Your exercise session is over. You're back at your desk or home carrying on with life, you know, making dinner, pushing papers or changing diapers.

But your body is still burning calories, silently, efficiently, slyly. Even after most exercise if over, calories continue to get gobbled. You probably call it "afterburn." For the record, exercise scientists call it "excess post-exercise oxygen consumption," or EPOC. OK, OK, we'll call it afterburn.

Pretty cool that you can do nothing and still keep the fires burning. But the level, type and length of the something you do before you stop have a big effect on the afterburn.

How intense must activity be to get an afterburn? -- Studies show that you don't get much of an effect if your exercise intensity is much below 60-65 percent of your maximum heart rate. If you rate your perceived exertion on a scale of 1-10, that'll put you at about a 2-3, or light to low-moderate. Stopping to smell the flowers every few feet won't accomplish much. You'll have to move continuously and with moderate determination. The more intense the exercise, the more effective of an afterburn. For the most bang for your buck, shoot for vigorous activity at about 75-80 percent of your maximum heart rate, or 5-6 on the 1-10 scale of perceived exertion.

How long does it have to be? -- Even 20-40-minute walks can earn you some extra calorie use, but not huge amounts. You'll get the most out of a session that's at least 60 minutes, studies seem to show.

How much extra burn do you earn? -- Achieve 60 minutes of moderate to vigorous activity, and you'll nearly double the afterburn compared to a 20- or 40-minute session. That could account for an extra 80 to 100 calories over the first three hours. Now that doesn't sound like much, but if you gain an extra 90-calorie expenditure, four times a week, that's 360 calories. Keep that up for a year and you've lost an extra 5 pounds or so.

How long does the afterburn last? -- Researchers are still using the great cop-out here: "More research is needed." Nevertheless, one study published earlier this year showed that fit people continued to burn more calories at least 39 hours after they stopped exercise, and that their bodies chose to use nearly double the fat during that time than in inactive people. Whatever the exact length, you can assume the more intense and longer the activity, the longer the afterburn will last. In all cases, it will start higher and slowly taper off over at least several hours.

What if I workout twice in one day? – You’ll probably burn more than if you workout just once, even if the sessions are shorter. That’s because your inner fires use up the most right after you’re done, then slowly die out. So you’ll get that immediate hot heat twice.

Oh, and ... well ... why? -- They don't know. At least not exactly. They speculate that it has something to do with increased levels of certain hormones circulating in the system, changes in the way the body uses fat, or body temperature changes. They also don't really know if the body chronically adapts to this or simply kicks in the effect after individual workouts.

But, hey, who are we to complain. Keep it moderate to vigorous, the longer the better, and cash in for hours after the sweating's done.