Latest research in football - week 17 - 2023

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 Myocardial Work Index in Professional Football Players: A Novel Method for Assessment of Cardiac Adaptation

Reference: J Clin Med. 2023 Apr 23;12(9):3059. doi: 10.3390/jcm12093059.

Authors: Elena Refoyo, Jesús Troya, Ana de la Fuente, Almudena Beltrán, Oscar Luis Celada, Leonel Díaz-González, Roberto Pedrero-Tomé, Manuel García-Yébenes, Jose María Villalón

Summary: The global myocardial work index (GWI), a novel, valid, and non-invasive method based on speckle-tracking echocardiography, could provide value for calculating left ventricular (LV) function and energy consumption in athletes. We prospectively analyzed a single-center cohort of Spanish First-Division football players who attended a pre-participation screening program from June 2020 to June 2021, compared to a control group. All the individuals underwent an electrocardiogram and echocardiography, including two-dimensional speckle tracking and 4D-echo. The study aimed to evaluate the feasibility of myocardial work in professional football players and its correlations with other echocardiographic parameters. The study population comprised 97 individuals (49 professional players and 48 controls). The mean age was 30.48 ± 7.20 years old. The professional football players had significantly higher values of LVEDV (p < 0.001), LVESV (p < 0.001), LV-mass index (p = 0.011), PWTd (p = 0.023), and EA (p < 0.001) compared with the control group. In addition, the professional players had lower GCW (p = 0.003) and a tendency to show lower GWI values (p < 0.001). These findings could suggest that professional football players have more remodeling and less MW, related to their adaptation to intensive training. Significant differences in GLS (p = 0.01) and GWE (p = 0.04) were observed as a function of the septal thickness of the athletes. Irrespective of the MW variable, the parameters with better correlations across all the populations were SBP, DBP, and GLS. The GWI is a novel index to assess cardiac performance, with less load dependency than strain measurements. Future GWI analyses are warranted to understand myocardial deformation and other pathological differential diagnoses.



#2 Risk Factors for Sustaining a Second ACL Injury after Primary ACL Reconstruction in Female Football Players: A Study Investigating the Effects of Follow-Up Time and the Statistical Approach

Reference: Sports Med Open. 2023 May 12;9(1):29. doi: 10.1186/s40798-023-00571-x.

Authors: Anne Fältström, Martin Hägglund, Joanna Kvist, Luciana D Mendonça

Summary: Studies evaluating risk factors for sustaining an anterior cruciate ligament (ACL) injury have different, sometimes contrasting, results. Different follow-up times and statistical approaches may be a reason for these differences. The aim of this study was to explore if different follow-up times and statistical approaches, classification and regression tree (CART) analysis and Cox regression, would impact on the association between various candidate risk factors and ACL injury in female football players. In total, 112 active female football players, 18 ± 8 months after ACL reconstruction (mean age ± SD, 20 ± 2 years), were included and followed for at least 36 months. At baseline, all players underwent assessment of range of motion of knee and ankle joints, functional tests, and answered questionnaires regarding knee function, psychological and personality traits. Nineteen independent variables were included for the CART analysis and for univariable Cox regression and compared using four different follow-up times: 0-12, 0-24, 0-36, and 0->36 months. Forty-three (38%) players sustained a second ACL injury. The identified risk factors varied depending on follow-up time both with CART analysis and with Cox regression. CART identified 12 of the 19 independent variables and selected between 5 and 6 of the variables in the four different follow-up times associated with second ACL injury. The accuracy of the different follow-up times for the CART varied between 86 and 93% with 77-96% sensitivity and 70-81% specificity. Cox regression identified two risk factors: knee extension at 0-36 months and 0->36 months, and time between primary injury and surgery at 0->36 months. The accuracy varied between 54 and 64% with 44-88% sensitivity and 32-71% specificity. The identified risk factors associated with a second ACL injury varied depending on the follow-up time and statistical approach used. Thus, in future research on risk factors, the time athletes are followed up and the type of statistical methods used are important to discuss.



#3 Low adoption in women's professional football: teams that used the Nordic Hamstring Exercise in the team training had fewer match hamstring injuries

Reference: BMJ Open Sport Exerc Med. 2023 May 5;9(2):e001523. doi: 10.1136/bmjsem-2022-001523. eCollection 2023.

