Final answer:
1) Type I fibers, also known as slow oxidative or slow-twitch fibers, are specialized for endurance. They use aerobic respiration to produce ATP and are efficient at carrying oxygen, allowing for prolonged activity without rapid fatigue.
Step-by-step explanation:
The type of skeletal muscle fibers specialized for endurance is type I fibers. These fibers, also known as slow oxidative or slow-twitch fibers, are rich in mitochondria, capillaries, and myoglobin, which provide them with a red color. They utilize aerobic respiration to produce ATP, allowing them to carry oxygen efficiently and sustain aerobic activities for long durations, making them less prone to fatigue.
Type IIa fibers, also known as fast oxidative fibers, are capable of both aerobic and anaerobic respiration but fatigue more quickly than type I fibers. On the other hand, Type IIb fibers (or type IIx), known as fast glycolytic fibers, are the fastest fibers that primarily use anaerobic glycolysis and are designed for short, intense bursts of activity, leading to quicker fatigue.
Endurance athletes typically have a higher proportion of type I fibers in their muscles, which supports prolonged activities like long-distance running or cycling. This adaptation results from their consistent endurance training, which encourages the development of muscle characteristics conducive to long-lasting aerobic activity.