Journal of Strength & Conditioning Research:
The ACTN3 R577X Polymorphism Is Associated With Muscle Power in Male Japanese Athletes
Kikuchi, Naoki1; Nakazato, Koichi2; Min, Seok-ki2; Ueda, Dai3; Igawa, Shoji4
1Sports Training Center, Nippon Sport Science University, Tokyo, Japan;
2Laboratory of Exercise Physiology, Nippon Sport Science University, Tokyo, Japan;
3Faculty of Health and Nutrition, Bunkyo University, Kanagawa, Japan; and
4Laboratory of Sports Nutrition, Nippon Sport Science University, Tokyo, Japan
Address correspondence to Naoki Kikuchi, email@example.com.
Kikuchi, N, Nakazato, K, Min, S-k, Ueda, D, and Igawa, S. The ACTN3 R577X polymorphism is associated with muscle power in male Japanese athletes. J Strength Cond Res 28(7): 1783–1789, 2014—In this study, we investigated whether the ACTN3 R577X polymorphism is associated with muscular power in Japanese collegiate athletes by analyzing the mean and peak power results of a 30-second Wingate anaerobic test (WAnT) with respect to the ACTN3 R577X genotype in 253 Japanese athletes (144 men and 109 women). Each athlete performed a 30-second WAnT with a resistance equal to 7.5% of his or her body weight. Genotyping for the ACTN3 R577X (rs1815739) polymorphism was performed using the TaqMan approach. The ACTN3 R577X genotypes exhibited a Hardy-Weinberg equilibrium distribution in our population. The relative and absolute mean power results of the 30-second WAnT did not differ significantly among the genotypes. However, the relative peak power result of the WAnT was significantly higher in the R-allele-dominant model groups than in the XX group in male but not female athletes. These results suggest that the ACTN3 R allele is associated with the relative peak power during the WAnT in male Japanese collegiate athletes.
Elite athletic performance is a complex phenotype determined by several environmental factors, including dietary, physical training, and social influences. Genetic variation may also contribute to interindividual differences in athletic performance, and a recent review noted that more than variants of 200 genes are associated with fitness-related phenotypes (20). One of the most potent of these, the α-actinin-3 (ACTN3) R577X polymorphism, has been associated with muscle fiber composition (22), muscle strength (14), and elite performance (8,10,25).
The ACTN3 R allele and RR genotype have been found to be associated with top-level power-oriented athletic performance in a broad variety of ethnic groups, including Israelis (5), Finns (17), Greeks (18), Russians (4), and Japanese (12). In contrast, previous studies in whites found that the ACTN3 XX genotype confers better endurance performance in the general population (21,25). Although previous studies (1) reported that the ACTN3 RR genotype is associated with endurance performance, the role of the XX genotype in endurance performance remains unclear.
The relationship between the ACTN3 R577X genotype and muscular phenotype has been examined in the general population in several ethnic groups. Women with the XX genotype have lower baseline elbow flexor isometric strength (3), lower knee extensor peak torque (24), and a smaller thigh muscle (26) in comparison with women with RR genotype. Similar associations have been observed in competitive athletes. We recently confirmed a linear correlation between the frequency of the ACTN3 R allele (RR or RX) and actual competition results in Japanese wrestlers (12), as reported by others (4). Taken together, there appears to be a relationship between the ACTN3 genotype and muscle function.
Previous studies (7,15) did not specifically examine the relationship between ACTN3 genotype and anaerobic performance, especially in trained athletes. Anaerobic performance is generally estimated by tests such as the vertical jump and the Wingate test, and such information helps athletes and their coaches evaluate and adjust their conditioning programs. The Wingate anaerobic power test (WAnT) in particular is frequently used to measure anaerobic performance (13,27). The peak power (the highest-power performance during any 5-second period) and mean power (the total power performance during the entire 30-second period) are traditionally considered good general indices of anaerobic power and capacity. The WAnT has been confirmed to be an accurate indicator of athletic performance (13). Exploration of the association between the ACTN3 genotype and the actual anaerobic performance phenotype is important to help trained athletes, especially those in power-oriented sports, to design more suitable individualized training programs. Despite this importance, the WAnT was not employed in the previous studies (7,15) concerning the specific role of the ACTN3 genotype in trained athletes.
The purpose of this study was to examine the relationship between the ACTN3 R577X polymorphism genotype and the athletic phenotype in Japanese collegiate athletes, using the WAnT to estimate each participant's maximum anaerobic capacity.
