Which is a characteristic of Type I muscle fibers?

Type I muscle fibers, also known as slow-twitch fibers, are distinctly characterized by their primary reliance on oxidative metabolism for energy production. This metabolic pathway utilizes oxygen to convert carbohydrates and fats into energy, enabling sustained muscle contraction over extended periods. This characteristic makes Type I fibers particularly well-suited for endurance activities such as long-distance running or cycling, where the demand for prolonged, low-intensity muscle activity is high.

These fibers are also highly vascularized and contain a greater number of mitochondria, which enhances their capacity for aerobic energy production. Consequently, they are significantly more fatigue-resistant compared to fast-twitch fibers, allowing them to perform effectively in scenarios that require sustained physical effort.

The other characteristics mentioned in the question highlight traits of different muscle fiber types. For instance, fast-twitch fibers are more involved in explosive activities and are less capable of sustaining prolonged exertion, hence displaying characteristics opposite to those of Type I fibers.