AFAA Personal Trainer Certification Practice Exam

Which muscle fiber type is predominantly utilized during endurance events such as marathons?

1. Fast twitch

2. Slow twitch

3. Intermediate twitch

4. Static fibers

The correct answer is: Slow twitch

The muscle fiber type predominantly utilized during endurance events such as marathons is slow twitch fibers. These fibers are specifically adapted for prolonged activities, allowing for sustained contractions over extended periods without fatigue. Slow twitch fibers, also known as Type I fibers, have a high density of mitochondria and myoglobin, which enables them to efficiently use oxygen for aerobic metabolism. This characteristic supports endurance tasks, as they are able to produce energy over long durations while maintaining lower levels of fatigue compared to other fiber types. This makes them ideal for activities like running long distances, where endurance is essential for performance. In contrast, fast twitch fibers are more suited for short bursts of power and strength, such as sprinting or weightlifting. Intermediate twitch fibers can exhibit properties of both slow and fast twitch, but they are not the primary fibers engaged in endurance events. Static fibers, which are not a recognized classification of muscle fibers in this context, do not play a role in dynamic movements that are critical in endurance activities. Therefore, slow twitch fibers are central to endurance performance, allowing athletes to optimize their aerobic capacity and sustain intense physical activity over long durations.