Genes for Elite Power and Sprint Performance: ACTN3 Leads the Way

ACTN3 R577X Polymorphism Is Associated With the Incidence and Severity of Injuries in Professional Football Players

OBJECTIVE

The ACTN3 R577X gene variant results in the absence of the α-actinin-3 protein in ∼18% of humans worldwide and has been associated with athletic performance and increased susceptibility to eccentric muscle damage. The aim of this study was to investigate the association between ACTN3 R577X variant and indirect muscle disorders/injuries in professional football players.

DESIGN

A case-control, genotype-phenotype association study.

INTERVENTION

Two hundred fifty-seven male professional Italian football players (from Serie A, Primavera, Allievi, and Giovanissimi; age = 21.2 ± 5.3 years) and 265 nonathletic controls were recruited for the study. Genomic DNA was extracted using a buccal swab, and the ACTN3 R577X genotype was performed using a PCR method. Structural-mechanical injuries and functional muscle disorders were collected from a subgroup of 169 football players during the period of 2009 to 2014.

MAIN OUTCOME MEASURE

We hypothesized that the 577XX genotype would be associated with higher predisposition to muscle injuries (compared with the other genotypes).

RESULTS

ACTN3 XX (α-actinin-3 deficiency) players had 2.66 higher odds for an injury incidence than their ACTN3 RR counterparts (95% confidence interval [CI]: 1.09-6.63, P = 0.02), whereas RX and RR players had similar injury incidence. Furthermore, ACTN3 XX players had 2.13 higher odds for having a severe injury compared with their RR counterparts (95% CI: 1.25-3.74, P = 0.0054), whereas RX individuals had 1.63 higher odds for having a severe injury compared with the RR players (95% CI: 1.10-2.40, P = 0.015).

CONCLUSIONS

The ACTN3 R577X polymorphism is associated with the incidence and severity of muscle injuries in professional football players; players with the ACTN3 577XX genotype have higher odds of having muscle injuries than their RR counterparts.

CLINICAL RELEVANCE

Discovering the complex relationship between gene variants and muscle injuries may assist coaches, physiologists, and the medical community to development tailored injury prevention program for football players, which could provide a new edge for successful competition.

Sequence analysis and expression profiling of the equine ACTN3 gene during exercise in Arabian horses

The ACTN3 gene codes for α-actinin-3, a protein localized in the Z-line in the skeletal muscle. Actinin-3 is critical in anchoring the myofibrillar actin filaments and plays a key role in muscle contraction. ACTN3 (α-actinin-3) cross-links glycogen phosphorylase (GP), which is the key enzyme catalysing glycogen metabolism. The aim of present study was to establish the expression level of the ACTN3 gene (for both isoforms separately and together in the gene expression analysis) in the gluteus medius muscle in order to verify if the α-actinin-3 gene can be related to training intensity in Arabian horses. A structural analysis of the ACTN3 gene was performed simultaneously to identify polymorphisms that can be related to racing performance traits. Our results showed the significant decrease (p < 0.05) of ACTN3 expression in the skeletal muscle of Arabian horses during the training periods preparing for flat-racing, and this decrease differed by the intensity of the exercises. The highest mRNA abundance measured for all ACTN3 genes was detected in the muscle of untrained horses, while the lowest expression was identified at the end of the racing season when horses had fully adapted to the physical effort. This gene expression profile was confirmed for both ACTN3 isoforms. The analysis of the ACTN3 sequence allowed us to identify 14 polymorphisms, which were localized in the promoter region, the 5'UTR (7 SNPs), exons (2 SNPs) and introns (5 SNPs). Two of them, a novel c.2334C>T - splice variant and the g.1104G>A polymorphism in the promoter region, were proposed as the causative mutations that might affect gene expression. The presented gene expression analyses indicated the significant role of the ACTN3 gene in adaptation to physiological effort in horses. Due to previous reports and our findings, further studies should be conducted to verify the usage of the ACTN3 gene as a potential genetic marker for determining exercise performance in Arabian horses and other horse breeds.

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

A common null polymorphism (rs1815739; R577X) in the gene that codes for α-actinin-3 (ACTN3) has been related to different aspects of exercise performance. Individuals who are homozygous for the X allele are unable to express the α-actinin-3 protein in the muscle as opposed to those with the RX or RR genotype. α-actinin-3 deficiency in the muscle does not result in any disease. However, the different ACTN3 genotypes can modify the functioning of skeletal muscle during exercise through structural, metabolic or signaling changes, as shown in both humans and in the mouse model. Specifically, the ACTN3 RR genotype might favor the ability to generate powerful and forceful muscle contractions. Leading to an overall advantage of the RR genotype for enhanced performance in some speed and power-oriented sports. In addition, RR genotype might also favor the ability to withstand exercise-induced muscle damage, while the beneficial influence of the XX genotype on aerobic exercise performance needs to be validated in human studies. More information is required to unveil the association of ACTN3 genotype with trainability and injury risk during acute or chronic exercise.

Performance prediction models based on anthropometric, genetic and psychological traits of Croatian sprinters

Elite athletes differ from each other in their characteristics according to their discipline. This study aimed to identify performance predictors in elite Croatian sprinters taking into consideration their anthropometric, psychological and genetic characteristics. One hundred and four elite Croatian sprinters (68 males and 36 females) participated in this study. Of them, 38 are currently competing in the 100-metre dash. The others are former sprinters. The participants underwent direct anthropometric assessment. Participants were also tested by means of the Competitive State Anxiety Inventory-2 and for ACE and ACTN3 polymorphisms. Multiple linear regression analysis was applied to identify the best model for performance prediction. Different models were developed for males and females. Anthropometric traits accounted for 44% of the variance in performance for males, 62% for females. Once other traits (psychological for females) were entered into the model, no additional contribution to the variance was observed. The most significant predictors of higher running velocity were bicristal diameter and foot dimensions in males, and leg length and clean one-repetition maximum in females. The findings suggest that performance in sprinters is associated with anthropometric characteristics, with biomechanical implications that may be used to provide a more complete evaluation of sprinters' performance.

Muscle Androgen Receptor Content but Not Systemic Hormones Is Associated With Resistance Training-Induced Skeletal Muscle Hypertrophy in Healthy, Young Men

The factors that underpin heterogeneity in muscle hypertrophy following resistance exercise training (RET) remain largely unknown. We examined circulating hormones, intramuscular hormones, and intramuscular hormone-related variables in resistance-trained men before and after 12 weeks of RET. Backward elimination and principal component regression evaluated the statistical significance of proposed circulating anabolic hormones (e.g., testosterone, free testosterone, dehydroepiandrosterone, dihydrotestosterone, insulin-like growth factor-1, free insulin-like growth factor-1, luteinizing hormone, and growth hormone) and RET-induced changes in muscle mass (n = 49). Immunoblots and immunoassays were used to evaluate intramuscular free testosterone levels, dihydrotestosterone levels, 5α-reductase expression, and androgen receptor content in the highest- (HIR; n = 10) and lowest- (LOR; n = 10) responders to the 12 weeks of RET. No hormone measured before exercise, after exercise, pre-intervention, or post-intervention was consistently significant or consistently selected in the final model for the change in: type 1 cross sectional area (CSA), type 2 CSA, or fat- and bone-free mass (LBM). Principal component analysis did not result in large dimension reduction and principal component regression was no more effective than unadjusted regression analyses. No hormone measured in the blood or muscle was different between HIR and LOR. The steroidogenic enzyme 5α-reductase increased following RET in the HIR (P < 0.01) but not the LOR (P = 0.32). Androgen receptor content was unchanged with RET but was higher at all times in HIR. Unlike intramuscular free testosterone, dihydrotestosterone, or 5α-reductase, there was a linear relationship between androgen receptor content and change in LBM (P < 0.01), type 1 CSA (P < 0.05), and type 2 CSA (P < 0.01) both pre- and post-intervention. These results indicate that intramuscular androgen receptor content, but neither circulating nor intramuscular hormones (or the enzymes regulating their intramuscular production), influence skeletal muscle hypertrophy following RET in previously trained young men.

