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Inherited Traits - Athletic Performance - ACTN3 - Information

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Would you like to know whether your genetics give you an advantage in either power or endurance sports?

Muscle fiber composition:  Fast twitch, Slow twitch

The ACTN3 gene encodes the alpha-actinin-3 protein which is present in fast-twitch muscle fibers. These types of skeletal muscle are responsible for generating force at high velocity. There is a variant form of the ACTN3 gene which has a single base substitution in the DNA and is referred to as R577X. Individuals lacking the variant gene have the R/R genotype whereas those possessing the mutation can have either one (R/X genotype) or two (X/X genotype) copies of the variant gene. This variant form of the ACTN3 gene is very common in the general population. Approximately  20%-30% of the population (over 1 billion people worldwide) have two mutant genes (X/X genotype), and there is not any obvious effect on individuals who have either one or two copies of the variant gene.

Although having one or two variant forms of the ACTN3 gene does not have any harmful effect, an individual's ACTN3 genotype does affect their athletic ability. These correlations have been derived from genetic studies of elite athletes. The ACTN3 genotype has been analyzed in athletes that have risen to very high levels in competitive sports that require predominantly either power or endurance.  These studies have demonstrated that there are genetic contributions to power and endurance ability.

An individual's ACTN3 genotype determines the composition of their fast twitch muscle fibers. The ACTN3 X gene does not produce the alpha-actinin-3 protein. Therefore, an individual's ACTN3 genotype (R/R, R/X or X/X) affects the amount of alpha-actinin-3 protein present in their fast twitch muscle fibers. It is now well established that the ACTN3 genotype of an individual has affects their athletic performance.  This research has demonstrated the following association between an individual's ACTN3 genotype and athletic performance:

R/R genotype:  power advantage

X/X genotype:  endurance advantage

R/X genotype :  contributes to both power and endurance

By knowing your ACTN3 genotype, you can modify your  training regime to optimize your athletic performance.  You can also choose to focus on sports or events where your personal genetics give you an advantage.

When you undergo genetic testing with Genomic Express, we will determine which versions of the ACTN3 gene you have and, therefore, your fast twitch muscle fiber composition. This comprehensive report gives you both your ACTN3 genotype and an explanation of how it affects your athletic performance. It summarizes the scientific research, including references to the original articles, that have established these correlations. Your report also explains how your ACTN3 genotype affects your performance in a variety of different sports. This information will allow you to optimize your athletic training based on your muscle fiber composition. It is also valuable for choosing the sport, or position/event within a sport, where you have the greatest opportunity to excel.


Let Genomic Express help you learn more about your own genetics in order to develop an optimal approach to sports and athletic training.

Additional information:


Yang, N., et al. (2003) ACTN3 Genotype is Associated with Human Elite Athletic Performance. American Journal of Human Genetics 73, 627-631.

MacArthur , D.G. and North, K.N. (2007) ACTN3: A Genetic Influence on Muscle Function and Athletic Performance. Exercise Sport Science Reviews 35 (1), 30-34.

Yang, N., et al. (2009)  alpha-Actinin 3 and Performance. Med. Sport Sci.54, 88-101.

            This genetic test is provided by Genomic Express, Inc. for educational and informational purposes only. It is not intended for the diagnosis or treatment of any diseases or disorders. Clients should consult with their own physician or other qualified health care provider for any medical or health needs. Genomic Express, Inc. shall not be held liable for any damages incurred as a result of the use of this information or caused by products described herein. 

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