Latest research in football - week 38 - 2019

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 Longitudinal emotional process among adolescent soccer player in intensive training centre
Reference: J Sports Sci. 2019 Sep 9:1-12. doi: 10.1080/02640414.2019.1662538. [Epub ahead of print]
Authors: Saby Y, Pupier Y, Guillet-Descas E, Nicolas M, Martinent G
Summary: Grounded in Lazarus's (1999) cognitive motivational relational theory of emotions, this study aimed to explore longitudinal relationships between appraisals, everyday emotions related to the competitive environment and emotional regulation strategies during a competitive season. Forty adolescent soccer players (Mage = 15.8) involved in an intensive training centre from a professional club voluntarily participated to the study. A series of hierarchical linear modelling analyses were conducted upon the 9 measurement times to: (a) examine the relationships between appraisals (threat, challenge, loss), pleasant (happiness, excitement) and unpleasant (anxiety, dejection, anger) emotions, and emotional regulation strategies (adaptive and less adaptive); and (b) ascertain whether the relationships between appraisals and emotions were mediated by emotion regulation strategies. The results of the random coefficient regression models showed: (a) positive relationships between challenge appraisal, adaptive emotion regulation, and pleasant emotions as well as between threat and loss appraisals, less adaptive emotion regulation and unpleasant emotions; and (b) mediating effects of emotional regulation strategies in the appraisals - emotions relationships. As a whole, this study furthered knowledge base about the competitive environment in showing that appraisals, emotion regulation and emotions are intertwined psychological constructs in a dynamic relationship allowing athletes to continuously adjust to their constantly changing everyday demands.

#2 Artificial-turf surfaces for sport and recreational activities: microbiota analysis and 16S sequencing signature of synthetic vs natural soccer fields
Reference: Heliyon. 2019 Aug 29;5(8):e02334. doi: 10.1016/j.heliyon.2019.e02334. eCollection 2019 Aug.
Authors: Valeriani F, Margarucci LM, Gianfranceschi G, Ciccarelli A, Tajani F, Mucci N, Ripani M, Romano Spica V
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Summary: Synthetic fibres are used in place of the natural grass worldwide, for realizing playgrounds, soccer fields and even domestic gardens or recreational structures. An intensive use of artificial turf is currently observed in sports facilities, due to lower costs, higher sustainability in recycling of materials, and advantages related to athletic practice and performance. However, even if chemical and physical risks were studied, the microbiological component was not fully addressed, especially considering a comprehensive evaluation of the microbiota in synthetic vs natural playground surfaces. Here, we investigated the microbial community present on soccer fields, using Next Generation Sequencing and a 16S amplicon sequencing approach. Artificial and natural turfs show own ecosystems with different microbial profiles and a mean Shannon's diversity value of 2.176 and 2.475, respectively. The bacterial community is significantly different between facilities (ANOSIM: R = 0.179; p < 0.001) and surface materials (ANOSIM: R = 0.172; p < 0.005). The relative abundance of potentially pathogenic bacterial OTUs was higher in synthetic than in natural samples (ANOVA, F = 2.2). Soccer fields are characterized by their own microbiota, showing a different 16S amplicon sequencing signature between natural and artificial turfs.

#3 The Running and Technical Performance of U13 to U18 Elite Japanese Soccer Players During Match Play
Reference: J Strength Cond Res. 2019 Sep 6. doi: 10.1519/JSC.0000000000003300. [Epub ahead of print]
Authors: Goto H, Saward C
Summary: The aims of the current study were (a) to examine age-related differences in match running performance with 2 different approaches (speed vs. metabolic power) in U13-U18 Japanese elite soccer players and (b) to examine age-related differences in technical match performance in U13-U18 Japanese elite soccer players. Participants were 110 outfield players from academies of 2 professional soccer clubs in Japan. Forty-eight 11-a-side official league matches (13, 6, 9, 7, 6, and 7 matches for U13, U14, U15, U16, U17, and U18 age-groups, respectively) were analyzed (152 complete match files). Global positioning system (15 Hz) and video analysis were used to analyze running and technical performance during matches, respectively. Total distance covered in absolute terms (U13 < [U14 and U15] < [U16-U18]; p < 0.05 for all), high-intensity running distance ([U13-U15] < [U16-U18]; p < 0.05 for all), and distance covered during the metabolic power zone of ≥35 W·kg relative to match playing time ([U13 < U16], [U13-U15] < [U17 and U18]; p < 0.05 for all) increased with age. The speed zone based approach (high-intensity running distance, ≥4.0 m·s) underestimated high-intensity demands compared with the metabolic power zone based approach (≥20 W·kg) by ∼33 to ∼57% (p < 0.01 for all), with the underestimation declining with age (p < 0.001). Pass accuracy improved with age from 73% at U13 to 85% at U18 (p < 0.001). Therefore, distance covered at high speeds and at high metabolic powers, and pass accuracy increase with age. Moreover, the speed zone based approach underestimates the demands of match play in Japanese elite youth soccer players. The current results could support coaches to develop players, identify talent, and produce age-specific training programs.

