25. February 2022

Latest research in football - week 2 - 2022

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 In-season head-coach changes have positive short- and long-term effects on team perfor-mance in men's soccer-evidence from the Premier League, Bundesliga, and La Liga

Reference: J Sports Sci. 2022 Jan 3;1-8. doi: 10.1080/02640414.2021.2014688. Online ahead of print.

Authors: Sebastian Zart, Arne Güllich

Summary: The study investigated effects of in-season head-coach changes (HCC) on the subsequent team performance in men's English, German, and Spanish premier soccer leagues. A pre-post matched-controls design involved 149 HCC-teams and 3,960 games in 2010-19. Analyses (paired t-test, repeated-measurement ANOVA) revealed five central findings. 1. An HCC was preceded by a spell of under-performance, with a particular performance collapse in the two last pre-HCC rounds. 2. Performance showed an instant, strong improvement in the first post-HCC game. 3. The performance remained increased up to 16 post-HCC rounds. 4. Post-HCC performance also exceeded teams' initial baseline performance earlier before the HCC. Accordingly, the summed performance through 8, 12, and 16 post-HCC rounds exceeded the performance through 8, 12, and 16 pre-HCC rounds (0.92 < Cohen's d < 1.17). 5. HCC-teams' pre-post performance development differed from matched non-HCC control teams. In sum, the present evidence suggests positive short, medium, and long-term HCC effects at the highest professional soccer level. Theoretical hypotheses discussed in the literature - the "common-sense," "ritual-scapegoating," "vicious-circle," and "mean-reversion" hypotheses - are partly inconsistent with the present evidence. However, the evidence is fully consistent with a new hypothesis introduced here: the hypothesis of relief from a coach's performance-suppressing factor (RCPSF).

#2 Metabolic Signature of Leukocyte Telomere Length in Elite Male Soccer Players

Reference: Front Mol Biosci. 2021 Dec 16;8:727144. doi: 10.3389/fmolb.2021.727144. eCollection 2021.

Authors: Shamma Al-Muraikhy, Maha Sellami, Alexander S Domling, Najeha Rizwana, Abdelali Agouni, Fatima Al-Khelaifi, Francesco Donati, Francesco Botre, Ilhame Diboun, Mohamed A Elrayess

Download link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8716766/pdf/fmolb-08-727144.pdf

Summary: Biological aging is associated with changes in the metabolic pathways. Leukocyte telomere length (LTL) is a predictive marker of biological aging; however, the underlying metabolic pathways remain largely unknown. The aim of this study was to investigate the metabolic alterations and identify the metabolic predictors of LTL in elite male soccer players. Levels of 837 blood metabolites and LTL were measured in 126 young elite male soccer players who tested negative for doping abuse at anti-doping laboratory in Italy. Multivariate analysis using orthogonal partial least squares (OPLS), univariate linear models and enrichment analyses were conducted to identify metabolites and metabolic pathways associated with LTL. Generalized linear model followed by receiver operating characteristic (ROC) analysis were conducted to identify top metabolites predictive of LTL. Sixty-seven metabolites and seven metabolic pathways showed significant associations with LTL. Among enriched pathways, lysophospholipids, benzoate metabolites, and glycine/serine/threonine metabolites were elevated with longer LTL. Conversely, monoacylglycerols, sphingolipid metabolites, long chain fatty acids and polyunsaturated fatty acids were enriched with shorter telomeres. ROC analysis revealed eight metabolites that best predict LTL, including glutamine, N-acetylglutamine, xanthine, beta-sitosterol, N2-acetyllysine, stearoyl-arachidonoyl-glycerol (18:0/20:4), N-acetylserine and 3-7-dimethylurate with AUC of 0.75 (0.64-0.87, p < 0.0001). This study characterized the metabolic activity in relation to telomere length in elite soccer players. Investigating the functional relevance of these associations could provide a better understanding of exercise physiology and pathophysiology of elite athletes.

#3 Energy Expenditure of Female International Standard Soccer Players

Reference: Med Sci Sports Exerc. 2021 Dec 28. doi: 10.1249/MSS.0000000000002850. Online ahead of print.

Authors: James C Morehen, Christopher Rosimus, Bryce P Cavanagh, Catherine Hambly, John R Speakman, Kirsty J Elliot-Sale, Marcus P Hannon, James P Morton

Summary: The aim was to quantify total daily energy expenditure (TEE) of international adult female soccer players. Twenty-four professional players were studied during a twelve-day period where they participated in an international training camp (also inclusive of two competitive games) representing the English national team. TEE was assessed via the doubly labelled water (DLW) method during the full 12 days as well as the initial 4-day period prior to game one. Energy intake (EI) was also assessed (via weighed food analysis) during the initial 4-day period to permit estimation of energy availability (EA). Mean TEE did not differ (P = 0.31) between the 12-day (2693 ± 432 kcal.day-1; range: 2105-3507; 54 ± 6 kcal.kg-1 fat free mass, FFM) versus the 4-day assessment period (2753 ± 359 kcal.day-1; range: 1942-3280; 56 ± 8 kcal.kg-1 FFM). Mean four-day EI was 1923 ± 357 kcal.day-1 (range: 1639-2172) and mean activity energy expenditure was 1069 ± 278 kcal.day-1 (range: 155-1549 kcal.day-1). When assessed for estimated EA, 88% of players were categorised with low EA status according to the threshold of <30 kcal.kg-1 FFM. Mean daily carbohydrate intake equated to 3.3 ± 0.7 g.kg-1 body mass. When compared with previously published data from adult male players, we demonstrate that the relative daily energetic requirements of engaging in professional soccer training and match play is comparable between sexes. From a practical perspective, data suggest that practitioners should likely focus education and behaviour change strategies on "fuelling" for match play and training to optimise both player health and performance.

