Latest research in football - week 42 - 2021

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 Automated Classification of Changes of Direction in Soccer Using Inertial Measurement Units

Reference: Sensors (Basel). 2021 Jul 6;21(14):4625. doi: 10.3390/s21144625.

Authors: Brian Reilly, Oliver Morgan, Gabriela Czanner, Mark A Robinson

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Summary: Changes of direction (COD) are an important aspect of soccer match play. Understanding the physiological and biomechanical demands on players in games allows sports scientists to effectively train and rehabilitate soccer players. COD are conventionally recorded using manually annotated time-motion video analysis which is highly time consuming, so more time-efficient approaches are required. The aim was to develop an automated classification model based on multi-sensor player tracking device data to detect COD > 45°. Video analysis data and individual multi-sensor player tracking data (GPS, accelerometer, gyroscopic) for 23 academy-level soccer players were used. A novel 'GPS-COD Angle' variable was developed and used in model training; along with 24 GPS-derived, gyroscope and accelerometer variables. Video annotation was the ground truth indicator of occurrence of COD > 45°. The random forest classifier using the full set of features demonstrated the highest accuracy (AUROC = 0.957, 95% CI = 0.956-0.958, Sensitivity = 0.941, Specificity = 0.772. To balance sensitivity and specificity, model parameters were optimised resulting in a value of 0.889 for both metrics. Similarly high levels of accuracy were observed for random forest models trained using a reduced set of features, accelerometer-derived variables only, and gyroscope-derived variables only. These results point to the potential effectiveness of the novel methodology implemented in automatically identifying COD in soccer players.



#2 Co-Attendance Communities: A Multilevel Egocentric Network Analysis of American Soccer Supporters' Groups

Reference: Int J Environ Res Public Health. 2021 Jul 9;18(14):7351.  doi: 10.3390/ijerph18147351.

Authors: Adam R Cocco, Matthew Katz, Marion E Hambrick

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Summary: The growth of professional soccer in the United States is evident through the rapid expansion of franchises and increased game attendance within Major League Soccer (MLS) and the United Soccer League (USL). Coinciding with this growth is the emergence of European-style supporters' groups filling sections of MLS and USL stadiums. In this study, the authors utilized an egocentric network analysis to explore relationships among supporters' group members for two professional soccer clubs based in the United States. Egocentric network research focuses on the immediate social environment of individuals and is often viewed as an alternative approach to sociocentric (i.e., whole network) analyses. This study employed hierarchical linear modeling as an example of multilevel modeling with egocentric data, using ego- and alter-level variables to explain the strength of co-attendance ties. The results indicate the perceived commitment of fellow fans to the team, shared membership in a supporters' group, age, and interactions with other fans in team settings related to higher levels of co-attendance. The outcomes of this study are both theoretical, as they advance an understanding of sport consumer behavior within soccer supporters' groups, and methodological, as they illustrate the unique value of employing egocentric network analysis in sport fan research.



#3 Chronic effects of flywheel training on physical capacities in soccer players: a systematic review

Reference: Res Sports Med. 2021 Jul 27;1-21.  doi: 10.1080/15438627.2021.1958813. Online ahead of print.

Authors: William J C Allen, Kevin L De Keijzer, Javier Raya-González, Daniel Castillo, Giuseppe Coratella, Marco Beato 

Summary: The aims of the current systematic review were to evaluate the current literature surrounding the chronic effect of flywheel training on the physical capacities of soccer players, and to identify areas for future research to establish guidelines for its use.Studies were identified following a search of electronic databases (PubMed and SPORTDiscus) in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols (PRISMA).Eleven studies met the inclusion criteria and were included. The methodological quality of the included studies ranged between 10 and 18 with an average score of 15 points using the PEDro scale. The training duration ranged from 6 weeks to 27 weeks, with volume ranging from 1 to 6 sets and 6 to 10 repetitions, and frequency from 1 to 2 times a week. This systematic review reported that a diverse range of flywheel training interventions can effectively improve strength, power, jump, and changes of direction in male soccer players of varying levels.Flywheel training interventions improve the physical capacities of soccer players of varying levels. Nonetheless, the current literature suggests contrasting evidence regarding flywheel training induced changes in sprint speed and acceleration capacity of soccer players.



#4 Test-retest reliability of a functional electromechanical dynamometer on swing eccentric hamstring exercise measures in soccer players

Reference: PeerJ. 2021 Jul 14;9:e11743. doi: 10.7717/peerj.11743. eCollection 2021.

