Latest research in football - week 51 - 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 Are goals scored just before halftime worth more? An old soccer wisdom statistically tested
Reference: PloSONE. 2020 Oct 20;15(10):e0240438. doi: 10.1371/journal.pone.0240438.
Authors: Henrich R Greve, Jo Nesbø, Nils Rudi, Marat Salikhov
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Summary: There is an old soccer wisdom that a goal scored just before halftime has greater value than other goals. Many dismiss this old wisdom as just another myth waiting to be busted. To test which is right we have analysed the final score difference through linear regression and outcome (win, draw, loss) through logistic regression. We use games from many leagues, control for the halftime score, comparing games in which a goal was scored after 1 minute remained of regulation time with games in which it was scored before the 44th minute. Our main finding is that the home team scoring just before halftime influence these outcomes to its advantage, compared with scoring earlier with the same halftime score. We conclude that a goal scored just before halftime has greater value than other goals provided it is scored by the home team. In other words; the wisdom may be old, but it's still wise.

#2 Assessing Interlimb Jump Asymmetry in Young Soccer Players: The My Jump 2 App
Reference: Int J Sports Physiol Perform. 2020 Oct 19;1-9. doi: 10.1123/ijspp.2019-0981. Online ahead of print.
Authors: Matheus Barbalho, Ana Francisca Rozin Kleiner, Bianca Callegari, Ramon Costa de Lima, Givago da Silva Souza, Anselmo de Athayde Costa E Silva, Victor Silveira Coswig
Summary: Jumps are important evaluation tools for muscle strength and power and for interlimb asymmetries. Different jump tests are well related to athletic performance, prediction of injury risk, and common motor gestures of several sports such as soccer. Low-cost mobile applications (apps) have gained popularity for this measure. The authors hypothesized that the My Jump 2 app would be a valid tool to assess drop-jump performance and interlimb asymmetry in soccer players. Eleven male soccer players took part in this study (18.2 [1.3] y, 69.9 [9.5] kg, 174 [6.6] cm). The athletes performed each test twice on a force plate (gold-standard method), while the jumps were recorded through the mobile app. Measures with the My Jump 2 app were applied by 2 evaluators, independently and in duplicate (interrater and intrarater reliability). The agreement analysis between both evaluations was done using an intraclass correlation coefficient and Bland-Altman plots. Compared with the force platform, the app tested showed excellent reliability for the drop jump's flight time and interlimb asymmetry (intraclass correlation coefficient > .98). For interlimb contact-time asymmetry, the values were 18.4 (9.9) and 19.1 (9.9) milliseconds for the My Jump 2 app and the force platform, respectively (P = .88). For flight-time asymmetries, the values were 389.7 (114.3) and 396.8 (112.5) milliseconds for the My Jump 2 app and the force platform, respectively (P = .88). The My Jump 2 app is a valid tool to assess drop-jump and interlimb asymmetry in soccer players.

#3 Soccer-Related Concussions Among Swedish Elite Soccer Players: A Descriptive Study of 1,030 Players
Reference: Front Neurol. 2020 Sep 23;11:510800. doi: 10.3389/fneur.2020.510800. eCollection 2020.
Authors: Sofie Hänni, Fredrik Vedung , Yelverton Tegner, Niklas Marklund, Jakob Johansson
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Summary: There are growing concerns about the short- and long-term consequences of sports-related concussion, which account for about 5-9% of all sports injuries. We hypothesized there may be sex differences in concussion history and concussion-related symptoms, evaluated among elite soccer players in Sweden. Soccer players (n = 1,030) from 55 Swedish elite soccer teams participated in this study. Questionnaires were completed prior to the start of the 2017 season. Player history of soccer-related concussion (SoRC), symptoms and management following a SoRC were evaluated. Before the start of the season the players completed a baseline questionnaire assessing previous concussions. The Sports Concussion Assessment Tool 3 was included with regard to symptom evaluation. Out of 993 responding players 334 (34.6%) reported a previous SoRC and 103 players (10.4%) reported a SoRC during the past year. After sustaining a SoRC, 114 players (34.2%) reported that they continued their ongoing activity without a period of rest, more commonly female (44.9%) than male players (27.7%; P = 0.002). Symptom resolution time was 1 week or less for 61.3% of the players that reported having persisting symptoms. A positive correlation was observed between number of previous concussions and prevalence of three persisting symptoms: fatigue (P < 0.001), concentration/memory issues (P = 0.002) and headache (P = 0.047). About 35% of male and female elite soccer players in Sweden have experienced a previous SoRC, and about 10% experienced a SoRC during the last year. Female players continued to play after a SoRC, without a period of rest, more often than males. A higher risk of persisting symptoms was observed in players with a history of multiple concussions.