#4 Application of the arm-cranking 30-second Wingate Anaerobic Test (the WAnT) to assess power in amputee football players

Reference: Acta Bioeng Biomech. 2021;23(3):13-23.

Authors: Agnieszka Magdalena Nowak, Bartosz Molik, Andrzej Kosmol, Mateusz Szczepaniak, Jolanta Marszałek

Summary: The aim of this work was to determine anaerobic performance in male amputee football players considering types and levels of limb impairment, playing position, anthropometric parameters, and comparing the findings to reference values. Relationship between parameters in the laboratory anaerobic test and the handgrip test was checked. The 30-second Wingate Anaerobic Test (peak power, mean power, relative peak power, relative mean power, time to achieve peak power, fatigue index) on the arm-crank ergometer (LODE ANGIO), the FUTREX 6100 (Futrex, Gaithersburg, USA) and the handgrip test were used in amputee football players (n = 23). Anthropometric measurements were collected. There were no differences in anaerobic results between players considering types and levels of limb impairment. Forwards had significantly higher relative mean and peak power ( p = 0.049, d = 0.82; p = 0.049, d = 0.81), and lower amputation-adjusted body mass index ( p = 0.001, d = 1.50) than defenders. For peak power, 19 out 23 achieved, and for relative peak power, 22 out 23 achieved results from "average" to "elite". Peak power strongly correlated to handgrip strength results. Amputee football requires a high level of power from players. Maintaining appropriate body composition is important for amputee football players to have better anaerobic performance during the game. The 30-second Wingate Anaerobic Test can be used to assess anaerobic performance in AF players. Sport-specific anaerobic performance laboratory tests and field-based tests using in indirect upper limbs' peak power monitoring would be beneficial for coaches.

#5 A big data analysis of Twitter data during premier league matches: do tweets contain information valuable for in-play forecasting of goals in football?

Reference: Soc Netw Anal Min. 2022;12(1):23. doi: 10.1007/s13278-021-00842-z. Epub 2021 Dec 29.

Authors: Fabian Wunderlich, Daniel Memmert

Download link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8714875/pdf/13278_2021_Article_842.pdf

Summary: Data-related analysis in football increasingly benefits from Big Data approaches and machine learning methods. One relevant application of data analysis in football is forecasting, which relies on understanding and accurately modelling the process of a match. The present paper tackles two neglected facets of forecasting in football: Forecasts on the total number of goals and in-play forecasting (forecasts based on within-match information). Sentiment analysis techniques were used to extract the information reflected in almost two million tweets from more than 400 Premier League matches. By means of wordclouds and timely analysis of several tweet-based features, the Twitter communication over the full course of matches and shortly before and after goals was visualized and systematically analysed. Moreover, several forecasting models including a random forest model have been used to obtain in-play forecasts. Results suggest that in-play forecasting of goals is highly challenging, and in-play information does not improve forecasting accuracy. An additional analysis of goals from more than 30,000 matches from the main European football leagues supports the notion that the predictive value of in-play information is highly limited compared to pre-game information. This is a relevant result for coaches, match analysts and broadcasters who should not overestimate the value of in-play information. The present study also sheds light on how the perception and behaviour of Twitter users change over the course of a football match. A main result is that the sentiment of Twitter users decreases when the match progresses, which might be caused by an unjustified high expectation of football fans before the match.

#6 Dataset for field experiments analyzing discrimination in amateur soccer

Reference: Data Brief. 2021 Dec 23;40:107751. doi: 10.1016/j.dib.2021.107751. eCollection 2022 Feb.

Authors: Cornel Nesseler, Carlos Gomez-Gonzalez, Helmut Dietl, Christoph Halser

Download link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8718725/pdf/main.pdf

Summary: This paper presents data of field experiments that analyze discrimination in amateur soccer. The studies created fake accounts and asked amateur soccer coaches to come for a trial practice. The fake accounts had either a native- or a foreign-sounding name. The dataset is based on three published studies that analyzed discrimination in 23 countries. The dataset contains 24,915 observations and several variables that are interesting for further research. This data can be used to compare discrimination in amateur soccer with discrimination in diverse fields, such as migration, economics, or political science.

#7 Reliability and usefulness of maximum soccer-specific jump test: a valid and cost-effective system to measure on soccer field

Reference: Sports Biomech. 2022 Jan 10;1-15. doi: 10.1080/14763141.2021.2024244. Online ahead of print.

