Latest research in football - week 7 - 2020

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 Sprint versus isolated eccentric training: Comparative effects on hamstring architecture and performance in soccer players
Reference: PLoS One. 2020 Feb 11;15(2):e0228283. doi: 10.1371/journal.pone.0228283. eCollection 2020.
Authors: Mendiguchia J, Conceição F, Edouard P, Fonseca M, Pereira R, Lopes H, Morin JB, Jiménez-Reyes P
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Summary: The purpose of this study was to compare the effects of hamstring eccentric (NHE) strength training versus sprint training programmed as complements to regular soccer practice, on sprint performance and its mechanical underpinnings, as well as biceps femoris long head (BFlh) architecture. In this prospective interventional control study, sprint performance, sprint mechanics and BFlh architecture variables were compared before versus after six weeks of training during the first six preseason weeks, and between three different random match-pair groups of soccer players: "Soccer group" (n = 10), "Nordic group" (n = 12) and "Sprint group" (n = 10). For sprint performance and mechanics, small to large pre-post improvements were reported in "Sprint group" (except maximal running velocity), whereas only trivial to small negative changes were reported in "Soccer group" and "Nordic group". For BFlh architecture variables, "Sprint" group showed moderate increase in fascicle length compared to smaller augment for the "Nordic" group with trivial changes for "Soccer group". Only "Nordic" group presented small increases at pennation angle. The results suggest that sprint training was superior to NHE in order to increase BFlh fascicle length although only the sprint training was able to both provide a preventive stimulus (increase fascicle length) and at the same time improve both sprint performance and mechanics. Further studies with advanced imaging techniques are needed to confirm the validity of the findings.

#2 Acute effects of two different initial heart rates on testing the repeated sprint ability in elite women's soccer players
Reference: J Sports Med Phys Fitness. 2020 Feb 5. doi: 10.23736/S0022-4707.19.10311-8. [Epub ahead of print]
Authors: Ruscello B, Esposito M, Fusco C, Ceccarelli C, Pomponi S, Filetti C, Pantanella L, Gabrielli P, D'ottavio S
Summary: Repeated Sprint Ability (RSA) in women's soccer is crucial to ensure high level of performance during the game. Aim of this study is to investigate the acute effects of two different initial heart rates intensities on fatigue when testing the RSA. Since there are many kinds of pre-match warming-ups, the heart rate reached at the end of two different warm-up protocols (~90vs.≈60%HRmax) as an indicator of internal load has been selected and the respective RSA performances were compared. RSA tests were performed by 19 elite women soccer players (Age: 22.5±3.3 years, height 163.9±7.3 cm, body mass 54.3±6.4 kg, BMI 20.6±1.5 kg·m-2) with two sets of ten shuttle-sprints (15+15m) with a 1:3 exercise to rest ratio, in different days (randomized order) with different initial HR% (60 & 90% HRmax). In order to compare the different sprint performances a Fatigue Index (FI%) was computed; the blood lactate concentrations (BLa-) were measured before and after testing, to compare metabolic energy. Significant differences among trials within each sets (P<0.01) were found, as evidence of fatigue. Differences between sets were not found, (Factorial ANOVA 2x10; P>0.05). Although the BLa- after warm-up was higher between 90% vs. 60% HRmax (P<0.05), at the completion of RSA tests - after 3 minutes - the differences were considerably low and not significant (P>0.05). This study shows that, contrary to male soccer, the initial heart rates, induced by different modes of warming-up, do not affect the overall performance while testing RSA in women's soccer players.

