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Fast and Slow Twitch Muscle Fibers

Have you ever wondered why some people are better long-distance runners and others better sprinters? It is because our muscles are made up of two main types of fibers - slow-twitch and fast-twitch. Not all muscles in the same person are one type or the other, and particular muscles such as postural muscles are always slow twitch some they can serve their function.

muscles can be predominently fast or slow twitch

Slow-Twitch Muscles

Slow-twitch fibers contract slowly and can be used for longer periods of time. Postural muscle of the back are composed of mostly slow-twitch muscle fibers. Athletes who run long distances need more slow-twitch fibers in their legs. Slow-twitch muscle fibers rely on oxygen as their main energy source.

Fast-Twitch Muscles

Fast-twitch fibers contract quickly and provide strength and speed, though they also fatigue more quickly. Sprinters require short but intense bursts of energy and therefore need more fast-twitch muscle fibers. Fast-twitch muscle fibers rely on ATP and glycogen as their main energy source. As ATP sources can be rapidly depleted, lactic acid is a by product of the breakdown of glycogen, fast-twitch fibers can only be active for a short period of time.

Related Pages

• The Mechanisms of Muscle Fatigue
• A fitness test to estimate muscle fiber composition
• List of all skeletal muscles of the human body
• Explanation of the body's energy systems

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Disclaimer

The above information is presented as a general guide. The author and publisher take no responsibility for any possible consequences of any treatment, procedure, exercise, action or application of medication based on this information. See more: Disclaimer.