What defines Type 2 muscle fibers in terms of fatigue resistance?

Type 2 muscle fibers, also known as fast-twitch fibers, are characterized by their moderate resistance to fatigue when compared to the other types of muscle fibers. These fibers generate energy primarily through anaerobic metabolism, allowing for quick and powerful bursts of activity, which makes them particularly suited for activities such as sprinting or weightlifting. However, because they rely heavily on anaerobic processes, they do not sustain prolonged activity as efficiently as Type 1 fibers (slow-twitch fibers) that are more fatigue-resistant and use aerobic metabolism.

The moderate resistance to fatigue means that Type 2 fibers can sustain powerful contractions for a limited duration before they become fatigued. This distinguishes them from Type 1 fibers, which have a high resistance to fatigue and can maintain activity over long periods, and from Type 2b fibers, which have low resistance and fatigue quickly under sustained effort. Thus, this unique characteristic of Type 2 fibers is critical for understanding their role in various physical activities and exercise regimens.