Ugh.. naysayers.
Chi is natural. And it is exactly what Zac said it was.. An explanation for something not understood. Now, we understand it. It's called science. It's called willpower. It's called physics. Any number of things. A person can exert will to change his body temperature, for instance.
This does NOT NEGATE THE IDEA. It means that there's an explanation. It's not magic or mysticism, and it never was. It jsut is. A natural force. In science, a multitude of different forces. But to say, "Well, Chi doesn't really exist because it's an explanation for something else" is.. well.. short-sighted. Just because something has two different names doesn't mean that one name is better than the other.
Chi is the cultivation and disciplining of certain natural aspects of human existence. Including movement. Including hormonal regulation. It's a discipline more than just a "force." To dismiss Chi away is to lose something precious. Just because we KNOW that Chi cultivation is actually regulating certain hormonal responses through meditation/breathing/etc. doesn't mean that it isn't profound. Tell me how you can do that without disciplining Chi, or using it as a concept rather than a science. The amazing thing is that meditation can do this by visualisation or by meditation.. it doesn't matter what's actually going on.