The aim of the study was to investigate the possible association between the BDKRB2 gene and training-induced improvements in swimming performance in well-trained swimmers. One hundred Polish swimmers (52 men and 48 women, aged 18.1 ± 1.9 years), who competed in national and international competitions at middle- (200 m) and long-distance events (=400 m), were included in the study. Athletes' genotype and allele distributions were analyzed in comparison to 230 unrelated sedentary subjects, who served as controls, with the ?2 test. All samples were genotyped for the BDKRB2 -9/+9 polymorphism by polymerase chain reaction. The effects of genotype on swimming performance improvements were analyzed with two-way (3 × 2; genotype × time) analysis of variance with metric age as a covariate. The training period of 1.9 ± 0.4 years had a significant (p < 0.01) effect on swimming performance, both in female and male athletes. Both in female and male athletes, the BDKRB2 gene -9/+9 polymorphism had no significant effect on swimming performance. An interaction effect of BDKRB2 gene -9/+9 polymorphism × time was found for swimming performance only in male athletes. Post hoc analyses showed that swimmers with the +9/+9 BDKRB2 genotype had a greater improvement in swimming performance than swimmers with the -9/+9 polymorphism (p = 0.05). No interaction effects for gender × BDKRB2 gene -9/+9 polymorphism were found for either swimming performance or improvement in swimming performance. These results suggest that the response to long-term exercise training could be modulated by the BDKRB2 gene -9/+9 polymorphism in male athletes. In well-trained swimmers, BDKRB2 gene variation was not found to be an independent determinant of swimming performance.
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