Authors: Jan Ekstrand, Anna Hallén, Håkan Gauffin, Håkan Bengtsson

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Summary: The primary objective was to study the reach, effectiveness, adoption, implementation and maintenance of the Nordic Hamstring Exercise (NHE) programme in women's elite teams in Europe in the 2020-21 season. The secondary objective was to compare hamstring injury rates between teams that used the NHE programme regularly in team training and teams that did not. Eleven teams participating in the Women's Elite Club Injury Study during the 2020-21 season provided data about injury rates and the implementation of the NHE programme. One team (9%) used the full original NHE programme, and four teams used the programme in the team training during parts of the season (team training group, n=5). Five teams did not use the NHE, or used it only sporadically for individual players, and one team used NHE only for players with a previous or current hamstring injury (no team training group, n=6). The team training group had a lower incidence of hamstring injuries during match-play (1.4 vs 4.0, p=0.028) than the non-team training group while no difference between groups was shown for the hamstring injury incidence in training (0.6 vs 0.7, p=0.502). A low adoption of the NHE programme was reported during the 2020-21 season. However, teams that used NHE for the whole team or most players had a lower hamstring injury incidence at match-play than teams that did not use the NHE or used it for individual players only.



#4 Symbolic consumption as a non-traditional predictor of brand loyalty in the sports industry, football club segment

Reference: Heliyon. 2023 Apr 18;9(4):e15474. doi: 10.1016/j.heliyon.2023.e15474. eCollection 2023 Apr.

Authors: Alfredo Guzmán Rincón, Ruby Lorena Carrillo Barbosa, Marelby Amado Mateus, Néstor Ordoñez Saavedra

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Summary: Brand loyalty is one of the main objectives of marketing, due to its impact on the sustainability of organisations; however, the explanation of how this type of loyalty is built in the sports industry is complex, due to the way it is organised. Traditionally, brand loyalty in this industry has been explained by satisfaction, service quality, commitment and trust, thus other variables that have been analysed from the marketing field have not been included in the models developed for the sports industry. The aim of this article was to explore the relationship between symbolic consumption as a non-traditional predictor of brand loyalty in the sports industry, more specifically in the football club segment. For this purpose, a quantitative cross-sectional study was defined, with a non-probabilistic sampling. To test the proposed relationship, modelling by means of partial least squares structural equations was chosen. The results showed that symbolic consumption is positively related to brand loyalty in the sports industry in the football club segment, with a large effect size. This study becomes a starting point for scholars who wish to further explore the relationship between symbolic consumption and brand loyalty in the context of sport. Likewise, for marketing professionals in the sports industry, it suggests the importance of symbolic consumption for the design of strategies that enable the creation of brand loyalty in consumers in the case of football clubs. In this sense, marketing professionals should seek to create advertising and promotional campaigns that appeal to strengthen the relationship of the sports consumer with their social groups based on the actual and ideal self-concept, as lifestyle.



#5 Highlighting Shooting Opportunities in Football

Reference: Sensors (Basel). 2023 Apr 24;23(9):4244. doi: 10.3390/s23094244.

Authors: Ilias Loutfi, Luis Ignacio Gómez-Jordana, Angel Ric, João Milho, Pedro Passos

Summary: The purpose of the present study was to create a two-dimensional model which illustrates a landscape of shooting opportunities at goal during a competitive football match. For that purpose, we analysed exemplar attacking subphases of each team when the ball was in the last 30 m of the field. The player's positional data (x and y coordinates) and the ball were captured at 25 fps and processed to create heatmaps that illustrated the shooting opportunities that were available in the first and second half in different field areas. Moreover, the time that the shooting opportunities were available was estimated. Results show that in the observed match, most of the shooting opportunities lasted between 1 and 2 s, with only a few opportunities lasting more than 2 s. The shooting opportunities did not display a homogenous distribution over the field. The obtained heatmaps provide valuable and specific information about each team's shooting opportunities, allowing the identification of the most vulnerable areas. Additionally, the amount, duration, and location of the shooting opportunities have shown significant differences between teams. This customizable model is sensitive to the features of shooting opportunities and can be used in real-time video analysis for individual and collective performance analysis.



