After exercise, the body generates heat like any engine and needs cooling. This is what the skin does. The blood vessels of the skin will expand rapidly, increasing the blood flow of the skin, increasing the skin temperature and sweating. Heat is dissipated into the air with sweat through the skin, and some body wastes are discharged at the same time. Brain endorphins and brain-derived neurotrophic factors can make people feel happy. Exercise and electrochemical signals are emitted from the cerebral cortex and transmitted to the intersection of muscle fibers through neurons. Exercise increases the blood flow of the brain, and brain cells begin to operate at a higher level, making people more alert, awake and happy during exercise.