Latest research in football - 38 - 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 How Numerical Unbalance Constraints Physical and Tactical Individual Demands of Ball Possession Small-Sided Soccer Games
Reference: Front Psychol. 2020 Jul 14;11:1464. doi: 10.3389/fpsyg.2020.01464. eCollection 2020.
Authors: Nuno André Nunes, Bruno Gonçalves, Diogo Coutinho, Bruno Travassos
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Summary: This study aimed to explore the effects of playing different unbalanced ball possession small-sided games on external workload (distance covered while walking, running, and sprinting, and max speed), tactical individual actions (number of passes with dominant and non-dominant foot), and internal load (rating of perceived exertion, RPE) in under-23 soccer players. Participants played 4v2, 4v3, 4v4, 4v5, and 4v6 small-sided games (SSGs) on a 30 × 25 m playing area. Data were analyzed under an opponent-based perspective, by fixing one team (4vX), and by cooperation-based perspective according to teammates (4v2+X). Global Position System (GPS) monitors were used to collect and compute external workloads and individual tactical actions, and Borg Scale CR10 was used to evaluate RPE. High-Superiority (4v2), Superiority (4v3), and Very Low-Cooperation (4v2+0) formats allow players in balanced teams to cover more distance while walking; on the other side, Inferiority (4v5), High-Inferiority (4v6), and Very High-Cooperation (4v2+4) allow players to sprint more and practice more tactical individual actions as a resultant emergent behavior; all players in SSG conditions with a lower number of conditions, perceived the exercise as more intense, especially in situations with less than two players. Overall, playing in high inferiority situations (4v2 and 4v6) may be used to increase physical demand for the outnumbered team, while coaches may use low superiority situations to adjust the task complexity when developing the players' tactical individual actions.

#2 Acute Effects of ACL Injury-Prevention Warm-Up and Soccer-Specific Fatigue Protocol on Dynamic Knee Valgus in Youth Male Soccer Players
Reference: Int J Environ Res Public Health. 2020 Aug 4;17(15):E5608. doi: 10.3390/ijerph17155608.
Authors: Marco Andrés García-Luna , Juan Manuel Cortell-Tormo, Miguel García-Jaén, Manuel Ortega-Navarro, Juan Tortosa-Martínez
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Summary: Childhood anterior cruciate ligament (ACL) injuries-which can pose a major risk to a child's sporting career-have been on the rise in the last few decades. Dynamic knee valgus (DKV) has been linked to an increased risk of ACL injury. Therefore, the aim of this study was to analyze the acute effects of an ACL injury prevention protocol (ACL-IPP) and a soccer-specific fatigue protocol (SSFP) on DKV in youth male soccer players. The research hypothesis was that DKV would be reduced by the ACL-IPP and increased by the SSFP. Eighteen youth male soccer players were divided according to baseline DKV. Those with moderate or large DKV performed a neuromuscular training protocol based on activation of the abductor and external rotator hip muscles. Those with little or no DKV performed a soccer-specific fatigue protocol. DKV was assessed using the single-leg squat pre- and post-protocols in both legs. The ACL-IPP significantly decreased DKV during single-leg squat (p < 0.01, effect size = 1.39), while the SSFP significantly increased baseline DKV in the dominant leg during single-leg squat (p = 0.012; effect size = 1.74). In conclusion, the ACL-IPP appears to acutely reduce the DKV in youth male soccer players, and the SSFP seems to acutely increase the DKV in those players who showed a light or no DKV in a non-fatigue situation. By using the SSFP, it may be possible to determine which players would benefit from injury prevention programs due to increased DKV during game scenarios, while hip abductor and external rotator neuromuscular training may be beneficial for players who have moderate and severe DKV during single-leg squat under non-fatigued scenarios.

