What Are Type II Muscle Cells

Type II muscle fibers (sometimes called fast-twitch or fast-glycolytic fibers) can execute a much faster speed of contraction than Type I muscle fibers. This is to say that Type II muscle fibers are designed to generate force more rapidly, thereby allowing them to be more powerful. This will allow a job to be performed in a shorter amount of time. Meanwhile, Type II muscle fibers are relatively limited in their ability to generate ATP by aerobic means. So, when these cells break down glucose to pyruvate and generate a couple ATP in the process, much of the pyruvate that is formed will then be converted to lactic acid (lactate). This is because these muscle cells have less mitochondria and receive less oxygen as they are served by fewer blood vessels (see Table 11.1 and Figure 8.3).

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