The Genetic Link

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Article by: Katherine Lawless

Is the speed gene the key to athletic performance? The answer is only a spit away


It is widely accepted that genetic factors are strongly linked with athletic performance.[1] After receiving my own 23andMe wellness results, I learned that I was a carrier of the speed gene-- α-Actinin-3 (ACTN3) R577X polymorphism -- which is known to be common in elite power athletes. According to 23andMe, at national and international levels of athletic competitions, this gene seems to make a difference when it comes to athletes’ success.[2]

What is the “speed gene”?

The ACTN3 gene is only carried by a small portion of the population – in Europe, only 18% [2]. The gene regulates the ACTN3 protein, which is produced in fast-twitch muscle fibers. ACTN3 protein deficiency results in a lower proportion of fast-twitch muscle fibers (more slow-twitch muscle fibers) which is associated with endurance athletes. ACTN3 protein efficiency results in a higher proportion of fast-twitch muscle fibers, which allows fast muscle contractions for sprinting and high muscle strength.[2][3]

The most common polymorphism of the ACTN3 gene is R577X, a C-to-T base substitution of an arginine base (R) to a premature stop codon (X). In this blog we will focus more on the extremes of the gene: RR genotype (R allele) and the XX genotype (XX allele).[1][2]

Each genotype of the speed gene has a different role and association when it comes to muscle composition. The XX genotype contains a full ACTN3 protein deficiency and the RR genotype has ACTN3 protein efficiency. Both have significant differences when you compare power performance, muscle injury, and flexibility.[3]

Power performance

Those who carry the ACTN3 gene are not all professional athletes, I know for certain that I am not. However, for carriers who are involved in professional sports, it can make quite a difference when it comes to their performance.[3]  

A study by Heffernan A.M et al. was conducted on rugby players from the Rugby Union (RU) in the United Kingdom. They collected Oragene·DNA saliva samples from RU athletes and controls and divided the athletes into subgroups representing their respective roles in rugby: forwards and backs. They wanted to see if each subgroup differed in ACTN3 genotype and how that affected their performance.[4]

  • The players who play the back position had a higher proportion of the R allele; backs are known for their speed generation.
  • The players in the forward position had a higher proportion of the XX allele; forwards are known for their sustained endurance activity.[4]

Muscle injury

Muscle injury is a concern for every professional athlete. Interestingly, different ACTN3 genotypes can indicate whether you are more prone to muscle injury.

R allele carriers are known to have greater levels of muscle mass (specifically type-II fibers) indicating strong capabilities to sprint at great speeds like the backs in rugby. [3],[4] 

Since R allele carriers have strong speed capabilities one would think they’d be more prone to muscle injury, however, it is quite the opposite. X allele carriers who have strong endurance capabilities are more likely to have muscle injury.[3] 
  • Kim J.H et al (2014) performed a study with a cohort of Korean ballerinas regarding ankle sprains. They found that the R allele was under-represented, and that those who carried the XX allele had more ankle injuries.[5]
  • Massidda M et al (2017) found that the XX allele carries were 2.6 times more likely to suffer an injury than the R allele carriers in football players. These injuries were even more likely to be of increased severity.[6]


Flexibility is an important aspect of performance and is crucial for specific sports such as gymnastics, divers, dancers, etc. Kikuchi N et al. conducted a study to determine the trunk flexibility of athletes who carry different alleles of the ACTN3 gene. Their goal was to determine which allele provides the best flexibility by collecting Oragene·DNA saliva samples from two fitness cohorts.[1] 

They discovered:

Trunk flexibility of the R allele group was significantly lower than the XX allele group. Individuals with XX alleles have a higher trunk flexibility. Flexibility is very important for cardiovascular health and can lower the risk of developing a number of diseases.

The XX allele is considered to have a survival advantage to humans, due to its full ACTN3 protein deficiency, allowing for increased muscle flexibility than the average human.[1]

If you are a carrier of the speed gene, no matter which genotype you carry, you have an athletic advantage in one way or another. Do you carry the ACNT3 gene and if so, how do you use your athletic ability?

Oragene self-collection kits were used in the above research studies. If you are interested in trying Oragene saliva collection kits for your own project, click on the free kits request button or email

Request free trial kits of any DNA Genotek saliva kit


[1] Kikuchi N et al. Association between ACTN3 R577X polymorphism and trunk flexibility in 2 different cohorts. Int J Sports Med. 38(5): 402-406 (2017).

[2] 23andMe report:

[3] Pickering C et al. ACTN3: More than just a gene for speed. Front Physiol. 8:1080 (2017).

[4] Heffernan S.M et al. Association of ACTN3 R577X but ACE I/D gene variants with elite rugby union player status and playing position. Physiol Genomics. 48(3): 196-201 (2016).

[5] Kim J.H et al. Genetic associations of body composition, flexibility and injury risk with ACE, ACTN3 and COL5A1 polymorphisms in Korean ballerinas. Nutrition Biochem. 18:205-214 (2014).

[6] Massidda M et al. ACTN3 R577X polymorphism is associated with the incidence and severity of injuries in professional football players. Clin. J Sport Med. [Epub ahead of print] (2017).

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