Trait overview: Muscle performance (ACTN3)

Wednesday, April 01, 2020. Author Alex Auld

Trait overview: Muscle performance (ACTN3)

ACTN3 is the famous ‘gene for speed’. It codes for a protein called alpha-actinin-3, which supports forceful, high-velocity contraction of fast-twitch muscle fibers.

However, not all of us are able to reap the numerous benefits of alpha-actinin-3, with one variant of the ACTN3 gene resulting in a complete inability to produce the protein.

While being deficient in this protein has no negative health effects, it is thought to be a disadvantage when it comes to speed and power-based athletic performance.


ACTN3 production

There are two key variants of the ACTN3 gene - the ‘R’ variant (or allele) and the ‘X’ variant (or allele). 

The R allele codes for the alpha-actinin-3 protein as normal. 

In the X allele, however, there is a change in the DNA sequence from a C (Cytosine) to a T (Thymine). This change prevents the alpha-actinin-3 from being produced. 

As with all genes, we inherit two copies of the ACTN3 gene (one from our mother and one from our father). This means there are three possible combinations (or genotypes) of ACTN3:

  • RR 
  • RX
  • XX

Having one or two copies of the R allele (RX and RR genotypes) allows the alpha-actinin-3 protein to be produced. Those with two copies of the R allele (RR genotype) will produce more alpha-actinin-3. 

Those with two copies of the X allele (the XX genotype), which is approximately 18% of people globally, do not produce any functional alpha-actinin-3 at all.

Alpha-actinin-3 and athletic performance

There is a wealth of research that suggests that the presence of the R allele provides an advantage with sprint, strength and power-based sports that require forceful, explosive muscle contractions.

For example, the production of alpha-actinin-3 is significantly associated with elite power athlete status, to the point that one study of Olympic power athletes found that none of the subjects carried the XX genotype.

Within the general population, research has found that carriers of the R variant have greater muscle mass, greater baseline strength, greater strength gains in response to training, faster sprint times and a higher proportion of fast twitch muscle fibers compared to XX individuals.

The ACTN3 gene is also thought to influence our muscle recovery after exercise. Studies have suggested that the lack of alpha-actinin-3 protein results in greater exercise-induced muscle damage in XX individuals. As a result they require longer recovery times between workouts.

The XX genotype and athletic performance

You may be wondering whether there are any benefits to having the XX genotype? It certainly doesn’t sound like it so far!

Well, as a physiological trade-off, this genotype appears to provide an advantage for endurance activity, such as long-distance running, cycling and rowing.

Studies have found that world class endurance athletes were 3.7 times more likely to have the XX genotype compared to national-level athletes, and that a higher-than-expected proportion of elite European marathon runners and Tour de France cyclists have this genotype.

Despite these findings, it’s important to note that the relationship between the XX genotype and endurance performance is far less pronounced than that between the R allele and spring/strength/power performance. 

Remember – genes aren’t the whole picture

If you have the XX genotype and are concerned about being disadvantaged when it comes to power, strength and sprint activities - worry not!

Genetics are only part of the picture; environmental factors such as training, diet and lifestyle all play a major role in exercise performance. 

For example, when it comes to differences in our proportion of fast and slow twitch fibers, studies suggest that about 40% of variation is attributable to environmental factors, such as how we exercise.

Your Muscle performance (ACTN3) trait

The three possible ACTN3 genotypes give rise to three individual trait bands for the FitnessGenes muscle performance (ACTN3) trait:

  1. You produce no alpha-actinin-3 (XX)
  2. You produce alpha-actinin-3 (RX)
  3. You produce high levels of alpha-actinin-3 (RR)

For those members classified in the ‘you produce no alpha-actinin-3’ trait band, recommended actions may include performing compound exercises to reduce age-related muscle mass loss and long duration bodyweight isometric holds to help improve tendon strength and stiffness.

Discover your personal trait

Does your athletic performance benefit from the production of alpha-actinin-3, or does your ACTN3 genotype lend itself more towards endurance based activity?

Discover your alpha-actinin-3 activity, alongside other muscle-building traits including testosterone level, hypertrophy (mTOR) and IGF-1, by unlocking your unique genetic code with FitnessGenes.

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