Genetic polymorphisms related to muscular strength and flexibility are associated with artistic gymnastic performance in the Japanese population

ABSTRACT

This study aimed to examine how genetic polymorphisms related to muscular strength and flexibility influence artistic gymnastic performance in an attempt to identify a novel polymorphism associated with flexibility. In study 1, the passive straight-leg-raise (PSLR) score and aromatase gene CYP19A1 rs936306 polymorphism, a key enzyme for estrogen biosynthesis, were assessed in 278 individuals. In study 2, athletes (281 gymnasts and 1908 other athletes) were asked about their competition level, and gymnasts were assessed using the difficulty score (D-score) for each event. Muscular strength- (ACTN3 R577X rs1815739 and ACE I/D rs4341) and flexibility-related (ESR1 rs2234693 T/C and CYP19A1 rs936306 C/T) genetic polymorphisms were analyzed. In study 1, males with the CYP19A1 CT + TT genotype showed significantly higher PSLR scores than those with the CC genotype. In study 2, male gymnasts with the R allele of ACTN3 R577X showed a correlation with the floor, rings, vault, and total D-scores. In addition, male gymnasts with the C allele of ESR1 T/C and T allele of CYP19A1 C/T polymorphisms were correlated with the pommel horse, parallel bars, horizontal bar, and total D-scores. Furthermore, genotype scores of these three polymorphisms correlated with the total D-scores and competition levels in male gymnasts. In contrast, no such associations were observed in female gymnasts. Our findings suggest that muscular strength- and flexibility-related polymorphisms play important roles in achieving high performance in male artistic gymnastics by specifically influencing the performance of events that require muscular strength and flexibility, respectively.

Highlights

• Estrogen-related CYP19A1 polymorphism is a novel determinant of flexibility in males.

• Muscular strength- and flexibility-related polymorphisms play important roles in high performance in male artistic gymnastics.

• Genotypes of ACTN3 R577X, ESR1 rs2234693, and CYP19A1 rs936306 may contribute to training plan optimization and event selection in artistic gymnastics.

KEY WORDS:

• single nucleotide polymorphism
• α-actinin-3
• estrogen receptor α
• cytochrome P450 aromatase
• gymnast
• difficulty score

Introduction

Higher physical fitness, including muscular strength, cardiorespiratory fitness, and flexibility, is associated with better competition levels in athletes as well as the prevention of chronic diseases in the general population (Blair et al., 1989; Komatsu et al., 2017; Leong et al., 2015; Yamamoto et al., 2009). The R577X polymorphism in the α-actinin-3 gene (ACTN3) and I/D polymorphism in the angiotensin-converting enzyme (ACE) are the most studied physical fitness-related genetic polymorphisms (Montgomery et al., 1998; Yang et al., 2003). The α-actinin-3 protein is a major component of the Z-line in muscles and is only expressed in fast-twitch fibers. The ACTN3 R577X polymorphism, a common nonsense mutation in ACTN3, causes α-actinin-3 deficiency (North et al., 1999), and X allele carriers show reduced muscle strength by regulating skeletal muscle fiber composition (Kumagai et al., 2018; Vincent et al., 2007). Although the detailed mechanisms have not been elucidated, it has been suggested that the D and I alleles of the ACE I/D polymorphism contribute to muscular strength-and endurance-related performances, respectively (Montgomery et al., 1998; Nazarov et al., 2001). The associations between these genetic polymorphisms and physical performances have been validated by a meta-analysis (Ma et al., 2013). However, although the heritability estimates of flexibility are 50% (Schutte, Nederend, Hudziak, de Geus, & Bartels, 2016), flexibility-related genetic polymorphisms are poorly understood.

