Fast twitch fibers are best described as which?

Fast twitch fibers are best described as which?

• A. Muscle fiber that uses aerobic metabolism exclusively
• B. Muscle fiber that contains many mitochondria and can utilize oxygen
• C. Muscle fiber that contains few mitochondria and cannot utilize oxygen; they rely on anaerobic
• D. Muscle fiber that is slow to contract and fatigues slowly

Answer: (C)

Fast-twitch fibers are built for quick, powerful contractions and rely mainly on anaerobic energy production. They have relatively few mitochondria, so they’re not efficient at using oxygen to make ATP. That’s why they generate energy quickly through glycolysis for short bursts and tend to fatigue rapidly. In contrast, slow-twitch fibers are more oxidative, with many mitochondria and strong aerobic capacity, supporting sustained activity. The other descriptions mix in features of oxidative, slow-twitch fibers or contradict the rapid, high-intensity nature of fast-twitch fibers.

Fast-twitch fibers are built for quick, powerful contractions and rely mainly on anaerobic energy production. They have relatively few mitochondria, so they’re not efficient at using oxygen to make ATP. That’s why they generate energy quickly through glycolysis for short bursts and tend to fatigue rapidly. In contrast, slow-twitch fibers are more oxidative, with many mitochondria and strong aerobic capacity, supporting sustained activity. The other descriptions mix in features of oxidative, slow-twitch fibers or contradict the rapid, high-intensity nature of fast-twitch fibers.