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

What type of muscle fibers are associated with quick fatigue and high force production?

1. Slow-twitch fibers

2. Type 1 fibers

3. Type 2 fibers

4. Type 3 fibers

The correct answer is: Type 2 fibers

Type 2 fibers, also known as fast-twitch fibers, are associated with quick fatigue and high force production. These muscle fibers are designed for rapid and powerful movements, making them ideal for activities that require strength and speed, such as sprinting or weightlifting. They are capable of generating more force than slow-twitch fibers due to their greater cross-sectional area and higher recruitment of motor units during intense activities. Fast-twitch fibers rely primarily on anaerobic metabolism, which allows for quick bursts of energy but leads to the accumulation of fatigue-inducing byproducts, resulting in quicker exhaustion compared to slow-twitch fibers. This characteristic is why they are more suited for short-duration, high-intensity efforts. Understanding the function and capabilities of Type 2 fibers helps personal trainers design effective training programs that align with individual performance goals, particularly in sports emphasizing explosive power.