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Anaerobic vs. Aerobic Energy

How Anaerobic and Aerobic Energy Powers Muscles?

In simple terms, how muscles are powered varies according to the time spent exercising. To begin with, (about the first two minutes of exercise), the body cannot get enough oxygen to supply the heart and muscles which need to work faster than normal. So the muscles are forced to rely upon non-oxygen sources of energy (anaerobic). Then, as the supply of oxygen rises, muscles move into aerobic metabolism. As follows:

Stage 1. Anaerobic ATP-PC Energy System

This occurs during roughly the first 15 seconds of continuous exercise. The muscle is powered by energy-rich ATP (adenosine triphosphate) molecules (located in the muscle itself). If muscular contractions continue for longer than this, the energy must be sourced from glycogen, which is also stored in the muscles.

Stage 2. Anaerobic Glycolysis

This occurs during roughly the first two minutes of continuous exercise. During this time, once ATP-PC is exhausted, the muscles are supplied with energy from their own glycogen sources. [Glycogen is blood-glucose, specially stored in the muscles.] If you exercise continuously for longer than about 2 minutes, you eventually burn up all of the glycogen stored within the individual muscle.

Stage 3. Energy from Glycogen During Aerobic Activity

This stage lasts for about 20 minutes. During this period of continuous exercise, if you breathe correctly, the muscles are powered by more glycogen (stored blood-glucose) which comes via the bloodstream from the liver (and other muscles) to help you continue exercising.

Stage 4. Aerobic Fat-Burning

This is the final stage. After about 20 minutes of continuous exercise, the body's stores of glycogen become exhausted, and the body starts using stored body fat for fuel to power the muscles. This process of fat metabolism occurs in the presence of oxygen. This is how sustained aerobic exercise helps to burn fat and thus causes weight loss. In fact, the body continues to burn body fat - even after your exercise has ceased - which it converts to blood glucose and uses to replenish its stores of glycogen in the liver and muscles. Thus fat-burning continues for several hours.

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