#3 Tactical Variables Related to Gaining the Ball in Advanced Zones of the Soccer Pitch: Analysis of Differences Among Elite Teams and the Effect of Contextual Variables
Reference: Front Psychol. 2020 Jan 21;10:3040. doi: 10.3389/fpsyg.2019.03040. eCollection 2019.
Authors: Fernandez-Navarro J, Ruiz-Ruiz C, Zubillaga A, Fradua L
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Summary: Attacking tactical variables have been commonly studied in soccer to analyze teams' performance. However, few studies investigated defensive tactical variables during match-play and the influence of contextual variables on them. The aims of the present study were (1) to examine the defensive behaviors of soccer teams when gaining the ball in advanced zones of the pitch and (2) to evaluate the effect of contextual variables on these defensive behaviors. A sample of 1,095 defensive pieces of play initiated in the opposing half of the pitch obtained from 10 matches of the season 2010/11 of La Liga and involving 13 teams was collected using the semiautomated tracking system Amisco Pro. Five defensive tactical variables, the outcome of defensive pieces of play, and contextual variables (i.e., match status, venue, quality of opposition, and match period) were recorded for every defensive piece initiated in the opposing half of the pitch. Results showed that there were significant differences among teams in the outcome of defensive pieces of play originating from the opposing half (χ2 = 111.87, p < 0.01, φc = 0.22), and in the outcome of offensive pieces of play following ball gains (χ2 = 49.92, p < 0.001, φc = 0.22). Cluster analysis revealed four groups describing different defensive behaviors from high-pressure to a defense close to their own goal. Match status (χ2 = 25.87, p < 0.05, φc = 0.11) and quality of opposition (χ2 = 21.19, p < 0.05, φc = 0.10) were the contextual variables that showed a significant effect on defensive pieces of play initiated in the opposite half of the pitch. Teams winning gained more balls in the zone close to their own goal, and losing teams gained more balls in advanced zones of the pitch. Moreover, the greater the quality of the opponent the lesser the chance of gaining the ball in advanced zones of the pitch. Neither venue or match period influenced the defensive pieces of play analyzed. Soccer teams could employ a similar analysis to improve their performance and prepare for opposition teams in competition.

#4 Individualized Breakfast Programs or Glycogen Super-Compensation: Which Is the Better Performing Strategy? Insights from an Italian Soccer Referees Cohort

Reference: Int J Environ Res Public Health. 2020 Feb 5;17(3). pii: E1014. doi: 10.3390/ijerph17031014.
Authors: Regnoli R, Rovelli M, Gianturco V, Pregliasco FE, Bodini BD, Gianturco L
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Summary: The role of soccer referees has grown in importance in the last decades, as has attention to their performance, which may be influenced and improved with specific and evolved training programs. Today, multiple specialists are working as a team in order to develop effective training programs. Moreover, for athletes, it is becoming more and more important to be attentive to nutrition. By considering such items, in this study, we aimed to investigate the nutritional habits of a group of referees belonging to the Italian Soccer Referees' Association (on behalf of AIA-FIGC). Our main aim was to spread a "culture of nutrition" in refereeing, starting with a survey on referees' breakfast attitudes and in order to disseminate such a "culture", we chose top-level elite referees who were younger subjects (despite the average 4 years' experience). Therefore, we enrolled 31 subjects (aged 22.74 ± 1.79, BMI 22.30 ± 1.53) and asked them about their breakfast habits. Then, for measuring their performance, we used the conventional fitness test named Yo-Yo (YYiR1), performed in three different sessions (test 1, test 2, test 3). Test 1 was carried out without any nutritional indications, test 2 was given after individualized breakfast suggestions by a designed dietician, and test 3 after an individualized glycogen super-compensation strategy. The Wilcoxon statistical analysis indicates that following an individualized breakfast strategy may enhance referees' performance (p < 0.0001), whereas no significant effects were observed with the glycogen super-compensation option. However, further studies will be necessary to better address this topic and clarify whether high-carbohydrates (high-CHO) intake may be useful in other sports.

#5 Influence of Contextual Variables in the Changes of Direction and Centripetal Force Generated during an Elite-Level Soccer Team Season
Reference: Int J Environ Res Public Health. 2020 Feb 4;17(3). pii: E967. doi: 10.3390/ijerph17030967.
Authors: Granero-Gil P, Bastida-Castillo A, Rojas-Valverde D, Gómez-Carmona CD, de la Cruz Sánchez E, Pino-Ortega J
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Summary: The study of the contextual variables that affect soccer performance is important to be able to reproduce the competition context during the training sessions. Therefore, the aim of the present study was to evaluate the effect of match outcome as related to goal difference (large win, >2 goals, LW; narrow win, 1-2 goals, NW; drawing, D; narrow loss, 1-2 goals, NL; or large loss, >2 goals, LL), match location (home, H; away, A; neutral, N), type of competition (international, INT; national, NAT; friendly, F), phase of the season (summer preseason, SPS; in-season 1, IS1; winter preseason, WPS; in-season 2), and the field surface (natural grass, NG; artificial turf, TF) on the change of direction (COD) and centripetal force (CentF) generated during official games. Thirty male elite-level soccer players (age: 26.57 ± 5.56 years) were assessed while using WIMU PROTM inertial devices (RealTrack Systems, Almeria, Spain) in 38 matches during the 2017-2018 season, selecting for analysis the number of COD at different intensities and the CentF, depending on the turn direction. Statistical analyses comprised a one-way ANOVA with the Bonferroni post-hoc and t-test for independent samples. The main results showed that the match outcome (ωp² = 0.01-0.04; NW = D = NL > LL), match location (ωp² = 0.01-0.06; A = N > H), type of competition (ωp² = 0.01-0.02; INT > NAT > F), and period of the season (ωp² = 0.01-0.02; SPS = IS1 = WPS > IS2) all exert some influence. No effect was found for the playing surface. Therefore, match outcome, match location, type of competition, and period of the season influence the demands of centripetal force and changes of direction. These aspects should be considered in the design of training sessions and microcycle workload planning during the season to improve competitive success.

