Latest research in football - week 40 - 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 Is Playing Soccer More Osteogenic for Females Before the Pubertal Spurt?
Reference: J Hum Kinet. 2019 Jul 5;67:153-161. doi: 10.2478/hukin-2018-0074. eCollection 2019 Jun.
Authors: Lozano-Berges G, Matute-Llorente Á, Gómez-Bruton A, González-Agüero A, Vicente-Rodríguez G, Casajús JA
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Summary: The aims of this study were to assess bone mass in children and adolescent soccer players and to evaluate the influence of both gender and pubertal status on bone mass. A total of 110 soccer players (75 males / 35 females; 12.73 ± 0.65 / 12.76 ± 0.59 years) participated in this cross-sectional study. They were divided into two groups according to their pubertal status. Bone and lean masses were measured with Dual-energy X-ray Absorptiometry. An independent t-test and an adjusted by subtotal lean and training experience multivariate analysis of covariance were used to analyse the differences in bone mass values between genders and maturity status. Female soccer players presented higher bone mass values than their male counterparts in most of the measured weight-bearing sites. Moreover, when stratifying by pubertal status, peripubertal and postpubertal females had higher subtotal body and lumbar spine bone mass than males. Comparing between pubertal status groups before adjustment, both male and female postpubertal players showed higher bone mass than their pubertal counterparts. After adjusting, these differences disappeared and, in fact results were inverted as bone mass at the femoral neck was higher in both male and female peripubertal soccer players than in postpubertal players. Bone mass seems to be more intensely stimulated by playing soccer in female than male players, particularly in the lumbar spine. The results of peripubertal players showing higher bone mass at the femoral neck after adjusting suggest that playing soccer during the peripubertal stage could

#2 Decrease in Attentional Performance After Repeated Bouts of High Intensity Exercise in Association-Football Referees and Assistant Referees
Reference: Front Psychol. 2019 Sep 6;10:2014. doi: 10.3389/fpsyg.2019.02014. eCollection 2019.
Authors: Schmidt SL, Schmidt GJ, Padilla CS, Simões EN, Tolentino JC, Barroso PR, Narciso JH, Godoy ES, Costa Filho RL
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Summary: Referees and assistant referees are submitted to high physical stress during matches. Pressure to make decisions in front of large crowds is another potential stressor. These two stressors can impair attention executive control, depending on physical fitness and individual vulnerability or resilience to situational pressure. Error percentage for referees and assistants may reach around 14% during a soccer match. Although previous studies have suggested that soccer referees and assistants should take cognitive assessments, they are only required by Fédération Internationale de Football Association (FIFA) to demonstrate knowledge of the rules and pass annually in a fitness test (FIFA-Test). This study aimed to assess attention performance in referees and assistants before and after the mandatory FIFA-Test. It is hypothesized that the high physical demands associated with the pressure to pass the FIFA-Test would interfere with attention performance. The sample included 33 referees and 20 assistants. The Continuous Visual Attention Test (CVAT) consisted of a 15-min Go/No-go task. Performance in the CVAT is based on four variables: omission and commission errors, reaction time, and variability of reaction time (VRT). Failure in the CVAT was defined by a performance below the 5th percentile of the age- and sex-matched normative data in at least one variable of the CVAT. Before the FIFA-Test all participants performed the CVAT. The second CVAT began 3-7 min directly following completion of the FIFA-test. Considering only the officials who passed both the FIFA-Test and the first CVAT (19 referees and 15 assistants), 44% (9 referees and 6 assistants) exhibited a performance decline in the second CVAT. A significant increase in VRT was found after the high intensity exercise. As increase in VRT is thought to reflect executive dysfunctions and lapses of attention, we concluded that physical fitness alone may not be enough to help officials cope with the physical and contextual stresses associated with the FIFA-Test. These data suggest that over 35% of soccer referees and their assistants who were considered physically able to referee matches may not be mentally prepared for the attentional demands of refereeing soccer matches.

