Which fiber type is fast-twitch glycolytic?

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Multiple Choice

Which fiber type is fast-twitch glycolytic?

Fast-twitch glycolytic fibers are built for rapid, powerful contractions and rely mainly on anaerobic glycolysis for ATP, which lets them generate a lot of force quickly but fatigue fast. The fiber type that fits this profile in humans is Type IIx. It has high fast myosin ATPase activity, large diameter, and a high content of glycolytic enzymes, with relatively few mitochondria and low myoglobin, so it produces energy mainly through glycolysis and tires quickly as lactate accumulates. In contrast, Type IIa fibers are fast oxidative glycolytic and use both glycolysis and oxidative respiration, offering a balance between speed and endurance, while Type I fibers are slow-twitch and rely on oxidative metabolism for endurance. In some animals, the fastest glycolytic fibers are labeled Type IIb, but in humans the fast glycolytic counterpart is Type IIx.

Fast-twitch glycolytic fibers are built for rapid, powerful contractions and rely mainly on anaerobic glycolysis for ATP, which lets them generate a lot of force quickly but fatigue fast. The fiber type that fits this profile in humans is Type IIx. It has high fast myosin ATPase activity, large diameter, and a high content of glycolytic enzymes, with relatively few mitochondria and low myoglobin, so it produces energy mainly through glycolysis and tires quickly as lactate accumulates. In contrast, Type IIa fibers are fast oxidative glycolytic and use both glycolysis and oxidative respiration, offering a balance between speed and endurance, while Type I fibers are slow-twitch and rely on oxidative metabolism for endurance. In some animals, the fastest glycolytic fibers are labeled Type IIb, but in humans the fast glycolytic counterpart is Type IIx.

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