Authors: Antonio Jesús Sánchez-Sánchez, Luis Javier Chirosa-Ríos, Ignacio Jesús Chirosa-Ríos, Agustín José García-Vega, Daniel Jerez-Mayorga 

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Summary: The use of a functional electromechanical dynamometer (FEMD) has been proposed as a valid and effective tool to evaluate specific movement patterns. The aim of this study was to determine the reliability of FEMD on swing eccentric hamstring exercise (SEHE) measures in soccer players. Nineteen federated male soccer players (20.74 ± 4.04 years) performed the SEHE at three different isokinetic velocities (20-40-60 cm/s). These evaluations were conducted in four sessions, two for familiarization and two for registration. The average and maximum load (N) of the three isokinetic velocities was calculated from the values obtained from the FEMD (Dynasystem®, Bangalore). The main results of this research showed that the reliability was high for the average load in the condition of 40 cm/s, presenting the highest ICC value (0.94). For maximum load, reliability was high in the condition of 20 cm/s. The manifestation of the most reliable load was the maximum load (ICC = 0.91-0.87). FEMD (Dynasystem®, Bangalore) is a reliable device to evaluate the eccentric strength of the hamstring muscles in soccer players.



#5 Comparison of women's collegiate soccer header kinematics by play state, intent, and outcome

Reference: J Biomech. 2021 Jul 9;126:110619.  doi: 10.1016/j.jbiomech.2021.110619. Online ahead of print.

Authors: Tanner M Filben, N Stewart Pritchard, Kathryn E Hanes-Romano, Logan E Miller, Christopher M Miles, Jillian E Urban, Joel D Stitzel

Summary: Although most head impacts in soccer are headers, limited knowledge exists about how header magnitude varies by on-field scenario. This study aimed to compare head kinematics during on-field headers by play state (i.e., corner kick, goal kick, free kick, throw-in, drill, or live ball), intent (i.e., pass, shot, or clearance), and outcome (i.e., successful or unsuccessful). Fifteen female collegiate soccer players were instrumented with mouthpiece-based head impact sensors during 72 practices and 24 games. A total of 336 headers were verified and contextualized via film review. Play state was associated with peak linear acceleration, rotational acceleration, and rotational velocity (all p < .001) while outcome was associated with peak linear acceleration (p < .010). Header intent was not significantly associated with any kinematic metric. Headers during corner kicks (22.9 g, 2189.3 rad/s2, 9.87 rad/s), goal kicks (24.3 g, 2658.9 rad/s2, 10.1 rad/s), free kicks (18.0 g, 1843.3 rad/s2, 8.43 rad/s), and live balls (18.8 g, 1769.7 rad/s2, 8.09 rad/s) each had significantly greater mean peak linear acceleration (all p < .050), rotational acceleration (all p < .001), and rotational velocity (all p < .001) than headers during drills (13.0 g, 982.4 rad/s2, 5.28 rad/s). Headers during goal kicks also had a significantly greater mean rotational acceleration compared to headers during live ball scenarios (p < .050). Successful headers (18.3 g) had a greater mean peak linear acceleration compared to unsuccessful headers (13.8 g; p < .010). Results may help inform efforts to reduce head impact exposure in soccer.



#6 Association between Clinical Vision Measures and Visual Perception and Soccer Referees' On-field Performance

Reference: Optom Vis Sci. 2021 Jul 1;98(7):789-801.  doi: 10.1097/OPX.0000000000001722.

Authors: Antonio M G Baptista, Pedro M Serra, Muhammad Faisal, Brendan T Barrett 

Summary: The decisions taken by soccer officials are critically important to game management. Understanding the underlying processes that mediate expert performance in soccer refereeing may lead to a better standard of officiating. Vision is the dominant source of incoming information upon which officials rely to make their on-field decisions. We tested the hypothesis that performance on generic tests of vision and visual perception predicts domain-specific performance in elite-level soccer referees (R) and assistant referees (AR). We assessed the vision of R and AR who officiate at the highest level in Portugal. To be eligible for inclusion, R and AR had to have officiated for at least two consecutive seasons across the 2014/2015, 2015/2016, and 2016/2017 seasons. A single, rank-order list of the performance of eligible officials was created based on the rank-order list for each season that was made by the Portuguese Soccer Federation. Clinical vision measures included visual acuity and stereoacuity, and visual perception measures were gathered using the Test of Visual Perceptual Skills, Third Edition. A total of 59 officials participated (21 R, 38 AR), 17 of whom officiated at the international level. The R and AR groups did not differ in vision or visual perception measures. We found that better stereoacuity (P < .001) and visual memory (P = .001) are associated with a higher rank order of on-field performance after adjusting for the age, experience, the national/international status, and the regional affiliation of the officials. Together, these two measures explain 22% of the variance in rank-order performance. This is the first study to show a link between the vision of officials and their on-field performance. The origin and significance of these findings remain to be established, and further work is required to establish whether they are component skills in the domain of soccer refereeing.