#6 Experience as a Determinant of Declarative and Procedural Knowledge in School Football
Reference: Int J Environ Res Public Health. 2020 Feb 7;17(3). pii: E1063. doi: 10.3390/ijerph17031063.
Authors: García-Ceberino JM, Gamero MG, Feu S, Ibáñez SJ
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Summary: The study of declarative and procedural knowledge makes it possible to ascertain what cognitive processes are like during motor learning. This study aimed to compare, according to the methodology, gender and experience (football practise), and the levels of declarative and procedural knowledge after the implementation of two intervention programmes on school football including one based on the tactics learning and the other on the technique learning. A total of 41 students in the 5th year of primary education from a state school from Spain, distributed in two class groups, participated in the study. Each class group participated in a different intervention programme. The sample of subjects was equal (tactical programme (n = 20) and technical programme (n = 21)). A panel of 13 experts validated both programmes. Levels of knowledge were measured using the Tactical Knowledge Assessment test in football. A descriptive analysis was performed to characterise the sample. Moreover, a t-test for independent samples, a t-test for related samples, and a 2 × 2 ANOVA (analysis of variance) were performed to compare the levels of knowledge between the pre-test and the post-test, according to the methodology, gender, and experience of the students. Results indicate that both intervention programmes induced higher levels of declarative and procedural knowledge in the post-test. Similarly, there were no significant differences with regard to the applied methodology. This fact is due to the heterogeneous character of the class groups with gender and experience showing effects on the levels of knowledge. The boys possessed greater experience and a higher level of knowledge compared to the girls.

#7 Measures of PHV and the effect on directional dynamic stability to identify risk factors for injury in elite football
Reference: J Sports Med Phys Fitness. 2020 Feb 5. doi: 10.23736/S0022-4707.20.10352-9. [Epub ahead of print]
Authors: Rhodes D, Alexander J, Jeffrey J, Birdsall D, Maden-Wilkinson J
Summary: The purpose was to analyse the relationship between Peak Height Velocity (PHV) and Dynamic Balance (Y-Balance) vs non-peak growth to identify risk factors for non-contact lower limb injuries using a retrospective study design in elite youth footballers. Ninety-Three elite category 1 academy football players completed Y-Balance assessment during the preseason screening assessment. Data in relation to Y-Balance and Peak Height Velocity measures was than analysed retrospectively and correlated against injury audit data to identify relationships between the variables. A significant correlation was identified between Peak Height Velocity (PHV) and measures of directional dynamic stability utilising Y-Balance assessment (p ≤ 0.001). No significant correlations were identified between PHV and injury or injury and dynamic stability scores (p > 0.05). Injury occurrence for players within predicted periods of PHV was represented as 45%, within the cohort contained within the study. Evidently periods of growth and maturation within elite academy footballers has a detrimental effect on directional dynamic stability performance. However, caution must be taken with interpreting the significance of this relationship and the effect it has on injury occurrence. Consideration must be given to quantifying key aetiological factors associated with injury during adolescence and refrain from reliance on measures of PHV.

#8 Selecting Training-Load Measures to Explain Variability in Football Training Games
Reference: Front Psychol. 2020 Jan 24;10:2897. doi: 10.3389/fpsyg.2019.02897. eCollection 2019.
Authors: Zurutuza U, Castellano J, Echeazarra I, Guridi I, Casamichana D
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Summary: The purpose of this study was to investigate the structure of interrelationships among external (eT) and internal (iT) training intensity metrics and how these vary depending on game format in soccer. The variables were collected from 16 semi-professional players in seven types of small, medium, large-sided, and simulated games (SG). The eT variables were (per min): peak velocity (Vmax), total distance (DTmin), distance covered at velocities less than 60% (D < 60%min), between 60 and 80% (D > 60%min), and more than 80% (D > 80%min) of the maximal velocity, player load (PLmin), and distance covered accelerating at more than 2 m⋅s-2 (Daccmin) and decelerating at less than -2 m⋅s-2 (Ddecmin). The iT variables were: Edwards arbitrary units (EDWmin) and time spent at more than 80% of the maximal heart rate (T > 80% HRmin). All game formats were represented by three principal components (PC), explaining from 66.9 to 76.0% of the variance. The structure of the interrelationships among variables involved similar distributions in the PCs that are related to energetic production systems, such as the strength/neuromuscular dimension (PLmin and/or Daccmin and Ddecmin, complemented by DTmin and D < 60%min), the endurance/cardiovascular dimension (EDWmin), and the velocity/locomotion dimension (Vmax, D > 60%min, or D > 80%min). A particular combination of external and internal intensity measures is required to describe the training load of game formats.

