The ACTN3 Gene – Genetics and performance

Dr Andrew Chappell DFAC Pro Natural Bodybuilder, BSc (Hons), MSc, PhD, RNutr (Sport & Exercise)

Take home points

  • The ACTN3 gene deletion is present in around a 5th of individuals
  • The ACTN3 gene plays a role in muscle fibre structure
  • People without the ACTN3 gene may be more susceptible to muscle damage
  • People without the ACTN3 gene may have less type 2 muscle fibre
  • People without the ACTN3 gene may not be as strong as those with the gene
  • Elite endurance athletes are more likely to be ACTN3 gene deficient
  • Olympic sprinters and power athletes are more likely to have the ACTN3 gene
  • The ACTN3 gene may be an important indicator of muscle strength
  • Multiple genes are ultimately responsible for determining someone’s ability to add muscle size and strength

The ACTN3 is a gene responsible for making a protein called  α-actinin 3 which forms crosslinks between actin thin filaments in the Z bands of muscle fibres (see figure 1). This gene is absent in around 18% of healthy white individuals which may have consequences for exercise performance and fitness. Those without the gene likely compensate by producing a different protein α-actinin 2, which are incorporated into Z bands.  Individuals without the ACTN3 gene are more susceptible to muscle damage, particularly from eccentric exercise since the Z bands may not be as strong. ACTN3 may also play an important role in glucose metabolism, and consequently muscle fibre type selection.

Figure 1. Structure of a muscle fibre, and α-actinin 3 incorporation into Z discs. Individuals with the ACTN3 gene deletion have altered Z disc compositions which may influence force generation.

In a study of over 500 individuals, 400 healthy white controls were compared to over 100 elite white Australian athletes. Athletes were grouped in terms of their sports as either endurance or sprint/power athletes, while athletes that were in ambiguous categories were excluded from analysis. Blood samples were taken from all involved and the results from the study are presented in figure 2 below. Briefly, our genes are inherit from our parents, so we get one copy of a gene from our mum and one copy from our dad. Genes can also be dominant and recessive, but that’s a different story. The results of the investigation identified there was a trend for strength and power athletes to have 1 or 2 copies of the ACTN3 gene, while endurance athletes were more likely to be deficient in the ACTN3 gene.

Figure 2. Frequency of ACTN3 genes in a population of white Australians. Healthy controls are compared to competitive athletes including Olympians.

Results from this study, lend some weight to the hypothesis that the ACTN3 gene might play a significant role in selecting for athletes likely to be good at power or endurance events. Further studies have since went on to demonstrate similar findings e.g. people playing power sports, or operating in power position are more likely to have at least one functioning ACTN3 gene.

What does this mean for the bodybuilder or fitness enthusiast? Your decision to take up sport or pursue an activity shouldn’t come down to a single genetic factor. People should play sport or take part in activities, first and foremost for enjoyment and health. Secondly, it’s possible that having two active copies of something like the ACTN3 gene really only matters at the absolute extremes of athletic performance beyond the range of normal human activity. So unless your high level, it probably doesn’t matter. Thirdly, multiple factors contribute towards muscle size, strength and performance, for example limb and tendon length, significantly impact leverage, and the stretch shorten reflex important in movements like jumping. If you don’t have the right shape, then you’ll never deadlift a 1000 lbs or be able to high jump over 2 meters, regardless of genes. Fourthly, it doesn’t come down to just one gene. For example those lacking in the gene encoding for myostatin, an important protein involved in switching off the muscle building process, could be just as, and/or quite likely more muscular and powerful than someone with 2 working copies of the ACTN3 gene. You have over 24,000 genes so that’s endless permutations, and combinations which could confer a sporting advantage. Finally, environment is important. Without the correct training, and dietary programmes combined with a psychologically nurturing environment even the most naturally talented of athletes will fail to reach their full potential. Your genes are important, but let us help you reach your full potential, with ProPrep Coaching and be sure to check out our sign up page.

Read the full paper that inspired this article below:

Yang, N., MacArthur, D.G., Gulbin, J.P., Hahn, A.G., Beggs, A.H., Easteal, S. and North, K., 2003. ACTN3 genotype is associated with human elite athletic performance. The American Journal of Human Genetics, 73(3), pp.627-631.

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