Latest research in football - week 36 - 2021

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases. 


Following studies were retrieved for this week:

#1 The Influence of Social Support and Ability Perception on Coping Strategies for Competitive Stress in Soccer Players: The Mediating Role of Cognitive Assessment

Reference: Front Psychol. 2021 May 25;12:554863.  doi: 10.3389/fpsyg.2021.554863. eCollection 2021.

Authors: Zhao Dai, Qiang Liu, Wenhui Ma, Chengwei Yang

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Summary: The aim was to explore the effect of social support and ability perception on stress coping strategies for competitive stress, and to reveal the mediating effects of primary and secondary evaluation, so as to further improve the theoretical model of stress coping in soccer players. A total of 331 male athletes from 22 teams in the Chengdu Middle School Campus Football League were taken as survey samples, and surveys were conducted on their stress experience, social support, ability perception, cognitive assessment, and coping strategies for competition stress. SPSS 21.0 and AMOS 21.0 statistical analysis software were used. Descriptive statistics, correlation analysis, exploratory factor analysis (EFA), and confirmatory factor analysis (CFA) were used to process the obtained data.  Positive primary assessment acted as a full mediator in the relationship between social support and secondary assessments, and negative primary assessment acted as a partial mediator in the relationship between competence perception and secondary assessments; Secondary assessment played a partial mediating role between positive primary assessment and positive coping strategies, and a full mediating role between negative primary assessment and positive coping strategies; Secondary assessments played the mediator neither between social support and a coping strategy for stress nor competence perception and a coping strategy for stress; (4) Positive primary assessment, positive negative assessment, and secondary assessment all had significant positive benefits for positive coping. Still, the impact of positive primary assessment on positive coping was significantly better than negative primary assessment and secondary assessment.  The coping strategy for the competitive stress model proposed by this study has a very good fit for the causal model. It can be used to explain the observed data from soccer players in middle schools. The primary and secondary assessments play different roles in the model. The combination of problem focuses and emotional focus on the positive stress coping strategy is suitable in the field of competitive sports. Still, the relevant research results need to be further explored and verified in the future.



#2 The Efficacy of Heat Acclimatization Pre-World Cup in Female Soccer Players

Reference: Front Sports Act Living. 2021 May 25;3:614370.  doi: 10.3389/fspor.2021.614370. eCollection 2021.

Authors: César M P Meylan, Kimberly Bowman, Trent Stellingwerff, Wendy A Pethick, Joshua Trewin, Michael S Koehle

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Summary: The efficacy of a 14-day field-based heat acclimatization (HA) training camp in 16 international female soccer players was investigated over three phases: phase 1: 8 days moderate HA (22. 1°C); phase 2: 6 days high HA (34.5°C); and phase 3: 11 days of post-HA (18.2°C), with heart rate (HR), training load, core temp (T c), and perceptual ratings recorded throughout. The changes from baseline (day-16) in (i) plasma volume (PV), (ii) HR during a submaximal running test (HRex) and HR recovery (HRR), and (iii) pre-to-post phase 2 (days 8-13) in a 4v4 small-sided soccer game (4V4SSG) performance were assessed. Due to high variability, PV non-significantly increased by 7.4% ± 3.6% [standardized effect (SE) = 0.63; p = 0.130] from the start of phase 1 to the end of phase 2. Resting T c dropped significantly [p < 0.001 by -0.47 ± 0.29°C (SE = -2.45)], from day 1 to day 14. Submaximal running HRR increased over phase 2 (HRR; SE = 0.53) after having decreased significantly from baseline (p = 0.03). While not significant (p > 0.05), the greatest HR improvements from baseline were delayed, occurring 11 days into phase 3 (HRex, SE = -0.42; HRR, SE = 0.37). The 4v4SSG revealed a moderate reduction in HRex (SE = -0.32; p = 0.007) and a large increase in HRR (SE = 1.27; p < 0.001) from pre-to-post phase 2. Field-based HA can induce physiological changes beneficial to soccer performance in temperate and hot conditions in elite females, and the submaximal running test appears to show HRex responses induced by HA up to 2 weeks following heat exposure.



#3 Age at Nomination Among Soccer Players Nominated for Major International Individual Awards: A Better Proxy for the Age of Peak Individual Soccer Performance?

