It's true, rigorous exercise can keep our bodies warm for hours after we stop. Why? That's what Gina Kolata tries to reveal in a recent Personal Best column. Trouble is, no one really knows why. One theory, put forth by Glenn Kenny, a professor in the School of Human Kinetics at the University of Ottawa, claims simply that the body has a hard time getting rid of all the heat generated by exercise. Kenny says his research disproves the widespread (and optimistic) conviction that our metabolism remains elevated after exercise and we therefor continue to burn calories. Another researcher, one who worked with hardcore athletes–sprinters– found that their metabolism did remain elevated for as long as seven hours after exercise, and suggests that the robust metabolism could be keeping his athletes warm. Maybe. Finally, Kolata offers this explanation to why we remain warm hours after exercise: "It might be caused by…the body’s efforts to repair subtle tissue damage from all that exercise. The immune system can kick in, and so can enzymes that repair muscles and require heat-producing energy."