Latest research in football - week 2 - 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 Change of direction asymmetry across different age categories in youth soccer

Reference: PeerJ. 2020 Jul 27;8:e9486. doi: 10.7717/peerj.9486. eCollection 2020. 

Authors: Athos Trecroci, Alessio Rossi, Thomas Dos'Santos, Damiano Formenti, Luca Cavaggioni, Stefano Longo, F Marcello Iaia, Giampietro Alberti  

Download link:

Summary: In youth, the development of change of direction (COD) and sprint performance is a key component for successfully competing in soccer across age. During a COD, the presence of directional asymmetries may be detrimental due to the unpredictable nature of the sport. Therefore, the aims of the study were to investigate asymmetries in COD ability and to examine the differences in COD and sprint performance across age in young soccer players. Sixty-eight sub-elite soccer players of different age categories (U18, U17, U16, U15) were tested on a 10-m linear sprint test and 90°COD (5-m entry and exit) test in both directions. Asymmetric index (AI) of COD deficit was obtained for dominant (fastest) and non-dominant directions (slowest). The results showed that U16 were more asymmetrical than U18, U17, and U15 from large to moderate effects. The sprint time improved linearly across age with U18 and U15 displaying the fastest and slowest 10-m sprint performance (p < 0.01), respectively. Moreover, COD ability measured by COD deficit did not change across age (p > 0.05). Given the results of this study, practitioners are encouraged to assess asymmetries between dominant and non-dominant directions rather than solely players' COD ability in young soccer players. 



#2 Normative data for hip strength, flexibility and stiffness in male soccer athletes and effect of age and limb dominance

Reference: Phys Ther Sport. 2020 Nov 5;47:53-58. doi: 10.1016/j.ptsp.2020.11.022. Online ahead of print. 

Authors: Juliana M Ocarino, Renan A Resende, Natalia F N Bittencourt, Ricardo V A Correa, Luciana M Mendonça, Guilherme F Reis, Thales R Souza, Sergio T Fonseca

Download link:

Summary: The objective was to establish normative data for hip strength, flexibility, and stiffness in male soccer athletes and to investigate the effect of age and limb dominance on these variables. A total of 293 asymptomatic male soccer athletes were assessed. Elite youth players aged 15-17 years and professional adult players aged 18-29 years old. Rectus femoris, iliopsoas, hamstring muscle flexibility, passive hip stiffness, and isometric hip strength were measured using a goniometer, inclinometer, and handheld dynamometer, respectively. escriptive and mixed analyses of variance were used as statistical procedures. The dominant limb had lower iliopsoas (P = 0.010) and rectus femoris (P = 0.003) flexibility and higher external rotators torque compared to the non-dominant limb (P = 0.006) in both age groups. In adult athletes, the dominant limb had lower hip stiffness than the non-dominant limb (P = 0.002). Adults had higher hip external rotator torque than younger athletes (P < 0.0001). No differences were observed for hamstrings flexibility and hip extensors torque. This study provided normative data of hip strength, flexibility, and stiffness for youth and adult male soccer athletes. In addition, there were no clinically relevant inter-limb differences. 



#3 Change-of-Direction Performance in Elite Soccer Players: Preliminary Analysis According to Their Playing Positions

Reference: Int J Environ Res Public Health. 2020 Nov 12;17(22):E8360. doi: 10.3390/ijerph17228360. 

Authors: Dorsaf Sariati, Raouf Hammami, Mokhtar Chtara, Alessandro Zagatto, Daniel Boullosa, Cain C T Clark, Anthony C Hackney, Urs Granacher, Nizar Souissi, Hassane Zouhal 

Download link:

Summary: Our objective was to examine the relationship between change of direction (CoD) performance, with (CoDb), and without the ball (CoDwb), and selected measures of physical fitness (jump performance, speed, balance) in elite soccer players, according to players' positions. Forty elite male soccer players performed the change-of-direction and acceleration test (CODAT) with (CODATb), and without the ball (CODATwb), 5- and 20-m sprint tests, the 5-jump test (5JT), and the Y-balance test (YBT). Analyses of the whole sample showed significant correlations between all CODAT measures (CODATwb and CODATb, respectively) and sprint 5-m (r = 0.72, p < 0.001; r = 0.52, p < 0.01), sprint 20-m (r = 0.54, p < 0.03; r = 0.45, p < 0.05), jump (r = -0.62, p < 0.01; r = -0.64, p < 0.01) and balance (r = -0.50, p < 0.01; r = -0.83, p < 0.001) performances. Correlations were significantly different between player positions (defender, midfielder and striker). When examining the entire sample, the single best predictor of CODATwb was performance in the 5-m test with an explained variance of 52% (p < 0.001). For CODATb, the Y-balance performance explained 68% of the variance of performance (p < 0.001). In conclusion, soccer coaches and fitness trainers are advised to improve players' CoD using neuromuscular training that mimic crucial match actions. Meanwhile, CoD testing and training should be designed in line with the demands of playing position. 



