Washington Master Esthetics Practice Exam

Which type of muscle fibers are used primarily for endurance activities?

1. Fast-twitch fibers

2. Type I fibers

3. Type II fibers

4. Intermediate fibers

The correct answer is: Type I fibers

The correct answer is Type I fibers. These muscle fibers are also known as slow-twitch fibers and are specifically designed for endurance and long-duration activities. They have a high capacity for oxygen uptake and are rich in mitochondria, which means they can efficiently use oxygen to generate energy through aerobic metabolism. This characteristic allows Type I fibers to sustain prolonged efforts without fatigue, making them ideal for activities such as distance running, cycling, and swimming. In contrast, fast-twitch fibers (Type II fibers) are geared toward short bursts of power and strength activities, such as sprinting or weightlifting. They generate quick, forceful contractions but fatigue rapidly. Intermediate fibers, while having characteristics of both Type I and Type II fibers, do not primarily function in endurance activities the way that Type I fibers do. Understanding these distinctions is critical for anyone involved in fitness training or exercise physiology, as it helps tailor training programs to the specific needs of different activities.