Muscle Fiber Types

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I am a marathon runner. What type of muscle fiber are predominant in my body?

Muscle Fiber Types

Your skill at specific activities is partially determined by your ratio of muscle fiber types. Slow-twitch fibers (Type I) are resistant to fatigue. They are associated with long duration aerobic activities. Fast-twitch fibers (Type IIa) are capable of quick muscular contractions. These fibers are moderately resistant to fatigue. Fast-twitch fibers (Type IIb) also produce quick muscular contractions. However, they are associated with activities requiring quick bursts of energy, such as sprinting. In general, marathon runners have a higher percentage of slow-twitch muscle fibers, whereas sprinters have more fats-twitch fibers.

The ratio of muscle fiber types is genetically determined. Therefore, it will vary in each individual. However, both types of muscle fiber can improve their metabolic capabilities through strength training. Keep in mind that your core muscles are considered slow-twitch muscle fibers, since they are responsible for maintaining posture and balance against the forces of gravity. As such, training the core is an important part of any weight training workout.



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