Latest research in football - week 4 - 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 Train Like You Compete? Physical and Physiological Responses on Semi-Professional Soccer Players
Reference: Int J Environ Res Public Health. 2020 Jan 24;17(3). pii: E756. doi: 10.3390/ijerph17030756.
Authors: Castillo-Rodríguez A, Cano-Cáceres FJ, Figueiredo A, Fernández-García JC
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Summary: Decision-making in soccer has repercussions and depends on the environment of training or competition. The demands on the players can reveal if the decision-making is similar or different from that required during competition. The aim of this study was to assess the physical and physiological responses of players in training matches (TM) and official competition matches (CM) according to the playing position (external defenders, internal defenders, midfielders, and forwards/extremes). Twenty semi-professional male soccer players and 10 CM (n = 40) and 10 TM (n = 40) were studied using global positioning system technology, and paired and one-way ANOVA tests were carried out to compare physical (distances and number of sprints) and physiological (heart rates) responses with the factors a) match environments (TM and CM) and b) the playing position, respectively. The results revealed that during CM, players covered higher total distance, partial distances, and sprints at different speeds (0-21 km/h) and produced higher physiological responses. Midfielders covered the greatest total distance in both TM (7227.6 m) and CM (11,225.9 m), in comparison to the other playing positions. However, forwards and extremes spent more time (56.8% of the CM [d = 0.78]) at 76% to 84% of their maximal heart rates. First, the physical and physiological responses in TM were significantly lower than in CM. Second, these responses were different according to the playing position, so this study was able to verify the exact amount of variation between the load produced in TM and CM. These results will help the coach and technical staff to design training tasks to complement the responses found in TM.

#2 T helper cell-related changes in peripheral blood induced by progressive effort among soccer players
Reference: PLoS One. 2020 Jan 28;15(1):e0227993. doi: 10.1371/journal.pone.0227993. eCollection 2020.
Authors: Kostrzewa-Nowak D, Nowak R
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Summary: The regulatory mechanisms affecting the modulation of the immune system accompanying the progressive effort to exhaustion, particularly associated with T cells, are not fully understood. We analysed the impact of two progressive effort protocols on T helper (Th) cell distribution and selected cytokines. Sixty-two male soccer players with a median age of 17 (16-29) years performed different protocols for progressive exercise until exhaustion: YO-YO (YYRL1) and Beep. Blood samples for all analyses were taken three times: at baseline, post-effort, and in recovery. The percentage of Th1 cells increased post-effort and in recovery. The post-effort percentage of Th1 cells was higher in the Beep group compared to the YYRL1 group. Significant post-effort increase in Th17 cells was observed in both groups. The post-effort percentage of regulatory T cells (Treg) increased in the Beep group. An increased post-effort concentration of IL-2, IL-6, IL-8 and IFN-γ in both groups was observed. Post-effort TNF-α and IL-10 levels were higher than baseline in the YYRL1 group, while the post-effort IL-17A concentration was lower than baseline only in the Beep group. The recovery IL-2, IL-4, TNF-α and IFN-γ levels were higher than baseline in the YYRL1 group. The recovery IL-4, IL-6, IL-8, TNF-α and IFN-γ values were higher than baseline in the Beep group. The molecular patterns related to cytokine secretion are not the same between different protocols for progressive effort. It seems that Treg cells are probably the key cells responsible for silencing the inflammation and enhancing anti-inflammatory pathways

