The Neigong Jin (內功四經) is an ancient martial art book with four chapters on training. It starts with saying the chi can only move with proper body structure. It describes how every body parts should be to get a proper overall structure. It goes on to explain using baqua to explain characters of every major body parts, it's inter-relationship with each others, and the inter-changing. It is a great book to read.
difficult to achieve higher levels of practice without giving up base human desires, instincts and
emotions
I chatted with a Sihung a month ago. He has learnt and researched martial arts from the age of 15 until his recent retirement, searching for for high level masters and spent lot of money on it. A master told him that the neigong training starts with focus on "the third eye", then other spots, and to Dantien. Then went on saying these are concepts, and should be dumped to get into the real training from keeping himself in emptiness, train, and wait for things to happen. I heard the same thing from various old masters before.
I read a neigong book given to me by an old master before he was gone. The book is mostly about the universe, the energy around it, to give up oneself to love and care people around, family, our own country and everything under the universe. Water can only be poured in a cup when it is empty. By the time we can empty ourselves then "something" can attach to us. What that "something" depends on how oneself be. Good person attracts good energy, and bad person gets to the dark side. So wudai is those high level old masters tried to pass on, and to the right person. I think people nowadays don't care about it too much.
LHBF trains on the same path from body to heart, to yi, to chi, to zhen, to move, and to emptiness. I don't care about the controversy and rumours on its history. It truthfully directs practitioners a path to attain certain level. It trains to fight, and most importantly to fight for good courses. Be a good person with a good heart.