#4 The Academic Background of Youth Soccer Coaches Modulates Their Behavior During Training
Reference: Front Psychol. 2020 Sep 24;11:582209. doi: 10.3389/fpsyg.2020.582209. eCollection 2020.
Authors: David Agustí, Rafael Ballester, Jordi Juan-Blay, William G Taylor, Florentino Huertas
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Summary: This investigation aims to explore the relationship between the academic backgrounds of youth soccer coaches (U10 and U12 age groups) in Spain and the type of verbal behavior used during training sessions. The sample consisted of 70 coaches divided into two groups, depending on whether or not they had engaged with a university-level academic studies related to Physical Education and or Sport Sciences. A modified version of the "Coach Analysis and Intervention System" (CAIS), developed by Cushion et al. (2012), was used to collect data. A total of 32,886 verbal behaviors were noted and analyzed. Our results suggest that the coaches with university academic backgrounds frequently use more verbal behaviors and that these could be associated with positive effects on the players' learning and development processes. We suggest it is important to develop specific training programs aimed at optimizing the coaches' communicative and socio-affective skills in order to maximize their impact in youth athletes' learning process.

#5 Perceived barriers to implementation of injury prevention programs among collegiate women's soccer coaches
Reference: J Sci Med Sport. 2020 Sep 29;S1440-2440(20)30775-1. doi: 10.1016/j.jsams.2020.09.016.
Authors: Celeste Dix, David Logerstedt, Amelia Arundale, Lynn Snyder-Mackler
Summary: Knee injury prevention programs (IPPs) reduce knee and anterior cruciate ligament (ACL) injury rates in female athletes, however, implementation of IPPs is low. The purpose of this study was to identify barriers to implementation of IPPs among collegiate women's soccer coaches. A custom survey based on the RE-AIM (reach, effectiveness, adoption, implementation, maintenance) framework and existing literature was sent to 151 out of 153 women's National Collegiate Athletic Association (NCAA) soccer coaches in the NCAA's Eastern Region. Ten respondents reported that they did not use an IPP (Non-users), and nineteen respondents reported that they did use an IPP (Users). "Cost" was the most highly ranked barrier (median rank: 2) to implementing an IPP among Non-users. For the statement, "Who should be responsible for completing an IPP," Users said "Coaches" (47%) and "Other" (21%), while Non-users said "Strength and conditioning" (50%) and "Athletic trainers" (30%). Respondents who marked "Other", elaborated that it was the responsibility of coaches, athletes, and additional staff members. Cost was the primary barrier to implementation of an IPP. Since the majority of Non-users indicated that implementation of an IPP was the responsibility of a non-coaching staff member, cost may be a surrogate for the expense of hiring an additional staff member rather than the cost of performing the IPP itself. Additionally, using a team-based approach that encompasses athletes, coaches, and non-coaching staff members may support long-term implementation of IPPs.