Authors: Alberto Fílter, Jesús Olivares, Alejandro Molina, Jaime Morente-Sánchez, José Robles, Fabio Y Nakamura, Alfredo Santalla, Irineu Loturco, Bernardo Requena

Summary: The aims of this study were (a) to assess intra-session reliability and usefulness of the soccer-specific maximum vertical jump (heading test, HT) and (b) to analyse the validity of the easy-to-use and cost-effective instrument (smartphone camera, MOB) compared with gold-standard instrument (3D motion capture system, MOCAP) to obtain the vertical jump performance during HT. Twelve semi-professional high-level and fifteen amateur soccer male players (23.9 ± 3.6 years) performed three HT attempts, and kinematic data were recorded with MOB and MOCAP. Intra-class correlation coefficient (ICC) and coefficient of variation (CV) were used as measures of intra-session reliability. T-test with Cohen's effect size (ES), Pearson's product moment and Bland-Altman analysis were used to obtain MOB validity. Regarding intra-session reliability, the CV was 1.13%, and ICC was 0.98, considered acceptable. Respecting validity criteria did not reveal significant differences (p < 0.05; effect size = 0.06, considered trivial), 'almost perfect' correlation (Pearson) (r = 0.98; p < 0.05), and strong agreement were obtained between MOB and MOCAP. This finding showed a test (HT) with a specific character, using cost-effective instrument and applicable to all soccer fields (adjusted to the standardised lines in the soccer field), all of them backed-up by reliability, usefulness and validity criteria.

#8 Individual-based Creatine Kinase Reference Values in Response to Soccer Match-play

Reference: Int J Sports Med. 2022 Jan 9. doi: 10.1055/a-1678-7340. Online ahead of print.

Authors: João Ribeiro, Petrus Gantois, Vitor Moreira, Francisco Miranda, Nuno Romano, Fábio Yuzo Nakamura

Summary: The aim of the present study was to determine the creatine kinase reference limits for professional soccer players based on their own normal post-match response. The creatine kinase concentration was analyzed in response to official matches in 25 players throughout a 3-year period. Samples were obtained between 36-43 hours following 70 professional soccer matches and corresponded to 19.1±12.1 [range: 6-49] samples per player. Absolute reference limits were calculated as 2.5th and 97.5th percentile of the samples collected. Creatine kinase values were also represented as a percentage change from the individual's season mean and represented by 90th, 95th and 97.5th percentiles. The absolute reference limits for creatine kinase concentration calculated as 97.5th and 2.5th percentiles were 1480 U.L-1 and 115.8 U.L-1, respectively. The percentage change from the individual's season mean was 97.45±35.92% and players were in the 90th, 95th and 97.5th percentiles when the percentages of these differences were 50.01, 66.7, and 71.34% higher than player's season mean response, respectively. The data allowed us to determine whether the creatine kinase response is typical or if it is indicative of a higher than normal creatine kinase elevation and could be used as a practical guide for detection of muscle overload, following professional soccer match-play.

#9 The effects of virtual soccer game on balance, gait function, and kick speed in chronic incomplete spinal cord injury: a randomized controlled trial

Reference: Spinal Cord. 2022 Jan 8. doi: 10.1038/s41393-021-00745-y. Online ahead of print.

Authors: Yeongsang An, Chanhee Park

Summary: The aim was to evaluate the effects of virtual soccer game on balance, gait function, and kick speed in individuals with spinal cord injuries. The participants were randomized into either an experimental group (EG) or a control group for treatment 3 days/week over 4 weeks. The clinical outcomes included the results of the chair stand test (CST), timed up-and-go (TUG) test, and 10 m walking test (10MWT). The virtual reality (VR) content outcome measure was kick speed. The independent t-test results indicated that the participants in the EG exhibited superior performances in the CST, TUG test, 10MWT, and kick speed test (all P < 0.05). Our results provide novel, promising clinical evidence that VR rehabilitation improves both dynamic and static balance and reduces the risk of falls in patients with incomplete SCI of Asia impairment scale grades C-D.

#10 Effect of a cervical collar on head and neck acceleration profiles during emergency spinal immobilisation and extrication procedures in elite football (soccer) players: protocol for a randomised, controlled cross-over trial

Reference: BMJ Open Sport Exerc Med. 2021 Dec 27;7(4):e001157. doi: 10.1136/bmjsem-2021-001157. eCollection 2021.

Authors: Michael J Callaghan, Tom Hughes, John Davin, Russell Hayes, Neil Hough, Daniel Torpey, David Perry, Sam Dawson, Eoghan Murray, Richard K Jones

Download link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8718494/pdf/bmjsem-2021-001157.pdf

Summary: When immobilisation after a cervical spine or head injury is required, the role of the rigid cervical collar is unclear and controversial. There is a need for further studies investigating the use of a rigid cervical collar when head and neck trauma occurs in sport. This study will compare present practice (immobilisation with a cervical collar) to the same procedure without a collar during a simulated spinal immobilisation and extraction scenario from the field of play to the side-line in football (soccer). It will use a prospective cohort within-subjects cross over randomised, controlled trial design. Healthy participants will assume the role of players with a head or neck injury. Clinical practitioners will perform the immobilisation and extrication procedure according to current clinical guidelines. Three dimensional linear and angular acceleration profiles of the head and torso will be measured and the time taken to complete the procedure. The interventions will be a 'cervical collar' or 'no collar' in random order. Data from the IMUs will be transferred wirelessly to a computer for analysis. Accordingly, within-subject differences between each condition (collar vs no collar) will be assessed with parametric or non-parametric inferential statistics.

