Latest research in football - week 51 - 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 Effects of Short-Term Dynamic Balance Training on Postural Stability in School-Aged Football Players and Gymnasts

Reference: Front Psychol. 2021 Nov 17;12:767036. doi: 10.3389/fpsyg.2021.767036. eCollection 2021.

Authors: Rouven Kenville, Tom Maudrich, Sophie Körner, Johannes Zimmer, Patrick Ragert

Download link:

Summary: Static and dynamic balance abilities enable simple and complex movements and are determinants of top athletic performance. Balance abilities and their proficiency differ fundamentally with respect to age, gender, type of balance intervention, and type of sport. With this study, we aim to investigate whether 4weeks of dynamic balance training (DBT) improves static balance performance in school-aged gymnasts and football players. For this purpose, young male gymnasts (n=21) and male football players (n=20) completed an initial static balance assessment consisting of two one-legged stance (left and right foot) and two two-legged stance (eyes open and eyes closed) tasks. Subsequently, all participants underwent a 4-week intervention. DBT consisting of nine individual tasks was performed two times per week. Another static balance assessment followed 1day after the last training session and retention was assessed 2weeks later. Dynamic balance scores and total path length were analyzed via rank-based repeated measures designs using ANOVA-type statistics. The influence of factors GROUP and TIME on the static and dynamic balance performance was examined. Prior to DBT, young gymnasts showed better static balance performance than football players. However, after intervention, both groups improved in both one-legged stance tasks and also had high retention rates in these tasks. No significant improvements were seen in either group in the two-legged balance tests. Both groups improved in the dynamic balance tasks, although no differences in learning rates were evident. Our findings imply an inter-relationship between both static and dynamic balance components. Consequently, training regimes should include both balance components to facilitate early development of balance ability.



#2 Nutritional optimization for female elite football players-topical review

Reference: Scand J Med Sci Sports. 2021 Dec 5. doi: 10.1111/sms.14102. Online ahead of print.

Authors: Maysa V de Sousa, Anne-Marie Lundsgaard, Peter M Christensen, Lars Christensen, Morten B Randers, Magni Mohr, Lars Nybo, Bente Kiens, Andreas M Fritzen

Download link:

Summary: Women's football is an intermittent sport characterized by frequent intense actions throughout the match. The high number of matches with limited recovery time played across a long competitive season underlines the importance of nutritional strategies to meet these large physical demands. In order to maximize sport performance and maintain good health, energy intake must be optimal. However, a considerable proportion of female elite football players does not have sufficient energy intake to match the energy expenditure, resulting in low energy availability that might have detrimental physiologic consequences and impair performance. Carbohydrates appear to be the primary fuel covering the total energy supply during match-play, and female elite football players should aim to consume sufficient carbohydrates to meet the requirements of their training program and to optimize the replenishment of muscle glycogen stores between training bouts and matches. However, several macro- and micronutrients are important for ensuring sufficient energy and nutrients for performance optimization and for overall health status in female elite football players. The inadequacy of macro-and micronutrients in the diet of these athletes may impair performance and training adaptations, and increase the risk of health disorders, compromising the player's professional career. In this topical review, we present knowledge and relevant nutritional recommendations for elite female football players for the benefit of sports nutritionists, dietitians, sports scientists, healthcare specialists, and applied researchers. We focus on dietary intake and cover the most pertinent topics in sports nutrition for the relevant physical demands in female elite football players as follows: energy intake, macronutrient and micronutrient requirements and optimal composition of the everyday diet, nutritional and hydration strategies to optimize performance and recovery, potential ergogenic effects of authorized relevant supplements, and future research considerations.



#3 Return to play after treating acute muscle injuries in elite football players with radial extracorporeal shock wave therapy

Reference: J Orthop Surg Res. 2021 Dec 7;16(1):708. doi: 10.1186/s13018-021-02853-0.

Authors: James P M Morgan, Mario Hamm, Christoph Schmitz, Matthias H Brem

Download link:

Summary: The aim was to compare lay-off times achieved by treating acute muscle injuries in elite football players with a multimodal therapy approach that includes a specific protocol of almost daily radial extracorporeal shock wave therapy (rESWT) with corresponding data reported in the literature. We performed a retrospective analysis of treatments and recovery times of muscle injuries suffered by the players of an elite football team competing in the first/second German Bundesliga during one of the previous seasons. A total of 20 acute muscle injuries were diagnosed and treated in the aforementioned season, of which eight (40%) were diagnosed as Type 1a/muscular tightness injuries, five (25%) as Type 2b/muscle strain injuries, four (20%) as Type 3a/partial muscle tear injuries and three (15%) as contusions. All injuries were treated with the previously mentioned multimodal therapy approach. Compared with data reported by Ekstrand et al. (Br J Sports Med 47:769-774, 2013), lay-off times (median/mean) were shortened by 54% and 58%, respectively, in the case of Type 1a injuries, by 50% and 55%, respectively, in the case of Type 2b injuries as well as by 8% and 21%, respectively, in the case of Type 3a injuries. No adverse reactions were observed. Overall, the multimodal therapy approach investigated in this study is a safe and effective treatment approach for treating Type 1a and 2b acute muscle injuries amongst elite football players and may help to prevent more severe, structural muscle injuries.



#4 Antioxidants Markers of Professional Soccer Players During the Season and their Relationship with Competitive Performance

Reference: J Hum Kinet. 2021 Oct 31;80:113-123. doi: 10.2478/hukin-2021-0089. eCollection 2021 Oct.

