English Premier League and English Football League academy managers' experiences of how psychosocial skills and characteristics are identified and developed in youth academy soccer players.

Psychological skills and characteristics (PSCs) are vital for player development, yet there is a lack of agreement on which are important and how they should be identified and developed in academy players, creating barriers to implementation into curricula. The key stakeholder with considerable insight into PSC development is the academy manager (AM). The aims of this study were (a) explore AMs' experiences of PSC identification and development, (b) identify challenges AMs feel affect development of PSCs. Nine AMs (i.e. Category 1; n = 3, Category 2; n = 3 and Category 3; n = 3) comprising an average coaching experience of 20.4 ± 7.4 years and time in the role of 5.2 years ±3.2 years participated in semi-structured interviews. Reflexive thematic analysis generated themes identified ideal PSC outcomes that AMs felt were important. AMs identified current practices within academies alongside challenges: transitions, need to upskill coaches, access to additional support from external partners and National Governing Bodies. There was consensus that PSCs are key drivers of progression and that embedding them into the pathway was critical to facilitating development. Academies should think carefully about design, implementation and evaluation of programmes to support player PSC development for success during and after soccer careers.

Vertical Strength Transfer Phenomenon Between Upper Body and Lower Body Exercise: Systematic Scoping Review.

BACKGROUND: There are a myriad of exercise variations in which upper body (UB) and lower body (LB) exercises have been intermittently used. However, it is still unclear how training of one body region (e.g. LB) affects adaptations in distant body areas (e.g. UB), and how different UB and LB exercise configurations could help facilitate physiological adaptations of either region; both referred to in this review as vertical strength transfer. OBJECTIVE: We aimed to investigate the existence of the vertical strength transfer phenomenon as a response to various UB and LB exercise configurations and to identify potential mechanisms underpinning its occurrence. METHODS: A systematic search using the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) for Scoping Reviews protocol was conducted in February 2024 using four databases (Web of Science, MEDLINE, Scopus and CINAHL) to identify peer-reviewed articles that investigated the vertical strength transfer phenomenon. RESULTS: Of the 5242 identified articles, 24 studies met the inclusion criteria. Findings suggest that the addition of UB strength training to LB endurance exercise may help preserve power-generating capacity for the leg muscle fibres. Furthermore, systemic endocrine responses to high-volume resistance exercise may beneficially modulate adaptations in precedingly or subsequently trained muscles from a different body region, augmenting their strength gains. Last, strength training for LB could result in improved strength of untrained UB, likely due to the increased central neural drive. CONCLUSIONS: Vertical strength transfer existence is enabled by neurophysiological mechanisms. Future research should involve athletic populations, examining the potential of vertical strength transfer to facilitate athletic performance and preserve strength in injured extremities.

Physical match demands across different playing positions during transitional play and high-pressure activities in elite soccer.

This study explored physical match demands across different playing positions during transitional play, to inform the need for position-specific training interventions. Data was collected using 10 Hz GPS units from 10 competitive matches including 23 elite soccer players of the 1st Polish Division (Ekstraklasa) in season 2020-21. A total of 4249 positional observations were made; center backs (n = 884), full backs (n = 972), central defensive midfielders (n = 236), central attacking midfielders (n = 270), central midfielders (n = 578), wingers (n = 778), and attackers (n = 531). Match data reflected distances covered per minute (m · min-1): total distance (TD), high-speed running distance (HSRD, > 19.8 km · h-1), sprint distance (SD, > 25.2 km · h-1), and the frequency of high-intensity accelerations and decelerations (A+D, > 3 m · s-2; n · min-1). Total absolute sprint distance (SD, > 25.2 km · h-1) and total relative sprint distance (Rel B5) were also quantified. A univariate analysis of variance revealed position-specific differences. Significant effects of position were found for all analysed metrics during transitional play (large ESs; p <.001). Central attacking midfielders displayed higher TD (m · min-1), fullbacks covered highest SD (m · min-1) and wingers achieved the highest A+D (n · min-1) (p ≤ 0.05). Centre backs displayed the lowest physical outputs when compared to all other positions, except in A+D (n · min-1) during defensive transitions (p ≤ 0.05). Attackers displayed the highest physical metrics during high pressure activities (p ≤ 0.05). Coaches should carefully consider positional transitional demands to better inform training design. With specific attention paid to drills that replicate game play.