#9 Navigation ability test: a new specific test to asses spatial orientation ability in football players and healthy
Reference: J Sports Med Phys Fitness. 2020 Feb 4. doi: 10.23736/S0022-4707.20.10110-5. [Epub ahead of print]
Authors: Gamba P, Guidetti R, Guidetti G
Summary: This paper describes a new specific test to asses spatial and orientation abilities: Navigation Ability Test (NAT). The goal of this study was to determine if football players and normal subjects use vestibular information to keep track of their positions while walking through the Navigation Ability Test. This study was conducted total of 120 patients, underwent to Navigation Ability Test (NAT): 60 football players and 60 of normal subjects recruited on the basis of no history of vertigo/balance disorders and a negative otoneurological instrumental examination and the second group of the football players and were recruited from Division B, Division Under-21 and Women's League. Patients were enrolled in the study of the met all the following inclusion criteria. Our results showed differences between sexes during navigation tasks are not related to spatial learning per se, but appear to be the consequence of difference in ability to effectively use specific types of distal information such as room geometry. The Navigation Ability Test showed the route- times walked with eyes closed are always longer than in normal people and the mistakes improved with training. These results suggest that Navigation Ability Test could suggest to the coach and trainers valuable information about the characteristics of the players and how they should play in the field. Although there are some intrinsic difficulties, for example in creating patient-specific versions of the test, preliminary normative data indicate that this original test is workable and provides important information in therapy rehabilitation for vestibular disorder.

#10 Lower-Limb Biomechanics in Football Players with and without Hip-related Pain
Reference: Med Sci Sports Exerc. 2020 Feb 18. doi: 10.1249/MSS.0000000000002297. [Epub ahead of print]
Authors: King MG, Semciw AI, Schache AG, Middleton KJ, Heerey JJ, Sritharan P, Scholes MJ, Mentiplay BF, Crossley KM.
Summary: The purpose was to evaluate the differences in lower-limb biomechanics between adult sub-elite competitive football players with and without hip-related pain during two contrasting tasks: walking and the single-leg drop jump (SLDJ); and to determine whether potential differences, if present, are sex-dependent. Eighty-eight football players with hip-related pain (23 women, 65 men) and 30 asymptomatic control football players (13 women, 17 men) who were currently participating in competitive sport were recruited. Biomechanical data were collected for the stance phase of walking and the SLDJ. Pelvis, hip, knee and ankle angles, as well as the impulse of the external joint moments, were calculated. Differences between groups and sex-specific effects were calculated using linear regression models. Compared to their asymptomatic counterparts, football players with hip-related pain displayed a lower average pelvic drop angle during walking (P =0.03) and greater average pelvic hike angle during the SLDJ (P <0.05). Men with hip-related pain displayed a smaller total range of motion (excursion) for the transverse plane pelvis angle (P = 0.03) and a smaller impulse of the hip external rotation moment (P <0.01) during walking compared to asymptomatic men. Women with hip-related pain displayed a greater total range of motion (excursion) for the sagittal plane knee angle (P = 0.01) during walking compared to asymptomatic women. Overall, few differences were observed in lower-limb biomechanics between football players with and without hip-related pain, irrespective of the task. This outcome suggests that, despite the presence of symptoms, impairments in lower-limb biomechanics during function do not appear to be a prominent feature of people with hip-related pain who are still participating in sport.

