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010-111 · Question #14

Type II muscle fibers:

The correct answer is C. Are recruited at a higher percentage of maximum force than Type I fibers. Type II fast-twitch fibers are recruited only at higher percentages of maximum voluntary force, following the size principle, and fatigue rapidly due to their reliance on anaerobic glycolysis. They are not suited for sustained endurance or oxidative fat metabolism.

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Question

Type II muscle fibers:

Options

  • AHave a high capacity to generate energy through the electron transport system.
  • BHave a high capacity to generate energy from fat.
  • CAre recruited at a higher percentage of maximum force than Type I fibers.
  • DHave high endurance capabilities.

How the community answered

(31 responses)
  • A
    3% (1)
  • B
    6% (2)
  • C
    81% (25)
  • D
    10% (3)

Why each option

Type II fast-twitch fibers are recruited only at higher percentages of maximum voluntary force, following the size principle, and fatigue rapidly due to their reliance on anaerobic glycolysis. They are not suited for sustained endurance or oxidative fat metabolism.

AHave a high capacity to generate energy through the electron transport system.

High capacity for the electron transport system (oxidative phosphorylation) is a hallmark of Type I slow-twitch fibers due to their dense mitochondrial content, not Type II fibers.

BHave a high capacity to generate energy from fat.

Fat oxidation is an aerobic process favored by Type I fibers; Type II fibers rely predominantly on anaerobic glycolysis and have limited capacity for fat-derived energy.

CAre recruited at a higher percentage of maximum force than Type I fibers.Correct

Henneman's size principle states that motor units are recruited from smallest to largest as force demands increase, meaning Type I slow-twitch fibers are activated first and Type II fast-twitch fibers are recruited progressively as the required force approaches higher percentages of maximum. This makes Type II fibers active at intensities above the threshold already covered by Type I fibers.

DHave high endurance capabilities.

High endurance and fatigue resistance are characteristics of Type I slow-twitch fibers; Type II fibers fatigue rapidly due to limited oxidative capacity.

Concept tested: Type II muscle fiber recruitment threshold and characteristics

Topics

#Type II muscle fibers#fast-twitch fibers#muscle recruitment#force production

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