#3 You Don't Bend It Like Beckham if You're Female and Reminded of It: Stereotype Threat Among Female Football Players
Reference: Front Psychol. 2019 Aug 28;10:1963. doi: 10.3389/fpsyg.2019.01963. eCollection 2019.
Authors: Grabow H, Kühl M
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Summary: Originally, the stereotype threat effect - poorer performance due to a fear of fulfilling a negative stereotype about one's group - was demonstrated for cognitive tasks (e.g. Steele and Aronson, 1995, or Steele, 1997). Drawing on the widespread stereotype of women being unable to play football we experimentally tested (N = 80) whether a respective threat affected female football players' goal scoring precision, i.e. a complex and demanding motor task. Those participants who were reminded of the stereotype scored significantly less hits than those not reminded. Additionally, deviations from the instruction during task execution (e.g. shooting from another distance than demanded or using the wrong foot) were recorded. Stereotype threat did not affect this comparatively more cognitive task of following instructions correctly. In order to explore underlying mechanisms of the observed stereotype effect, several potential mediators, e.g. measures of cognitive interference, or collective identification, were tested. None emerged as an unquestionable link between threat and motor performance. We discuss, however, why collective identification - in comparison to cognitive demand - appears to be the more promising explanatory concept.

#4 Corrigendum: Football Players Do Not Show "Neural Efficiency" in Cortical Activity Related to Visuospatial Information Processing During Football Scenes: An EEG Mapping Study
Reference: Front Psychol. 2019 Aug 27;10:1877. doi: 10.3389/fpsyg.2019.01877. eCollection 2019.
Authors: Del Percio C, Franzetti M, De Matti AJ, Noce G, Lizio R, Lopez S, Soricelli A, Ferri R, Pascarelli MT, Rizzo M, Triggiani AI, Stocchi F, Limatola C, Babiloni C
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#5 Strategies for Maintaining the Coach-Analyst Relationship Within Professional Football Utilizing the COMPASS Model: The Performance Analyst's Perspective
Reference: Front Psychol. 2019 Sep 10;10:2064. doi: 10.3389/fpsyg.2019.02064. eCollection 2019.
Authors: Bateman M, Jones G
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Summary: There is a considerable body of research by that has investigated the coach-athlete relationship in sport. However, given the multi-disciplinary nature of modern elite coaching, there is a scarcity of research focusing on the relationship between coaches and other members of the coaching and support team. This study examined the perceptions of six elite professional football analyst's relationships with their respective coaches. Semi structured interviews utilizing the COMPASS Framework were conducted focusing on Conflict, Openness, Motivation, Preventative Strategies, Assurance, Support, and Social Networks. The results verified that the COMPASS Model of relationship maintenance was applicable to this dyad. Content analysis indicated that there was 215 raw data units comprising of 16 higher order themes across the model which was further broken down into 29 lower order themes. All aspects of the model were found to contribute toward a positively maintained relationship. Having an open relationship underpinned by honesty and being able to provide an opinion was seen as the highest rated attribute that was closely followed by supporting the coach by understanding their requirements for successful coaching practice. Not meeting the coach's expectations was found to cause conflict and was further highlighted by an inductive analysis that revealed the existence of a relationship that is fundamentally dictated by the coach. Implications of this investigation are that professionals which support elite performers need to set out clear expectations of working practice and hierarchies in order to minimize the chance of internal conflict that can impact on the service levels received by the performer.

#6 A study protocol for the development and internal validation of a multivariable prognostic model to determine lower extremity muscle injury risk in elite football (soccer) players, with further exploration of prognostic factors
Reference: Diagn Progn Res. 2019 Sep 19;3:19. doi: 10.1186/s41512-019-0063-8. eCollection 2019.
Authors: Hughes T, Riley R, Sergeant JC, Callaghan MJ
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Summary: Indirect muscle injuries (IMIs) are a considerable burden to elite football (soccer) teams, and prevention of these injuries offers many benefits. Preseason medical, musculoskeletal and performance screening (termed periodic health examination (PHE)) can be used to help determine players at risk of injuries such as IMIs, where identification of PHE-derived prognostic factors (PF) may inform IMI prevention strategies. Furthermore, using several PFs in combination within a multivariable prognostic model may allow individualised IMI risk estimation and specific targeting of prevention strategies, based upon an individual's PF profile. No such models have been developed in elite football and the current IMI prognostic factor evidence is limited. This study aims to (1) develop and internally validate a prognostic model for individualised IMI risk prediction within a season in elite footballers, using the extent of the prognostic evidence and clinical reasoning; and (2) explore potential PHE-derived PFs associated with IMI outcomes in elite footballers, using available PHE data from a professional team. This is a protocol for a retrospective cohort study. PHE and injury data were routinely collected over 5 seasons (1 July 2013 to 19 May 2018), from a population of elite male players aged 16-40 years old. Of 60 candidate PFs, 15 were excluded. Twelve variables (derived from 10 PFs) will be included in model development that were identified from a systematic review, missing data assessment, measurement reliability evaluation and clinical reasoning. A full multivariable logistic regression model will be fitted, to ensure adjustment before backward elimination. The performance and internal validation of the model will be assessed. The remaining 35 candidate PFs are eligible for further exploration, using univariable logistic regression to obtain unadjusted risk estimates. Exploratory PFs will also be incorporated into multivariable logistic regression models to determine risk estimates whilst adjusting for age, height and body weight. This study will offer insights into clinical usefulness of a model to predict IMI risk in elite football and highlight the practicalities of model development in this setting. Further exploration may identify other relevant PFs for future confirmatory studies and model updating, or influence future injury prevention research.