Reference: Front Psychol. 2021 May 24;12:661523. doi: 10.3389/fpsyg.2021.661523. eCollection 2021.

Authors: Geir Oterhals, Håvard Lorås, Arve Vorland Pedersen

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Summary: Individual soccer performance is notoriously difficult to measure due to the many contributing sub-variables and the variety of contexts within which skills must be utilised. Furthermore, performance differs across rather specialised playing positions. In research, soccer performance is often measured using combinations of, or even single, sub-variables. All too often these variables have not been validated against actual performance. Another approach is the use of proxies. In sports research, the age of athletes when winning championship medals has been used as a proxy for determining their age of peak performance. In soccer, studies have used the average age of players in top European leagues or in the Champions League to determine the age of individual peak performance. Such approaches have methodological shortcomings and may underestimate the peak. We explore the use of a new proxy, the age at nomination for major individual awards, to determine the average age at peak individual soccer performance. A total of 1,981 players nominated for major awards from 1956 to 2019 were included, and a subset of 653 retired players was extracted, thus including players' complete careers. Players' average ages at nomination, at their first nomination, and at their last ever nomination were calculated, and differences across playing positions were calculated together with changes over time in the average age at peak. Based on our proxy, the age of individual peak soccer performance occurs around 27-28 years, varying across playing positions from 26 to 31 years. A player's first peak, on average, seems to coincide with known peaks of physiological variables; their last-ever peak occurs long after physiological performance has started to decline, indicating that the decline can be compensated for by other variables. The peak age is higher than previously reported for soccer; however, it is similar to those in other team ball sports. The average age at peak performance has increased over time, especially in the last decade. Our approach of using proxies for unearthing information about hidden features of otherwise immeasurable complex performance appears to be viable, and such proxies may be used to validate sub-variables that measure complex behaviour.



#4 Construct validity of age at predicted adult height and BAUS skeletal age to assess biological maturity in academy soccer

Reference: Ann Hum Biol. 2021 Mar;48(2):101-109.  doi: 10.1080/03014460.2021.1913224.

Authors: Ludwig Ruf, Sean Cumming, Sascha Härtel, Anne Hecksteden, Barry Drust, Tim Meyer

Summary: The assessment of biological maturity status plays an important role in talent identification and development programs. The aim was to compare age at predicted adult height and BAUS skeletal age as indicators of biological maturity status in youth soccer players using a construct-validity approach. Participants were 114 players from the U12 to U17 age groups of a professional youth soccer academy. Maturity status was determined via percentage of predicted adult height based upon the Khamis-Roche method (somatic maturity) and assessed via the SonicBone BAUSTM system (skeletal maturity). Convergent and known-groups validity were evaluated between maturity assessment methods and by comparing maturity-related selection biases across age groups. Although maturity status indicators were largely interrelated (r = .94, 95%CL 0.91-0.96), concordance (κ = 0.31 to 0.39) and Spearman's rank-order correlations (ρ = 0.45-0.52) of classification methods were moderate. A selection bias towards early maturing players emerged in the U14 age group which remained relatively consistent through to the U17 age group. Results confirm the construct-validity of both methods to assess biological maturity status although further validation relative to established indicators of biological maturity is needed. Furthermore, caution is also warranted when interpreting maturity status classification methods interchangeably given the poor concordance between classification methods.



#5 Toward Improved Triadic Functioning: Exploring the Interactions and Adaptations of Coaches, Parents and Athletes in Professional Academy Soccer Through the Adversity of COVID-19

Reference: Front Psychol. 2021 May 19;12:609631.  doi: 10.3389/fpsyg.2021.609631. eCollection 2021.

