Fast-twitch fibers differ from slow-twitch fibers in that
A) they are more common in the leg muscles of champion sprinters than marathon runners.
B) they have more mitochondria.
C) they fatigue less rapidly.
D) their abundance is more a product of training than of genetics.
E) they are more common in postural muscles than in finger muscles.

Question

Quizplus · Accepted Answer

Fast-twitch fibers are more common in the leg muscles of champion sprinters than marathon runners, indicating a genetic difference in muscle fiber composition.

Answer: C 
 Fast-twitch fibers fatigue less rapidly than slow-twitch fibers. This allows them to produce quick, powerful bursts of energy but for shorter durations.

Answer: D
 While genetics do play a role in determining muscle fiber composition, the abundance of fast-twitch fibers can also be influenced by training. High-intensity, explosive exercises like weightlifting can increase the number and size of fast-twitch fibers.

Therefore, choices A, C, and D are the best answers. Choices B and E are incorrect as they do not accurately describe the differences between fast-twitch and slow-twitch fibers.

Fast-Twitch Fibers Differ from Slow-Twitch Fibers in That