#3 Short-Term Compound Training on Physical Performance in Young Soccer Players
Reference: Sports (Basel). 2020 Jul 30;8(8):E108. doi: 10.3390/sports8080108.
Authors: Athos Trecroci, Marco Duca, Damiano Formenti, Giampietro Alberti, F Marcello Iaia, Stefano Longo
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Summary: This study aimed to investigate the effects of a five-week compound training (with strength and plyometric exercises performed on separate days) on sprint, change of direction, and vertical jump in young soccer players. Eighteen novices in strength and plyometric training were assigned to either a compound training (CMPT) or a control condition (CNT). Both groups trained three times per week. One session was dedicated to soccer-specific drills. The other two weekly sessions were dedicated to circuit-based training routines employing on one-day strength exercises and on the other day plyometric exercises in the CMPT group. At the same time, the CNT group performed two weekly soccer-specific training sessions. All players were tested by 15-m sprint, change-of-direction and acceleration test (CODAT), squat jump, and countermovement jump with arms swing tests. CMPT group improved CODAT, squat jump and countermovement jump to a higher extent compared to CNT group (large vs small or trivial effects, p < 0.05), while both groups had similar 15-m sprint performance (p > 0.05). These results support the use of compound training to improve change of direction and vertical jump performances in young novice soccer players, which are unfamiliar with structured and advanced strength and plyometric training.

#4 A Longitudinal Prospective Study: The Effect of Annual Seasonal Transition and Coaching Influence on Aerobic Capacity and Body Composition in Division I Female Soccer Players
Reference: Sports (Basel). 2020 Jul 30;8(8):E107. doi: 10.3390/sports8080107.
Authors: Troy M Purdom, Kyle S Levers, Chase S McPherson, Jacob Giles, Lindsey Brown
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Summary: This study assessed how seasonal transitions and coaching influence affect aerobic capacity (AC) and body composition across the annual training cycle (ATC). Eleven division 1 female soccer players were tested after five predesignated time blocks (B1-B5): post-season 2016 (B1), nine-week transition (B2), spring season (B3), pre-season (B4), and post-season 2017 (B5). Height, weight, and body composition (fat-free mass (FFM)) were measured prior to a standardized 5 min treadmill running and dynamic movement warm up before a maximal AC test. Statistical analysis included a 4 × 5 repeated-measures analysis of variance (ANOVA) (dependent variable × time) with the Fishers Least Significant Difference (LSD) post-hoc test when relevant; data are presented as mean ± standard deviation, effect size (ES), and percent change (%). The statistical analysis revealed that the ATC had a significant main effect on AC and FFM (F3,4 2.81, p = 0.001; η2 = 0.22). There were significant increases in AC across the transition period (B1-B2) with reduced training volume (∆ + 12.9%, p = 0.001; ES = 0.50) while AC and FFM peaked after the spring season with directed concurrent training paired with adequate rest B1-B3 (∆ + 16.4%, p < 0.01; ES = 0.81). AC decreased across the pre-season with indirect training (B3-B4) (∆ - 7.0%, p = 0.02; ES = 0.50) and remained suppressed without change (p > 0.05) across the competitive season (B4-B5). Rest, concurrent training, and directed training positively affected AC, while indirect training and high training loads with little rest negatively affected AC.

#5 Does the distribution of the weekly training load account for the match results of elite professional soccer players?
Reference: Physiol Behav. 2020 Aug 1;225:113118. doi: 10.1016/j.physbeh.2020.113118. Online ahead of print.
Authors: Rafael Oliveira, João P Brito, Nuno Loureiro, Vitor Padinha, Bruno Ferreira, Bruno Mendes
Summary: The aim of the study was to compare training load (TL) of the days preceding a win, draw or defeat in a sample of elite professional soccer players across the in-season 2015/16. Twenty elite soccer players participated in this study. Total distance covered, high-speed running distance (HSRD), average speed, session rate of perceived exertion (s-RPE) and Hooper index scores (HI) were collected. Data from 24 weeks with one match were analysed through the match-day (MD-5, 4, 3, 2, 1) and MD+1. The main finding emerges in MD-1, where a longer training duration preceding draws (95.1 ± 1.5 min) > defeats (91.5 ± 1.6 min) > wins (84.7 ± 0.5 min) was found, while total distance and average speed were higher in wins (3628.6 ± 57.2 m) > draws (3391.3 ± 153.3 m) > defeats (3236.1 ± 113.7 m) and draws (130.7 ± 17.6 m/min) > wins (86.0 ± 6.9 m/min) > defeats (54.8 ± 7.1 m/min), respectively. HSRD was higher in draws (42.8 ± 0.6 m) > wins (36.1 ± 1.7 m) > defeats (35.8 ± 1.7 m). In MD+1, there were differences in HI between wins vs draws (p<0.01). The results are drawn from one team that participated in UEFA Champions League. It was observed that different TL applied in training sessions can influence match result. Our findings can be considered in future soccer planning and periodization to win matches. This study emphasizes the use of HI especially in the day following the match.

