Fed up with the polar vortex? If so, consider this: Shivering may actually share some of the benefits of exercise—at least in terms of burning fat. Researchers studied shivering in a group of 10 men and women. First the volunteers rested under a temperature-controlled blanket, which dropped from 80 degrees Fahrenheit to a chilly 54. Then they cycled on an exercise bike. Researchers took blood samples during both activities. Turns out, shivering and exercise spurred muscles to secrete similar amounts of irisin—a hormone that tells brown fat to turn up the furnace—even though exercise took 10 times as much effort. The researchers say the metabolic pathway may have evolved to save us energy. Shivering alone is a costly survival mechanism—it relies on muscle contraction to warm us. Whereas shivering-activated brown fat can convert chemical energy directly to heat. The study is in the journal Cell Metabolism.