Authors: James Maurice, Tracey J Devonport, Camilla J Knight

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Summary: On March 23rd, 2020, elite soccer academies in the UK closed in compliance with the government enforced lockdown intended to contain the COVID-19 pandemic. This forced parents, players, and coaches to reconsider how they interacted with, and supported, one another. The aims of the present study were (a) to explore the perceptions of players, parents, and coaches (i.e., the athletic triangle) regarding how they interacted and collaborated with one another during the COVID-19 pandemic to support wellbeing and performance, and; (b) to identify opportunities to enhance workings of those within the athletic triangle resulting from adaptions made following enforced lockdown. Using an interpretive description methodology, semi-structured interviews were conducted with five coaches, six players, and six parents from an English elite academy soccer club. Interviews were analyzed using thematic analysis. Findings highlighted (a) the importance of support and the different means of communication used between members of the athletic triangle to facilitate such support; (b) the increased understanding of each member of the athletic triangle, leading to enhanced relationships, and; (c) how members of the athletic triangle adapted practice to facilitate relationship development during the pandemic and beyond. The identification of these considerations has implications for coach and parent education initiatives to allow for optimal functioning of the athletic triangle as elite academy soccer clubs return from lockdown. These include (a) the importance of continued communication between coach, athlete and parent; (b) increasing understanding of each individual within the athletic triangle; and (c) utilizing key interpersonal and technological skills learnt during the lockdown to further facilitate engagement within the athletic triangle.



#6 Post-exercise Recovery Methods Focus on Young Soccer Players: A Systematic Review

Reference: Front Physiol. 2021 May 20;12:505149. doi: 10.3389/fphys.2021.505149. eCollection 2021.

Authors: Julio Calleja-González, Juan Mielgo-Ayuso, Álvaro Miguel-Ortega, Diego Marqués-Jiménez, Miguel Del Valle, Sergej M Ostojic, Jaime Sampaio, Nicolás Terrados, Ignacio Refoyo

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Summary: Prescription of post-match or post-training recovery strategies in young soccer players is a key point to optimize soccer performance. Considering that the effectiveness of recovery strategies may present interindividual variability, scientific evidence-based recovery methods and protocols used in adults are possibly not applicable to young soccer players. Therefore, the current systematic review primarily aimed to present a critical appraisal and summary of the original research articles that have evaluated the effectiveness of recovery strategies in young male soccer players and to provide sufficient knowledge regarding the effectiveness of the recovery methods and strategies. A structured search was carried out following the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines until November 31, 2020, using the next data bases: WOS, PubMed, Cochrane Library, Evidence Database (PEDro), Evidence Based Medicine (EBM) Search review, EMBASE, and Scopus. There were no filters applied.  A total of 638 articles were obtained in the initial search. After the inclusion and exclusion criteria, the final sample was 10 articles focusing on recovery in young male players. Neuromuscular performance can be recovered using WVB but not with SS, and water immersion protocols may also be useful, but their positive effects are not significant, and it is unable to distinguish the best water immersion method; match running performance maintenance may be achieved using water immersion protocols but no other recovery methods have been investigated; EIMD and inflammatory responses could be positively affected when water immersion and AR are applied, although SS seems to be ineffective; perceptual responses also seem to be better with CWI and WVB, but contradictory results have been found when AR is applied, and SS had no positive impact. Finally, it is important to consider that AR strategies may modify HR response and soccer-specific performance.



#7 Soccer player activity prediction model using an internet of things-assisted wearable system

Reference: Technol Health Care. 2021 May 27.  doi: 10.3233/THC-213010. Online ahead of print.

Authors: Lei Wu, Juan Wang, Long Jin, K Marimuthu

Summary: Soccer is one of the world's most successful sports with several players. Quality player's activity management is a tough job for administrators to consider in the Internet of Things (IoT) platform. Candidates need to predict the position, intensity, and path of the shot to look back on their results and determine the stronger against low shot and blocker capacities. In this paper, the IoT-assisted wearable device for activity prediction (IoT-WAP) model has been proposed for predicting the activity of soccer players. The accelerometer built wearable devices formulates the impacts of multiple target attempts from the prevailing foot activity model that reflect a soccer player's characteristics. The deep learning technique is developed to predict players' various actions for identifying multiple targets from the differentiated input data compared to conventional strategies. The Artificial Neural Network determines a football athlete's total abilities based on football activities like transfer, kick, run, sprint, and dribbling. The experimental results show that the suggested system has been validated from football datasets and enhances the accuracy ratio of 97.63%, a sensitivity ratio of 96.32%, and a specificity ratio of 93.33% to predict soccer players' various activities.



