Qi is thought to be the universal energy that runs everything, right down to the smallest molecule. An example of qi would be that the ancient Chinese could see that when we are healthy, food is carried down the alimentary canal. Stomach qi goes down, carrying food in the digestive tract to the small intestine. The concept of stomach qi was inferred directly from visible events. Qi does not coincide with the Western notion of energy.
Energy is consumed in the contraction of the muscles.
It is not ascending or descending energy. The ancient Chinese observed that these entities, all-important for the support of human life, reflected important aspects of nature as a whole. The five phases also correspond to organs in the body. Yin and yang constitute a binary system of correspondence that is logically matching to the five phases. All yin phenomena are the same in nature and relate to their yang opposites in like fashion.