Authors: Jesus Gustavo Ponce-Gonzalez, Juan Corral-Pérez, Eduardo Sáez de Villarreal, Jose Vicente Gutierrez-Manzanedo, Guillermo De Castro-Maqueda, Cristina Casals

Download link:

Summary: The aim of this study was to assess antioxidant markers before and after a mid-season of professional soccer players from the 3rd Spanish Division, and to correlate antioxidant markers with competitive performance. Sixty-five male players (age = 25.3 ± 4.2 yr, body mass = 73.2 ± 6.7 kg, body height = 177.8 ± 5.7 cm) from three soccer clubs from Cádiz (Spain) participated in the study. Body composition, maximal aerobic capacity (VO2max), and baseline antioxidant blood markers (Total Antioxidant Status (TAS) and Reduced glutathione/Oxidized glutathione ratio) were assessed in the first week of the championship season (pre-test) and after 18 weeks in the mid-season (post-test). Soccer performance was registered according to the official classification ranking at both the mid-season and at the end of the season; ranking positions for Team A were 2nd and 1st, for Team B were 5th and 5th, while for Team C were 12th and 14th, respectively. Regression analyses showed that TAS and VO2max were able to independently predict (p < 0.05) performance in our participants. Moreover, antioxidant levels showed significant main effects on performance (p < 0.001); where a higher antioxidant capacity was observed in the best performance soccer team, both before and after the mid-season. Notwithstanding, the competitive period compromised the antioxidant status since TAS levels significantly decreased after the 18-week training program and competition compared with baseline values in all soccer teams (p < 0.001). These results suggest the need of monitoring antioxidants in soccer players to prevent excessive oxidative stress and cellular damage which could compromise success in competition, by adjusting the training loads, diet or ergogenic aids, if needed.



#5 Uncommon Bone Injuries in Soccer Players

Reference: J Hum Kinet. 2021 Oct 31;80:125-138. doi: 10.2478/hukin-2020-0032. eCollection 2021 Oct.

Authors: Krzysztof Ficek, Paweł Gwiazdoń, Radosław Skowronek, Natalia Kędra, Kamila Kluczniok, Magdalena Strózik, Grzegorz Hajduk

Download link:

Summary: Soccer is the most common team sport in the world. A significant number of players are associated with a large number of injuries. Injuries occur in a variety of contexts regardless of the age or performance level of players. The vast majority of injuries involve soft tissues. Bone injuries are less common, but usually result in long-term exclusion from the game. Three different types of fractures related to soccer are classified as acute types, stress fractures and avulsion. This manuscript outlines the diagnostic procedures and treatments for stress fractures, avulsion fractures and bone cyst. The common feature of the described injuries includes frequent difficulties associated with the correct diagnosis and treatment direction. In therapeutic treatment, the doctor and the patient often have to choose between conservative treatment and surgical treatment, which in many cases is not simple. We suggest that in the event of injuries to soccer players, surgical treatment should be used, shortening the time to return to full sports activity. A very important element of the therapeutic process is proper rehabilitation, which should be individually tailored to the patient in order to optimize the treatment process. Some of the rehabilitation protocols should be permanently incorporated into the warm-up protocols for training. Such a procedure has a preventive effect.



#6 The Effects of Successive Soccer Matches on the Internal Match Load, Stress Tolerance, Salivary Cortisol and Jumping Performance in Youth Soccer Players

Reference: J Hum Kinet. 2021 Oct 31;80:173-184. doi: 10.2478/hukin-2021-0092. eCollection 2021 Oct.

Authors: Julio Cesar Barbosa de Lima Pinto, Romerito Sóstenes Canuto de Oliveira, Nicole Leite Galvão-Coelho, Raissa Nóbrega de Almeida, Alexandre Moreira, Arnaldo Luis Mortatti

Download link:

Summary: The study aim was to analyze the effects of successive matches on the internal match load, stress tolerance, salivary cortisol concentration and countermovement vertical jump height in twelve youth soccer players (16.6 ± 0.5 yr; 175 ± 8 cm; 65 ± 8 kg) who performed four official matches within a four day-period with a 24-h recovery interval between the matches. The internal match load, monotony index and competitive strain, as well as stress tolerance were examined. Saliva samples were collected and countermovement vertical jump height was assessed 60 min pre and 30 min post each match; delta of salivary cortisol and countermovement vertical jump height for each match were analyzed. Salivary cortisol was analyzed using an enzyme-linked immunosorbent assay. The results of ANOVA with repeated measures showed no differences between matches for the internal match load (p > 0.05). The scores of the monotony index and competitive strain were 4.3 (±2.3) and 8104 (±6795) arbitrary units, respectively. There was no difference for stress tolerance between matches (p > 0.05). Delta values of salivary cortisol were not different among the assessed matches (F(3,33) = 1.397, p = 0.351, η2: 0.09); however, delta of countermovement vertical jump height decreased from match 1 to match 4 (F(3,33) = 8.64, p < 0.001, η2: 0.44). The current findings suggest that participating in four successive matches, with 24-h of recovery in between, may not lead to changes in stress tolerance and salivary cortisol of youth players, but it may induce a decrease in players' jumping performance after the fourth match.



#7 A Practical Approach to Monitoring Biomarkers of Inflammation and Muscle Damage in Youth Soccer Players During a 6-Month Training Cycle

Reference: J Hum Kinet. 2021 Oct 31;80:185-197. doi: 10.2478/hukin-2021-0093. eCollection 2021 Oct.

Authors: Tomasz Podgórski, Jakub Kryściak, Beata Pluta, Jacek Adrian, Jakub Marynowicz, Magdalena Krzykała, Marek Konefał, Paweł Chmura, Jan Chmura, Marcin Andrzejewski

Download link:

Summary: The aim of the study was to determine the effects of a 6-month training cycle on muscle damage and inflammatory markers in youth male soccer players. Twenty-one soccer players were tested four times: at the beginning (T1) and immediately after the pre-season period (T2), in the middle (T3) and at the end of the competitive period (T4). Muscle damage and inflammatory markers were determined in blood taken 36 hours after the match. Throughout the training cycle significant increases (p < 0.05) of creatine kinase (T1: 254.4 U·L-1; T4: 304.2 U·L-1) and lactate dehydrogenase (T1: 382.8 U·L-1; T4: 453.2 U·L-1) activities were observed. Significant changes (p < 0.05) in platelet count (T1: 210.5·109·L-1; T4: 234.2·109·L-1), percentage of lymphocyte (T1: 39.80%; T4: 42.97%), monocyte (T1: 6.88%; T4: 9.99%) and granulocyte (T1: 53.32%; T4: 47.05%) as well as in granulocyte-to-lymphocyte (T1: 1.41; T4: 1.17) and lymphocyte-to-monocyte (T1: 6.21; T4: 4.46) ratios were noted. The correlation analysis revealed statistically significant relationships (p < 0.05) between: myoglobin and the percentage of leukocyte subpopulations and the granulocyte to lymphocyte ratio; lactate dehydrogenase and the percentage of monocyte; lactate and leukocyte count. In conclusion, the reported muscle damage and inflammatory markers in T3 and T4 indicate the need for fatigue status monitoring in youth soccer players, especially in the competitive period. Moreover granulocyte to lymphocyte and lymphocyte to monocyte ratios proved to be sensitive to fatigue changes and therefore can provide coaches and sport scientists with a broader perspective on the biochemical monitoring of training status in soccer players.