#3 Are Elite Soccer Teams' Preseason Training Sessions Associated With Fewer In-Season Injuries? A 15-Year Analysis From the Union of European Football Associations (UEFA) Elite Club Injury Study
Reference: Am J Sports Med. 2020 Jan 28:363546519899359. doi: 10.1177/0363546519899359. [Epub ahead of print]
Authors: Ekstrand J, Spreco A, Windt J, Khan KM
Summary: Preseason training develops players' physical capacities and prepares them for the demands of the competitive season. In rugby, Australian football, and American football, preseason training may protect elite players against in-season injury. However, no study has evaluated this relationship at the team level in elite soccer. The aim of this study was to investigate whether the number of preseason training sessions completed by elite soccer teams was associated with team injury rates and player availability during the competitive season. It was hypothesized that elite soccer teams who participate in more preseason training will sustain fewer injuries during the competitive season. We used the Union of European Football Associations (UEFA) injury dataset to analyze 44 teams for up to 15 seasons (total, 244 team-seasons). Separate linear regression models examined the association between the number of team preseason training sessions and 5 in-season injury measures. Injury-related problems per team were quantified by totals of the following: (1) injury burden, (2) severe injury incidence, (3) training attendance, (4) match availability, and (5) injury incidence. Teams averaged 30 preseason training sessions (range, 10-51). A greater number of preseason training sessions was associated with less injury load during the competitive season in 4 out of 5 injury-related measures. Our linear regression models revealed that for every 10 additional preseason training sessions that the team performed, the in-season injury burden was 22 layoff days lower per 1000 hours (P = .002), the severe injury incidence was 0.18 severe injuries lower per 1000 hours (P = .015), the training attendance was 1.4 percentage points greater (P = .014), and the match availability was 1.0 percentage points greater (P = .042). As model fits were relatively low (adjusted R2 = 1.3%-3.2%), several factors that contribute to in-season injury outcomes were unaccounted for. Teams that performed a greater number of preseason training sessions had "healthier" in-season periods. Many other factors also contribute to in-season injury rates. Understanding the benefit of preseason training on in-season injury patterns may inform sport teams' planning and preparation.

#4 Effects of Small-Sided Soccer Games on Physical Fitness, Physiological Responses, and Health Indices in Untrained Individuals and Clinical Populations: A Systematic Review
Reference: Sports Med. 2020 Jan 27. doi: 10.1007/s40279-019-01256-w. [Epub ahead of print]
Authors: Zouhal H, Hammami A, Tijani JM, Jayavel A, de Sousa M, Krustrup P, Sghaeir Z, Granacher U, Ben Abderrahman A
Summary: Small-sided soccer games (SSSG) are a specific exercise regime with two small teams playing against each other on a relatively small pitch. There is evidence from original research that SSSG exposure provides performance and health benefits for untrained adults. The aim of this systematic review was to summarize recent evidence on the acute and long-term effects of SSSG on physical fitness, physiological responses, and health indices in healthy untrained individuals and clinical populations. This systematic literature search was conducted in four electronic databases (PubMed, Web of Science, SPORTDiscus) from inception until June 2019. The following key terms (and synonyms searched for by the MeSH database) were included and combined using the operators "AND", "OR", "NOT": ((soccer OR football) AND ("soccer training" OR "football training" OR "soccer game*" OR "small-sided soccer game*") AND ("physical fitness" OR "physiological adaptation*" OR "physiological response*" OR health OR "body weight" OR "body mass" OR "body fat" OR "bone composition" OR "blood pressure")). The search syntax initially identified 1145 records. After screening for titles, abstracts, and full texts, 41 studies remained that examined the acute (7 studies) and long-term effects (34 studies) of SSSG-based training on physical fitness, physiological responses, and selected alth indices in healthy untrained individuals and clinical populations. No training-related injuries were reported in the 41 acute and long-term SSSG studies. Typically, a single session of SSSG lasted 12-20 min (e.g., 3 × 4 min with 3 min rest or 5 × 4 min with 4 min rest) involving 4-12 players (2 vs. 2 to 6 vs. 6) at an intensity ≥ 80% of HRmax. Following single SSSG session, high cardiovascular and metabolic demands were observed. Specifically, based on the outcomes, the seven acute studies reported average heart rates (HR) ≥ 80% of HRmax (165-175 bpm) and mean blood lactate concentrations exceeding 5 mmol/l (4.5-5.9 mmol/l) after single SSSG sessions. Based on the results of 34 studies (20 with healthy untrained, 10 with unhealthy individuals, and 4 with individuals with obesity), SSSG training lasted between 12 and 16 weeks and was performed 2-3 times per week. SSSG had positive long-term effects on physical fitness (e.g., Yo-Yo IR1 performance), physiological responses including maximal oxygen uptake (VO2max) [+ 7 to 16%], and many health-related markers such as blood pressure (reductions in systolic [- 7.5%] and diastolic [- 10.3%] blood pressure), body composition (decreased fat mass [- 2 to - 5%]), and improved indices of bone health (bone mineral density: [+ 5 to 13%]; bone mineral content: [+ 4 to 5%]), and metabolic (LDL-cholesterol [- 15%] as well as cardiac function (left-ventricular internal diastolic diameter [+ 8%], end diastolic volume [+ 21%], left-ventricular mass index [+ 18%], and left-ventricular ejection fraction [+ 8%]). Irrespective of age or sex, these health benefits were observed in both, untrained individuals and clinical populations. In conclusion, findings from this systematic review suggest that acute SSSG may elicit high cardiovascular and metabolic demands in untrained healthy adults and clinical populations. Moreover, this type of exercise is safe with positive long-term effects on physical fitness and health indices. Future studies are needed examining the long-term effects on physical fitness and physiological adaptations of different types of SSSG training (e.g., 3 vs. 3; 6 vs. 6) in comparison to continuous or interval training in different cohorts.

