Latest research in football - week 39 Part 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 Effects of Warm-up on Hamstring Stiffness, Stress-Relaxation, Flexibility and Knee Proprioception in Young Soccer Players

Reference: J Athl Train. 2021 Jun 29.  doi: 10.4085/1062-6050-0416.20. Online ahead of print.

Authors: Danguole Satkunskiene, Mani Mirab Zadeh Ardekani, Ra'ad M Khair, Goda Kutraite, Kristina Venckuniene, Audrius Snieckus, Sigitas Kamandulis

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Summary: Nerves or fascia may limit motion in young soccer players, thereby contributing to frequent hamstring injuries. Nerve gliding exercises and self-myofascial release techniques may enhance the range of motion. The aim of this study was to compare the acute effect of foam rolling (FR) and neurodynamic nerve gliding (NDNG) on hamstring flexibility, passive stiffness, viscoelasticity and proprioception during the warm-up of soccer players. Fifteen male soccer players on the same team (age 18.0 ± 1.4 years, body mass 76.9 ± 7.8 kg, height 183 ± 6 cm). FR and NDNG included six sets of 45 s with 15 s rest between each set. Over a two-week period subjects performed NDNG and FR on two separate occasions. Hip flexion angle (SLR), knee extension range of motion (ROM), knee joint position sense (AKJPS), hamstring passive resistance torque (PRT), stiffness (STFmax and STF80%) and viscoelasticity (stress-relaxation test (SRT)). A significant interaction between time and intervention was found for knee ROM (p = 0.017), PRT (p = 0.044), and STFmax (p = 0.042). NDNG induced an increase in ROM (p = 0.011), PRT (p = 0.008), and STFmax (p = 0.030). Both NDNG and FR induced an increase in SLR (p < 0.001). No interaction or main effects was found for SRT and AKJPS. The inclusion of NDNG in the warm-up routine increased the ROM more in comparison with FR and may be of benefit to soccer players.



#2 Prior Injury, Health-Related Quality of Life, Disablement, and Physical Activity in Former Women's Soccer Players

Reference: J Athl Train. 2021 Jun 29.  doi: 10.4085/1062-6050-0731.20. Online ahead of print.

Authors: Shannon J Cross, Diane L Gill, Pam Kocher Brown, Erin J Reifsteck 

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Summary: Former collegiate athletes may be at risk for negative health outcomes like lower health-related quality of life (HRQoL), higher disablement, and lower lifetime physical activity (PA) participation. A history of severe sports injury may play a role in these outcomes. The aim was to assess the role prior sports injury plays in self-reported HRQoL, levels of disablement, and PA behaviors of former Division I women's soccer players. Former NCAA Division I women's soccer players (n = 382, Mage = 36.41 ± 7.76) completed demographics, injury history, the Patient-Reported Outcomes Measurement Information System (PROMIS; HRQoL), the Disablement for the Physically Active Scale (DPA; disablement), and the Godin Leisure Time Physical Activity Questionnaire (PA). The dependent variables were physical and mental component summary scores for HRQoL and disablement, and frequency of moderate-to-vigorous PA. Means, standard deviations, and correlations among the main outcome variables were examined for those who reported a severe injury (n = 261) and those who did not (n = 121). To address the primary aim of the study, multiple regression analyses were used to predict PA, disablement, and HRQoL based on history of severe injury, accounting for age. Having a severe injury was significantly predictive of having worse physical disablement and worse physical HRQoL, with severe injury predicting a greater than 5-point increase and 2-point decrease on the respective scales. Injury status was not predictive of mental disablement, mental HRQoL, or PA. The majority of participants reported suffering a prior severe soccer-related injury, which may have a negative long-term impact on health outcomes for former women's soccer players. Athletic trainers should be aware of risk for decreased HRQoL and increased disablement with injury and encourage continued monitoring of relevant patient-reported outcomes (PROs).



#3 Post-match recovery profile of leukocyte cell subsets among professional soccer players

Reference: Sci Rep. 2021 Jun 25;11(1):13352. doi: 10.1038/s41598-021-92956-9.