#7 An Accessible, 16-Week Neck Strength Training Program Improves Head Kinematics Following Chest Perturbation in Young Soccer Athletes

Reference: J Sport Rehabil. 2021 Jul 30;1-8.  doi: 10.1123/jsr.2020-0537. Online ahead of print.

Authors: Enora Le Flao, Andrew W Pichardo, Sherwin Ganpatt, Dustin J Oranchuk

Summary: Neck size and strength may be associated with head kinematics and concussion risks. However, there is a paucity of research examining neck strengthening and head kinematics in youths. In addition, neck training is likely lacking in youth sport due to a perceived inadequacy of equipment or time. Examine neck training effects with minimal equipment on neck strength and head kinematics following chest perturbations in youth athletes. Twenty-five (14 men and 11 women) youth soccer athletes (9.8 [1.5] y). Sixteen weeks of twice-weekly neck-focused resistance training utilizing bands, body weight, and manual resistance. Head kinematics (angular range of motion, peak anterior-posterior linear acceleration, and peak resultant linear acceleration) were measured by an inertial motion unit fixed to the apex of the head during torso perturbations. Neck-flexion and extension strength were assessed using weights placed on the forehead and a plate-loaded neck harness, respectively. Neck length and circumference were measured via measuring tape. Neck extension (increase in median values for all: +4.5 kg, +100%, P < .001; females: +4.5 kg, +100%, P = .002; males: +2.2 kg, +36%, P = .003) and flexion (all: +3.6 kg, +114%, P < .001; females: +3.6 kg, +114%, P = .004; males: +3.6 kg, +114%, P = .001) strength increased following the intervention. Men and women both experienced reduced perturbation-induced head pitch (all: -84%, P < .001). However, peak resultant linear acceleration decreased in the female (-53%, P = .004), but not male (-31%, P = 1.0) subgroup. Preintervention peak resultant linear acceleration and extension strength (R2 = .21, P = .033) were the closest-to-significance associations between head kinematics and strength. Young athletes can improve neck strength and reduce perturbation-induced head kinematics following a 16-week neck strengthening program. However, further research is needed to determine the effect of improved strength and head stabilization on concussion injury rates.



#8 Whole-body energy transfer strategies during football instep kicking: implications for training practices

Reference: Sports Biomech. 2021 Jul 27;1-16.  doi: 10.1080/14763141.2021.1951827. Online ahead of print.

Authors: Simon Augustus, Penny E Hudson, Nick Harvey, Neal Smith

Summary: Knowledge of whole-body energy transfer strategies during football instep kicking can help inform empirically grounded training practices. The aim of this study was thus to investigate energy transfer strategies of 15 semi-professional players performing kicks for speed and accuracy. Three-dimensional kinematics and GRFs (both 1000 Hz) were incorporated into segment power analyses to derive energy transfers between the support leg, torso, pelvis and kick leg throughout the kick. Energy transferred from support leg (r = 0.62, P = 0.013) and torso (r = 0.54, P = 0.016) into the pelvis during tension arc formation and leg cocking was redistributed to the kick leg during the downswing (r = 0.76, P < 0.001) and were associated with faster foot velocities at ball contact. This highlights whole-body function during instep kicking. Of particular importance were: (a) regulating support leg energy absorption, (b) eccentric formation and concentric release of a 'tension arc' between the torso and kicking hip, and (c) coordinated proximal to distal sequencing of the kick leg. Resistance exercises that replicate the demands of these interactions may help develop more powerful kicking motions and varying task and/or environmental constraints might facilitate development of adaptable energy transfer strategies.



#9 Motion Analysis of Match Play in U14 Male Soccer Players and the Influence of Position, Competitive Level and Contextual Variables

Reference: Int J Environ Res Public Health. 2021 Jul 7;18(14):7287.  doi: 10.3390/ijerph18147287.

