NETA Personal Trainer Practice Exam

Type 2a muscle fibers, also known as fast-twitch oxidative fibers, are characterized by their ability to generate force quickly while also having a moderate resistance to fatigue. They can use both aerobic and anaerobic metabolism, making them well-suited for activities that require a powerful burst of energy over a sustained effort but not endurance levels that would extend for long periods.

400-meter sprints are ideal for primarily recruiting Type 2a muscle fibers. This distance requires a balance of speed, strength, and endurance, allowing these muscle fibers to dominate the energy production needed. The speed and intensity involved in a 400-meter sprint demand fast-twitch muscle fiber activation but the length of the sprint also means that athletes need to rely on some aerobic metabolism, a characteristic of Type 2a fibers.

In contrast, activities like running a marathon primarily engage Type 1 slow-twitch fibers, which are more efficient for long-distance and endurance tasks. 1RM weight training and heavy powerlifting predominantly recruit Type 2b fibers, which generate maximum force but fatigue quickly, suitable for short bursts of intense effort rather than sustained activities.

Thus, the 400-meter sprint effectively demonstrates the primary utilization of Type 2a muscle fibers due to the requirements of both