#8 Soccer, concussions, and safety: Perceptions of parents of youth soccer participants

Reference: J Safety Res. 2021 Jun;77:255-262.  doi: 10.1016/j.jsr.2021.03.008. Epub 2021 Mar 29.

Authors: Sungwon Kim, Daniel P Connaughton

Summary: The rate of concussions in youth soccer is among the highest of all youth sports. Parents play an important role in caring for their children and making decisions regarding whether they should participate in a sport, such as soccer, where concussions are well known. This study examined parental perceptions regarding: (a) coaches' role in concussion management, (b) heading restriction policies, and (c) overall concussion risk and participation issues. Online surveys were completed by 419 parents of youth soccer players who participated in the largest U.S. youth soccer programs nationwide. Findings indicated 44.5% of the respondents had considered keeping their children from playing organized soccer and 47.2% were concerned about a potential decline in youth soccer participation due to concussions. Nearly 69% of responding parents agreed that heading should be banned for participants 10 years old or younger, while 56.5% thought heading should not be limited for participants 13 or older. Only 35% of parents were very confident about their child's coach's ability to properly identify concussions and remove those suspected of a concussion from play. Parents' socioeconomic status (SES), soccer coaching and playing experience, and previous history of concussion(s) were key predictors of greater perceived risk about concussions. Findings from this study shed light on parents' perceptions about concussions and related safety issues in youth soccer. Understanding what parents believe about concussions is vital to preserve youth soccer participation and can be used to strengthen education and policies that promote a safer environment for youth sport participants. Practical Applications: Youth soccer coaches can benefit from stronger, comprehensive educational efforts at the league/club level. Additionally, parents of youth athletes who are in the lower SES communities should be targeted to receive concussion safety information and/or interventions that would improve their knowledge, attitude, and practices regarding concussion safety.



#9 Effects of 14-weeks betaine supplementation on pro-inflammatory cytokines and hematology status in professional youth soccer players during a competition season: a double blind, randomized, placebo-controlled trial 

Reference: Soc Sports Nutr. 2021 Jun 5;18(1):42.  doi: 10.1186/s12970-021-00441-5.

Authors: Hadi Nobari, Jason M Cholewa, Jorge Pérez-Gómez, Alfonso Castillo-Rodríguez

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Summary: Systemic elevations in pro-inflammatory cytokines are a marker of non-functional over reaching, and betaine has been shown to reduce the secretion of pro-inflammatory cytokines in vitro. The aim of this study was to investigate the effects of betaine supplementation on tumor necrosis factor alpha (TNF-α), interleukins-1 beta (IL-1β), - 6 (IL-6) and the complete blood cell (CBC) count in professional youth soccer players during a competitive season. Twenty-nine soccer players (age, 15.5 ± 0.3 years) were randomly divided into two groups based on playing position: betaine group (BG, n = 14, 2 g/day) or placebo group (PG, n = 15). During the 14-week period, training load was matched and well-being indicators were monitored daily. The aforementioned cytokines and CBC were assessed at pre- (P1), mid- (P2), and post- (P3) season. Significant (p < 0.05) group x time interactions were found for TNF-α, IL-1β, and IL-6. These variables were lower in the BG at P2 and P3 compared to P1, while IL-1β was greater in the PG at P3 compared to P1 (p = 0.033). The CBC count analysis showed there was significant group by time interactions for white blood cells (WBC), red blood cells (RBC), hemoglobin (Hb), and mean corpuscular hemoglobin concentration (MCHC). WBC demonstrated increases at P3 compared to P2 in PG (p = 0.034); RBC was less at P3 compared to P1 in BG (p = 0.020); Hb was greater at P2 compared to P1, whilst it was less at P3 compared to P3 for both groups. MCHC was greater at P3 and P2 compared to P1 in BG, whereas MCHC was significantly lower at P3 compared to P2 in the PG (p = 0.003). The results confirmed that 14 weeks of betaine supplementation prevented an increase in pro-inflammatory cytokines and WBC counts. It seems that betaine supplementation may be a useful nutritional strategy to regulate the immune response during a fatiguing soccer season.



#10 Assessment of Muscle Volume Using Magnetic Resonance Imaging (MRI) in Football Players after Hamstring Injuries

Reference: Eur J Sport Sci. 2021 Jun 10;1-17.  doi: 10.1080/17461391.2021.1942226. Online ahead of print.