Women show higher flexibility than men (Kumagai et al., 2019; Morse, 2011). Furthermore, flexibility differs during the menstrual cycle (Bell et al., 2009; Eiling, Bryant, Petersen, Murphy, & Hohmann, 2007), implying that estrogen may be a key determinant of flexibility. Estrogen is biosynthesized from androgen by cytochrome P450 aromatase (CYP19A1), an enzyme responsible for a key step in estrogen biosynthesis, and its effects are primarily mediated by estrogen receptor α (ERα). The C allele of the rs2234693 C/T polymorphism in the estrogen receptor α gene (ESR1) reportedly shows higher ERα expression than the T allele (Herrington et al., 2002), whereas the T allele of the rs936306 C/T polymorphism in CYP19A1 shows higher circulating estradiol levels than the C allele in young men (Kumagai et al., 2022) and postmenopausal women (Hosono et al., 2015). Although we previously demonstrated that the rs2234693T/C polymorphism in ESR1 is associated with flexibility (Kumagai et al., 2019), the effect of the CYP19A1 rs936306 polymorphism on flexibility has not been elucidated.

The physical fitness required for athletic success differs among sports. Artistic gymnastics is one of the most unique sports; gymnasts exhibit extraordinarily higher flexibility than other athletes. In addition to high flexibility, high muscular strength is necessary for better competition (Bencke et al., 2002; Faria & Faria, 1989). Therefore, improving these physical abilities is recommended in daily training (Sands, Caine, & Borms, 2003), and top-level gymnasts exhibit higher flexibility and muscular strength than other gymnasts (Bencke et al., 2002; Faria & Faria, 1989; Gannon & Bird, 1999; Nelson, Johnson, & Smith, 1983). Although few studies have investigated the frequency of the ACTN3 R577X and ACE I/D polymorphisms in gymnasts (Massidda, Vona, & Calo, 2009; Massidda, Vona, & Calo, 2011), the association between gymnastic performance and flexibility-related genetic polymorphisms remains unclear.

Therefore, this study aimed to investigate whether: (1) the CYP19A1 rs936306 polymorphism influences flexibility and (2) muscular strength- and flexibility-related genetic polymorphisms influence gymnastic performance.

Materials and methods

Study 1

Overall, 158 male and 120 female nonprofessional athletes from several sports, who were physically active and young, participated in study 1 (Supplementary Table 1). This cohort included six male (3.8%) and 11 female (9.2%) gymnasts. No apparent neurological, orthopedic, or neuromuscular problems were observed in any participant. Passive straight-leg raise (PSLR) was assessed as previously reported (Miyamoto, Hirata, Kimura, & Miyamoto-Mikami, 2017). Briefly, the participants visited the laboratory at least 20 min before the measurements, and PSLR tests were performed. The room temperature of the laboratory was maintained at 24 ± 2°C to minimize temperature-induced effects. Participants were not allowed to perform warmup or stretching exercises prior to testing. All PSLR tests were performed on both legs by the same examiner, and the intraclass correlation coefficient for the PSLR was 0.966. The participants laid in a supine position with their legs straight on the examination bed. The pelvis and non-testing leg were secured on a bed with non-elastic straps to avoid a posterior pelvic tilt. The examiner held one hand gently on the knee of the test leg to maintain it straight and raised the leg with the other hand placed near the ankle until the examiner felt tightness. The hip flexion angle from the resting position was measured using a digital inclinometer (MLT-100, Sakai Medical, Japan) attached 3–4 cm proximal to the lateral malleolus and was adopted as the score. Written informed consent was obtained from each participant in accordance with the tenets of the Declaration of Helsinki. This study was approved by the ethics committee of Juntendo University.

