Latest research in football - week 52 - 2017

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 A Unique Rectus Femoris Injury in an Adolescent Professional Soccer Player: A Case Report
Reference: JBJS Case Connect. 2014 Oct/Dec/Nov;4(4):e115. doi: 10.2106/JBJS.CC.M.00290.
Authors: Huri G, Dubin JM, Ozgonen K, Kaya D, Doral MN
Summary: A sixteen-year-old professional soccer player presented with persistent pain in the right thigh of two years' duration and the inability to return to play. Evaluation revealed a chronic rupture of the rectus femoris muscle. Because physiotherapy and rehabilitation failed to help, a surgical repair was performed. He returned to his previous activity level within nine months after surgery. Rupture of the proximal part of the rectus femoris should be acknowledged in the differential diagnosis, especially when presenting with persistent pain in the anterior aspect of the thigh lasting more than one year. Delayed repair might be recognized as a reasonable option for chronic rupture of the proximal part of the rectus femoris.

#2 Power and endurance in Hong Kong professional football players
Reference: Asia Pac J Sports Med Arthrosc Rehabil Technol. 2016 Jun 10;5:1-5. doi: 10.1016/j.asmart.2016.05.001. eCollection 2016 Jul.
Authors: Chan HC, Fong DT, Lee JW, Yau QK, Yung PS, Chan KM
Summary: The purpose of this study was to investigate the power and endurance characteristics of Hong Kong professional football players. Training recommendations can be deduced based on the comparison between Hong Kong and international football players. Eighty-eight Hong Kong professional football players (height, 177.2 ± 6.4 cm; weight, 70.6 ± 7.6 kg; age, 25.6 ± 5.0 years) in the first division league participated in a battery of tests, which included: (1) height, (2) weight, (3) countermovement jump, (4) 30-m sprinting, and (5) Yo-Yo Intermittent Recovery Test Level 2. Compared with the test results of the first division players in other countries as reported in the literature (Norway, France, and Scandinavian countries), Hong Kong players were shorter in height (0.1-2.1%), lighter in weight (5.5-8.3%), fair in vertical jump height (-4.8-17%), slower in acceleration (4.2-5.1%) and maximum speed (3-14.2%), and had poorer aerobic and anaerobic endurance (22.9%). The present study suggests that Hong Kong football players (or players with similar physique and ability) need to improve their power and endurance.

#3 Halftime Rewarm-up With Intermittent Exercise Improves the Subsequent Exercise Performance of Soccer Referees
Reference: J Strength Cond Res. 2018 Jan;32(1):211-216. doi: 10.1519/JSC.0000000000002197.
Authors: Yanaoka T, Yamagami J, Kidokoro T, Kashiwabara K, Miyashita M
Summary: This study investigated the effect of halftime rewarm-up (RW) with intermittent exercise on the subsequent exercise performance of soccer referees, determined by the Yo-Yo Intermittent Recovery Test level 1 (Yo-Yo IR1). Using a randomized cross-over design, 10 male referees were required to complete 2 trials. The trials consisted of the Loughborough Intermittent Shuttle Test, halftime, and Yo-Yo IR1 periods. During halftime, participants either rested on a chair (Control) or performed a halftime RW exercise for 15 minutes. The halftime RW protocol comprised 2.15 minutes of seated rest, followed by 2.15 minutes of running at 70% of the maximum heart rate (HRmax)-this cycle of recovery and running was repeated for a total of 13 minutes. The halftime RW protocol started at 1 minute after the commencement of the halftime period and concluded 1 minute before its end. The Yo-Yo IR1 performance, blood glucose, free fatty acids (FFAs), triglycerides (TGs), creatine kinase (CK), and lactate concentrations, the rating of perceived exertion, mean HR, and HRmax were analyzed. The Yo-Yo IR1 performance was higher in the halftime RW trial than in the control trial (3,095 ± 326 vs. 2,904 ± 421 m, P ≤ 0.05). The mean HR and HRmax, blood glucose, FFA, TG, CK, and lactate concentrations did not differ between the trials. The rating of perceived exertion during the halftime RW, but not after the Yo-Yo IR1 period, was higher than that in the control trial. In conclusion, this study showed that halftime RW with intermittent exercise improves the subsequent exercise performance.

