AC variant of the gene ACTN3 which inhibits fast-twitch muscles and seems to be less prevalent in sprinters has been studied. A separate study1 indicated ethnic differences: Approximately 20% of a sample of Caucasians, approximately 25% of a sample of Asians, and approximately 1% of a sample of Africans had the gene variant. One variable is whether or not the gene variant is present and the other is which of the three ethnic groups the individual belongs to.