#4 The Reliability of Potential Fatigue-Monitoring Measures in Elite Youth Soccer Players
Reference: J Strength Cond Res. 2019 Sep 6. doi: 10.1519/JSC.0000000000003317. [Epub ahead of print]
Authors: Fitzpatrick JF, Hicks KM, Russell M, Hayes PR
Summary:  Monitoring fatigue is of vital importance to practitioners; however, logistics and concerns about reliability may impede the use of certain measures. This study aimed to quantify the reliability of potential measures of fatigue; a subjective wellness questionnaire, jump performance tests, and tri-axial accelerometer variables derived during submaximal shuttle running in elite youth soccer players. A secondary aim was to establish the minimum test duration that could be used for the submaximal shuttle run while maintaining good reliability. Seventeen male youth team players (age: 17.4 ± 0.5 years) were assessed on 2 occasions, spaced 7 days apart. Typical error, coefficient of variation (CV%), interclass correlation (ICC), and minimum detectable change were calculated for a subjective wellness questionnaire, countermovement jump (CMJ), squat jump (SJ) and drop jump contact time (DJ-CT), drop jump height (DJ-JH), and reactive strength (DJ-RSI). A novel submaximal shuttle running test was also used to assess tri-axial accelerometer data reliability. Results suggest that CMJ, SJ, DJ-CT, and DJ-RSI have good test-retest reliability (CV% = 4.5-7.7; ICC = 0.80-0.88); however DJ-JH did not show acceptable reliability (CV% = 6.0; ICC = 0.76). Good reliability was found for all tri-axial accelerometer variables during a 3-minute (2-minute analysis) submaximal shuttle run (CV% = 2.4-8.0; ICC = 0.81-0.95), except for % PlayerLoad anterior-posterior (%PLAP) (CV% = 7.2; ICC = 0.63). The subjective wellness questionnaire demonstrated poor reliability for all items (CV% = 11.2-30.0; ICC = 0.00-0.78). The findings from this study provide practitioners with valuable information about the reliability of a range of potential fatigue-monitoring measures. This can be used to help make accurate decisions about the magnitude of change in these assessments when used in practice.

#5 Effects of a blocked versus an alternated sequence of balance and plyometric training on physical performance in youth soccer players
Reference: BMC Sports Sci Med Rehabil. 2019 Sep 2;11:18. doi: 10.1186/s13102-019-0131-y. eCollection 2019.
Authors: Muehlbauer T, Wagner V, Brueckner D, Schedler S, Schwiertz G, Kiss R, Hagen M
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Summary: The sequence of blocked balance training (BT) followed by blocked plyometric training (PT) showed greater improvements in physical performance than vice versa and is explained by a preconditioning effect of BT-related adaptations on subsequent adaptations induced by PT. However, it remains unclear whether beneficial effects can also be induced using alternating instead of blocked BT and PT exercise sequences. Thus, we examined the effects of a blocked versus an alternated sequence of BT and PT on physical performance in trained individuals. Twenty young soccer players (13 years) were randomly assigned to a blocked (n = 10) or an alternated (n = 10) intervention group. Both groups trained balance and plyometric exercises for six weeks (two sessions/week). The exercises were conducted in a blocked (three weeks of BT followed by three weeks of PT) or an alternated sequence (weekly change of BT and PT). Assessment of pre- and post-training performance included measures of balance, muscle power, speed, and agility. Mainly significant main effects of Test (i.e., pre- to post-test improvements) were observed for the Y-balance test (p ≤ 0.014, 1.3 ≤ Cohen's d ≤ 1.81), the squat jump (p = 0.029, d = 1.36), the countermovement jump (p = 0.002, d = 2.21), the drop jump (p = 0.004, d = 1.96), the split times/total time over 15-m sprinting (p ≤ 0.001, 2.02 ≤ d ≤ 3.08), and the figure-T agility run (p < 0.001, d = 3.80). Further, tendencies toward significant Test x Group interactions were found for several items of the Y-balance test and for SJ height in favor of the blocked BTPT group. Our results indicate that the combined training of balance and plyometric exercises is effective to improve proxies of physical performance in youth soccer players. In addition, there is a limited advantage in some parameters of balance and muscle power for the blocked as compared to the alternated sequence of BT and PT.

