Which muscle type is more anaerobic, produces more speed and strength, and fatigues faster?

• A. Type I fibers
• B. Type II fibers
• C. Smooth muscle
• D. Cardiac muscle

Answer: (B)

Fast-twitch Type II muscle fibers are the ones designed for quick, powerful actions and rely more on anaerobic energy production. They contract rapidly and generate high force due to faster cross-bridge cycling and greater myosin ATPase activity, along with a larger fiber diameter. Because they depend largely on glycolysis for energy, they can produce energy quickly but fatigue quickly as lactate builds up and energy substrates are depleted. In contrast, slow-twitch Type I fibers rely on oxidative metabolism, are more endurance-oriented, and resist fatigue. Smooth and cardiac muscle are different tissue types with distinct energy systems and contraction patterns, not the fast glycolytic skeletal fibers described here.