#5 Pubic stress fracture presenting as a strain of adductor longus in a 16-year-old elite soccer player with Crohn's disease: a case report
Reference: J Can Chiropr Assoc. 2019 Dec;63(3):197-204.
Authors: Marshall C, Gringmuth R
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Summary: Adductor strains are the most commonly reported muscle injuries in adolescent soccer players and the second most common muscle injuries in adult players. Health practitioners should be aware of possible differential diagnoses, such as a pubic stress fracture or pubic apophysitis when athletes present with chronic groin pain. The purpose was to present a rare case of a unilateral pelvic stress fracture of a 16-year old elite soccer player with a history of Crohn's disease. Case notes of two sports-based practitioners were reviewed and compiled retrospectively. Following activity restriction, a period of rest, conservative care, and progressive rehabilitation, this athlete was able to achieve a pain-free state with near equal iso-kinetic strength bilaterally as measured by Cybex 6000 (Cybex International Inc., Medway, MA, USA) muscle testing. Full activity was resumed 10 months after initial presentation and the athlete was able to return to playing professional soccer. This case report presents a rare diagnosis of a unilateral pubic stress fracture presenting as a strain of adductor longus. Although quite rare, differential diagnoses such as a potential underlying stress fracture should be considered when presented with chronic or recurrent groin pain.

