Isokinetic muscular strength and performance in youth football: relationships with age, seasonal variation and injury

The primary aim of the current project was to investigate the isokinetic muscular strength and performance of elite male youth footballers, and the relationships with age, seasonal variation and injury. A secondary aim was to use the information gathered to target muscle strain injury prevention strategies to particular age groups and times, and evaluate the effect. The primary aim was achieved by establishing normative patterns for muscular strength and performance of elite male youth footballers (grouped according to chronological and biological age) across a competitive season of youth football in Chapters Four and Five. Isokinetic muscular strength (characterised by peak torque (PT) and peak torque relative to body weight (PTBW)) of the hamstrings (H) and quadriceps (Q) using both concentric (CQ, CH) and eccentric muscle actions (EH) was evaluated. Muscular performance of the same muscle groups (characterised by H:Q ratios (conventional (CHQ) functional (FHQ)), asymmetry (dominant (dom):non dominant (ndom) leg ratios (e.g. CQ:CQ)), and angle of peak torque (AoPT)) was also investigated which necessitated an isokinetic speed of 60 °/s. Isokinetic evaluation was completed three times over the course of a regular playing season (start of season (SS) mid season (MS) and end of season (ES)). Participants were grouped according to chronological age (n=152, under 12 (U12) - under 18 (U18)) and biological maturation (according to Pubertal Development Scale (PDS 1 - 5) n=134). Forty seven participants completed SS, MS and ES isokinetic evaluation. Bilateral isokinetic evaluation consisted of five maximal repetitions of CQ and CH, followed by five repetitions of EH, leg dominance was counter-balanced. Repetitions two-four were used to calculate PT, PTBW, dom:ndom and AoPT for CQ, CH and EH, CHQ and FHQ; these measures were compared across chronological and biological age groups using a mixed model ANOVA. Dom:ndom CQ, CH and EH were compared across chronological and biological age groups using a one way ANOVA, while the relationship between AoPT and PT/PTBW was considered using a Pearson’s correlation. Additionally, the relationship between chronological and biological age, and PT/PTBW was investigated using a mixed model ANOVA within PDS group three. For analysis of seasonal variation a mixed model ANOVA was applied for all isokinetic measurements which considered time (SS, MS, ES), leg dominance (dom, ndom) and age group (U12 -U15) with a further mixed model ANOVA performed on CQ:CQ, CH:CH and EH:EH. Where appropriate SIDAK corrections were applied and the level of significance was accepted at p≤0.05. The main findings were that youth footballers did not increase their PT and PTBW EH in-line with CQ and CH as chronological and biological ageing progressed, this lead to a significant FHQ imbalance at U18. Dom:ndom CH comparisons identified that the chronologically younger and biologically less developed groups displayed a significantly stronger dom leg which may be explained through the concepts of skill acquisition and trainability. Biological age was not found to exert any additional effect over and above that of chronological ageing as significant differences in muscle strength still existed according to chronological age group within PDS group three. Additionally, AoPT EH and PT EH were found to be significantly negatively correlated on both legs which supported a potential mechanism for non contact hamstring muscle strain injury during running. Analysis of seasonal variation revealed that all PTBW measures showed a MS decrease. This may be related to breaks in normal training activity and links appropriately to times of peak injury