The heat energy is what produces body temperature. As a person exercises or works, body temperature goes up as a result of the greater amount of energy needed to do the exercise or work. It is not uncommon for an athlete s core body temperature to increase to 104 degrees f, particularly in hot weather. The mechanical energy is the force that causes the body to function or do work.
Every bodily function is carried out due to mechanical energy production.
The structure of ATP is such that it has an adenosine base with three phosphate molecules attached. It is in the bonds that connect the phosphates. When the bond is broken, energy is released creating the heat and mechanical work. The formula can be reversed causing ATP to be re-synthesized. In fact, for the body to sustain life, ATP must be re-synthesized over and over.