Lifetime Fitness Practice Exam 2026 - Complete Prep Guide

Fast-twitch fibers, also known as Type II fibers, are characterized by their ability to contract rapidly and generate a significant amount of force in a short period of time. This makes them particularly useful for activities that require explosive strength, such as sprinting or weightlifting. However, this quick contraction also means they rely predominantly on anaerobic energy pathways, which are less efficient for prolonged exertion. Consequently, fast-twitch fibers fatigue quickly compared to slow-twitch fibers, which are built for endurance and can sustain activity over longer periods due to their ability to utilize aerobic metabolism.

The rapid fatigue of fast-twitch fibers is due to the limited store of glycogen and higher lactic acid production during intense activity. Thus, while they are essential for high-intensity, short-duration tasks, they are not suited for endurance activities. This unique characteristic is what distinguishes fast-twitch fibers from other types, such as slow-twitch fibers, which facilitate endurance and stamina.