International Sports Sciences Association (ISSA) Trainer Practice Exam

Type I muscle fibers, also known as slow-twitch fibers, are indeed predominantly aerobic, which means they primarily use oxygen to generate energy. These fibers are highly efficient at using oxygen for energy production, which allows them to sustain prolonged activities, making them ideal for endurance exercises such as long-distance running and cycling. Slow-twitch fibers are characterized by a rich supply of capillaries, high levels of mitochondria, and a greater amount of myoglobin, all of which enhance their ability to perform aerobic metabolism.

In contrast, Type II muscle fibers, or fast-twitch fibers, predominantly rely on anaerobic metabolism for short bursts of high-intensity activities. This distinction highlights how Type I fibers are specifically adapted for endurance and activities that require sustained muscle contraction over long periods. The aerobic capability of Type I fibers is crucial for athletes engaged in endurance sports, where utilizing oxygen efficiently is vital for performance.