What are the common characteristics of fast twitch muscle fibers?

Fast twitch muscle fibers, also known as type II fibers, are characterized by their ability to contract quickly and generate a lot of force. These fibers are built for power and speed, making them essential for activities that require short bursts of intense effort, such as sprinting, weightlifting, or explosive movements in sports.

Due to their reliance on anaerobic metabolism, fast twitch fibers can produce energy quickly but do not sustain activity for long periods, leading to rapid fatigue. This is in contrast to slow twitch muscle fibers, which are designed for endurance and are more resistant to fatigue, enabling them to perform well during prolonged activities such as long-distance running.

The other options highlight features associated with either slow twitch fibers or general metabolic traits that do not specifically define fast twitch fibers. For instance, using fast twitch fibers for endurance activities contradicts their primary function, which is geared toward short, powerful bursts of activity. Similarly, while it's true that fast twitch fibers can be larger than slow twitch fibers, this characteristic is less about their functional capacity compared to their speed and fatigue rates. Thus, the description that they contract quickly and tire rapidly accurately encapsulates the essential nature of fast twitch muscle fibers.