#4 Correlation between Pupilometer and the Vestibular/Ocular Motor Screening in Division I Female Collegiate Soccer Athletes 

Reference: Neurology. 2020 Nov 17;95(20 Supplement 1):S2-S3. doi: 10.1212/01.wnl.0000719880.39493.e2. 

Authors: John Heick, Lauren Entsler 

Summary: The objective of this study was to explore the correlation between pupilometer and Vestibular Ocular Motor Screening on Division 1 female collegiate soccer players. Concussions are one of the most prevalent acquired neurologic conditions occurring in young adults with an estimated 1.6 to 3.8 million head injuries. Concussions are assessed with a variety of measures such as the Vestibular/Ocular Motor Screen (VOMS). Visual disruptions are frequently observed following concussion with an estimated 65%-90% of patients complaining of visual disruption. A pupilometer measures objective pupillary activity such as pupil constriction latency, diameter, speed of constriction and dilation, and reflex recovery time. This prospective study recruited Division I female soccer athletes aged 18 to 28. Athletes were excluded if they had a lower extremity injury in the past 3 months that caused the athlete to miss more than 1 day of practice, had a history of a head injury in the past 6 months, or were diagnosed with a visual, vestibular, or balance disorder. Twenty-six female Division I collegiate soccer athletes (mean age of 20.46 ± 2.36 years) completed baseline pupilometer and VOMS testing. Three of the twenty-six had borderline pupillary index scores and five had abnormal VOMS scores at baseline. One athlete had a concussion during the 2019 season and at retest, pupilometer results were normal but two VOMS components were abnormal. The pupilometer and VOMS were poorly correlated. While the neurocognitive consequences of participation in soccer is becoming uncertain, the current study suggests that 11% of female soccer athletes without a diagnosis of a concussion had abnormal pupilometer results and 19% had abnormal VOMS scores. Evidence is mounting that repetitive hits to the head can lead to potential neurocognitive impairments. Future studies are warranted to examine baseline measures across age in female soccer athletes. 



#5 Characteristics of Potential Concussive Events in Three Elite Soccer Tournaments

Reference: Neurology. 2020 Nov 17;95(20 Supplement 1):S10. doi: 10.1212/01.wnl.0000719960.65926.65. 

Author: Nicholas Charles Armstrong 

Summary: The aim was to determine the characteristics of potential concussive events (PCEs) in professional soccer. Soccer players are at risk of sustaining sport-related concussions. The acute and chronic effects of concussive and sub-concussive impacts to the head are potentially detrimental to both players and healthcare systems worldwide. Identifying patterns in the nature and characteristics of these injuries may help sporting organizations understand how to reduce the burden of sport-related brain injuries. The present study analyzed the 2014 and 2018 FIFA World Cups (WC), and the 2016 Euro Cup (EC). Between the three tournaments, a total of 179 professional international matches were played. The researchers collected data pertaining to PCEs including mechanism of injury, location on the head, and number of concussion symptoms. A total of 237 PCEs were identified over 179 matches (1.32 per match, 40.12 per 1,000 hours of exposure). The most common mechanism of injury was elbow-to-head (n = 68, 28.7%), followed by head-to-head (n = 55, 23.2%) and hand/fist-to-head (n = 36, 15.2%). The impact locations most frequently affected were the frontal region (n = 54, 22.8%), followed by the parietal and occipital regions (n = 47, 19.8%), temporal region (n = 46, 19.4%), anterior surface of the mandible (n = 43, 18.1%), and nasal/maxilla region (n = 39, 16.5%). Most players (n = 210, 88.6%) showed two or more signs of concussion. Our study intended to investigate the prevalence, identification and nature of PCEs in professional soccer tournaments. Our findings indicate that different contexts and mechanisms of head contact and contact to different regions of the head can be associated with varying signs of concussion. Ultimately, promoting and enforcing enhanced concussion prevention initiatives in elite soccer can have an impact at all levels of the game. These findings may assist physicians, athletes, soccer organizations and other stakeholders worldwide with the care of injured players and the implementation of new rules and regulations to better protect their players. 