#11 Study protocol for a prospective cohort study identifying risk factors for sport injury in adolescent female football players: the Karolinska football Injury Cohort (KIC)

Reference: BMJ Open. 2022 Jan 12;12(1):e055063. doi: 10.1136/bmjopen-2021-055063.

Authors: Ulrika Tranaeus, Nathan Weiss, Victor Lyberg, Martin Hagglund, Markus Waldén, Urban Johnson, Martin Asker, Eva Skillgate

Download link: https://bmjopen.bmj.com/content/bmjopen/12/1/e055063.full.pdf

Summary: Football is a popular sport among young females worldwide, but studies concerning injuries in female players are scarce compared with male players. The aim of this study is to identify risk factors for injury in adolescent female football players. The Karolinska football Injury Cohort (KIC) is an ongoing longitudinal study that will include approximately 400 female football academy players 12-19 years old in Sweden. A detailed questionnaire regarding demographics, health status, lifestyle, stress, socioeconomic factors, psychosocial factors and various football-related factors are completed at baseline and after 1 year. Clinical tests measuring strength, mobility, neuromuscular control of the lower extremity, trunk and neck are carried out at baseline. Players are followed prospectively with weekly emails regarding exposure to football and other physical activity, health issues (such as stress, recovery, etc), pain, performance and injuries via the Oslo Sports Trauma Research Center Overuse Injury Questionnaire (OSTRC-O). Players who report a substantial injury in the OSTRC-O, that is, not being able to participate in football activities, or have reduced their training volume performance to a moderate or major degree, are contacted for full injury documentation. In addition to player data, academy coaches also complete a baseline questionnaire regarding coach experience and education.

#12 Patterns of Injury in the Spanish Football League Players

Reference: Int J Environ Res Public Health. 2021 Dec 27;19(1):252. doi: 10.3390/ijerph19010252.

Authors: Iván Prieto-Lage, Juan Carlos Argibay-González, Adrián Paramés-González, Alexandra Pichel-Represas, Diego Bermúdez-Fernández, Alfonso Gutiérrez-Santiago

Download link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8751156/pdf/ijerph-19-00252.pdf

Summary: The study of football injuries is a subject that concerns the scientific community. The problem of most of the available research is that it is mainly descriptive. The objective of this study is to discover and analyse the patterns of injury in the Spanish Football League (2016-2017 season). The sample data consisted of 136 given injuries identified by the official physicians of the football clubs. The analysis was performed by using traditional statistic tests, T-pattern detection and polar coordinate analysis. The analysis revealed several patterns of injury: (a) The defender suffered a rupture of the hamstring muscles after a sprint, (b) knee sprains happened due to a received tackle, (c) fibrillar adductor rupture appeared mostly among defenders and (d) fibrillar ruptures took place mostly throughout the first part. There is a marked shift in the tendency regarding the player who gets more injured, from the midfielder to the defender. The most common injury was fibrillar rupture. The most common scenario in which this injury occurred was that in which the player injured himself after a sprint (24%). A week without competing seems to be insufficient as a prevention mechanism for injuries.

#13 The Role of the Results of Functional Tests and Psychological Factors on Prediction of Injuries in Adolescent Female Football Players

Reference: Int J Environ Res Public Health. 2021 Dec 23;19(1):143. doi: 10.3390/ijerph19010143.

Authors: Ulrika Tranaeus, Andreas Ivarsson, Urban Johnson, Nathan Weiss, Martin Samuelsson, Eva Skillgate

Download link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8750218/pdf/ijerph-19-00143.pdf

Summary: Football is a popular sport among adolescent females. Given the rate of injuries in female footballers, identifying factors that can predict injuries are important. These injuries are often caused by complex reasons. The aim of this study was to investigate if the combination of demographic (age, number of training and match play hours/week), psychosocial (perceived stress, adaptive coping strategies) and physiological factors (functional performance) can predict a traumatic injury in adolescent female footballers. A cohort consisting of 419 female football players aged 13-16 years was established. Baseline questionnaires covered potential risk factors for sport injuries, and measurements included football-related functional performance tests. Data were collected prospectively with a weekly online questionnaire for 52 weeks covering, e.g., injuries, training, and match play hours/week. A total of 62% of the players reported at least one traumatic injury during the 52 weeks. The coping strategy "positive reframing" had the strongest association with the risk of traumatic injuries. The combination of more frequent use of the coping strategy, positive reframing, and high levels of physical performance capacity may prevent a traumatic injury in adolescent female footballers. Coaches are encouraged to adopt both physiological and psychological factors when preventing injuries in young female footballers.