#6 Head impacts in semiprofessional male Soccer players: a prospective video analysis over one season of competitive games
Reference: Brain Inj. 2020 Oct 18;1-6. doi: 10.1080/02699052.2020.1831067. Online ahead of print.
Authors: Hélène Cassoudesalle, Maxime Bildet, Hervé Petit, Patrick Dehail
Summary: Soccer exposes players to head injuries and involves repeated intentional head impacts through heading the ball. Our objective was to investigate the rate of both intentional headers and involuntary head impacts in semiprofessional male soccer players during one season. In this prospective cohort study, we followed 54 men (16-35 years) playing in two soccer clubs participating in the same regional French championship throughout the 2017-2018 season. All head impacts that occurred in competitive games were analyzed using video recordings. Player position, game exposure, referee's decision were also reported. Head impact incidence rate (IR) per 1000 player-hours, with the 95% confidence intervals (CIs) were calculated. Results: Headers IR was 3584.7 per 1000 player-hours (95% CI = 3431.9, 3737.5). Forwards and center-backs performed a higher number of headers. Involuntary head impacts IR was 44.1/1000 player-hours (95% CI = 27.1, 60.9). Just under half led the referee to stop playing time for a caregiver examination. Three concussions with a loss of consciousness after a head-to-head impact in a heading duel were recorded. Conclusions: Intentional headers were relatively common, contrary to involuntary head impacts that were however mainly due to heading duels. Head-to-head impact should lead to a systematic exit from the game for suspicion of concussion.

#7 The Effect of Fixture Congestion on Performance During Professional Male Soccer Match-Play: A Systematic Critical Review with Meta-Analysis
Reference: Sports Med. 2020 Oct 17. doi: 10.1007/s40279-020-01359-9. Online ahead of print.
Authors: Ross Julian, Richard Michael Page, Liam David Harper
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Summary: Fixture congestion (defined as a minimum of two successive bouts of match-play, with an inter-match recovery period of < 96 h) is a frequent and contemporary issue in professional soccer due to increased commercialisation of the sport and a rise in the number of domestic and international cup competitions. To date, there is no published systematic review or meta-analysis on the impact of fixture congestion on performance during soccer match play. We sought to conduct a systematic review and meta-analysis of the literature related to the effects of fixture congestion on physical, technical, and tactical performance in professional soccer match-play. Adhering to PRISMA guidelines and following pre-registration with the Open Science Framework ( ), a comprehensive and systematic search of three research databases was conducted to identify articles related to soccer fixture congestion. For inclusion in the systematic review and meta-analysis, studies had to include male professional soccer players, a congestion period that contained two matches ≤ 96 h, and have outcome measures related to physical, technical or tactical performance. Exclusion criteria comprised non-male and/or youth players, data that only assessed impact of congestion on injury, used simulated protocols, or were grey literature, such as theses or dissertations. Out of sixteen articles included in the systematic review, only five were eligible for the meta-analysis, and the only variable that was measured consistently across studies was total distance covered. Fixture congestion had no impact on total distance covered [p = 0.134; pooled standardized mean difference; Hedge's G = 0.12 (- 0.04, 0.28)]. Between-study variance, heterogeneity, and inconsistency across studies were moderate [Cochrane's Q = 6.7, p = 0.150, I2 = 40.7% (CI 0.00, 93.34)]. Data from articles included in the systematic review suggest fixture congestion has equivocal effects on physical performance, with variation between studies and low quality of research design in some instances. Tactical performance may be negatively impacted by fixture congestion; however, only one article was identified that measured this element. Technical performance is unchanged during fixture congestion; however, again, research design and the sensitivity and relevance of methods and variables require improvement. Total distance covered is not impacted by fixture congestion. However, some studies observed a negative effect of fixture congestion on variables such as low- and moderate-intensity distance covered, perhaps suggesting that players employ pacing strategies to maintain high-intensity actions. There is a lack of data on changes in tactical performance during fixture congestion. With ever increasing numbers of competitive matches scheduled, more research needs to be conducted using consistent measures of performance (e.g., movement thresholds) with an integration of physical, technical and tactical aspects.

