I sometimes teach the martial art of aikido. The way I was originally taught, you had to learn how to “feel the flow of ki” (basically life energy) through you and from your opponent, and you had to make sure that your movements — both physical and mental — were such that your “ki” would blend with and guide the “ki” of your opponent. Even after I stopped believing in ki, though, there were some core elements of the art that I just couldn’t do, let alone teach, without thinking and talking in terms of ki flow.
A great example of this is the “unbendable arm“. This is a pretty critical thing to get right for most aikido techniques. And it feels really weird. Most people when they first get it think that the person trying to fold their arm isn’t actually pushing because it doesn’t feel like effort to keep their arm straight. Many students (including me once upon a time) end up taking this basic practice as compelling proof that ki is real. Even after I realized that ki wasn’t real, I still had to teach unbendable arm this way because nothing else seemed to work.
…and then I found anatomical resources like Becoming a Supple Leopard.