ACSM Personal Trainer Certification Practice Exam

What are Type IIB fibers primarily characterized as?

1. Aerobic fibers

2. Intermediate fibers

3. Fast glycolitic fibers

4. Slow oxidative fibers

The correct answer is: Fast glycolitic fibers

Type IIB fibers, also known as fast glycolytic fibers, are primarily characterized by their ability to generate energy primarily through anaerobic metabolism. These fibers are geared towards short bursts of high-intensity activities, such as sprinting or heavy lifting, due to their high capacity for power and speed. They contain fewer mitochondria and lower levels of myoglobin compared to other fiber types, which contributes to their quick fatigue during prolonged exercise. The glycolytic capacity allows for rapid ATP production, making them ideal for activities that require immediate energy but do not sustain for long durations. While other muscle fiber types, such as slow oxidative fibers and intermediate fibers, focus more on endurance and aerobic metabolism, Type IIB fibers specifically thrive on anaerobic pathways, thus aligning them with high-intensity, short-duration events. Therefore, labeling Type IIB fibers as fast glycolytic accurately captures their primary characteristics in terms of energy production and performance capabilities.