#8 Effects of Intensity Modulated Total-Body Circuit Training Combined with Soccer Training on Physical Fitness in Prepubertal Boys after a 6-Month Intervention

Reference: J Hum Kinet. 2021 Oct 31;80:207-222. doi: 10.2478/hukin-2021-0102. eCollection 2021 Oct.

Authors: Michał Boraczyński, Tomasz Boraczyński, Jan Gajewski, Anna Malwina Kamelska-Sadowska, Piotr Gronek, James Laskin

Download link:

Summary: The purpose of this study was to examine the effects of a 6-month high- or moderate-intensity total-body circuit training (CT) program on physical fitness in prepubertal soccer players. Sixty-seven prepubertal boys with a mean age of 11.2 ± 0.7 years completed the study. Participants from a soccer academy were randomly assigned either to a high-intensity CT group (HCT, n = 22) or a moderate-intensity CT group (MCT, n = 24). A control group (CON, n = 21) comprised age-matched individuals who were not involved in any regular training regime. CT protocols were included in the experimental group's training sessions 3 times per week over 24 weeks as part of their usual weekly training regime. Based on the HR zone method, CT protocols included high- or moderate-intensity (85-95% HRmax or 75-85% HRmax) series of 3 different sets of upper- and lower-body strength exercises with articular and muscular mobilization, all culminated with 40-m sprints. Physical fitness was evaluated by the Eurofit test which included the flamingo balance (FLB), plate tapping (PLT), sit-and-reach (SAR), standing broad jump (SBJ), handgrip (HG), sit-ups (SUP), bent arm hang (BAH), 10×5 m shuttle run (SHR), and the Physical Working Capacity test (PWC170). The two-way ANOVA indicated group×time interaction effects for 5 components: the largest was for the SBJ (F2,63 = 42.895, p < 0.001, η2 = 0.577), and the lowest for the SHR (F2,63 = 5.006, p < 0.01, η2 = 0.137) indicating better improvements in the HCT compared to the MCT group. Furthermore, for HCT and MCT groups the highest pre- to post-intervention percentage changes were for the FLB and the SAR, while in the CON group the changes of all physical fitness components were not significant (p < 0.05). In conclusion, the intensity-controlled total-body CT protocol incorporated into a standard soccer training program is effective for enhancement in physical fitness performance in prepubertal soccer players.



#9 Exploration of the Age-Category Soccer Performance Effects During Ball Possession Small-Sided Games

Reference: J Hum Kinet. 2021 Oct 31;80:251-262. doi: 10.2478/hukin-2021-0109. eCollection 2021 Oct.

Authors: Nuno André Nunes, Bruno Gonçalves, Jonathan Sj Fenner, Adam Lee Owen, Bruno Travassos

Download link:

Summary: Small-sided games have been adopted as an integral part of soccer training, however, the use of task constraints by the coach and the action capabilities of both players and teams require further investigation. The aim of this investigation was to explore the age-category effects (under-11: U11, under-15: U15 and under-23: U23) on external training workloads (total distance covered, distance covered while walking, running and sprinting, number of sprints and maximum sprint speed), internal training load metrics (rate of perceived exertion, RPE) and tactical individual actions (passing number with dominant and non-dominant foot, and max passing speed) during 4 vs. 4 ball possession small-sided game constrained within three different playing areas (small: 20 x 15 m, medium: 25 x 20 m, and large: 30 x 25 m). Results revealed substantial differences (all p < .001) for each specific playing area observed across many of the external workload measures. For every area analysed, U23 players covered more distance walking, whereas U11 and U15 players covered more distances at higher intensities. Additionally, significant differences were found for the RPE (small playing area: p = .001; large playing area: p < .001) with U23 and U15 players showing higher scores compared with U11 ones. It can be concluded that a 4 vs. 4 ball possession small-sided game can provide different performance related stimuli to players, depending on age category and the playing surface area. Therefore, coaches and individuals involved with training and development of soccer players across all age groups should be aware of the key variables highlighted in this study before planning training drills.



#10 The Dirty League: English Premier League Provides Higher Incentives for Fouling as Compared to Other European Soccer Leagues

Reference: J Hum Kinet. 2021 Oct 31;80:263-276. doi: 10.2478/hukin-2021-0095. eCollection 2021 Oct.

Authors: Ashwin A Phatak, Robert Rein, Daniel Memmert

Download link:

Summary: Fouling in soccer has been studied from an ethical standpoint as a measure of aggression. However, there is limited research related to fouling for performance. The present study investigated fouling as a factor influencing performance in European soccer leagues. Out of possession fouls (FPGNorm), yellow cards (YCFNorm), and their ratio (YCPFPG) were used as predictors of points (Pts) and goals conceded (GA) at the end of the season using three separate linear regression models. Furthermore, 5-fold cross-validation was used to measure out sample reliability. All the models significantly predicted GA and Pts (p < 0.001). Models predicting GA showed higher reliability than models predicting points. Cross validation (CV) results suggested that FPGNorm and YCPFPG models showed a small standard deviation (SD) in the R2 results whereas the results from YCFNorm were not reliable to high SD in the 5-fold CV results. In summary, FPGNorm and YCPFPG seem to predict success (low GA and high Pts) across European soccer leagues, with EPL showing the maximum effect. The findings of the current study and the methodology can be applied to an actual game analysis by coaches in multiple invasion sports. Normalizing for out of possession time is a crucial step for the time spent in particular phases of play, which has not been done in previous research while analyzing 'key performance indices' (KPIs). Normalization can successfully introduce domain-specific knowledge into predictors, which can be used in complex algorithms improving predictions and investigation of underlying mechanisms.



#11 Running Performance and Hormonal, Maturity and Physical Variables in Starting and Non-Starting Elite U14 Soccer Players During a Congested Match Schedule

Reference: J Hum Kinet. 2021 Oct 31;80:287-295. doi: 10.2478/hukin-2021-0096. eCollection 2021 Oct.

