What trait is characteristic of Type I muscle fibers?

Type I muscle fibers, also known as slow-twitch fibers, are primarily designed for endurance and prolonged activities. One of their defining traits is high fatigue resistance, which means they can sustain activity over longer periods without tiring. This characteristic is due to their efficient use of oxygen, enabling them to perform aerobic metabolism. The abundance of mitochondria in Type I fibers supports this trait by facilitating energy production through oxidative phosphorylation, providing a steady supply of ATP for extended muscle contractions.

This endurance capacity makes Type I fibers particularly suitable for activities such as long-distance running, cycling, and other aerobic exercises where stamina and sustained effort are required. Understanding this trait helps in distinguishing these fibers from Type II muscle fibers, which are more geared towards short bursts of activity and rapid energy release but fatigue more quickly.