Overview
ACTN3 encodes a structural protein exclusively found in fast-twitch (Type II) muscle fibers. The R577X variant is one of the most famous genetic variants in sports and determines whether you are more predisposed for sprint/power or endurance.
11q13.2 (Chromosome 11)
Fitness
Autosomal recessive
XX: ~18%, RR: ~30%, RX: ~52%
Function & Significance
Alpha-actinin-3 is a structural protein that stabilizes the Z-discs in fast-twitch muscle fibers. These fibers are responsible for explosive movements such as sprinting and power development.
🏃 The “Sprinter Gene”
ACTN3 became famous as the “sprinter gene” because:
- RR Genotype: More common among elite sprinters and power athletes
- XX Genotype: More common among endurance athletes
- RX Genotype: Balanced profile
About 1 billion people worldwide have the XX genotype and produce no functional ACTN3 protein!
🧬 Relevant SNPs
The R577X variant (rs1815739):
11:66560624
/
Significance: R577X Polymorphism
• CC (RR): Functional ACTN3, optimal for sprint/power
• TT (XX): No ACTN3, better for endurance
• CT (RX): One functional copy, balanced
🏋️ Practical Significance
For Athletes:
- RR Type: Focus on sprint, strength training, explosive movements
- XX Type: Focus on endurance, marathon, cycling
- RX Type: Versatile training potential, good all-round athletes
Important: Training and environment have a much greater influence than genetics! ACTN3 explains only a small part of athletic performance.
📚 Data Sources
The information on this page is based on the following scientific sources:
- OMIM: #102574 – Online Mendelian Inheritance in Man
- dbSNP: rs1815739 – SNP Database (NCBI)
- ClinVar: Clinical Variant Database (NCBI)
- PubMed: Sports Genetics Research
- Sports Gene Database: Athletic Performance Genetics
Last Update: February 2026
Biological Function
Analyzed Markers
R577X - CC(RR): Sprint/Power, TT(XX): Endurance, CT(RX): Balanced