Shivering is a way of generating heat by making muscles contract rapidly and repeatedly.

The longer version

Rapid muscle contractions release heat as a by-product, because muscle is not perfectly efficient and a large share of the chemical energy it burns ends up as warmth rather than movement. Shivering exploits that: the body triggers many small, alternating contractions across large muscle groups, producing heat without producing useful motion.

The command originates in the brain's temperature-control centre, which receives information from sensors in the skin and in the blood. Blood vessels in the skin narrow at the same time so the warmth stays in the core. The result is a noticeable rise in heat production within moments. Sustained shivering uses fuel quickly, so it cannot continue indefinitely at full intensity.

Where this entry sits

These facts look at how the human body works in ordinary moments, from breathing and blinking to balance and sleep. They focus on anatomy, senses, and small reactions that happen constantly without any conscious effort. The full list sits on the Human Body page, where every entry is listed in order.