Which type of muscle fiber is classified as "fast twitch"?

Fast-twitch muscle fibers, classified as Type 2 fibers, are designed for quick and powerful movements. They are characterized by their ability to produce rapid and forceful contractions but tend to fatigue more quickly than their slow-twitch counterparts. Type 2 fibers rely on anaerobic metabolism for energy, meaning they function efficiently in short bursts of intense activity, such as sprinting or weightlifting.

In contrast, Type 1 fibers, also known as slow-twitch fibers, are more suited for endurance activities. They utilize aerobic metabolism, enabling them to sustain prolonged efforts like long-distance running or cycling without fatigue. The classification system typically does not include Type 3 or Type 4 fibers as commonly recognized categories in muscle physiology, reinforcing that Type 2 fibers are indeed the fast-twitch variant central to high-intensity, explosive movements.