Go for a walk or a jog. If it’s too cold outside, hit the gym, or just do some jumping jacks, pushups, or other exercises indoors. Not only will it warm you up, it helps build and keep your muscles, which also burn calories and make body heat. If you’re healthy enough for it, vigorous exercise might even raise your core body temperature, at least for a while.This will help you stay warmer. It also prevents muscle loss – muscles are important to create body heat.