Which statement best describes slow-twitch fibers?

• A. They fatigue quickly and rely on anaerobic metabolism
• B. They are fatigue-resistant and rely on aerobic metabolism
• C. They contract rapidly and rely on glycogen reserves
• D. They have both fast and slow properties but cannot adapt

Answer: (B)

Slow-twitch fibers are built for endurance and long-duration activity. They have many mitochondria, a rich network of capillaries, and high myoglobin content, all of which support efficient, sustained delivery and use of oxygen. This setup favors aerobic metabolism (oxidative phosphorylation), allowing these fibers to produce ATP steadily during prolonged effort with minimal fatigue. They contract more slowly and generate less force, but they can keep working for extended periods, such as in posture or distance activities. In contrast, they rely less on quick, glycogen-driven, anaerobic energy bursts. So the statement that slow-twitch fibers are fatigue-resistant and rely on aerobic metabolism best describes their characteristics.