The ACTN3 gene closely relates to the expression of strength and power with its main function to stabilise sarcomeres during athletic movements requiring explosive bursts (Berman & North, 2010). The ACTN3 gene has 2 main polymorphisms which are ACTN3 577R and ACTN3 577X. These can be found with three different alleles which include RR, XX and RX. Both RR and RX are closely related to increased type II fibre cross sectional area and increased muscle strength (Berman & North, 2010). Whereas the XX allele appears to decrease type II fibre cross sectional area, decrease muscle strength and increase endurance (Berman & North, 2010). It is thought that these genes may have a big influence on training responses, post-exercise recovery and exercise associated injury risk so lets explore these areas a bit deeper.
Training responses:
Studies have investigated the effects of ACTN3 gene on modulating training responses. A study by Norman et al. (2014) investigated mTOR signalling pathway 140 minutes after 3 Wingate cycling tests. The results suggest that the phosphorylation of mTOR and p70S6K (both associated with increased protein synthesis) was significantly smaller in the XX group than it was in the RR and RX genotype groups (Norman et al., 2014). These results indicate phosphorylation of mTOR is greater in RR and RX genotypes leading to increased protein synthesis. The study also examined glycogen levels immediately after 30s of Wingate cycling. The results showed a significant decrease in glycogen with RR and RX when compared to XX in type II muscle fibres (Norman et al., 2014). These results indicate that individuals with XX genotype restrict glycogen utilisation during anaerobic activity, which promotes the maintenance of high glycogen levels (Norman et al., 2014).
Studies on older adults have been performed with Pereira et al. (2012) implementing a 12 week speed and power program to Caucasian women (mean age = 65.5). The results found that the RR genotype demonstrated the greatest increase in 1RM, jump ability and the sit to stand test when compared to the XX genotype (Pereira et al., 2012). Similarly, Delmonico et al., (2007) investigated knee extensor concentric peak power with a 10 week unilateral knee extensor strength training program. The findings indicated that in men (mean age = 65) there was a significant increase in peak power after the 10 week training program with the RR group when compared to the XX group (Delmonico et al., 2007). The results were the same for women (mean age = 64) where the RR group was significantly higher than the XX group (Delmonico et al., 2007).
Post-exercise recovery:
Several studies have looked at the ACTN3 gene and its association with post-exercise recovery. A study by Pimenta et al. (2011) investigated muscle damage with eccentric training in Brazilian soccer players on the different ACTN3 genetic profiles (XX, RX and RR). The study concluded that post eccentric training, players with the XX gene were more susceptible to muscle damage and presented a higher catabolic state when compared to RX and RR groups (Pimenta et al., 2011). Another study by Vincent et al. (2010) found after bouts of eccentric exercise, indicators of muscle damage were higher in XX groups when compared to RR groups. The study also found that the 577X polymorphism did not differentially influence post exercise activation of other anabolic/catabolic genes or genetic markers for exercise induced muscle damage (Vincent et al., 2010).
Injury risk:
It seems evident through various studies that there is an association with the XX genotype and increased risk of ankle injuries. Qi et al. (2016) found that R577X polymorphism was correlated with increased risk and severity of non-acute ankle sprain in the Chinese Han population and also stated that it can be used as an independent risk predictor for ankle sprains. A study by Kim et al. (2014) substantiates this point where eight ballerinas were tested for their injury risk on joints and found that not only does the ACTN3 gene have an impact on the ballerinas performance capacity but also indicates that genotype XX are at higher risk for ankle joint injury. Another study found that soccer players with the XX genotype were more likely to suffer non-contact soft tissue injuries than the RR or RX genotype (Massidda et al., 2019; Clos et al., 2019). The mechanism behind these injuries may be the fact that the XX genotype is associated with decreased testosterone levels (Ahmetov et al., 2014). High testosterone will increase muscle strength and hypertrophy which in turn will increase stability and balance of joints therefore leading to decreased risk of injury.
Based upon the information and studies reviewed it has become evident that screening athletes for the ACTN3 gene may prove to be beneficial. It can provide information such as how the athlete will respond to certain training stimuli, if the athlete is more susceptible to muscular damage after training and also if they are at increased risk for certain injuries such as ankle sprains. With this information provided, a strength and conditioning coach can use this to tailor specific training interventions especially to those with the XX genotype to maximise performance.
References:
Ahmetov, I. I., Donnikov, A. E., & Trofimov, D. Y. (2014). Actn3 genotype is associated with testosterone levels of athletes. Biology of sport, 31(2), 105-108. doi:10.5604/20831862.1096046
Berman, Y., & North, K. (2010). A Gene for Speed: The Emerging Role of α-Actinin-3 in Muscle Metabolism. Physiology, 25(4), 250-259. https://doi.org/10.1152/physiol.00008.2010
Clos, E., Pruna, R., Lundblad, M., Artells, R., & Esquirol Caussa, J. (2019). ACTN3 single nucleotide polymorphism is associated with non-contact musculoskeletal soft-tissue injury incidence in elite professional football players. Knee Surgery, Sports Traumatology, Arthroscopy, 27(12), 4055-4061. https://doi.org/10.1007/s00167-019-05381-x
Delmonico, M., Kostek, M., Doldo, N., Hand, B., Walsh, S., & Conway, J. et al. (2007). Alpha-Actinin-3 (ACTN3) R577X Polymorphism Influences Knee Extensor Peak Power Response to Strength Training in Older Men and Women. The Journals Of Gerontology Series A: Biological Sciences And Medical Sciences, 62(2), 206-212. https://doi.org/10.1093/gerona/62.2.206
Massidda, M., Voisin, S., Culigioni, C., Piras, F., Cugia, P., & Yan, X. et al. (2019). ACTN3 R577X Polymorphism Is Associated With the Incidence and Severity of Injuries in Professional Football Players. Clinical Journal Of Sport Medicine, 29(1), 57-61. https://doi.org/10.1097/jsm.0000000000000487
Norman, B., Esbjörnsson, M., Rundqvist, H., Österlund, T., Glenmark, B., & Jansson, E. (2014). ACTN3 genotype and modulation of skeletal muscle response to exercise in human subjects. Journal Of Applied Physiology, 116(9), 1197-1203. https://doi.org/10.1152/japplphysiol.00557.2013
Pereira, A., Costa, A., Izquierdo, M., Silva, A., Bastos, E., & Marques, M. (2012). ACE I/D and ACTN3 R/X polymorphisms as potential factors in modulating exercise-related phenotypes in older women in response to a muscle power training stimuli. AGE, 35(5), 1949-1959. https://doi.org/10.1007/s11357-012-9461-3
Pimenta, E., Coelho, D., Cruz, I., Morandi, R., Veneroso, C., & de Azambuja Pussieldi, G. et al. (2011). The ACTN3 genotype in soccer players in response to acute eccentric training. European Journal Of Applied Physiology, 112(4), 1495-1503. https://doi.org/10.1007/s00421-011-2109-7
Qi, B., Liu, J., & Liu, G. (2016). Genetic association between ACTN3 polymorphism and risk of non-acute ankle sprain. Genetics And Molecular Research, 15(4). https://doi.org/10.4238/gmr15048962
Vincent, B., Windelinckx, A., Nielens, H., Ramaekers, M., Van Leemputte, M., Hespel, P., & Thomis, M. (2010). Protective role of α-actinin-3 in the response to an acute eccentric exercise bout. Journal Of Applied Physiology, 109(2), 564-573. https://doi.org/10.1152/japplphysiol.01007.2009
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