Which fibers are fatigable, contract rapidly, are anaerobic and ideal for short-term powerful movements, and depend on glycogen reserves for fuel?

• A. Slow twitch (red fibers)
• B. Fast twitch (white fibers)
• C. Intermediate twitch fibers
• D. Oxidative fibers

Answer: (B)

This is about muscle fiber types and how they generate energy for different kinds of movement. The fast-twitch, glycolytic fibers are the ones that contract rapidly and generate high power, but they fatigue quickly because they rely mainly on anaerobic glycolysis using stored glycogen for fuel. Their metabolism produces energy quickly without relying on oxygen, which fits short, explosive movements like sprinting or heavy lifting. They appear lighter in color (the “white” fibers) due to lower myoglobin content and fewer mitochondria, reflecting their emphasis on rapid, glycolytic ATP production. In contrast, slow-twitch fibers are fatigue-resistant and rely on aerobic metabolism, using more myoglobin and mitochondria; intermediate fibers have properties between the two. So the described characteristics align with fast-twitch (glycolytic, anaerobic) fibers.