ACTN3 Genotype in Professional Sport Climbers

Ginszt, M, Michalak-Wojnowska, M, Gawda, P, Wojcierowska-Litwin, M, Korszeń-Pilecka, I, Kusztelak, M, Muda, R, Filip, AA, and Majcher, P. ACTN3 genotype in professional sport climbers. J Strength Cond Res 32(5): 1311–1315, 2018—The functional RR genotype of the alpha-actinin-3 (ACTN3) gene has been reported to be associated with elite sprint/power athlete status. Although large and rapidly increasing number of studies have investigated the associations between the ACTN3 genotypes and athletic performance in various sport disciplines, there is a lack of studies on the genetic predisposition in sport climbing, which was selected to be part of the next Summer Olympic Games in Tokyo 2020 with three subdisciplines (“lead climbing,” “speed climbing,” and “bouldering”). The aim of the study is to determine the frequency distribution of ACTN3 genotypes and alleles in professional lead climbers and boulderers. 100 professional sport climbers from Poland, Russia, and Austria were divided into 2 equal groups: professional boulderers and professional lead climbers were involved in the study. ACTN3 allele frequencies and genotypes were compared with 100 sedentary controls. Genotypes were determined using polymerase chain reaction–restriction fragment length polymorphism method. The percent distribution of RR genotype in the boulderers was significantly higher than in lead climbers and controls (62 vs. 26%; 33%, respectively; χ² = 17.230, p = 0.0017). The frequencies of ACTN3 R allele in boulderers differed significantly from lead climbers and controls (77 vs. 51%; 58%, respectively; χ² = 15.721, p = 0.0004). The proportion of the ACTN3 RR genotype is significantly higher in boulderers than in lead climbers and may be related to the specific type of predisposition to this subdiscipline.

Polygenic Study of Endurance-Associated Genetic Markers NOS3 (Glu298Asp), BDKRB2 (-9/+9), UCP2 (Ala55Val), AMPD1 (Gln45Ter) and ACE (I/D) in Polish Male Half Marathoners

The purpose of this study was to investigate individually and in combination the association between the ACE (I/D), NOS3 (Glu298Asp), BDKRB2 (-9/+9), UCP2 (Ala55Val) and AMPD1 (Gln45Ter) variants with endurance performance in a large, performance-homogenous cohort of elite Polish half marathoners. The study group consisted of 180 elite half marathoners: 76 with time < 100 minutes and 104 with time > 100 minutes. DNA of the subjects was extracted from buccal cells donated by the runners and genotyping was carried out using an allelic discrimination assay with a C1000 Touch Thermal Cycler (Bio-Rad, Germany) instrument with TaqMan® probes (NOS3, UCP2, and AMPD1) and a T100™ Thermal Cycler (Bio-Rad, Germany) instrument (ACE and BDKRB2). We found that the UCP2 Ala55Val polymorphism was associated with running performance, with the subjects carrying the Val allele being overrepresented in the group of most successful runners (<100 min) compared to the >100 min group (84.2 vs. 55.8%; OR = 4.23, p < 0.0001). Next, to assess the combined impact of 4 gene polymorphisms, all athletes were classified according to the number of 'endurance' alleles (ACE I, NOS3 Glu, BDKRB2 -9, UCP2 Val) they possessed. The proportion of subjects with a high (4-7) number of 'endurance' alleles was greater in the better half marathoners group compared with the >100 min group (73.7 vs. 51.9%; OR = 2.6, p = 0.0034). These data suggest that the likelihood of becoming an elite half marathoner partly depends on the carriage of a high number of endurance-related alleles.

The Potential Role of Genetic Markers in Talent Identification and Athlete Assessment in Elite Sport

In elite sporting codes, the identification and promotion of future athletes into specialised talent pathways is heavily reliant upon objective physical, technical, and tactical characteristics, in addition to subjective coach assessments. Despite the availability of a plethora of assessments, the dependence on subjective forms of identification remain commonplace in most sporting codes. More recently, genetic markers, including several single nucleotide polymorphisms (SNPs), have been correlated with enhanced aerobic capacity, strength, and an overall increase in athletic ability. In this review, we discuss the effects of a number of candidate genes on athletic performance, across single-skilled and multifaceted sporting codes, and propose additional markers for the identification of motor skill acquisition and learning. While displaying some inconsistencies, both the ACE and ACTN3 polymorphisms appear to be more prevalent in strength and endurance sporting teams, and have been found to correlate to physical assessments. More recently, a number of polymorphisms reportedly correlating to athlete performance have gained attention, however inconsistent research design and varying sports make it difficult to ascertain the relevance to the wider sporting population. In elucidating the role of genetic markers in athleticism, existing talent identification protocols may significantly improve—and ultimately enable—targeted resourcing in junior talent pathways.

Factors that Influence the Performance of Elite Sprint Cross-Country Skiers

BACKGROUND

Sprint events in cross-country skiing are unique not only with respect to their length (0.8-1.8 km), but also in involving four high-intensity heats of ~3 min in duration, separated by a relatively short recovery period (15-60 min).

OBJECTIVE

Our aim was to systematically review the scientific literature to identify factors related to the performance of elite sprint cross-country skiers.

METHODS

Four electronic databases were searched using relevant medical subject headings and keywords, as were reference lists, relevant journals, and key authors in the field. Only original research articles addressing physiology, biomechanics, anthropometry, or neuromuscular characteristics and elite sprint cross-country skiers and performance outcomes were included. All articles meeting inclusion criteria were quality assessed. Data were extracted from each article using a standardized form and subsequently summarized.

RESULTS

Thirty-one articles met the criteria for inclusion, were reviewed, and scored an average of 66 ± 7 % (range 56-78 %) upon quality assessment. All articles except for two were quasi-experimental, and only one had a fully-experimental research design. In total, articles comprised 567 subjects (74 % male), with only nine articles explicitly reporting their skiers' sprint International Skiing Federation points (weighted mean 116 ± 78). A similar number of articles addressed skating and classical techniques, with more than half of the investigations involving roller-skiing assessments under laboratory conditions. A range of physiological, biomechanical, anthropometric, and neuromuscular characteristics was reported to relate to sprint skiing performance. Both aerobic and anaerobic capacities are important qualities, with the anaerobic system suggested to contribute more to the performance during the first of repeated heats; and the aerobic system during subsequent heats. A capacity for high speed in all the following instances is important for the performance of sprint cross-country skiers: at the start of the race, at any given point when required (e.g., when being challenged by a competitor), and in the final section of each heat. Although high skiing speed is suggested to rely primarily on high cycle rates, longer cycle lengths are commonly observed in faster skiers. In addition, faster skiers rely on different technical strategies when approaching peak speeds, employ more effective techniques, and use better coordinated movements to optimize generation of propulsive force from the resultant ski and pole forces. Strong uphill technique is critical to race performance since uphill segments are the most influential on race outcomes. A certain strength level is required, although more does not necessarily translate to superior sprint skiing performance, and sufficient strength-endurance capacities are also of importance to minimize the impact and accumulation of fatigue during repeated heats. Lastly, higher lean mass does appear to benefit sprint skiers' performance, with no clear advantage conferred via body height and mass.