Authors: Dorota Kostrzewa-Nowak, Paweł Wityk, Andrzej Ciechanowicz, Robert Nowak

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Summary: This study assessed the impact of cumulative match time on the distribution of CD45+ cell subtests in the capillary blood of professional soccer players. Twenty-two males (aged 18-30 years) took part in the 36-week study. Participants playing up to 540 in cumulative match time and less than 30 min in each single match during the observation period formed the control group. White blood cell (WBC) phenotyping and creatine kinase (CK) plasma activity analyses were performed. Also, counts for WBC subsets were determined. No significant differences in the hematological parameters or lymphocyte and NK cell percentages were observed between the control and study groups. Changes in the T cell percentage were significant during weeks 11 and 30 and in Th and Tc cell percentages during weeks 2 and 26. Significant correlations were found between the cumulative match time and Th, NK, and B cell percentages; monocyte counts; and CK activity in the control group. However, for the study group, correlations were found between cumulative match time and Th, Tc, and B cell percentages; CK activity; and the CK ratio. Our study suggests that the distribution of CD45+ cells might be a useful tool for monitoring the immune status of professional soccer players.



#4 Overseas Air Medical Repatriation of National Soccer Players Infected With Coronavirus Disease 2019 and Contacted Staff From Austria to South Korea

Reference: Case Reports Air Med J. Jul-Aug 2021;40(4):282-286.  doi: 10.1016/j.amj.2021.03.014. Epub 2021 Apr 2.

Authors: Hyo-Jeong Choi 1, Ho-Jung Kim 2, Gon Seo 3

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Summary: Korea rarely has a system to transport patients from abroad. However, single-patient transfers are steadily being performed, and there was an experience of transferring a large number of personnel regardless of whether they were confirmed or not due to coronavirus disease 2019. Recently, a national soccer game was held abroad, and a total of 8 players and staff were infected. A total of 15 people were transported through a charter fully equipped with quarantine equipment by a medical response team with experience in air transport.



#5 The Communication and Passing Contributions of Playing Positions in a Professional Soccer Team

Reference: J Hum Kinet. 2021 Jan 30;77:223-234.  doi: 10.2478/hukin-2020-0052. eCollection 2021 Jan.

Authors: Scott McLean, Paul M Salmon, Adam D Gorman, Karl Dodd, Colin Solomon

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Summary: Determining the connectivity of team members in sport provides important information on team functioning. In soccer, teams that are highly connected via passing have been shown to be more successful compared to teams less connected via passing. In addition to passing connectivity, players are connected with each other via intra-team communication (ITC) through verbal instruction, and nonverbal cues. Despite ITC being a known component of effective teamwork to enhance strategy, efficiency, motivation and concentration, ITC of individual playing positions has not previously been measured during soccer games, nor has it been associated with passing connections in a performance context. In this study, the received ITC that was perceived to be beneficial to performance during 22 competitive professional soccer matches was measured, in conjunction with the passing connections between team members. In total, 526 ITC ratings were collected and analysed, and a total of 7,693 passes were analysed. From the ITC and passing measures, a player connectivity index (PCI) representing the coupling of ITC and passing, was developed to determine the overall connectivity of the individual playing positions. Social network analysis (SNA) centrality metrics were used to determine the connectivity of the playing positions. There were significant (p < .05) main effects between playing positions for beneficial ITC, passing, and the PCI for centrality metrics, indicating that different playing positions interact with other team members differently. Pairwise comparisons indicated significant differences between individual playing positions for ITC, passing and the PCI. The two central defenders and the two central defensive midfielders had the highest mean values for ITC, passing, and the PCI compared to the other playing positions. The current findings suggest that central defenders and central defensive midfielders are positioned tactically to be highly involved in the build-up of passing moves, and to deliver beneficial task related information to team members. These findings have implications for performance analysis, coaches, and for talent identification.



#6 The Relative Age Effect on Anthropometry, Body Composition, Biological Maturation and Motor Performance in Young Brazilian Soccer Players

Reference: J Hum Kinet. 2021 Jan 30;77:147-157.  doi: 10.2478/HUKIN-2021-0017. eCollection 2021 Jan.

