Which type of muscle fiber is more resistant to fatigue and used for endurance activities?

The correct answer is Type I fibers. These muscle fibers, also known as slow-twitch fibers, are highly resistant to fatigue and are predominantly used for endurance activities, such as long-distance running or cycling. Type I fibers are rich in mitochondria, myoglobin, and capillary density, enabling them to utilize oxygen more efficiently for aerobic metabolism. This energy production supports prolonged physical activity without quickly depleting energy stores, allowing for sustained performance over time.

The properties of Type I fibers make them particularly suited for activities that require endurance, as they generate energy through oxidative phosphorylation, which is a more efficient process for producing ATP compared to the systems used by fast-twitch fibers. In contrast, Type II fibers, which are fast-twitch fibers, are more suited for short bursts of strength and power activities, as they fatigue more quickly. Type III and Type IV fibers are not standard classifications and do not represent scientifically recognized muscle fiber types in the same way; therefore, they are not relevant to this question. Understanding the role and characteristics of muscle fiber types is crucial for designing effective training programs tailored to specific athletic goals or performance needs.