Perhaps you are one in seven people on the planet who are estimated to have a mutation in their ACTN3 gene. This mutation causes a deficiency in alpha-actinin-3, a protein that effects fast-twitch-fiber activity.
Studies in elite athletes have shown that the ACTN3 gene may influence endurance athletes. So while the non-mutant version of the gene is associated with sprint performance, the mutant version is associated with endurance.
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