You may continue burning calories after your workout ends.
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The formula for gaining or losing weight is simple: If you consume more calories than you burn during a given time, you add weight; if you burn more calories than you ingest, you lose weight. Excess weight is stored in fat cells across your body, becoming energy reserves you tap into when your food intake does not supply your energy requirements. When your reserves become too large, however, working out can help shrink them down to size.
Use EPOC to Lose Weight
When you need extra energy during a workout, your body can tap into fat stores immediately, and depending on your workout's intensity, you may continue to burn fat after your workout ends. Excess post-exercise oxygen consumption, or EPOC, measures the number of post-workout calories you burn relative to your normal caloric needs at rest. EPOC ranges from 65 to 150 calories per session. If you work out five times per week, that may mean burning 7 pounds of fat per year after your workouts, according to Dr. Len Kravitz of the University of New Mexico. The physical process of burning fat is the same, whether it's burned during or after a workout.
About Fat Cells
Everyone has billions of fat cells, which potentially can be filled with chemicals called triglycerides. The cells typically vary between 0.2 and 0.9 micrograms in size, depending on the amount of excess fat in your body. In other words, if you consume more calories than you burn, your fat cells expand. Additionally, if you have enough excess fat, you can gain additional fat cells. If you work out regularly and create a calorie deficit, your fat cells begin to shrink.
How Fat Is Released
When your body requires extra energy, it sends a message along hormonal pathways to your fat cells. An enzyme within your fat cells -- hormone-sensitive lipase -- receives the message and breaks down the triglycerides into glycerol plus three fatty acids. These smaller pieces leave the fat cell, enter the bloodstream and travel to areas in need of more fuel. Your liver absorbs the glycerol, while the fatty acids go to muscle tissues as well as the liver.
How Fat Is Absorbed
When they reach your liver and muscle tissue, the glycerol and fatty acids released from fat cells go through additional chemical processes, transforming them into usable energy. Initially, the former fat components enter the liver and muscle cells' mitochondria -- structures outside a cell's nucleus where the cell's power is produced. A series of reactions occurs, producing compounds such as citric acid and, eventually, adenosine triphosphate, which powers your muscle cells. The process also produces water -- which is released as either sweat or urine -- plus heat, which helps maintain your body temperature.