What are fast twitch muscle fibers?

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Fast twitch muscle fibers, also known as type II muscle fibers, are generally associated with high intensity, short bouts of physical activity. They generally contain fewer capillaries and mitochondria, which means less blood and oxygen is delivered to them. Because of the lack of blood supply, they are also often referred to as white fibers in comparison to type I fibers that are higher in capillary content (commonly called red fibers). Type II muscle fibers are larger in size, quick to produce maximal tension, and fatigue more quickly than type I fibers. They are important for producing movements that require great amounts of force and power such as sprinting, jumping and throwing.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.