Worst Case Scenarios in Soccer Training and Competition: Analysis of Playing Position, Congested Periods, and Substitutes.

Aim: To understand mean (WCSmean) and peak (WCSpeak) worst case scenarios within training and game play in male professional soccer. Methods: Thirty-one (n = 31) first team players were monitored across 37 matches and 14 MD-3 sessions. Playing status was distinguished, football drills analyzed, and performance explored in long-period: >6 days, moderate-period: 5-6 days, and congested-period: ≤4 days. Relative total distance (TD), high-speed running distance (HSRD, >19.8 km·h-1), sprint distance (SD, >25.2 km·h-1), accelerations/decelerations (A+D, >3 m·s-2), accelerations (Acc, >3 m·s-2), and decelerations (Dec, >-3 m·s-2) were measured as well as Maximum acceleration (Max Acc; m·s-2) and deceleration (Max Dec; m·s-2). Results: Analysis of variance found differences between matches and training in WCSmean for TD, HSRD, SD, and Max Dec in all positions (p < .001; partial η2 > .275). Fullbacks displayed differences between match and training in Max Acc (moderate ESs; p < .001), while center backs and central midfielders in Max Dec (large ESs; p > .05). Main effects of playing status were discovered for all metrics except Max Dec (p < .001; partial η2 > .124). Analysis showed differences between long- and congested-period for A+D and Dec (large ESs; p ≤ .05). Conclusions: Findings provide more insights into short peak intensity demands of soccer showing that the maximum high velocity action of acceleration and deceleration is not being replicated in training. Nonstarters lack maximum intensity exposure in matches (WCSpeak) increasing the gap between training and competition even higher during congested fixture periods.

Reliability of phase-specific outcome measurements in change-of-direction tests using a motorized resistance device.

This study aims to determine test-retest reliability of phase-specific information during initial acceleration, deceleration, and re-acceleration phases of different change-of-direction (CoD) tests using a motorized resistance device (MRD). A total of 21 participants (16 males and five females, with mean age of 22.3 ± 3.9 years, body mass of 75.2 ± 6.9 kg, height of 177.9 ± 6.8 cm) completed the modified 505 (m505), 10-0-5, and 15-0-5 CoD tests on four different test sessions while exposed to an external load (3 kg) provided by the MRD. Outcome variables included overall and phase-specific kinetic (force, power, and impulse) and kinematic (time, distance, velocity, and acceleration/deceleration) data during the initial acceleration, deceleration, and re-acceleration phases. The deceleration and re-acceleration phases were further divided into two subphases, namely, early and late subphases, using 50% of maximum velocity. Reliability was assessed using an intraclass correlation coefficient (ICC), coefficient of variation (CV), typical error (TE), and minimal detectable change (MDC). Good to excellent ICC values (>0.75) and acceptable (<10%) to good (<5%) CV values were observed for most outcome measurements. Specifically, 80.1% (822 out of 1,026) of all variables showed good or better relative reliability (i.e., ICC ≥ 0.75), while 97.0% (995 out of 1,026) of all variables showed acceptable or better absolute reliability (i.e., CV < 10%). In conclusion, the present study demonstrates that the MRD can obtain reliable phase-specific outcome measurements across different CoD tests, providing coaches and researchers with new opportunities to advance our understanding of CoD ability and inform more advanced CoD training prescriptions.

Measuring maximal horizontal deceleration ability using radar technology: reliability and sensitivity of kinematic and kinetic variables.

Radar technology has the potential for providing new insights into maximal horizontal deceleration ability. This study aimed to investigate the intra- and inter-day reliability and sensitivity of kinematic and kinetic variables obtained from a novel, maximal horizontal deceleration test, using radar technology. Thirty-eight university sport athletes completed testing for intra-day analysis. Twelve of these participants also completed the deceleration test on a second day for inter-day analysis. The maximal horizontal deceleration test required participants to decelerate maximally following 20 m maximal horizontal sprint acceleration. Reliability was assessed using the intraclass correlation coefficient (ICC) and coefficient of variation (CV%). Sensitivity was evaluated by comparing typical error (TE) to the smallest worthwhile change (SWC). A number of kinematic and kinetic variables had good (ICC > 0.75, CV < 10%) overall intra-day reliability, and were sensitive to detect small-to-moderate changes in deceleration performance after a single familiarisation session. Only kinetic variables had good overall inter-day reliability and were sensitive to detect moderate changes in deceleration performance. The utilisation of this test protocol to assess maximal horizontal deceleration can provide new insights into individual maximal horizontal deceleration capabilities. Future work using this or similar approaches may provide insights into the neuromuscular performance qualities needed to decelerate maximally.