LIMITATIONS

Generalization of findings from one study to the next is challenging considering the array of experimental tasks, variables defining performance, fundamental differences between skiing techniques, and evolution of sprint skiing competitions. Although laboratory-based measures can effectively assess on-snow skiing performance, conclusions drawn from roller-skiing investigations might not fully apply to on-snow skiing performance. A low number of subjects were females (only 17 %), warranting further studies to better understand this population. Lastly, more training studies involving high-level elite sprint skiers and investigations pertaining to the ability of skiers to maintain high-sprint speeds at the end of races are recommended to assist in understanding and improving high-level sprint skiing performance, and resilience to fatigue.

CONCLUSIONS

Successful sprint cross-country skiing involves well-developed aerobic and anaerobic capacities, high speed abilities, effective biomechanical techniques, and the ability to develop high forces rapidly. A certain level of strength is required, particularly ski-specific strength, as well as the ability to withstand fatigue across the repeated heats of sprint races. Cross-country sprint skiing is demonstrably a demanding and complex sport, where high-performance skiers need to simultaneously address physiological, biomechanical, anthropometric, and neuromuscular aspects to ensure success.

The Effect of ACTN3 Gene Doping on Skeletal Muscle Performance

Loss of expression of ACTN3, due to homozygosity of the common null polymorphism (p.Arg577X), is underrepresented in elite sprint/power athletes and has been associated with reduced muscle mass and strength in humans and mice. To investigate ACTN3 gene dosage in performance and whether expression could enhance muscle force, we performed meta-analysis and expression studies. Our general meta-analysis using a Bayesian random effects model in elite sprint/power athlete cohorts demonstrated a consistent homozygous-group effect across studies (per allele OR = 1.4, 95% CI 1.3-1.6) but substantial heterogeneity in heterozygotes. In mouse muscle, rAAV-mediated gene transfer overexpressed and rescued α-actinin-3 expression. Contrary to expectation, in vivo "doping" of ACTN3 at low to moderate doses demonstrated an absence of any change in function. At high doses, ACTN3 is toxic and detrimental to force generation, to demonstrate gene doping with supposedly performance-enhancing isoforms of sarcomeric proteins can be detrimental for muscle function. Restoration of α-actinin-3 did not enhance muscle mass but highlighted the primary role of α-actinin-3 in modulating muscle metabolism with altered fatiguability. This is the first study to express a Z-disk protein in healthy skeletal muscle and measure the in vivo effect. The sensitive balance of the sarcomeric proteins and muscle function has relevant implications in areas of gene doping in performance and therapy for neuromuscular disease.

ACTN3 genotype and physical function and frailty in an elderly Chinese population: the Rugao Longevity and Ageing Study

Objective

To examine the associations of the actinin alpha 3 gene (ACTN3) R577X polymorphism with physical performance and frailty in an older Chinese population.

Methods

Data from 1,463 individuals (57.8% female) aged 70-87 years from the Rugao Longevity and Ageing Study were used. The associations between R577X and timed 5-m walk, grip strength, timed Up and Go test, and frailty index (FI) based on deficits of 23 laboratory tests (FI-Lab) were examined. Analysis of variance and linear regression models were used to evaluate the genetic effects of ACTN3 R577X on physical performance and FI-Lab.

Results

The XX and RX genotypes of the ACTN3 R557X polymorphism accounted for 17.1 and 46.9%, respectively. Multivariate regression analysis revealed that in men aged 70-79 years, the ACTN3 577X allele was significantly associated with physical performance (5-m walk time, regression coefficient (β) = 0.258, P = 0.006; grip strength, β = -1.062, P = 0.012; Up and Go test time β = 0.368, P = 0.019). In women aged 70-79 years, a significant association between the ACTN3 577X allele and the FI-Lab score was observed, with a regression coefficient of β = 0.019 (P = 0.003). These findings suggest an age- and gender-specific X-additive model of R577X for 5-m walk time, grip strength, Up and Go Test time, and FI-Lab score.

Conclusion

The ACTN3 577X allele is associated with an age- and sex-specific decrease in physical performance and an increase in frailty in an older population.

Analysis of sports-relevant polymorphisms in a large Brazilian cohort of top-level athletes

In recent years, there have been an increasing number of genetic variants associated with athletic phenotypes. Here, we selected a set of sports-relevant polymorphisms that have been previously suggested as genetic markers for human physical performance, and we examined their association with athletic status in a large cohort of Brazilians. We evaluated a sample of 1,622 individuals, in which 966 were nonathletes, and 656 were athletes: 328 endurance athletes and 328 power athletes. Only the AGT M268T minor allele was nominally associated with the endurance status. Conversely, we found that seven polymorphisms are more frequent in power athletes (MCT1 D490E, AGT M268T, PPARG P12A, PGC1A G482S, VEGFR2 Q472H, NOS3 C/T, and ACTN3 R577X). For all of these polymorphisms, power athletes were more likely than nonathletes or endurance athletes to carry the major allele or the homozygous genotype for the major allele. In particular, MCT1 D490E, AGT M268T, NOS3 C/T, and ACTN3 R577X showed stronger associations. Our findings support a role for these variants in the achievement of power athletic status in Brazilians: MCT1 D490E (T allele), AGT M268T (G allele), PPARG (C allele), PGC1A G482S (C allele), VEGFR2 Q472H (T allele), NOS3 C/T (T allele), and ACTN3 R577X (R allele).

No association between ACTN3 R577X and ACE I/D polymorphisms and endurance running times in 698 Caucasian athletes

BACKGROUND

Studies investigating associations between ACTN3 R577X and ACE I/D genotypes and endurance athletic status have been limited by small sample sizes from mixed sport disciplines and lack quantitative measures of performance.

AIM

To examine the association between ACTN3 R577X and ACE I/D genotypes and best personal running times in a large homogeneous cohort of endurance runners.

METHODS

We collected a total of 1064 personal best 1500, 3000, 5000 m and marathon running times of 698 male and female Caucasian endurance athletes from six countries (Australia, Greece, Italy, Poland, Russia and UK). Athletes were genotyped for ACTN3 R577X and ACE ID variants.

RESULTS

There was no association between ACTN3 R577X or ACE I/D genotype and running performance at any distance in men or women. Mean (SD) marathon times (in s) were for men: ACTN3 RR 9149 (593), RX 9221 (582), XX 9129 (582) p = 0.94; ACE DD 9182 (665), ID 9214 (549), II 9155 (492) p = 0.85; for women: ACTN3 RR 10796 (818), RX 10667 (695), XX 10675 (553) p = 0.36; ACE DD 10604 (561), ID 10766 (740), II 10771 (708) p = 0.21. Furthermore, there were no associations between these variants and running time for any distance in a sub-analysis of athletes with personal records within 20% of world records.

CONCLUSIONS

Thus, consistent with most case-control studies, this multi-cohort quantitative analysis demonstrates it is unlikely that ACTN3 XX genotype provides an advantage in competitive endurance running performance. For ACE II genotype, some prior studies show an association but others do not. Our data indicate it is also unlikely that ACE II genotype provides an advantage in endurance running.

ACTN3: More than Just a Gene for Speed

Over the last couple of decades, research has focused on attempting to understand the genetic influence on sports performance. This has led to the identification of a number of candidate genes which may help differentiate between elite and non-elite athletes. One of the most promising genes in that regard is ACTN3, which has commonly been referred to as “a gene for speed”. Recent research has examined the influence of this gene on other performance phenotypes, including exercise adaptation, exercise recovery, and sporting injury risk. In this review, we identified 19 studies exploring these phenotypes. Whilst there was large variation in the results of these studies, as well as extremely heterogeneous cohorts, there is overall a tentative consensus that ACTN3 genotype can impact the phenotypes of interest. In particular, the R allele of a common polymorphism (R577X) is associated with enhanced improvements in strength, protection from eccentric training-induced muscle damage, and sports injury. This illustrates that ACTN3 is more than just a gene for speed, with potentially wide-ranging influence on muscle function, knowledge of which may aid in the future personalization of exercise training programmes.

