Physical training changes the functions and structure of the heart. It is well-known fact that active muscles require more oxygen and nutrients. To fulfil these requirements, more blood must be supplied to these muscles during exercise. As the muscles become better trained, the circulatory system adopts to increase blood flow to them. The blood supply is increased to the muscles due to following reasons-
(a) Increased blood volume.
(b) Increased in capillaries of trained muscles.
(c) Better and more effective redistri-bution of blood.
(d) Good opening of present capillaries in trained muscles.
