Cooling down, is the period which allowed your body to make a smooth transition from moderate or vigorous exercise to resting state.
As you exercise your physiological state will change from state to a higher state “the cool down” will help you to retain back and adjust to the normal state which is sager than just suddenly stop exercising.
As you exercise, the cardiac output will increases which it cause the heart beat as well the amount of blood pumped per a beat to increases. As the blood shift away from the vital organ to help the muscle to start exercising it need more oxygen and extra nutrients. After finish exercise everything goes back to normal states and return to resting level. As you exercise your muscle work as blood pump it help to return the blood to the heart by contracting and relaxing.
How to cool down?
It’s as simple as warming up before exercise. As warming up to reach the target zone, cool down is the opposite which allowed the body to shift from the target zone to the resting state. Starching is the best example of cooling down. Which it also help to lengthen the muscles and give you a better flexibility.