AGTR2 and sprint/power performance: a case-control replication study for rs11091046 polymorphism in two ethnicities

We aimed to replicate, in a specific athletic event cohort (only track and field) and in two different ethnicities (Japanese and East European, i.e. Russian and Polish), original findings showing the association of the angiotensin-II receptor type-2 gene (AGTR2) rs11091046 A>C polymorphism with athlete status. We compared genotypic frequencies of the AGTR2 rs11091046 polymorphism among 282 track and field sprint/power athletes (200 men and 82 women), including several national record holders and Olympic medallists (214 Japanese, 68 Russian and Polish), and 2024 control subjects (842 men and 1182 women) (804 Japanese, 1220 Russian and Polish). In men, a meta-analysis from the two combined cohorts showed a significantly higher frequency of the C allele in athletes than in controls (odds ratio: 1.62, P=0.008, heterogeneity index I²=0%). With regard to respective cohorts, C allele frequency was higher in Japanese male athletes than in controls (67.7% vs. 55.9%, P=0.022), but not in Russian/Polish male athletes (61.9% vs. 51.0%, P=0.172). In women, no significant results were obtained by meta-analysis for the two cohorts combination (P=0.850). The AC genotype frequency was significantly higher in Russian/Polish women athletes than in controls (69.2% vs. 42.1%, P=0.022), but not in Japanese women athletes (P=0.226). Our results, in contrast to previous findings, suggested by meta-analysis that the C allele of the AGTR2 rs11091046 polymorphism is associated with sprint/power track and field athlete status in men, but not in women.

Genetic testing for exercise prescription and injury prevention: AIS-Athlome consortium-FIMS joint statement

BACKGROUND

There has been considerable growth in basic knowledge and understanding of how genes are influencing response to exercise training and predisposition to injuries and chronic diseases. On the basis of this knowledge, clinical genetic tests may in the future allow the personalisation and optimisation of physical activity, thus providing an avenue for increased efficiency of exercise prescription for health and disease.

RESULTS

This review provides an overview of the current status of genetic testing for the purposes of exercise prescription and injury prevention. As such there are a variety of potential uses for genetic testing, including identification of risks associated with participation in sport and understanding individual response to particular types of exercise. However, there are many challenges remaining before genetic testing has evidence-based practical applications; including adoption of international standards for genomics research, as well as resistance against the agendas driven by direct-to-consumer genetic testing companies. Here we propose a way forward to develop an evidence-based approach to support genetic testing for exercise prescription and injury prevention.

CONCLUSION

Based on current knowledge, there is no current clinical application for genetic testing in the area of exercise prescription and injury prevention, however the necessary steps are outlined for the development of evidence-based clinical applications involving genetic testing.

Advances in Exercise, Fitness, and Performance Genomics in 2015

This review of the exercise genomics literature encompasses the highest-quality articles published in 2015 across seven broad topics: physical activity behavior, muscular strength and power, cardiorespiratory fitness and endurance performance, body weight and adiposity, insulin and glucose metabolism, lipid and lipoprotein metabolism, and hemodynamic traits. One study used a quantitative trait locus for wheel running in mice to identify single nucleotide polymorphisms (SNPs) in humans associated with physical activity levels. Two studies examined the association of candidate gene ACTN3 R577X genotype on muscular performance. Several studies examined gene-physical activity interactions on cardiometabolic traits. One study showed that physical inactivity exacerbated the body mass index (BMI)-increasing effect of an FTO SNP but only in individuals of European ancestry, whereas another showed that high-density lipoprotein cholesterol (HDL-C) SNPs from genome-wide association studies exerted a smaller effect in active individuals. Increased levels of moderate-to-vigorous-intensity physical activity were associated with higher Matsuda insulin sensitivity index in PPARG Ala12 carriers but not Pro12 homozygotes. One study combined genome-wide and transcriptome-wide profiling to identify genes and SNPs associated with the response of triglycerides (TG) to exercise training. The genome-wide association study results showed that four SNPs accounted for all of the heritability of △TG, whereas the baseline expression of 11 genes predicted 27% of △TG. A composite SNP score based on the top eight SNPs derived from the genomic and transcriptomic analyses was the strongest predictor of ΔTG, explaining 14% of the variance. The review concludes with a discussion of a conceptual framework defining some of the critical conditions for exercise genomics studies and highlights the importance of the recently launched National Institutes of Health Common Fund program titled "Molecular Transducers of Physical Activity in Humans."

Nine genetic polymorphisms associated with power athlete status - A Meta-Analysis

OBJECTIVES

In this study the association between genetic polymorphisms and power athlete status with possible interference by race and sex was investigated to identify genetic variants favourable for becoming a power athlete.

DESIGN

This meta-analysis included both, case-control and Cohort studies.

METHODS

Databases of PubMed and Web of Science were searched for studies reporting on genetic polymorphisms associated with the status of being a power athlete. Thirty-five articles published between 2008 and 2016 were identified as eligible including a total number of 5834 power athletes and 14,018 controls. A series of meta-analyses were conducted for each of the identified genetic polymorphisms associated with power athlete status. Odds ratios (ORs) based on the allele and genotype frequency with corresponding 95% confidence intervals (95%CI) were calculated per genetic variant. Heterogeneity of the studies was addressed by Chi-square based Q-statistics at 5% significance level and a fixed or random effects model was used in absence or presence of heterogeneity respectively. Stratified analyses were conducted by race and sex to explore potential sources of heterogeneity.

RESULTS

Significant associations were found for the genetic polymorphisms in the ACE (rs4363, rs1799752), ACTN3 (rs1815739), AGT (rs699), IL6-174 (rs1800795), MnSOD (rs1799725), NOS3 (rs1799983, rs2070744) and SOD2 (rs4880) genes.

CONCLUSIONS

Nine genetic polymorphisms have been identified in the meta-analyses to have a significant association with the status of being a power athlete. Nevertheless, more research on the investigated genes needs to be done to draw comprehensive conclusions.

Exercise-induced modification of the skeletal muscle transcriptome in Arabian horses

It has been found that Arabian and Thoroughbred horses differ in muscle fiber structure and thus in physiological changes occurring in muscles during exercise. The aim of the present study was to identify the global gene expression modifications that occur in skeletal muscle following a training regime to prepare for flat racing. Whole transcriptomes of muscle (gluteus medius) were compared between three time points of tissue collection: T0 (untrained horses), T1 (horses after intense gallop phase), and T2 (horses at the end of racing season), 23 samples in total. The numerous groups of exercise-regulated differentially expressed genes (DEGs) were related to muscle cell structure and signaling and included insulin-like growth factor 1 receptor ( IGF1R), insulin receptor ( INSR), transforming growth factor beta receptors 1 and 2 ( TGFBR1, TGFBR2), vascular endothelial growth factor B ( VEGFB); epidermal growth factor ( EGF), hepatocyte growth factor ( HGF), and vascular endothelial growth factor D ( FIGF). In Arabian horses, exercise modified the expression of genes belonging to the PPAR signaling pathway (e.g., PPARA, PPARD, and PLIN2), calcium signaling pathway, and pathways associated with metabolic processes (e.g., oxidative phosphorylation, fatty acid metabolism, glycolysis/gluconeogenesis, and citrate cycle). According to detected gene expression modifications, our results suggested that in Arabian horses, exercise switches energy generation toward fatty acid utilization and enhances glycogen transport and calcium signaling. The use of the RNA-Seq approach in analyzing the skeletal muscle transcriptome allowed for the proposal of a panel of new candidate genes potentially related to body homeostasis maintenance and racing performance in Arabian horses.