incidence highlighted in youth football. In order to achieve the secondary aim of the current project Chapters Four, Five and Six investigated the relationship between isokinetic muscular strength and performance, muscle strain injury of the thigh, and injury risk attenuation. A retrospective and prospective injury audit was undertaken for the elite male youth football participants. For the retrospective approach participants were grouped according to chronological age (n=147) or biological age (n=128) and indicated using a self-report injury form their history (ever, (Hx)) or recent history (12 months, (Hx12)) of hamstring, quadriceps and adductor injuries. Approximately each player had an Hx of muscle strain injury and 0.56-0.59 of players had an Hx12. The hamstrings were the most commonly injured muscle group and the prevalence of muscle strain injury Hx and Hx12 increased with chronological and biological age. The prospective audit (n=50) identified that 0.16 of players sustained a muscle strain injury during the season, 0.08 of these being to the hamstrings. Between group comparisons (one way ANOVA with SIDAK correction) were also performed to investigate the difference in isokinetic measures between those participants who had an Hx12 of muscle strain injury and those who did not. It was discovered that for Hx12 of an injury to the dom hamstrings the injured group had less PTBW CH and EH on the dom leg. The injured group also had more inner range AoPT CH. These findings linked appropriately to the reported mechanisms and risk factors for hamstring injury but the exact direction of cause and effect could not be established. To this end a logistic regression analysis was undertaken in an attempt to predict which group (injured vs. non injured the 50 participants would belong to, using evidenced based risk factors in the experimental model. No predictive relationship between risk factors (including altered isokinetic muscular strength and performance) could be established. The information regarding the relationship between injury and muscular strength and performance may highlight a role for isokinetic screening to ensure adequate rehabilitation from injury. Injury risk attenuation strategies were investigated through an exercise intervention using the U18 age group following a break from football activity. The participants were split based on their FHQ at initial isokinetic evaluation (via odd and even placing) to form control (n=8) and intervention groups (n=8). Isokinetic evaluation was conducted as previously outlined and the exercise intervention targeted the hamstrings. Only six of the control group and seven of the intervention group completed the study and were compared using a mixed model ANOVA. Results showed that the intervention group were not significantly different to the control group post intervention for any of the isokinetic muscular strength and performance measures, though both groups significantly improved over time for the ndom leg CHQ and PTBW EH, and FHQ improved for both legs. Contamination of the control group may explain the lack of significant difference between groups. However, the exercise intervention was not targeted to individuals who displayed prior alterations to isokinetic muscular strength and performance, and this approach was discussed using the results of one member of the intervention group. In summary, the current project achieved the stated aims by discovering normative patterns of isokinetic muscular strength and performance according to age and seasonal variation. Injury risk attenuation strategies were targeted appropriately to the U18 age group following a break from football activity. However, the applied evidence based exercise may have been more effective if targeted to ‘risk’ after isokinetic screening

