The genetic contribution to muscular strength and power in elite rugby athletes

Callus, Peter Celestino (2023) The genetic contribution to muscular strength and power in elite rugby athletes. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Muscular strength and power are key determinants of performance in elite rugby and accordingly, established measures of strength/power have been used to assess and monitor athletes, inform training interventions and training prescription, and discriminate athletes between levels of competition. Multiple genetic variants are thought to influence strength/power; exerting a combined effect that in addition to environmental factors produces the inter-individual variation observed in diverse populations. To date, ~62 genetic variants have been found to influence strength/power phenotypes, however, how these genetic variants combine to affect strength/power phenotypes in athletic populations is unclear. Furthermore, there is a scarcity of investigations that have considered the exploration of genotype-phenotype associations in elite athletes – in particular, whether specific genetic variants have an influence on the athletes’ strength/power, or on their performance during competition. Consequently, the overall aim of the current thesis was to characterise strength/power and the genetic characteristics of elite rugby athletes using established measures of strength/power and 10 single nucleotide polymorphisms, and investigate whether the 10 variants, individually and collectively, were associated with measures of strength/power and/or in-game performance variables. 567 elite rugby athletes and 1138 non-athletes were genotyped for 10 polymorphisms found in 9 genes (ACE rs4341, ACTN3 rs1815739, AMPD1 rs17602729, FTO rs9939609, HIF1A rs11549465, NOS3 rs2070744, KDR rs1870377, PTK2 rs7460 and rs7843014, TRHR rs7832552) and data of isometric mid-thigh pull (IMTP) and countermovement jump (CMJ) were collected for 263 athletes and 14 non-athletes. Differences in CMJ and IMTP variables were observed between athletes and non-athletes and between playing positions, whilst polymorphisms within ACTN3, FTO, HIF1A and TRHR were found to be associated with athlete status, with the latter two also associated with playing position. In addition, polymorphisms within NOS3 and TRHR were associated with IMTP whilst those within FTO and PTK2 were associated with CMJ. In-game performance data were acquired for 291 athletes during eight seasons (2012–13 to 2019–20) of rugby union competition in the highest professional competitive leagues, and associations were observed between polymorphisms within ACTN3 and TRHR and in-game variables, namely involvement in tackling, frequency of carries and the ability to gain territory. Furthermore, the polygenic influence of seven of the SNPs expressed as a Total Genotype Score was associated with involvement in tackling within the forwards. Accordingly, forwards possessing 8–9 or 10–14 favourable alleles were involved in 9.5% and 16.5% more tackles compared to those possessing 1–7 favourable alleles, respectively. In addition, backs possessing 9–14 favourable alleles gained 26.3% more territory than those possessing 1–8 favourable alleles. Most of these results identify novel genetic associations in an elite rugby context. In conclusion, there appears to be a genotype-dependent influence on strength/power phenotypes and competitive performance within elite rugby athletes that varies with positional roles. Further research is needed to replicate the associations observed in comparable and larger athletic cohorts. Nonetheless, the work presented here has added to our understanding of the genetic contribution to strength/power and competitive performance of elite rugby athletes, which when combined with physiological data, may have implications for management and performance enhancement of elite rugby athletes in future.