ACTN3 R577X Gene Variant Is Associated With Muscle-Related Phenotypes in Elite Chinese Sprint/Power Athletes

Yang, R, Shen, X, Wang, Y, Voisin, S, Cai, G, Fu, Y, Xu, W, Eynon, N, Bishop, DJ, and Yan, X. ACTN3 R577X gene variant is associated with muscle-related phenotypes in elite Chinese sprint/power athletes. J Strength Cond Res 31(4): 1107-1115, 2017-The ACTN3 R577X polymorphism (rs1815739) has been shown to influence athletic performance. The aim of this study was to investigate the prevalence of this polymorphism in elite Chinese track and field athletes, and to explore its effects on athletes' level of competition and lower-extremity power. We compared the ACTN3 R577X genotypes and allele frequencies in 59 elite sprint/power athletes, 44 elite endurance athletes, and 50 healthy controls from Chinese Han origin. We then subcategorized the athletes into international level and national level and investigated the effects of ACTN3 genotype on lower-extremity power. Genotype distribution of the sprint/power athletes was significantly different from endurance athletes (p = 0.001) and controls (p < 0.001). The frequency of the RR genotype was significantly higher in international-level than that in the national-level sprint/power athletes (p = 0.004), with no international-level sprint/power athletes with XX genotype. The best standing long jump and standing vertical jump results of sprint/power athletes were better in the RR than those in the RX + XX genotypes (p = 0.004 and p = 0.001, respectively). In conclusion, the ACTN3 R577X polymorphism influences the level of competition and lower-extremity power of elite Chinese sprint/power athletes. Including relevant phenotypes such as muscle performance in future studies is important to further understand the effects of gene variants on elite athletic performance.

The influence of α-actinin-3 deficiency on bone remodelling markers in young men

There is a large individual variation in the bone remodelling markers (BRMs) osteocalcin (OC), procollagen 1 N-terminal propeptide (P1NP) and β-isomerized C-terminal telopeptide (β-CTx), as well as undercarboxylated osteocalcin (ucOC), at rest and in response to exercise. α-actinin-3 (ACTN3), a sarcomeric protein, is expressed in skeletal muscle and osteoblasts and may influence BRM levels and the cross-talk between muscle and bone. We tested the levels of serum BRMs in α-actinin-3 deficient humans (ACTN3 XX) at baseline, and following a single bout of exercise. Forty-three healthy Caucasian individuals were divided into three groups (ACTN3 XX, n=13; ACTN3 RX, n=16; ACTN3 RR, n=14). Participants completed a single session of High Intensity Interval Exercise (HIIE) on a cycle ergometer (8×2-min intervals at 85% of maximal power). Blood samples were taken before, immediately after, and three hours post exercise to identify the peak changes in serum BRMs. There was a stepwise increase in resting serum BRMs across the ACTN3 genotypes (XX>RX>RR) with significantly higher levels of tOC ~26%, P1NP ~34%, and β-CTX (~33%) in those with ACTN3 XX compared to ACTN3 RR. Following exercise BRMs and ucOC were higher in all three ACTN3 genotypes, with no significant differences between groups. Serum levels of tOC, P1NP and β-CTX are higher in men with ACTN3 XX genotype (α-actinin-3 deficiency) compared to RR and RX. It appears that the response of BRMs and ucOC to exercise is not explained by the ACTN3 genotype.

Polygenic study of endurance-associated genetic markers ACE I/D, ACTN3 Arg(R)577Ter(X), CKMM A/G NcoI and eNOS Glu(G)298Asp(T) in male Gorkha soldiers

Background

Gorkhas, a sub-mountainous population of the Himalayan region, are known for strength and bravery. In the present study when “Gorkha” is used without brackets, we are mentioning Gorkhas of Tibeto-Burman origin. Physical capability, strength and endurance are important components of fitness associated with genetic traits. The aim of this study was to examine the endurance potential of male Gorkha soldiers, based on endurance-related genetic markers ACE I/D, ACTN3 Arg (R)577Ter(X), CKMM A/G NcoI and eNOS Glu(G)298Asp(T).

Methods

Genotypic and allelic frequencies were determined in 374 male Gorkha soldiers (Tibeto-Burman). These frequencies were compared with frequencies obtained from Gorkha (Indo-Aryan), high-altitude natives (Tibeto-Burman) and Indian lowlanders (Indo-Aryan). “Total genotype score” (TGS) was calculated from accumulated combination of polymorphisms with maximum value “100” for theoretically “optimal” polygenic score. Probability of occurrence of “optimal” endurance profile was also determined.

Results

ACE II genotypic frequency was highest in Tamangs followed by Gurungs, Rais, Limbus and Magars. No statistical difference in genotypic and allelic frequency of ACTN3 Arg(R)577Ter(X) was noted within the groups. Rais showed the highest CKMM A allele frequency (0.908) compared to other Gorkha (Tibeto-Burman) groups. Limbus and Tamangs showed the highest eNOS G allele frequency (0.938 and 0.915, respectively) compared to that of other groups. Probability of male Gorkha soldiers possessing a theoretically optimal polygenic endurance profile for four candidate polymorphisms was ~3.35% (1 in 30). Four percent of the population of male Gorkha soldiers (15 in 374) exhibited an optimal TGS 100, and 16% exhibited TGS 87 for endurance compared to male Indian soldiers belonging to the lowland (Indo-Aryan) and Gorkha (Indo-Aryan) populations suggesting an overall more “favourable” polygenic profile in the male Gorkha soldier (Tibeto-Burman) population.

Conclusions

This study presents evidence of higher frequency of endurance-associated genes in the Gorkhas implying thereby that such genetically endowed individuals from the population may be selected and trained for achieving excellence in endurance-related elite sports activities.

Electronic supplementary material

The online version of this article (doi:10.1186/s40798-017-0085-0) contains supplementary material, which is available to authorized users.

Strength adaptation to squat exercise is different between Caucasian and South Asian novice exercisers

This study compared the progression of muscular strength (MS) adaptation between age-matched Caucasian (CAUC) and South Asian (SOU) men during 6 weeks (3× week^-1) of resistance training. MS was determined pre and post intervention by 3-repetition maximum (3RM) strength tests, and data were analysed using repeated measures ANOVA. Pre-intervention upper and lower body 3RM were similar between groups and both upper and lower body 3RM increased in CAUCs (P < .001) and SOUs (P < .001) following resistance training. However, lower body strength adaptation (3RM) was higher in CAUCs compared with SOUs (P = .002). There was a significant group × time interaction in strength progression of the squat exercise (P = 0.03) from session 7 through to 18 (completion). The present study offers novel but provisional data that lower body strength adaptation is slower in SOU than CAUC men despite comparable adaptation to upper body strength.

Evidence for ACTN3 as a genetic modifier of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is characterized by muscle degeneration and progressive weakness. There is considerable inter-patient variability in disease onset and progression, which can confound the results of clinical trials. Here we show that a common null polymorphism (R577X) in ACTN3 results in significantly reduced muscle strength and a longer 10 m walk test time in young, ambulant patients with DMD; both of which are primary outcome measures in clinical trials. We have developed a double knockout mouse model, which also shows reduced muscle strength, but is protected from stretch-induced eccentric damage with age. This suggests that α-actinin-3 deficiency reduces muscle performance at baseline, but ameliorates the progression of dystrophic pathology. Mechanistically, we show that α-actinin-3 deficiency triggers an increase in oxidative muscle metabolism through activation of calcineurin, which likely confers the protective effect. Our studies suggest that ACTN3 R577X genotype is a modifier of clinical phenotype in DMD patients.

