Effects of the ACTN3 R577X Genotype on the Muscular Strength and Range of Motion Before and After Eccentric Contractions of the Elbow Flexors

Abstract

The purpose of present study was to examine the association between ACTN3 R577X genotype and functional characteristics of elbow flexors before and after isokinetic eccentric contractions (ECCs). Fifty-two men (age: 20.8±3.8 years, height: 172.5±5.9 cm, body mass: 64.7±6.5 kg, BMI: 21.7±1.7) who had not participated in any regular resistance training for at least 1 year prior to this study were recruited. ECCs consisted of five sets of six maximal voluntary isokinetic (30°/s) ECCs of the elbow flexors with a range of motion (ROM) from 90° flexion to 0° (full extension). Measurements of maximal voluntary isometric contraction (MVC) torque, ROM, and muscle soreness were taken before, immediately after, and 1, 2, 3, and 5 days after ECCs. Genotyping results were analyzed for identifying ACTN3 R577X polymorphism (rs1815739) using TaqMan approach. The genotype frequencies of the ACTN3 R577X polymorphism were RR 26.9% (n=14), RX 50.0% (n=26), and XX 23.1% (n=12). There were no significant differences in MVC torque, ROM, and soreness between three genotype groups of ACTN3 R577X. However, MVC at baseline was greater in RR homozygotes than in X-allele carriers (combined XX and RX; p<0.05). ROM in RR homozygotes at baseline was lower than that of X-allele carriers. Although a significant decrease in ROM was observed in X-allele carriers until 3 days after ECCs, a significant ROM reduction in RR homozygotes was observed only immediately after ECCs. Our data indicated that ACTN3 RR genotype has higher MVC and lower flexibility than X-allele carriers at baseline, but the effect of ACTN3 R577X genotype on these two parameters is limited after ECCs.

ACTN3 R577X Genotype and Exercise Phenotypes in Recreational Marathon Runners

“…An alternative hypothesis for the survival of the 577XX genotype emerges from our data and previous research. Higher values of muscle flexibility and range of motion have been found for XX individuals in different joints [20,21,22], which, although negative for running economy, might confer enhanced muscle function. In the present study, likely higher trunk flexibility and ankle dorsiflexion values were identified in XX runners, which might be associated with a higher ground-force application [59] and lower leg stiffness during running [60].…”

“…Indeed, the X-allele has been associated with higher levels of several markers of muscle damage after exercise in amateur athletes [17,18,19]. Conversely, a higher muscle flexibility and a superior range of motion has been reported in XX individuals versus their RR referents [20,21,22], although some authors have failed to replicate this finding [23]. Although more flexible muscles are less susceptible to eccentric exercise-induced damage [24], higher muscle flexibility values do not seem to attenuate marathon-induced muscle damage in XX runners [17,18,19].…”

More than a ‘speed gene’: ACTN3 R577X genotype, trainability, muscle damage, and the risk for injuries

“…However, a lower trunk flexibility has been found in XX ballerinas when compared to R allele carriers (Kim et al 2014b). In regards to other joints, a reduced range of motion in the elbow has been found in RR homozygotes (Kikuchi et al 2018). The discrepancies in the outcomes of these investigations indicates that a clear effect of the ACTN3 R577X genotype on muscle flexibility and range of motion is yet to be elucidated.…”

Table_1.DOCX

“…To our knowledge, only a few studies compared the susceptibility to EIMD between the different ACTN3 genotypes (Clarkson et al, 2005;Vincent et al, 2010;Seto et al, 2011;Pimenta et al, 2012;Venckunas et al, 2012;Belli et al, 2017;Del Coso et al, 2017a,b;Kikuchi et al, 2018;Broos et al, 2019;Coelho et al, 2019). One of these studies was conducted in an animal model and showed that the force loss and changes in the histological markers of EIMD were greater in the extensor digitorum longus of XX mice following the forced lengthening contractions (Seto et al, 2011).…”

“…It has been proposed that ACTN3 polymorphisms influence the susceptibility to EIMD (Del Coso et al, 2019a). However, the role of ACTN3 polymorphism in modulating the susceptibility to EIMD is still debated with the studies showing that susceptibility to EIMD is greater in the RR individuals (Venckunas et al, 2012), X allele carriers (Seto et al, 2011;Belli et al, 2017;Del Coso et al, 2017a,b;Kikuchi et al, 2018), or similar among the different genotypes (Clarkson et al, 2005).…”