#14 Quantitative Analysis of Performance Recovery in Semi-Professional Football Players after the COVID-19 Forced Rest Period

Reference: Sensors (Basel). 2021 Dec 29;22(1):242. doi: 10.3390/s22010242.

Authors: Luigi Truppa, Lorenzo Nuti, Stefano Mazzoleni, Pietro Garofalo, Andrea Mannini

Download link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8749879/pdf/sensors-22-00242.pdf

Summary: This study proposes the instrumental analysis of the physiological and biomechanical adaptation of football players to a fatigue protocol during the month immediately after the COVID-19 lockdown, to get insights into fitness recovery. Eight male semi-professional football players took part in the study and filled a questionnaire about their activity during the lockdown. At the resumption of activities, the mean heart rate and covered distances during fatiguing exercises, the normalized variations of mean and maximum exerted power in the Wingate test and the Bosco test outcomes (i.e., maximum height, mean exerted power, relative strength index, leg stiffness, contact time, and flight time) were measured for one month. Questionnaires confirmed a light-intensity self-administered physical activity. A significant effect of fatigue (Wilcoxon signed-rank test p < 0.05) on measured variables was confirmed for the four weeks. The analysis of the normalized variations of the aforementioned parameters allowed the distinguishing of two behaviors: downfall in the first two weeks, and recovery in the last two weeks. Instrumental results suggest a physiological and ballistic (i.e., Bosco test outcomes) recovery after four weeks. As concerns the explosive skills, the observational data are insufficient to show complete recovery.

#15 Effects of Soccer Exercise on Balance Ability and Kinesthesia of the Lower Limb Joints in Children Aged 5-6 Years

Reference: Motor Control. 2022 Jan 10;1-13. doi: 10.1123/mc.2021-0093. Online ahead of print.

Authors: Kebin Shen, Yunxi Liu

Summary: Age-, height- and weight-matched children were recruited to the experimental group (EG; n = 31) and control group (n = 32). Following a 16-week soccer training program, balance ability and dominant-side lateral knee and ankle kinesthesia changes were tested. Regarding balance ability, the Sway Index, when children stood on a firm or foam surface with their eyes closed in the static balance test, and the dynamic balance test time were 13.5%, 11.6%, and 14.3% lower in the EG than in the control group, respectively. The scores in the left and right directions were 23.7% and 24.2% higher in the EG, respectively. Regarding kinesthesia, the angle of knee extension and ankle metatarsal flexion and dorsiflexion were 13.4%, 20.0%, and 16.8% lower in the EG than in the control group. These results indicate children in the EG had a better performance. After soccer exercise, children aged 5-6 years displayed improved balance in the left and right directions and improved knee extension, ankle plantarflexion, and dorsiflexion kinesthesia.

#15 Lower-Limb Muscle Contractile Properties, Explosive Power and the Subjective Response of Elite Soccer Players to the COVID-19 Lockdown

Reference: Int J Environ Res Public Health. 2022 Jan 1;19(1):474. doi: 10.3390/ijerph19010474.

Authors: Armin H Paravlic, Bostjan Simunic, Sasa Pisot, Matej Kleva, Kaja Teraz, Matjaz Vogrin, Uros Marusic, Rado Pisot

Download link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8744705/pdf/ijerph-19-00474.pdf

Summary: The present study examined the effects of the lockdown period on basic anthropometric measures, countermovement jumping performance, skeletal muscle contractile properties derived from tensiomyography (TMG), injury incidence, and self-assessed general well-being in elite soccer players. A total of 266 players were assessed before (PRE) and 32 players were reassessed 11 days after (POST) the COVID-19 period. Significant changes in the TMG parameters were observed POST compared to PRE: contraction time (Tc) increased from 6% to 50% in vastus lateralis [VL] (p = 0.009) and biceps femoris [BF] (p < 0.001), respectively; whereas radial displacement (Dm) increased for 19% in BF (p = 0.036) and 17% in VL (p < 0.001), respectively. Jumping performance remained unchanged from PRE to POST In addition, athletes rated the lockdown period as a positive event and felt psychologically better during the lockdown, primarily because they spent more time with family members and friends. Although there were no differences in any of the variables describing lower limb muscle power following the two-month lockdown, the altered contractile properties of the assessed muscles suggest suboptimal conditioning of the football players.

#16 A Compound Hop Index for Assessing Soccer Players' Performance

Reference: J Clin Med. 2022 Jan 4;11(1):255. doi: 10.3390/jcm11010255.

