The numbers don't exactly make you want to leap out of your chair — 95 calories for a mile around the track; 300 calories for an hour of step aerobics.

Think about how much effort it takes to burn off a slice of pecan torte at 390 calories per serving, and that's without the whipped cream. Even a slice of bread has 90 or 100 calories.

Before you give up and concede defeat to all caloric temptations, take heart with this concept: constant motion.

You are diligent about your Monday, Wednesday, Friday workouts, and that's great. Keep it up. But remember, the human body was designed to move virtually every waking moment. Exercise shouldn't be confined to 45 minutes, three days a week.

"It is only in the 20th century that we have become completely inactive," says Phillip Clifford, professor of physiology at the Medical College of Wisconsin. "People used to burn off a lot more calories."

Clifford talks about the virtue of fighting fat one calorie at a time, over the course of a day. How much you burn depends on your weight, the intensity of what you do and the efficiency with which you do it.