Are elite athletes born or made? It depends. Genetic factors can positively contribute to sports performance. However, only if you have a good training, well planned and personalized, a suitable diet, a restful sleep, and an emotional balance, you can become a real elite athlete. And what is more important, you can have a long-lasting and successful career. In any case, a recent study suggests that genetics can affect injury susceptibility and the recovery process (read reference below 1). 

Football, for example, is a power driven, explosive sport based on sprints, sudden accelerations and decelerations, rapid changes of direction and actions like kicking the ball. Consequently, competitive football practice is associated with a high incidence of muscle injuries. Specifically, two per player and season in UEFA (read reference below 2) teams. The time-loss from competition as a result of a player’s injury is a major problem for professional teams, causing potential decrease in performance as well as financial costs.

On the one hand, non-modifiable factors such as age, previous injuries, muscle architecture, ethnicity. On the other, modifiable factors such as flexibility, fatigue or muscle weakness. Both can affect the risk of non-contact muscle injuries. But now it is suggested that gene polymorphism might also be involved. 

Particularly, polymorphism R577X (a gene variant) in ACTN3, a skeletal muscle structure encoding alpha-actinin-3 protein, is receiving increasing attention. Recent studies have already found an association between alpha-actinin-3 and greater probabilities of developing injuries (read reference below 3,4).

Alpha-actinin-3: The Speed Protein

To put it simply, we could say that muscles have fibres with slow-twitch (in charge of low or mid intensity repetitive efforts), or fibres with fast-twitch (high intensity efforts). In a football player, fast-twitch fibres (more explosive) prevail.

ACTN3 gen encodes the muscle protein synthesis alpha-actinin 3. It is a key protein for fast-twitch muscle fibre composition, which is needed to create explosive contractions. Alpha-actinin 3 also has a protective role stabilising filament in muscle contractions.

Study Goal: The Association between Genes and Injury Risk

Depending on their genes, a person could have the protein alpha-actinin 3 or not (due to the variation in ACTN3 gene). This variation is called polymorphism R577X.

The starting point for Rodas and Clos (2021) research is that there is recent data that suggest an association between polymorphism R577X in ACTN3 gene, which encodes alpha-actinin 3 protein, and soft tissue injury risk (non-contact), and recovery time after the injury in elite football players.

46 players (22 males and 24 females) from the first male and female teams of Barcelona FC were assessed in 5 consecutive seasons (from July 2015 to June 2020). The sample included the best football player in the world according to FIFA. There were many FIFA World Cup and UEFA main competitions winners In the male team. The female team won twice the Primera Iberdrola competition, and got to the Champions League semi-finals in the seasons under study. They were also the champions of Champions League 2021.

In that period, the same medical staff (including physicians, physiotherapists, athletic trainers, and fitness trainers) recorded all the injuries and supervised standard protocols for muscle injury recovery. The occurrence of muscle injury was evidenced in ultrasound or magnetic resonance. Only muscle-type injuries (in soft tissues) resulting from football training sessions or competitions, and located in the lower limbs, were recorded. In fact, a total of 96 muscle injuries were recorded in the sample of football players during the investigation period.

Traumatic muscle injuries produced by contact with another player were ruled out, and the data recorded were introduced into a validated electronic medical record software. All non-contact soft tissue muscle injuries were diagnosed, classified, and recorded using a classification system developed by the club’s medical staff, following international guidelines. The time needed to return to play was calculated as the time (in days) since the moment of the  injury until the player returned to the training session or competition, as detailed in FC Barcelona Guide.

Genotype Distribution

To classify athletes, blood samples of each participant were collected, following the most demanding protocols, and they were distributed by genotypes. 

The genotype is the genetic information that an organism has in DNA form. Normally, the genome of a species includes numerous variants or polymorphisms in many of its genes. The genotype is used to determine which specific variations the individual has.

As we explained earlier, depending on their genes, a person could have the protein alpha-actinin 3 or not (due to the variation in ACTN3 gene), resulting in 3 different genotypes: RX, RR and XX. People with XX are the ones unable to express alpha-actinin 3, as opposed to RR or RX. In this study, the genotype distribution was: 

• RR: 14.3%, 
• RX: 47.8% and 
• XX: 10.9%.

XX Genotype and Muscle Injury Risk

The results of the study showed a tendency towards a greater non-contact muscle injury associated with XX genotype (all the players had injuries in the 5-year period of this study). Besides, XX players also needed more time to return to play. While RR and RX players return to training sessions and competitions in 17-20 days, XX player needed an average of 36 days.

There is some rationale to support a potential increase in alpha-actinin 3 deficiencies in muscle catabolism (the process of breaking down complex organic nutrients to obtain useful energy for the cells) after a football game. These deficiencies might lead the muscle to a lower capacity to tolerate the strain produced by explosive sports such as football. 

In conclusion, genotype XX might be associated with a greater non-contact muscle injury risk and with the recovery time. However, it is still being investigated to confirm the initial hypothesis since the size of the sample was small; nevertheless, the quality of the participants and the excellent protocol used in the study period offers a solid base to go further with the initial hypothesis.

Besides, it is new and interesting data to be considered by the medical, rehabilitation and physiotherapy staff, even when evidence is preliminary to consider this genetic finding a detection tool for predicting muscle injuries associated with sport. 

References:

1 Rodas G, Moreno-Pérez V, Del Coso J, Florit D, Osaba L, Lucia A. Alpha-Actinin-3 Deficiency Might Affect Recovery from Non-Contact Muscle Injuries: Preliminary Findings in a Top-Level Soccer Team. Genes (Basel). 2021 May 18;12(5):769. 

2 Ekstrand, J.; Hägglund, M.; Waldén, M. Injury incidence and injury patterns in professional football: The UEFA injury study. Br. J. Sports Med. 2011, 45, 553–558.

3 Massidda, M.; Voisin, S.; Culigioni, C.; Piras, F.; Cugia, P.; Yan, X.; Eynon, N.; Calò, C.M. ACTN3 R577X Polymorphism Is Associated with the Incidence and Severity of Injuries in Professional Football Players. Clin. J. Sport Med. 2019, 29, 57–61. [CrossRef] [PubMed]

4 Clos, E.; Pruna, R.; Lundblad, M.; Artells, R.; Esquirol Caussa, J. ACTN3 single nucleotide polymorphism is associated with non-contact musculoskeletal soft-tissue injury incidence in elite professional football players. Knee Surg. Sport. Traumatol. Arthrosc.