Why Does the Body Shiver in the Cold?

Shivering in the cold is not a sign that muscles have simply become too cold and lost control. It is an active heat-producing response organised by the thermoregulatory system. Temperature information from the skin and deeper tissues reaches the nervous system. When heat loss may exceed heat production, the brain recruits several defences, including narrowing blood vessels near the skin and triggering involuntary skeletal-muscle contractions: shivering.

Muscle contraction consumes chemical energy, including energy supplied through ATP. Ordinary movement converts some of that energy into mechanical work and also releases heat. Shivering has no clear external task; its small, repeated contractions mainly raise metabolic rate, and the resulting heat helps offset heat lost to the environment. A research review identifies shivering muscle as an important source of heat in cold-exposed adults, while also showing wide variation in which muscles people recruit and in the balance between continuous and burst shivering.

This helps explain why writing or fastening a button becomes difficult while shivering. The body has organised rapid involuntary movement to make heat, but that movement interferes with fine voluntary control. Goosebumps and shivering are both cold defences, but they do different work. Goosebumps provide little insulation in humans, whereas shivering directly increases heat production.

Shivering does not mean the body can resist cold indefinitely. Prolonged wet cold, confusion or extreme cooling is a safety concern, and shivering can diminish during severe hypothermia. Stopping shivering should not be read as proof that someone has warmed up. This article explains physiology and is not medical diagnosis.

https://pmc.ncbi.nlm.nih.gov/articles/PMC5605160/