#8 Effect of Playing Position, Match Half, and Match Day on the Trunk Inclination, G-Forces, and Locomotor Efficiency Experienced by Elite Soccer Players in Match Play
Reference: Sensors (Basel). 2020 Oct 14;20(20):E5814. doi: 10.3390/s20205814.
Authors: José M Oliva-Lozano, Elisa F Maraver, Víctor Fortes, José M Muyor
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Summary: The rapid growth of wearable sensors has allowed the analysis of trunk kinematics during the match, which is necessary for having a better understanding of the postural demands of soccer players. However, some contextual variables may have an impact on the physical demands of the players. This study aimed to analyze the effect of three contextual variables (playing position, match half, and match day) on the sagittal trunk inclination, G-forces, and locomotor efficiency experienced by soccer players in match play. Then, wearable sensors were used to collect the trunk kinematics during 13 matches. Firstly, positional differences were found on the trunk inclination (p = 0.01) and the G-forces experienced by the players (p < 0.001). For example, the greatest and lowest trunk inclination was found for FW (~34.01°) and FB (~28.85°) while the greatest and lowest G-forces were found for WMF (1.16 G) and CD (1.12 G), respectively. However, there were no positional differences in the locomotor efficiency (p = 0.10). Secondly, the match half had a significant effect on the trunk inclination (p = 0.01) and the G-forces experienced by the players (p < 0.001) with significantly lower values observed during the second half. No differences between halves were found on the locomotor efficiency for any playing position (p = 0.41). Finally, no significant effect of match day on any variable was observed. This investigation is one of the first steps towards enhancing the understanding of trunk kinematics from elite soccer players. The positional differences found on the trunk inclination and G-forces imply that the development of position-specific training drills considering the postural demands is necessary to prepare the players not only for the physical demands but also for successful performance in the field of regard. The resistance to fatigue needs to be trained given the differences between halves.

#9 Effects of Combined Strength and Resisted Sprint Training on Physical Performance in U-19 Elite Soccer Players
Reference: J Strength Cond Res. 2020 Oct 15. doi: 10.1519/JSC.0000000000003829. Online ahead of print.
Authors: Mehdi Ben Brahim, Rim Bougatfa, Emna Makni, Pablo Prieto Gonzalez, Hussain Yasin, Raghad Tarwneh, Wassim Moalla, Mohamed Elloumi
Summary: This study assessed the effects of combined muscular strength and resisted sprint training using both sled and weight vest compared with regular soccer training on physical fitness of lower limbs in U-19 elite soccer players. Thirty-four male soccer players (age: 18.8 ± 0.8 years, height: 1.81 ± 0.05 m, body mass: 76.4 ± 4.9 kg, and body fat mass: 11.3 ± 4.2%) were randomly assigned into a resisted sprint training group (RSTG, n = 20), using both weight vest and sled, and a control group (CONTG, n = 14). Sprinting ability (5 m and 20 m), squat jump (SJ) and counter-movement jump (CMJ) tests, 1 repetition maximum of half-back squat (1RM half-back squat), and soccer ball-shooting speed were assessed before and after a 6-week training program. Within-group interactions showed significant combined muscular strength and resisted sprint training effects were observed for all the tests' measurements (effect sizes = 0.97 and 3.69 for 20-m sprint and SJ, respectively). However, significant increases of performances were observed for 5-m and 20-m sprinting time ( = 0.25, p < 0.01 and = 0.22, p < 0.01, respectively), SJ and CMJ ( = 0.78, p < 0.0001 and = 0.34, p < 0.001, respectively), 1 repetition maximum (1-RM) half-back squat ( = 0.45, p < 0.0001), and soccer ball-shooting speed ( = 0.41, p < 0.0001) in RSTG with large effect size, whereas the CONTG showed significant performances increase only for CMJ (p < 0.05), 1RM half-back squat (p < 0.01), and soccer ball-shooting speed (p < 0.05). We conclude that combined strength and both horizontal (weighted sled) and vertical (weighted vest) resisted sprint training are more effective than regular soccer training for enhancing sprinting and jumping abilities as well as ball-shooting speed in soccer.

