An investigation into the capabilities and affecting factors of isometric mid-thigh pull force production in elite youth soccer players

Abstract

Elite youth soccer player’s performance depends on a multitude of factors (Stolen et al. 2005). Muscular force production capability is of likely importance due to the frequency of powerful actions that occur within match play (Faude et al. 2012). Little is known though of the training undertaken at elite youth soccer academies to increase muscular force production capabilities particularly across maturation groups. There is also little evidence around the nature, or genetic influence on this variable in these populations. Greater knowledge on these areas would be beneficial to aid an understanding of performance and to plan practical interventions. Eight weeks of training for players in the under 9 (U9) through to under 21 (U21) age groups (Chapter 3) were recorded to investigate the duration of each training type completed. The total training duration increased from U9 to U14 before reducing at U15 and then remaining unchanged through to, and including, the U21 age group. Soccer training accounted for 97 ± 4 % of session time in the U9 to U14 groups and 74 ± 3 % in the U15 to U21 groups. The remainder of training was made up of work that was not soccer based. The data in this case study suggest that training time is focussed on the technical/tactical development throughout the academy, particularly in the younger age groups. Study 2, part A (Chapter 4) provided baseline isometric maximal voluntary force (MVF) data for players and an maturation-matched non-elite control group. MVF was slightly higher in the elite compared to control cohorts during an isometric mid-thigh pull (IMTP, 118.29 ± 13.47 N compared to 109.69 ± 17.00 N). Such data may indicate that ability to produce force, specifically isometric MVF, may not be a crucial determinant of performance in elite youth soccer based on this sample. The purpose of study 2, part B (Chapter 4) was to establish the effect of 8 weeks typical training on elite youth soccer players’ IMTP MVF. This was also compared to a non-elite control cohort matched for maturation status and not undertaking training. Isometric MVF did not change in either group over the 8 week period (P = 0.386). These data suggest that this elite youth soccer training simply maintained current strength levels and was not sufficient to elicit increases in isometric MVF. Study 3 (Chapter 5) examined variations in four separate genes, all identified as potentially having an influence on muscular force production capabilities: PPARA rs4253778, NOS3 rs2070744, COLIA1 rs2249492 and VDR rs2228570. Allele and genotype frequency was determined along with the influence of those single nucleotide polymorphisms (SNPs) on isometric MVF. Only NOS3 was different in genotype distribution between cohorts with TT genotype showing 45.0 % and 30.4 % frequency in elite and control cohorts respectively (P < 0.001). Furthermore, no difference was seen between cohorts for isometric MVF data when comparing influence of any genotypes of any gene. These data provide novel information around genotype frequency in this population and would suggest that the gene variations examined here might not play a role in force production in these populations. Overall, these findings suggest that muscular force production may be important for elite youth soccer performance, but that current training practices to improve this characteristic should be revised. This seems especially relevant given the lack of genetic association with force production in the gene variations examined here, i.e. elite youth soccer players do not appear to be selected based on a genetic predisposition for greater isometric force production capabilities.