Isokinetic muscular strength and performance in youth football : relationships with age, seasonal variation and injury

The primary aim of the current project was to investigate the isokinetic muscular strength and performance of elite male youth footballers, and the relationships with age, seasonal variation and injury. A secondary aim was to use the information gathered to target muscle strain injury prevention strategies to particular age groups and times, and evaluate the effect.The primary aim was achieved by establishing normative patterns for muscular strength and performance of elite male youth footballers (grouped according to chronological and biological age) across a competitive season of youth football in Chapters Four and Five. Isokinetic muscular strength (characterised by peak torque (PT) and peak torque relative to body weight (PTBW)) of the hamstrings (H) and quadriceps (Q) using both concentric (CQ, CH) and eccentric muscle actions (EH) was evaluated. Muscular performance of the same muscle groups (characterised by H:Q ratios (conventional (CHQ) functional (FHQ)), asymmetry (dominant (dom):non dominant (ndom) leg ratios (e.g. CQ:CQ)), and angle of peak torque (AoPT)) was also investigated which necessitated an isokinetic speed of 60 °/s. Isokinetic evaluation was completed three times over the course of a regular playing season (start of season (SS) mid season (MS) and end of season (ES)).Participants were grouped according to chronological age (n=152, under 12 (U12) - under 18 (U18)) and biological maturation (according to Pubertal Development Scale (PDS 1 - 5) n=134). Forty seven participants completed SS, MS and ES isokinetic evaluation. Bilateral isokinetic evaluation consisted of five maximal repetitions of CQ and CH, followed by five repetitions of EH, leg dominance was counter-balanced. Repetitions two-four were used to calculate PT, PTBW, dom:ndom and AoPT for CQ, CH and EH, CHQ and FHQ; these measures were compared across chronological and biological age groups using a mixed model ANOVA. Dom:ndom CQ, CH and EH were compared across chronological and biological age groups using a one way ANOVA, while the relationship between AoPT and PT/PTBW was considered using a Pearson’s correlation. Additionally, the relationship between chronological and biological age, and PT/PTBW was investigated using a mixed model ANOVA within PDS group three. For analysis of seasonal variation a mixed model ANOVA was applied for all isokinetic measurements which considered time (SS, MS, ES), leg dominance (dom, ndom) and age group (U12 -U15) with a further mixed model ANOVA performed on CQ:CQ, CH:CH and EH:EH. Where appropriate SIDAK corrections were applied and the level of significance was accepted at p≤0.05.The main findings were that youth footballers did not increase their PT and PTBW EH in-line with CQ and CH as chronological and biological ageing progressed, this lead to a significant FHQ imbalance at U18. Dom:ndom CH comparisons identified that the chronologically younger and biologically less developed groups displayed a significantly stronger dom leg which may be explained through the concepts of skill acquisition and trainability. Biological age was not found to exert any additional effect over and above that of chronological ageing as significant differences in muscle strength still existed according to chronological age group within PDS group three. Additionally, AoPT EH and PT EH were found to be significantly negatively correlated on both legs which supported a potential mechanism for non contact hamstring muscle strain injury during running. Analysis of seasonal variation revealed that all PTBW measures showed a MS decrease. This may be related to breaks in normal training activity and links appropriately to times of peak injury incidence highlighted in youth football.In order to achieve the secondary aim of the current project Chapters Four, Five and Six investigated the relationship between isokinetic muscular strength and performance, muscle strain injury of the thigh, and injury risk attenuation.A retrospective and prospective injury audit was undertaken for the elite male youth football participants. For the retrospective approach participants were grouped according to chronological age (n=147) or biological age (n=128) and indicated using a self-report injury form their history (ever, (Hx)) or recent history (12 months, (Hx12)) of hamstring, quadriceps and adductor injuries. Approximately each player had an Hx of muscle strain injury and 0.56-0.59 of players had an Hx12. The hamstrings were the most commonly injured muscle group and the prevalence of muscle strain injury Hx and Hx12 increased with chronological and biological age. The prospective audit (n=50) identified that 0.16 of players sustained a muscle strain injury during the season, 0.08 of these being to the hamstrings.Between group comparisons (one way ANOVA with SIDAK correction) were also performed to investigate the difference in isokinetic measures between those participants who had an Hx12 of muscle strain injury and those who did not. It was discovered that for Hx12 of an injury to the dom hamstrings the injured group had less PTBW CH and EH on the dom leg. The injured group also had more inner range AoPT CH. These findings linked appropriately to the reported mechanisms and risk factors for hamstring injury but the exact direction of cause and effect could not be established. To this end a logistic regression analysis was undertaken in an attempt to predict which group (injured vs. non injured the 50 participants would belong to, using evidenced based risk factors in the experimental model. No predictive relationship between risk factors (including altered isokinetic muscular strength and performance) could be established. The information regarding the relationship between injury and muscular strength and performance may highlight a role for isokinetic screening to ensure adequate rehabilitation from injury.Injury risk attenuation strategies were investigated through an exercise intervention using the U18 age group following a break from football activity. The participants were split based on their FHQ at initial isokinetic evaluation (via odd and even placing) to form control (n=8) and intervention groups (n=8). Isokinetic evaluation was conducted as previously outlined and the exercise intervention targeted the hamstrings. Only six of the control group and seven of the intervention group completed the study and were compared using a mixed model ANOVA. Results showed that the intervention group were not significantly different to the control group post intervention for any of the isokinetic muscular strength and performance measures, though both groups significantly improved over time for the ndom leg CHQ and PTBW EH, and FHQ improved for both legs. Contamination of the control group may explain the lack of significant difference between groups. However, the exercise intervention was not targeted to individuals who displayed prior alterations to isokinetic muscular strength and performance, and this approach was discussed using the results of one member of the intervention group.In summary, the current project achieved the stated aims by discovering normative patterns of isokinetic muscular strength and performance according to age and seasonal variation. Injury risk attenuation strategies were targeted appropriately to the U18 age group following a break from football activity. However, the applied evidence based exercise may have been more effective if targeted to ‘risk’ after isokinetic screening