#7 Limited positive effects on jump-landing technique in girls but not in boys after 8 weeks of injury prevention exercise training in youth football
Reference: Knee Surg Sports Traumatol Arthrosc. 2019 Sep 20. doi: 10.1007/s00167-019-05721-x. [Epub ahead of print]
Authors: Lindblom H, Waldén M, Carlfjord S, Hägglund M
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Summary: The aim was to evaluate changes in jump-landing technique in football-playing boys and girls after 8 weeks of injury prevention training. Four boys' and four girls' teams (mean age 14.1 ± 0.8 years) were instructed to use either the original Knee Control injury prevention exercise programme (IPEP) or a further developed IPEP, Knee Control + , at every training session for 8 weeks. Baseline and follow-up testing of jump-landing technique included drop vertical jumps (DVJ), assessed subjectively and with two-dimensional movement analysis, and tuck jump assessment (TJA). Only minor differences in intervention effects were seen between the two IPEPs, and results are therefore presented for both intervention groups combined. At baseline 30% of the boys showed good knee control during the DVJ, normalised knee separation distances of 77-96% (versus hip) and a median of 3 flaws during the TJA. Among girls, 22% showed good knee control, normalised knee separation distances of 67-86% and a median of 4 flaws during the TJA. At follow-up, boys and girls performed significantly more jumps during TJA. No changes in jump-landing technique were seen in boys, whereas girls improved their knee flexion angle at initial contact in the DVJ (mean change + 4.7°, p < 0.001, 95% CI 2.36-6.99, d = 0.7) and their TJA total score (- 1 point, p = 0.045, r = - 0.4). The study showed small positive effects on jump-landing technique in girls, but not in boys, after 8 weeks of injury prevention training.

#8 Prevention of severe knee injuries in men's elite football by implementing specific training modules
Reference: Knee Surg Sports Traumatol Arthrosc. 2019 Sep 20. doi: 10.1007/s00167-019-05706-w. [Epub ahead of print]
Authors: Krutsch W, Lehmann J, Jansen P, Angele P, Fellner B, Achenbach L, Krutsch V, Nerlich M, Alt V, Loose O
Summary: Injury prevention of knee injuries by means of training and warm-up exercises has been investigated in several studies in amateur football. However, the number of investigations in elite football is limited despite the currently higher injury incidence of severe knee injuries. Therefore, the purpose of this study was to investigate whether specifically adapted preventive training modules may reduce severe knee injuries in elite football. In a prospective controlled cohort study of elite football players in Germany, an injury prevention programme with 5 modules was implemented in the season of 2015-2016. The training modules were specifically adapted to this skill level and based on scientific evidence, team coach preferences, and the specific environment of this playing level. Of the 62 teams taking part in this study, 26 used the new trainings modules and 36 continued their standard programme as a control group. Success of the programme was documented by means of an injury report over one season. The primary outcome was reduction in severe knee injuries. A pre-seasonal investigation had identified five modules to be implemented in the training routine. Postural stability, mobilisation of lower extremity joints, leg and trunk stabilisation, jumping, and landing exercises as well as agility movements were incorporated into the programme to prevent severe knee injuries in elite football. Over the season, the study group (529 players) with the adapted training modules had sustained 52 severe knee injuries (incidence: 0.38 per 1000 h football exposure; prevalence: 9.8%) compared to 108 severe knee injuries in the control group (601 players) using the standard programme (incidence: 0.68 per 1000 h football exposure; prevalence: 18.0%; p < 0.05). The overall injury incidence for any other type of injury was comparable between the two groups (3.3 vs. 3.4 in h 1000 football, n.s.). Appropriate preventive training modules reduce severe knee injuries in elite football significantly. The key for the sustainability of preventive training measures are programmes specifically adapted to the demands of the playing level and to the preferences of the coaches