Authors: Juliana Melo Altimari, Leandro Ricardo Altimari, Henrique Bortolotti, Adalberto Ferreira Junior, Juliano Moro Gabardo, Cosme Franklim Buzzachera, Ariobaldo Frisselli, Antonio Carlos de Moraes

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Summary: The present study aimed to investigate the influence of months of birth on anthropometry, body composition, biological maturation, and motor performance in young Brazilian soccer players. Young Brazilian soccer players from the Under-13 (n = 50; 13.6 ± 0.3 years), Under-15 (n = 50; 15.5 ± 0.4 years), and Under-17 categories (n = 46; 17.7 ± 0.3 years) took part in this study. Athletes were divided according to chronological age, 1st tertile (January to April); 2nd tertile (May to August); and 3rd tertile (September to December). Anthropometry, body composition, biological maturation, and motor performance variables were evaluated for all participants. There were no differences between the U-13, U-15, and U-17 categories regarding birth tertiles (p > 0.05). Differences between the ages and birth tertiles were observed for the stature, body mass, and lean body mass (p < 0.05). Moreover, differences were found in maturational status between the ages and birth tertiles (p < 0.05). In general, U-13 players showed lower values compared to U-15 and U-17 players in tests of motor performance. In addition, there was a difference in motor performance between the birth tertiles only for RSA variables. The months of birth influenced the stature, body mass, lean body mass, and repeated sprint ability in the U-13 and U-15 categories. Thus, care should be taken during the process of talent selection, as many young players could be underestimated due to their date of birth.



#7 Acute Effects on Physical Performance Measures after 45 Min of Official Competition in Youth Soccer Players

Reference: J Funct Morphol Kinesiol. 2021 Jun 4;6(2):49. doi: 10.3390/jfmk6020049.

Authors: Federico Gazzo, Julián Giráldez, Rodrigo Villaseca-Vicuña, José Antonio González-Jurado, Santiago Zabaloy

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Summary: An improved understanding of soccer players' match-related physical performance and recovery may help conditioning programs and re-warm up strategies to increase team performance during official competitions. Therefore, the aim of this study was to analyze the acute effects of 45 min of official competition (first half in matches) on physical performance variables in U-16 youth soccer players. (2) 20 male soccer players (age: 14.4 ± 0.5 years; height: 1.70 ± 0.05 cm; body mass: 65.1 ± 11.6 kg) were recruited to participate in this study. Data was collected from five official matches. Participants performed the assessments in two stages of each match: after the pre-match warm-up and after the first half. Tests included rate of perceived exertion (RPE), 30-m sprint and countermovement (CMJ). (3) Statistically significant differences were found (p < 0.001) when the measurements prior to the game were compared with those recorded after half time across all variables. Effect sizes (ES) were very large for RPE (ES = 1.82), moderate for 30-m sprint times (ES = 0.64) and small for CMJ (ES = -0.25). (4). After 45 min of official competition, our results suggest that U-16 soccer players demonstrated a reduction in sprint and jump performance, in addition to a higher RPE. Hence, this information could be useful when designing re-warming strategies that can be performed before the second half.



#8 Comparison of Official and Friendly Matches through Acceleration, Deceleration and Metabolic Power Measures: A Full-Season Study in Professional Soccer Players

Reference: Int J Environ Res Public Health. 2021 Jun 2;18(11):5980.  doi: 10.3390/ijerph18115980.

Authors: Hadi Nobari, Sara Mahmoudzadeh Khalili, Rafael Oliveira, Alfonso Castillo-Rodríguez, Jorge Pérez-Gómez, Luca Paolo Ardigò

