Which of the following best describes Type I muscle fibers?

Type I muscle fibers, also known as slow-twitch fibers, are characterized by their ability to sustain prolonged, endurance-based activities. They are rich in mitochondria and hemoglobin, which allows them to utilize oxygen efficiently and generate energy through aerobic metabolism. This makes them particularly well-suited for activities that require stamina, such as long-distance running or cycling. Their slow contraction speed and high resistance to fatigue enable them to perform effectively over extended periods without tiring quickly.

In contrast, options that suggest fast-twitch characteristics, or low resistance to fatigue, do not accurately describe Type I fibers. Fast-twitch fibers, on the other hand, are geared towards short bursts of power and speed, typically utilized in anaerobic activities. They tire quickly due to their reliance on anaerobic metabolism, which produces energy without using oxygen, leading to a rapid accumulation of lactic acid and subsequent fatigue. Therefore, understanding the specific attributes of Type I fibers helps clarify why they are aligned with endurance and aerobic activities.