One of the main differences between chi kung and nei kung is that originally, traditionally, before it was bastardized by the money grubbers, Nei kung meant entire systems of self developement, which are said to contain ten thousand techniques. (depends on how you count)
Real nei kung addresses all aspects of self development, physical, mental, emotional, and spiritual.
Chi kung, on the other hand, consists of sets of exercises which are very small subsets of nei kung system methods. A chi kung 'system' may have as few as a couple of techniques, to many tens of techniques. When it starts to get into the hundreds, like the original Wild Goose chi kung (Dayan chi kung) then it is more like nei kung, although it is called chi kung ... for the same reason I call Tien Shan a chi kung, because when you practice or teach it only a limited number of techniques can be performed, obviously.
So, when someone is 'doing' it, they are doing chi kung, but if they are serious students of one of the holistic systems then it is called ni kung.
What happens is that some jokers who are either liars or who have been misinformed by previous liars upline, offer some pathetic exercise and call it nei kung.
In the past, before there wer big cities, books, and internet; when masters were few, and students were serious, nei kung was the Way, and chi kung was more or less unheard of. Then with the advent of commercialism, most people became interested in chi kung, and nei kung was nearly forgotten. Then, after that, people got wind of the fact that nei kung is superior, more powerful, and more complete than chi kung so it became popular to 'sell' nei kung to the masses.
Most of these 'sellers', before the internet, started selling it by writing books. I think this is an important point, because they focussed on methods which are more mental and much simpler, ones that aren't much exercise, if any at all.
In fact, big parts of real nei kung is a lot of exercise, and for people who are not in good condition it can BE brutal. Any weakness a person has, whether it be physical or emotional, will cause some real pain until it is fixed, or cured. If you find any nei kung which is not brutally physical, then it is a lie, and it has been wimpified in order to make it acceptable to the consumers.
