PDHPE

From +4 to +5 minutes the heart rate is slowly falling at this point and it does not return to resting levels immediately. After exercise the body still requires oxygen to help with the removal of waste products, such as carbon dioxide and lactic acid, from the muscles and for the rebuilding of ATP (the molecule that provides energy for the contracting muscles). The oxygen required following exercise is known as excess post-exercise oxygen consumption (EPOC).
Note: There is also a higher body temperature than normal during and after exercise as the working muscles produce heat. As a result the heart rate may remain elevated to assist with the cooling of the body.