Intermediate fibers, also known as fast oxidative-glycolytic fibers, are
fast twitch muscle fibers which have been converted via endurance training. These fibers are slightly larger in diameter, have more
mitochondria
A mitochondrion (; ) is an organelle found in the Cell (biology), cells of most Eukaryotes, such as animals, plants and Fungus, fungi. Mitochondria have a double lipid bilayer, membrane structure and use aerobic respiration to generate adenosi ...
as well as a greater blood supply and more endurance than typical fast twitch fibers. Most of the body's muscles are composed of these intermediate fibers.
References
* Visualizing Human Biology, Kathleen Anne Ireland, David J. Tenenbaum, raken jilani
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Muscular system