Muscles Are Trained Fat-Burners:
The more time spent during aerobic activity, the more trained the muscles will become in fat metabolism. Trained muscles can burn fat more efficiently and require less glucose, even during strenuous exercise.
After physical activity has ceased, "fat-burning" may continue at an accelerated rate for some time. Some reports suggests that fat metabolism remains elevated for at least six hours after completion.
Another report suggests there is increased fat use 24 hours after an hour-long aerobic session. The body's adaptation to strenuous and prolonged aerobic exercise burns more fat all day, not just during the exercise. In other words, consistent exercise for more than one hour will most likely raise an individuals resting metabolic rate, which means you consistently burn more fat even while not exercising.