The Anti-Inflammatory Effects of Vitamin D and Exercise

Elevated inflammation is associated with several chronic diseases, including obesity. Exercise is an established effective treatment of this condition by decreasing adiposity and independently regulating inflammatory pathways. The potential for vitamin D to confer anti-inflammatory benefits has been explored in cell culture studies, but few have explored its action at the whole body level. PURPOSE: To investigate the relationship between inflammatory markers in trained and untrained individuals with vitamin D levels either above or below a suggested optimal concentration. METHODS: College-aged females (N = 63), both trained and untrained, reported to the lab four times: to assess body size and composition, for blood collection, for a maximal aerobic test, and a test of anaerobic power. Blood was analyzed for serum 25OHD and CRP concentrations, stimulated with LPS to assess IL-6 production. Samples were prepared for FACS analysis for CD14, CD16, and TLR4 expression. RESULTS: Trained individuals presented with higher 25OHD levels, even prior to stratification into high and low groups (p = 0.015). VO2peak was significantly higher (p \u3c 0.0001) and fatigue during the test for anaerobic power was significantly lower (p = 0.021) in trained individuals. Untrained individuals had a higher average body weight (p = 0.039) and estimated percent body fat (p = 0.011) compared to trained individuals, although the average estimated percent body fat of both groups was higher than the recommended level for this age group. Additionally, measures of sun exposure were negatively correlated with measures of body size and composition, although these relationships did not exist between serum 25OHD. CONCLUSION: In this study, regular physical activity was associated with higher serum 25OHD, lower BMI, waist circumference, and estimated percent body fat as well as reduced LPS-stimulated IL-6 production. Optimal vitamin D status did not appear to provide any additional health related or anti-inflammatory benefit in those with regular physical activity habits. However, in individuals not participating in a regular exercise program, the potential for vitamin D to mediate inflammation appeared more likely. More specifically, untrained people with optimal vitamin D status had lower numbers of total monocytes, CD14+CD16- cells, and decreased TLR4 expression on CD14+CD16+ cells; however, these differences did not translate into a change in overall cell function or markers of systemic inflammation as there was no difference between optimal and suboptimal groups with respect to LPS-stimulated IL-6 production or resting CRP concentrations. An expanded exploration of the relationship between vitamin D and inflammation may include assessing other inflammatory biomarkers, immune cell types, the vitamin D receptor, and the role of adipose tissue

A multidisciplinary investigation into the talent identification and development process in an English football academy

Introduction: The purpose of a player development pathway is to realise the most effective methods to support young individuals to maximise their potential (MacNamara & Collins, 2015). Within a modern football academy setting, the essential developmental characteristics are often termed environmental, psychological, sociological, physiological, technical, and tactical attributes (Sarmento et al., 2018). Although these factors have been explained to independently facilitate the acquisition of expert performance, fully-integrated multidisciplinary evidence from an English context is unknown. Therefore, the aim of this study was two-fold; firstly, to analyse these respective features to determine what outcomes support greater age-specific performance within the Foundation Development Phase (FDP; under-9 to 11s) and Youth Development Phase (YDP; under-12 to 16s) at an English professional football academy. Following this investigation, this thesis examined what characteristics facilitated age-specific development across two football seasons within the same group. Methods: During the first season, a total of 98 outfield academy players (FDP n=40; YDP n=58) participated. Two professional coaches from each age group (n=14) ranked their players from top to bottom in relation to current ability from a holistic perspective. This created a linear classification with a group of ‘high-performers’ (top third) and ‘low-performers’ (bottom third) within both the FDP and YDP. Results were standardised using z-scores and the assumptions were tested using a two-tailed independent samples t-test. A total of 87 outfield players who progressed into the second season were further analysed within their respective phase (FDP n=36; YDP n=51). A combination of 34 holistic factors, that discriminated high- and low-performers in the initial investigation, were measured at two time points across two football seasons with the Participation History Questionnaire (PHQ), Psychological Characteristics for Developing Excellence Questionnaire (PCDEQ), socio-economic status, growth and maturation data, physical performance, technical tests, match analysis statistics, perceptual-cognitive expertise (PCE), and game test situations. Development was measured by comparing the delta change between the overall player profile scores from two seasonal reports. Stepwise regression analyses were conducted to assess the predictive capability of these variables on overall development. Results: Multiple factors from environmental, psychological, sociological, physiological, technical, and tactical examinations significantly discriminated high- and low-performers, within both the FDP and YDP. Following these initial findings, developmental results illustrated significant technical and tactical characteristics within the FDP, whilst significant environmental, physiological, technical, and tactical attributes were observed within the YDP. When focussing on these factors combined, total touches change (p=0.023), taking advantage of openings quality (p=0.003), and PCE ‘post’ score change (p=0.029) explained a combined 11.5% of the variance within the FDP. Within the YDP, PCE ‘at’ score (p=0.21), total sports played change (p=0.008), and total match-play hours (p=0.009) explained a combined 34.1% of the variance. Discussion: Identifying talented players as young as 8 years of age is a complex and holistic process. Thus, academy coaches and practitioners must understand the significant features, such as practice history and multi-sport engagement, psychological characteristics, socio-economic factors, physical performance abilities, technical attributes, and tactical decision making when identifying and recruiting individuals. From a talent development viewpoint, results from the FDP support the importance of technical and tactical development during middle childhood compared to other influential factors. From a YDP perspective, results support the significance of the environment players are exposed to, whilst also illustrating the importance of PCE as a key ingredient within adolescence, to support greater overall development. Therefore, professional football academies are encouraged to deliver technical and tactical specific developmental activities within the FDP, whilst offering a substantial games programme, alongside other opportunities to participate in multi-sport activities across both age phases, to support superior development. Further evidence is needed within an English context, through collaboration with other academy environments, to support these findings, whilst greater longitudinal data is also required to understand which of these characteristics are necessary to ultimately achieve senior professional status.University of ExeterOpen Innovation PlatformExeter City Football Clu