#4 Defining the Process of a Cardiovascular Risk Assessment Program: Lessons Learnt From Cardiac Assessment of Elite Soccer Players in the United Kingdom
Reference: Clin J Sport Med. 2017 Dec 14. doi: 10.1097/JSM.0000000000000534. [Epub ahead of print]
Authors: Speers C, Seth AN, Patel KC, Rakhit DJ, Gillett MJ
Summary: Retrospectively analyze the cardiac assessment process for elite soccer players, and provide team physicians with a systematic guide to managing longitudinal cardiac risk. Cardiac assessments incorporating clinical examination, 12-lead ECG, echocardiography, and health questionnaire. Soccer players at 5 professional clubs in England, the United Kingdom. Data was retrospectively collected, inspected, and analyzed to determine their clinical management and subsequent follow-up. Over 2 years, 265 soccer players, aged 13 to 37 years with 66% of white European ethnicity, were included in the cohort. Eleven percent had "not-normal" assessments, of these assessments, 83% were considered gray screens, falling into three broad categories: structural cardiac features (including valvular abnormalities), functional cardiac features, and electrocardiogram changes. After cardiology consultation, all assessments were grouped into low, enhanced and high-risk categories for ongoing longitudinal risk management. Overall clear-cut pathology was identified in 2%. Cardiovascular assessment is a vital tool in identifying athletes at risk of sudden cardiac death to mitigate their risk through surveillance, intervention, or participation restriction. The decision whether a player is fit to play or not requires a robust risk assessment followed by input from a multidisciplinary team that includes both the team physician and cardiologist. This educational article proposes a clinical management pathway to aid clinicians with this process.

#5 Rehabilitation of Injured Soccer Players
Reference: Phys Sportsmed. 1979 Aug;7(8):58-67. doi: 10.1080/00913847.1979.11948469.
Author: Smodlaka VN.
Summary: Treatment of soccer injuries revolves around preventing pain, edema, and reinjury, and rehabilitation is aimed at restoring the players' high levels of physical fitness.

#6 Self-controlled video feedback on tactical skills for soccer teams results in more active involvement of players
Reference: Hum Mov Sci. 2017 Dec 15;57:194-204. doi: 10.1016/j.humov.2017.12.005. [Epub ahead of print]
Authors: van Maarseveen MJJ, Oudejans RRD, Savelsbergh GJP
Summary: Many studies have shown that self-controlled feedback is beneficial for learning motor tasks, and that learners prefer to receive feedback after supposedly good trials. However, to date all studies conducted on self-controlled learning have used individual tasks and mainly relatively simple skills. Therefore, the aim of this study was to examine self-controlled feedback on tactical skills in small-sided soccer games. Highly talented youth soccer players were assigned to a self-control or yoked group and received video feedback on their offensive performance in 3 vs. 2 small-sided games. The results showed that the self-control group requested feedback mostly after good trials, that is, after they scored a goal. In addition, the perceived performance of the self-control group was higher on feedback than on no-feedback trials. Analyses of the conversations around the video feedback revealed that the players and coach discussed good and poor elements of performance and how to improve it. Although the coach had a major role in these conversations, the players of the self-control group spoke more and showed more initiative compared to the yoked group. The results revealed no significant beneficial effect of self-controlled feedback on performance as judged by the coach. Overall, the findings suggest that in such a complex situation as small-sided soccer games, self-controlled feedback is used both to confirm correct performance elements and to determine and correct errors, and that self-controlled learning stimulates the involvement of the learner in the learning process.

#7 May Heading in Soccer Result in Traumatic Brain Injury? A Review of Literature
Reference: Med Arch. 2017 Oct;71(5):356-359. doi: 10.5455/medarh.2017.71.356-359.
Authors: Bunc G, Ravnik J, Velnar T
Summary: Globally, soccer is the most popular team sport, unifying many fans all around the world. The epidemiological studies so far have confirmed that head playing and hitting the ball with head may cause minor head injuries, which exert their effects in a cumulative way. Literature search for this review was conducted and data about traumatic brain injury collected from various sources. The consequences of head injury are evident as chronic changes in cognition, including disturbances in concentration and slowing of mental and physical agility. Various recommendations have been issued for the prevention of chronic negative cumulative effects of soccer ball head playing. In addition, the professional soccer players are also exposed to more intense craniocerebral trauma, such as concussions and contusions. These patients require treatment of skilled sports physicians, neurologists and neurosurgeons and some may need long to return to the sport scene again.