#6 Associations of Apolipoprotein E ε4 Genotype and Ball Heading With Verbal Memory in Amateur Soccer Players
Reference: JAMA Neurol. 2020 Jan 27. doi: 10.1001/jamaneurol.2019.4828. [Epub ahead of print]
Authors: Hunter LE, Freudenberg-Hua Y, Davies P, Kim M, Lipton RB, Stewart WF, Srinivasan P, Hu S, Lipton ML
Summary: Emerging evidence suggests that long-term exposure to ball heading in soccer, the most popular sport in the world, confers risk for adverse cognitive outcomes. However, the extent to which the apolipoprotein E ε4 (APOE ε4) allele, a common risk factor for neurodegeneration, and ball heading are associated with cognition in soccer players remains unknown. The purpose was to determine whether the APOE ε4 allele and 12-month ball heading exposure are associated with verbal memory in a cohort of adult amateur soccer players. A total of 379 amateur soccer players were enrolled in the longitudinal Einstein Soccer Study from November 11, 2013, through January 23, 2018. Selection criteria included participation in soccer for more than 5 years and for more than 6 months per year. Of the 379 individuals enrolled in the study, 355 were genotyped. Three players were excluded for reporting extreme levels of heading. Generalized estimating equation linear regression models were employed to combine data across visits for a cross-sectional analysis of the data. At each study visit every 3 to 6 months, players completed the HeadCount 12-Month Questionnaire, a validated, computer-based questionnaire to estimate 12-month heading exposure that was categorized as low (quartiles 1 and 2), moderate (quartile 3), and high (quartile 4). Verbal memory was assessed at each study visit using the International Shopping List Delayed Recall task from CogState was used as outcome measures.  A total of 352 soccer players (256 men and 96 women; median age, 23 years [interquartile range, 21-28 years]) across a total of 1204 visits were analyzed. High levels of heading were associated with worse verbal memory performance (β = -0.59; 95% CI, -0.93 to -0.25; P = .001). There was no main association of APOE ε4 with verbal memory (β = 0.09; 95% CI, -0.24 to 0.42; P = .58). However, there was a significant association of APOE ε4 and heading with performance on the ISRL task (χ2 = 7.22; P = .03 for overall interaction). In APOE ε4-positive players, poorer verbal memory associated with high vs low heading exposure was 4.1-fold greater (APOE ε4 negative, β = -0.36; 95% CI, -0.75 to 0.03; APOE ε4 positive, β = -1.49; 95% CI, -2.05 to -0.93), and poorer verbal memory associated with high vs moderate heading exposure was 8.5-fold greater (APOE ε4 negative, β = -0.13; 95% CI, -0.54 to 0.29; APOE ε4 positive, β = -1.11, 95% CI, -1.70 to -0.53) compared with that in APOE ε4-negative players. This study suggests that the APOE ε4 allele is a risk factor for worse memory performance associated with higher heading exposure in the prior year, which highlights that assessing genetic risks may ultimately play a role in promoting safer soccer play.

#7 Effects of Soccer Match-Play on Unilateral Jumping and Interlimb Asymmetry: A Repeated-Measures Design
Reference: J Strength Cond Res. 2020 Jan 24. doi: 10.1519/JSC.0000000000003389. [Epub ahead of print]
Authors: Bishop C, Read P, Stern D, Turner A
Summary: The aims of this study were two-fold: (a) determine the effects of repeated soccer match-play on unilateral jump performance and interlimb asymmetries and (b) examine associations between asymmetry and commonly reported external load variables collected during competition. Single-leg countermovement jumps and drop jumps were collected before and immediately after 5 soccer matches in elite academy soccer players. Global positioning system data were also collected during each match as part of the routine match-day procedures. Single-leg countermovement jump height and concentric impulse showed significant reductions after matches (p < 0.01; effect size [ES]: -0.67 to -0.69), but peak force did not (p > 0.05; ES: -0.05 to -0.13). Single-leg drop jump height and reactive strength also showed significant reductions after matches (p < 0.01; ES: -0.39 to -0.58). No meaningful reductions in asymmetry were present at the group level, but individual responses were highly variable. Significant associations between postmatch reactive strength asymmetry and explosive distance (r = 0.29; p < 0.05), relative explosive distance (r = 0.34; p < 0.05), high-speed running (r = 0.35; p < 0.05), and relative high-speed running (r = 0.44; p < 0.01) were observed. These findings show that unilateral jump tests are more appropriate than asymmetry to detect real change after soccer competition, and practitioners should be cautious about using asymmetry to inform decision-making during the temporal recovery period.

