It is supported by diet. Endurance is the cornerstone, upon which all our daily living is based. What we do is limited by our ability to get oxygen into, and carbon dioxide out of, our bodies. Strength is our ability to temporarily produce more work than what we are normally producing. A man cannot do as much work as a draft horse over a long period of time, but we are capable of producing as much as 10 horsepower over a short period of time.
Flexibility is defined as the range of motion present at a joint, in a specific plane and direction.
Diet plays the supporting role in developing endurance, strength or flexibility. The determination of an optimal diet is greatly complicated by our lack of knowledge as to what chemical reactions take place within our bodies. Too much energy content, and we store energy in the form of fat.