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Updated: Jul 11, 2026
07:04
Fiber Type Identification of Human Skeletal Muscle
Published on: September 22, 2023
ACTN3 (R577X) genotype is associated with fiber type distribution
Barbara Vincent1, Katrien De Bock, Monique Ramaekers
1Research Centre for Exercise and Health, Department of Biomedical Kinesiology, Faculty of Kinesiology and Rehabilitation Sciences, Katholieke Universiteit Leuven, Leuven, Belgium.
Physiological Genomics
|September 13, 2007
Summary
The ACTN3 R577X gene variant influences muscle fiber type distribution and strength. Individuals with the RR genotype exhibit greater fast-velocity muscle power compared to XX genotype carriers.
Area of Science:
- Exercise Physiology
- Genetics
- Muscle Biology
Background:
- Alpha-actinin-3 is a structural protein in type II muscle fibers.
- The ACTN3 R577X polymorphism can lead to alpha-actinin-3 deficiency.
- Genetic factors significantly influence muscle fiber type proportions.
Purpose of the Study:
- To investigate the association between the ACTN3 R577X polymorphism and muscle fiber type distribution.
- To quantify the relationship between the polymorphism and fast-velocity knee extension strength.
Main Methods:
- Genotyping for ACTN3 R577X in 90 healthy young men.
- Measurement of isometric and dynamic knee extensor strength.
- Muscle biopsies and immunohistochemistry to determine fiber type composition in XX and RR genotype groups.
Main Results:
- RR genotype homozygotes demonstrated significantly higher dynamic quadriceps torques at high velocities (300 degrees /s) compared to XX homozygotes.
- Significant differences in muscle fiber characteristics were observed between genotype groups.
- The RR genotype group had a greater percentage and number of type IIx fibers compared to the XX genotype group.
Conclusions:
- The ACTN3 R577X polymorphism is associated with differences in muscle fiber type distribution.
- The findings suggest that the ACTN3 polymorphism influences muscle power through its effect on fiber type proportions.
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