#8 Maturity Related Differences in Body Composition Assessed by Classic and Specific Bioimpedance Vector Analysis among Male Elite Youth Soccer Players
Reference: Int J Environ Res Public Health. 2020 Jan 22;17(3). pii: E729. doi: 10.3390/ijerph17030729.
Authors: Toselli S, Marini E, Maietta Latessa P, Benedetti L, Campa F
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Summary: The aim of this study was to analyze the efficiency of classic and specific bioelectrical impedance vector analysis (BIVA) in the assessment of maturity related differences in body composition among male elite youth soccer players, and to provide bioelectrical impedance reference data for this category. A group of 178 players (aged 12.1 ± 1.6 years) were registered in a professional Italian soccer team participating in the first division (Serie A). They were divided into three groups according to their maturity status while bioelectrical resistance and reactance were obtained. The classic and specific BIVA procedures were applied, which correct bioelectrical values for body height and body geometry, respectively. Percentage of fat mass (FM%) and total body water (TBW (L)) were estimated from bioelectrical values. Age-specific z-scores of the predicted age at peak height velocity identified 29 players as earlier-, 126 as on time-, and 23 as later-maturing. TBW was higher (p < 0.01) in adolescents classified as "early" maturity status compared to the other two groups and classic BIVA confirmed these results. Conversely, no differences in FM% were found among the groups. Specific vector length showed a higher correlation (r = 0.748) with FM% compared with the classic approach (r = 0.493). Classic vector length showed a stronger association (r = -0.955) with TBW compared with specific (r = -0.263). Specific BIVA turns out to be accurate for the analysis of FM% in athletes, while classic BIVA shows to be a valid approach to evaluate TBW. An original data set of bioelectric impedance reference values of male elite youth soccer players was provided.

#9 Spatio-temporal investigation of surface soil hardness on professional football field
Reference: Environ Monit Assess. 2020 Jan 30;192(2):151. doi: 10.1007/s10661-020-8087-7.
Authors: Biraderoglu M, Kaplan S, Basaran M
Summary: The present study was conducted to identify the minimum number of sampling points to monitor surface hardness of the pitches through geostatistical methods and to determine spatial and temporal distribution of surface hardness in autumn, winter, spring, and summer periods. Initial samplings were performed from 126 points and with data reduction, the optimum number of sampling points was identified as 77. In upcoming sampling periods, surface hardness and soil temperature were directly measured in situ and disturbed soil samples taken from 77 points were subjected to moisture content, bulk density, and texture analyses (clay-C, silt-Si, and sand-S). In autumn period, surface hardness highly correlated with soil temperature and moisture content (r2 = - 0.438 and - 0.344, p < 0.01). Surface hardness significantly correlated only with soil temperature in winter period and only with bulk density in summer period (respectively r2 = - 0.366 and 0.234, p < 0.01). Average surface hardness values in autumn, winter, spring, and summer periods were respectively measured as 5.99, 6.55, 5.84, and 5.92%. Semivariograms generated for hardness were modeled with spherical model in all periods and a certain nugget effect was detected in all periods. Maximum likelihood distance for autumn, winter, spring, and summer periods was respectively measured as 65, 40, 45, and 46 m. It was concluded based on present findings that geostatistical methods could reliably be used to monitor surface hardness of football pitches and then proper and timely interventions could be made to sections not complying with FIFA standards.

#10 The Influence of Time of Season on Injury Rates and the Epidemiology of Canadian Football Injuries
Reference: Clin J Sport Med. 2020 Feb 6. doi: 10.1097/JSM.0000000000000824. [Epub ahead of print]
Authors: Robbins SM, Bodnar C, Donatien P, Mirza R, Zhao ZY, Hoeber S, Naidu D, Redelmeier A, Steele RJ, Shrier I
Summary: The purpose was to describe injury rates and injury patterns in the Canadian Football League (CFL) according to time during the season, player position, injury type, and injury location. Depending on the analysis, time of season (preseason, regular, and playoffs), player position, injury type, and injury location. Medical attention and time-loss injury rates per 100 athletes at risk (AAR), and prevalence of time-loss injuries per week. The average game injury rate was 45.2/100 AAR medical attention injuries and 30.7/100 AAR time-loss injuries. Injury rates declined by 1% per week over the season for both medical attention (rate ratio = 0.99) and time-loss (rate ratio = 0.99) injuries, with a substantial decline during the playoffs compared with preseason (rate ratio = 0.70-0.77). The number of ongoing time-loss injuries increased over the course of the regular season. Quarterbacks, offensive backs, and linebackers had the highest game injury rates. Joint/ligament and muscle/tendon injuries were the most common injury types for games and practices, respectively. The lower extremity was the most commonly affected area, specifically the lower leg/ankle/foot and hip/groin/thigh. There was a 1% decline in injury rate per week during the season and a 30% decline during the playoffs. The number of ongoing time-loss injuries increased over the regular season. Current results can aid league officials and medical staff in making evidence-based decisions concerning player safety and health.

