Latest research in football - week 14 - 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 The Lower Limb Assessment Score: A valid measure of hypermobility in elite football?
Reference: Phys Ther Sport. 2019 Mar 15;37:86-90. doi: 10.1016/j.ptsp.2019.03.007. [Epub ahead of print]
Authors: Paul Johnson A, Ward S, Simmonds J
Summary: This study aims to validate the Lower Limb Assessment Score against the current gold standard Beighton Scale within an adult elite footballing population to allow for future research to explore the influence of lower limb specific hypermobility on injury incidence. Thirty-six male, professional footballers aged between 18 and 37 years old participated in this study. The Sensitivity, specificity, positive predictive value, negative predictive value and Spearman's rank correlation between the LLAS and Beighton Scale were used as outcome measures. There was significant strong correlation between LLAS and Beighton Scale scores (ρ = 0.732; p < 0.001). The LLAS displayed a sensitivity of 67% and specificity of 94% when a cut off of ≥4/12 was applied to the screening data. This cut off point also yielded moderate Positive Predictive Validity (50%) and excellent Negative Predictive Validity (97%). The present study suggests that the LLAS is a valid test for identifying lower limb hypermobility within an adult male footballing population when a cut off of ≥4/12 is used.

#2 Soccer Footedness and Between-Limbs Muscle Strength: Systematic Review and Meta-Analysis
Reference: Int J Sports Physiol Perform. 2019 Apr 11:1-12. doi: 10.1123/ijspp.2018-0336. [Epub ahead of print]
Authors: DeLang MD, Rouissi M, Bragazzi NL, Chamari K, Salamh PA.
Summary: Limb dominance and consequent between-limbs muscle strength in soccer players should be explored to determine a standard musculoskeletal profile to maintain and establish during screening protocols and postinjury rehabilitation. The primary aim of this review was to identify dominant- vs non-dominant-lower-extremity muscle-strength characteristics of healthy soccer players, with secondary aims to consider available between-limbs outcome measures and directions for future research. Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were followed. Five electronic databases were used for study identification with guidance from a medical librarian. Inclusion criteria consisted of studies employing a cross-sectional design assessing soccer players of all ages, genders, and levels of play that identified limb dominance and associated lower-extremity muscle strength as a main purpose of the experiment. The literature search identified 3471 articles. After screening titles, abstracts, and full texts, 17 articles were included in the review. Peak torques and hamstring-to-quadriceps ratios via isokinetic dynamometry were commonly used, and subsequent meta-analyses were conducted to yield remarkable between-limbs symmetry. Additional results of individual studies also demonstrate symmetry, except 1 article of velocity-dependent measures that reported greater strength in the dominant limb. In soccer, between-limbs muscle strength measured by maximal isokinetic dynamometry demonstrates symmetry across ages, genders, and levels of play. Future testing using alternative measures that more specifically replicate the movement demands of soccer players may further classify between-limbs characteristics.

#3 Player Migration and Soccer Performance
Reference: Front Psychol. 2019 Mar 21;10:616. doi: 10.3389/fpsyg.2019.00616. eCollection 2019.
Authors: Lago-Peñas C, Lago-Peñas S, Lago I
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Summary: The aim of this study is to examine the relationship between migrating soccer players and the annual ranking of the national teams according to the World Football Elo Rating. The sample includes annual data for 243 countries over the period 1994-2018. Migration is captured with the number of migrating players by country in the "big-five" leagues. The causal relationship between the two variables is examined by using Granger causality test. Four control variables are included: the political regime, per capita income, population, and regional soccer confederations. It was hypothesized that (i) the better the ranking of the national teams in the Elo rating, the higher the number of migrating players in the "big-five" leagues (shop-window hypotheses) and that (ii) while the shop-window effect takes place in the short-run, the annual Elo rating of a national team is positively affected by expatriate players in the medium or long-run, but not in the short-run (blending hypotheses). The results shed light on two crucial issues. First, causality mainly goes from national soccer performance to migrating soccer players rather than the other way around. Second, the timing of the two effects is quite different. While those players giving an outstanding performance when their national team is doing well are immediately bought by clubs from more highly ranked leagues (the shop-window effect), it takes at least 4 years for the additional skills acquired by migrated players to have a positive effect on the national soccer performance (the blending effect).