#6 Assessment of Selected Exercise-induced CD3+ Cell Subsets and Cell Death Parameters Among Soccer Players
Reference: J Med Biochem. 2019 Mar 26;38(4):437-444. doi: 10.2478/jomb-2019-0013. eCollection 2019 Oct.
Authors: Nowak R, Kostrzewa-Nowak D
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Summary: Molecular mechanisms of biological adaptation to training in professional soccer players are unclear. The aim of this study was to assess the impact of progressive physical effort on peripheral T-cells and their molecular response. Thirteen soccer players form Pogo Szczecin S.A., a top league soccer club, (median age 21, range 18- 31, years old) performed progressive efficiency tests on a mechanical treadmill until exhaustion at the start (period 1) and the end (period 2) of a competition round. Venous blood T-lymphocyte subsets, selected hallmarks of cell death and plasma cytokine levels were determined by flow cytometry three times: pre-exercise, post-exercise, and in recovery. Although significant changes in T, Tc and Tc-naïve cell percentages were found in both periods, Th-naïve cell percentages were altered only in period 1. Post-exercise IL-10 plasma levels were higher than pre-exercise, while an increase in TNF-α levels was noticed in recovery from both periods. An increase in recovery IL-12p70 levels was observed in the second period. Increases in the percentage of T-cells with disrupted mitochondrial membrane potentials, elevated levels of phosphorylated H2AX histones and increases in early apoptotic T-cells were also observed. The immune system in soccer players creates space for naïve CD3+CD8+ cells by inducing mechanisms of cell death. It seems that the cumulative effect of physical activity during a competition round induced an adaptive mechanism, since the cell death process was induced faster during period 2.

#7 Clustering algorithm for formations in football games
Reference: Sci Rep. 2019 Sep 11;9(1):13172. doi: 10.1038/s41598-019-48623-1.
Authors: Narizuka T, Yamazaki Y
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Summary: In competitive team sports, players maintain a certain formation during a game to achieve effective attacks and defenses. For the quantitative game analysis and assessment of team styles, we need a general framework that can characterize such formation structures dynamically. This paper develops a clustering algorithm for formations of multiple football (soccer) games based on the Delaunay method, which defines the formation of a team as an adjacency matrix of Delaunay triangulation. We first show that heat maps of entire football games can be clustered into several average formations: "442", "4141", "433", "541", and "343". Then, using hierarchical clustering, each average formation is further divided into more specific patterns (clusters) in which the configurations of players are different. Our method enables the visualization, quantitative comparison, and time-series analysis for formations in different time scales by focusing on transitions between clusters at each hierarchy. In particular, we can extract team styles from multiple games regarding the positional exchange of players within the formations. Applying our algorithm to the datasets comprising football games, we extract typical transition patterns of the formation for a particular team.

#8 Effects of Temporary Numerical Imbalances on Collective Exploratory Behavior of Young and Professional Football Players
Reference: Front Psychol. 2019 Aug 27;10:1968. doi: 10.3389/fpsyg.2019.01968. eCollection 2019.
Authors: Canton A, Torrents C, Ric A, Gonçalves B, Sampaio J, Hristovski R
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Summary: The aim of this study was to explore how the use of temporary numerical imbalances during small-sided Game SSGs affects team's exploratory behaviors (i.e., variety and quantity of responses given in an ever-changing game context and its rate of change) in different age groups. Two different age groups (under-15 and under-23) of football players participated in the study. For each age group, three teams of five players played six small-sided games of 5 min duration in different conditions: (i) numerical balance (GK + 4 vs. 4 + GK); (ii) temporary numerical imbalance, which consisted of a numerical change of teammates and opponents every one minute. Latitude and longitude GPS coordinates were used to determine the positioning-derived variables. The dynamic overlap (i.e. the measure of average similarity of the game patterns that take place in increasingly larger time intervals) was used to provide information of the rate and breadth of exploratory behavior. The results revealed that the long-term exploratory breadth increased for the under-23 age group. Non-clear effects were found for the short-term rate of exploration, but with an increasing trend. In the under-15 group, the exploratory behavior was more likely to increase in the long term. The increase for the short-term rate of exploration was unclear, but it follows an increasing trend. These results suggest that the use of temporary numerical imbalances could offer coaches more dynamic training situations and different adaptive training environments similar to matches.

