010-111 · Question #229
In comparison to type I muscle fibers, type II fibers ______.
The correct answer is C. Are recruited at a higher percentage of maximum force. Type II (fast-twitch) muscle fibers are recruited only when higher force output is demanded, following Henneman's size principle, which states that larger motor units are activated at greater percentages of maximum force.
Question
In comparison to type I muscle fibers, type II fibers ______.
Options
- AHave a higher capacity to generate energy through the electron transport system
- BHave a higher capacity to generate energy from fat
- CAre recruited at a higher percentage of maximum force
- DAre capable of greater endurance
How the community answered
(71 responses)- A14% (10)
- B4% (3)
- C75% (53)
- D7% (5)
Why each option
Type II (fast-twitch) muscle fibers are recruited only when higher force output is demanded, following Henneman's size principle, which states that larger motor units are activated at greater percentages of maximum force.
Type I (slow-twitch) fibers have a higher capacity for oxidative phosphorylation via the electron transport chain due to their greater mitochondrial density, not type II.
Type I fibers rely more heavily on fat oxidation (beta-oxidation) for sustained energy, whereas type II fibers depend primarily on glycolytic pathways.
Type II fibers are fast-twitch motor units with larger motor neurons, recruited later in the recruitment order per Henneman's size principle - only when the required force exceeds what type I fibers can generate. This means they are activated at a higher percentage of maximum voluntary force, making this the key distinguishing characteristic relative to type I fibers.
Type I fibers are fatigue-resistant and suited for prolonged activity, giving them greater endurance capacity than type II fibers.
Concept tested: Type I vs Type II muscle fiber recruitment thresholds
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