#6 Injury Types and Training Habits among Soccer (Football) Athletes

Reference: Orthop Rev (Pavia). 2023 May 13;15:74883. eCollection 2023.

Authors: Jai Patel, Rohan Mangal, Thor Stead, Andrew Barbera, Latha Ganti

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Summary: For soccer athletes, injuries are frequent and pose a considerable health and financial burden for individuals and families. While studies have previously assessed the incidence of soccer injuries and preventive strategies male athletes use to reduce these occurrences, few have included women and players of varying skill levels. The aim was to report the frequency of injuries in a cohort of male and female soccer athletes and describe the training habits that have helped prevent injury. Two hundred (n=200) United States participants completed a questionnaire on soccer practicing frequency, habits, injuries, and treatments. A screening question ensured all respondents had played soccer for at least one year and determined eligibility for the study. Participant information related to age, sex, education, income, and race was also collected. JMP statistical software was used to analyze collected data and build multivariate regressions, mosaic plots, and histograms. The mean number of practice sessions per week was 3.60 +/- 1.64, and the median experience playing soccer was 2-4 years. Older participants were more likely to practice once (p = 0.0001) or twice (p= 0.0008) per week. Women were less likely to include warmups before playing soccer (p = 0.022). This was problematic as participants who did not include a proper warmup routine were more likely to have been absent from play for longer amounts of time following injury (p = 0.032). The four most common injury sites were knees (n = 35, 17.5%), ankles (n = 31, 15.5%), shoulders (n = 25, 12.5%), and head/neck (n = 24, 12%). 140 (47.62%) patients used pain medication as their main remedy, 128 (43.54%) went to physical therapy, and 26 (10.78%) underwent surgery. In any sample of soccer athletes involving variations in sex, race, and competitive play, injuries are highly common. Few studies before this one have included female athletes, and our findings highlight an important discrepancy in training habits between sexes. Women are less likely to follow a warmup regimen and are thus injured for longer. Incorporating dynamic stretching and plyometrics are particularly helpful to stay healthy.



#7 The Women's Soccer Health Study: From Head to Toe

Reference: Sports Med. 2023 May 17;1-10. doi: 10.1007/s40279-023-01860-x. Online ahead of print.

Authors: Daphne I Ling, Jo A Hannafin, Heidi Prather, Heidi Skolnik, Theresa A Chiaia, Polly de Mille, Cara L Lewis, Ellen Casey

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Summary: Women are under-represented in the sports literature despite increasing rates of sports participation. Our objective was to investigate the risks and benefits of an elite women's soccer career in five health domains: general, musculoskeletal, reproductive endocrinology, post-concussion, and mental. An online survey was distributed to retired US college, semi-professional, professional, and national team soccer players using personal networks, email, and social media. Short validated questionnaires were used to evaluate the health domains, including the Patient-Reported Outcomes Measurement Information System (PROMIS), Single Assessment Numerical Evaluation (SANE), Post-Concussion Symptom Scale (PCSS), and Patient Health Questionnaire (PHQ). A total of 560 eligible players responded to the survey over a 1-year period. The highest competitive levels were 73% college, 16% semi-professional, 8% professional, and 4% national team. The mean number of years since retirement was 12 (SD = 9), and 17.0% retired for involuntary reasons. The mean SANE scores (0-100 scale as percentage of normal) were knee = 75% (SD = 23), hip = 83% (SD = 23), and shoulder = 87% (SD = 21). The majority (63%) reported that their current activity level included participation in impact sports. A substantial proportion of players reported menstrual irregularities during their careers: 40% had fewer periods with increasing exercise and 22% had no periods for ≥ 3 months. The players (n = 44) who felt that post-concussion symptoms were due to soccer reported more time-loss concussions (F[2] = 6.80, p = 0.002) and symptom severity (F[2] = 30.26, p < 0.0001). Players who recently retired (0-5 years) reported the highest anxiety/depression scores and lowest satisfaction rates compared with those who retired 19+ years ago. Health concerns include musculoskeletal injuries, post-concussion symptoms, and lower mental health in the early years following retirement. This comprehensive survey provides initial results that will lay the foundation for further analyses and prioritize research studies that can help all female athletes.