Authors: Nils Mühlenfeld MD, Ida Bo Steendahl, Daniel P Berthold MD, Tim Meyer MD, Thomas Hauser MD, Nils Wagner MD, Anna-Lena Sander MD, Ingo Marzi MD, Benjamin Kaltenbach MD, Ibrahim Yel MD, Thomas Vogl MD, Katrin Eichler MD

Summary: Muscle injuries of the hamstrings are among the most frequent in football and a main cause for significant time away from training and competition. The purpose of this study was to prospectively evaluate the loss of muscle volume in recreational football players three and six weeks after initial trauma. We hypothesized that significant muscle volume loss occurs within 6 weeks after the initial injury event. Twenty recreational football players (mean-age=25 ± 4years; mean-height=181 ± 8cm; mean-weight=81 ± 10kg) with type3a (minor partial muscle tear) and type3b (moderate partial muscle tear) injuries were included. Muscle volume was determined using established methods for the hamstrings and the quadriceps femoris muscle within 3 days and after 3 and 6 weeks following the initial injury. The injured hamstrings lost 6.5% (mean=64cm3(95%CI=31-98cm3),p<0.001), the healthy hamstrings lost 2.1% (mean=21cm3(3-44cm3),p=0.096) of muscle volume after six weeks. The quadriceps in the injured leg lost 3.8% (mean=78cm3(51-104cm3),p<0.001) and 4.5% (83cm3(45-121cm3),p<0.001) in the healthy leg. Muscle volume loss inversely correlated with activity levels in the healthy leg for the quadriceps (r=0.96(0.90-0.98);R2=0.92;p<0.001) and the hamstrings (r=0.72(0.40-0.88);R2=0.51;p<0.001), as well as the quadriceps in the injured leg (r=0.70(0.37-0.87);R2=0.49;p<0.001), but not the injured hamstrings. Muscle volume ratio of hamstrings to quadriceps in the control limb was 0.52 ± 0.06 and 0.53 ± 0.06 in the injured leg. The rehabilitation period of six weeks did not have a relevant negative or a positive effect on ratios. Significant muscle volume loss in the upper thigh occurs in recreational soccer players within three, and within six weeks after a hamstring injury and lies between 2 and 7%.



#11 Ticks on the turf: investigating the presence of ixodid ticks on and around football fields in Germany

Reference: Exp Appl Acarol. 2021 Jun 9.  doi: 10.1007/s10493-021-00628-0. Online ahead of print.

Authors: Olaf Kahl, Daniel Kämmer, Ingrid Bulling, Martin Komorek, Christof von Eiff, Claudius Malerczyk

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Summary: Ixodes ricinus is the most abundant tick species and an important vector of pathogens in Germany and in large parts of Europe. A few other ixodid tick species, e.g., Dermacentor reticulatus, may also be of eco-epidemiological relevance. As ticks are not only found in natural but also in suburban areas (parks, gardens), the present study investigated whether ticks occur on and near football grounds thus posing a potential risk to players and visitors. Thirty-two football grounds from all 16 German federal states were selected, mainly situated adjacent to a green area (forest, park). Ticks were collected by the conventional flagging method in spring 2018, and nymphs and adults were counted and morphologically determined. Altogether 807 nymphal and adult ticks were collected from 29 football grounds: 714 I. ricinus, 64 Ixodes inopinatus, 2 Ixodes frontalis, 24 Ixodes sp. ticks, and 3 D. reticulatus. Ixodes inopinatus was found in 13 out of 16 German states. Three ticks were even found on the turf of two football fields. It can be concluded that ticks occur quite frequently and sometimes in high abundance near football grounds situated close or adjacent to a forest or a park.



#12 Finding Neymar: The Role of Colour in the Detection and Discrimination of Football Kits

Reference: Perception. 2021 Jun 9;3010066211019370.  doi: 10.1177/03010066211019370. Online ahead of print.