#8 The Neuromuscular Determinants of Unilateral Jump Performance in Soccer Players are Direction-Specific
Reference: Int J Sports Physiol Perform. 2017 Dec 28:1-28. doi: 10.1123/ijspp.2017-0589. [Epub ahead of print]
Authors: Murtagh C, Nulty C, Vanrenterghem J, O'Boyle A, Morgans R, Drust B, Erskine R
Summary: The purpose was to investigate differences in neuromuscular factors between elite and non-elite players, and to establish which factors underpin direction-specific unilateral jump performance. Elite (n=23; age, 18.1 ± 1.0 yrs; BMI, 23.1 ± 1.8 kg/m2) and non-elite (n=20; age, 22.3 ± 2.7 yrs; BMI, 23.8 ± 1.8 kg/m2) soccer players performed three unilateral countermovement jumps (CMJs) on a force platform in the vertical, horizontal-forward and medial directions. Knee extension isometric maximum voluntary contraction (iMVC) torque was assessed using isokinetic dynamometry. Vastus lateralis fascicle length and angle of pennation (AoP), and quadriceps femoris muscle volume (Mvol) and physiological cross sectional area (PCSA) were assessed using ultrasonography. Vastus lateralis activation was assessed via  torque (365.7±66.6 vs. 320.1±62.6 N·m; P=0.045), Mvol (2853±508 vs. 2429±232 cm3, P=0.001) and PCSA (227±42 vs. 193±25 cm2, P=0.003) than non-elite. In both cohorts, unilateral vertical and unilateral medial CMJ performance correlated with Mvol and PCSA (r≥0.310 P≤0.043). In elite soccer players, unilateral vertical and unilateral medial CMJ performance correlated with upward phase vastus lateralis activation, and AoP (r≥0.478, P≤0.028). Unilateral horizontal-forward CMJ peak vertical power did not correlate with any measure of muscle size or activation but correlated inversely with AoP (r=-0.413; P=0.037). Whilst larger and stronger quadriceps differentiated elite from non-elite players, relationships between neuromuscular factors and unilateral jump performance were shown to be direction-specific. These findings support a notion that improving direction-specific muscular power in soccer requires improving a distinct neuromuscular profile.

#9 Relationships Between the External and Internal Training Load in Professional Soccer: What Can We Learn From Machine Learning?
Reference: Int J Sports Physiol Perform. 2017 Dec 28:1-18. doi: 10.1123/ijspp.2017-0299. [Epub ahead of print]
Authors: Jaspers A, Beeck TO, Brink MS, Frencken WGP, Staes F, Davis JJ, Helsen WF
Summary: Machine learning may contribute to understanding the relationship between the external load and internal load in professional soccer. Therefore, the relationship between external load indicators and the rating of perceived exertion (RPE) was examined using machine learning techniques on a group and individual level. Training data were collected from 38 professional soccer players over two seasons. The external load was measured using global positioning system technology and accelerometry. The internal load was obtained using the RPE. Predictive models were constructed using two machine learning techniques, artificial neural networks (ANNs) and least absolute shrinkage and selection operator (LASSO), and one naive baseline method. The predictions were based on a large set of external load indicators. Using each technique, one group model involving all players and one individual model for each player was constructed. These models' performance on predicting the reported RPE values for future training sessions was compared to the naive baseline's performance. Both the ANN and LASSO models outperformed the baseline. Additionally, the LASSO model made more accurate predictions for the RPE than the ANN model. Furthermore, decelerations were identified as important external load indicators. Regardless of the applied machine learning technique, the group models resulted in equivalent or better predictions for the reported RPE values than the individual models. Machine learning techniques may have added value in predicting the RPE for future sessions to optimize training design and evaluation. Additionally, these techniques may be used in conjunction with expert knowledge to select key external load indicators for load monitoring.

