The internal side,to me ,is me knowing my body and mind and how it works and how to apply it in all sorts of situations and positions to get the most power or the best pull or push or drag or whatever.
If I need to do a powerfull right hook and have more weight on my right leg its different mechanics and leverage etc than if i have more weight on my left.And in a fight no one can know what position a person will be in because its random and ever changing.
So I have to get a feel for my own personal body and whats going on.
Basicaly,to me, its Physiology and Biochemistry.
But once a person is in front of me trying to take my head of I have to concentrate on whats outside so its external and hope everything I worked on 'internaly' kicks in.
Though I definitly think knowing how to fight on a basic level must come first then looking deeper can come later.
has alot of great stuff on the 'internal' side and comes from a practical fighting angle (NHB).Some parts also explain Trad Chinese ideas in a modern,practical way.(Eg fa jing ,pu, tim, tun, toh