Estudio de las características contráctiles de la musculatura del tren inferior y de las distribuciones genotípicas del gen ACTN3 en voleibol de élite

Resumo

The ACTN3 gene encodes the synthesis of the intramuscular protein α-actinina-3. This protein, situated in the Z muscular line, has a structural function, giving more stability to the contractile elements of the muscular fibre. The enhanced stability would cause a better transmission of strength. This protein is not to be found in all human beings, due to a mutation in the ACTN3 gene. As a consequence, two alleles (R and X) appear. These genes would allow to synthetize the α-actinine-3 protein. The combination of these alleles causes three distinct genotypes: RX, RR, and XX. The XX genotype bearer cannot express the protein α-actinine-3, and have been associated with possible benefits in resistance sports, while RR and RX genotype bearers do express α-actinine-3 in their fast muscle fibres and these genotypes have been linked to benefits in strength/velocity sports. Nevertheless, the lack of consistency regarding the relation between the ACTN3 gene and sport performance has oriented this research towards the analysis of the influence of the ACTN3 gene in professional volleyball players. The study has been conducted using two types of research design based on relational comparative methodology: a case-control study, and an association study. In the first type, the genotypic distributions of the ACTN3 of a group of professional players were compared to those of other samples: athletes and non-athletes; male and female athletes; best and worst teams at the end of the regular season of the top volleyball national league. The study of the genotype-phenotype correlation has been carried out by means of a comparative analysis between the contractile characteristics of the lower body muscles in volleyball players bearing all the ACTN3 genotypes. The sample was formed of 139 athletes (79 men and 60 women) of the highest competitive volleyball category in Spain, and control group of 137 university students (75 men and 52 women) non-athletes but physically active. The prevalence of ACTN3 genotypes in male athletes both from the group of volleyball players and from the control group has been respectively of 31% and 32,7% for the XX genotype, 50,7% and 44,9% for the genotype RX, and 18,3% and 22,4% for the genotype RR. In women athletes the figures were: 18,6% and 18,9% for the XX genotype, 52,5% and 56,8% for the RX genotype, and 28,8% and 24,3% for the RR genotype. The genotypic distribution of the volleyball players’ group was different compared to that encountered by other authors in groups of athletes and non-athletes. Nevertheless, no difference in genotypic distribution has been found neither between the volleyball players group and the control group, or between genders. Some differences were found in the genotypic distribution in female players between the best and worst teams, but these differences were contrary to our expectations, since the best teams showed less prevalence of players with RR genotype. The analysis of the genotype-phenotype correlation showed differences only in two out of the six tensiomyographic parameters chosen in the vastus lateralis of the quadriceps: the contraction time and the normalized response speed. Players bearing the RR genotype showed an average contraction time of 25,07±2,94 ms., while RX genotype bearers scored 29,20±5,52 ms. (p=0,030). The normalized response speed reached 32,51±3,35 mm/ms in RR genotype players and 28,53±5,08 mm/ms. in XX genotype players (p=0,031). In all other tensiomyographic parameters and core muscles analyzed no statistically relevant difference was found. Based on these results, it is possible to conclude that the genotypic distribution of ACTN3 shows no difference between the group composed of professional athletes participating to the Spanish volleyball Superliga and the sample of physically active no-athletes population. The same lack of differences has been shown between genders as well as between top ranked and low ranked teams at the end of the regular season of the Spanish volleyball Superliga. Furthermore, the contractile characteristics of male and female players showed no difference relatively to the ACTN3 gene, except when taking into consideration the contraction time and the normalized response speed of the vastus lateralis of the quadriceps in volleyball players.