The Role of Relative Age, Community Size, and Positive Youth Development on Female Youth Soccer Participation

Objective: The overarching purpose of this dissertation was to use relative age as a basis to examine the developmental sport experience of youth and explore factors related to sport engagement and positive youth development in organized, female soccer in Ontario, Canada. Female dropout trends were documented for the first time in a longitudinal manner (i.e., covering the pre-adolescent to post-adolescent transition years) in a popular youth sport context. Analyses were informed by multiple points of reference (i.e., date of birth, participation records, competition level, community size and density, and self-report of the participants). New research avenues were explored to generate hypotheses for future research; which included neighbourhood level variables and developmental assets. Methods: An anonymized dataset of all female registrants in a one-year cohort was provided by Ontario Soccer. This dataset included all registration entries across a seven-year period (age 10 to 16 years). A total of 38,248 registration entries for 9,915 participants were available for examination. Several quantitative approaches were used across three studies, including Kaplan Meier and Cox regression survival analyses, odds ratio analyses, discriminant analysis, binary logistic regression, and chi-square analysis. Results: The key finding of the current research suggests that relative age continues to be an important variable with respect to youth sport participation and continued engagement; with the relatively oldest being more likely to participate and remain engaged between the ages of 10 to 16 years. Competition level was observed to be an important variable, with ‘competitive’ and ‘recreational’ trajectories varying in terms of relative age distribution and retention rates (55.9% vs. 20.7% continued to participate at age 16 years, respectively). In general, mid-sized and less densely populated communities appeared to provide the greatest likelihood of participation in youth soccer; although considerable within-category variation was observed. Built environment emerged as a potential avenue for future research. Overall developmental asset scores did not appear to be protective against sport dropout; but relatively younger female soccer players scored higher in two internal asset categories, commitment to learning and positive values, suggesting sport-related challenges may further individual development in these areas. Conclusions: Relative age effects continue to contribute to participation and development inequities in sport. Detailed research into the underlying mechanisms and potential intervention strategies is still required. Future studies should be guided by an appropriate theoretical framework; the selection of which depends on the primary goal(s) of the research

The utilisation of the Rugby League Athlete Profiling battery for assessing the anthropometric and physical characteristics of rugby league players