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Summary: Soccer is a popular team sport and highly demanding activity that requires high effort and long-term training plans. The goals of this study were to compare the accelerations, decelerations and metabolic power between official and friendly full matches, between the first and second halves of the matches, and between both halves of official and friendly matches. Twelve professional soccer players (age, 28.6 ± 2.7 years; height, 182.1 ± 8.6 cm; body mass, 75.3 ± 8.2 kg; BMI, 22.6 ± 0.7 kg/m2) participated in this study. A total of 33 official and 10 friendly matches were analyzed from the Iranian Premier League. All matches were monitored using GPSPORTS systems Pty Ltd. The following variables were selected: total duration of the matches, metabolic power, accelerations Zone1 (<2 m·s-2) (AccZ1), accelerations Zone2 (2 to 4 m·s-2) (AccZ2), accelerations Zone3 (>4 m·s-2) (AccZ3), decelerations Zone1 (<-2 m·s-2) (DecZ1), decelerations Zone2 (-2 to -4 m·s-2) (DecZ2) and decelerations Zone3 (>-4 m·s-2) (DecZ3). The major finding was shown in metabolic power, where higher values occurred in friendly matches (p < 0.05 with small effect size). Furthermore, total duration, AccZ3, DecZ1, DecZ2, and DecZ3 were revealed to be higher in official matches, while AccZ1 and AccZ2 were higher in friendly matches. The second half of the official matches revealed higher values for total duration compared to friendly matches (p < 0.05, moderate effect size). In conclusion, this study observed higher values of metabolic power in friendly matches compared to official matches. AccZ3, DecZ1, DecZ2, and DecZ3 were higher in official matches, while AccZ1 and AccZ2 were higher in friendly matches.



#9 The Role of Motor Imagery in Predicting Motor Skills in Young Male Soccer Players

Reference: Int J Environ Res Public Health. 2021 Jun 10;18(12):6316.  doi: 10.3390/ijerph18126316.

Authors: Dariusz Zapała, Emilia Zabielska-Mendyk, Andrzej Cudo, Marta Jaśkiewicz, Marcin Kwiatkowski, Agnieszka Kwiatkowska

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Summary: The study aimed to find out whether the imagery ability within the two subcomponents of motor imagery (visual and kinesthetic) allows predicting the results in simple response time task and eye-hand coordination task in a group of young male soccer players (9-15 years old). Non-specific simple response time and eye-hand coordination play a key role in predicting specific sports performance level. Participants performed Reaction Time Task, Eye-Hand Coordination Task, and completed Motor Imagery Questionnaire-Revised. Data were submitted to the structural equations analysis based on the maximum likelihood method in order to estimate a structural model of relationship between variables. Results indicate visual rather than kinesthetic motor imagery is associated with non-specific motor skills. Higher scores on the visual motor imagery scale were observed to correlate with faster reaction times and better coordination in the study group. This supports the idea that during learning a new perceptual-motor-task the visual control is required. Results provide the evidence for the specific role of the third-person perspective imagery in young athletes playing soccer.



#10 Effect of Online Training during the COVID-19 Quarantine on the Aerobic Capacity of Youth Soccer Players

Reference: Int J Environ Res Public Health . 2021 Jun 8;18(12):6195.  doi: 10.3390/ijerph18126195.

Authors: Paweł Kalinowski, Jakub Myszkowski, Jakub Marynowicz

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Summary: Motor abilities, such as endurance and the optimal level of physical activity, play a fundamental role in football as they are necessary to maintain the high effectiveness of the training process. The aim of this study was the observation of the trend of changes in the level of cardiorespiratory endurance of young football players in a one-year cycle overlapping with the COVID-19 lockdown and an assessment of the impact of the training intervention during home confinement. The participants of the study were 24 young football players. We analysed the results of the study in a one-year training cycle (lockdown from 11 March 2020 to 6 May 2020). The cardiorespiratory endurance was measured using the Multistage 20 m Shuttle Run test-Beep Test. A repeated measures analysis of variance was used in the study. Detailed comparisons were made using Tukey's HSD test. Statistically significant differences were noted in endurance in a one year cycle: F(5.115) = 22.65; p < 0.001; partial Eta-squared = 0.50. An increase in the level of endurance by mean = 179.17 m, SD ± 189.87 m was noted between T1 and T6. After the break caused by the COVID-19 restrictions, a decrease in the level of cardiorespiratory endurance was noted. Only after two training mesocycles was a significant increase in the mean value noted compared to the period before the pandemic (p < 0.05). With the negative impact of restrictions in mind, coaches and physiotherapists should exercise caution when planning training, taking into consideration the level of physical activity during the pandemic.



