It is a matter of common experience that we shiver in winter if we are not wearing woollen clothes. And even if we want to stop it we cannot do much about it. Do you know why do we shiver on a cold day?
Physiologically speaking, shivering is an automatic movement of the muscles. When we shiver our muscles tighten and relax very quickly over and over again. Each time when our muscles contract, the muscle cells burn more food for energy and as a result of this, heat is produced. Thus shivering is a mechanism of the body which helps to keep it warm. It keeps the body temperature from falling beyond a certain point. This is a process in which our muscles work hard and keep the body warm. Sometimes, shivering is not enough to warm us up properly. We, therefore, often jump up and down and flap our arms on cold days. Thus extra uses of muscles produce more heat in the body.
We wouldn’t shiver if we do some exercise or play a physical game. Physical activities make our muscles work hard and warm up the body. Shivering, in fact, does the same job without any exercise.