ACE Personal Trainer Practice Exam

In terms of muscle fiber classification, Type 2a fibers are primarily known for which attributes?

1. High-speed, low endurance

2. Speed, fatigue resistance, and moderate force production

3. Fatigue-prone but high force production

4. Low speed and high oxidative capacity

The correct answer is: Speed, fatigue resistance, and moderate force production

Type 2a muscle fibers, also known as fast oxidative fibers, are characterized by their ability to generate speed and power while also being more fatigue-resistant than Type 2b fibers. They possess a combination of the qualities that make them advantageous for both anaerobic and aerobic activities. These fibers are capable of producing moderate levels of force, which makes them suitable for activities that require both strength and endurance, such as middle-distance running or interval training. The presence of myoglobin gives them a reddish color and supports their oxidative capacity, allowing for better endurance than purely fast-twitch fibers. This unique blend of attributes allows Type 2a fibers to maintain performance during longer bouts of high-intensity work to some degree, unlike fibers that are purely fast-twitch and more susceptible to fatigue. Thus, the classification of Type 2a fibers focuses on their speed, fatigue resistance, and moderate force production, which is why this choice accurately describes their primary attributes.