Authors: Liam Burnell, Peter Thompson

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Summary: Association Football (hereafter football) is a fast-moving sport in which rapid decisions need to be made; where are other players, are they on my team? Two experiments investigated how kit variations affect the search of teammates. Experiment 1 confirmed that discriminability is slower when playing in crossed kits (e.g., red shirts-blue shorts vs. blue shirts-red shorts), versus uniform kits (e.g., all red vs. all blue). Experiment 2 found that there is significant confusion when both teams wear the same-coloured shorts. Based on these findings, we suggest changes to the Laws of the game concerning kit colours.



#13 Load Monitoring Practice in European Elite Football and the Impact of Club Culture and Financial Resources

Reference: Front Sports Act Living. 2021 May 20;3:679824. doi: 10.3389/fspor.2021.679824. eCollection 2021.

Authors: Kobe C Houtmeyers, Jos Vanrenterghem, Arne Jaspers, Ludwig Ruf, Michel S Brink, Werner F Helsen

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Summary: Load monitoring is considered important to manage the physical training process in team sports such as Association Football. Previous studies have described the load monitoring practices of elite English football clubs and clubs with an established sports-science department. An examination of a broader international sample is currently not available. In addition, previous research has suggested factors that may improve the implementation of load monitoring practices, such as a strong club belief on the benefit of evidence-based practice (EBP) and high club financial resources. However, no study has examined yet the actual impact of these factors on the monitoring practices. Therefore, this study aims (1) to provide an overview of load monitoring practices in European elite football and (2) to provide insight into the differences in implementation between clubs by examining the impact of the club beliefs on the benefit of EBP and the club financial resources. An online survey, consisting of multiple choice and Likert scale questions, was distributed among sports-science and sports-medicine staff (n = 99, 50% response rate). Information was asked about the types of data collected, collection purposes, analysis methods, and staff involvement. The results indicated that external load data (e.g., global navigation satellite system, accelerometer…) was collected the most whilst respondents also indicated to collect internal load (e.g., heart rate, rating of perceived exertion…) and training outcome data (e.g., aerobic fitness, neuromuscular fatigue…) for multiple purposes. Considerable diversity in data analysis was observed suggesting that analysis is often limited to reporting the gathered data. Sports-science staff were responsible for data collection and analysis. Other staff were involved in data discussion to share decision-making. These practices were positively impacted by a stronger club belief on the benefit of EBP and greater financial resources. Creating an organizational culture, characterized by a strong belief on the benefit of EBP, is important to increase the impact of load monitoring. However, the actual potential may still be largely determined by financial resources. High-level clubs could therefore play a leading role in generating and sharing knowledge to improve training practices and player health.



#14 Reliability, validity, and maturation-related differences of frontal and sagittal plane landing kinematic measures during drop jump and tuck jump screening tests in male youth soccer players

Reference: Phys Ther Sport. 2021 May 28;50:206-216. doi: 10.1016/j.ptsp.2021.05.009. Online ahead of print.

Authors: Francisco Javier Robles-Palazón, Iñaki Ruiz-Pérez, Jon L Oliver, Francisco Ayala, Pilar Sainz de Baranda

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Summary: The aim was to determine the inter-rater and intra-rater reliability of frontal and sagittal plane landing kinematic measures during drop jump (DVJ) and tuck jump (TJA) tasks in male youth soccer players, to assess the concurrent validity between DVJ and TJA tests, and to evaluate the ability of both tasks to detect differences between players' stage of maturation. 223 male youth soccer players participated. Frontal plane knee projection angles (FPPA), and hip (HF), knee (KF) and ankle (AF) flexion angles at initial contact (IC) and peak flexion (PF) (i.e., the deepest landing position) in the sagittal plane were assessed. Good-to-excellent inter- and intra-rater reliability (ICC > 0.75; TEMST < 0.3; CVTE < 5%) for the FPPA, HF and KF during DVJ and TJA tasks were found. A low concurrent validity between DVJ and TJA measures was reported. Differences by maturity status (BF10 > 10; error < 10; δ > 0.6) were only identified for the TJA. Pre-PHV group reported higher FPPA, HF-IC, HF-PF, and KF-IC values, as well as lower AF-IC than post-PHV. Pre-PHV also displayed greater HF-IC and KF-IC than circa-PHV group. Although both tests are reliable, the TJA might be viewed as a more informative tool given it shows greater FPPA and can also detect differences by maturity status.


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