All the living processes occur throughout the interplay of enzymes. One of the outputs of the enzymatic processes is the involvement of heat. Heat is given out during exercises because exercises increase various metabolic reactions in the body. It is this heat that has significant healing activities. Lack of exercise only leads to deficiency of this major element of the body.
Heat is that propels the physical movements in the body apart from the enzymatic reactions.
In a heated area, blood flow is more. Even irritation is a form of heat. Whenever there is more blood flow, there is more supply of nutrients and more removal of waste and toxins. All movements in the body accelerate blood flow. Yoga is that which produce the heat that drives the flow of blood.