Study 2

Overall, 2278 Japanese athletes were asked about their participation in primary sports, number of playing years, and competition level (regional, national, and international) using a questionnaire. Athletes with less than three years of competitive experience in their primary sport were excluded from the analyses, and the final sample size was 281 artistic gymnasts and 1908 athletes engaged in other sports. Artistic gymnastics includes six events for males and four events for females: floor, pommel horse, rings, vault, parallel bars, and horizontal bar for males; vault, uneven bars, beam, and floor for females. The present scoring system in gymnastics comprises of two scores: a difficulty score (D-score) and an execution score (E-score). Because the D-score reflects the difficulty of the performance and skills of each gymnast, we assessed the D-scores of each event according to the 2017 Code of Points by the International Gymnastics Federation. Overall, 245 gymnasts (167 male and 78 female) had their D-scores calculated using the 2017 Code of Points. The D-scores of the floor, pommel horse, rings, vault, parallel bars, and horizontal bar were assessed for male gymnasts, while those of the vault, uneven bars, beam, and floor were assessed for female gymnasts (Supplementary Table 2). The minor allele frequencies of each genetic polymorphism, such as the R allele of ACTN3 R577X, D allele of ACE I/D, C allele of ESR1 rs2234693, and T allele of CYP19A1 rs936306 in 1908 athletes engaged in other sports were 0.48, 0.36, 0.42, and 0.39, respectively. Because these minor allele frequencies were similar to those in the general Japanese population (0.47, 0.35, 0.43, and 0.40, respectively) (https://jmorp.megabank.tohoku.ac.jp/202008/), we defined these athletes as the control group. This study was included in the Japanese Human Athlome Project in the “Athlome Project Consortium” (Pitsiladis et al., 2016). Written informed consent was obtained from each athlete, in accordance with the tenets of the Declaration of Helsinki. This study was approved by the Ethics Committees of Juntendo University, Nippon Sports Science University, and Tenri University.

Genotyping analysis

Similar to our previous studies (Kumagai et al., 2019), total DNA was isolated from saliva using an Oragene® DNA collection kit (DNA Genotek, ON, Canada) in accordance with the manufacturer’s instructions. DNA concentration was quantified using a NanoDrop 8000 UV-Vis spectrophotometer (Thermo Fisher Scientific, DE, USA). Subsequently, the DNA samples were adjusted to a concentration of 10 ng/μL with TE buffer and stored at 4°C. Genetic polymorphisms in ACTN3 R577X (rs1815739), ACE C/G (I/D) (rs4341), ESR1 (rs2234693), and CYP19A1 (rs936306) were genotyped using a real-time thermocycler in endpoint analysis mode (LightCycler 480; Roche Applied Science, Mannheim, Germany) using TaqMan® SNP Genotyping Assays (assay ID: C____590093_1_, C__29403047_10, C___3163590_10, and C___1664161_10, respectively). The ACE I/D genotype (rs4340) was determined using the ACE C/G genotype (rs4341), which is in perfect linkage disequilibrium with the I/D genotype as follows: C/C as I/I, C/G as I/D, and G/G as D/D (Tanaka et al., 2003). In total, 5 μL of the genotyping mixture containing 2.5 μL of the TaqMan® GTXpressTM Master Mix (2x), 0.0625 μL of the TaqMan® SNP Genotyping Assay (40x), and 1.4375 μL of distilled water was mixed with 1 μL of genomic DNA (10 ng/μL) for each reaction. Two to four negative controls were included for each plate. Allelic discrimination analysis was performed using the LightCycler 480 SW software, version 1.5.1.62 (Roche Applied Science). In a different cohort from this study, we genotyped 87 samples in duplicate and confirmed that no samples were mismatched for all four analyzed genetic polymorphisms.