Interchangeability of optical tracking technologies: potential overestimation of the sprint running load demands in the English Premier League.

PURPOSE: The purpose of this study was to assess the agreement between match-derived running load outputs; total distance (TD), high-speed running (HSR) and sprint distance (SPR) obtained by two optical tracking systems. METHODS: Data were collected from 31 elite footballers from the first team and under-21 squads of an English Premier League (EPL) football club across three competitive matches. One EPL game (game 2) and one under-21 Premier League game (game 3) were played at the team's home stadium and one EPL game (game 1) at an away venue. All matches were tracked concomitantly using eight colour cameras sampling at 10 Hz (PROZONE®) and six high-definition motion cameras sampling at 25 Hz (TRACAB®). RESULTS: TD displayed a perfect (r = 0.99) correlation while HSR and SPR displayed very large (r = 0.81 and r = 0.73) correlations between TRACAB® and PROZONE®. Mean biases were 5% for TD, -3% for HSR and 61% for SPR. Between games, mean biases for TD were 6% for game 1, and 5% for game 2 and game 3. For HSR, 9% for game 1, -5% for game 2 and 6% for game 3 and for SPR, 31% for game 1, 71% for game 2 and 84% for game 3. CONCLUSION: TD and HSR can be interchanged between PROZONE® and TRACAB®, to allow accurate interpretation between the two optical systems. PROZONE® overestimated SPR compared to the TRACAB®, with the magnitude of difference considered meaningful, altering interpretation of historical match outputs, sprint volume trends in the EPL and forecasts of the modern game.

Biomechanical and Neuromuscular Performance Requirements of Horizontal Deceleration: A Review with Implications for Random Intermittent Multi-Directional Sports.

Rapid horizontal accelerations and decelerations are crucial events enabling the changes of velocity and direction integral to sports involving random intermittent multi-directional movements. However, relative to horizontal acceleration, there have been considerably fewer scientific investigations into the biomechanical and neuromuscular demands of horizontal deceleration and the qualities underpinning horizontal deceleration performance. Accordingly, the aims of this review article are to: (1) conduct an evidence-based review of the biomechanical demands of horizontal deceleration and (2) identify biomechanical and neuromuscular performance determinants of horizontal deceleration, with the aim of outlining relevant performance implications for random intermittent multi-directional sports. We highlight that horizontal decelerations have a unique ground reaction force profile, characterised by high-impact peak forces and loading rates. The highest magnitude of these forces occurs during the early stance phase (< 50 ms) and is shown to be up to 2.7 times greater than those seen during the first steps of a maximal horizontal acceleration. As such, inability for either limb to tolerate these forces may result in a diminished ability to brake, subsequently reducing deceleration capacity, and increasing vulnerability to excessive forces that could heighten injury risk and severity of muscle damage. Two factors are highlighted as especially important for enhancing horizontal deceleration ability: (1) braking force control and (2) braking force attenuation. Whilst various eccentric strength qualities have been reported to be important for achieving these purposes, the potential importance of concentric, isometric and reactive strength, in addition to an enhanced technical ability to apply braking force is also highlighted. Last, the review provides recommended research directions to enhance future understanding of horizontal deceleration ability.

A low-volume Nordic hamstring curl programme improves change of direction ability, despite no architectural, strength or speed adaptations in elite youth soccer players.

Nordic hamstring curls (NHC) are a commonly used injury intervention method in amateur team sports. Seventeen elite male academy soccer players performed an 8-week low volume NHC programme. Pre-post intervention measures of isokinetic eccentric knee flexor (KF) strength, linear speed, COD performance, hamstring muscle thickness, pennation angle and fascicle length were recorded. No significant main effects were observed for measures of isokinetic KF strength (P ≥ 0.19), linear sprint speed (P ≥ 0.47) or hamstring muscle architecture (P ≥ 0.30). However, significance was noted for improved COD performance (P < 0.01; mean difference, -0.06, p = 0.001, 95% CI = 0.03 to 0.09; d = 0.80), exceeding the minimal detectable difference (MDD = 0.05 s). A low-volume NHC intervention may contribute to significant improvements in COD ability, independent of no significant changes in eccentric KF strength, linear sprint speed or muscle architectural properties in elite youth soccer players.

