I voted having to do with qi, but my definition of qi is different. To me qi is your state of being, and isn't mystical in any sense. Its the stress your under, and how you deal with it. Its the blood running through you, and the quality of the sources of nutrition you receive. Its the meridians, and your nerve pathways. And exerting your qi is also proper body alignment, proper force, proper speed, and proper state of mind. But whats proper is completely subjective to you, and cultivating good qi is being in balance with and understanding the self.