Statistical analysis

All data are expressed as the mean ± standard deviation. Hardy–Weinberg equilibrium was tested using the chi-squared test. The Kolmogorov–Smirnov normality test was used to assess the normality of all parameters. The unpaired t-test, Wilcoxon rank sum test, Tukey HSD test, and Steel–Dwass test were applied to compare the values between each group. Cohen d was calculated to assess the effect size. The Spearman correlation coefficient was applied to determine the correlation between D-scores and genotype or genotype scores. Independent correlates of the PSLR and D-scores of the floor, rings, vault, pommel horse, parallel bar, horizontal bar, and total D-score were examined using multivariate linear regression analyses to consider possible confounders. The D-scores of the floor and vault were log-transformed to obtain normal distributions before the multivariate linear regression analyses. The chi-square test and Cochran–Armitage trend test were used to determine the association between competition levels and genotype or genotype scores. Statistical significance was set at P < 0.05. Statistical analyses were performed using JMP Pro version 12 (SAS Institute Inc.) and the R programming environment (v4.0.3) using R Studio (v1.4.1103).

Results

The characteristics of 278 athletes are listed in Supplementary Table 1. Female participants exhibited significantly higher PSLR scores than did male participants (78.4 ± 13.6 vs. 66.3 ± 9.8 degrees, P < 0.001). The genotyping success rate was 97.3% for CYP19A1 C/T. The association between the CYP19A1 C/T polymorphism and PSLR is shown in Figure 1. Male participants with the T allele exhibited significantly higher PSLR scores than those with the CC genotype (P = 0.034, effect size d = 0.36; Figure 1A), whereas no significant association was found in female participants (P = 0.942, effect size d = 0.01; Figure 1B). The association between the CYP19A1 rs936306 polymorphism and PSLR remained significant by regression analysis after considering the sport in male participants (P = 0.046).

Figure 1. Passive straight-leg raise (PSLR) score in male (A) and female (B) participants with the CYP19A1 rs936306 genotype in accordance with the alleles present (i.e. CC, CT, or TT). The genotyping success rate was 97.3% for CYP19A1 C/T, and the CYP19A1 C/T polymorphism was in Hardy-Weinberg equilibrium (P = 0.315). Unpaired t-tests were used to compare the CC genotype and T allele carriers (CT + TT genotype).

To clarify the influence of muscular strength- and flexibility-related genetic polymorphisms on the D-scores of gymnasts, 245 gymnasts with D-scores for all events were analyzed (Supplementary Table 2). The genotyping success rate for the following polymorphisms were: 98.4% for ACTN3 R577X, 98.8% for ACE I/D, 99.2% for ESR1 rs2234693, and 98.8% for CYP19A1 rs936306. For male gymnasts, the RR carriers of ACTN3 R577X showed significantly higher D-scores for the vault (P < 0.05) than the X allele carriers, and the number of R alleles was significantly correlated with the D-score for the vault (r = 0.156, P < 0.05). Although not statistically significant, the RR carriers of ACTN3 R577X showed higher D-scores for the floor and rings than the X allele carriers (P = 0.086 and P = 0.084, respectively) (Supplementary Figure 1A). Male gymnasts with the T allele of CYP19A1 showed a significantly higher D-score for the horizontal bar than those with the CC genotype (P < 0.05). Although not statistically significant, male gymnasts with the C allele of ESR1 rs2234693 and the T allele of CYP19A1 tended to have higher D-scores for the pommel horse and parallel bars than those with the TT and CC genotypes, respectively (Supplementary Figure 1C and 1D). In contrast, no significant associations were observed in female gymnasts (Supplementary Figure 2). We then analyzed the combined effect of these three genetic polymorphisms on male gymnastic performance using genotype scores (ACTN3 R577X: RR = 2, RX = 1, XX = 0; ESR1 rs2234693: TT = 0, TC + CC = 2; CYP19A1 rs936306: CC = 0, CT + TT = 2). The genotype scores were significantly correlated with the D-scores for the rings (r = 0.155, P < 0.05), pommel horse (r = 0.159, P < 0.05), parallel bars (r = 0.207, P < 0.01), horizontal bar (r = 0.217, P < 0.01), and total D-score (r = 0.190, P < 0.05; Figure 2). Multivariate linear regression analyses revealed that the associations between the ACTN3 R577X polymorphism and vault, CYP19A1 rs936306 polymorphism and parallel bars and horizontal bar, and genotype score and parallel bars, horizontal bar, and total D-score remained significant after considering height, weight, and plying years (Supplementary Table 3).

