In the last few years, the football world has shown an unstoppable interest in breaching the gender gap with the aim of reaching the wanted equality between women and men. Genetics, however, seems to follow its own criteria when determining the performance and the possibility of injuries of professional female football players against their male counterparts.

Alpha-actinin-3, The Speed and Explosion Protein

Alpha-actinin-3, encoded by ACTN3 gene, is a structural protein of the muscle fibre with a key role at the Z-disc, since it provides contractile elements of the muscle fibre with greater stability, which would explains a greater capacity to generate strength.

Actinin-3 is only expressed in fast muscle fibres, which suggests that the role of this protein is specific for fast muscle contractions or those performed with high levels of strength.¹ This is, it is a necessary protein for the muscles to explosively contract.

ACTN3 gen has three genotype combinations: XX, RX and RR. ACTN3 gene has a genetic variation, usually known as the R577X polymorphism. This polymorphism is present in around 20% of the world’s population.  This genetic variation makes individuals with XX genotype to be functional alpha-actinin-3 deficient. Individuals with RR or RX genotype do have functional alpha-actinin-3.

It’s been proven that XX individuals possess several negative phenotypes, such as lower muscle strength² and muscle volume³, impaired capacity to tolerate muscle strain⁴ and decreased bone mineral density⁵.

Football and R577X Polymorphism

In sports, R577X polymorphism is one of the most studied genetic variations, since many researchers have proven that XX athletes are underrepresented in elite power-oriented sports.^{6, 7, 8.}

Besides, in some of these previous researches, there is evidence that XX athletes have a greater tendency to non-contact muscle injuries compared to RR and RX athletes.

Among power-oriented sports, football is the ideal scenario to investigate R577X polymorphism. Football is clearly ‘power/explosive’, and it is characterized by the repetition of high-intensity actions, such as sudden accelerations, decelerations, sprints, changes of direction, and jumping⁹.

In fact, previous research proved that the XX genotype, which is not capable of expressing alpha-actinin-3, could be an impairment to becoming a professional football player (the presence of XX players in professional football teams is lower than in non-athlete control populations¹⁰). XX genotypes have a higher tendency to suffer non-contact muscle injuries than RR players,^{11, 12} and they need a longer period of recovery before returning to play after these kinds of injuries¹³.

However, these findings have been done in professional male football player samples. The influence of ACTN3 XX genotype in non-contact muscle injuries or in any type of injury has not been proven in female football players.

Does R577X polymorphism affect professional male and female players equally?

The purpose of a recent investigation carried out by Juan del Coso el al. (2022) Association of the ACTN3 rs1815739 Polymorphism with Physical Performance and Injury Incidence in Professional Women Football Players was to determine the influence of the R577X polymorphism on physical performance variables and the injury incidence of professional players competing in the women’s Spanish first division of football. The hypothesis was that XX players would have lower jump and sprint performance and a higher injury rate of non-contact muscle injuries than RR players.

In a cross-sectional study, the performance and epidemiology of non-contact muscle injuries were recorded in a group of 191 professional female football players. Participants played for any of the nine out of the 18 teams that competed in the women’s Spanish first division of football (Primera Iberdrola) in the 2020–2021 season

For this investigation, a battery of physical performance tests was performed (ankle dorsiflexion, sit-and-reach distance, countermovement jump, and sprint) in the pre-season and the injuries resulting from their training routines or competitions were recorded during the whole 2020–2021 season.

Results of the Study

From the study sample, 28.3 % of the female players had RR genotype, 52.9 % had RX genotype, and 8.8 % had XX genotype. These are the most representative results:

-Jump height, sprint time, seat-and-reach distance, and right and left ankle dorsiflexion was similar in RR, RX and XX.

-The incidence of injuries during training and matches did not show differences among genotypes.

-The proportions of players with a non-contact muscle injury, ligament injury, and bone injury were also similar among genotypes.

-The distribution of players according to the number of injuries, injury severity, exposure type, recurrence, and mode of onset was similar in the 3 genotypes.

– In all three genotypes, the thigh was the most common location for the injury.

– The ankle was the second most common location for RR and XX players, while the knee was the second most common location for RX players. In any case, the distribution of injuries according to the location was not affected by the genotype.

Conclusions of the Study

Although there need to be confirmatory studies, it seems that the XX genotype may have a less harmful influence on football performance in women than in men.

It is important to mention that the physical, physiological and tactical characteristics of women’s football, in comparison to males’ football¹⁴, may have influenced these findings. Existing literature has found that female football players cover less distance and at lower speeds during matches,¹⁵ and present lower performance in sprints, jumps, and intermittent endurance than male counterparts^{16, 17}. As for the tactical side, women’s football teams seem to display a more direct style of play, with fewer passes per possession, and a lower passing tempo than men’s teams^{18, 19}. These physiological and tactical differences between the characteristics of elite women’s and men’s football may contribute to the insignificance of alpha-actinin-3 deficiency in women.

Although the study was carried out in a homogeneous sample of female football players participating in the same competition, the sample size was relatively low and not all the teams were subject to identical training, competition, and diet protocols.

Additionally, the protocols developed by the staff of the teams to prevent and to treat injuries were not identical. Therefore, the fact of reaching any definitive conclusions about the lack of association of the ACTN3 genotype with football performance and injury incidence in professional women players should be made with caution. Future investigations in other samples of professional or elite women athletes should be carried out to replicate the results of this study. Additionally, the current study was focused on only one genetic polymorphism, while sports performance and injury susceptibility may be influenced by other genetic variants not studied in the current experiment.

In any case and in this study, the ACTN3 genotype did not affect the mode of the onset, the time needed for return to play, the type of injury or the distribution of the body location of the injuries. In summary, professional women players with different genotypes of the R577X polymorphism possessed similar values in football-specific performance and injury incidence. From a practical perspective, the genotyping of ACTN3 may not be useful to predict performance or injury incidence in professional women football players: the influence of this genotype on women’s football seems negligible, at least in comparison to the harmful effect of the  ACTN3 XX genotype found in male football players.

Sources:

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