Experimental Approach to the Problem
We used a cross-sectional design to examine the association between the ACTN3 R577X polymorphism and WAnT results (mean power and peak power) in 253 Japanese trained athletes. The experimental period was from July through August 2012. All subjects were in the preseason training phase for their respective sports. Each subject performed a 30-second WAnT using a resistance equal to 7.5% of his or her body weight. All of the subjects were involved in top-level intercollegiate sports and had extensive weight training experience. Each subject also completed a questionnaire concerning his or her training status and athletic experience.
We enrolled 253 Japanese collegiate athletes (144 men and 109 women; age range, 18–22 years) in this study. The subjects' general characteristics and specific sports events are shown in Table 1. The participants were informed of the purpose and method of the study to ensure that they understood completely, and each provided written informed consent to participate. The study was approved by the ethics committee of Nippon Sport Science University in Japan (010-G01) and was conducted in accordance with the Declaration of Helsinki for Human Research.
Genotyping of a DNA polymorphism in the ACTN3 gene was performed in 253 Japanese collegiate athletes. DNA samples were obtained from the subjects' buccal cells by rubbing the inner surface of each subject's mouth with a cotton swab. After collection, the cells were lysed in 50 µl of lysis solution (20 mmol·L−1 Tris-HCI (pH 8.0) containing 5 mmol·L−1 ethylenediaminetetraacetic acid, 400 mmol·L−1 NaCI, 0.3% sodium dodecyl sulfate, and 10 mg·ml−1 proteinase K) and incubated at 55° C for 30 minutes. The samples were then stored at 4° C until polymerase chain reaction (PCR). Genotyping for the ACTN3 R577X polymorphism was performed by real-time PCR using a TaqMan probe (rs1815739, Pre-Designed SNP Genotyping assays; Applied Biosystems, Foster City, CA, USA). Polymerase chain reaction cycling was performed using a heat block (CFD-3120J1, BioRad, Hercules, CA, USA) as follows: an initial melting step at 95° C for 10 minutes followed by 39 cycles consisting of 92° C for 15 seconds and 60° C for 1 minute and then a melting curve from 65° C to 95° C (3).
The WAnT was performed on a PowerMaxV II (Combi, Tokyo, Japan) using a resistance equal to 7.5% of the athlete's body weight for both the male and female athletes. Each subject first performed a 3–5 minute warm-up on a cycle ergometer in which he or she strived to achieve a warm-up heart rate of 130–140 b·min−1. We evaluated the mean power and peak power during the 30-second test. All subjects performed the WAnT and underwent DNA sampling at the same time of the experimental day. The experimental period was from July through August 2012.
The SPSS statistical package version 16.0 for Windows (SPSS, Inc., Chicago, IL, USA) was used to perform all statistical evaluations. Allele frequencies were determined by gene counting. Pearson's χ2 test and Fisher's exact test were used to confirm that the observed genotype frequencies exhibited a Hardy-Weinberg equilibrium distribution. Differences in the mean and peak power results of the WAnT among the ACTN3 R577X genotypes were tested using analysis of variance (with Tukey's multiple comparison test) and between the XX and R-dominant model (RR and RX genotypes) groups using unpaired t-tests. Linear regression analysis was performed to estimate the degree of variance in the mean and peak power results of the WAnT associated with the ACTN3 R577X genotype. The enough number of subjects was determined by a sample size estimation using the data from previous studies that examine the relationship between ACTN3 genotype and muscle phenotype (13,27). The estimation was based on the effect size of 0.3, alpha level of 0.05, and a power (1-β) of 0.80. Statistical calculation was performed by G*power (6). We confirmed that the sample size was enough for the design of this study. The level of significance was set at p ≤ 0.05.
The ACTN3 genotypes exhibited a Hardy-Weinberg equilibrium distribution among athletes (all athletes: χ2 = 0.26 and p = 0.702; male athletes: χ2 = 0.004 and p = 0.944; female athletes: χ2 = 1.44 and p = 0.312). The genotype frequencies and the allele frequency of the ACTN3 R577X polymorphism are shown in Table 2. None of the subjects' characteristics differed significantly among the ACTN3 R577X genotypes.
The anaerobic power (absolute/relative) results of the WAnT with respect to the ACTN3 R577X genotype and the R-dominant model in male athletes are shown in Table 3. The relative WAnT peak power differed significantly among the ACTN3 genotypes: athletes with the RR genotype had a significantly higher relative peak power than those with the RX (p = 0.039) or XX (p = 0.024) genotype. The R-dominant model (RR and RX genotypes) showed significantly higher relative peak power than the XX genotype (p = 0.045). Among the female athletes, however, the WAnT power did not differ significantly among the ACTN3 R577X genotypes (Table 4). The ACTN3 R577X genotype accounted for 4.6% of the variability in the relative peak power result of the WAnT among the male athletes (p = 0.006).