The complex genetics of gait speed: genome-wide meta-analysis approach

Emerging evidence suggests that the basis for variation in late-life mobility is attributable, in part, to genetic factors, which may become increasingly important with age. Our objective was to systematically assess the contribution of genetic variation to gait speed in older individuals. We conducted a meta-analysis of gait speed GWASs in 31,478 older adults from 17 cohorts of the CHARGE consortium, and validated our results in 2,588 older adults from 4 independent studies. We followed our initial discoveries with network and eQTL analysis of candidate signals in tissues. The meta-analysis resulted in a list of 536 suggestive genome wide significant SNPs in or near 69 genes. Further interrogation with Pathway Analysis placed gait speed as a polygenic complex trait in five major networks. Subsequent eQTL analysis revealed several SNPs significantly associated with the expression of PRSS16, WDSUB1 and PTPRT, which in addition to the meta-analysis and pathway suggested that genetic effects on gait speed may occur through synaptic function and neuronal development pathways. No genome-wide significant signals for gait speed were identified from this moderately large sample of older adults, suggesting that more refined physical function phenotypes will be needed to identify the genetic basis of gait speed in aging.

Association Between MCT1 A1470T Polymorphism and Fat-Free Mass in Well-Trained Young Soccer Players

The aim of this study was to investigate the association between the MCT1 A1470T polymorphism and fat-free mass in young Italian elite soccer players. Participants were 128 Italian male soccer players. Fat-free mass was estimated for each of the soccer player using age- and gender-specific formulas with plicometry. Genotyping for the MCT1 A1470T polymorphism was performed using polymerase chain reaction. The MCT1 A1470T genotypes were in agreement with the Hardy-Weinberg equilibrium distribution. The percentage of fat-free mass was significantly higher in soccer players with the TT genotype and in the T-allele-dominant model group (TT + AT) compared with the soccer players with the AA genotype. The MCT1 T allele is associated with the percentage of fat-free mass in young elite male soccer players. Elucidating the genetic basis of body composition in athletes could potentially be used as an additional tool for strength and conditioning professionals in planning and adjusting training. However, these results are preliminary and need to be replicated in more cohorts.

Ethics of genetic testing and research in sport: a position statement from the Australian Institute of Sport

As Australia's peak high-performance sport agency, the Australian Institute of Sport (AIS) has developed this position statement to address the implications of recent advances in the field of genetics and the ramifications for the health and well-being of athletes. Genetic testing has proven of value in the practice of clinical medicine. There are, however, currently no scientific grounds for the use of genetic testing for athletic performance improvement, sport selection or talent identification. Athletes and coaches should be discouraged from using direct-to-consumer genetic testing because of its lack of validation and replicability and the lack of involvement of a medical practitioner in the process. The transfer of genetic material or genetic modification of cells for performance enhancement is gene doping and should not be used on athletes. There are, however, valid roles for genetic research and the AIS supports genetic research which aims to enhance understanding of athlete susceptibility to injury or illness. Genetic research is only to be conducted after careful consideration of a range of ethical concerns which include the provision of adequate informed consent. The AIS is committed to providing leadership in delivering an ethical framework that protects the well-being of athletes and the integrity of sport, in the rapidly changing world of genomic science.

Letter to the editor: A genetic-based algorithm for personalized resistance training

In a recent paper entitled “A genetic-based algorithm for personalized resistance training”, Jones et al. [1] presented an algorithm of 15 performance-associated gene polymorphisms that they propose can determine an athlete’s training response by predicting power and endurance potential. However, from the design of their studies and the data provided, there is no evidence to support these authors’ assertions. Progress towards such a significant development in the field of sport and exercise genomics will require a paradigm shift in line with recent recommendations for international collaborations such as the Athlome Project (see www.athlomeconsortium.org). Large-scale initiatives, involving numerous multi-centre and well-phenotyped exercise training and elite performance cohorts, will be necessary before attempting to derive and replicate training and/or performance algorithms.

Concurrent exercise training: do opposites distract?

Specificity is a core principle of exercise training to promote the desired adaptations for maximising athletic performance. The principle of specificity of adaptation is underpinned by the volume, intensity, frequency and mode of contractile activity and is most evident when contrasting the divergent phenotypes that result after undertaking either prolonged endurance or resistance training. The molecular profiles that generate the adaptive response to different exercise modes have undergone intense scientific scrutiny. Given divergent exercise induces similar signalling and gene expression profiles in skeletal muscle of untrained or recreationally active individuals, what is currently unclear is how the specificity of the molecular response is modified by prior training history. The time course of adaptation and when 'phenotype specificity' occurs has important implications for exercise prescription. This context is essential when attempting to concomitantly develop resistance to fatigue (through endurance-based exercise) and increased muscle mass (through resistance-based exercise), typically termed 'concurrent training'. Chronic training studies provide robust evidence that endurance exercise can attenuate muscle hypertrophy and strength but the mechanistic underpinning of this 'interference' effect with concurrent training is unknown. Moreover, despite the potential for several key regulators of muscle metabolism to explain an incompatibility in adaptation between endurance and resistance exercise, it now seems likely that multiple integrated, rather than isolated, effectors or processes generate the interference effect. Here we review studies of the molecular responses in skeletal muscle and evidence for the interference effect with concurrent training within the context of the specificity of training adaptation.

Direct-to-consumer genetic testing for predicting sports performance and talent identification: Consensus statement

The general consensus among sport and exercise genetics researchers is that genetic tests have no role to play in talent identification or the individualised prescription of training to maximise performance. Despite the lack of evidence, recent years have witnessed the rise of an emerging market of direct-to-consumer marketing (DTC) tests that claim to be able to identify children's athletic talents. Targeted consumers include mainly coaches and parents. There is concern among the scientific community that the current level of knowledge is being misrepresented for commercial purposes. There remains a lack of universally accepted guidelines and legislation for DTC testing in relation to all forms of genetic testing and not just for talent identification. There is concern over the lack of clarity of information over which specific genes or variants are being tested and the almost universal lack of appropriate genetic counselling for the interpretation of the genetic data to consumers. Furthermore independent studies have identified issues relating to quality control by DTC laboratories with different results being reported from samples from the same individual. Consequently, in the current state of knowledge, no child or young athlete should be exposed to DTC genetic testing to define or alter training or for talent identification aimed at selecting gifted children or adolescents. Large scale collaborative projects, may help to develop a stronger scientific foundation on these issues in the future.

Genetic variation and exercise-induced muscle damage: implications for athletic performance, injury and ageing

Prolonged unaccustomed exercise involving muscle lengthening (eccentric) actions can result in ultrastructural muscle disruption, impaired excitation-contraction coupling, inflammation and muscle protein degradation. This process is associated with delayed onset muscle soreness and is referred to as exercise-induced muscle damage. Although a certain amount of muscle damage may be necessary for adaptation to occur, excessive damage or inadequate recovery from exercise-induced muscle damage can increase injury risk, particularly in older individuals, who experience more damage and require longer to recover from muscle damaging exercise than younger adults. Furthermore, it is apparent that inter-individual variation exists in the response to exercise-induced muscle damage, and there is evidence that genetic variability may play a key role. Although this area of research is in its infancy, certain gene variations, or polymorphisms have been associated with exercise-induced muscle damage (i.e. individuals with certain genotypes experience greater muscle damage, and require longer recovery, following strenuous exercise). These polymorphisms include ACTN3 (R577X, rs1815739), TNF (-308 G>A, rs1800629), IL6 (-174 G>C, rs1800795), and IGF2 (ApaI, 17200 G>A, rs680). Knowing how someone is likely to respond to a particular type of exercise could help coaches/practitioners individualise the exercise training of their athletes/patients, thus maximising recovery and adaptation, while reducing overload-associated injury risk. The purpose of this review is to provide a critical analysis of the literature concerning gene polymorphisms associated with exercise-induced muscle damage, both in young and older individuals, and to highlight the potential mechanisms underpinning these associations, thus providing a better understanding of exercise-induced muscle damage.