Authors: Vinicius Zanetti, Marcelo Saldanha Aoki, Paul Bradley, Christopher Carling, Thomas Kisil Marino, Alexandre Moreira

Download link:

Summary: This study examined changes in match running performance (MRP) in Under-14 soccer players (13.5 ± 0.7 yrs) during a congested match schedule (CMS) (4 matches played within a 5-day period). It also examined the difference in salivary testosterone (sT) concentration, somatic maturation, jumping tests, and Yo-Yo Intermittent Recovery Test Level 1 (Yo-Yo IR1) between the players selected to play (SLG; group who participated in all matches) and players non-selected to play (NSG). A significant difference was observed for the frequency of decelerations (DEC) across matches (match 4 vs. matches 1, 2 and 3; p = 0.05; partial ƞ2 = 0.20). No difference between matches was observed for total running distance (TRD), high-speed running distance (HSRD), and frequency of accelerations (ACC) (p > 0.05). A wide range for within-player coefficient of variation (CV) values was observed for all MRP variables (range: 10.5 = TRD to 30.6 = HSRD). No difference between SLG and NSG for any of the assessed variables was observed (p > 0.05). The findings suggest that DEC was the most pertinent variable for monitoring changes in MRP during the CMS. In addition, at an elite youth soccer level, the biological maturity and fitness might not influence selection to play.



#12 Metabolic Changes After a 24-Week Soccer-Based Adaptation of the Diabetes Prevention Program in Hispanic Males: A One-Arm Pilot Clinical Trial

Reference: Front Sports Act Living. 2021 Nov 12;3:757815. doi: 10.3389/fspor.2021.757815. eCollection 2021.

Authors: Jennifer K Frediani, Jianheng Li, Alan Bienvenida, Melinda K Higgins, Felipe Lobelo

Download link:

Summary: One third of the U.S. adult population is estimated to have obesity-associated prediabetes. Hispanics have a 50% higher type 2 diabetes death rate compared to non-Hispanic whites, yet low participation in lifestyle change programs, making this subgroup an important target for prevention. Our objective was to determine the feasibility and the effects of an intervention implementing the Center for Disease Control and Prevention National Diabetes Prevention Program (NDPP) plus recreational soccer (RS) in Hispanic men. Overweight and obese Hispanic men, aged 30-57 years with prediabetes at screening were recruited (n = 41). Trained soccer coaches led 30-min facilitated discussion of the NDPP modules after each RS session, with two sessions per week for 12 weeks and once per week for the following 12 weeks. The 1-h RS sessions followed the Football Fitness curriculum. Assessments included body mass index, waist circumference, bioelectrical impedance analysis (InBody 270), blood pressure, glycated hemoglobin (HbA1c), and validated physical fitness tests. Multilevel mixed models assessed the outcomes as a function of time and cohort and incorporated an unstructured covariance structure to examine the changes from baseline to 24 weeks. All analyses were conducted as intent-to-treat using SAS v 9.4.  Hispanic males (n = 41; mean age 41.7 [0.1] years) were obese at baseline (mean BMI 32.7, standard error of mean [0.7], mean weight 93.9 [2.2] kg). Attendance rate was 65% overall at 12 weeks but differed between cohorts. Five mild injuries occurred over the trial. After 24 weeks of the NDPP+RS intervention, there were significant decreases in systolic and diastolic blood pressure (%change -4.7[SE 2.4]; 95% CI [-11.5, -1.7] and -6.1 [1.7] mmHg; [-9.6, -2.6], respectively), HbA1c (-0.2 [0.1]; [-0.3, -0.1]), Despite significant reductions in weight (-3.8 [0.7]; [-5.2, -2.5]), waist circumference (-6.6 [0.7] cm; [-8.0, -5.1]), body fat % (-1.9 [0.5]; [-2.8, -1.0]), lean body mass was preserved (-0.9 [0.3]; [-1.6, -0.2]). A 24-week soccer-based adaptation of the Diabetes Prevention Program is safe and feasible among middle-aged Latino men.



#13 The effects of visual cognitive tasks on landing stability and lower extremity injury risk in high-level soccer players

Reference: Gait Posture. 2021 Nov 26;92:230-235. doi: 10.1016/j.gaitpost.2021.11.031. Online ahead of print.

Authors: Yuanyuan Ren, Cenyi Wang, Lei Zhang, Aming Lu

Download link:

Summary: Visual cognition plays a pivotal role in sports. It is widely recognized that there is an intriguing coupling that they could affect each other through interaction between visual cognition and motor control, but few studies linked the effects of visual cognitive tasks on landing stability to postural control and injury risk. The research question was whether visual cognitive tasks affect the landing stability and lower limb injury risk of professional soccer players? The current study used a three-dimensional Multiple Object Tracking (MOT) task to simulate visual cognitive difficulties experienced in soccer matches. Fifteen male high-level soccer athletes (height: 181.43 ± 7.36 cm, weight: 75.37 ± 10.67 kg, training years: 10.07 ± 2.98 yr) from our school team were recruited and completed a landing action from a high platform with and without MOT tasks. Vicon infrared high-speed motion capture system and three-dimensional force measuring platform were used to collect various outcomes simultaneously. The Time to Stabilization (TTS) during landing was significantly prolonged, while the Medial-Lateral Stability Index (MLSI), Anterior-Posterior Stability (APSI), Dynamic Postural Index Stability Index (DPSI), the trajectory lengths, and envelope area of COP during landing were also increased during MOT dual-task. The decline of these indicators reflected the deterioration in postural stability and greater requirements for maintaining balance which could increase the risk of injury in soccer athletes. We advocate that adequate visual attention and visual information processing might play critical roles in maintaining dynamic balance through the supraspinal neural network.



#14 Lung function and ventilatory response to exercise in asymptomatic elite soccer players positive for COVID-19

Reference: Pulmonology. 2021 Nov 18;S2531-0437(21)00206-3. doi: 10.1016/j.pulmoe.2021.11.002. 

Authors: A Di Paco, S Mazzoleni, M Vitacca, L Comini, N Ambrosino

Download link:



#15 Hamstring injury patterns in professional male football (soccer): a systematic video analysis of 52 cases

Reference: Br J Sports Med. 2021 Dec 7;bjsports-2021-104769. doi: 10.1136/bjsports-2021-104769. 

