A person whose genetic makeup makes him or her a better marathon runner than a sprinter probably has more ________ in his or her leg muscles.

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Quizplus · Accepted Answer

Slow fibers, also known as Type I fibers, have a high oxidative capacity and utilize aerobic metabolism to produce energy. This allows them to sustain activity for longer periods of time, making them favorable for endurance activities like marathon running. Fast fibers, also known as Type II fibers, have a high glycolytic capacity and rely on anaerobic metabolism to produce energy quickly, which is beneficial for short bursts of high-intensity activity like sprinting. Intermediate fibers, also known as Type IIa fibers, have characteristics in between slow and fast fibers. Dark fibers and noncontractile fibers are not valid terms in muscle fiber classification.

A Person Whose Genetic Makeup Makes Him or Her a Better