The easiest way for an adult to rapidly increase their core temperature is through shivering. The activity of muscles generates a moderate amount of heat as a byproduct of movement. Fresh from the womb, infants lack significant musculature and can’t shiver themselves warm. Instead they are usually born with a layer of chubby rolls of insulating white fat. When their core temperature begins to drop, BAT turns on, sucks white fat from their system, and releases a cascade of heat energy.