Authors: Łukasz Oleksy, Aleksandra Królikowska, Anna Mika, Maciej Kuchciak, Daniel Szymczyk, Marian Rzepko, Grzegorz Bril, Robert Prill, Artur Stolarczyk, Paweł Reichert

Summary: Athletes regularly have to pass a series of tests, among which one of the most frequently used functional performance measures are single-leg hop tests. As the collected individual results of tests constitute a large amount of data, strategies to decrease the amount of data without reducing the number of performed tests are being searched for. Therefore, the study aimed to present an effective method to reduce the hop-test battery data to a single score, namely, the Compound Hop Index (CHI) in the example of a soccer team. A male, first-league soccer team performed a battery of commonly used single-leg hop tests, including single hop and triple hop for distance tests and the six-meter timed hop test. Gathered data, including Limb Symmetry Indexes of the three tests, normalized to body height for the single- and triple-hop-tests distance separately for right and left legs, and the time of the six-meter timed hop test separately for right and left legs were standardized to z-scores. Consecutively, the z-scores were averaged and formed CHI. The developed CHI represents a novel score derived from the average of z-scores that significantly reduces, clarifies, and organizes the hop performance-measures data.

#17 Assessment of Peak Physical Demands in Elite Women Soccer Players: Can Contextual Variables Play a Role?

Reference: Res Q Exerc Sport. 2022 Jan 13;1-9. doi: 10.1080/02701367.2021.2004297. Online ahead of print.

Authors: Jaime González-García, Verónica Giráldez-Costas, Rodrigo Ramirez-Campillo, Barry Drust, Blanca Romero-Moraleda

Summary: The aim was to describe and compare the peak physical demands through the worst-case scenario method (WCS), according to different rolling average (RA) time epochs (i.e. 1 min, 3 min, and 5 min) and contextual variables in women soccer players. Using an observational-comparative study design, an elite women soccer team from the Spanish 1st league division was monitored during 27 matches. Nine WCS-dependent variables were assessed, including total distance (TD), high-speed running distance (HSR), sprint distance (SP), acceleration, and deceleration distance at different intensities by players position (i.e., central defenders [CD], wide defenders [WD], central midfielders [CM], wide midfielders [WM], forwards [F]), match half, location, and match outcome. The 1-min RA showed the lowest variability (CV = 9.8-65.8%) for all nine dependent variables. The WD presented the highest TD (168 ± 15.71 m/min). Differences between positions were observed for: CM<F (-10.19 m/min), CM<WM (-11.20 m/min), and CM<WD (-12.70 m/min). For SP: CM<F (-10.03 m/min), CM<WM (-11.91 m/min), CM<WD (-10.03 m/min), and CM<CD (-5.31 m/min). The WCS-dependent variables were also affected by match half and match outcome. 1-min RA time epochs allow greater accuracy and reliability to identify nine key WCS outcomes in elite women soccer players. Different contextual variables, particularly player's position, influenced the peak periods.

#17 Effect of a cervical collar on head and neck acceleration profiles during emergency spinal immobilisation and extrication procedures in elite football (soccer) players: protocol for a randomised, controlled cross-over trial

Reference: BMJ Open Sport Exerc Med. 2021 Dec 27;7(4):e001157. doi: 10.1136/bmjsem-2021-001157. eCollection 2021.

Authors: Michael J Callaghan, Tom Hughes, John Davin, Russell Hayes, Neil Hough, Daniel Torpey, David Perry, Sam Dawson, Eoghan Murray, Richard K Jones

Download link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8718494/pdf/bmjsem-2021-001157.pdf

#18 The Reliability of Transcranial Magnetic Stimulation-Derived Corticomotor Inhibition as a Brain Health Evaluation Tool in Soccer Players

Reference: Sports Med Open. 2022 Jan 14;8(1):7. doi: 10.1186/s40798-021-00399-3.

Authors: Thomas G Di Virgilio, Magdalena Ietswaart, Ragul Selvamoorthy, Angus M Hunter

Download link: https://sportsmedicine-open.springeropen.com/track/pdf/10.1186/s40798-021-00399-3.pdf

Summary: The suitability of corticomotor inhibition and corticospinal excitability to measure brain health outcomes and recovery of sport-related head impact (concussion and subconcussion) depends on good inter-day reliability, which is evaluated in this study. Transcranial magnetic stimulation (TMS) reliability in soccer players is assessed by comparing soccer players, for whom reliability on this measure may be reduced due to exposure to head impacts, to generally active individuals not engaged in contact sport. TMS-derived corticomotor inhibition and corticospinal excitability were recorded from the rectus femoris muscle during two testing sessions, spaced 1-2 weeks apart in 19 soccer players (SOC-age 22 ± 3 years) and 20 generally active (CON-age 24 ± 4 years) healthy volunteers. Inter-day reliability between the two time points was quantified by using intra-class correlation coefficients (ICC). Intra-group reliability and group differences on actual measurement values were also explored. Good inter-day reliability was evident for corticomotor inhibition (ICCSOC = 0.61; ICCCON = 0.70) and corticospinal excitability (ICCSOC = 0.59; ICCCON = 0.70) in both generally active individuals and soccer players routinely exposed to sport-related head impacts. Corticomotor inhibition showed lower coefficients of variation than excitability for both groups (InhibSOC = 15.2%; InhibCON = 9.7%; ExcitabSOC = 41.6%; ExcitabCON = 39.5%). No group differences between soccer players and generally active individuals were found on the corticomotor inhibition value (p > 0.05), but levels of corticospinal excitability were significantly lower in soccer players (45.1 ± 20.8 vs 85.4 ± 6.2%Mmax, p < 0.0001). Corticomotor inhibition also showed excellent inter-rater reliability (ICC = 0.87). Corticomotor inhibition and corticospinal excitability are stable and maintain good degrees of reliability when assessed over different days in soccer players, despite their routine exposure to head impacts. However, based on intra-group reliability and group differences of the levels of excitability, we conclude that corticomotor inhibition is best suited for the evaluation of neuromuscular alterations associated with head impacts in contact sports.