The research described in this thesis used a standardised battery of tests called the ‘Rugby League Athlete Profiling (RLAP)’ battery for assessing the anthropometric and physical characteristics of UK-based rugby league players. The overall purpose of this research was to determine the utility of the RLAP battery, which involved establishing the use of RLAP across numerous professional clubs over a three-year period, determining the measurement properties of the tests included and investigating the factors associated with a change in the characteristics. An early version of the RLAP battery existed [called SPARQ] and was provided by the Rugby Football League with scope to alter this as part of this programme of research. Before determining if an alteration to the battery was required, it was essential to understand the tests that are currently used in rugby league for assessing the anthropometric and physical characteristics of players. As such, the systematic review initially sought to determine the volume of performance tests used in rugby league along with their measurement properties. Based on the results, it was evident that a shorter sprint distance (< 20 m) ought to be included in the battery. It was also clear that only one field-based method for measuring muscle strength was available, though had received minimal research. Furthermore, the review highlighted that no rugbyspecific intermittent running test had previously been used and that RLAP was the first battery to include such a test. Therefore, based on these results, the battery was rebranded to RLAP, which included a stature, body mass, a 10 m and 20 m sprint test, a rugby-specific intermittent test, a change of direction test, measures of lower- and whole-body power. With the RLAP battery confirmed, it was then used and the reliability (Chapter 4) and discriminant validity (Chapter 5) of its elements determined. Results indicated that the RLAP battery is reliable and does not require habituation. Furthermore, the calculation of the required change, which includes the worthwhile change and random error of each test, provides researchers and practitioners with a single value that can be used as an analytical goal to evaluate a true change in characteristics with confidence. All components of the RLAP battery (except 10 m sprint time) possessed adequate discriminant validity between youth, academy and senior rugby league players, suggesting this battery can accurately distinguish between playing standards. As noted in above, the review highlighted a rugby-specific intermittent test has yet to be established in the literature before its inclusion in the RLAP battery. Whilst it appeared to be suitable and, based on Chapters 3 and 4, is reliable and possesses discriminant validity, the test itself had received no previous attention. Given the novelty of this test, it was unknown if this test was better associated with the responses to rugby league match performance and what the physiological responses were to this test. As such, Chapter 5 sought to determine the concurrent validity of this test and compare it against the traditional Yo-Yo Intermittent Recovery test level 1 (Yo-Yo IR1). The results indicated the association between prone Yo-Yo IR1 distance and the external, internal and perceptual responses to simulated match-play was improved when compared to the Yo-Yo IR1. Chapter 6 demonstrated that starting each 40 m shuttle in a prone position increases the internal, external and perceptual loads whilst reducing the total distance achieved. The degree of shared covariance between the prone Yo-Yo IR1 and Yo-Yo IR1 suggest the rugby-specific test provided insight into additional characteristics associated with rugby league performance. In studies that have reported on the anthropometric and physical characteristics, few have considered the multiple factors that might influence these with no studies conducted in rugby league. Chapter 7 sought to determine the complex interaction between anthropometric and physical characteristics that requires careful consideration by those involved in developing youth and academy athletes. The results also revealed a number of contextual factors such as season phase, league ranking, playing age and playing position that can influenced the change in characteristics over the course of a competitive season. The findings of this study highlight how some characteristics are impaired towards the end of the season, thus providing a rationale for considering in-season training loads and the application of short training interventions to off-set these negative changes. Based on negative changes in some anthropometric and physical characteristics towards the end of the year, Chapter 8 reported on the efficacy of two in-season sprint interval interventions for enhancing the physical characteristics of rugby league players. Furthermore, the study provided insight into the sensitivity of the RLAP battery for detecting changes in the characteristics of rugby league players. The results highlighted that two weeks of rugby-specific and running-based sprint interval training appeared affective for promoting the physical characteristics of rugby league players with minimal deleterious effects on wellness and neuromuscular function. Using the reliability statistics from Chapter 1, the mean change for prone Yo-Yo IR1 in the rugbyspecific group met the required change whilst changes approached this value for the running-based group despite contrasting loads. In all, this study demonstrated that sprint interval training that includes sport-specific actions is a suitable and effective training modality that can be used in-season. In addition, the result demonstrated how the prone Yo-Yo IR1 was sensitive to change across the intervention period whilst others were not sensitive to sprint interval training due to the lack of specificity. This thesis provides a thorough evaluation of the RLAP battery that can be used by researcher and practitioners to assess the anthropometric and physical characteristics of rugby league players. The battery is reliable and possess discriminant validity, while the prone Yo-Yo IR1 has concurrent validity and is sensitive to change during a lowvolume in-season training intervention. Overall, this thesis provides justification for the tests included and comprehensively examines the utility of this battery for assessing the anthropometric and physical characteristics of rugby league players. Practically, this battery of tests can be used by researcher and applied practitioners in rugby league with an understanding of the reliability, validity and sensitivity of the tests along with some factors that might influence the characteristics of players across a season

