Slow twitch fibers are described as which of the following?

• A. Muscle fiber that contains few mitochondria and cannot utilize oxygen
• B. Muscle fiber that contains many mitochondria and uses oxygen poorly
• C. Muscle fiber that contains many mitochondria, good for oxygen utilization
• D. Muscle fiber that relies primarily on anaerobic glycolysis

Answer: (C)

Slow-twitch fibers are oxidative and fatigue-resistant, designed for endurance by using oxygen continuously to produce energy. That means they contain many mitochondria and are very good at utilizing oxygen—matching the description of a fiber with abundant mitochondria and efficient oxygen use. The other statements don’t fit because having few mitochondria implies limited aerobic capacity; saying they use oxygen poorly contradicts the very idea of oxidative metabolism; and relying mainly on anaerobic glycolysis describes a pathway more typical of fibers that rely on quick bursts of effort and fatigue quickly, rather than sustained activity.