#19 Exploring the Use of Player Load in Elite Soccer Players

Reference: Sports Health. 2022 Jan 17;19417381211065768. doi: 10.1177/19417381211065768.

Authors: José M Oliva-Lozano, Daniele Conte, Víctor Fortes, José M Muyor

Summary: The aims of this study were to (1) analyze the distribution of the player load (PLTOTAL) in 3 axes of movement (PLAP, anterior-posterior; PLML, medial-lateral; PLV, vertical) during elite soccer matches, (2) investigate the effect of playing position on PL-related variables, and (3) explore the association between PLTOTAL and distance covered by the players. The hypothesis was that despite different load distribution between axes of movement, PLTOTAL might be used as a body load indicator for all playing positions. Data were collected from elite soccer players using WIMU Pro tracking systems, which included inertial sensors. The axis of movement had a significant effect on the distribution of the load (P < 0.001; conditional R2 = 0.91), with the greatest contribution from the PLV (P < 0.001; d = 5.41-5.86). Moreover, no effect of playing position on PLTOTAL, PLV, PLML, or PLAP was observed (P > 0.05). Finally, a large correlation was found between PLTOTAL and distance covered, and the linear mixed model showed that distance may be predicted by the PLTOTAL (conditional R2 = 0.81; P < 0.001). Differences in load distribution were based on the axis of movement, although playing position had no effect on any variable. The selection of either distance covered, which is representative of a 2-dimensional analysis, or PLTOTAL, which is representative of a 3-dimensional analysis, may be adequate for monitoring locomotor demands or accelerometer-derived load. Training strategies that focus on the vertical component of match play should be adopted. In addition, given that PLTOTAL is an accelerometry-based metric, which combines the accelerations in anterior-posterior, medial-lateral, and vertical planes, strength and conditioning coaches may use this parameter as a measure of total body load.

#20 Impact of climatic conditions projected at the World Cup in Qatar 2022 on repeated maximal efforts in soccer players

Reference: PeerJ. 2021 Dec 22;9:e12658. doi: 10.7717/peerj.12658. eCollection 2021.

Authors: Wiktor Chodor, Paweł Chmura, Jan Chmura, Marcin Andrzejewski, Ewa Jówko, Tomasz Buraczewski, Adrian Drożdżowski, Andrzej Rokita, Marek Konefał

Download link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8710061/pdf/peerj-09-12658.pdf

Summary: This study aimed to investigate the relationship between the climatic conditions predicted for the 2022 FIFA World Cup in Qatar and the capacity for repeated maximum effort (RSA), of soccer players. Twenty-four semi-professional soccer players participated in the study. The exercise test consisted of ten 6-second maximal efforts on a cycloergometer. A 90-second passive rest interval was used. Mechanical parameters were recorded in each repetition, and biochemical parameters at rest and even repetitions. The test was performed in a Weiss Technik WK-26 climate chamber under two different conditions: (1) thermoneutral (TNC - 20.5 °C; 58.7% humidity); (2) predicted for the 2022 World Cup in Qatar (QSC - 28.5 ± 1.92 °C; 58.7 ± 8.64% humidity). Significantly higher mean maximum power values were recorded in the second repetition under QSC conditions (1731,8 ± 214,4 W) (p = 0.025). A significantly longer time to reach maximum power was also recorded under TNC conditions compared to QSC conditions in repetition 2 (1,32 ± 0,33 s), (1,05 ± 0,29 s) (p = 0.016) and 6 (1,41 ± 0,48 s), (1,17 ± 0,25) (p = 0.036). There was a significantly higher rate of power loss, between repetition 2 (p = 0.023) and 4 (p = 0.043) under QSC conditions, compared to TNC. Considering the biochemical parameters, a significantly higher pO2 concentration was registered under QSC conditions in the 10th repetition (p = 0.006). The ambient temperature during exercise should be taken into account to determine the anaerobic exercise capacity of the athletes. At higher temperatures, there is a greater capacity for maximal effort, in terms of maximal power achieved, but with a greater decrease in performance.

#21 Head Impact Exposure and Biomechanics in University Varsity Women's Soccer

Reference: Ann Biomed Eng. 2022 Jan 18;1-12. doi: 10.1007/s10439-022-02914-3. Online ahead of print.