Authors: Erling Algroy, Halvard Grendstad, Amund Riiser, Tone Nybakken, Atle Hole Saeterbakken, Vidar Andersen, Hilde Stokvold Gundersen

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Summary: This study aimed to investigate match running performance in U14 male soccer players in Norway, and the influence of position, competitive level and contextual factors on running performance. Locomotion was monitored in 64 different U14 players during 23 official matches. Matches were played at two different competitive levels: U14 elite level (n = 7) and U14 sub-elite level (n = 16). The inclusion criterion was completed match halves played in the same playing position. The variables' influence on match running performance was assessed using mixed-effect models, pairwise comparisons with Bonferroni correction, and effect size. The results showed that the U14 players, on average, moved 7645 ± 840 m during a match, of which 1730 ± 681 m (22.6%) included high-intensity running (HIR, 13.5-18.5 km·h-1) and sprinting (>18.5 km·h-1). Wide midfielders (WM) and fullbacks (FB) covered the greatest sprint distance (569 ± 40 m) and, in addition to the centre midfield position (CM), also covered the greatest total distance (TD) (8014 ± 140 m) and HIR distance (1446 ± 64 m). Centre forwards (CF) performed significantly more accelerations (49.5 ± 3.8) compared other positions. TD (7952 ± 120 m vs. 7590 ± 94 m) and HIR (1432 ± 57 m vs. 1236 ± 43 m) were greater in U14 elite-level matches compared with sub-elite matches. Greater TD and sprint distances were performed in home matches, but, on the other hand, more accelerations and decelerations were performed in matches played away or in neutral locations. Significantly higher TD, HIR and sprinting distances were also found in lost or drawn matches. In conclusion, physical performance during matches is highly related to playing position, and wide positions seem to be the most physically demanding. Further, competitive level and contextual match variables are associated with players' running performance.



#10 Postural balance impairment in Tunisian second division soccer players with groin pain: A case-control study

Reference: Phys Ther Sport. 2021 Jul 15;51:85-91.  doi: 10.1016/j.ptsp.2021.07.003. Online ahead of print.

Authors: Fatma Chaari, Haithem Rebai, Sébastien Boyas, Abderrahmane Rahmani, Thouraya Fendri, Mohammed A Harrabi, Sonia Sahli

Summary: The aim was to compare postural balance outcomes between soccer players with and without groin pain (GP). Fifty-four soccer players, 27 with GP (GP group: GPG) and 27 healthy ones (control group: CG) participated in this study. Static and dynamic postural balance were assessed with a force platform and Y-balance test (Y-BT), respectively. Hip abduction, internal rotation (IR), external rotation (ER) and total rotation (TR) of both limbs were evaluated. The GPG exhibited significant higher centre of pressure values in the bipedal posture only on the foam surface in eyes opened and closed compared to controls. Besides, they had lower anterior, posteromedial and posterolateral reach distances and composite Y-BT score on the injured limb (IL) compared to non-injured limb (NIL) and dominant-limb (DL) of the CG. Moreover, they showed lower abduction, IR, ER, and TR on the IL compared to NIL and DL. Dynamic unipedal postural balance disorder could be one of the limiting factors of performance in soccer players with non-time loss GP. Hence, postural balance data in these players could enable sport coaches and physical therapists to better understand the mechanisms contributing for performance decrease.



#11 Observed and predicted ages at peak height velocity in soccer players

Reference: PLoS One. 2021 Jul 26;16(7):e0254659.  doi: 10.1371/journal.pone.0254659. eCollection 2021.

Authors: Robert M Malina, Manuel J Coelho-E-Silva, Diogo V Martinho, Paulo Sousa-E-Siva, Antonio J Figueiredo, Sean P Cumming, Miroslav Králík, Sławomir M Kozieł

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Summary: The purpose of the study was to evaluate predicted maturity offset (time before age at PHV) and age at PHV (chronological age [CA] minus maturity offset) in a longitudinal sample of 58 under-13 club level soccer players in central Portugal for whom ages at PHV were estimated with the SITAR model. Two maturity offset prediction equations were applied: the original equation which requires CA sitting height, estimated leg length, height and weight, and a modified equation which requires CA and height. Predicted maturity offset increased, on average, with CA at prediction throughout the age range considered, while variation in predicted maturity offset and ages at PHV within CA groups was considerably reduced compared to variation in observed ages at offset and at PHV. Predicted maturity offset and ages at PHV were consistently later than observed maturity offset and age at PHV among early maturing players, and earlier than observed in late maturing players. Both predicted offset and ages at PHV with the two equations were, on average, later than observed among players maturing on time. Intra-individual variation in predicted ages at PHV with each equation was considerable. The results for soccer players were consistent with similar studies in the general population and two recent longitudinal studies of soccer players. The results question the utility of predicted maturity offset and age at PHV as valid indicators of maturity timing and status.