Figure 2. D-scores of detailed events in male gymnasts in accordance with the genotype score of the ACTN3 R577X, ESR1 rs2234693, and CYP19A1 rs936306 polymorphisms. The Spearman correlation coefficient was applied to compare the values. The R² values for the rings, pommel horse, parallel bars, horizontal bars, and total D-score were 0.024, 0.025, 0.043, 0.047, and 0.036, respectively. Genotype score was calculated as follows: ACTN3 R577X: RR = 2, RX = 1, XX = 0 ESR1 rs2234693: TT =  0, TC + CC = 2 CYP19A1 rs936306: CC = 0, CT + TT = 2

The characteristics of the 2189 athletes, including 281 gymnasts, are shown in Supplementary Table 4. The genotyping success rate for the following polymorphisms were: 99.1% for ACTN3 R577X, 99.3% for ACE I/D, 98.0% for ESR1 rs2234693, and 98.8% for CYP19A1 rs936306. The genotype frequencies of each genetic polymorphism in the gymnast and control groups are shown in Figure 3 and Supplementary Table 5. The frequencies of the occurrence of male gymnasts with the R allele of ACTN3 R577X, the C allele of ESR1 rs2234693, and the T allele of CYP19A1 rs936306 increased with increasing competition levels (Figure 3A-D). The frequency of the ACE I/D genotype was significantly different between all male gymnasts (regional, national, and international) and controls under the I-allele additive model (P = 0.004) (Supplementary Table 5). The C allele of ESR1 T/C and T allele of CYP19A1 rs936306 were higher in international-level male gymnasts than in the control group under the dominant models (P = 0.097 and P = 0.042, respectively; Figure 3C-D and Supplementary Table 5). Consistent with the results of D-scores, the genotype scores of ACTN3 R577X, ESR1 rs2234693, and CYP19A1 rs936306 were positively correlated with the frequency of international-level male gymnasts (Figure 4). In female gymnasts, although the number of R allele carriers of ACTN3 R577X increased with competition level, no significant associations were observed (Figure 3E and Supplementary Table 5). The frequency of the occurrence of female gymnasts with genotype II of the ACE I/D polymorphism tended to increase with increasing competition levels, whereas no associations were found in the ESR1 rs2234693 and CYP19A1 rs936306 polymorphisms (Figure 3G–H and Supplementary Table 5).

Figure 3. The frequency of the ACTN3 R577X (A and E), ACE I/D (B and F), ESR1 rs2234693 T/C (C and G), and CYP19A1 rs936306 C/T genotypes (D and H) in male (A-D), and female gymnasts (E-H). The chi-square test and Cochran-Armitage trend tests were used to compare the values. The dotted lines indicate the frequencies in the other athletes.

Figure 4. Frequencies of male gymnasts in each competition level in accordance with the genotype score of the ACTN3 R577X, ESR1 rs2234693, and CYP19A1 rs936306 polymorphisms. The chi-square test and Cochran–Armitage trend tests were used to compare the values. Genotype score was calculated as follows: ACTN3 R577X: RR = 2, RX = 1, XX = 0 ESR1 rs2234693: TT =  0, TC + CC = 2 CYP19A1 rs936306: CC = 0, CT + TT = 2