Australian Football
#1 Physical characteristics of players within the Australian Football League participation pathways: a systematic review
Reference: Sports Med Open. 2017 Dec 19;3(1):46. doi: 10.1186/s40798-017-0109-9.
Authors: Haycraft JAZ, Kovalchik S, Pyne DB, Robertson S
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Summary: Australian football (AF) players require endurance, strength, speed, and agility to be successful. Tests assessing physical characteristics are commonly used for talent identification; however, their ability to differentiate between players across the Australian Football League's (AFL) participation pathway remains unclear. The objective of this review was to quantify the physical characteristics of male AF players across the AFL participation pathway. A search of databases was undertaken. Studies examining tests of physical performance were included, with 27 meeting the inclusion/exclusion criteria. Study appraisal was conducted using a checklist of selection criteria. The 20-m sprint time was the most reported test, followed by vertical jump (VJ), AFL planned agility, and 20-m multi-stage fitness test (MSFT). The fastest times for 20-m sprint were for Elite AFL players (range 2.94-3.13 s), with local-level players the slowest (3.22-4.06 s). State Junior Under (U) 18s (58-66 cm) had higher jumps than senior players, with the lowest jumps reported for Local U10s (mean 31 cm). No elite-level data were reported for the AFL planned agility or 20-m MSFT. AFL planned agility times were only reported for talent pathway levels, with large performance variability evident across all levels (8.17-9.12 s). Only mean 20-m MSFT scores were reported from Local U10s to National Draft Camp (6.10-13.50 shuttles). Talent pathway players exhibit similar mean test scores irrespective of the physical test, with the exception of 20-m sprint and VJ. Physical tests can discriminate between local participation level players but are less useful within the AFL talent pathway.

American Football
#1 Motor function in former professional football players with history of multiple concussions
Reference: J Neurotrauma. 2017 Dec 19. doi: 10.1089/neu.2017.5290. [Epub ahead of print]
Authors: Tarazi A, Tator C, Wennberg R, Ebraheem A, Green RE, Colella B, Saverino C, Khodadadi M, Misquitta K, Tartaglia MC
Summary: The objective of this study was to assess the incidence of motor impairment in former professional Canadian Football League (ex-CFL) players with multiple concussions. We investigated motor symptoms and signs in 45 ex-CFL players with multiple concussions and 25 age-and education matched healthy controls with no history of concussion. Neurological assessment included items from the SCAT3 (Sport Concussion Assessment Tool 3) and the Unified Parkinson's Disease Rating Scale part III (UPDRS-Part III). A performance-based measurement of manual motor function was undertaken using the Grooved Pegboard test. Cognition was measured with patient-reported outcomes for memory, executive and behavioral symptoms as well as performance-based measures of memory and executive function. Symptoms of anxiety and depression were measured using the Personality Assessment Inventory. There was no significant difference between the ex-CFL players and controls on the UPDRS-Part III scores, and neither group reported clinically significant motor complaints. Ex-CFL players did not perform differently from control subjects on the Grooved Pegboard test. In contrast, with regard to cognitive and mood testing, players were more symptomatic: The ex-CFL players reported significantly more memory (77.8% vs. 16%, respectively, p<0.001), executive (53.3% vs. 8%, respectively, p<0.001), and behavioral symptoms (66.7% vs. 20%, respectively, p<0.001). No significant differences were found when comparing ex-CFL players and controls in performance on memory and executive tests. In summary, in a group of retired CFL players who self-reported declines in memory, executive and behavioral symptoms, no motor symptoms were reported and no motor signs were detected.

#2 Epidemiology of Injuries Sustained as a Result of Intentional Player Contact in High School Football, Ice Hockey, and Lacrosse: 2005-2006 Through 2015-2016
Reference: Orthop J Sports Med. 2017 Dec 12;5(12):2325967117740887. doi: 10.1177/2325967117740887. eCollection 2017 Dec.
Authors: Bartley JH, Murray MF, Kraeutler MJ, Pierpoint LA, Welton KL, McCarty EC, Comstock RD
Summary: Lacrosse and ice hockey are quickly growing in popularity, while football remains the most popular sport among high school student-athletes. Injuries remain a concern, given the physical nature of these contact sports. The purpose was to describe the rates and patterns of injuries sustained as a result of intentional player contact in United States high school boys' football, ice hockey, and lacrosse. We conducted a secondary analysis of High School RIO (Reporting Information Online) data, including exposure and injury data collected from a large sample of high schools in the United States from 2005-2006 through 2015-2016. Data were analyzed to calculate rates, assess patterns, and evaluate potential risk factors for player-to-player contact injuries. A total of 34,532 injuries in boys' football, ice hockey, and lacrosse occurred during 9,078,902 athlete-exposures (AEs), for a rate of 3.80 injuries per 1000 AEs in the 3 contact sports of interest. The risk of injuries was found to be greater in competition compared with practice for all 3 sports, with the largest difference in ice hockey (rate ratio, 8.28) and the smallest difference in lacrosse (rate ratio, 3.72). In all 3 contact sports, the most commonly injured body site in competition and practice caused by both tackling/checking and being tackled/checked was the head/face. However, a significantly greater proportion of concussions sustained in football were the result of tackling compared with being tackled (28.2% vs 24.1%, respectively). In addition, a significantly greater proportion of concussions were sustained in competition compared with practice for all 3 sports. This study is the first to collectively compare injury rates and injury patterns sustained from intentional player-to-player contact in boys' high school football, ice hockey, and lacrosse. Notably, there was a relatively high risk of injuries and concussions during football practices.