#10 Neck and Trunk Strength Training to Mitigate Head Acceleration in Youth Soccer Players
Reference: J Strength Cond Res. 2020 Oct 15. doi: 10.1519/JSC.0000000000003822. Online ahead of print.
Authors: Carsten Müller, Karen Zentgraf
Summary: Heading in soccer involves repetitive head accelerations that may be detrimental for brain health. One way to mitigate adverse effects may be to increase head-neck stabilization and thus reduce the kinematic response after intentional headers. This study aimed to (a) assess associations between neck strength and head kinematics and (b) evaluate an exercise intervention designed to increase strength and attenuate head acceleration during intentional heading in youth soccer players. In 22 athletes, we used accelerometers to assess associations between neck strength and peak linear acceleration (PLA). We attached the accelerometers to the occiput and sternum, allowing us to differentiate between total, trunk, and head PLA. Longitudinally, we evaluated the effects of a 14-week twice-weekly resistance training in a subsample of 14 athletes compared with regular soccer training (N = 13). Results showed that female athletes had lower isolated neck strength (p ≤ 0.004), lower functional neck strength (p ≤ 0.017), and higher total PLA during purposeful headers compared with males (17.2 ± 3.5 g and 13.0 ± 2.3 g, respectively, at 9.6 m·s ball velocity during impact; p = 0.003). The intervention group showed moderate to large strength gains ( = 0.16-0.42), resulting in lower PLA (total -2.4 g, trunk -0.8 g, and head -1.5 g) during headers. We conclude that a resistance training focusing on cervical and trunk musculature is practicable in youth soccer, elicits strength gains, and helps to mitigate PLA during purposeful heading. Results should encourage youth strength and conditioning professionals to incorporate neck exercises as a risk reduction strategy into their training routine.

#11 Factors affecting peak impact force during soccer headers and implications for the mitigation of head injuries
Reference: PLoS One. 2020 Oct 16;15(10):e0240162. doi: 10.1371/journal.pone.0240162. eCollection 2020.
Authors: Joshua Auger, Justin Markel, Dimitri D Pecoski, Nicolas Leiva-Molano, Thomas M Talavage, Larry Leverenz, Francis Shen, Eric A Nauman
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Summary: It has been documented that up to 22% of all soccer injuries are concussions. This is in part due to players purposely using their head to direct the ball during play. To provide a more complete understanding of head trauma in soccer athletes, this study characterized the effects of four soccer ball characteristics (size, inflation pressure, mass, velocity) on the resulting peak impact force as it relates to the potential for incurring neurophysiological changes. A total of six hundred trials were performed on size 4 and 5 soccer balls as well as a novel lightweight soccer ball. Impact force was measured with a force plate and ball velocity was determined using motion capture. These data were used, in conjunction with dimensional analysis to relate impact force to ball size, mass, velocity, and pressure. Reasonable reductions in allowable ball parameters resulted in a 19.7% decrease in peak impact force. Adjustments to ball parameters could reduce a high cumulative peak translational acceleration soccer athlete down into a previously defined safer low loading range. In addition, it was noted that water absorption by soccer balls can result in masses that substantially increase impact force and quickly surpass the NCAA weight limit for game play. Additional research is required to determine whether varying soccer ball characteristics will enable soccer players to avoid persistent neurophysiological deficits or what additional interventions may be necessary and the legal implications of these data are discussed.