#6 Concussion among soccer players in the 2017 Brazilian championship - the gap between protocol and medical practice 

Reference: Concussion. 2020 Oct 28;5(4):CNC83. doi: 10.2217/cnc-2020-0015. 

Authors: Cármine Porcelli Salvarani, Lucas Ribeiro de Medeiros, Fernando Henrique Sapatero, Diego Ciotta de Castro, Vinícius Simon Tomazini, Leonardo Henrique Micheletti Sotocorno, Paulo Sérgio Teixeira da Costa, Bruno Bueno Pimenta, Diego Almeida de Oliveira, Eduardo Almeida Dias, Eduardo Vinícius Colman da Silva

Download link:

Summary: The present study aims to report traumatic brain injury (TBI) among soccer players in the 2017 Brazilian Soccer Championship and discuss the protocols for concussion evaluation. This is an observational study utilizing video analysis of 380 matches. TBI was considered as any event in which one or more soccer player(s) had a head trauma. For potential concussion diagnosis, we analyzed players with one of the following signs: slowness to get up, disorientation, motor incoordination, loss of consciousness, head clutching and impact seizure. There were 374 TBIs in total. The average time for medical assessment was 1'35". 13 players had concussion with an average time of 3'19″ for medical evaluation. Four players were replaced after having a concussion. There is a gap between concussion protocols and medical practices in Brazilian elite soccer. Further discussion about soccer replacement rules are imperative. 



#7 The acute effect of wearable resistance load and placement upon change of direction performance in soccer players

Reference: PLoS One. 2020 Nov 18;15(11):e0242493. doi: 10.1371/journal.pone.0242493. eCollection 2020. 

Authors: Johannes Istvan Rydså, Roland van den Tillaar

Download link:

Summary: The aim of the study was to examine the acute effect of different lower limb wearable resistance on placement (shank vs thigh) and various loads (1-5% of body mass) upon change of direction (COD) ability. Twelve male soccer players (age: 23.3 ± 2.5 years; height: 179.2 ± 7.4 cm; body mass: 78.3 ± 7.1 kg) performed a change of direction test with different additional loads fixed on either the shank or thigh. Measurement consisted of total time, 90° and 45° split times. large effects of the different wearable resistance placement (p<0.05) and load (p<0.001) were found for total and split change of direction time performance. Change of direction times were higher with shank loading compared with thigh loading. It was concluded that lower limb wearable resistance loading with different loads had an acute effect upon change of direction performance in male soccer players. Furthermore, that distal placement (shank vs thigh) with similar body mass load had a larger effect upon COD performance. 



#8 The Effects of a Soccer-Specific Fitness Test on Eccentric Knee Flexor Strength

Reference: J Sport Rehabil. 2020 Nov 20;1-5. doi: 10.1123/jsr.2019-0532. Online ahead of print. 

Authors: Christopher Michael Brogden, Lewis Gough, Adam Kelly 

Summary: Physiological fitness testing, such as the Yo-Yo Intermittent Recovery Test (YYIR) is a key requirement of the Elite Player Performance Plan, introduced by the English Premier League. Eccentric hamstring strength has been identified as a risk factor for hamstring injuries in soccer players, with fatigue highlighted to further exasperate this issue. The aim of the current study was to examine the effect of the YYIR level 1 (YYIR1) on eccentric knee flexor strength assessed using the NordBord in youth soccer players. A total of 67 male academy soccer players (age = 16.58 [0.57] y; height = 175.45 [5.85] cm; mass = 66.30 [8.21] kg) volunteered to participate in the current study during the English competitive soccer season. Participants conducted eccentric hamstring strength assessments using the NordBord prior to and immediately postcompletion of the YYIR1, with outcome measures of peak force and peak force relative to body mass recorded. Paired t tests highlighted increased absolute eccentric knee flexor strength values (P < .001) immediately post-YYIR1 for both the dominant and nondominant limbs, with the same trend (P < .001) observed for eccentric strength relative to body mass. The results of this study indicate that the YYIR1 does not induce eccentric knee flexor fatigue and as such is not a valid assessment method to assess the effects of fatigue on hamstring function. However, results do suggest that the NordBord may be considered a viable and more accessible alternative to detect pre-post fitness test/fatigue protocol differences in eccentric knee flexor peak strength while working in the field. 



#9 Relative age-related differences between different competitive levels and field positions in young soccer players

Reference: Res Sports Med. 2020 Nov 26;1-11. doi: 10.1080/15438627.2020.1853540. Online ahead of print. 

