AFAA Personal Trainer Certification Practice Exam

What is a main feature of fast twitch muscle fibers?

1. High aerobic endurance

2. Resistance to fatigue

3. Short duration, high-intensity activities

4. Utilized for maintaining posture

The correct answer is: Short duration, high-intensity activities

Fast twitch muscle fibers are primarily designed for short bursts of power and speed, making them essential for activities that require high-intensity, explosive movements. These fibers contract quickly and generate a significant amount of force, which is ideal for sports and exercises that involve sprinting, jumping, or lifting heavy weights over a brief period. Their adaptation is geared toward anaerobic metabolism, allowing them to perform well in scenarios where oxygen availability is limited, thus making them less efficient for longer-duration, sustained activities. In contrast, the other options emphasize different muscle fiber characteristics. High aerobic endurance, for instance, is a trait of slow twitch muscle fibers, which rely on aerobic metabolism and are well-suited for prolonged activities. Similarly, resistance to fatigue is more pronounced in slow twitch fibers, as they are designed for endurance rather than the rapid, powerful contractions of fast twitch fibers. Lastly, utilizing muscles for maintaining posture involves slow twitch fibers as well, which are constantly engaged to support the body against gravity. Understanding the primary function of fast twitch fibers aids in designing effective training programs that align with specific athletic goals or performance outcomes.