Rs1815739

From SNPedia

This SNP, in the ACTN3 gene, encodes a premature stop codon in a protein likely to be important in muscle function. The polymorphism alters position 577 of the alpha-actinin-3 protein, and while the most common nucleotide at this position, (C), encodes an arginine (amino acid code R), the stop codon is refered to as X. Hence, the SNP is referred to as R577X, with homozygotes being either RR or XX and heterozygotes being RX.

The main report studying a relatively small number of Australian elite (ie ~Olympic) athletes found that, at least in females, the R allele (ie rs1815739(C)) is associated with sprinters, while the X allele (rs1815739(T)) is associated with endurance athletes. No female or Olympic-level sprinters were XX homozygotes (rs1815739(T;T)). The association tended the same way but was statistically weaker in males. [PMID 12879365]

There have been several subsequent studies, but few with large sample sizes and thus few with much statistical power. An example of a typical study: no increase in endurance ability was associated with the X allele in elite male cyclists. [PMID 16612741]

An extensive blog post from one of the original authors of this research.