Discussion

The present study investigated the influence of the CYP19A1 rs936306 polymorphism on flexibility (studies 1 and 2) and that of muscular strength- and flexibility-related genetic polymorphisms on gymnastic performance in the Japanese population, including Olympians and world champions (study 2). In study 1, male participants with the CYP19A1 CT + TT genotype showed significantly higher flexibility than those with the CC genotype. In study 2, the number of muscular strength-related R alleles of the ACTN3 R577X polymorphism was positively correlated with D-scores for the floor, rings, and vault. The flexibility-related C allele of ESR1 rs2234693 and T allele of CYP19A1 rs936306 polymorphisms were associated with D-scores for the pommel horse, parallel bars, and horizontal bars. Furthermore, the genotype scores of these three genetic polymorphisms in male gymnasts were markedly correlated with the total D-score and frequency of international-level gymnasts. In contrast, no significant association was observed in female gymnasts. Collectively, our findings suggest that the muscular strength-related R allele of the ACTN3 R577X polymorphism and flexibility-related C allele of the ESR1 rs2234693 and T allele of the CYP19A1 rs936306 polymorphisms play important roles in achieving high performance in male artistic gymnasts.

High muscular strength is crucial for ensuring high gymnastic performance (Bencke et al., 2002; Faria & Faria, 1989), especially in the floor and vault (Bradshaw, 2004; Bradshaw & Le Rossignol, 2004). Massidda et al. demonstrated that the frequency of the XX genotype of ACTN3 R577X was lower in international-level gymnasts than in the control group in an Italian population (Massidda et al., 2009), suggesting that the R allele of ACTN3 R577X, which is related to higher muscular strength (Vincent et al., 2007), was associated with high gymnastic performance. Supporting this result, the present study observed that the genotype frequency of the R allele carriers (i.e. RR + RX) increased with competition levels in male gymnasts (regional: 59.5%, national: 73.9%, international: 82.6%). Along with the competition level, we also observed that male gymnasts with the R allele exhibited higher D-scores for the floor, vault, rings, and total D-score than those with the X allele. These results supported the finding that muscular strength is necessary for high performance in the floor and vault (E. Bradshaw, 2004; E. J. Bradshaw & Le Rossignol, 2004) and suggested that muscular strength plays an important role in rings as well. These differences in D-scores may explain the association between the ACTN3 R577X polymorphism and gymnastic competition levels in males. In contrast, the genetic polymorphism in ACTN3 R577X was not associated with competition levels and D-scores in female gymnasts. Therefore, the ACTN3 R577X polymorphism served as a determinant of gymnastic performance only in male artistic gymnasts.

The ACE I/D polymorphism is another well-studied athlete-related genetic polymorphism. The D allele is associated with sprint/power ability in the European population (Gayagay et al., 1998; Ma et al., 2013; Montgomery et al., 1998). However, a contrasting association has been observed in the Asian population; the I allele is associated with sprint/power performance, whereas the D allele is associated with endurance (Kim et al., 2010; Tobina et al., 2010; Wang et al., 2013). Consistent with these findings, we demonstrated that males with the ACE II genotype showed a lower percentage of slow-twitch fibers, suggesting that the II genotype was associated with sprint/power performance in the Asian population (Kumagai et al., 2018). The present study found that the I allele frequency of ACE I/D was higher in male gymnasts than that in the control group, and it increased with increasing competition levels in female gymnasts. These results indicated the necessity of muscle strength among gymnasts.

Flexibility in the skeletal muscle is mainly influenced by collagenous connective tissue (Gajdosik, 2001), and estrogen is a well-known suppressor of collagen synthesis (Kwan et al., 1996). Women show higher flexibility than men (Kumagai et al., 2019; Morse, 2011). In addition, flexibility differs during the menstrual cycle in young women, with the highest flexibility occurring during the ovulation phase when the circulating estrogen levels increase (Bell et al., 2009; Eiling et al., 2007). CYP19A1 is the enzyme responsible for estrogen biosynthesis, and the T allele of the rs936306 C/T polymorphism in CYP19A1 shows higher circulating estradiol levels than the C allele (Hosono et al., 2015; Kumagai et al., 2022). The effects of estrogen are primarily mediated by ERα, and the C allele of ESR1 rs2234693 is suggested to upregulate ESR1 transcription (Herrington et al., 2002). This study demonstrated that male participants with the T allele (i.e. TT + TC) of CYP19A1 rs936306 exhibited significantly higher flexibility than those with the CC genotype, and we previously reported that C allele carriers of ESR1 rs2234693 exhibited higher flexibility than those with the TT genotype (Kumagai et al., 2019). Furthermore, male gymnasts with the T allele of CYP19A1 and the C allele of ESR1 showed higher D-scores for the pommel horse, parallel bars, and/or horizontal bars than those with the C allele and T allele, suggesting that flexibility is important in these events. Thus, these findings suggest that the genetic polymorphisms CYP19A1 rs936306 and ESR1 rs2234693 are possible determinants of gymnastic performance by regulating flexibility in male participants.

