Which fiber type is largest, fastest, and fatigues quickly?

Which fiber type is largest, fastest, and fatigues quickly?

• A. Type I
• B. Type IIA
• C. Type IIB
• D. Type IIx

Answer: (C)

Fast glycolytic fibers carry the most speed and power but tire quickly. They have the largest diameter among the fiber types, contract rapidly, and rely mainly on anaerobic metabolism, which enables quick, strong bursts but leads to rapid fatigue due to lactate buildup and lower mitochondrial and capillary density. In humans, this fastest, most fatigable group is Type IIx (often called Type IIb in some species). By contrast, Type I fibers are slow and highly fatigue-resistant, and Type IIa fibers are fast but more fatigue-resistant than IIx. So the fiber type that’s largest, fastest, and fatigues quickly is the fast glycolytic group (Type IIx).

Fast glycolytic fibers carry the most speed and power but tire quickly. They have the largest diameter among the fiber types, contract rapidly, and rely mainly on anaerobic metabolism, which enables quick, strong bursts but leads to rapid fatigue due to lactate buildup and lower mitochondrial and capillary density. In humans, this fastest, most fatigable group is Type IIx (often called Type IIb in some species). By contrast, Type I fibers are slow and highly fatigue-resistant, and Type IIa fibers are fast but more fatigue-resistant than IIx. So the fiber type that’s largest, fastest, and fatigues quickly is the fast glycolytic group (Type IIx).