Final answer:
Slow-twitch muscle fibers, or type I muscle fibers, are responsible for aerobic endurance activities and are characterized by their ability to sustain contractions over long periods of time. They are dense with capillaries, mitochondria, and myoglobin, allowing them to carry more oxygen and support aerobic activity. Slow-twitch fibers are relied upon in endurance events like long-distance running or cycling.
Step-by-step explanation:
Slow-twitch muscle fibers, also known as type I muscle fibers, are a type of skeletal muscle cell that is mainly responsible for aerobic activities such as long-distance running. These fibers are dense with capillaries and rich in mitochondria and myoglobin, which allows them to carry more oxygen and sustain aerobic activity. Slow-twitch fibers have the ability to contract for long periods of time but with less force compared to fast-twitch fibers. They are relied upon primarily in endurance events like distance running or cycling.