Which fiber type is most oxidative and fatigue-resistant?

Which fiber type is most oxidative and fatigue-resistant?

• A. Type IIa
• B. Type IIx
• C. Type IIb
• D. Type I

Answer: (D)

The main idea tested is how muscle fiber types differ in their ability to use oxygen and resist fatigue. Slow-twitch fibers have a high number of mitochondria, more myoglobin, and a rich capillary supply, which together support sustained aerobic metabolism. Because they rely on oxygen and fats (and carbohydrates) for energy, they produce ATP efficiently over long periods and fatigue much more slowly. This makes them the most oxidative and fatigue-resistant. Fast-twitch fibers, on the other hand, favor anaerobic pathways and provide quick, powerful contractions. They have fewer mitochondria and capillaries and lower myoglobin, so they tire more quickly, especially during prolonged effort. Among fast-twitch types, IIa is somewhat intermediate in oxidative capacity and fatigue resistance, while IIx and IIb are more glycolytic and fatigue-prone.

The main idea tested is how muscle fiber types differ in their ability to use oxygen and resist fatigue. Slow-twitch fibers have a high number of mitochondria, more myoglobin, and a rich capillary supply, which together support sustained aerobic metabolism. Because they rely on oxygen and fats (and carbohydrates) for energy, they produce ATP efficiently over long periods and fatigue much more slowly. This makes them the most oxidative and fatigue-resistant.

Fast-twitch fibers, on the other hand, favor anaerobic pathways and provide quick, powerful contractions. They have fewer mitochondria and capillaries and lower myoglobin, so they tire more quickly, especially during prolonged effort. Among fast-twitch types, IIa is somewhat intermediate in oxidative capacity and fatigue resistance, while IIx and IIb are more glycolytic and fatigue-prone.