To the best of our knowledge, this study included the largest number of Japanese athletes among similar studies performed to date and therefore provides useful insight into the role of the ACTN3 R577X genotype in trained individuals. Our major finding is that the ACTN3 R allele, especially when homozygous, influences the relative WAnT peak power of Japanese male athletes. We also showed by regression analysis that the ACTN3 R577X genotype accounts for approximately 4.6% of the variance in the relative peak power result of the WAnT in Japanese male athletes.
Two major energy sources are required during the WAnT. The first is the adenosine triphosphate-phosphocreatine system, which lasts only for 3–15 seconds during maximum effort. The second system is anaerobic glycolysis, which can be sustained for the remainder of the all-out effort. The peak power recorded is the maximal power output achieved for 5 seconds, usually the first 5 seconds, of the WAnT (27). We found that the ACTN3 R allele was associated with the relative peak power result of the WAnT in the male Japanese athletes. Because the peak power was observed within the first 5 seconds of the test in all subjects, this result suggests that athletes with the R allele may possess a higher-capacity phosphagen system, and we cannot exclude the possibility that the glycolytic system is also affected by the ACTN3 genotype.
We also found that 4.6% of the variability in the relative peak power result of the WAnT among the male Japanese athletes was attributable to the ACTN3 R577X genotype. A previous study on the general population reported that the ACTN3 R577X polymorphism is responsible for 1–2% of the variation in muscle strength (3,24). However, no association between the ACTN3 R577X genotype and the muscle power results of the WAnT was reported in individuals who were active but not athletes (9,22). On the other hand, Massidda et al. (15) reported that the ACTN3 R577X genotype accounted for 8.0% of the variation in squat-jump performance in elite soccer players. These results suggest that the contribution of the ACTN3 R577X genotype becomes more apparent in competitive athletes, as we had hypothesized. We propose that the contribution of the ACTN3 R allele manifests during strenuous sporting activities, as shown in this study.
This study detected a significant relationship between the ACTN3 R577X genotype and muscle power only in male athletes. Because the relationship between the ACTN3 R577X genotype and the muscle phenotype with respect to sex has not previously been examined in the Japanese population, we believe that our results are the first documented evidence for a sex-dependent effect of the ACTN3 R/X polymorphism. Previous studies did show that the absence of α-actinin-3 protein negatively influences the peak isokinetic torque during knee extension in middle-aged women but not men (24). Moran et al. (16) reported that men with the R allele (RR or RX) had better sprinting ability than those with the XX genotype. These results support the possibility of sex-dependent effects of the ACTN3 R577X genotype on muscle phenotype and athletic performance.
The possible mechanisms underlying the association between the ACTN3 R577X polymorphism and power-oriented performance have been discussed in detail elsewhere. Recent findings have indicated that the percentage of surface coverage and the number of type IIx fibers is greater in individuals with the RR genotype group than in those with the XX genotype among both athletes (2) and nonathletes (20).
In this study, we examined the relationship between a single genetic factor and anaerobic performance in Japanese athletes. We also recently showed a significant relationship between a combination of 2 polymorphisms (ACTN3 R577X and ACE I/D) and elite performance (11). However, a comprehensive understanding requires consideration of potential confounding factors such as other polymorphisms and environmental factors.
In summary, we found a positive relationship between the ACTN3 R577X genotype and the relative peak power result of the WAnT in male Japanese athletes. Our data indicate that the ACTN3 R allele (RR and RX genotypes) is associated with power output capacity.
The ACTN3 R577X genotype can provide useful information (e.g., talent selection and genotype-based customization for training) for athletes, especially well-trained men and their strength and conditioning coaches and sports coaches. According to our previous study (12), athletes with the ACTN3 R allele (RR and RX) have an advantage over XX individuals in terms of power-oriented performance. Furthermore, Vincent et al. (23) described a protective role of the α-actinin-3 protein (completely absent in XX individuals) against muscle damage after eccentric training. In addition, professional soccer players with the XX genotype exhibited higher CK activities, α-actin concentrations, and levels of cortisol than did their RR counterparts (19).
Therefore, individuals with the XX genotype, being completely deficient in the α-actinin-3 protein, exhibit inferior skeletal muscle function in terms of force generation from contraction or a poor ability to recover from high-intensity intermittent exercise. These factors might predict some aspects of response to training and thus provide useful information for strength and conditioning coaches.
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gene polymorphism; anaerobic power; Wingate test; collegiate athlete
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