Authors: Thomas Gronwald, Christian Klein, Tim Hoenig, Micha Pietzonka, Hendrik Bloch, Pascal Edouard, Karsten Hollander

Summary: The aim was to closely describe the injury inciting events of acute hamstring injuries in professional male football (soccer) using systematic video analysis. Video footage from four seasons (2014-2019) of the two highest divisions in German male football was searched for moderate and severe (ie, time loss of >7 days) acute non-contact and indirect contact match hamstring injuries. Two raters independently categorised inciting events using a standardised procedure to determine specific injury patterns and kinematics. 52 cases of hamstring injuries were included for specific pattern analysis. The pattern analysis revealed 25 sprint-related (48%) and 27 stretch-related hamstring injuries (52%). All sprint-related hamstring injuries occured during linear acceleration or high-speed running. Stretch-related hamstring injuries were connected with closed chain movements like braking or stopping with a lunging or landing action and open chain movements like kicking. The kinematic analysis of stretch-related injuries revealed a change of movement involving knee flexion to knee extension and a knee angle of <45° at the assumed injury frame in all open and closed chain movements. Biceps femoris was the most affected muscle (79%) of all included cases. Despite the variety of inciting events, rapid movements with high eccentric demands of the posterior thigh are likely the main hamstring injury mechanism. This study provides important data about how hamstring injuries occur in professional male football and supports the need for demand-specific multicomponent risk reduction programmes.



#16 The between-week reliability of neuromuscular, endocrine, and mood markers in soccer players and the repeatability of the movement demands during small-sided games

Reference: J Sports Med Phys Fitness. 2021 Dec 9. doi: 10.23736/S0022-4707.21.12993-7. Online ahead of print.

Authors: William Sparkes, Anthony N Turner, Matthew Weston, Mark Russell, Michael Johnston, Liam P Kilduff

Summary: Establishing the reliability and repeatability of both the movement demands and the consequential responses of athletes applied settings is important. Therefore, the primary aim of this study was to assess the between- week reliability of potential fatigue monitoring methods in soccer players. Secondary aims were to establish the repeatability of the movement demands and the changes in monitoring variables from the same small-sided game (SSG) protocol programmed on consecutive weeks. Twelve semi-professional soccer players (age, 21±2 years; mass, 80.1±6.8kg; height, 1.81±0.06m) performed the same SSG protocol (4vs4+goalkeepers; 6x7-min, 2-min inter-set recovery) separated by 7 days. Movement demands were monitored using global positioning systems (GPS), with countermovement jump (CMJ), saliva (testosterone and cortisol), and brief assessment of mood (BAM+) collected immediately pre and post SSG training. Results suggest that CMJ variables and hormonal markers have good between-week reliability when measuring athletes at rest (CV, 2.1-7.7%; ICC, 0.82-0.98), however BAM+ did not (CV, 23.5%; ICC, 0.47). GPS variables presented low to high repeatability during SSG training, with reliability statistics varying between metrics (CV, 4.4-62.4%; ICC, 0.30-0.81). In detecting responses from pre- to post-SSG training, CMJ and hormonal markers showed moderate to very-high reliability (ICC, 0.68-0.99), whilst BAM + did not (ICC, 0.12). The findings from this study suggest CMJ and hormonal markers provide good between-week reliability, yet caution should be applied when using short subjective questionnaires. Additionally, some movement demands may not be repeatable when programming the same SSG session on separate occasions.



#17 The influence of sleep quality and quantity on soccer injuries in professional teams

Reference: J Sports Med Phys Fitness. 2021 Dec 9. doi: 10.23736/S0022-4707.21.13016-6. Online ahead of print.

Authors: Mohammad A Yabroudi, Zakariya H Nawasreh, Wessam A Dabas, Elham J Al-Shorman, Ahmad A Darwish, Hadi A Samaneh, Khaldoon M Bashaireh

Summary: There is inconsistency in the relationship between sleeping measures and the occurrence of soccer injuries. Further, most studies investigated sleeping quantity and quality during soccer season but not during off-season. The purpose of this study was to determine the influence of sleeping off-season and during soccer season on the occurrence of injuries in professional soccer players. It was hypothesized that lower sleeping hours and players' thought of inadequate sleeping quantity and quality during off-season and soccer season would associate with the occurrence of soccer injuries. One-hundred and fifty-two professional soccer players (premier league and division I teams, age: 21.82±4.44, BMI: 22.21±2.74, sex: men(n=91), women (n=61)) answered questions related to their sleeping duration and whether that amount of sleep was enough prior to (off-season) and during soccer season. The sleep questions related to sleep quantity were derived from the Arabic Pittsburgh Sleep Quality Index. Players indicated also. Players indicated their injury profile, medical treatment, and time loss due to soccer injury. Sleeping measures were evaluated using univariate and multivariate logistic regression models to determine predictors of soccer injuries. Sixty-eight players (44.73%) were injured. Lower total sleeping time during off-season (OR:0.66, 95%CI:0.51-0.85, p=0.002), answering no on "did you regularly get enough sleep during off-season" (OR: 5.64, 95%CI: 2.58-12.27, p<0.001), and answering no on "do you think that your sleeping hours during off-season were enough" (OR:4.76, 95%CI: 1.98-11.46, p=0.001) associated significantly with soccer injuries (R2:38). Lower total sleeping time and not getting regularly enough sleeping time during off-season associated with more soccer injuries. This highlights the influence of sleeping quantity and quality off-season on the occurrence of soccer injuries among professional players.



#18 The influence of muscle strength and aerobic fitness on functional recovery in professional soccer

Reference: J Sports Med Phys Fitness. 2021 Dec 9. doi: 10.23736/S0022-4707.21.13401-2. Online ahead of print.

Authors: Will Abbott, Tom Clifford

Summary: Well-developed physical qualities may protect athletes from exercise-induced muscle damage and accelerate recovery following exercise. This study examined the influence of muscle strength and aerobic fitness on recovery from competitive soccer matches. Fourteen players from the English Premier League 2 (Age, 18 ± 1 yrs; height, 1.78 ± 0.54 m; mass, 73.8 ± 6.3 kg) were equally divided (median split) into a higher or lower group for muscle strength and aerobic fitness, according to their isometric mid-thigh pull (IMPT) and maximal aerobic speed test (MAST) scores, respectively. The following markers of recovery were assessed before (48-h pre-match), 12 h (M+1), 36 h (M+2) and 60 h (M+3) after ~3 matches: countermovement jump height (CMJ), reactive strength index (RSI), muscle soreness (DOMS) and wellbeing. IMTP was positively correlated with the recovery of CMJ, RSI and DOMS following matches (P<0.05). In the high IMTP group, DOMS was lower at M+1 to M+3 (all P≤0.002; ES≥2.10), CMJ was ≥4% greater at M+1 to M+3 (all P≤0.001; ES≥2.21) and RSI was ≥3% higher at M+2 and M+3 (all P≤0037; ES≥1.25). Players in the H-MAST group did not recover quicker for any variable (all P>0.05). This study showed that stronger players recovered quicker after matches and highlights the importance of lowerbody strength training for soccer players.



