Final answer:
High capillary density, high myoglobin content, and high resistance to fatigue characterize slow oxidative (SO) fibers, also known as type-I muscle fibers, used in endurance activities.
Step-by-step explanation:
The skeletal muscle types described by high capillary density, high myoglobin content, and high resistance to fatigue are slow oxidative (SO) fibers, also known as type-I muscle fibers. These fibers are dense with capillaries and contain a large amount of mitochondria and myoglobin, contributing to their characteristic red color and ability to sustain aerobic activity for extended periods without fatigue.
Slow-twitch muscle fibers are utilized primarily in endurance activities, as they are designed for long-duration contractions and are slow to fatigue.