Authors: I Peña-González, A Javaloyes, J M Sarabia, M Moya-Ramón

Summary: The aims of this study were to report the relative age effect in different competitive levels and field positions and to analyse the differences within and between different competitive levels and field positions. Data for 203 young soccer players (14.2 ± 1.1 years) included anthropometrics and physical performance (Countermovement jump [CMJ], 30-m sprint, T-test and Yo-Yo IR1). Their competitive level and their field position were registered. The percentage of relative older players (1stHY) was higher in the better competitive levels (L1: 80.6%, p <.001; L2: 68.2%, p <.001 and L3: 58.5%, p <.01), but it was similar between field positions (DF: 68.1%, p <.001; MF: 69.6%, p <.001 and FW: 67.2%, p <.001). Anthropometrical and physical performance differences were found between players of different competitive levels but not between relative older and younger players in each competitive level and field position. The relative age effect is higher in the better competitive levels. Anthropometrical and physical performance differences between players are not due to the relative age but to the level of competition. Relatively older players do not seem to be more likely to be selected for specific field positions. The causes of relative age effect need more research. 



#10 Lower Extremity Movement Quality Does Not Moderate Internal Training Load Response of Male Collegiate Soccer Athletes

Reference: J Athl Train. 2020 Nov 25. doi: 10.4085/1062-6050-0322.20. Online ahead of print. 

Authors: Tara A Condon Ms Atc, Timothy Eckard, Alain J Aguilar, Barnett S Frank, Darin A Padua, Erik A Wikstrom

Summary: Training load and movement quality are associated with injury risk in athletes. Given these associations, it is important to understand how movement quality may moderate training load so that appropriate prevention strategies be employed. The aim was to determine how absolute and relative internal training load change over the course of a men's NCAA soccer season, and determine how movement quality, assessed using the Landing Error Scoring System (LESS), moderates relative internal training load. One NCAA Division I male collegiate soccer team was recruited and followed over two consecutive seasons. Fifty-two athletes (height = 1.81 ± .06 m, mass = 75.74 ± 6.64 kg, age = 19.71 ± 1.30 years) consented to participate and forty six met the criteria to be included in the final statistical analysis. Daily absolute internal training load was tracked over the course of two seasons using a rated perceived exertion scale and time which were subsequently used to calculate absolute and relative internal training loads. Movement quality was assessed using the LESS and categorized participants as poor movers (LESS >5) and good movers (LESS <4). The 46 athletes included in the final analysis included 29 poor movers and 17good movers. Absolute (p < 0.001) and relative (p<0.001) internal training load differed across weeks of the season. However, movement quality did not moderate relative (p=0.264) internal training load. Absolute and relative training load changed across weeks of a male collegiate soccer season. Movement quality did not impact relative training load but further research with larger sample sizes are needed to confirm this result. 



#11 Soccer-Specific Reactive Repeated-Sprint Ability in Elite Youth Soccer Players: Maturation Trends and Association With Various Physical Performance Tests 

Reference: J Strength Cond Res. 2020 Dec;34(12):3538-3545. doi: 10.1519/JSC.0000000000002362. 

Authors: Michele Di Mascio, Jack Ade, Craig Musham, Olivier Girard, Paul S Bradley 

Summary: Repeated-sprint ability is an important physical prerequisite for competitive soccer and deviates for players in various stages of growth and development. Thus, this study investigated reactive repeated-sprint ability in elite youth soccer players in relation to maturation (age at peak height velocity) and its association with performance of other physical tests. Elite male youth players from an English Premier League academy (U12, n = 8; U13, n = 11; U14, n = 15; U15, n = 6; U16, n = 10; and U18, n = 13) completed the reactive repeated-sprint test (RRST; 8 × 30-m sprints with 30-second active recovery), and other physical tests including the Yo-Yo intermittent recovery test level 2 (Yo-Yo IR2), arrowhead agility test, countermovement jump test with arms (CMJA), in addition to 10- and 20-m straight-line sprints. Reactive repeated-sprint test (RRST) performance (total time across 8 sprints) progressively improved from U12 to U16 (p < 0.01; effect size [ES]: 1.0-1.9), yet with no differences found between U16 and U18. No between-group differences in RRST performance were evident after accounting for age at peak height velocity (p > 0.05; ES: <0.3). Correlation magnitudes between performance on the RRST and other tests were trivial to moderate for the Yo-Yo IR2 (r = -0.15 to 0.42), moderate to very large for the arrowhead agility test (r = 0.48-0.90), moderate to large for CMJA (r = -0.43 to 0.66), and trivial to large for 10- and 20-m sprints (r = 0.05-0.61). The RRST was sensitive at tracking maturation trends in elite youth players, although performance improvements were not as marked from 15 to 16 years of age. RRST performance correlates with several physical qualities decisive for competitive soccer (agility, speed, power, and aerobic endurance). 



