Neuromuscular response to match load in female youth soccer with consideration to unlimited substitutions.

Abstract

The aim of this thesis was to examine the neuromuscular response to match-play in female adolescent soccer with consideration to unlimited substitutions. Previous studies of female adolescent match-play have not included analysis of substitution match loads and previous studies of neuromuscular response in adolescent female soccer players have been limited to simulated match-play. This thesis assessed sprint-speed ability in adolescent female soccer players to determine an appropriate sprint-speed threshold to analyse sprint-speed movement during match-play, analysed match load for full-match and substitute players across several matches, and examined neuromuscular responses to match-play using exercise performance tests. In Study 1 (Chapter 4), two methods of data collection — timing gates (SmartSpeed PRO system timing gates, Fusion Sport, Queensland, Australia) and a global positioning system (GPS; GPSports HPU system, Canberra, Australia) — were used to assess sprint speed in a cohort of 64 high-level U16 female players, over a short, match-specific sprint distance of 20 m and a maximal effort run over a longer distance. Previous studies have shown that sprint speed increases with age until a plateau around 15 or 16 years with smaller increases in sprint speed into adulthood (Vescovi et al., 2011). Determining an appropriate sprint-speed threshold for female players under the age of 16 was of importance prior to assessing match-play. Both sprint tests were determined to be reliable with reproducible results (between-session ICC for MEAN: > 0.80; CV < 5%). Mean speed in the flying 10 m sprint split measured via timing gates was 6.96 ± 0.35 m·s-1. Mean maximal sprint speed assessed via GPS in the maximal effort run over a >30 m distance was 7.25 ± 0.33 m·s-1. Utilising 80 – 85% of flying 10 m split sprint speed (Bradley & Vescovi, 2015) yielded a sprint-speed threshold of 5.57 – 5.92 m·s-1, which aligns closely with the previously utilised 5.56 m·s-1 threshold determined from adult female soccer player sprint speeds (Bradley & Vescovi, 2015; Ramos et al., 2019; Vescovi, 2014). This study found that the sprint-speed threshold previously utilised for female adolescent match-play analysis could be used for match analysis of players ≥14 years of age. In Study 2 (Chapter 5) of this thesis, GPS was used to track player movement during match-play to determine match load for 36 players in two U16 teams over 20 matches during the regular season. Positional differences, differences between full-match and substitute match loads, and differences in match load between 1st and 2nd match halves were assessed. The established sprint-speed threshold was used to assess sprint-speed efforts during match-play in addition to accelerations and deceleration calculated from speed data determined with the GPS. Match loads were affected by position, with Forward players completing higher sprint-speed distances (F: 219.0 m > M: 123.5 m & D: 153.3 m) and more sprint speed efforts (F: 13 > M: 8 & D: 9), and Midfield players observed to have higher total distances (M: 8388.8 m > F: 7801.8 m & D: 7601.5 m), work rates (M: 105.1 m·min-1 > F: 97.5 m·min-1 & D: 95.2 m·min-1), and low-speed distances (M: 7750.2 m > F: 6939.3 m & D: 6944.0 m). These between-position differences were similarly observed in substitution conditions. Within-position differences between full-match and substitute players did not reveal significant differences for Forward players. Midfield and Defender substitute players had significantly higher work rates, relative high-speed running distances, and relative acceleration and deceleration counts compared to full-match Midfield and Defender players. Examination of between-half differences in match load revealed significant decreases in total distance, low-speed running distance, average speed, and deceleration counts for all positions and significantly decreased acceleration counts into the 2nd half for Midfield and Defender players. Sprint-speed running distances were not observed to decrease between match halves. Further, between-half decreases were largely absent for Forward and Defender substitutes, but not for Midfield substitute players. The study provides coaches and support staff with new information about the match loads of substitute players in consideration of unlimited substitutions in youth soccer. Acceleration and deceleration counts may provide more reliable tracking of performance decline during match-play compared to speed-based analysis. Substitution match loads and positional differences highlighted in the study also provide further information to inform training programming to enhance player development. In Study 3 (Chapter 6), 211 player-sessions were collected with 36 participants over 20 matches including match load and results of three exercise performance tests for neuromuscular response (NMR). Tests were performed pre- and post-match to assess NMR to match-play, including a countermovement jump (CMJ) test, maximal hop test for reactive strength index (RSI), and submaximal hop test for relative leg stiffness. The effects of position, substitution, chronological age, and maturation on NMR were assessed, in addition to effects of match load on NMR. The maximal hop test for RSI was not found to be a useful tool to assess NMR in the current study. Maturation and chronological age effects were observed, with pre- to post-match CMJ height significantly decreased in the Year 2 and Mat 2 groups but maintained CMJ height in Year 1 and Mat 1 groups. In analysis of relationships between match load and NMR, deceleration was found to be negatively correlated with pre- to post-match CMJ response. This negative correlation with CMJ response was present in analysis of full-match, but not substitute conditions, where full-match players recorded higher total deceleration counts as determined in Study 2. Overall, relative leg stiffness was found to decrease from pre- to post-match and was not different between positions. Significantly increased contact time and significantly decreased flight time to calculate leg stiffness were observed in full-match conditions; these significant differences were not observed in substitution conditions. Positive relative leg stiffness responses were also observed for some individual player-sessions. Magnitude-based inferences also revealed variations in NMR per team per match, reflecting individual differences in NMR. Negative NMR in CMJ tests and changes to relative leg stiffness represent altered neuromuscular control to the lower limb and may be considered indicators of fatigue and increased injury risk in response to match-play which coaches and support staff should be aware of in efforts to prevent injury. Together, the data presented in this thesis provide new information for understanding the match loads of substitute players, further knowledge of positional differences in match loads, and new understanding of neuromuscular responses to match-play in female adolescent soccer. Reliable methods to determine sprint speed utilising GPS over different distances provide further performance assessment tools for coaches. Match loads described in the current work provide data for the development of position- and substitution-specific training, especially with regards to high-speed and high-intensity movement including sprint-speed efforts and accelerations and decelerations. Further, the data provide important information for use of substitutions to mitigate performance decrements during match-play. Neuromuscular response data provide indications of fatigue development due to match-play that should be considered to inform recovery and injury prevention in female adolescent soccer.