The Dose-Response Effects of Dissociation Training on Measures of Neuromuscular Control during Performance Screening in Male Youth Footballers

AIMS: Movement screens purportedly identify compensatory kinematics that predispose athletes to injury (Kiesel et al., 2011). The efficacy of assessing select competencies and prescribing remedial training based on screen outcomes however remains equivocal. The Foundation Performance Matrix Screen© (FPMS) supposedly profiles injury risk, subsequently directing its independent motor control Dissociation Training (DT) (Mottram and Comerford, 2008). However, there appears to be no research evidencing that DT can improve FPMS score or reduce injury. Therefore this study aimed to investigate the doseresponse of DT on kinematic and kinetic measures of neuromuscular control in male elite academy footballers. METHOD: The dose-response to DT therefore remains to be established. With institutional ethics approval, elite U15/16 and U17/18 male academy footballers comprised group one (n = 6) (G1) and group two (n = 8) (G2) respectively. G1 performed DT 1x week while G2 performed DT 3x week over eight weeks. Centre of pressure (CoP) total, anterior-posterior (X) and medial-lateral (Y) displacements (cm), sway velocity (cm∙s -1) and ellipse area (cm2) were recorded from participants’ non-dominant leg during a single leg stance test (SLST) and Y balance test™ (YBT). Force platform time to stabilisation (TTS), peak vertical ground reaction force (PVGRF) and loading rates were recorded from a 20cm bilateral drop jump landing (DJL). The FPMS and YBT were scored according to respective guidelines. All tests were performed barefoot. Cohen’s d effect size (ES) was calculated from differences in means. RESULTS: Small ES for G1 (ES -0.180; 95% CI, −1.94 - 0.60) and G2 (ES −0.136; 95% CI, −0.12 - 1.62) FPMS scores were observed. Large ES for DJL loading rates (ES -1.89, 95% CI, 0.046 - 0.079) and YBT normalised anterior reach (ES 1.416, 95% CI, 66.30 - 73.29) were observed for G1 compared to G2 where trivial (ES 0.072, 95% CI, 0.067 - 0.095) and moderate effects (ES 1.104, 95% CI, 66.84 - 72.90) respectively, were observed. The magnitude of change for G1 was consistently greater for all DJL and YBT measures. Furthermore, SLST performance for G1 improved for all CoP measures whereas G2 decreased. CONCLUSION: The measures used to assess neuromuscular function indicate eight weeks DT had meaningful effects on neuromuscular control, however, the magnitude of effects were greater for G1 than G2. As SLST, YBT and DJL indicated greater effects and are all proposed to predict injury, they could be a suitable surrogate marker for assessing the effects of DT. These findings also suggest that a lower dose of DT is sufficient provided training is individualised

Unravelling tennis performance:creating monitoring tools to measure and understand technical and tactical skills

The key in elite tennis performance is suggested to be the combination of outstanding technical and tactical skills. However, little is known about which specific skills are important to progress towards elite tennis performance. Moreover, there are no reliable, valid and feasible tools to assess technical and tactical skills in youth tennis players. Therefore, in this thesis, tools with sufficient psychometric properties were developed to measure technical and tactical skills in a tennis-specific context - contributing to both scientific and practical purposes. An on-court tennis test was developed to assess technical skills based on accuracy (target areas), ball speed (radar system) and percentage errors. A new instrument with closed-ended questions was designed to examine tactical skills, in particular ‘Anticipation and positioning’, ‘Game intelligence and adaptability’, ‘Decision-making’, and ‘Recognizing game situations’. Our studies showed that outstanding technical skills, especially accuracy under increased task complexity (i.e. high temporal and cognitive pressure), were considered essential to progress towards elite tennis performance. Findings of this thesis also suggest that these technical skills continue to develop in adolescence in a group of youth talented tennis players. From a practical perspective, the tools created in this thesis are valuable for coaches and players to enhance tennis performance. In addition to monitoring the progress of players, tools can assist in identifying relative strengths and weaknesses of players as well as provide essential information about underlying skills that require most attention to progress towards elite performance