Type 2b muscle fibers are best described as which of the following?

• A. Slow-twitch fibers optimized for endurance
• B. Intermediate speed fibers used for mid-distance events
• C. Fast-twitch fibers suited to sprinting and maximal effort tasks
• D. A combination of slow and fast properties with variable endurance

Answer: (C)

Type 2b fibers are fast-twitch glycolytic fibers. They contract rapidly and generate high force, making them ideal for sprinting and other maximal-effort tasks that last only a short time. They rely mainly on anaerobic glycolysis for energy, so they can produce power quickly but fatigue quickly and have limited endurance. Structurally, they show high myosin ATPase activity and relatively low mitochondrial density and capillary supply, supporting fast contractions but not long-lasting work. This profile explains why they’re described as fast-twitch suited to sprinting and maximal efforts rather than endurance or mid-distance work. The idea of a blend of slow and fast properties would imply more oxidative capacity, and slow-twitch fibers are tuned for endurance, which is why those options don’t fit as well.