#6 Description of acute and chronic load, training monotony and strain over a season and its relationships with well-being status: A study in elite under-16 soccer players
Reference:  Physiol Behav. 2020 Aug 1;225:113117. doi: 10.1016/j.physbeh.2020.113117. Online ahead of print.
Authors: Hadi Nobari, Rodrigo Aquino, Filipe Manuel Clemente, Mousa Khalafi, Jose Carmelo Adsuar, Jorge Pérez-Gómez
Summary: This study described the weekly variations of acute (wAL), chronic (wCL), acute:chronic workload ratio (wACWR), training monotony (wTM), and training strain (wTS) of perceived load, such as wellness indicators over a competitive season. In addition, we analyzed the associations between training load metrics and weekly reports. Twenty-nine under 16 years old elite players were daily monitored for 20 consecutive weeks during the season by individual observations. Training and match load were obtained using the session rating of perceived exertion. Well-being status relative to stress, fatigue, delayed onset muscle soreness (DOMS), and sleep quality/disorders were daily monitored using the Hooper index method. The results revealed that the highest values of wAL, wCL, and wTS were verified in the mid-season and the lowest values in the start-season. The highest values of accumulated weekly fatigue, stress, and DOMS were observed in the end-season, and the lowest values of sleep and stress in the start-season while the lowest values of fatigue and DOMS were observed in the mid-season. Regarding the load variability, the results showed the highest values between-week variations to wTS (15%; week-8 to 9) and the lowest reduction to wACWR (-19%; week-9 to 10). The highest within-week variations were verified to wACWR (coefficient of variation =19%; week-18) and the lowest to wCL (coefficient of variation =6%, week-19). Wellness indicators were moderate-large related to acute load, monotony and strain (r = 0.46-0.67). Overall Hooper index was the best predictor of the acute load (R2 = 0.45). These results provide new insights for coaches and practitioners about perceived loads and well-being variations over a season in elite youth level.

#7 Upper respiratory symptoms (URS) and salivary responses across a season in youth soccer players: A useful and non-invasive approach associated to URS susceptibility and occurrence in young athletes
Reference: PLoS One. 2020 Aug 4;15(8):e0236669. doi: 10.1371/journal.pone.0236669. eCollection 2020.
Authors: Renata Fiedler Lopes, Luciele Guerra Minuzzi, António José Figueiredo, Carlos Gonçalves, Antonio Tessitore, Laura Capranica, Ana Maria Teixeira, Luis Rama
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Summary: This study examined the effect of a competitive season on salivary responses [cortisol (sC), testosterone (sT), Testosterone/Cortisol ratio (sT/C), Immunoglobulin A (sIgA), sIgA secretion rate (srIgA), alpha-amylase (sAA)] and upper respiratory symptoms (URS) occurrence in three teams of male soccer players (Under-15, Under-17 and Under-19 yrs.). Training and competition volumes, salivary biomarkers and URS were determined monthly. No differences were found for monthly training volume between teams. Incidence of URS was higher for the U15 (44.9% of the total cases). Higher sT and srIgA were observed for the U19, lower sC were found for the U17 and sAA showed higher values for the U15 throughout the season. In the U15, significant difference (p = .023) was found for sIgA concentration with higher concentration values in January compared to December (-42.7%; p = .008) and the sT showed seasonal variation (p < .001) with the highest value in January significantly different from October (-40.2%; p = .035), November (-38.5%; p = 0.022) and December (-51.6%; p = .008). The U19 presented an increase in sC in March compared to February (-66.1%, p = .018), sT/C were higher in February compared to March (-58.1%; p = .022) and sAA increased in March compared to September (-20.5%; p = .037). Negative correlations, controlled for age group, were found between URS occurrence and srIgA (r = -0.170, p = .001), sAA (r = -0.179, p = .001) and sT (r = -0.107, p = .047). Monitoring salivary biomarkers provides information on mucosal immunity with impact in URS occurrence. Coaches could manipulate training loads to attenuate the physical stressors imposed on athletes, especially at demanding and stressful periods.