#12 Effects of Age on Match-related Acceleration and Deceleration Efforts in Elite Soccer Players

Reference: Int J Sports Med. 2021 Jul 26.  doi: 10.1055/a-1337-2961. 

Authors: Miguel Lorenzo-Martínez, Francisco J Corredoira, Carlos Lago-Peñas, Roberto López-Del Campo, Fabio Nevado-Garrosa, Ezequiel Rey

Summary: The aim of this study was to examine the effects of chronological age on acceleration and deceleration match performance in professional soccer players. A total of 5317 individual match observations were collected on 420 professional players competing in the Spanish LaLiga during the 2018-2019 season, using a multiple-camera computerised tracking system (TRACAB; ChyronHego, Melville, NY, USA). Players were classified using a k-means cluster analysis into four different age groups: 17-23 years, 24-27 years, 28-30 years, and 31-38 years. Linear mixed models were adjusted to compare the players' match performance according to their age group and playing position (central defenders, external defenders, central midfielders, external midfielders, and forwards). The results showed that players aged between 31-38 years performed a significantly less total number of accelerations (ES=0.30-0.48) and decelerations (ES=0.29-0.49) in comparison with younger players. These age-related physical performance declines were more pronounced among central defenders, central midfielders, and forwards. However, no significant effects were obtained for players' maximum acceleration and deceleration capacities. The current findings provide useful information for coaches and strength and conditioning specialists to better understand the effects of age on players' physical performance and to develop age-tailored training programs.



#13 Professional Soccer and Dementia Risk-The Ugly Side of the Beautiful Game

Reference: JAMA Neurol. 2021 Aug 2.  doi:0.1001/jamaneurol.2021.2246. Online ahead of print.

Authors: Breton M Asken, Gil D Rabinovici

Summary: While an increased risk for late-life neurodegenerative disease and dementia has consistently been observed in professional athletes with very high exposure to repetitive head impacts, such as former professional boxers and US football players, much less is known about neurologic outcomes in sports with lower head trauma exposure. Soccer, known to most of the world as football, is by far the most popular sport globally, with an estimated 270 million active players worldwide.1 The Brazilian superstar Pelé famously referred to soccer as “the beautiful game,” inspired by the fancy footwork and orchestral movement displayed by footballers at the highest level. However, heading the ball (known as headers) is also an integral part of the game, and additional incidental head impacts occur via collisions with other players or the ground. A 2017 summit on head injury in soccer concluded that the frequency of headers increases from the youth level to the professional level.2 Both overall header exposure and the force of impact generated by headers were deemed relatively low but with considerable individual variability. Linear forces generated by heading the ball can range from as low as 5g to as high as 60g. Studies have inconsistently detected acute and chronic sequelae of soccer headers,3 with some studies reporting associations between more frequent headers, worse cognitive test performance, and compromised white matter integrity on magnetic resonance imaging.4



#14 Association of Field Position and Career Length With Risk of Neurodegenerative Disease in Male Former Professional Soccer Players

Reference: JAMA Neurol. 2021 Aug 2;e212403.  doi: 10.1001/jamaneurol.2021.2403. Online ahead of print.

Authors: Emma R Russell, Daniel F Mackay, Katy Stewart, John A MacLean, Jill P Pell, William Stewart