#8 A color-related bias in offside judgments in professional soccer: A matter of figure-background contrast?

Reference: PLoS One. 2023 May 16;18(5):e0285500. doi: 10.1371/journal.pone.0285500. eCollection 2023.

Authors: Peter Wühr, Daniel Memmert

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Summary: We investigated the impact of outfit colors on the frequency of offside judgments in soccer. In a recent laboratory study, observers made more offside judgments against forwards wearing the outfit of Schalke 04 (blue shirts, white shorts) than against forwards wearing the outfit of Borussia Dortmund (yellow shirts, black shorts), when figure-background luminance contrast was higher for the former team. Here, we investigated whether a similar effect is present in real matches of the German Bundesliga. Study 1 revealed a higher offside score for Schalke 04 than for Borussia Dortmund in matches between these clubs. Studies 2-4 showed higher offside scores for teams wearing a blue/white outfit, and lower offside scores for teams wearing a yellow/black outfit, in their matches against all other Bundesliga teams. Together, results suggest that more offside judgments are made against teams of higher salience, possibly induced by differences in figure-background contrast. Notably, this color-related bias occurred in our study even though a Video-Assistant Referee (VAR) supervised the (offside) decisions of the Assistant Referees.



#9 Evaluation of Reaction Time during the One-Leg Balance Activity in Young Soccer Players: A Pilot Study

Reference: Children (Basel). 2023 Apr 19;10(4):743. doi: 10.3390/children10040743.

Authors: Fábio Saraiva Flôres, Joana Lourenço, Lucy Phan, Simon Jacobs, Renata Matheus Willig, Priscila Ellen Pinto Marconcin, Nuno Casanova, Denise Soares, Filipe Manuel Clemente, Ana Filipa Silva

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Summary: This study's aim was two-fold: (i) to test the intra-session reliability of the one-leg balance activity test; and (ii) to assess the influence of age on reaction time (RT) and the differences between dominant and non-dominant feet. Fifty young soccer players with an average age of 12.4 ± 1.8 years were divided into two groups: younger soccer players (n = 26; 11.6 ± 0.9 years) and older soccer players (n = 24; 14.2 ± 0.8 years). Each group then completed four trials (two with each leg) of the one-leg balance activity (OLBA) to evaluate RT under a single-leg stance. Mean RT and the number of hits were calculated, and the best trial was also selected. T-tests and Pearson correlations were performed for statistical analysis. Values for RT were lower, and the number of hits was higher while standing on the non-dominant foot (p = 0.01). MANOVA revealed that the "Dominant Leg" factor did not affect the multivariate composite (Pillai Trace = 0.05; F(4, 43) = 0.565; p = 0.689; Partial ETA Squared = 0.050; Observed Power = 0.174). The "Age" factor did not present an effect on the multivariate composite (Pillai Trace = 0.104; F(4, 43) = 1.243; p = 0.307; Partial ETA Squared = 0.104; Observed Power = 0.355). The results of the present investigation demonstrate that RT may be lower while standing on the non-dominant foot.



#10 The relationship of personality and executive functions in high-level soccer athletes: expertise-and gender-specific differences

Reference: Front Sports Act Living. 2023 Apr 28;5:1130759. doi: 10.3389/fspor.2023.1130759. eCollection 2023.

Authors: Jan Spielmann, Adam Beavan, Jan Mayer

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Summary: Psycho-cognitive factors such as personality and executive functions (EFs) are influential parameters when it comes to examining expertise in high-level soccer. Therefore, the profiles of those athletes are relevant both from a practical and scientific point of view. The aim of this study was to investigate the relationship between personality traits and executive functions with age group as an influential factor in high-level male and female soccer players. Personality traits and executive functions of 138 high-level male and female soccer athletes from the U17-Pros teams were assessed using the big-five paradigm. A series of linear regressions investigated contributions of personality on EF assessments and team, respectively. Linear regression models showed both negative and positive relationships between various personality traits, executive function performance and the influence of expertise and gender. Together, a maximum of 23% (R2 = 6%-23%) of the variance between EFs with personality and various teams, demonstrating that many unaccounted-for variables remain at play. The results of this study demonstrate the inconsistent relationship between personality traits and executive functions. The study calls for more replication studies to help strengthen the understanding of relationships between psycho-cognitive factors in high-level team sport athletes.