#11 Relationships between Fitness Status and Match Running Performance in Adult Women Soccer Players: A Cohort Study

Reference: Medicina (Kaunas). 2021 Jun 13;57(6):617.  doi: 10.3390/medicina57060617.

Authors: Lillian Gonçalves, Filipe Manuel Clemente, Joel Ignacio Barrera, Hugo Sarmento, Francisco Tomás González-Fernández, Luiz H Palucci Vieira, António José Figueiredo, Cain C T Clark, J M Cancela Carral

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Summary: The aim of this study was twofold: (i) to analyze the relationships between fitness status (repeated-sprint ability (RSA), aerobic performance, vertical height jump, and hip adductor and abductor strength) and match running performance in adult women soccer players and (ii) to explain variations in standardized total distance, HSR, and sprinting distances based on players' fitness status.  The study followed a cohort design. Twenty-two Portuguese women soccer players competing at the first-league level were monitored for 22 weeks. These players were tested three times during the cohort period. The measured parameters included isometric strength (hip adductor and abductor), vertical jump (squat and countermovement jump), linear sprint (10 and 30 m), change-of-direction (COD), repeated sprints (6 × 35 m), and intermittent endurance (Yo-Yo intermittent recovery test level 1). Data were also collected for several match running performance indicators (total distance covered and distance at different speed zones, accelerations/decelerations, maximum sprinting speed, and number of sprints) in 10 matches during the cohort.  Maximal linear sprint bouts presented large to very large correlations with explosive match-play actions (accelerations, decelerations, and sprint occurrences; r = -0.80 to -0.61). In addition, jump modalities and COD ability significantly predicted, respectively, in-game high-intensity accelerations (r = 0.69 to 0.75; R2 = 25%) and decelerations (r = -0.78 to -0.50; R2 = 23-24%). Furthermore, COD had significant explanatory power related to match running performance variance regardless of whether the testing and match performance outcomes were computed a few or several days apart.  The present investigation can help conditioning professionals working with senior women soccer players to prescribe effective fitness tests to improve their forecasts of locomotor performance.



#12 Hamstring Injuries Prevention in Soccer: A Narrative Review of Current Literature

Reference: Review Joints. 2020 May 25;7(3):115-126.  doi: 10.1055/s-0040-1712113. eCollection 2019 Sep.

Authors: Gian Nicola Bisciotti, Karim Chamari, Emanuele Cena, Giulia Carimati, Alessandro Bisciotti, Andrea Bisciotti, Alessandro Quaglia, Piero Volpi

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Summary: Hamstring injuries and reinjuries are one of the most important sport lesions in several sport activities including soccer, Australian football, track and field, rugby, and in general in all sport activities requiring sprinting and acceleration. However, it is important to distinguish between the lesions of the biceps femoris and semitendinosus and semimembranosus. Indeed, three muscles representing the hamstring complex have a very different injury etiology and consequently require different prevention strategies. This fact may explain, at least in part, the high incidence of reinjuries. In soccer, hamstring injuries cause an important rate of time loss (i.e., in average 15-21 matches missed per club per season). The hamstring injury risk factors may be subdivided in three categories: "primary injury risk factors" (i.e., the risk factors mainly causing a first lesion), "recurrent injury risk factors" (i.e., the risk that can cause a reinjury), and bivalent injury risk factors" (i.e., the risk factors that can cause both primary injuries and reinjuries). The high incidence of hamstring lesions caused consequently an important increase in hamstring injury research. However, although the prevention has increased paradoxically, epidemiological data do not show a loss in injuries and/or reinjuries but, on the contrary, they show an increase in hamstring injuries. This apparent paradox highlights the importance both of the improvement in the prevention programs quality and the criteria for return to play after hamstring injury.



#13 Uniform Manifold Approximation and Projection Analysis of Soccer Players

Reference: Entropy (Basel). 2021 Jun 23;23(7):793.  doi: 10.3390/e23070793.