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Summary: Neurodegenerative disease mortality is higher among former professional soccer players than general population controls. However, the factors contributing to increased neurodegenerative disease mortality in this population remain uncertain. The aim was to investigate the association of field position, professional career length, and playing era with risk of neurodegenerative disease among male former professional soccer players. This cohort study used population-based health record linkage in Scotland to evaluate risk among 7676 male former professional soccer players born between January 1, 1900, and January 1, 1977, and 23 028 general population control individuals matched by year of birth, sex, and area socioeconomic status providing 1 812 722 person-years of follow-up. Scottish Morbidity Record and death certification data were available from January 1, 1981, to December 31, 2016, and prescribing data were available from January 1, 2009, to December 31, 2016. Database interrogation was performed on December 10, 2018, and data were analyzed between April 2020 and May 2021. Outcomes were obtained by individual-level record linkage to national electronic records of mental health and general hospital inpatient and day-case admissions as well as prescribing information and death certification. Risk of neurodegenerative disease was evaluated between former professional soccer players and matched general population control individuals. In this cohort study of 30 704 male individuals, 386 of 7676 former soccer players (5.0%) and 366 of 23 028 matched population control individuals (1.6%) were identified with a neurodegenerative disease diagnosis (hazard ratio [HR], 3.66; 95% CI, 2.88-4.65; P < .001). Compared with the risk among general population control individuals, risk of neurodegenerative disease was highest for defenders (HR, 4.98; 95% CI, 3.18-7.79; P < .001) and lowest for goalkeepers (HR, 1.83; 95% CI, 0.93-3.60; P = .08). Regarding career length, risk was highest among former soccer players with professional career lengths longer than 15 years (HR, 5.20; 95% CI, 3.17-8.51; P < .001). Regarding playing era, risk remained similar for all players born between 1910 and 1969. The differences in risk of neurodegenerative disease observed in this cohort study imply increased risk with exposure to factors more often associated with nongoalkeeper positions, with no evidence this association has changed over the era studied. While investigations to confirm specific factors contributing to increased risk of neurodegenerative disease among professional soccer players are required, strategies directed toward reducing head impact exposure may be advisable in the meantime.



#15 Confirmation of early non-bulbar onset of amyotrophic lateral sclerosis in Spanish league soccer players

Reference: J Neurol Sci. 2021 Jul 24;428:117586.  doi: 10.1016/j.jns.2021.117586. Online ahead of print.

Authors: Josep Gamez, Francesc Carmona

Summary: Sports-related activity has been proposed as a risk factor for ALS, particularly among professionals playing American football and soccer, with a reported prevalence between two and forty times higher than the general population. Early onset (by two decades) was described among Italian soccer players as early as 2005. This study aims to characterise the phenotype of seven Spanish retired professional and semi-professional soccer players. The cases were identified using the following sources: (i) personal archives from a leading ALS Unit, (ii) PubMed and specialised websites, and (iii) self-reports of patients in the media. Age and site of onset, survival time, history of trauma, playing position and time between retirement and first symptoms were investigated for soccer players in the Spanish league diagnosed between 2000 and 2020. Seven ALS cases were identified. The mean age at onset was 41.5 years (SD 9.2, median 45.5, range 31.5-51.2). Onset was bulbar in one individual, while six experienced spinal onset. Three patients had the flail arm syndrome variant. Two cases were goalkeepers, two defenders and three midfielders. Four had a history of trauma (two serious). Survival time for the two deceased patients was 71.8 months. Mean time between retirement and first symptoms was 9.4 years (SD 8.0, median 15.2, range 0.1-17.5). Our study has the largest sample size of non-Italian league soccer professionals and semi-professionals, and our results corroborate early onset (by 23.7 years). Unlike the Italian cohorts, bulbar onset is rare, and upper limb onset is most common.



#16 Expertise Classification of Soccer Goalkeepers in Highly Dynamic Decision Tasks: A Deep Learning Approach for Temporal and Spatial Feature Recognition of Fixation Image Patch Sequences

Reference: Front Sports Act Living. 2021 Jul 26;3:692526. doi: 10.3389/fspor.2021.692526. eCollection 2021.

Authors: Benedikt Hosp, Florian Schultz, Enkelejda Kasneci, Oliver Höner

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Summary: The focus of expertise research moves constantly forward and includes cognitive factors, such as visual information perception and processing. In highly dynamic tasks, such as decision making in sports, these factors become more important to build a foundation for diagnostic systems and adaptive learning environments. Although most recent research focuses on behavioral features, the underlying cognitive mechanisms have been poorly understood, mainly due to a lack of adequate methods for the analysis of complex eye tracking data that goes beyond aggregated fixations and saccades. There are no consistent statements about specific perceptual features that explain expertise. However, these mechanisms are an important part of expertise, especially in decision making in sports games, as highly trained perceptual cognitive abilities can provide athletes with some advantage. We developed a deep learning approach that independently finds latent perceptual features in fixation image patches. It then derives expertise based solely on these fixation patches, which encompass the gaze behavior of athletes in an elaborately implemented virtual reality setup. We present a CNN-BiLSTM based model for expertise assessment in goalkeeper-specific decision tasks on initiating passes in build-up situations. The empirical validation demonstrated that our model has the ability to find valuable latent features that detect the expertise level of 33 athletes (novice, advanced, and expert) with 73.11% accuracy. This model is a first step in the direction of generalizable expertise recognition based on eye movements.