#11 Predictive modeling of the ratings of perceived exertion during training and competition in professional soccer players

Reference: J Sci Med Sport. 2023 May 8;S1440-2440(23)00081-6. doi: 10.1016/j.jsams.2023.05.001.

Authors: Emmanuel Vallance, Nicolas Sutton-Charani, Patrice Guyot, Stéphane Perrey

Summary: Evaluate the ability of predicting the ratings of perceived exertion from the external load variables in professional soccer players through a chronological perspective (i.e., past features values are considered additional features) through machine learning models by considering the playing position. Thirty-eight elite soccer players aged 19-27 years were observed during 151 training sessions, 44 matches across a full season. External load variables (58 derived from Global Positioning System and 30 from accelerometers) and the internal load derived from ratings of perceived exertion were collected for each player and each session and match. Machine learning models (linear regression, K-NN, decision trees, random forest, elastic net regression, XGBoost) were compared and interpreted in order to deepen the relationship between external load variables and ratings of perceived exertion according to the player position in a predictive perspective. Application of the machine learning models on the dataset provided enough predictive power to reduce the Root Mean Squared Error of 60 % from dummy predictions. The most accurate models (Root Mean Squared Error ≈ 1.1 for random forest and = 1 for XGBoost) highlighted a memory effect in subsequent ratings of perceived exertion values. Past ratings of perceived exertion values over one month were the strongest predicting factors of ratings of perceived exertion as compared to various external load indicators. The tree-based machine learning models showed statistically significant predictive ability, indicating valuable information for understanding the training load responses based on ratings of perceived exertion changes.



#12 Most common movements preceding goal scoring situations in female professional soccer

Reference: Sci Med Footb. 2023 May 19;1-9. doi: 10.1080/24733938.2023.2214106. Online ahead of print.

Authors: David Martínez-Hernández, Mark Quinn, Paul Jones

Summary: This study aimed to assess movements occurring during goal scoring situations in a female professional league.Data from all the goals on the Women's Super League 2018/2019 were collected through time-motion analysis using a modified version of the Bloomfield Movement Classification with differences analysed through chi-square. Analysis was performed on players (assistant, scorer [attackers], defender of assistant and defender of scorer [defenders]), movements, intensities and directions.Linear advancing motion (walking, jogging, running or sprint) (total percentage [95% CI] 37% attackers and 32.7% defenders) was the most common action preceding a goal, followed by deceleration (21.5% attackers; 18.4% defenders) and turn (19.2% attackers; 17.6% defenders). Other movements involved but with lower percentages were change in angle run (cut and arc run), ball blocking, lateral advancing motion (crossover and shuffle) and jumps. Players displayed similar tendencies but presented variations based on the role, with attackers performing more linear actions, subtle turns and cuts and defenders more ball blocking actions, lateral movements and high intensity linear actions and decelerations. Assistant performed the less percentage of involvements with at least 1 high intensity action (67.4%), scorer and defender of assistant showed similar values (86.3% and 87.1%), while defender of scorer had the highest percentage (97.3%).This study shows the importance of linear actions with other movements also being of high significance but with differentiated characteristics based on the role. This study could help practitioners design drills for the enhancement of physical capabilities related to movements occurring in goal scoring situations.



#13 Ethnic discrimination in Scandinavia: evidence from a field experiment in women's amateur soccer

Reference: Humanit Soc Sci Commun. 2023;10(1):230. doi: 10.1057/s41599-023-01734-7. Epub 2023 May 11.

