Which of the following is a characteristic of a type II muscle fiber?

• A. Primarily uses aerobic metabolism
• B. Fast contraction speed
• C. Rich in myoglobin
• D. High resistance to fatigue

Answer: (B)

Verified step by step guidance

1. Understand the characteristics of muscle fiber types: Type I (slow-twitch) and Type II (fast-twitch). Type I fibers are associated with endurance activities, relying on aerobic metabolism, rich in myoglobin, and have high resistance to fatigue. Type II fibers are designed for short bursts of power and speed, relying more on anaerobic metabolism, and have faster contraction speeds.
2. Analyze the options provided in the question. The characteristics listed include: 'Primarily uses aerobic metabolism,' 'Fast contraction speed,' 'Rich in myoglobin,' and 'High resistance to fatigue.'
3. Compare each characteristic to the known traits of Type II muscle fibers. Type II fibers are known for fast contraction speed, lower myoglobin content compared to Type I fibers, reliance on anaerobic metabolism, and lower resistance to fatigue.
4. Eliminate the options that align more closely with Type I muscle fibers. For example, 'Primarily uses aerobic metabolism,' 'Rich in myoglobin,' and 'High resistance to fatigue' are traits of Type I fibers, not Type II fibers.
5. Identify the correct characteristic of Type II muscle fibers from the remaining options. Based on the comparison, 'Fast contraction speed' is the defining trait of Type II muscle fibers.