How do Type I and Type II muscle fibers differ in terms of metabolism and fatigue?

• A. Type I slow-twitch fibers rely on oxidative metabolism, have high endurance, and are fatigue resistant; Type II fast-twitch fibers rely on glycolysis, generate more force, and fatigue quickly
• B. Type I slow-twitch fibers rely on glycolysis, have low endurance, and fatigue quickly; Type II fast-twitch fibers rely on oxidative metabolism, generate less force
• C. Type I slow-twitch fibers rely on oxidative metabolism but fatigue quickly; Type II fast-twitch rely on glycolysis and fatigue slowly
• D. Type I slow-twitch fibers rely on glycolysis and have high endurance; Type II fast-twitch rely on oxidative metabolism and fatigue resistance

Answer: (A)

Type I slow-twitch fibers are built for endurance. They rely on oxidative metabolism, using many mitochondria and myoglobin to generate ATP through aerobic pathways. This setup supports prolonged activity and makes them highly resistant to fatigue.

Type II fast-twitch fibers favor quick, powerful efforts. They rely more on glycolysis for rapid ATP production, which supports fast, forceful contractions but tends to exhaust quickly as byproducts build up and oxidative support is lower. That combination explains why these fibers generate more force in short bursts and tire sooner.

So, the description that Type I fibers use oxidative metabolism with high endurance and fatigue resistance, while Type II fibers rely on glycolysis, produce more force, and fatigue quickly, aligns with how these fiber types are structured and function.