ACVR1B rs2854464 Is Associated with Sprint/Power Athletic Status in a Large Cohort of Europeans but Not Brazilians

Skeletal muscle strength and mass, major contributors to sprint/power athletic performance, are influenced by genetics. However, to date, only a handful of genetic variants have been associated with sprint/power performance. The ACVR1B A allele (rs rs2854464) has previously been associated with increased muscle-strength in non-athletic cohort. However, no follow-up and/or replications studies have since been conducted. Therefore, the aim of the present study was to compare the genotype distribution of ACVR1B rs2854464 between endurance athletes (E), sprint/power (S/P) athletes, mixed athletes (M), and non-athletic control participants in 1672 athletes (endurance athletes, n = 482; sprint/power athletes, n = 578; mixed athletes, n = 498) and 1089 controls (C) of both European Caucasians (Italian, Polish and Russians) and Brazilians. We have also compared the genotype distribution according to the athlete's level of competition (elite vs. sub-elite). DNA extraction and genotyping were performed using various methods. Fisher's exact test (adjusted for multiple comparisons) was used to test whether the genotype distribution of rs2854464 (AA, AG and GG) differs between groups. The A allele was overrepresented in S/P athletes compared with C in the Caucasian sample (adjusted p = 0.048), whereas there were no differences in genotype distribution between E athletes and C, in neither the Brazilian nor the Caucasian samples (adjusted p > 0.05). When comparing all Caucasian athletes regardless of their sporting discipline to C, we found that the A allele was overrepresented in athletes compared to C (adjusted p = 0.024). This association was even more pronounced when only elite-level athletes were considered (adjusted p = 0.00017). In conclusion, in a relatively large cohort of athletes from Europe and South America we have shown that the ACVR1B rs2854464 A allele is associated with sprint/power performance in Caucasians but not in Brazilian athletes. This reinforces the notion that phenotype-genotype associations may be ethnicity-dependent.

ACTN3 R577X and ACE I/D gene variants influence performance in elite sprinters: a multi-cohort study

Background

To date, studies investigating the association between ACTN3 R577X and ACE I/D gene variants and elite sprint/power performance have been limited by small cohorts from mixed sport disciplines, without quantitative measures of performance. Aim: To examine the association between these variants and sprint time in elite athletes.

Methods

We collected a total of 555 best personal 100-, 200-, and 400-m times of 346 elite sprinters in a large cohort of elite Caucasian or African origin sprinters from 10 different countries. Sprinters were genotyped for ACTN3 R577X and ACE ID variants.

Results

On average, male Caucasian sprinters with the ACTN3 577RR or the ACE DD genotype had faster best 200-m sprint time than their 577XX (21.19 ± 0.53 s vs. 21.86 ± 0.54 s, p = 0.016) and ACE II (21.33 ± 0.56 vs. 21.93 ± 0.67 sec, p = 0.004) counterparts and only one case of ACE II, and no cases of ACTN3 577XX, had a faster 200-m time than the 2012 London Olympics qualifying (vs. 12 qualified sprinters with 577RR or 577RX genotype). Caucasian sprinters with the ACE DD genotype had faster best 400-m sprint time than their ACE II counterparts (46.94 ± 1.19 s vs. 48.50 ± 1.07 s, p = 0.003). Using genetic models we found that the ACTN3 577R allele and ACE D allele dominant model account for 0.92 % and 1.48 % of sprint time variance, respectively.

Conclusions

Despite sprint performance relying on many gene variants and environment, the % sprint time variance explained by ACE and ACTN3 is substantial at the elite level and might be the difference between a world record and only making the final.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2462-3) contains supplementary material, which is available to authorized users.

Analysis of the ACTN3 heterozygous genotype suggests that α-actinin-3 controls sarcomeric composition and muscle function in a dose-dependent fashion

A common null polymorphism (R577X) in ACTN3 causes α-actinin-3 deficiency in ∼ 18% of the global population. There is no associated disease phenotype, but α-actinin-3 deficiency is detrimental to sprint and power performance in both elite athletes and the general population. However, despite considerable investigation to date, the functional consequences of heterozygosity for ACTN3 are unclear. A subset of studies have shown an intermediate phenotype in 577RX individuals, suggesting dose-dependency of α-actinin-3, while others have shown no difference between 577RR and RX genotypes. Here, we investigate the effects of α-actinin-3 expression level by comparing the muscle phenotypes of Actn3(+/-) (HET) mice to Actn3(+/+) [wild-type (WT)] and Actn3(-/-) [knockout (KO)] littermates. We show reduction in α-actinin-3 mRNA and protein in HET muscle compared with WT, which is associated with dose-dependent up-regulation of α-actinin-2, z-band alternatively spliced PDZ-motif and myotilin at the Z-line, and an incremental shift towards oxidative metabolism. While there is no difference in force generation, HET mice have an intermediate endurance capacity compared with WT and KO. The R577X polymorphism is associated with changes in ACTN3 expression consistent with an additive model in the human genotype-tissue expression cohort, but does not influence any other muscle transcripts, including ACTN2. Overall, ACTN3 influences sarcomeric composition in a dose-dependent fashion in mouse skeletal muscle, which translates directly to function. Variance in fibre type between biopsies likely masks this phenomenon in human skeletal muscle, but we suggest that an additive model is the most appropriate for use in testing ACTN3 genotype associations.

Evidence for ACTN3 as a Speed Gene in Isolated Human Muscle Fibers

Purpose

To examine the effect of α-actinin-3 deficiency due to homozygosity for the ACTN3 577X-allele on contractile and morphological properties of fast muscle fibers in non-athletic young men.

Methods

A biopsy was taken from the vastus lateralis of 4 RR and 4 XX individuals to test for differences in morphologic and contractile properties of single muscle fibers. The cross-sectional area of the fiber and muscle fiber composition was determined using standard immunohistochemistry analyses. Skinned single muscle fibers were subjected to active tests to determine peak normalized force (P₀), maximal unloading velocity (V₀) and peak power. A passive stretch test was performed to calculate Young’s Modulus and hysteresis to assess fiber visco-elasticity.

Results

No differences were found in muscle fiber composition. The cross-sectional area of type II_a and II_x fibers was larger in RR compared to XX individuals (P<0.001). P₀ was similar in both groups over all fiber types. A higher V₀ was observed in type II_a fibers of RR genotypes (P<0.001) but not in type I fibers. The visco-elasticity as determined by Young’s Modulus and hysteresis was unaffected by fiber type or genotype.

Conclusion

The greater V₀ and the larger fast fiber CSA in RR compared to XX genotypes likely contribute to enhanced whole muscle performance during high velocity contractions.

Genes and exercise intolerance: insights from McArdle disease

McArdle disease (glycogen storage disease type V) is caused by inherited deficiency of a key enzyme in muscle metabolism, the skeletal muscle-specific isoform of glycogen phosphorylase, “myophosphorylase,” which is encoded by the PYGM gene. Here we review the main pathophysiological, genotypic, and phenotypic features of McArdle disease and their interactions. To date, moderate-intensity exercise (together with pre-exercise carbohydrate ingestion) is the only treatment option that has proven useful for these patients. Furthermore, regular physical activity attenuates the clinical severity of McArdle disease. This is quite remarkable for a monogenic disorder that consistently leads to the same metabolic defect at the muscle tissue level, that is, complete inability to use muscle glycogen stores. Further knowledge of this disorder would help patients and enhance understanding of exercise metabolism as well as exercise genomics. Indeed, McArdle disease is a paradigm of human exercise intolerance and PYGM genotyping should be included in the genetic analyses that might be applied in the coming personalized exercise medicine as well as in future research on genetics and exercise-related phenotypes.

