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 are also known as Type I muscle fibers and are used for endurance activities such as marathon running. These fibers are more efficient at using oxygen and can contract for long periods of time without fatigue. Fast fibers (Type II) are better for sprinting and other explosive activities, while intermediate fibers (Type IIA) have a mix of endurance and power capabilities. Dark fibers and red fibers are not terms commonly used to describe muscle fibers.

A Person Whose Genetic Makeup Makes Him or Her a Better