#11 A systematic review of genitourinary injuries arising from rugby and football
Reference: J Pediatr Urol. 2020 Jan 7. pii: S1477-5131(19)30443-7. doi: 10.1016/j.jpurol.2019.12.019. [Epub ahead of print]
Authors: Kim JK, Koyle MA, Lee MJ, Nason GJ, Ren LY, O'Kelly F
Summary: Genitourinary injuries in athletes engaging in high-impact sports such as football and rugby may have catastrophic consequences, especially in individuals with pre-existing urologic concerns, such as a solitary kidney. The purpose was to summarize the current literature on football-related or rugby-related genitourinary organ injuries in both adult and pediatric populations in an effort to risk stratify the likelihood of these injuries. An independent systematic literature search for records reporting football-related or rugby-related injuries was conducted by a certified librarian and reviewer in March 2019. The search electronic databases included Medline, EMBASE, Scopus, and Web of Science. All studies reporting football-related or rugby-related genitourinary injuries were included. Twenty-two records (11 research studies, 11 case reports) were identified. In the pediatric population, the reported football-related kidney injuries were 0.1-0.7% of all football-related injuries, 0.07-0.5% of all sports-related injuries, and 1.5-37.5% of all sports-related genitourinary injuries, with incidence ranging from 0.00000084 to 0.0000092 injuries per exposure (five studies). Pediatric football-related testicular injuries were reported to be 0.11% of all football injuries, 0-0.07% of all sports-related injuries, and 0-37.5% of all sports-related genitourinary injuries; injury per exposure was 0.0000092 (four studies). In adults, there was no proportion of genitourinary injuries that could be determined, and football-related kidney injury incidence was 0.000012 injuries per exposure (one study). No adult literature investigated testicular injuries. Eleven case reports were additionally identified. Review of the case reports suggests that patients with previously existing urologic abnormalities such as ureteropelvic junction obstruction may predispose an individual to kidney injuries. There is little to suggest that those engaged in football or rugby have a significant risk of genitourinary injury; therefore, future guidelines should reflect this.

#12 Injury in elite women's soccer: a systematic review
Reference: Phys Sportsmed. 2020 Feb 6:1-7. doi: 10.1080/00913847.2020.1720548. [Epub ahead of print]
Authors: Alahmad TA, Kearney P, Cahalan R
Summary: The objective was to summarize risk factors for injury in elite women's soccer. Ten electronic databases were searched for studies that explored risk factors for injury in elite women soccer players. Study cohorts were required to consist of adult (?18 years) elite players defined as 'the best performers in their country in a certain sport who are competing at national or international levels' [1]. Two reviewers independently assessed articles for eligibility. The CASP checklist was used for quality assessment of included studies, and the Oxford Center of Evidence-Based Medicine guidelines were used to determine their level of evidence. Eight studies were included in this review. Findings indicated an association between an increased injury risk and previous injury and increased joint laxity. There is additional evidence to support a relationship between injuries and higher soccer exposure, playing position, increased BMI, low H/Q ratio, player's level of balance and co-ordination, as well as various psychological issues. However, there were conflicting findings for the effect of postural control. Individual differences in Q-angle, intercondylar notch width or pelvic width measurements were not found to be associated with injury. The incidence of injury was higher in the dominant limb. The risk of injury in elite female soccer players is multifactorial, complex, and associated with a range of intrinsic, and extrinsic factors. More high-quality studies are needed to investigate each identified risk factor in order to inform effective injury screening.

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