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Exercise Anatomy and Physiology

Exercise Physiology Basics: Energy Systems, Cardiovascular and Respiratory Systems

Energy Systems

Learning how the body produces energy to perform movement is fascinating! This section provides a general overview of how the body utilizes fuel to exercise.

ATP (adenosine triphosphate) is a chemical compound that we get when our body breaks down carbohydrates and fats that we consume. These macronutrients provide fuel for the body in the form of ATP. ATP can be thought of as an energy currency. Note that protein is typically not used much during exercise. It has other uses so we do not spend time talking about it in regards to fuel for exercise.

We make ATP in two ways: aerobically and anaerobically. Both energy systems are always at work, but typically one predominates over the other depending on what we are doing.

  • Aerobically
    • Aerobic metabolism means that oxygen is utilized to produce energy. This is the energy system that the body depends on most of the time. It provides energy (think ATP) for sustained activities like walking, running, biking, etc. A sufficient amount of oxygen must be present in muscles to continue activity. We breath oxygen into our lungs which then gets picked up by our blood and transported to various part of the body. Exercising muscles automatically get more oxygen as the body adjusts to produce energy where it is needed.
    • Muscle cells contain mitochondria, which are considered the powerhouse of the cell. This is where oxygen is used to produce ATP. As you become more aerobically fit, your body adapts by making more mitochondria. More mitochondria means more oxygen utilization… which means you can make more ATP… and work at a more intense rate… and it won’t feel as difficult! (There are other adaptations as we become more aerobically fit, but this one relates to metabolism, which it is why it is explained here).
  • Anaerobically
    • Anaerobic metabolism means that no oxygen is needed to produce energy. This energy system is used for short bursts of energy, like sprinting, jumping, throwing, or lifting heavy weights. This system can provide a lot of energy (think ATP) quickly, but it cannot be sustained. ATP made anaerobically runs out quickly.


A Guide to Physical Fitness Copyright © by Jen Hilker. All Rights Reserved.

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