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Energy System Characteristics | |||
| System | Power | Capacity | Fuels Used |
| Phosphagen System | Very High | Very Low | creatine phosphate |
| Glycolysis | High | Low | blood glucose |
| Aerobic System | Low | Very High | blood glucose |
Fat, which is stored as triglyceride in adipose tissue underneath your skin and within skeletal muscles (called intramuscular triglyceride), is the other major fuel for the aerobic system, and is the largest store of energy in the body. When using fat, triglycerides are first broken down into free fatty acids and glycerol (a process called lipolysis). The free fatty acids, which are composed of a long chain of carbon atoms, are transported to the muscle mitochondria, where the carbon atoms are used to produce acetyl CoA (a process called beta-oxidation). Following acetyl CoA formation, fat metabolism is identical to carbohydrate metabolism, with acetyl CoA entering the Krebs cycle and the electrons being transported to the electron transport chain to form ATP and water. The oxidation of free fatty acids yields many more ATP than the oxidation of glucose or glycogen. For example, the oxidation of the fatty acid palmitate produces 129 ATP. No wonder you can sustain an aerobic activity longer than an anaerobic one.
More: 3 Long-Run Principles to Remember
Understanding how energy is produced for physical activity is the basis for getting the most out of your workouts. So, next time you get done with a workout and think, "I have a lot of energy," you'll know exactly where you got it.
Energy System Workouts |
| Be sure you warm-up and cool-down before and after each workout. |
| Phosphagen System:
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| Glycolysis:
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| Aerobic System:
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More: Should You Run More Miles?
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