Authors: António M Lopes, José A Tenreiro Machado

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Summary: In professional soccer, the choices made in forming a team lineup are crucial for achieving good results. Players are characterized by different skills and their relevance depends on the position that they occupy on the pitch. Experts can recognize similarities between players and their styles, but the procedures adopted are often subjective and prone to misclassification. The automatic recognition of players' styles based on their diversity of skills can help coaches and technical directors to prepare a team for a competition, to substitute injured players during a season, or to hire players to fill gaps created by teammates that leave. The paper adopts dimensionality reduction, clustering and computer visualization tools to compare soccer players based on a set of attributes. The players are characterized by numerical vectors embedding their particular skills and these objects are then compared by means of suitable distances. The intermediate data is processed to generate meaningful representations of the original dataset according to the (dis)similarities between the objects. The results show that the adoption of dimensionality reduction, clustering and visualization tools for processing complex datasets is a key modeling option with current computational resources.



#14 Poor Motor Coordination Elicits Altered Lower Limb Biomechanics in Young Football (Soccer) Players: Implications for Injury Prevention through Wearable Sensors

Reference: Sensors (Basel). 2021 Jun 25;21(13):4371.  doi: 10.3390/s21134371.

Authors: Stefano Di Paolo, Stefano Zaffagnini, Nicola Pizza, Alberto Grassi, Laura Bragonzoni

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Summary: Motor coordination and lower limb biomechanics are crucial aspects of anterior cruciate ligament (ACL) injury prevention strategies in football. These two aspects have never been assessed together in real scenarios in the young population. The present study aimed to investigate the influence of motor coordination on lower limb biomechanics in young footballers during an on-the-pitch training. Eighteen juvenile football players (10 y ± 2 m) were enrolled. Each player performed a training drill with sport-specific movements (vertical jump, agility ladders, change of direction) and the Harre circuit test (HCT) to evaluate players' motor coordination. Wearable inertial sensors (MTw Awinda, Xsens) were used to assess lower limb joint angles and accelerations. Based on the results of the HCT, players were divided into poorly coordinated (PC) and well-coordinated (WC) on the basis of the literature benchmark. The PC group showed a stiffer hip biomechanics strategy (up to 40% lower flexion angle, ES = 2.0) and higher internal-external hip rotation and knee valgus (p < 0.05). Significant biomechanical limb asymmetries were found only in the PC group for the knee joint (31-39% difference between dominant and non-dominant limb, ES 1.6-2.3). Poor motor coordination elicited altered hip and knee biomechanics during sport-specific dynamic movements. The monitoring of motor coordination and on-field biomechanics might enhance the targeted trainings for ACL injury prevention.



#15 An Exploratory Data Analysis on the Influence of Role Rotation in a Small-Sided Game on Young Soccer Players

Reference: Int J Environ Res Public Health. 2021 Jun 24;18(13):6773.  doi: 10.3390/ijerph18136773.

Authors: Moisés Falces-Prieto, Francisco Tomás González-Fernández, Jaime Matas-Bustos, Pedro Jesús Ruiz-Montero, Jesús Rodicio-Palma, Manuel Torres-Pacheco, Filipe Manuel Clemente

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Summary: The aim of the present study was to analyze the behavior of players in a standard small-sided game (SSG) according to the role played (offensive (OF), defensive (DF), and wildcard (W)) and its relationship with physical demands (PHYD), technical performance (TP), and internal load (RPE). A total of 24 young highly trained male soccer players (under 16: n = 12; under 19: n = 12) participated. During the SSG, the players alternated the three roles (OF, DF, and W). The duration of each repetition was 4 min with a passive rest of 3 min between them. Furthermore, it emphasized the high demand in all defensive parameters. In addition, DF roles showed higher values in PHYD and RPE, followed by the OF roles, and finally by the W roles. A complementary, positive moderate correlation was found between PHYD and RPE in the U16 dataset (r = 0.45, p < 0.006). Very large positive correlations were also found between PHYD and RPE in the U19 and merged dataset (r = 0.78, p < 0.001 and r = 0.46, p < 0.63, respectively). This information could be useful for coaches in order to structure the roles in SSGs and control training load.



#16 Effects of Combined Creatine and Sodium Bicarbonate Supplementation on Soccer-Specific Performance in Elite Soccer Players: A Randomized Controlled Trial

Reference: Int J Environ Res Public Health. 2021 Jun 28;18(13):6919.  doi: 10.3390/ijerph18136919.