We observed significant associations between estrogen-related genetic polymorphisms and gymnastic performance in male participants but not in female participants. We speculate that circulating estradiol levels may influence these observations. Estradiol is a female sex hormone, and it is well known that circulating estradiol levels are much higher in young women than in men. Therefore, high circulating estradiol levels may cover the impact of estrogen-related polymorphisms in female participants.

Our study had several limitations. The small sample size was the first limitation of this study. Although we observed statistically significant associations between genetic polymorphisms and D-scores in study 2, the smallest sample size was four international-level female gymnasts. This sample size was not sufficient to detect reliable results and may have resulted in false-positive and false-negative results. The lack of validation cohorts, especially of different ethnicities, was a second limitation. The association between ACTN3 R577X polymorphism and athletic performance has been confirmed in multiple ethnicities. Contrarily, this is the first study that observed the influences of estrogen-related genetic polymorphisms on athletic performance. Further studies are necessary to validate these observations. The third limitation was the lack of information over the influence of athletic performance. Many factors influence athletic performance, and one factor (i.e. genetic polymorphism) is not sufficient to explain it. Consideration of more factors will help in a better understanding.

To our knowledge, the present study is the first to investigate the influence of genetic polymorphisms on detailed gymnastic performance, as well as the effect of CYP19A1 polymorphisms on flexibility. Male participants with the T allele of CYP19A1 rs936306 exhibited higher flexibility than CC genotype carriers. In addition, the present study demonstrated that the R allele of ACTN3 R577X, C allele of ESR1 rs2234693, and T allele of CYP19A1 rs936306 were possible determinants of gymnastic performance in men. Furthermore, the genotype scores of muscular strength- and flexibility-related genetic polymorphisms were positively correlated with the total D-score and competition level. These results suggest that muscular strength- and flexibility-related polymorphisms play important roles in achieving high performance in male artistic gymnastics by specifically influencing the performance of events that require muscular strength and flexibility, respectively. Our results may contribute to the optimization of training plans and the selection of events based on the genotypes of participating gymnasts.

Acknowledgments

We thank Dr. Mariko Kanaya, Dr. Atsushi Sano, and Dr. Yoshio Watanabe at the University of Tsukuba, Mr. Yukio Takeda at Komazawa University, Mr. Yutaka Goto at International Budo University, Mr. Daisuke Murayama at Shigakkan University, Mr. Ryuichiro Yamashita at Kyushu Kyoritsu University, Dr. Shogo Miyazaki at Shizuoka Sangyo University, Mr. Satoshi Syuto at Keio University, and Mr. Yoshihiro Saito at Central Sports Co., Ltd. for their help in recruiting the athletes. We would also like to thank Editage (https://www.editage.com/) for English language editing.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This study was supported in part by JSPS KAKENHI Scientific Research (B) [Grant Number 18H03155] to N.F. and [Grant number 16H03233] to N.M., Young Scientists (A) [Grant Number 17H04752] to E.M., Young Scientists [Grant number 18K17863 to H.K.], the MEXT-Supported Program for the Strategic Research Foundation at Private Universities (to Juntendo University),; The Institute of Health and Sports Science & Medicine, Juntendo University; and a Tenri University Research Grant (N. Kamiya.).