#8 The effects of an integrative training program on elite young soccer players' physical performance
Reference: J Sports Med Phys Fitness. 2020 Jul 30. doi: 10.23736/S0022-4707.20.11195-2. Online ahead of print.
Authors: Christos Karydopoulos, Dimitrios Kapralos, Evangelia Kouidi, Yiannis Michailidis, Thomas Metaxas
Summary: The aim of this study was to investigate the effects of a short duration and low weekly frequency integrative program on sprint, agility and jump performance in elite youth soccer players. Twenty-eight elite youth soccer players, members of two professional clubs, playing in the U19 developmental championship participated in this study. They were divided into 2 groups: the intervention group (EG,n=15) and the control group (CG, n=13). The duration of the intervention program was 8 weeks with a frequency of twice per week. The performance of the participants in the 10 meters and 30 meters speed, countermovement jump (CMJ), squat jump (SJ) and agility (Illinois agility test, Arrowhead agility test) was measured at the beginning and the end of the 8-week study. There was no statistically significant difference in any performance measured between the two groups. The results of the present study indicate that the addition of allowing frequency and short duration training intervention program did not enhance the physical fitness indicators, in high-level young soccer players.

#9 Virtual immersive sensorimotor training (VIST) in collegiate soccer athletes: A quasi-experimental study
Reference: Heliyon. 2020 Jul 24;6(7):e04527. doi: 10.1016/j.heliyon.2020.e04527. eCollection 2020 Jul.
Authors: Jennifer C Reneker, W Cody Pannell, Ryan M Babl  , Yunxi Zhang, Seth T Lirette, Felix Adah, Matthew R Reneker
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Summary: A burgeoning area of innovation in sports is the use of extended realities to provide athletes with novel training environments. Evidence has demonstrated that virtual environments can be useful therapeutic tools with demonstrated positive outcomes. The purpose of this pilot investigation was to determine the effects of virtual immersive sensorimotor training intervention by quantifying 1) the training effect measured via change in performance pre-to post-intervention on the virtual reality exercises, 2) the difference in the in clinical measures of functional sensorimotor control, 3) the injury incidence rate, and 4) on-field performance during soccer competitions. Statistical analyses were used to describe differences between an experimental and a control group. Participants were recruited from the men and women's soccer teams at two universities in the United States. Participants at one university were in the experimental group (n = 78) and received virtual immersive sensorimotor training, consisting of nine novel exercises in headset virtual reality, twice each week for six weeks. Participants at the second university were in the control group (n = 52). The virtual exercises were developed with reference to the rehabilitative principles of neuroplasticity to train various neurologic processes, contributing to overall sensorimotor control. This includes vestibular, visual and oculomotor activities, cervical neuromotor control training, movement coordination, and postural/balance exercises. The results indicate significant positive training effects pre-to post-intervention in seven of the nine training exercises (p ≤ 0.005) and improvement in clinical tests of cervical neuromotor control, balance, and inspection time (p ≤ 0.009) in the experimental group compared to the control. One of the virtual training exercises was positively associated with on-field performance (p = 0.022). No differences in injury rate or overall on-field performance metrics between the experimental and control were detected. This research study provides evidence of training and positive transfer from virtual to real-world environments, supporting the use of these novel virtual exercises to improve measures of sensorimotor control in healthy soccer athletes.

