The Effect Of ACTN3 Genotype On Self-reported One-mile Running Time In Young, Recreationally Active Women

Abstract

Alpha-actinins form a crosslink between actin filaments and adjacent sarcomeres, and play a role in signaling and energy metabolism. Alpha-actinin-3, is encoded by the ACTN3 gene and only presents in Type II muscle fibers. Homozygosity for the 577X allele (XX) results in complete deficiency of α-actinin-3 and a compensatory upregulation of α-actinin-2, whereas heterozygosity (RX) and homozygosity for the 577R allele (RR) provide for the production of α-actinin-3. Research has reported a greater proportion of elite female distance runners are homozygous for the 577X allele compared to controls. However, no study to date has examined that apparent relationship in recreational women runners. PURPOSE: To examine the effect of ACTN3 genotype on self-reported one-mile running personal records (PR) in young, recreationally active women. METHODS: Thirty nine participants, grouped by the presence (RR+RX: n=27, age: 21.7 ± 3.8 years, BMI: 22.9 ± 3.3 kg/m2) or absence (XX: n=12, age: 21.2 ± 3.2 years, BMI: 21.5 ± 1.8 kg/m2) of the 577R allele, reported one-mile running PR. Genotype effects were examined using independent-sample t-tests and magnitude-based inference (MBI). RESULTS: A trend (p=0.065) toward faster one-mile times was observed in XX genotypes (415.7 ± 78.9 s) when compared to the RR+RX group (480.3 ± 104.8 s). MBI revealed a mechanistically beneficial effect of XX genotype (mean difference; ± 90% CI; -65 s, ± 57 s). Similar observations were made among a subset of thirteen faster runners, who reported a one-mile PR of less than seven minutes (RR+RX: n=7, age: 21.9 ± 5.0 years, BMI: 20.9 ± 3.4 kg/m2; XX: n=6, age: 19.5 ± 0.5 years; BMI: 21.8 ± 1.5 kg/m2). Though not statistically significant (p=0.378), those in the XX group (355.8 ± 46.5 s) reported 5.4% faster times than those in the RR+RX group (376.3 ± 33.6 s). MBI revealed a mechanistically beneficial effect of XX genotype (-20 s; ± 40 s). CONCLUSION: These findings suggest a potential benefit of XX genotype on middle-distance endurance performance. This is in agreement with prior investigations that have linked XX genotype to endurance capabilities in elite female athletes.