Validity of Velocity Measurements of a Motorized Resistance Device During Change of Direction.

The aim of this study was to determine validity of velocity measurements of a motorized resistance device (MRD) during change of direction (CoD). Eight male (age: 22.1 ± 4.2 yrs; weight: 83.3 ± 17.1 kg; height: 181.6 ± 12.6 cm) and three female participants (age: 21.7 ± 1.5 yrs; mass: 69.7 ± 2.4 kg; height: 167.0 ± 3.6 cm) completed the modified 505 CoD test (m505) with turning off the left and right foot while exposed to external loads (3, 6, and 9 kg) provided by the MRD. Three-dimensional kinematic data were measured (200 Hz) for all tests using a full-body marker set with an additional marker placed on the pulley used to attach the carabiner (CAR) at the end of the line from the MRD to the participant. Average velocity of overall center of mass (COMvel), pelvis (COMpelvis_vel), and pulley (CARvel) was then calculated and compared to the velocity measured by MRD (MRDvel) in 0.5 s intervals 1.5 s before and after CoD. Average velocities from these intervals were then compared using correlational, Bland-Altman analysis, coefficient of variation (CV), and statistical parametric mapping (SPM). Mostly, excellent correlations were observed and ranged from 0.93 to 1.00, 0.53 to 1.00 and 0.93 to 1.00 for the 3, 6, and 9 kg load conditions, respectively. CV values ranged from 0.3 to 3.2%, 0.8 to 4.3%, and 1.5 to 7.7% for the CARvel, COMpelvis_vel, and COMvel comparisons, respectively. The biases for CARvel comparisons ranged from -0.027 to 0.05 m/s, -0.246 to 0.128 m/s and -0.486 to 0.082 m/s across all load conditions and time intervals for the CARvel, COMpelvis_vel, and COMvel comparisons, respectively. SPM analysis indicated significant differences between MRDvel and COMvel and COMpelvis_vel over short time periods during the CoD, but no difference between MRDvel and CARvel. The velocity measurements obtained by a MRD during a m505 test are valid as low biases, low CV's, and high correlations are observed for the MRDvel to CARvel comparison. As single points of measurement (i.e., laser) has been proven useful to assess other athletic tasks (i.e., sprint running), the single point CARvel comparison is an appropriate comparison for validating MRDvel measurements during the m505 test.

Deceleration Training in Team Sports: Another Potential 'Vaccine' for Sports-Related Injury?

High-intensity horizontal decelerations occur frequently in team sports and are typically performed to facilitate a reduction in momentum preceding a change of direction manoeuvre or following a sprinting action. The mechanical underpinnings of horizontal deceleration are unique compared to other high-intensity locomotive patterns (e.g., acceleration, maximal sprinting speed), and are characterised by a ground reaction force profile of high impact peaks and loading rates. The high mechanical loading conditions observed when performing rapid horizontal decelerations can lead to tissue damage and neuromuscular fatigue, which may diminish co-ordinative proficiency and an individual's ability to skilfully dissipate braking loads. Furthermore, repetitive long-term deceleration loading cycles if not managed appropriately may propagate damage accumulation and offer an explanation for chronic aetiological consequences of the 'mechanical fatigue failure' phenomenon. Training strategies should look to enhance an athlete's ability to skilfully dissipate braking loads, develop mechanically robust musculoskeletal structures, and ensure frequent high-intensity horizontal deceleration exposure in order to accustom individuals to the potentially damaging effects of intense decelerations that athletes will frequently perform in competition. Given the apparent importance of horizontal decelerations, in this Current Opinion article we provide considerations for sport science and medicine practitioners around the assessment, training and monitoring of horizontal deceleration. We feel these considerations could lead to new developments in injury-mitigation and physical development strategies in team sports.

Drop jump neuromuscular performance qualities associated with maximal horizontal deceleration ability in team sport athletes.

