Which characteristic best explains why slow-twitch (type I) skeletal muscle fibers have a high resistance to fatigue?

• A. They have low capillary density and rely primarily on anaerobic glycolysis for ATP production.
• B. They have a large fiber diameter with low myoglobin content, maximizing rapid force production.
• C. They have few mitochondria and store minimal oxygen, but generate ATP mainly from creatine phosphate.
• D. They have abundant mitochondria and myoglobin and rely primarily on aerobic (oxidative) metabolism.

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the key characteristics of slow-twitch (type I) muscle fibers. These fibers are specialized for endurance and continuous activity over long periods without fatigue.
2. Step 2: Recognize that slow-twitch fibers have a high density of mitochondria, which are the organelles responsible for aerobic (oxidative) metabolism, allowing efficient ATP production using oxygen.
3. Step 3: Note the presence of abundant myoglobin in slow-twitch fibers, which binds oxygen and facilitates its delivery within the muscle cells, supporting sustained aerobic respiration.
4. Step 4: Contrast this with fast-twitch fibers, which rely more on anaerobic glycolysis and have fewer mitochondria and less myoglobin, making them more prone to fatigue.
5. Step 5: Conclude that the high resistance to fatigue in slow-twitch fibers is best explained by their abundant mitochondria and myoglobin, enabling them to rely primarily on aerobic metabolism for ATP production.