Which of the following types of skeletal muscle fibers is specialized for endurance?

• A. Fast oxidative fibers (Type IIa)
• B. Fast glycolytic fibers (Type IIb)
• C. Intermediate fibers
• D. Slow oxidative fibers (Type I)

Answer: (D)

Verified step by step guidance

1. Understand the characteristics of skeletal muscle fiber types: Skeletal muscle fibers are categorized based on their contraction speed and metabolic properties. The main types are slow oxidative fibers (Type I), fast oxidative fibers (Type IIa), and fast glycolytic fibers (Type IIb).
2. Recognize the specialization of slow oxidative fibers (Type I): These fibers are adapted for endurance activities due to their high mitochondrial density, abundant myoglobin content, and reliance on aerobic metabolism for energy production.
3. Compare slow oxidative fibers to other types: Fast oxidative fibers (Type IIa) are faster but less fatigue-resistant than Type I fibers, while fast glycolytic fibers (Type IIb) are specialized for short bursts of power and rely on anaerobic metabolism, making them less suited for endurance.
4. Understand the role of myoglobin and mitochondria: Slow oxidative fibers contain high levels of myoglobin, which stores oxygen, and numerous mitochondria, which facilitate sustained aerobic energy production during prolonged activities.
5. Conclude that slow oxidative fibers (Type I) are the correct answer: Their structural and functional adaptations make them ideal for endurance tasks, such as maintaining posture or long-distance running.