Yin Yang theory is based on Vibration and Temperature of the Human body compared to compared to it's environment.
All matter is vibrating at it's own frequency, regardless of living or non-living. This vibration determines temperature, and the state of matter(solid, liquid, gass, etc.).
Acording to Yin-Yang, anything heats up the body is Yang, and anything that cools down the body is Yin.
Anything that speeds up the body is Yang, and anything that slows down the body is Yin.