Aerobic and Anaerobic

Two of the most important terms used in endurance sports are aerobic and anaerobic. These will be referred to often throughout this book, not only as they relate to training but also in terms of how they are affected by diet, stress and other factors.

Take a snapshot of the body’s metabolism, and the most obvious feature is oxygen. As everyone knows, oxygen is essential for energy production. But not all energy is obtained with the help of oxygen. When oxygen is used to generate energy, it is called aerobic, and when the body derives energy without using oxygen it is termed anaerobic. But these common academic definitions are not very practical. Instead, a more relevant way to define aerobic and anaerobic is by the prominent fuels they use to produce energy: fat and sugar, respectively. Let’s define each as follows:

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  • Aerobic: the ability of the body to use more fat and less sugar (glucose) for energy.
  • Anaerobic: the ability of the body to use more sugar and less fat for energy.

The chemical generation of energy from fat and sugar occurs in the aerobic and anaerobic muscle fibers, which are important components of virtually all skeletal muscles in humans.

Note: Our body contains three kinds of muscles. Skeletal muscles are used for physical activity, and bulge when contracted; smooth muscle is contained in our intestine and blood vessels, and regulates the size of the passageways; and cardiac muscle is found in the heart, used for its “beating.” In this book, most of the time I will simply refer to skeletal muscle fibers as aerobic or anaerobic muscles.

Aerobic and anaerobic muscles perform a variety of activities in addition to generating movement. I will sometimes refer to these collectively as the aerobic system and the anaerobic system.