The purpose of this study was to investigate associations between, and within, drop jump (DJ) neuromuscular performance (NMP) qualities and maximal horizontal deceleration ability. We also compared DJ NMP qualities in "high" versus "low" horizontal deceleration ability athletes. Twenty-nine university athletes performed: (1) DJs on force plates from 20 (DJ20) and 40 cm (DJ40) heights and (2) maximal horizontal deceleration, measured using radar, following a 20 m acceleration. Maximal horizontal deceleration was evaluated using deceleration (HDEC; m·s-2), across the entire deceleration phase and during early and late deceleration sub-phases. Of the DJ variables assessed, DJ20 and DJ40 reactive strength index (RSI) and concentric mean force had the largest correlations with HDEC (r = -0.54 to -0.61) and the largest differences between high and low HDEC groups (d = 1.20 to 1.40). These correlations were stronger with the early than late HDEC sub-phase (r = -0.54 to -0.66 vs. r = -0.24 to -0.40). Notably, eccentric mean force in DJ40 had large correlations with both DJ20 and DJ40 concentric mean force (r = 0.67 to 0.77), whereas at DJ20 these correlations were small (r = 0.22 to 0.40). Similarly, DJ40 eccentric mean force had a much larger difference between the high and low HDEC groups than DJ20 (d = 1.11 vs. 0.51). These findings suggest DJ RSI from either height may be used as a proxy for HDEC ability, while DJ kinetic analyses should use a higher height to distinguish those with a better capacity to generate eccentric braking forces under increased eccentric loading demands. HIGHLIGHTSPlayers with greater drop jump reactive strength index (RSI) demonstrated superior horizontal deceleration ability.Drop jump RSI had a greater association with the early compared to the late horizontal deceleration sub-phase.Of the drop jump kinetic variables examined, concentric mean force had the largest associations with horizontal deceleration ability.

The Effect of High-Intensity Accelerations and Decelerations on Match Outcome of an Elite English League Two Football Team.

OBJECTIVES: Previous research has highlighted the frequency of high-intensity accelerations and decelerations in elite football. The influence of these actions on match performance outcomes has not been established. The aim of the present study was to identify the influence of high-intensity accelerations and decelerations on match performance outcomes (i.e., win, draw, lost). Comparisons were also made between team and positional high-intensity accelerations and decelerations recorded within the games. METHODS: 26 elite outfield footballers from an elite English Football League (EFL) Two team completed the present study. Global Positioning System (GPS) technology was utilised to quantify high-intensity accelerations and decelerations during 45 games in a competitive season. Magnitude analysis and the effects of results, positions and fixture periods were observed. RESULTS: Significant effects of results, periods and positions were observed (p ≤ 0.05), with the highest outputs observed in games won. Positionally, fullbacks and centre forwards in a 4-3-3 formation exhibited the greatest frequency of high-intensity accelerations and decelerations. Very large differences were observed between the frequency of high-intensity decelerations compared to accelerations in games won (g = 2.37), drawn (g = 2.99) and lost (g = 3.59). The highest team frequencies of high-intensity accelerations (n = 3330) and decelerations (n = 6482) were completed in games won. CONCLUSIONS: The frequency of high-intensity accelerations and decelerations has a significant impact on match performance outcomes in an elite English League Two football team. Consideration needs to be given to specific conditioning and recovery strategies to optimise high-intensity acceleration and deceleration performance in games. Caution should be taken as these findings are representative of one team within the EFL.

Relationships Between Eccentric and Concentric Knee Strength Capacities and Maximal Linear Deceleration Ability in Male Academy Soccer Players.

ABSTRACT: Harper, DJ, Jordan, AR, and Kiely, J. Relationships between eccentric and concentric knee strength capacities and maximal linear deceleration ability in male academy soccer players. J Strength Cond Res 35(2): 465-472, 2021-The purpose of this study was to investigate the relationships between maximal linear deceleration ability, and knee flexor (KF) and knee extensor (KE) strength. Fourteen male academy soccer players completed a 30-m linear sprint, a maximal linear deceleration test, and eccentric and concentric KF and KE contractions in both dominant leg (DL) and nondominant leg (NDL) at slower (60°·s-1) and faster (180°·s-1) angular velocities on an isokinetic dynamometer. Maximal linear deceleration ability was evaluated using distance-to-stop (DEC-DTS) and time-to-stop (DEC-TTS), with isokinetic peak torque representing KF and KE strength capacity. Relationships were established using Pearson's correlation coefficients (r) with magnitude-based inferences used to describe the uncertainty in the correlation. Both concentric KE and KF strength at 180°·s-1 in the NDL had the highest correlations with deceleration ability (r = -0.76 and r = -0.78, respectively). In the DL, concentric KE and KF strength at 180°·s-1 also had very likely large correlations with deceleration ability (r = -0.54 and -0.55, respectively). All correlations between eccentric KF strength and deceleration ability were unclear. At 180°·s-1, correlations between eccentric KE strength and deceleration ability were also unclear; however, at 60°·s-1, both DL (r = -0.63 to -0.64) and NDL (r = -0.54 to -0.55) had very likely large correlations with deceleration ability. These findings provide novel insights into the unilateral KF and KE strength capacities underpinning the ability to decelerate rapidly from high-sprint velocities.

