It’s an effect that Glenn Kenny, a professor in the School of Human Kinetics, Faculty of Health Sciences at the University of Ottawa, spent years investigating. He built a million-dollar machine  the only one in the world, he says  that can measure minute-by-minute changes in the body’s heat loss.

It looks like a giant can. The subject sits inside and, if exercise is being tested, pedals a recumbent bicycle. The device can detect the amount of heat dissipated by the subject’s body at every moment of exercise and at every moment of post-exercise rest under different conditions  warmer or cooler air temperatures, more or less humidity.

From experiments with the device, Dr. Kenny learned the reason for the feverlike state that arises when the body’s core temperature is elevated: not because you keep burning calories at the rate you did during exercise, but because the body has a hard time getting rid of the extra heat it generated during the exercise session. Heat dissipation is sharply reduced after exercise: for some reason the body just can’t seem to rid itself of the extra heat that it gained.

Dr. Kenny thinks that the effect is linked in some way to exercise’s effects on the cardiovascular system. But even though you may feel hot, you are not burning more calories, he says, so you are not going to lose more weight.

From other studies, in which he measured metabolic rates, he discounts claims that exercise might also increase the rate at which people burn calories for hours afterward. He found that any effect on metabolism after exercise was so small as to be almost immeasurable, and so fleeting it was gone within five minutes after exercise stops. His subjects, though, were not people like Dr. Laursen.

Joseph LaForgia’s subjects were. Or at least they were experienced athletes. Dr. LaForgia, an exercise physiologist at the University of South Australia, says people who exercise intensely  doing repeated sprints, for example  can experience a prolonged metabolic effect. Their metabolic rates can go up and remain elevated for seven hours after the session is finished.

Even so, the extra calories burned were about 10 percent of the calories burned during the intense exercise. As for people who exercised moderately, like most people do, the small increase in metabolism lasted no more than two hours and added up to only about 5 percent of the amount they burned while exercising. And since a modest exercise bout does not burn nearly as many calories as an intense one, people who exercised modestly ended up with very few extra calories burned afterward.