A frequent critique concerning exercise and fat loss is that you don't really burn a lot of calories during exercise. Since a pound of bodyfat equals roughly 3,500 calories on a superficial level it would appear that exercise is less important than limiting caloric intake. Even an intense bodybuilding workout that includes aerobic exercise will rarely if ever come close to oxidizing 3,500 calories.
Nevertheless, it's also undeniably true that exercise does appear to help control bodyfat levels, especially when used in conjunction with a decreased calorie intake. Most experts say this effect comes from an increased metabolic rate following exercise, and it's true that replenishing depleted energy stores, such as muscle glycogen, is an energy-intensive activity that slightly raises metabolism. Even so, most people are concerned with fat loss.
Does regular exercise allow you to burn more fat at rest? Exercise physiologists frequently point out that more muscle means more calories burned at rest for the simple reason that muscle is active tissue. A new study, however, suggests that an independent mechanism of increased fat burning at rest occurs after exercise.
The study, reported in the American Journal of Physiology (33:E1009-E1014; 2004), shows that such fat burning is independent of energy, carbohydrate and fat balances. It's also unrelated to fat cell release or even body composition. The researchers weren't sure what mechanism explains this increased post exercise fat burning.
One suggestion is that exercise may increase certain muscle proteins that act as fat transporters. The increased activity of the transporters helps to get fat into the portion of the cell where fat is oxidized in a manner similar to the way carnitine works. Unlike what happens with carnitine, these special fat transporters are only activated by regular exercise.
The above explains why exercise is essential for effective bodyfat loss. You burn more fat both during and after exercise.