Can Countermovement Jump Neuromuscular Performance Qualities Differentiate Maximal Horizontal Deceleration Ability in Team Sport Athletes?

This investigation aimed to determine the countermovement jump (CMJ) neuromuscular performance (NMP) qualities that differentiate between athletes with high or low horizontal deceleration ability. Twenty-seven male university team sport athletes performed a CMJ on vertical axis force plates and a maximal horizontal deceleration following a 20 m maximal horizontal sprint acceleration. The instantaneous velocity throughout the maximal horizontal deceleration test was measured using a radar device. The deceleration ability was evaluated using the average deceleration (HDEC, m·s-2) and change in momentum-referred to as the horizontal braking impulse (HBI, N·s·kg-1). Participants were dichotomised into high and low HDEC and HBI according to a median-split analysis, and CMJ variables calculated for the overall eccentric, eccentric-deceleration and concentric phases. When horizontal deceleration ability was defined by HDEC, the CMJ concentric (effect size (ES) = 0.95) and eccentric (ES = 0.72) peak forces were the variables with the largest difference between groups. However, when defined using HBI, the largest difference was the concentric (ES = 1.15) and eccentric (ES = -1.00) peak velocities. Only the concentric mean power was significantly different between the high and low groups for both HDEC (ES = 0.85) and HBI (ES = 0.96). These findings show that specific eccentric and concentric NMP qualities may underpin the horizontal deceleration abilities characterised by HDEC and HBI. Specific NMP training interventions may be beneficial to target improvements in either of these measures of horizontal deceleration abilities.

High-Intensity Acceleration and Deceleration Demands in Elite Team Sports Competitive Match Play: A Systematic Review and Meta-Analysis of Observational Studies.

BACKGROUND: The external movement loads imposed on players during competitive team sports are commonly measured using global positioning system devices. Information gleaned from analyses is employed to calibrate physical conditioning and injury prevention strategies with the external loads imposed during match play. Intense accelerations and decelerations are considered particularly important indicators of external load. However, to date, no prior meta-analysis has compared high and very high intensity acceleration and deceleration demands in elite team sports during competitive match play. OBJECTIVE: The objective of this systematic review and meta-analysis was to quantify and compare high and very high intensity acceleration vs. deceleration demands occurring during competitive match play in elite team sport contexts. METHODS: A systematic review of four electronic databases (CINAHL, MEDLINE, SPORTDiscus, Web of Science) was conducted to identify peer-reviewed articles published between January 2010 and April 2018 that had reported higher intensity (> 2.5 m·s-2) accelerations and decelerations concurrently in elite team sports competitive match play. A Boolean search phrase was developed using key words synonymous to team sports (population), acceleration and deceleration (comparators) and match play (outcome). Articles only eligible for meta-analysis were those that reported either or both high (> 2.5 m·s-2) and very high (> 3.5 m·s-2) intensity accelerations and decelerations concurrently using global positioning system devices (sampling rate: ≥ 5 Hz) during elite able-bodied (mean age: ≥ 18 years) team sports competitive match play (match time: ≥ 75%). Separate inverse random-effects meta-analyses were conducted to compare: (1) standardised mean differences (SMDs) in the frequency of high and very high intensity accelerations and decelerations occurring during match play, and (2) SMDs of temporal changes in high and very high intensity accelerations and decelerations across first and second half periods of match play. Using recent guidelines recommended for the collection, processing and reporting of global positioning system data, a checklist was produced to help inform a judgement about the methodological limitations (risk of detection bias) aligned to 'data collection', 'data processing' and 'normative profile' for each eligible study. For each study, each outcome was rated as either 'low', 'unclear' or 'high' risk of bias. RESULTS: A total of 19 studies met the eligibility criteria, comprising seven team sports including American Football (n = 1), Australian Football (n = 2), hockey (n = 1), rugby league (n = 4), rugby sevens (n = 3), rugby union (n = 2) and soccer (n = 6) with a total of 469 male participants (mean age: 18-29 years). Analysis showed only American Football reported a greater frequency of high (SMD = 1.26; 95% confidence interval [CI] 1.06-1.43) and very high (SMD = 0.19; 95% CI - 0.42 to 0.80) intensity accelerations compared to decelerations. All other sports had a greater frequency of high and very high intensity decelerations compared to accelerations, with soccer demonstrating the greatest difference for both the high (SMD = - 1.74; 95% CI - 1.28 to - 2.21) and very high (SMD = - 3.19; 95% CI - 2.05 to - 4.33) intensity categories. When examining the temporal changes from the first to the second half periods of match play, there was a small decrease in both the frequency of high and very high intensity accelerations (SMD = 0.50 and 0.49, respectively) and decelerations (SMD = 0.42 and 0.46, respectively). The greatest risk of bias (40% 'high' risk of bias) observed across studies was in the 'data collection' procedures. The lowest risk of bias (35% 'low' risk of bias) was found in the development of a 'normative profile'. CONCLUSIONS: To ensure that elite players are optimally prepared for the high-intensity accelerations and decelerations imposed during competitive match play, it is imperative that players are exposed to comparable demands under controlled training conditions. The results of this meta-analysis, accordingly, can inform practical training designs. Finally, guidelines and recommendations for conducting future research, using global positioning system devices, are suggested.

