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A muscle fiber, also spelled '''muscle fibre''' (see Spelling Differences ), also technically known as a '''myocyte''', is a single Cell of a Muscle . Muscle fibers contain many Myofibril s, the contractile unit of muscles. Muscle fibres are very long; a single fibre can reach a length of 30cm . Muscle fibres can be grouped according to what kind of Tissue they are found in -- Skeletal Muscle , Smooth Muscle , and Cardiac Muscle . The muscle cells of heart muscle tissue are called cardiomyocytes. SKELETAL MUSCLE FIBERS Skeletal Muscle fibers can be further divided into two basic types, type I (slow-twitch fibers) and type II (fast-twitch fibers). Type II is further divided, as follows: TYPE I Type I muscle fibers (slow-oxidative fibers) use primarily Cellular Respiration and, as a result, have relatively high endurance. To support their high-oxidative metabolism, these muscle fibers typically have lots of Mitochondria and Myoglobin , and thus appear red (what is typically termed "dark" meat in Poultry .) Type I muscle fibers are typically found in muscles of animals that require endurance, such as Chicken leg muscles or the wing muscles of migrating birds (e.g., Geese ). TYPE II Type II muscle fibers use primarily Anaerobic Metabolism and have relatively low endurance. These muscle fibers are typically used during tasks requiring short bursts of strength, such as Sprints or Weightlifting . Type II muscle fibers cannot sustain contractions for significant lengths of time, and are typically found in the white meat (e.g., the breast) of chicken. There are two sub-classes of type II muscle fibers, type IIa (Fast-Oxidative) and IIb (Fast-Glycolytic).
OTHER TERMINOLOGY Most sources use the I/IIa/IIb division described above. However, this distinction is much more clear in other animals (such as Chicken s) than they are in humans, where the muscle tissue usually contains combinations of different kinds of fibers in varying proportions. Some terms used to describe this blending include:
SEE ALSO EXTERNAL LINKS
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