#12 Sex and Sport Differences in College Lacrosse and Soccer Head Impact Biomechanics
Reference: Med Sci Sports Exerc . 2020 Nov;52(11):2349-2356. doi: 10.1249/MSS.0000000000002382.
Authors: Jason P Mihalik, Stephanie A Amalfe, Patricia R Roby, Cassie B Ford, Robert C Lynall, Kaitlin E Riegler, Elizabeth F Teel, Erin B Wasserman, Margot Putukian
Summary: Sport-related head impact biomechanics research has been male-centric and focused primarily on American football and ice hockey, which do not address popular sports in which both sexes participate. The purpose of this study was to quantify college female and male lacrosse and soccer head impact biomechanics. Head impact biomechanics were collected from college lacrosse and soccer players across two Division 1 college athletic programs (96 female athletes, 141 male athletes; age, 19.8 ± 1.3 yr; height, 174.8 ± 9.2 cm; mass, 72.4 ± 11.7 kg). We deployed helmetless head impact measurement devices (X2 Biosystems xPatch) before each event. Peak linear and rotational accelerations were log-transformed for random intercepts general linear mixed models, and subsequently categorized based on impact magnitude for additional categorical analyses. Most linear (69.4%) and rotational (72.3%) head impact accelerations sustained by our study cohort were categorized as mild. On average, male athletes sustained impacts with higher linear accelerations than females (P = 0.04), and lacrosse athletes sustained higher linear acceleration impacts than soccer athletes (P = 0.023). Soccer athletes sustained significantly higher-magnitude impacts during competitions versus practices (linear, P < 0.001, rotational, P < 0.001), whereas lacrosse athletes sustained higher-magnitude impacts during practices versus competition (linear, P < 0.001; rotational, P < 0.001). Male athletes sustained higher accelerations in competitions versus practice (linear, P = 0.004; rotational, P < 0.001), whereas female athletes sustained higher accelerations in practice versus competitions (linear, P < 0.001; rotational, P = 0.02). There were no interactions between sex and sport on impact magnitude. Male athletes and lacrosse athletes experience higher-magnitude head impacts. Given the limited literature in this area, future research should continue characterizing head impact biomechanics in women's and nonhelmeted sports as well as validate nonhelmeted head impact technologies.

#13 Will the real leaders please stand up? The emergence of shared leadership in semi-professional soccer teams
Reference: J Sci Med Sport. 2020 Sep 17;S1440-2440(20)30753-2. doi: 10.1016/j.jsams.2020.09.007.
Authors: Niels Mertens, Filip Boen, Niklas K Steffens, S Alexander Haslam, Katrien Fransen
Summary: High-quality leadership is often regarded as one of the main sources of competitive advantage. Especially within sport teams, a team's leadership structure has historically been considered to be stable across the season, with the coach and team captain as the formal, and often sole, leaders. In line with recent organizational research, the present study aims to broaden this perspective by also taking informal leaders into account and exploring how leadership structures among athletes within sport teams evolve over the course of a season. Using social network analysis, we analyzed the leadership structure of 20 semi-professional soccer teams (N=460 players, Mage=23.50 years; SD=4.55) at the start of the season and then again halfway through the season. More specifically, for each team we constructed a leadership network for four leadership roles (task, motivational, social, and external leadership) at these two time points. Findings suggest that leadership structures in sport teams can change considerably over the course of the competitive season, thereby challenging the classic view of stable, vertical leadership structures. The transition to more shared forms of leadership can be attributed to the emergence of informal leaders over time as players engage more strongly in leadership roles. Furthermore, our results suggest that as teams evolve towards shared leadership their functioning and performance benefits from these changes.
Conclusions: Based on these findings, we recommend that coaches actively implement a structure of shared leadership and seek to develop the leadership qualities of formal and informal athlete leaders.

#14 "All My Problems Go Away for 90 Minutes": How Football and Psychotherapy Improves Young Men's Mental Health
Reference: Am J Mens Health. Sep-Oct 2020;14(5):1557988320959992. doi: 10.1177/1557988320959992.
Authors: Amy McGrane , Niamh Bird, Chelsea Arten, Katriona O'Sullivan
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Summary: This qualitative research sought to establish the impact of an 8-week program combining football and one-to-one psychotherapy on young males' mental health, determining the factors that predict help-seeking behaviors in this group of men. Pre- and post-participation focus groups were used as the method of data collection. Six males (19-35 years old; M = 25.5) completed both pre-intervention and follow-up focus groups. Help-seeking behaviors were influenced by the appeal of football and the perception of the counselor being accessible. Barriers included gender norms, socialization, financial difficulties, and challenging social landscapes. Post-participation focus groups revealed that positive social and counseling relationships facilitated improved mental health. Sport was deemed an acceptable medium to deliver a mental health intervention as it increased social connections and facilitated help-seeking. Findings support previous research indicating that combining sports and psychotherapy positively impacts young males' mental health.

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