#4 Test-retest reliability of a hip strength assessment system in varsity soccer players
Reference: Phys Ther Sport. 2019 Mar 28;37:138-143. doi: 10.1016/j.ptsp.2019.03.013. [Epub ahead of print]
Authors: Desmyttere G, Gaudet S, Begon M
Summary: The purpose was to investigate test-retest reliability of a hip strength assessment system (GroinBar).  Twenty asymptomatic varsity soccer players participated in this study. Maximal isometric hip strength (adduction, abduction, internal and external rotation, flexion and extension) was assessed using the GroinBar. Intraclass correlation coefficient (ICC) and relative standard error of measurement (SEM) were calculated to evaluate reliability of peak (ICC3,1) (highest peak within 3 trials) and average peak (ICC3,3) (average of 3 trials) force and rate of force development (RFD). Hotelling's T2, were also used to compare bilateral and reciprocal ratios between dominant and non-dominant leg. ICC for both peak force and RFD values revealed moderate to good reliability (0.53-0.88 and 0.61-0.84, respectively), whereas reliability was good to excellent regarding their average values (0.77-0.95 and 0.81-0.92, respectively). SEM of average peak force and RFD values (4.1-9.4% and 8.2-13.9%, respectively) were lower than that of peak force and RFD values (5.7-13.0% and 10.7-19.1%, respectively). No significant difference was found in bilateral and reciprocal force ratios between dominant and non-dominant leg. The GroinBar is a reliable tool to assess hip muscle function in athletic populations and could be used for player screening and follow-up.

#5 A season long investigation into the effects of injury, match selection and training load on mental wellbeing in professional under 23 soccer players: A team case study
Reference: Eur J Sport Sci. 2019 Apr 6:1-7. doi: 10.1080/17461391.2019.1600586. [Epub ahead of print]
Authors: Abbott W, Brownlee TE, Harper LD, Naughton RJ, Richardson A, Clifford T
Summary: This study examined the influence of injury, match selection and training load on mental wellbeing (MW) in a squad of professional soccer players. Using a longitudinal design, twenty-five male soccer players (age, 20 ± 1 years, height, 1.80 ± 5.79 m, body mass 76.33 ± 7.52 kg) from the under 23 squad playing in the Premier League 2 division in the UK completed the Warwick-Edinburgh Mental Well-being Scale (WEMWBS) each week of the 2017/2018 season (37 weeks in total). Injury and non-selection for the match squad were the only significant predictors of MW (P < 0.05). Injury had the biggest influence on MW that was lower when injured vs. not injured (43.6 ± 5.0 vs. 49.9 ± 3.5, respectively, P = 0.001, ES = 1.48), accounting for 40% of the variation in MW. This increased to 50% when not being selected to play games was also considered. Weekly training loads measured by GPS (total distance, sprint distance and total duration) and individual player win rate did not influence MW (P > 0.05). These findings highlight the importance of monitoring MW in professional soccer players and suggest that injured players and those rarely selected for the match squad should be educated on the strategies available for managing their mental health and wellbeing.

#6 Tibial fractures following participation in recreational football: Incidence and outcome
Reference: Niger J Clin Pract. 2019 Apr;22(4):492-495. doi: 10.4103/njcp.njcp_148_18.
Authors: Nwosu C
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Summary: Football is responsible for 3.5%-10% of all injuries treated in hospital, but this may reflect the popularity of the sport rather than its dangers. Young people are particularly at risk of sports injury because of high levels of exposure at a time of major physiological change. Soccer players are susceptible to a variety of injuries due to contact, aggressive tackle, and high-speed collisions. The aim of this study was to determine the pattern of presentation, treatment, and outcome of tibial fractures following participation in recreational football activity; with the hope that knowledge gained from this study will help in preventing or reducing its occurrence. This is a retrospective study of all cases of tibial fractures following participation in recreational football presenting to the Orthopedic Unit of Federal Medical Center and Surgery Department of Sir Yahaya Memorial Hospital all in Birnin Kebbi, Kebbi State, north western Nigeria; from January 2012 to December 2017. Data were extracted from the accident and emergency register, operation register, and patients' case folders on biodata, diagnosis, mechanism of injury, associated injuries, type of surgical procedure, site of surgery, date of surgery, and postoperative complications. Data collected were analyzed using the Statistical Package for Social Sciences for Windows version 22. Results were presented with descriptive statistics. In total, 37 patients were included in the study. All of them were males. The age range is from 14 to 33 years with mean age of 23.6. 17 (45.9%) of the patients are in the 21- to 30-year age group. The right tibia was affected in 34 (91.9%) patients. None of the patients used shin guard. The mechanism of injury in all the cases was direct contact. About 31 (83.8%) of the fractures were closed. Seven (18.9%) of these patients were discharged against medical advice. Nineteen (51.3%) patients were managed nonoperatively with plaster of Paris casts. Ten (27.1%) of these patients had internal fixation with locked intramedullary nail. Tibial fractures following football occur mostly in males especially adolescents and youths. The right tibia was commonly affected and most of the injuries are closed. The most common mechanism of injury was direct contact.