Authors: Rebecca Kenny, Marko Elez, Adam Clansey, Naznin Virji-Babul, Lyndia C Wu

Download link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8765100/pdf/10439_2022_Article_2914.pdf

Summary: Soccer is a unique sport where players purposefully and voluntarily use their unprotected heads to manipulate the direction of the ball. There are limited soccer head impact exposure data to further study brain injury risks. The objective of the current study was to combine validated mouthpiece sensors with comprehensive video analysis methods to characterize head impact exposure and biomechanics in university varsity women's soccer. Thirteen female soccer athletes were instrumented with mouthpiece sensors to record on-field head impacts during practices, scrimmages, and games. Multi-angle video was obtained and reviewed for all on-field activity to verify mouthpiece impacts and identify contact scenarios. We recorded 1307 video-identified intentional heading impacts and 1011 video-verified sensor impacts. On average, athletes experienced 1.83 impacts per athlete-exposure, with higher exposure in practices than games/scrimmages. Median and 95th percentile peak linear and peak angular accelerations were 10.0, 22.2 g, and 765, 2296 rad/s2, respectively. Long kicks, top of the head impacts and jumping headers resulted in the highest impact kinematics. Our results demonstrate the importance of investigating and monitoring head impact exposure during soccer practices, as well as the opportunity to limit high-kinematics impact exposure through heading technique training and reducing certain contact scenarios.

#22 Poor Reliability of Measurement Instruments to Assess Acute Responses to Load in Soccer Players Irrespective of Biological Maturity Status

Reference: Pediatr Exerc Sci. 2022 Jan 19;1-10. doi: 10.1123/pes.2021-0070. Online ahead of print.

Authors: Ludwig Ruf, Barry Drust, Paul Ehmann, Sabrina Forster, Anne Hecksteden, Tim Meyer

Summary: The aim was to assess the short-term reliability of measurement instruments to quantify the acute psychophysiological response to load in adolescent soccer players in relation to biological maturity. Data were collected from 108 U12 to U17 soccer players on 2 consecutive weeks (pre, n = 32; at, n = 34; and post, n = 42 estimated peak height velocity). Measurements consisted of the Short Recovery and Stress Scale, a countermovement jump, assessment of leg stiffness, and a submaximal run to assess exercise heart rate and heart rate recovery. Test-retest reliability was assessed with the coefficient of variation (CV) and intraclass correlation coefficient (ICC). Items of the Short Recovery and Stress Scale showed poor reliability across maturity groups (CV = 7.0%-53.5%; ICC = .28 to .79). Only few countermovement jump variables (jump height, concentric impulse, and concentric velocity) possessed good reliability. For most variables of the countermovement jump, reliability was better for the post peak height velocity group followed by at-peak height velocity and prepeak height velocity. Very high levels of reliability across maturity groups were observed for exercise heart rate (CV < 1.8%; ICC > .94), while heart rate recovery was more variable (CV < 16.5%; ICC > .48). Results suggest that the majority of investigated variables have poor reliability, questioning their ability to detect small, yet meaningful changes in acute responses to load in adolescent soccer players.

#23 Return to Play and Player Performance After Meniscal Tear Among Elite-Level European Soccer Players: A Matched Cohort Analysis of Injuries From 2006 to 2016

Reference: Orthop J Sports Med. 2022 Jan 12;10(1):23259671211059541. doi: 10.1177/23259671211059541. eCollection 2022 Jan.

Authors: Ophelie Z Lavoie-Gagne, Avinaash Korrapati, Julia Retzky, David N Bernstein, Connor C Diaz, Elyse J Berlinberg, Enrico M Forlenza, Matthew S Fury, Nabil Mehta, Evan A O'Donnell, Brian Forsythe

Download link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8761888/pdf/10.1177_23259671211059541.pdf

Summary: Meniscal injuries are extremely common in soccer athletes, and little is known about postrecovery performance. The aim was to (1) identify characteristics associated with return to play (RTP) to the same league level and (2) evaluate long-term effects that injury and management approach may have on player performance. Using publicly available records, we identified athletes who sustained meniscal tears across the 5 major European soccer leagues (English Premier League, Bundesliga, La Liga, Ligue 1, and Serie A) between 2006 and 2016. Injured athletes were matched to controls 1:2 by demographics and performance. Investigations included rate of RTP to the same league level, reinjury, player characteristics associated with RTP within 2 seasons, long-term availability, field time, and performance metrics standardized to 90 minutes of play during the next 4 seasons. A total of 250 players sustaining meniscal tears were included, of which 106 (42%) received surgical management. Median absence was 57.5 days (interquartile range [IQR], 35-92) or 7 games (IQR, 4-12). Rate of RTP was 70%, and the reinjury rate 5% if a player could RTP. Age greater than 30 years was a negative predictor for RTP (odds ratio [OR], 0.62; P = .002), whereas higher preinjury goals per game (OR, 2.80; P = .04) and surgical management (OR, 1.38; P = .002) were positive predictors for RTP. Surgical management was associated with higher long-term availability (P < .01). As compared with the control, there were no significant differences in field time or performance metrics after RTP, either overall or by player position. As compared with nonoperative management, defenders undergoing surgery demonstrated decreased field time. Attackers and midfielders demonstrated similar field time and performance regardless of management. RTP of elite soccer athletes sustaining meniscal tear is contingent on age, preinjury performance, and management approach. Those who RTP to the same league level can be expected to demonstrate equivalent field time, performance, and long-term availability as noninjured athletes.

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