#9 Professional football clubs' involvement in health promotion in Spain: an audit of current practices
Reference: Health Promot Int. 2019 Sep 20. pii: daz097. doi: 10.1093/heapro/daz097. [Epub ahead of print]
Authors: Lozano-Sufrategui L, Pringle A, Zwolinsky S, Drew KJ
Summary: The implementation of effective community-based health interventions within Spanish football clubs has the potential to positively influence the public health agenda and enable the healthcare system in Spain to be more successful and sustainable. This paper aims to explore the involvement of Spanish football clubs in health promotion activities, their potential for future involvement and what that would require. A mixed methods explanatory sequential design, with a purposive sample of La Liga clubs. Data collection included online questionnaires and phone interviews. Quantitative methods enabled us to describe the number and types of programmes the clubs are currently involved in. Qualitative data was useful to further unpick the processes followed by the clubs in planning and developing health promotion programmes, while identifying any determinants to change. Seventeen clubs completed questionnaires and 11 participated in interviews. Clubs generally support inclusive programmes that target disadvantaged groups. Health-related programmes focus on healthy eating, physical activity and blood donation. Thematic analysis of interviews with 11 representatives of La Liga clubs resulted in three-key themes. These related to: (i) Diversity of programmes; (ii) (Lack of) evidence-based approaches to intervention design and evaluation and (iii) Contrasting views about a club's role in health promotion interventions. Spanish football clubs have potential to reach into communities that are currently underserved. However, there is limited infrastructure and understanding within the clubs to do this. Nevertheless, there is huge opportunity for organizations with public health responsibility in Spain to implement translational approaches within football-based settings.

#10 Defining a historic football team: Using Network Science to analyze Guardiola's F.C. Barcelona
Reference:  Sci Rep. 2019 Sep 19;9(1):13602. doi: 10.1038/s41598-019-49969-2.
Authors: Buldú JM, Busquets J, Echegoyen I, Seirul Lo F
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Summary: The application of Network Science to social systems has introduced new methodologies to analyze classical problems such as the emergence of epidemics, the arousal of cooperation between individuals or the propagation of information along social networks. More recently, the organization of football teams and their performance have been unveiled using metrics coming from Network Science, where a team is considered as a complex network whose nodes (i.e., players) interact with the aim of overcoming the opponent network. Here, we combine the use of different network metrics to extract the particular signature of the F.C. Barcelona coached by Guardiola, which has been considered one of the best teams along football history. We have first compared the network organization of Guardiola's team with their opponents along one season of the Spanish national league, identifying those metrics with statistically significant differences and relating them with the Guardiola's game. Next, we have focused on the temporal nature of football passing networks and calculated the evolution of all network properties along a match, instead of considering their average. In this way, we are able to identify those network metrics that enhance the probability of scoring/receiving a goal, showing that not all teams behave in the same way and how the organization Guardiola's F.C. Barcelona is different from the rest, including its clustering coefficient, shortest-path length, largest eigenvalue of the adjacency matrix, algebraic connectivity and centrality distribution.

#11 Improved maximal strength is not associated with improvements in sprint time or jump height in high-level female football players: a clusterrendomized controlled trial
Reference: BMC Sports Sci Med Rehabil. 2019 Sep 17;11:20. doi: 10.1186/s13102-019-0133-9. eCollection 2019.
Authors: Pedersen S, Heitmann KA, Sagelv EH, Johansen D, Pettersen SA
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Summary: Maximal strength increments are reported to result in improvements in sprint speed and jump height in elite male football players. Although similar effects are expected in females, this is yet to be elucidated. The aim of this study was to examine the effect of maximal strength training on sprint speed and jump height in high-level female football players. Two female football teams were team-cluster-randomized to a training group (TG) performing maximal strength training (MST) twice a week for 5 weeks, or control group (CG) doing their regular pre-season preparations. The MST consisted of 3-4 sets of 4-6 repetitions at ≥85% of 1 repetitions maximum (1RM) in a squat exercise. Sprint speed and jump height were assessed in 5-, 10- and 15 m sprints and a counter-movement jump (CMJ) test, respectively. Nineteen participants in TG (18.3 ± 2.7 years) and 14 in CG (18.3 ± 2.4 years) completed pre- and posttests and were carried forward for final analyses. There was no improvement in neither of the sprint times (p > 0.36), nor jump height (p = 0.87). The players increased their 1RM in squats (main of effect of time: p < 0.00, pη2 = 0.704), and an interaction effect of time x group was observed (p < 0.00, pη2 = 0.516) where the TG increased their 1RM more than the CT (between subjects effects: p < 0.001, pη2 = 0.965). MST improved maximal strength in female football players to a large extent; however, the improvement in maximal strength did not result in any transference to sprint speed or jump height.