#7 The Effect of the "11+ Kids" on the Isokinetic Strength of Young Football Players
Reference: Int J Sports Physiol Perform. 2019 Apr 8:1-19. doi: 10.1123/ijspp.2018-0827. [Epub ahead of print]
Authors: Zarei M, Abbasi H, Daneshjoo A, Gheitasi M, Johari K, Faude O, Rommers N, Rössler R
Summary: The "11+ Kids" injury prevention programme has shown to reduce injuries and related costs in youth football players under 14 years of age. A major argument to convince coaches to use this exercise-based injury prevention programme, is a potential performance enhancement of the players. Therefore, this study investigated the effects of the "11+ Kids" programme on isokinetic strength. Two teams were randomly assigned to the intervention and control group. The intervention group replaced their warm-up by the "11+ Kids" and the control group warmed-up as usual. Two days before and after the 10-week intervention, isokinetic strength of the hip adductors and abductors, knee flexors and extensors, and ankle invertors and evertors was tested. Thirty-one players (mean age 11.5 ± 0.8 years) completed the study. The intervention group showed large improvements in all isokinetic strength measures (p < 0.001 for all measures, Cohen's d 0.8 to 1.4), whereas the control group only showed negligible to medium positive effects (p-values from 0.006 to 0.718, Cohen's d -0.1 to 0.7). The intervention was beneficial compared to the control group regarding isokinetic strength of the hip adductors (p < 0.001), knee flexors (p = 0.002), as well as ankle evertors (p < 0.001) and invertors (p = 0.005). Given the relatively short intervention period of 10 weeks, the observed improvements relate to a practically meaningful effect of the intervention. The gain in strength may improve players' performance and may contribute to a reduction of injury risk in the long-term application.

#8 Assessment of Safety and Glycemic Control During Football Tournament in Children and Adolescents With Type 1 Diabetes-Results of GoalDiab Study
Reference: Pediatr Exerc Sci. 2019 Apr 7:1-7. doi: 10.1123/pes.2018-0264. [Epub ahead of print]
Authors: Gawrecki A, Araszkiewicz A, Szadkowska A, Biegański G, Konarski J, Domaszewska K, Michalak A, Skowrońska B, Adamska A, Naskręt D, Jarosz-Chobot P, Szypowska A, Klupa T, Zozulińska-Ziółkiewicz D
Summary: The purpose was to assess glycemic control and safety of children and adolescents with type 1 diabetes participating in a 2-day football tournament. In total, 189 children with type 1 diabetes from 11 diabetes care centers, in Poland, participated in a football tournament in 3 age categories: 7-9 (21.2%), 10-13 (42.9%), and 14-17 (36%) years. Participants were qualified and organized in 23 football teams, played 4 to 6 matches of 30 minutes, and were supervised by a medical team. Data on insulin dose and glycemia were downloaded from personal pumps, glucose meters, continuous glucose monitoring, and flash glucose monitoring systems. The median level of blood glucose before the matches was 6.78 (4.89-9.39) mmol/L, and after the matches, it was 7.39 (5.5-9.87) mmol/L (P = .001). There were no episodes of severe hypoglycemia or ketoacidosis. The number of episodes of low glucose value (blood glucose ≤3.9 mmol/L) was higher during the tournament versus 30 days before: 1.2 (0-1.5) versus 0.7 (0.3-1.1) event/person/day, P < .001. Lactate levels increased during the matches (2.2 [1.6-4.0] mmol/L to 4.4 [2.6-8.5] mmol/L after the matches, P < .001). Large football tournaments can be organized safely for children with type 1 diabetes. For the majority of children, moderate mixed aerobic-anaerobic effort did not adversely affect glycemic results and metabolic safety.

