Elimination of Influences of the ACTN3 R577X Variant on Oxygen Uptake by Endurance Training in Healthy Individuals.

Aim: To study the relationship between the ACTN3 R577X polymorphism and oxygen uptake (VO₂) before and after exercise training. Methods: Police recruits (N = 206, 25 ± 4 y) with RR (n = 75), RX (n = 97), and XX (n = 33) genotypes were selected. After baseline measures, they underwent 18 wk of running endurance training. Peak VO₂ was obtained by cardiopulmonary exercise testing. Results: Baseline body weight was not different among genotypes. At baseline, XX individuals displayed higher VO₂ at anaerobic threshold, respiratory compensation point, and exercise peak than did RR individuals (P < .003). Endurance training significantly increased VO₂ at anaerobic threshold, respiratory compensation point, and exercise peak (P < 2 x 10^-6), but the differences between XX and RR were no longer observed. Only relative peak VO₂ exercise remained higher in XX than in RR genotype (P = .04). In contrast, the increase in relative peak VO₂ was greater in RR than in XX individuals (12% vs 6%; P = .02). Conclusion: ACTN3 R577X polymorphism is associated with VO₂. XX individuals have greater aerobic capacity. Endurance training eliminates differences in peak VO₂ between XX and RR individuals. These findings suggest a ceiling-effect phenomenon, and, perhaps, trained individuals may not constitute an adequate population to explain associations between phenotypic variability and gene variations. [ABSTRACT FROM AUTHOR]