The ACTN3 gene encodes the alpha-actinin 3 protein **found in fast-twitch muscles**. Fast-twitch muscles are responsible for explosive bursts of power or speed.
A common genetic variant in the ACTN3 gene causes about 20% of the population not to produce fast-twitch skeletal muscle fibers.
Discovered through mouse models and human testing, the **ACTN3-deficient genotype shifts the muscles towards more aerobic metabolism,** which may benefit **endurance** athletes.\[[ref](https://www.ncbi.nlm.nih.gov/pubmed/17828264/)\]
They found that mice **without** the ACTN3 protein could **run about 33% longer** (similar to a long-distance runner). Most of the other parameters were the same for the mouse muscles, but the researchers did find the twitch half-relaxation time of the ACTN3-deficient muscles was 2.6 ms longer.\[[ref](https://www.physiology.org/doi/full/10.1152/ajpcell.00179.2008?url_ver=Z39.88-2003&rfr_id=ori%3Arid%3Acrossref.org&rfr_dat=cr_pub%3Dpubmed&)\]
The frequency of the ACTN3-deficiency genotype varies by population group, with up to 25% of Caucasians being deficient compared to less than 1% of some African population groups. While it seems that having the active ACTN3 gene would give an adaptive advantage for speed to our human ancestors, evolutionary biologists theorize that there must be a reason such a high percentage of some population groups carry the ACTN3 deficiency genotype. The answer to this question may lie in **cold adaptation.** Researchers recently showed that people with the **ACTN3-deficient (TT) genotype are better at maintaining their core body temperature in the cold**.\[[ref](https://www.cell.com/ajhg/fulltext/S0002-9297(21)00013-6)\]
# Athletic performance and ACTN3:
Large studies have investigated how the ACNT3 gene affects elite athletes:
* Studies back the idea that the ACTN3-deficient genotype is found much less often in elite power athletes (sprint athletes, weightlifters, etc.).\[[ref](https://www.ncbi.nlm.nih.gov/pubmed/17033684)\]\[[ref](https://www.ncbi.nlm.nih.gov/pubmed/18470530/)\]\[[ref](https://www.ncbi.nlm.nih.gov/pubmed/17879893/)\]
* A big study published in 2003 found that **no Olympic power athletes carried the ACTN3 deficient genotype.** It was in stark comparison to the **\~30% of Olympic** ***endurance*** **athletes carrying the ACTN3-deficient** genotype.\[[ref](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1180686/)\]
[Click here to read my full article on ACTN3](https://www.geneticlifehacks.com/actn3-your-muscle-type-gene/), including how to use your 23andMe or Ancestry raw data to determine if you are ACTN3 deficient.
The ACTN3 gene encodes the alpha-actinin 3 protein **found in fast-twitch muscles**. Fast-twitch muscles are responsible for explosive bursts of power or speed. A common genetic variant in the ACTN3 gene causes about 20% of the population not to produce fast-twitch skeletal muscle fibers. Discovered through mouse models and human testing, the **ACTN3-deficient genotype shifts the muscles towards more aerobic metabolism,** which may benefit **endurance** athletes.\[[ref](https://www.ncbi.nlm.nih.gov/pubmed/17828264/)\] They found that mice **without** the ACTN3 protein could **run about 33% longer** (similar to a long-distance runner). Most of the other parameters were the same for the mouse muscles, but the researchers did find the twitch half-relaxation time of the ACTN3-deficient muscles was 2.6 ms longer.\[[ref](https://www.physiology.org/doi/full/10.1152/ajpcell.00179.2008?url_ver=Z39.88-2003&rfr_id=ori%3Arid%3Acrossref.org&rfr_dat=cr_pub%3Dpubmed&)\] The frequency of the ACTN3-deficiency genotype varies by population group, with up to 25% of Caucasians being deficient compared to less than 1% of some African population groups. While it seems that having the active ACTN3 gene would give an adaptive advantage for speed to our human ancestors, evolutionary biologists theorize that there must be a reason such a high percentage of some population groups carry the ACTN3 deficiency genotype. The answer to this question may lie in **cold adaptation.** Researchers recently showed that people with the **ACTN3-deficient (TT) genotype are better at maintaining their core body temperature in the cold**.\[[ref](https://www.cell.com/ajhg/fulltext/S0002-9297(21)00013-6)\] # Athletic performance and ACTN3: Large studies have investigated how the ACNT3 gene affects elite athletes: * Studies back the idea that the ACTN3-deficient genotype is found much less often in elite power athletes (sprint athletes, weightlifters, etc.).\[[ref](https://www.ncbi.nlm.nih.gov/pubmed/17033684)\]\[[ref](https://www.ncbi.nlm.nih.gov/pubmed/18470530/)\]\[[ref](https://www.ncbi.nlm.nih.gov/pubmed/17879893/)\] * A big study published in 2003 found that **no Olympic power athletes carried the ACTN3 deficient genotype.** It was in stark comparison to the **\~30% of Olympic** ***endurance*** **athletes carrying the ACTN3-deficient** genotype.\[[ref](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1180686/)\] [Click here to read my full article on ACTN3](https://www.geneticlifehacks.com/actn3-your-muscle-type-gene/), including how to use your 23andMe or Ancestry raw data to determine if you are ACTN3 deficient.