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](images/muscle-showoff-pixa.jpg)
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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