Interday Reliability and Usefulness of a Reactive Strength Index Derived From 2 Maximal Rebound Jump Tests.

PURPOSE: To examine the interday reliability and usefulness of a reactive strength index (RSI) derived from a maximal 5-rebound jump test (5max RJT) and a maximal 10-rebound jump test (10/5 RJT). METHODS: Twenty male field-sport athletes (24.5 [3.0] y, 1.78 [0.1] m, 84.9 [5.2] kg) and 15 female participants (21.1 [0.9] y, 1.65 [0.73] m, 62.0 [5.1] kg) performed 2 maximal repetitions of the 5max RJT and the 10/5 RJT on 2 testing days after a specific warm-up. A 1-wk period separated testing days, and these sessions were preceded by a familiarization session. RSI was calculated by dividing jump height (in meters) by contact time (in seconds). The 5max RJT and the 10/5 RJT trial with the highest RSI on each testing day were used for reliability and usefulness analysis. RESULTS: Both tests were deemed reliable for determining RSI for male, female, and pooled male and female cohorts, as the intraclass correlation coefficients were ≥.80 and the coefficient of variation was ≤10%. Only the 5max RJT was rated as "good" at detecting the smallest worthwhile change in performance for female athletes (smallest worthwhile change: 0.10 > typical error: 0.07). The 5max RJT for men and the 10/5 RJT for men and women were rated "good" in detecting a moderate change in performance only. CONCLUSIONS: Both tests are reliable for the determination of RSI, but the usefulness of the tests in detecting the smallest worthwhile change is questionable.

Acute adaptations and subsequent preservation of strength and speed measures following a Nordic hamstring curl intervention: a randomised controlled trial.

This randomised controlled trial investigated changes in eccentric hamstring strength, 10m sprint speed, and change-of-direction (COD) performance immediately post Nordic hamstring curl (NHC) intervention and following a 3-week detraining period. Fourteen male team sports athletes were randomised to a do-as-usual control group (CG; n = 7) or to a NHC intervention group (NHC; n = 7). Isokinetic dynamometry at 180°/s evaluated eccentric hamstring strength immediately post-intervention as the primary outcome measure. Secondary outcomes included 10 m sprint time and COD. Each outcome was measured, pre, immediately post-intervention and following a 3-week detraining period. Immediately post-intervention significant group differences were observed in the NHC group for eccentric hamstring strength (31.81 Nm-1 vs. 6.44 Nm-1, P = 0.001), COD (-0.12 s vs. 0.20 s; P = 0.003) and sprint (- 0.06 s vs. 0.05 s; P = 0.024) performance. Performance improvements were maintained following a detraining period for COD (-0.11 s vs. 0.20 s; P = 0.014) and sprint (-0.05 s vs. 0.03 s, P = 0.031) but not eccentric hamstring strength (15.67 Nm-1 vs. 6.44 Nm-1, P = 0.145) These findings have important implications for training programmes designed to reduce hamstring injury incidence, whilst enhancing physical qualities critical to sport.