National Academy of Sports Medicine (NASM) Certified Personal Trainer (CPT) Practice Exam

Which of the following muscle types is typically larger and produces more force?

1. Fast-twitch muscle fibers

2. Slow-twitch muscle fibers

3. Type I fibers

4. Type IIa fibers

The correct answer is: Fast-twitch muscle fibers

Fast-twitch muscle fibers are typically larger and capable of producing more force compared to other muscle fiber types. These fibers are designed for power and strength activities, as they have a greater cross-sectional area, allowing them to generate more force during contraction. Fast-twitch fibers predominantly rely on anaerobic metabolism, which supports quick and explosive movements, such as sprinting or weightlifting. In contrast, slow-twitch muscle fibers, also known as Type I fibers, are more endurance-oriented, designed for prolonged, low-intensity activities. They are smaller in size, contain a higher number of mitochondria, and utilize aerobic metabolism, making them less capable of generating the same amount of force as fast-twitch fibers. Type IIa fibers, while also considered fast-twitch, are intermediate in terms of size and fatigue resistance. They can produce more force than slow-twitch fibers but generally not as much as the larger fast-twitch fibers. Therefore, the characteristic of being larger and producing more force distinctly identifies fast-twitch muscle fibers as the correct answer.