#12 Acute Surgical Excision of a Traumatic Fat Fracture in a Professional Soccer Player
Reference: J Orthop Case Rep. 2019;9(3):68-71. doi: 10.13107/jocr.2250-0685.1426.
Authors: Kayani B, Ayuob A, Onochie E, Haddad FS
Summary: Surgical excision of fat fractures is often reserved for patients with large chronic deformities to improve cosmetic appearance. To our knowledge, the acute surgical management of a traumatic fat fracture has not been previously reported. This case report describes the management of a professional soccer player that developed a traumatic fat fracture over the lateral thigh. The patient presented with persistent pain, reduced range of movement, and inability to participate in sporting activity. Symptoms were refractory to non-operative treatment. Following acute surgical excision of the fat fracture, the patient was able to make an early return to sporting activity with no complications at short-term follow-up. Acute surgical excision of a traumatic fat fracture may be used as an avenue for improving pain, enhancing functional rehabilitation, and facilitating early return to pre-injury level of function.

#13 The Influence of Caffeine Expectancies on Simulated Soccer Performance in Recreational Individuals
Reference: Nutrients. 2019 Sep 25;11(10). pii: E2289. doi: 10.3390/nu11102289.
Authors: Shabir A, Hooton A, Spencer G, Storey M, Ensor O, Sandford L, Tallis J, Higgins MF
Summary: Caffeine (CAF) has been reported to improve various facets associated with successful soccer play, including gross motor skill performance, endurance capacity and cognition. These benefits are primarily attributed to pharmacological mechanisms. However, evidence assessing CAF's overall effects on soccer performance are sparse with no studies accounting for CAF's potential psychological impact. Therefore, the aim of this study was to assess CAF's psychological vs. pharmacological influence on various facets of simulated soccer performance. Utilising a double-dissociation design, eight male recreational soccer players (age: 22 ± 5 years, body mass: 78 ± 16 kg, height: 178 ± 6 cm) consumed CAF (3 mg/kg/body mass) or placebo (PLA) capsules, 60 minutes prior to performing the Loughborough Intermittent Shuttle Test (LIST) interspersed with a collection of ratings of perceived exertion (RPE), blood glucose and lactate, heart rate and performing the Loughborough Soccer Passing Test (LSPT). Whole-body dynamic reaction time (DRT) was assessed pre- and post- LIST, and endurance capacity (TLIM) post, time-matched LIST. Statistical analysis was performed using IBM SPSS (v24) whilst subjective perceptions were explored using template analysis. Mean TLIM was greatest (p < 0.001) for synergism (given CAF/told CAF) (672 ± 132 s) vs. placebo (given PLA/told PLA) (533 ± 79 s). However, when isolated, TLIM was greater (p = 0.012) for CAF psychology (given PLA/told CAF) (623 ± 117 s) vs. pharmacology (given CAF/told PLA) (578 ± 99 s), potentially, via reduced RPE. Although DRT performance was greater (p = 0.024) post-ingestion (+5 hits) and post-exercise (+7 hits) for pharmacology vs. placebo, psychology and synergism appeared to improve LSPT performance vs. pharmacology. Interestingly, positive perceptions during psychology inhibited LSPT and DRT performance via potential CAF over-reliance, with the opposite occurring following negative perceptions. The benefits associated with CAF expectancies may better suit tasks that entail lesser cognitive-/skill-specific attributes but greater gross motor function and this is likely due to reduced RPE. In isolation, these effects appear greater vs. CAF pharmacology. However, an additive benefit may be observed after combining expectancy with CAF pharmacology (i.e. synergism).

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