#19 A Congested Match Schedule Alters Internal Match Load and Affects Salivary Immunoglobulin A Concentration in Youth Soccer Players

Reference: J Strength Cond Res. 2020 Jul 1. doi: 10.1519/JSC.0000000000003701. Online ahead of print.

Authors: Arnaldo Luis Mortatti, Romerito Sostenes Canuto de Oliveira, Julio Cesar Barbosa de Lima Pinto, Nicole Leite Galvao-Coelho, Raissa Nobrega de Almeida, Marcelo S Aoki, Alexandre Moreira

Summary: The aim of this study was to analyze the effects of a congested match schedule (CMS) undertaken after a tapering week, on internal match load (IML) and salivary immunoglobulin A (SIgA) concentration in 12 youth soccer players (16.6 +/- 0.5 years; 175 +/- 8 cm; 65 +/- 8 kg) who performed 4 official matches within a 4-day period. Internal match load was determined using the session-rating of perceived exertion method and the competitive strain (CS) and monotony index (MI) were also determined. Saliva sampling was conducted, before the last training day of a tapering week (training) preceding the CMS, 60 minutes before the first match (match-1), and 22 hours after match 4 (postmatch 4). Salivary immunoglobulin A was analyzed by ELISA. The results of the analysis of variance with repeated measures showed a significant difference for IML across the matches (p < 0.001). A significant reduction in SIgA was observed from prematch 1 to postmatch 4 (p = 0.019). Regarding the change in SIgA ([DELTA]SIgA), 58.3% of the players presented values equal/higher than the minimal detectable change. A large within-individual correlation was observed between [DELTA]SIgA and MI and CS (r = 0.71 and r = 0.72: p < 0.01, respectively). The current findings suggest that youth players participating in a CMS may present a decrease in mucosal immunity function. In addition, data suggest that the MI and CS may be used as valuable markers for monitoring competition load during CMS in youth soccer players.



#20 Do age and body size affect the eccentric knee flexor strength measured during the Nordic hamstring exercise in male soccer players?

Reference: Sports Biomech. 2021 Dec 9;1-11. doi: 10.1080/14763141.2021.2003850. Online ahead of print.

Authors: Vinícius de Borba Capaverde, Gabriel Dos Santos Oliveira, Felipe Xavier de Lima-E-Silva, João Breno Araujo Ribeiro-Alvares, Bruno Manfredini Baroni

Summary: The study aimed to verify how age, height, body mass and body mass index affects the eccentric knee flexor strength during the Nordic hamstring exercise (NHE) in male soccer players. Ten professional soccer clubs were included in this cross-sectional trial. Three hundred and eleven soccer players (192 from senior and 119 from under-20 teams) were assessed using a load-cell based device. Pearson's correlation tests were performed between peak force values (measured in Newtons) and age, height, body mass and body mass index. The individual-limb strength (n = 622 limbs) and the between-limb average strength (n = 322 players) presented no correlation with age (r = 0.12 for both) and height (r = 0.13; r = 0,15), and fair correlations with body mass (r = 0.37; r = 0,41) and body mass index (r = 0.40; r = 0,43). In conclusion, the male soccer players' eccentric knee flexor strength measured during the NHE execution is not affected by age or height. Body mass and body mass index play somewhat effect on strength, thus normalising absolute strength measures by body mass or body mass index can provide more accurate analysis in some contexts.



#21 Investigating the Sketchplan: A Novel Way of Identifying Tactical Behavior in Massive Soccer Datasets

Reference: IEEE Trans Vis Comput Graph. 2021 Dec 13;PP. doi: 10.1109/TVCG.2021.3134814. 

Authors: Daniel Seebacher, Thomas Polk, Halldor Janetzko, Daniel Keim, Tobias Schreck, Manuel Stein

Summary: Coaches and analysts prepare for upcoming matches by identifying common patterns in the positioning and movement of the competing teams in specific situations. Existing approaches in this domain typically rely on manual video analysis and formation discussion using whiteboards; or expert systems that rely on state-of-the-art video and trajectory visualization techniques and advanced user interaction. We bridge the gap between these approaches by contributing a light-weight, simplified interaction and visualization system, which we conceptualized in an iterative design study with the coaching team of a European first league soccer team. Our approach is walk-up usable by all domain stakeholders, and at the same time, can leverage advanced data retrieval and analysis techniques: a virtual magnetic tactic-board. Users place and move digital magnets on a virtual tactic-board, and these interactions get translated to spatio-temporal queries, used to retrieve relevant situations from massive team movement data. Despite such seemingly imprecise query input, our approach is highly usable, supports quick user exploration, and retrieval of relevant results via query relaxation. Appropriate simplified result visualization supports in-depth analyses to explore team behavior, such as formation detection, movement analysis, and what-if analysis. We evaluated our approach with several experts from European first league soccer clubs. The results show that our approach makes the complex analytical processes needed for the identification of tactical behavior directly accessible to domain experts for the first time, demonstrating our support of coaches in preparation for future encounters.



#22 Hamstring and ACL injuries impacts on hamstring-to-quadriceps ratio of the elite soccer players: A retrospective study

Reference: Phys Ther Sport. 2021 Dec 5;53:97-104. doi: 10.1016/j.ptsp.2021.12.001. Online ahead of print.