Authors: Rasmus K Storm, Cornel Nesseler, Marthe Holum, Andreas Nygaard, Tor Georg Jakobsen

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Summary: In this paper, we examine ethnic discrimination using sport as a laboratory. Applying a field experiment in the three Scandinavian countries-Sweden, Norway, and Denmark-we test whether foreign female minority groups experience greater rejection rates when seeking inclusion in amateur soccer clubs. Soccer coaches were contacted by e-mail using native and foreign-sounding names from selected groups, requesting to participate in trial practice. Previous findings show persistent discrimination of foreign minority groups in the labour market, and recent work suggests that discrimination also occurs in the context of soccer. Our findings from Scandinavia show that Sweden is the only country that shows statistically significant signs of discriminatory patterns, and the probability of experiencing discrimination increases with cultural distance. However, cultural distance appears to have no influence in Norway and Denmark. We further investigate whether male or female coaches demonstrate different discriminatory behaviour when being contacted, but our analysis shows almost no gender differences. Findings suggest that how men and women differ in their discriminatory behaviour is context specific. The differences identified across nations and previous studies are discussed to better understand the mechanisms of discrimination.



#14 Comparison of Strength and Power Characteristics Before ACL Rupture and at the End of Rehabilitation Before Return to Sport in Professional Soccer Players

Reference: Sports Health. 2023 May 19;19417381231171566. doi: 10.1177/19417381231171566.

Authors: Luca Maestroni, Anthony Turner, Konstantinos Papadopoulos, Daniel Cohen, Vasileios Sideris, Philip Graham-Smith, Paul Read

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Summary: Strength and power is often reduced on the involved versus contralateral limb and healthy controls after anterior cruciate ligament (ACL) reconstruction, but no study has compared with preinjury values at the time of return to sport (RTS). Divergent recovery patterns in strength and power characteristics will be present at RTS relative to preinjury baseline data and healthy matched controls. Isokinetic strength tests, bilateral and single-leg countermovement jumps (CMJ; SLCMJ) were measured before ACL rupture in 20 professional soccer players. These then had surgical reconstruction (ACL group) and completed follow-up testing before RTS. Healthy controls (uninjured group) were tested at the same time as the ACL group preinjury. Values recorded at RTS of the ACL group were compared with preinjury. We also compared the uninjured and ACL groups at baseline and RTS. Compared with preinjury, ACL normalized quadriceps peak torque of the involved limb (difference = -7%), SLCMJ height (difference = -12.08%), and Reactive Strength Index modified (RSImod) (difference = -5.04%) were reduced after ACL reconstruction. No significant reductions in CMJ height, RSImod, and relative peak power were indicated at RTS in the ACL group when compared with preinjury values, but deficits were present relative to controls. The uninvolved limb improved quadriceps (difference = 9.34%) and hamstring strength (difference = 7.36%) from preinjury to RTS. No significant differences from baseline were shown in SLCMJ height, power, and reactive strength of the uninvolved limb after ACL reconstruction. Strength and power in professional soccer players at RTS after ACL reconstruction were often reduced compared with preinjury values and matched healthy controls. Deficits were more apparent in the SLCMJ, suggesting that dynamic and multijoint unilateral force production is an important component of rehabilitation. Use of the uninvolved limb and normative data to determine recovery may not always be appropriate.



#15 Leadership experiences of elite football team physicians during the COVID-19 pandemic: a pilot study

Reference: BMJ Lead. 2022 Jul 21;leader-2022-000603. doi: 10.1136/leader-2022-000603. Online ahead of print.

Authors: Sean Carmody, Gurneet Brar, Andrew Massey, Craig Rosenbloom, Vincent Gouttebarge, Mike Davison

Summary: The purpose of this study was to explore the leadership experiences of elite football team physicians during the COVID-19 pandemic. A pilot-study based on a cross-sectional design by means of an electronic survey was conducted. The survey relied on 25 questions divided into distinct sections including among others professional and academic experience, leadership experiences and perspectives. A total of 57 physicians (91% male; mean age: 43 years) gave their electronic informed consent and completed the survey. All participants agreed that the demands of their role had increased during the COVID-19 pandemic. Fifty-two (92%) participants reported that they felt they were expected to take more of a leadership role during the COVID-19 pandemic. Eighteen (35%) reported feeling under pressure to make clinical decisions which were not in keeping with best clinical practice. Additional roles, duties and demands expected of team doctors during the COVID-19 pandemic were subdivided into communication, decision-making, logistical, and public health demands. The findings from this pilot study suggest that the way in which team physicians at professional football clubs operate has altered since the onset of the COVID-19 pandemic, with greater demands placed on leadership skills including decision-making, communication and ethical stewardship. This has potential implications for sporting organisations, clinical practice and research.


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