#10 Acceleration and sprint profiles of professional male football players in relation to playing position
Reference: PLoS One. 2020 Aug 6;15(8):e0236959. doi: 10.1371/journal.pone.0236959. eCollection 2020.
Authors: José M Oliva-Lozano, Víctor Fortes, Peter Krustrup, José M Muyor
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Summary: The study aims were to describe positional differences in the acceleration and sprint profiles of professional football players in match-play, and analyse start speeds required based on the intensity of accelerations and decelerations. This longitudinal study was conducted over thirteen competitive microcycles in a professional football team from LaLiga 123. Data were collected through electronic performance tracking systems. Every player was categorised based on the playing position: central defender (CD), full-back (FB), forward (FW), midfielder (MF), and wide midfielder (WMF). In respect of acceleration profile, positional differences were found for all variables (p < 0.05), except average magnitude of accelerations (ACCAVG, p = 0.56) and decelerations (DECAVG, p = 0.76). The sprint profile also showed positional differences for all variables (p < 0.05), apart from sprint duration (p = 0.07). In addition, although low-intensity accelerations required significantly greater start speeds (Vo) than high-intensity accelerations in WMF (0.4 ± 0.2 km/h; p < 0.05) and FW (0.4 ± 0.2 km/h; p < 0.05), no significant differences (p > 0.05) were found in CD, FB, and MF. However, high-intensity decelerations were performed at significantly higher Vo than low-intensity decelerations in MF (2.65 ± 0.1 km/h; p < 0.05), FW (3.3 ± 0.1 km/h; p < 0.05), FB (3.9 ± 0.4 km/h; p < 0.05), WMF (4.3 ± 0.3 km/h; p < 0.05), and CD (4.1 ± 0.7 km/h; p < 0.05). Therefore, positional differences exist for most variables of the acceleration and sprint profiles. In addition, different Vo were observed between high-intensity and low-intensity accelerations as well as high-intensity and low-intensity decelerations.

#11 Reaction of the Organisms of Young Football Players to City Smog in the Sports Training
Reference: Int J Environ Res Public Health. 2020 Jul 30;17(15):E5510. doi: 10.3390/ijerph17155510.
Authors: Henryk Duda, Łukasz Rydzik, Wojciech Czarny, Wiesław Błach, Karol Görner, Tadeusz Ambroży
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Summary: The essence of a sports training includes not only developing the skills necessary in a chosen sport but also particular care about athlete's health. This issue should be taken into account especially in case of children and youth engaged in sporting activities. In the paper there are issues connected to the control of physical effort abilities in the sports training of young football players and the assessment of the reaction of the body to physical exercise in city smog conditions (the environment of the city of Kraków) and clean air conditions (the environment of the town of Głuchołazy). This paper shows that, when assessing physical effort, one can consider not nly the results of physical tests but also the reaction of the body to a given physical load. One should remember that physical load depends not only on the methods used and the range of intensity, but also on the environmental conditions, like the quality of the air. Determining the reaction of the body to physical load (performance tests), taking into account the conditions in which the training takes place, prevents overloading and sets directions for rational sports training. The analysis of the results of the study leads to three main conclusions: (1) The planning of sports training has to consider not only the methods and means of the training but also environmental factors (air pollution); (2) Physical effort in smog conditions should be done with the use of antismog face masks; (3) The arrangement of sports training (particularly for youth) should strictly take into account the environment in which the training takes place.

#12 Effects of coordination training on the technical development in 10-13 years old football players
Reference: J Sports Med Phys Fitness. 2020 Jul 30. doi: 10.23736/S0022-4707.20.11270-2. Online ahead of print.
Authors: Mustafa Kösal, Gazanfer K GÜl, Murat Doğanay, Cristina Álvarez-García
Summary: The purpose of this study was to determine the effects of coordination training carried out by 10-13 years old male football players on the performance of dribbling, passing, shooting, ball bouncing and wall-volley skills. A total of 45 male football players were divided into three 15 participants groups. The experimental group performed 30 min coordination training three days a week for ten weeks while the control group one continued their routine training and control group two performed unstructured football training. Measurements included Mor and Christian, Yeagley and Johnson football skill tests. Pre- and post-test measurements were compared by an ANOVA 2 × 3. A significant level of P < 0.05 was established. All the skills, dribbling (P < 0.001), passing (P < 0.001), shooting (P < 0.001), ball bouncing (P = 0.047) and wall-volley (P < 0.001), improved after ten weeks in the experimental group, while only passing (P = 0.006), shooting (P = 0.007) and wall-volley (P< 0.001) improved in the control group one and none of the skills improved in the control group two (P > 0.05). The improvement was significant in the experimental group in comparison with the control groups (P < 0.001). The implementation of coordination exercises in combination with structured football training has been shown to be effective in improving general football ability among 10-13 male players.

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