Why do we shiver when it is cold?

A: Shivering occurs when the tension of the skeletal muscles rises beyond a critical level or when the body temperature falls below the critical level of 37.1 degrees C. Shivering is actually an involuntary contraction of muscles to maintain body temperature during fever and in cool environments. Acting through descending pathways that terminate on the motor neurons controlling the body’s skeletal muscles, the hypothalamus gradually increases skeletal-muscle tone. Thus shivering begins throughout the body when the tension of the skeletal muscles rises beyond the critical level, producing heat and increasing the temperature of the body within a matter of seconds. Studies reveal that shivering may produce as much as 42.5 cal/hr, almost seven times greater than man’s normal resting metabolism at room temperature.