#11 A Machine Learning Approach to Assess Injury Risk in Elite Youth Football Players
Reference: Med Sci Sports Exerc. 2020 Feb 19. doi: 10.1249/MSS.0000000000002305. [Epub ahead of print]
Authors: Rommers N, Rössler R, Verhagen E, Vandecasteele F, Verstockt S, Vaeyens R, Lenoir M, D'Hondt E, Witvrouw E
Summary: The purpose was to assess injury risk in elite-level youth football players based on anthropometric, motor coordination and physical performance measures with a machine learning approach. A total of 734 players in the U10 to U15 age categories (mean age: 11.7 +/- 1.7 years) from seven Belgian youth academies were prospectively followed during one season. Football exposure and occurring injuries were monitored continuously by the academies' coaching and medical staff, respectively. Preseason anthropometric measurements (height, weight, and sitting height) were taken and test batteries to assess motor coordination and physical fitness (strength, flexibility, speed, agility, and endurance) were performed. An extreme gradient boosting algorithms (XGBoost) was used to predict injury based on the preseason test results. Subsequently, the same approach was used to classify injuries as either overuse or acute. During the season, half of the players (n = 368) sustained at least one injury. Of the first occurring injuries, 173 were identified as overuse and 195 as acute injuries. The machine learning algorithm was able to identify the injured players in the hold-out test sample with 85% precision, 85% recall (sensitivity) and 85% accuracy (f1-score). Furthermore, injuries could be classified as overuse or acute with 78% precision, 78% recall and 78% accuracy. Our machine learning algorithm was able to predict injury and to distinguish overuse from acute injuries with reasonably high accuracy based on preseason measures. Hence, it is a promising approach to assess injury risk among elite-level youth football players. This new knowledge could be applied in the development and improvement of injury risk management strategies, to identify youth players with the highest injury risk.

#12 Quantitative assessment of the effect of acute anaerobic exercise on macular perfusion via swept-source optical coherence tomography angiography in young football players
Reference: Int Ophthalmol. 2020 Feb 15. doi: 10.1007/s10792-020-01303-w. [Epub ahead of print]
Authors: Karakucuk Y, Okudan N, Bozkurt B, Belviranlı M, Sezer T, Gorçuyeva S
Summary: The purpose was to evaluate the effect of acute anaerobic exercise on macular perfusion measured by swept-source optical coherence tomography angiography (SS-OCTA) in young football players. Football players with ages between 18 and 20 years were included into the study. After a detailed ophthalmological examination, physiological parameters including height (cm), body weight (kg), body fat percentage (%), systemic blood pressure (BP) (mmHg), hematocrit values (%), oxygen saturation pO2 (%) and heart rate (bpm) were recorded. Intraocular pressure (IOP) (mmHg) and SS-OCTA using DRI OCT Triton (Topcon, Tokyo, Japan) were measured immediately before and after Wingate test. Out of 20, 16 participants completed the study. All participants were males with a mean age of 18.12 ± .34 years. Systolic BP, hematocrit and heart rate increased, while pO2 and IOP decreased remarkably after Wingate test (p < .01). After anaerobic exercise, there was an increase in mean FAZ area in superficial capillary plexus (FAZs) which was not significant (p = .13), while decrease in FAZ area in deep capillary plexus (FAZd) (mm2) was remarkable (p = .04). No changes were observed in mean vessel density (VD) (%) in superficial capillary plexus (VDs), deep capillary plexus (VDd), choriocapillaris (VDcc), central macular thickness (CMT) (μm) and subfoveal choroidal thickness (SFCT) (μm) after Wingate test (p > .05). FAZd and some of the VD parameters showed a significant correlation with BP (p < .05). Acute anaerobic exercise seems not to alter either mean VD in retina and choroid or CMT and SFCT. Among OCTA parameters, only FAZd decreased remarkably.

#13 Playing tactics, contextual variables and offensive effectiveness in English Premier League soccer matches. A multilevel analysis
Reference: PLoS One. 2020 Feb 18;15(2):e0226978. doi: 10.1371/journal.pone.0226978. eCollection 2020.
Authors: González-Rodenas J, Aranda-Malaves R, Tudela-Desantes A, Nieto F, Usó F, Aranda R
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Summary: The aim of this study was to investigate the combined effects of tactical and contextual indicators on achieving offensive penetration and scoring opportunities in English Premier League (EPL) soccer matches. A total of 1971 team possessions from 20 random matches were evaluated by means of multidimensional observation. The EPL matches had a great proportion of fast attacks (36.0%) followed by combinative (29.6%), direct attacks (24.1%) and counterattacks (9.5%). Multilevel logistic regression models revealed that counterattacks (OR = 3.428; 95% CI: 2.004-5.864; P<0.001) were more effective to create goal scoring opportunities than combinative attacks, while direct attacks showed to be less effective (OR = 0.472; 95% CI: 0.264-0.845; P<0.05). Playing at home increased the probability (OR = 1.530; 95% CI: 1.097-2.135; P<0.05) of creating goal scoring opportunities compared with playing away. These findings show the multifactorial character of soccer and how different contextual and tactical indicators can influence the creation of offensive penetration and goal scoring opportunities in the English Premier League.

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