#9 Correction to: Injury Incidence, Prevalence and Severity in High-Level Male Youth Football: A Systematic Review
Reference: Sports Med. 2019 Sep 9. doi: 10.1007/s40279-019-01182-x. [Epub ahead of print]
Authors: Jones S, Almousa S, Gibb A, Allamby N, Mullen R, Andersen TE, Williams M
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#10 The association between watching football matches and the risk of cardiovascular events: A meta-analysis
Reference: J Sports Sci. 2019 Sep 9:1-9. doi: 10.1080/02640414.2019.1665246. [Epub ahead of print]
Authors: Lin LL, Gu HY, Yao YY, Zhu J, Niu YM, Luo J, Zhang C
Summary: The aim was to comprehensively shed light on whether viewing football games is associated with a higher risk of cardiovascular disease (CVD). Electronic databases were searched through 17 May 2018. All studies focusing on the association between viewing football matches and the fatal or non-fatal CVD were identified. Viewing football matches was associated with a higher risk of fatal overall CVD (RR: 1.06, 95%CI: 1.01-1.12) in both men (RR: 1.13, 95%CI: 1.004-1.28) and women (RR: 1.08, 95%CI: 1.01-1.15). Subgroup analysis showed that failure of the team has a higher risk of fatal overall CVD (RR: 1.29, 95%CI: 1.15-1.45). However, lower risk of fatal overall CVD from spectators was observed when team obtained a victory (RR: 0.80, 95%CI: 0.66-0.96). For non-fatal CVD, viewing football matches was associated with a higher risk of non-fatal overall CVD (RR: 1.24, 95%CI: 1.09-1.41) in both men (RR: 1.73, 95%CI: 1.12-2.69) and women (RR: 1.25, 95%CI: 1.08-1.45). Subgroup analysis showed that viewing football matches was associated with a higher risk of non-fatal myocardial infarction (RR: 1.20, 95%CI: 1.04-1.38) in both men and women (RR: 1.51, 95%CI: 0.99-2.28; RR: 1.21, 95%CI: 1.08-1.36, respectively). No significant increase was found in fatal or non-fatal stroke. Viewing football matches was associated with a higher risk of the fatal and non-fatal CVD, especially in male spectators. The victory of team could have a lower risk of fatal CVD. Therefore, precautionary measures should be required for the reduction of healthcare burden in football matches.

#11 Effect of poor cooperation between coaching and medical staff on muscle re-injury in professional football over 15 seasons
Reference: Open Access J Sports Med. 2019 Aug 5;10:107-113. doi: 10.2147/OAJSM.S221292. eCollection 2019.
Authors: Ghrairi M1,2,3, Loney T1, Pruna R2,4, Malliaropoulos N2,5, Valle X2,4.
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Summary: Muscle injury is the most common type of injury in football. Previous research has focused on traditional risk factors (eg, age, injury history, muscle imbalance/inflexibility) contributing to muscle re-injury. The effect of poor cooperation between the coaching and medical teams on the risk of re-injury remains unexplored in the sports medicine football literature. Examine the effect of poor cooperation between coaching and medical teams on muscle re-injury in professional football. Retrospective review of the medical files of 97 footballers of a professional team in Dubai over 15 consecutive seasons (2002-2017). Medical team recorded all injuries in each player's file. Data on the perceived level of cooperation between coaching and medical teams were available in the daily meeting notes from the head of the medical team. The level of perceived cooperation was ranked on a three-point Likert scale by the head of the medical team and depended on whether the coaching team accepted the player injury (excellent cooperation), brought some suggestion after discussion with the medical team (normal cooperation) or rejected it (poor cooperation). In total, 338 indirect muscle injuries (21 re-injuries) were recorded during 15 consecutive seasons., There was a significant increase in the mean number of total injuries (mean ± SE, 95% CI; 16±2, 12-21; P<0.0001), mean number of indirect muscle injuries (12±1, 95% CI 10-14; P<0.0001), and indirect muscle re-injuries (4±1, 95% CI 3-5; P<0.0001) during seasons with a poor perceived level of cooperation compared to seasons with a normal/excellent perceived level of cooperation. Findings suggest that poor cooperation between coaching and medical teams may increase the risk of muscle re-injury in professional football. Future studies conducted in different clubs, leagues, countries, and even sports are required to further explore the effect of cooperation between coaching and medical teams on the risk of re-injury.

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