Authors: Shahab Alizadeh, Javad Sarvestan, Zdeněk Svoboda, Fatemeh Alaei, Petr Linduška, Peyman Aghaie Ataabadi

Summary: This study aimed to compare the angle-specific (AS) and non-angle-specific (NAS) hamstring to quadriceps conventional and functional ratios between healthy, hamstring- and ACL-injured elite soccer players. One hundred and eleven players (27.42 ± 8.01 years, 182.11 ± 6.79 cm, 75.93 ± 7.25 kg) completed a series of concentric knee flexor and extensor strength in addition to eccentric knee flexor strength was measured at an angular velocity of 60°.s-1. Normalized and raw peak torque values, and the torque-angle profiles were extracted for analysis. Conventional and functional NAS (peak values) and AS (waveform ratios) hamstring to quadriceps ratios were calculated and compared between the groups. Healthy players produced greater functional and conventional ratios compared to players with either ACL or hamstring injury. Players with hamstring injury produced a lower AS functional ratios between 46° and 54° of knee flexion. Players suffering from ACL injury depicted a lower value for the AS functional ratio between 33° and 56° of knee flexion. Although NAS can identify soccer players with previous hamstring or ACL injury, the range where there is a strength deficiency is eluded. With the use of AS the range where the deficiency is present can be identified, and clinicians can benefit from this analysis to design robust rehabilitation protocols.



#23 Purposeful Heading Performed by Female Youth Soccer Players Leads to Strain Development in Deep Brain Structures

Reference: Neurotrauma Rep. 2021 Aug 3;2(1):354-362. doi: 10.1089/neur.2021.0014. eCollection 2021.

Authors: Jeffrey S Brooks, Wayne Allison, Alexandra Harriss, Kewei Bian, Haojie Mao, James P Dickey

Download link:

Summary: Head impacts in soccer have been associated with both short- and long-term neurological consequences. Youth players' brains are especially vulnerable given that their brains are still developing, and females are at an increased risk of traumatic brain injury (TBI) compared to males. Approximately 90% of head impacts in soccer occur from purposeful heading. Accordingly, this study assessed the relationship between kinematic variables and brain strain during purposeful headers in female youth soccer players. A convenience sample of 36 youth female soccer players (13.4 [0.9] years of age) from three elite youth soccer teams wore wireless sensors to quantify head impact magnitudes during games. Purposeful heading events were categorized by game scenario (e.g., throw-in, goal kick) for 60 regular season games (20 games per team). A total of 434 purposeful headers were identified. Finite element model simulations were performed to calculate average peak maximum principal strain (APMPS) in the corpus callosum, thalamus, and brainstem on a subset of 110 representative head impacts. Rotational velocity was strongly associated with APMPS in these three regions of the brain (r = 0.83-0.87). Linear acceleration was weakly associated with APMPS (r = 0.13-0.31). Game scenario did not predict APMPS during soccer games (p > 0.05). Results demonstrated considerable APMPS in the corpus callosum (mean = 0.102) and thalamus (mean = 0.083). In addition, the results support the notion that rotational velocity is a better predictor of brain strain than linear acceleration and may be a potential indicator of changes to the brain.



#24 Outcomes of revision anterior cruciate ligament reconstruction in soccer players : a cohort study

Reference: Bone Jt Open. 2021 Dec;2(12):1043-1048. doi: 10.1302/2633-1462.212.BJO-2021-0145.R1.

Authors: MARS Group

Download link:

Summary: There is limited information on outcomes of revision ACL reconstruction (rACLR) in soccer (association football) athletes, particularly on return to sport and the rate of additional knee surgery. The purpose of this study was to report return to soccer after rACLR, and to test the hypothesis that patient sex and graft choice are associated with return to play and the likelihood of future knee surgery in soccer players undergoing rACLR. Soccer athletes enrolled in a prospective multicentre cohort were contacted to collect ancillary data on their participation in soccer and their return to play following rACLR. Information regarding if and when they returned to play and their current playing status was recorded. If they were not currently playing soccer, they were asked the primary reason they stopped playing. Information on any subsequent knee surgery following their index rACLR was also collected. Player demographic data and graft choice were collected from their baseline enrolment data at rACLR. Soccer-specific follow-up was collected on 76% (33 male, 39 female) of 95 soccer athletes. Subsequent surgery information was collected on 95% (44 male, 46 female). Overall, 63% of athletes returned to soccer a mean 9.6 months (SD 5.8) after index revision surgery but participation in soccer decreased to 19% at a mean of 6.4 years (SD 1.3) after surgery. There was no significant association of patient sex or graft choice with return to play, time of return to play, or long-term return to play. Females were more likely than males to have subsequent knee surgery following rACLR (20% (9/46) vs 5% (2/44); p = 0.050). The rate of recurrent graft tear (5.6%; 5/90) was similar between males and females. Approximately two-thirds of soccer players return to sport after rACLR, but the rate of participation drops significantly over time. Neither patient sex nor graft choice at the time of rACLR were associated with return to play. Female soccer players face a higher risk for additional knee surgery after rACLR than male soccer players. 



#25 Characterization of Head Impact Exposure in Women's Collegiate Soccer

Reference: J Appl Biomech. 2021 Dec 15;1-10. doi: 10.1123/jab.2020-0304. Online ahead of print.

Authors: Tanner M Filben, Nicholas S Pritchard, Logan E Miller, Sarah K Woods, Megan E Hayden, Christopher M Miles, Jillian E Urban, Joel D Stitzel

Summary: Soccer players are regularly exposed to head impacts by intentionally heading the ball. Evidence suggests repetitive subconcussive head impacts may affect the brain, and females may be more vulnerable to brain injury than males. This study aimed to characterize head impact exposure among National Collegiate Athletic Association women's soccer players using a previously validated mouthpiece-based sensor. Sixteen players were instrumented during 72 practices and 24 games. Head impact rate and rate of risk-weighted cumulative exposure were compared across session type and player position. Head kinematics were compared across session type, impact type, player position, impact location, and ball delivery method. Players experienced a mean (95% confidence interval) head impact rate of 0.468 (0.289 to 0.647) head impacts per hour, and exposure rates varied by session type and player position. Headers accounted for 89% of head impacts and were associated with higher linear accelerations and rotational accelerations than nonheader impacts. Headers in which the ball was delivered by a long kick had greater peak kinematics (all P < .001) than headers in which the ball was delivered by any other method. Results provide increased understanding of head impact frequency and magnitude in women's collegiate soccer and may help inform efforts to prevent brain injury.



#26 Development and Validation of Prediction Formula of Wingate Test Peak Power From Force-Velocity Test in Male Soccer Players

Reference: Front Psychol. 2021 Nov 29;12:729247. doi: 10.3389/fpsyg.2021.729247. eCollection 2021.