Authors: Jooyoung Kim

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Summary: Creatine and sodium bicarbonate are both ergogenic aids for athletic performance. However, research on the combined creatine and sodium bicarbonate (CSB) supplementation in soccer is limited. This study investigated the changes in soccer-specific performance in elite soccer players after supplementing with CSB. Twenty well-trained elite soccer players participated in the study (age: 20.70 ± 1.08 years; height: 173.95 ± 2.81 cm; body weight: 70.09 ± 3.96 kg; soccer experience: 8 years; average training hours per week: 20 h). The participants were randomly allocated into CSB groups (CSB, n = 10) and placebo groups (PLA, n = 10). The CSB group took creatine (20 g/day) and sodium bicarbonate (0.3 g/kg/day); these two supplements were taken four times a day (morning, afternoon, evening, and before sleep) for seven days. Soccer-specific performance was assessed via 10- and 30-m sprint, coordination, arrowhead agility, and Yo-Yo intermittent recovery level 1 tests. Compared to the PLA group, the CSB group performed better in the 30-m sprint (CSB: -3.6% vs. PLA: -0.6%, p = 0.007, effect size (ES): 2.3) and both right and left arrowhead agility (right: CSB: -7.3% vs. PLA: -0.7%, p < 0.001, ES: 2.8; left: CSB: -5.5% vs. PLA: -1.2%, p = 0.001, ES: 2.1) tests. However, there were no differences in 10 m sprints, coordination, and Yo-Yo intermittent recovery level 1 tests between the two groups (p > 0.05). In conclusion, CSB supplementation improved sprint and agility in elite soccer players. However, it is still unclear whether such effect is synergistic effect of two supplements or the result of either one of them. Therefore, caution should be taken when interpreting the results, and the limitations should be examined further in future studies.



#17 Analysis of Head Impact Biomechanics in Youth Female Soccer Players Following the Get aHEAD Safely in Soccer™ Heading Intervention

Reference: Sensors (Basel). 2021 Jun 3;21(11):3859.  doi: 10.3390/s21113859.

Authors: Victoria E Wahlquist, Thomas W Kaminski

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Summary: The effects of repetitive head impacts associated with soccer heading, especially in the youth population, are unknown. The purpose of this study was to examine balance, neurocognitive function, and head impact biomechanics after an acute bout of heading before and after the Get aHEAD Safely in Soccer™ program intervention. Twelve youth female soccer players wore a Triax SIM-G head impact sensor during two bouts of heading, using a lightweight soccer ball, one before and one after completion of the Get aHEAD Safely in Soccer™ program intervention. Participants completed balance (BESS and SWAY) and neurocognitive function (ImPACT) tests at baseline and after each bout of heading. There were no significant changes in head impact biomechanics, BESS, or ImPACT scores pre- to post-season. Deficits in three of the five SWAY positions were observed from baseline to post-season. Although we expected to see beneficial changes in head impact biomechanics following the intervention, the coaches and researchers observed an improvement in heading technique/form. Lightweight soccer balls would be a beneficial addition to header drills during training as they are safe and help build confidence in youth soccer players.



#18 Relationships between Sleep, Athletic and Match Performance, Training Load, and Injuries: A Systematic Review of Soccer Players

Reference: Review Healthcare (Basel). 2021 Jun 26;9(7):808.  doi: 10.3390/healthcare9070808.

Authors: Filipe Manuel Clemente, José Afonso, Júlio Costa, Rafael Oliveira, José Pino-Ortega, Markel Rico-González 

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Summary: The purpose of this systematic review was to summarize available evidence regarding the relationships between sleep and (i) athletic and match performance, (ii) training load, and (iii) injuries in soccer players. A systematic review of EBSCOhost (SPORTDiscus), PubMed, Cochrane Library, FECYT (Web of Sciences, CCC, DIIDW, KJD, MEDLINE, RSCI, and SCIELO) databases was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A total of 297 titles were identified, of which 32 met the eligibility criteria. Results revealed that soccer players are no exception for sleep inadequacy. Although there was inconsistency in the findings, some studies suggested that sleep restrictions in soccer negatively affected athletic and match performance while also increasing the number and severity of musculoskeletal injuries. On the other hand, inconsistent results were found between sleep and athletic and match performance, and training load in soccer players. Physiological responses (and their intensity) during drill-based games were not influenced by changes in sleep. The available evidence is inconsistent; however, it appears to suggest that poor sleep affects soccer players' performance and increases the risk of injury. However, it remains important to study this complex relationship further.