#17 The Impact of Environmental Conditions on Player Loads During Preseason Training Sessions in Women's Soccer Athletes

Reference: J Strength Cond Res. 2021 Aug 11.  doi: 10.1519/JSC.0000000000004112. Online ahead of print.

Authors: Alexis B Austin, Sean M Collins, Robert A Huggins, Brittany A Smith, Thomas G Bowman

Summary: Our objective was to determine the impact of environmental conditions on player loads during preseason training sessions in women's soccer athletes. Eleven women's NCAA Division III soccer players (age = 20 ± 1 year, height = 167.28 ± 8.65 cm, body mass = 60.18 ± 5.42 kg, V[Combining Dot Above]O2max = 43.70 ± 3.95 ml·kg-1·min-1) volunteered to wear Global Positioning System (GPS) devices (Sports Performance Tracking, Melbourne, Australia) that provided measures of training session external intensity throughout all preseason practices (n = 15). We recorded wet-bulb globe temperature (WBGT), session Rating of Perceived Exertion-Training Load (sRPE-TL), and ΔBM during each preseason training session and set α ≤ 0.05. The combination of WBGT, sRPE-TL, and ΔBM explained 34% of the variance in GPS-based intensity score (proprietary measure) (F3,153 = 26.25, p < 0.001). Wet-bulb globe temperature (t156 = -2.58, p = 0.01), sRPE (t156 = 8.24, p < 0.001), and ΔBM (t156 = 2.39, p = 0.02) were significantly associated with intensity. The ΔBM from prepractice (60.00 ± 5.21 kg) to postpractice (59.61 ± 5.10 kg) was statistically significant (p < 0.001); however, ΔBM from the beginning of preseason (59.87 ± 5.31 kg) to the end of preseason (59.91 ± 5.58 kg) was not significant (p = 0.89). Despite relatively low to moderate environmental conditions, increases in WBGT were associated with reductions in GPS intensity and elevated internal load via sRPE-TL. Our findings support the association between exercise intensity and WBGT, internal load, and hydration status; thus, coaches and exercise scientists should take these factors into account when monitoring or interpreting intensity metrics. Furthermore, these findings support the continued use of environmental monitoring and hydration best-practice policies to limit exercise intensity in the heat so as to mitigate excessive heat stress.



#18 Injury Profile among Elite Youth Male Football Players in a German Academy

Reference: Int J Sports Med. 2021 Aug 9. doi: 10.1055/a-1516-4139. 

Authors: Ayham Jaber, Johannes Weishorn, Gregor Berrsche, Henning Ott, Yannic Bangert

Summary: Studies that report injuries in elite youth football players are scarce. So far, no such studies have been reported in Germany. The aim of this study is to descriptively and statistically report the incidence of injuries that resulted in time-loss ≥ 4 days in the TSG Hoffenheim football academy by 138 male players aged between 12 and 19 years during one season. A total of 109 injuries were sustained by 76 players: 6.9 injuries occurred per 1000 hours of matches (95% CI, 5.0-9.6) and 0.7 injuries per 1000 hours of training (95% CI, 0.5-0.9) with a ratio of 9.8. Some 66% of all injuries occurred during matches. Injuries involved the lower limb (81%), upper limb (9%), head & neck (5%) and trunk injuries (5%). 21 (19%) of all injuries were regarded as severe and resulted in time-loss > 28 days. U16-U19 teams sustained more injuries (74, 68%) than U12-U15 (35, 32%) (P= 0.032). The most frequent diagnosis was thigh strain (22%). Time-loss ranged from 4-339 days (SD: 40, Average: 23). Many injuries were a result of strain. Available injury prevention programs should be adhered to more strictly. Dedicated epidemiological studies are needed to optimize focused injury prevention programs.



#19 Preseason weight-bearing ankle dorsiflexion in male professional football players with and without a history of severe ankle injury: A novel analysis in an English Premier League club

Reference: Phys Ther Sport. 2021 Jul 28;52:21-29.  doi: 10.1016/j.ptsp.2021.07.006. Online ahead of print.

