Which muscle fiber type is optimized for endurance and fatigue resistance?

• A. Fast-twitch (Type II) fibers
• B. Slow-twitch (Type I) fibers
• C. Intermediate (Type IIa) fibers
• D. Striated fibers

Answer: (B)

Endurance and fatigue resistance come from a muscle fiber’s capacity to generate ATP through aerobic metabolism. Slow-twitch fibers pack many mitochondria, have abundant myoglobin, and receive a rich capillary supply, supporting sustained, slower contractions powered mainly by oxidative phosphorylation. This setup lets muscles work for long periods with minimal fatigue, which is why slow-twitch fibers excel in endurance tasks like long-distance running or maintaining posture. Fast-twitch fibers rely more on glycolysis for rapid, high‑force contractions and fatigue quickly; intermediate fibers blend oxidative and glycolytic traits; striated fibers is a general tissue description and does not specify endurance properties. Slow-twitch, Type I fibers are optimized for endurance and fatigue resistance.