#19 Actual and perceived motor competence mediate the relationship between physical fitness and technical skill performance in young soccer players

Reference: Eur J Sport Sci. 2021 Jun 30;1-20.  doi: 10.1080/17461391.2021.1948616. Online ahead of print.

Authors: Michael J Duncan, Emma L J Eyre, Mark R Noon, Rhys Morris, C Doug Thake, Neil D Clarke, Anna J Cunningham

Summary: This study examined the role of fundamental movement skills (FMS) and perceived competence in the relationship between physical fitness and technical soccer skills in children. Seventy boys aged 7-12 years of age (Mean ± SD = 9 ± 2 years) who were regularly engaged in grassroots soccer participated in the present study. The Test of Gross Motor Development-2 (Ulrich, 2001) was used to assess FMS and the Perceived Physical Ability Scale for Children (Colella, et al., 2008) was used to assess perceived competence. Technical skill was determined from three tests reflecting dribbling, passing and shooting. Z-scores of each measure were summed, creating a composite measure of technical skill. Three measures of physical fitness were employed; 15m sprint time, standing long jump, and seated medicine ball (1kg) throw. Z-scores for each measure were summed creating a composite measure of physical fitness. The relationship between technical skill and FMS, fitness, perceived competence and age was examined via path analysis. Results indicated two significant mediated pathways: from physical fitness to technical skills via FMS, and from physical fitness to technical skills via perceived competence. Once these mediators had been accounted for, there was no direct link from physical fitness to technical skills. Coaches should therefore seek to avoid one-sided delivery of practice by not solely focusing on football type drills, and focusing on a range of activities which enhance a broad foundation of FMS and promote strategies to positively influence a child's perception of their own competence.



#20 In-Season Internal and External Workload Variations between Starters and Non-Starters-A Case Study of a Top Elite European Soccer Team

Reference: Medicina (Kaunas). 2021 Jun 23;57(7):645.  doi: 10.3390/medicina57070645.

Authors: Rafael Oliveira, Luiz H Palucci Vieira, Alexandre Martins, João Paulo Brito, Matilde Nalha, Bruno Mendes, Filipe Manuel Clemente

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Summary: Interpretation of the load variations across a period seems important to control the weekly progression or variation of the load, or to identify in-micro- and mesocycle variations. Thus, the aims of this study were twofold: (a) to describe the in-season variations of training monotony, training strain and acute:chronic workload ratio (ACWR) through session ratings of perceived exertion (s-RPE), total distance and high-speed running (HSR); and (b) to compare those variations between starters and non-starters.  Seventeen professional players from a European First League team participated in this study. They were divided in two groups: starters (n = 9) and non-starters (n = 8). The players were monitored daily over a 41-week period of competition where 52 matches occurred during the 2015-2016 in-season. Through the collection of s-RPE, total distance and HSR, training monotony, training strain and ACWR were calculated for each measure, respectively. Data were analyzed across ten mesocycles (M: 1 to 10). Repeated measures ANOVA was used with the Bonferroni post hoc test to compare M and player status.  The results revealed no differences between starters vs. non-starters (p > 0.05). M6 had a greater number of matches and displayed higher values for monotony (s-RPE, total distance and HSR), strain (only for total distance) and ACWR (s-RPE, TD and HSR). However, the variation patterns for all indexes displayed some differences.  The values of both starters and non-starters showed small differences, thus suggesting that the adjustments of training workloads that had been applied over the season helped to reduce differences according to the player status. Even so, there were some variations over the season (microcycles and mesocycles) for the whole team. This study could be used as a reference for future coaches, staff and scientists.



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