Authors: Nicholas C Clark, Stuart D Campbell

Summary: Ankle injuries are common in professional football and have profound player/team/club consequences. The weight-bearing lunge-test (WBLT) assesses ankle dorsiflexion range-of-motion in football primary/secondary injury prevention and performance contexts. Data for uninjured and previously ankle-injured players in the English Premier League (EPL) is not available. This study analysed WBLT measurements (cm) within and between uninjured and previously severe ankle-injured players (injured-stiff group, injured-lax group) in one EPL club. Forty-nine players (age 22.9 ± 4.6 yr; height 181.6 ± 5.2 cm; mass 77.7 ± 7.6 kg) participated in this study. Prevalence (%) of previous unilateral severe ankle injury (USAI). Side-to-side (right/left, dominant/nondominant, injured/uninjured) WBLT comparisons at group-level (t-test [within-group]; Welch's ANOVA [between-group]; effect sizes [within-/between-group]) and individual-level (limb symmetry index [%]; absolute-asymmetry [%]) were used as outcome measures. Prevalence of USAI was 38.7%. There were no statistically-significant side-to-side differences for within-/between-group comparisons. Effect sizes: just-below-large (injured-stiff) and extremely-large (injured-lax) for within-group injured-side/uninjured-side comparisons; just-below-medium (injured-lax) to just-above-medium (injured-stiff) for injured-side comparisons to uninjured players. Absolute-asymmetries: uninjured players, 15.4±13.2%; injured-stiff, 21.8±33.6%; injured-lax 20.4±13.6%. Over one-third of players had previous USAI. Effect sizes indicate substantial within-group side-to-side differences and less substantial between-group differences. Across groups, some players had absolute-asymmetries that may elicit concern in ankle primary/secondary injury prevention and performance contexts.



#20 Optimizing the Explosive Force of the Elite Level Football-Tennis Players through Plyometric and Specific Exercises

Reference: Int J Environ Res Public Health. 2021 Aug 3;18(15):8228. doi: 10.3390/ijerph18158228.

Authors: Anamaria Gherghel, Dana Badau, Adela Badau, Liviu Moraru, Gabriel Marian Manolache, Bogdan Marian Oancea, Corina Tifrea, Virgil Tudor, Raluca Maria Costache

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Summary: The aim of the research was to implement an athletic program to improve the explosive force in order to optimize physical fitness at the level of elite football-tennis players and evaluate the progress made through specific tests using the Opto Jump. The research included 10 elite European and world-class players, on whom an experimental program was applied in order to improve the explosive force of the limbs in conditions of speed, endurance, and dynamic balance. Study tests: five vertical jumps on the spot, on the left/right leg; five back and forth jumps on the left/right leg; five left/right side jumps on the left/right leg; vertical jumps on both legs 60 s; BFS vertical jumps. For each test, the following parameters specific to the explosive force were statistically analyzed: contact time (s); flight time (s); jump height (cm), jump power (w/kg); RSI-Reactive Strength Index, defined as Height (m/s). In the study, the average value of the parameters specific to the jumps performed in each test was taken into account. During the study, the tests were performed and processed on the Opto Jump device and software. In all tests of the experiment monitored through Opto Jump, significant progress was made in the final test compared to the initial one, which demonstrates the efficiency of the physical training program implemented for the development of explosive force, with an impact on the sports performance of elite players. The most relevant results obtained for the left leg regarding the improvement of the explosive force of the lower limbs materialized in the jump height parameter was in the test of five vertical jumps on one leg on the spot, and for the right leg in the tests of: five back and forth jumps and five left/right side jumps. The most significant advances in the study were in the tests, in descending order of their weight: 60 s vertical jumps on both legs; five back-and-forth jumps and five left/right side jumps, five vertical jumps on one leg standing, and BFS vertical jumps.



#21 Should I Stay or Should I Go? The Impact of Social Networks on the Choice to Play for a National Team in Football

Reference: Int J Environ Res Public Health. 2021 Jul 21;18(15):7719.  doi: 10.3390/ijerph18157719.

Authors: Klaus Seiberth, Ansgar Thiel

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Summary: In the course of their careers, elite athletes are faced with crucial decisions. This applies particularly to adolescent athletes who additionally have to cope with a variety of age-related developmental tasks. For young top football players with a migrant background, this can be even more challenging as they often attract the interest of national associations. From a network-theoretical perspective, it can be considered likely that the decision to join a top national association is not taken independently of the players' networks. This article addresses the role of network actors within the players' decision-making process. Our analysis is guided by constructivist network theory and based on a qualitative research approach that used guided expert interviews as its core research tool. Ten interviews with German-born youth internationals with a migrant background were conducted. The present analysis reveals several network actors such as family, coaches and players' agents involved in the 'national team question'. Evidently, most relevant networks of players with a migrant background are sports-related. These networks turned out to be highly functionalized and leave only limited room for manoeuvring. At the same time, the interviews reveal 'structural holes' within the players' networks and indicate a considerable need for the optimization of talent counselling.



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