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Skeletal Muscle Fiber Types
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Skeletal Muscle Fiber Types
Fiber type and performance
The average person has an equal amount of Type I and Type II fibers
Different muscles have a different % of Type I and Type II fibers, depending on their function. Endurance muscles have a greater % of Type I fibers; power muscles have a greater % of Type II fibers.
2 Fiber Types
Figure 1. Muscle fiber histology. Adapted from Skeletal Muscle - From Myogenesis to Clinical Relations (362), by M. Meznaric and I. Erzen, 2012, InTech: London, UK. Copywright 2012 by Meznaric and Erzen.
Fiber type and Performance
Characteristics of Type II Fibers
Questions
References
PictureFit. (2015, June 2). Muscle Fibers Explained - Muscle Contraction and Muscle Fiber Anatomy [Video file]. Retrieved from <https://youtu.be/3L9JUfzh66I>
Powers, S. K. & Howley, E. T. (2015). Exercise Physiology: Theory and Application to Fitness and Performance (9th ed.). McGraw-Hill Education: Knoxville, TN.
1. Based on the characteristics listed of Type I and Type II, which fibers do you suspect to appear darker on histological samples? Why?
2. Does the rectus abdominis have more Type I fibers or Type II fibers?
3. What is the relationship between fiber type and aerobic capacity? Why is this?
Type I (slow-twitch)
Type IIx, IIa (fast-twitch)
Type IIx
1. Few mitochondria
2. Large anaerobic capacity
3. Fastest fiber type found in humans
4. Less efficient
Type IIa
1. "Intermediate"
2. Characteristics of both Type I and Type IIx
Large number of Type I fibers in endurance athletes
High % of Type I = High VO2 max
Power athletes tend to have a greater % of Type II fibers.
Characteristics of Type I fibers
1. Lots of mitochondria
2. Surrounded my more capillaries
3. High concentration of myoglobin
4. Contribute to aerobic metabolism
5. Resistant to fatigue
6. Efficient