How does α-actinin-3 deficiency alter muscle function? Mechanistic insights into ACTN3, the 'gene for speed'

An estimated 1.5 billion people worldwide are deficient in the skeletal muscle protein α-actinin-3 due to homozygosity for the common ACTN3 R577X polymorphism. α-Actinin-3 deficiency influences muscle performance in elite athletes and the general population. The sarcomeric α-actinins were originally characterised as scaffold proteins at the muscle Z-line. Through studying the Actn3 knockout mouse and α-actinin-3 deficient humans, significant progress has been made in understanding how ACTN3 genotype alters muscle function, leading to an appreciation of the diverse roles that α-actinins play in muscle. The α-actinins interact with a number of partner proteins, which broadly fall into three biological pathways-structural, metabolic and signalling. Differences in functioning of these pathways have been identified in α-actinin-3 deficient muscle that together contributes to altered muscle performance in mice and humans. Here we discuss new insights that have been made in understanding the molecular mechanisms that underlie the consequences of α-actinin-3 deficiency.

Association of ACTN3 R577X but not ACE I/D gene variants with elite rugby union player status and playing position

We aimed to quantify the ACE I/D and ACTN3 R577X (rs1815739) genetic variants in elite rugby athletes (rugby union and league) and compare genotype frequencies to controls and between playing positions. The rugby athlete cohort consisted of 507 Caucasian men, including 431 rugby union athletes that for some analyses were divided into backs and forwards and into specific positional groups: front five, back row, half backs, centers, and back three. Controls were 710 Caucasian men and women. Real-time PCR of genomic DNA was used to determine genotypes using TaqMan probes and groups were compared using χ² and odds ratio (OR) statistics. Correction of P values for multiple comparisons was according to Benjamini-Hochberg. There was no difference in ACE I/D genotype between groups. ACTN3 XX genotype tended to be underrepresented in rugby union backs (15.7%) compared with forwards (24.8%, P = 0.06). Interestingly, the 69 back three players (wings and full backs) in rugby union included only six XX genotype individuals (8.7%), with the R allele more common in the back three (68.8%) than controls (58.0%; χ² = 6.672, P = 0.04; OR = 1.60) and forwards (47.5%; χ² = 11.768, P = 0.01; OR = 2.00). Association of ACTN3 R577X with playing position in elite rugby union athletes suggests inherited fatigue resistance is more prevalent in forwards, while inherited sprint ability is more prevalent in backs, especially wings and full backs. These results also demonstrate the advantage of focusing genetic studies on a large cohort within a single sport, especially when intrasport positional differences exist, instead of combining several sports with varied demands and athlete characteristics.

Performance trade-offs and individual quality in decathletes

Many constraints of organismal design at the cell and organ level, including muscle fiber types, musculoskeletal gearing and control-surface geometry, are believed to cause performance trade-offs at the whole-organism level. Contrary to this expectation, positive correlations between diverse athletic performances are frequently found in vertebrates. Recently, it has been proposed that trade-offs between athletic performances in humans are masked by variation in individual quality and that underlying trade-offs are revealed by adjusting the correlations to 'control' quality. We argue that quality is made up of both intrinsic components, due to the causal mapping between morpho-physiological traits and performance, and extrinsic components, due to variation in training intensity, diet and pathogens. Only the extrinsic component should be controlled. We also show that previous methods to estimate 'quality-free' correlations perform poorly. We show that Wright's factor analysis recovers the correct quality-free correlation matrix and use this method to estimate quality-free correlations among the 10 events of the decathlon using a dataset of male college athletes. We found positive correlations between all decathlon events, which supports an axis that segregates 'good athletes' from 'bad athletes'. Estimates of quality-free correlations are mostly very small (<0.1), suggesting large, quality-free independence between events. Because quality must include both intrinsic and extrinsic components, the physiological significance of these adjusted correlations remains obscure. Regardless, the underlying architecture of the functional systems and the physiological explanation of both the un-adjusted and adjusted correlations remain to be discovered.

Muscle weakness in TPM3-myopathy is due to reduced Ca2+-sensitivity and impaired acto-myosin cross-bridge cycling in slow fibres

Dominant mutations in TPM3, encoding α-tropomyosinslow, cause a congenital myopathy characterized by generalized muscle weakness. Here, we used a multidisciplinary approach to investigate the mechanism of muscle dysfunction in 12 TPM3-myopathy patients. We confirm that slow myofibre hypotrophy is a diagnostic hallmark of TPM3-myopathy, and is commonly accompanied by skewing of fibre-type ratios (either slow or fast fibre predominance). Patient muscle contained normal ratios of the three tropomyosin isoforms and normal fibre-type expression of myosins and troponins. Using 2D-PAGE, we demonstrate that mutant α-tropomyosinslow was expressed, suggesting muscle dysfunction is due to a dominant-negative effect of mutant protein on muscle contraction. Molecular modelling suggested mutant α-tropomyosinslow likely impacts actin-tropomyosin interactions and, indeed, co-sedimentation assays showed reduced binding of mutant α-tropomyosinslow (R168C) to filamentous actin. Single fibre contractility studies of patient myofibres revealed marked slow myofibre specific abnormalities. At saturating [Ca(2+)] (pCa 4.5), patient slow fibres produced only 63% of the contractile force produced in control slow fibres and had reduced acto-myosin cross-bridge cycling kinetics. Importantly, due to reduced Ca(2+)-sensitivity, at sub-saturating [Ca(2+)] (pCa 6, levels typically released during in vivo contraction) patient slow fibres produced only 26% of the force generated by control slow fibres. Thus, weakness in TPM3-myopathy patients can be directly attributed to reduced slow fibre force at physiological [Ca(2+)], and impaired acto-myosin cross-bridge cycling kinetics. Fast myofibres are spared; however, they appear to be unable to compensate for slow fibre dysfunction. Abnormal Ca(2+)-sensitivity in TPM3-myopathy patients suggests Ca(2+)-sensitizing drugs may represent a useful treatment for this condition.

The genetics of human running: ACTN3 polymorphism as an evolutionary tool improving the energy economy during locomotion

BACKGROUND

Covering long distances was an important trait to human evolution and continues to be highlighted for health and athletic status. This ability is benefitted by a low cost of locomotion (CoL), meaning that the individuals who are able to expend less energy would be able to cover longer distances. The CoL has been shown to be influenced by distinct and even 'opposite' factors, such as physiological and muscular characteristics, which are genetically inherited. In this way, DNA alterations could be important determinants of the characteristics associated with the CoL. A polymorphism in the ACTN3 gene (R577X) has been related to physical performance, associating the X allele with endurance and the R allele with strength/power abilities.

AIM

To investigate the influence of ACTN3 genotypes on the CoL.

SUBJECTS AND METHODS

One hundred and fifty healthy male individuals performed two constant speed tests (at 10 and 12 km/h) to determine the CoL.

RESULTS

Interestingly, the results showed that heterozygous individuals (RX genotype) presented significantly lower CoL compared to RR and XX individuals.

CONCLUSIONS

It is argued that RX genotype might generate an intermediate strength-to-endurance phenotype, leading to a better phenotypic profile for energy economy during running and, consequently, for long-term locomotion.