chinese way of saying the body coordination methods and power training methods. For the body to generate power, muscles need to contract/expand. External is to thicken the muscles, and internal is to 1. relax muscles in their normal state, so contraction can be maximized when needed. 2. coordinate the muscles in the body in a structural way so that output of power can be maximized. This includes breathing and alignment…etc. That’s it, there’s nothing more than that.
This kind of conditioning is common to ALL martial arts in the world, and also in sports. So there is nothing mystical about it. We simply have a better understanding and better theory for them.
So the answer to the question? All (respectable) martial art schools and sports have “neijia” and “waijia” methods.