#9 The effects of TeaCrine® and caffeine on endurance and cognitive performance during a simulated match in high-level soccer players
Reference: J Int Soc Sports Nutr. 2019 Apr 18;16(1):20. doi: 10.1186/s12970-019-0287-6.
Authors: Bello ML, Walker AJ, McFadden BA, Sanders DJ, Arent SM
Summary: Theacrine (1,3,7,9-tetramethyluric-acid) is a pure alkaloid with a similar structure to caffeine and acts comparably as an adenosine receptor antagonist. Early studies have shown non-habituating effects, including increases in energy and focus in response to Teacrine®, the compound containing pure theacrine. The purpose of this study was to determine and compare the effects of Teacrine® and caffeine on cognitive performance and time-to-exhaustion during a simulated soccer game in high-level male and female athletes. Male and female soccer players (N = 24; MAge = 20.96 ± 2.05y, MMaleVO2max = 55.31 ± 3.39 mL/O2/kg, MFemaleVO2max = 50.97 ± 3.90 mL/O2/kg) completed a 90-min simulated treadmill soccer match over four randomized sessions (TeaCrine®, caffeine, TeaCrine® + caffeine, placebo). Cognitive testing at halftime and end-of-game including simple reaction time (SRT), choice RT (CRT), and cognitive-load RT with distraction questions (COGRT/COGRTWrong) was performed, with a run time-to-exhaustion (TTE) at 85% VO2max following end-of-game cognitive testing. Session times and pre-exercise nutrition were controlled. RM-MANOVAs with univariate follow-ups were conducted and significance was set at P < 0.05. TTE trended towards significance in TeaCrine® and TeaCrine® + caffeine conditions compared to placebo (P < 0.052). A condition main effect (P < 0.05) occurred with faster CRT in caffeine and TeaCrine® + caffeine compared to placebo. COGRTWrong showed a significant time main effect, with better accuracy at end-of-game compared to halftime (P < 0.05). A time x condition interaction in SRT (P < 0.05) showed placebo improved from halftime to end-of-game. The 27-38% improvements in TTE reflect increased performance capacity that may have important implications for overtime scenarios. These findings suggest TeaCrine® favorably impacts endurance and the combination with caffeine provides greater benefits on cognitive function than either supplement independently.

#10 Comparison of lateral abdominal muscle thickness of young male soccer players with and without low back pain
Reference:  Int J Sports Phys Ther. 2019 Apr;14(2):273-281.
Authors: Noormohammadpour P, Mirzaei S, Moghadam N, Mansournia MA, Kordi R
Summary: While researchers have investigated low back pain (LBP) and its association with the thickness of trunk muscles in the general population, few articles have studied this relationship in athletes. The purpose was to compare the lateral abdominal muscle thickness and other possible functional risk factors in young soccer players with and without LBP. Thirty young male soccer players, with and without LBP, from the Premier League participated in this study. The thicknesses of the external oblique, internal oblique and transversus abdominis muscles were measured via musculoskeletal ultrasound imaging, bilaterally. In addition, hamstring flexibility, lumbar spine flexion range of motion, and trunk extensor muscle endurance were measured and were compared in those with and without the history of LBP. The mean age of the subjects was 17.4 (+/- 1.1) years. There was no statistically significant difference between groups (p > 0.05). Subjects with a history of LBP during their lifetime of sports participation (sports life), within the prior year, and within the prior month had statistically significant lower external oblique muscle thickness bilaterally (p<0.05). Subjects with a sports life history of LBP had lower internal oblique muscle thickness on both sides (p<0.05). Moreover, those with a sports life history of LBP had significantly less hamstring flexibility than the non-LBP group on the dominant limb (p < 0.05). In this sample group of young soccer players, abdominal muscle ultrasound measurements were different between players with and without LBP. Further longitudinal studies are needed to evaluate the role of these muscles as LBP risk factor for soccer players.