#12 Intracranial bleeding following soccer-related head trauma in a young student with occult factor VII deficiency 

Reference: Clin Case Rep. 2020 Oct 3;8(11):2148-2151. doi: 10.1002/ccr3.3094. eCollection 2020 Nov. 

Authors: Nerea Lopetegui Lia, Abigael Luke, Syed Daniyal Asad, Shashank Sama, Leo J Wolansky, Upendra P Hegde 


Download link:

Summary: It is important to obtain coagulation tests to assess bleeding risk in trauma patients undergoing emergency surgery when a bleeding disorder may be obscured. Identifying specific clotting factor defects is critical in successful patient management. 



#13 Coronary artery z-score values in adolescent elite male soccer players 

Reference: Cardiol Young. 2020 Nov 24;1-5. doi: 10.1017/S1047951120004011. Online ahead of print. 

Authors: Stephan Gerling, Tobias Pollinger, Markus Johann Dechant, Michael Melter, Werner Krutsch, Holger Michel

Summary: With the increased training loads at very early ages in European elite youth soccer, there is an interest to analyse coronary artery remodelling due to high-intensity exercise. Prospective echocardiographic study in 259 adolescent elite male soccer players and 48 matched controls. The mean age was 12.7 ± 0.63 years in soccer players and 12.6 ± 0.7 years in controls (p > 0.05). Soccer players had significant greater indexed left ventricular mass (93 ± 13 g/m2 versus 79 ± 12 g/m2, p = 0.001). Both coronary arteries origin could be identified in every participant. In soccer players, the mean diameter of the left main coronary artery was 3.67 mm (SD ± 0.59) and 2.61 mm (SD ± 0.48) for right main coronary artery. Controls showed smaller mean luminal diameter (left main coronary artery, p = 0.01; right main coronary artery, p = 0.025). In soccer players, a total of 91% (n = 196) and in controls a total of 94% (n = 45) showed left main coronary artery z scores within the normal range: -2.0 to 2.0. In right main coronary artery, a pattern of z score values distribution was comparable (soccer players 94%, n = 202 vs. controls 84%, n = 40). A subgroup of soccer players had supernormal z score values (>2.0 to 2.5) for left main coronary artery (9%, n = 19, p = 0.01) and right main coronary artery (6%, n = 10, p = 0.025), respectively. Elite soccer training in early adolescence may be a stimulus strong enough to develop increased coronary arteries diameters. In soccer players, a coronary artery z score >2.0-2.5 might reflect a physiologic response induced by multiannual high-intensity training. 



#14 Relationships between Training Loads and Selected Blood Parameters in Professional Soccer Players during a 12-Day Sports Camp 

Reference: Int J Environ Res Public Health. 2020 Nov 19;17(22):8580. doi: 10.3390/ijerph17228580. 

Authors: Łukasz Radzimiński, Zbigniew Jastrzębski, Guillermo F López-Sánchez, Andrzej Szwarc, Henryk Duda, Aleksander Stuła, Jacek Paszulewicz, Paul Dragos

Download link:

Summary: The main purpose of this study is to assess the relations between training loads and selected blood parameters in professional soccer players during a preseason sports camp. Fifteen professional soccer players (age: 24.3 ± 5.25 year; height: 182.6 ± 6.75 cm; weight: 76.4 ± 6.72 kg) participated in the 12-day training camp. All the training sessions and friendly games were accurately analyzed with a GPS system. Blood samples were taken from the players and analyzed before the camp (PRE), in the middle (MID), and one day after the camp (POST). Mean total distance covered by the players during the camp was 85,205 ± 2685 m, high-intensity running 12,454 ± 1873 m, and sprinting 639 ± 219 m. The highest aspartate transaminase (AST), lactate dehydrogenase (LDH), creatine kinase (CK), and C-reactive protein (CRP) values were observed after six days of the camp. The application of intensive training during a 12-day sports camp can be associated with chronic muscle pain with high activity of some blood enzymes (CK, AST) and a high concentration of myoglobin (Mb). During training camps longer than 10 days, it would be necessary to apply, every second or third day, one day of rest, and the training load should not exceed two units every day. 


The Training Manager -