Question

Marathon runners use mostly slow-twitch muscle fibers, whereas sprinters use mostly fast-twitch fibers. Why do the two types of muscle fibers perform differently?

a Extensive training explains most of the difference between how the two types of muscle fibers work.
b Fast-twitch muscle cells have a greater blood supply.
c Only fast-twitch muscles can break down glucose to make ATP.
d They use different processes for making ATP.

Answer 1

Slow-twitch muscle fibers enable marathon runners to sustain long-duration aerobic activity, with a high content of oxygen-supporting components. In contrast, fast-twitch fibers allow sprinters rapid and powerful contractions suitable for short, anaerobic events but fatigue quickly.

Step-by-step explanation:

Marathon runners primarily use slow-twitch muscle fibers, while sprinters predominantly utilize fast-twitch muscle fibers. The two types of muscle fibers perform differently because of their physiological attributes. Slow-twitch fibers are characterized by high densities of capillaries, mitochondria, and myoglobin, enabling sustained aerobic activity and making them ideal for endurance events like marathon running.

In contrast, fast-twitch fibers can contract rapidly and powerfully but fatigue quickly, supporting short anaerobic activities such as sprinting. This is due to their lesser concentration of capillaries, mitochondria, and myoglobin in comparison to slow-twitch fibers. The muscles of a professional marathon runner are likely to have a higher percentage of slow-twitch fibers, and the reverse applies to sprinters, who would have a greater percentage of fast-twitch fibers.