#11 The effects of training on hormonal concentrations in young soccer players
Reference: J Cell Physiol. 2019 Apr 16. doi: 10.1002/jcp.28673. [Epub ahead of print]
Authors: Muscella A, Vetrugno C, Spedicato M, Stefàno E, Marsigliante S
Summary: The purpose was to test the hypothesis that football training would be accompanied by physiological adaptations and hormonal changes, we analyzed the effects of a whole football season on physical fitness and hormonal concentrations in youth football players. Male football players (n = 29, age 16.51 ± 0.7 years) in a regional professional league and male healthy control subjects (n = 30, age 17.1 ± 1 years) participated to the study. Blood cortisol, testosterone, and growth hormone (hGH) concentrations were assayed before the beginning of the training period (T0), just after the training period (T1), at the middle of the season (T2), and at the end of the season (T3). In each period physical tests and anthropometric measurements were also performed. Results showed significant differences in basal values of cortisol, testosterone, and growth hormone (hGH) in the four time points evaluated (P < 0.01). In addition, the concentrations of hGH were higher in the soccer players group than in control subjects (P < 0.001). Between the start of the training period and the end of the football season significant differences were observed in the anthropometric characteristics and in the physical form of the football players. Furthermore, the hormonal status was significantly correlated with the indicators of the lower limb power (squat-jump [SqJ], and counter-movement-jump [CMJ]) and those of aerobic performance (Yo-Yo intermittent recovery test level 1 (YYIRT1) and maximal oxygen consumption (VO2max )).These data underscore the importance of establishing training protocols that present the potential to promote positive adaptations without, at the same time, provoking overtraining of young players.

#12 Sport Participation and Specialization Characteristics Among Pediatric Soccer Athletes
Reference: Orthop J Sports Med. 2019 Mar 27;7(3):2325967119832399. doi: 10.1177/2325967119832399. eCollection 2019 Mar.
Authors: McLeod TV, Israel M, Christino MA, Chung JS, McKay SD, Lang PJ, Bell DR; PRiSM Sports Specialization Research Interest Group, Chan CM, Crepeau A, Davis E, Fletcher AL, Laniak J, McCaffrey K, Pacicca D, Riederer M, Rizzone K, Rush JK, Zaslow T
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Summary: Soccer is an increasingly popular sport for children and adolescents in the United States. Little is known about participation patterns related to sport specialization. The purpose was to investigate soccer participation levels and sport specialization characteristics among youth soccer athletes. Adolescent athletes aged between 12 and 18 years completed an online survey addressing participant demographics, sports and soccer participation history, and level of specialization. Descriptive analyses characterized participation, while chi-square and Kruskal-Wallis tests assessed the influence of specialization, sex, and grade on survey variables. Overall, 83.7% of 746 respondents participated in an organized soccer league outside of school, and 37% played in multiple leagues concurrently. Nearly three-quarters of respondents trained in soccer more than 8 months of the year, with those who participated in club soccer being more likely to train more than 8 months of the year. More respondents were classified as high specialization (37.5%), followed by moderate (35.6%) and low (28.6%) specialization. No differences between sexes were noted for level of specialization or quitting other sports to specialize in soccer, but male athletes were more likely to train more than 8 months per year compared with female athletes. Respondents in older grades (9th-10th and 11th-12th grades) were more likely to be highly specialized and quit other sports to focus on soccer. No differences between grade levels were found among respondents training more than 8 months per year. The study findings suggest that many youth soccer athletes participated in multiple teams or leagues at the same time and trained more than 8 months of the year. Characteristics including participation on a club team, level of specialization, and male sex were associated with a greater likelihood of exceeding the 8-month training recommendation.

#13 The relative age effect in European elite soccer: A practical guide to Poisson regression modelling
Reference: PLoS One. 2019 Apr 3;14(4):e0213988. doi: 10.1371/journal.pone.0213988. eCollection 2019.
Authors: Doyle JR, Bottomley PA
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Summary: Many disciplines of scholarship are interested in the Relative Age Effect (RAE), whereby age-banding confers advantages on older members of the cohort over younger ones. Most research does not test this relationship in a manner consistent with theory (which requires a decline in frequency across the cohort year), instead resorting to non-parametric, non-directional approaches. In this article, the authors address this disconnect, provide an overview of the benefits associated with Poisson regression modelling, and two managerially useful measures for quantifying RAE bias, namely the Indices of Discrimination and Wastage. In a tutorial-like exposition, applications and extensions of this approach are illustrated using data on professional soccer players competing in the top two tiers of the "Big Five" European football leagues in the search to identify paragon clubs, leagues, and countries from which others may learn to mitigate this form of age-discrimination in the talent identification process. As with OLS regression, Poisson regression may include more than one independent variable. In this way we test competing explanations of RAE; control for unwanted sources of covariation; model interaction effects (that different clubs and countries may not all be subject to RAE to the same degree); and test for non-monotonic versions of RAE suggested in the literature.

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