Authors: Pantelis T Nikolaidis, Beat Knechtle

Download link:

Summary: Peak power of the Wingate anaerobic test (WAnT), either in W (Ppeak) or in (rPpeak), has been widely used to evaluate the performance of soccer players; however, its relationship with force-velocity (F-v) test (e.g., whether these tests can be used interchangeably) has received little scientific attention so far. The aim of this work was to develop and validate a prediction equation of Ppeak and rPpeak from F-v characteristics in male soccer players. Participants were 158 adult male soccer players (sport experience 11.4 ± 4.5 years, mean ± standard deviation, approximately five weekly training units, age 22.6 ± 3.9 years, body mass 74.8 ± 7.8 kg, and height 178.3 ± 7.8 cm) who performed both WAnT and F-v test. An experimental (EXP, n = 79) and a control group (CON, n = 79) were used for development and validation, respectively, of the prediction equation of Ppeak and rPpeak from F-v test. In EXP, Ppeak correlated very largely with body mass (r = 0.787), fat-free mass (r = 0.765), largely with maximal power of F-v test (P max ; r = 0.639), body mass index (r = 0.603), height (r = 0.558), moderately with theoretical maximal force (F 0; r = 0.481), percentage of body fat (r = 0.471), fat mass (r = 0.443, p < 0.001); rPpeak correlated with rPmax (largely; r = 0.596, p < 0.001), theoretical maximal velocity (v 0; moderately; r = 0.341, p = 0.002), F 0 (small magnitude; r = 0.280, p = 0.012), BF (r = -0.230, p = 0.042), and fat mass (r = -0.242, p = 0.032). Ppeak in EXP could be predicted using the formula "44.251 + 7.431 × body mass (kg) + 0.576 × P max (W) - 19.512 × F0" (R = 0.912, R 2 = 0.833, standard error of estimate (SEE) = 42.616), and rPpeak from "3.148 + 0.218 × rPmax ( + v0 (rpm)" (R = 0.765, R 2 = 0.585, SEE = 0.514). Applying these formulas in CON, no bias was observed between the actual and the predicted Ppeak (mean difference 2.5 ± 49.8 W; 95% CI, -8.7, 13.6; p = 0.661) and rPpeak (mean difference 0.05 ± 0.71; 95% CI, -0.11, 0.21, p = 0.525). These findings provided indirect estimates of Ppeak of the WAnT, especially useful in periods when this test should not be applied considering the fatigue it causes; in this context, the F-v test can be considered as an alternative of exercise testing for estimating the average Ppeak of a group of soccer players rather than for predicting individual scores when the interindividual variation of performance is small.



#27 Small-sided games in female soccer players: a systematic review

Reference: J Sports Med Phys Fitness. 2021 Dec 16. doi: 10.23736/S0022-4707.21.12888-9. Online ahead of print.

Authors: Vicente de Dios-Álvarez, Miguel Lorenzo-Martínez, Alexis Padrón-Cabo, Ezequiel Rey

Summary: This systematic review aimed to analyse the literature on small-sided games (SSGs) from a physiological and physical perspective in female soccer players. A systematic review of Web of Science, PubMed, Scopus and SPORTDiscus was performed according to PRISMA (Preferred, Reporting Items for Systematic reviews and Meta-Analysis) guidelines. Studies informed about physical and/or, physiological responses during SSGs played by young and/or adult amateur and/or professional female soccer players were included. Information regarding study information, population, intervention data, instruments, variables analysed and outcomes were elucidated. The search returned 2944 records. After screening against set criteria, a total of 13 manuscripts were fully reviewed. The present review grouped studies according to the three following age categories taking sample's mean age into account: Under-19 as young players and senior female players (> 19 years old). The most common topics of analysis were (1) player number; (2) pitch area and game surface; (3) sex differences; (4) training regimens. This review provides useful information on the complex relationship between technical, physical and physiological interactions in SSGs and how manipulating these types of variables can improve the soccer training process.



#28 Spontaneous pneumomediastinum as a complication to cheering during the UEFA European Football Championship

Reference: Ugeskr Laeger. 2021 Dec 13;183(50):V09210749. [Article in Danish]

Authors: Chastine Kølster, Lasse Holmgaard Jensen, Malene Kirchmann

Download link:

Summary: Spontaneous pneumomediastinum is a rare condition caused by a bronchial or alveolar rupture. The condition is often benign and self-limiting, but rapid diagnosis is essential, and potentially dangerous differential diagnoses must be eliminated. In this case report, we present a 16-year-old male who developed voice changes, a sore throat and swelling of the neck in relation to football cheering. X-ray and CT findings showed pneumomediastinum and supraclavicular subcutaneous emphysema. No treatment was necessary, and after one week there were no symptoms left.



#29 Prevalence of binocular vision dysfunctions in professional football players

Reference: Clin Exp Optom. 2021 Dec 9;1-7. doi: 10.1080/08164622.2021.2002667. Online ahead of print.

Authors: Jorge Jorge, Alberto Diaz-Rey, Madalena Lira

Summary: The extent of binocular vision dysfunction in elite soccer players needs to be determined as it may impact performance. The purpose of the study was to investigate the prevalence of binocular vision dysfunctions in elite soccer players. One hundred and seven professional soccer players were evaluated. Refractive error was measured and the following binocular vision parameters were assessed: horizontal and vertical phoria for distance and near vision, the values of break and recovery for negative and positive fusional vergences at distance and near vision, vergence facility at distance and near vision, monocular accommodative facility at near vision, and near point of convergence (break and recovery points). All the athletes were men with a mean age of 24.4 ± 4.8 years. No athlete was diagnosed with divergence excess, divergence insufficiency, or basic exophoria. About 13.0% of the athletes have binocular vision dysfunctions related to esophoria (0.9% with esophoria at near vision and 12.1% with esophoria at distance and near vision). About 10.3% have convergence insufficiency and 2.8% were diagnosed with fusional vergence dysfunction. The only accommodation-related parameter analysed was accommodative infacility, and 6.5% of the athletes had this dysfunction. Vertical phoria was present in 3.7% of the athletes. No statistically significant differences were found based on in athletes with respect to ethnicity, position occupied on the field, age, ametropia or laterality. The overall prevalence of binocular vision dysfunction in elite soccer players was 36.4%. The most prevalent dysfunctions are related to the presence of esophoria (13.0%). The values found point out the need to include binocular vision assessment protocols in the visual assessment routine for athletes.


The Training Manager -