#3 White Matter Changes Related to Subconcussive Impact Frequency during a Single Season of High School Football
Reference: AJNR Am J Neuroradiol. 2017 Dec 21. doi: 10.3174/ajnr.A5489. [Epub ahead of print]
Authors: Kuzminski SJ, Clark MD, Fraser MA, Haswell CC, Morey RA, Liu C, Choudhury KR, Guskiewicz KM, Petrella JR
Summary: The effect of exposing the developing brain of a high school football player to subconcussive impacts during a single season is unknown. The purpose of this pilot study was to use diffusion tensor imaging to assess white matter changes during a single high school football season, and to correlate these changes with impacts measured by helmet accelerometer data and neurocognitive test scores collected during the same period. Seventeen male athletes (mean age, 16 ± 0.73 years) underwent MR imaging before and after the season. Changes in fractional anisotropy across the white matter skeleton were assessed with Tract-Based Spatial Statistics and ROI analysis. The mean number of impacts over a 10-g threshold sustained was 414 ± 291. Voxelwise analysis failed to show significant changes in fractional anisotropy across the season or a correlation with impact frequency, after correcting for multiple comparisons. ROI analysis showed significant (P < .05, corrected) decreases in fractional anisotropy in the fornix-stria terminalis and cingulum hippocampus, which were related to impact frequency. The effects were strongest in the fornix-stria terminalis, where decreases in fractional anisotropy correlated with worsening visual memory. Our findings suggest that subclinical neurotrauma related to participation in American football may result in white matter injury and that alterations in white matter tracts within the limbic system may be detectable after only 1 season of play at the high school level.

#4 Determination of priority and other hazardous substances in football fields of synthetic turf by gas chromatography-mass spectrometry: A health and environmental concern
Reference: Chemosphere. 2017 Dec 11;195:201-211. doi: 10.1016/j.chemosphere.2017.12.063. [Epub ahead of print]
Authors: Celeiro M, Dagnac T, Llompart M
Summary: Due to the high concern generated in the last years about the safety of recycled tire rubber used for recreational sports surfaces, this study aims at evaluating the presence of forty organic compounds including polycyclic aromatic hydrocarbons (PAHs), phthalates, adipates, vulcanisation additives and antioxidants in recycled tire crumb of synthetic turf football fields. Ultrasound Assisted Extraction (UAE) was successfully employed to extract the target compounds from the crumb rubber, and analysis was performed by gas chromatography-mass spectrometry (GC-MS). The transfer of the target chemicals from the crumb rubber to the runoff water and to the air above the rubber surface has also been evaluated employing solid-phase microextraction (SPME). Samples from fifteen football fields were analysed, and the results revealed the presence of 24 of the 40 target compounds, including 14 of the 16 EPA PAHs, with total concentrations up to 50 μg g-1. Heavy metals such as Cd, Cr and Pb were also found. A partial transfer of organic compounds to the air and runoff water was also demonstrated. The analysis of rain water collected directly from the football field, showed the presence of a high number of the target compounds at concentrations reaching above 100 μg L-1. The environmental risk arising from the burning of crumb rubber tires has been assessed, as well, analysing the crumb rubber, and the air and water in contact with this material, showing a substantial increase both of the number and concentration of the hazardous chemicals.

#5 Emergency Removal of Football Helmets
Reference: Phys Sportsmed. 1994 Sep;22(9):57-59. doi: 10.1080/00913847.1994.11947694.
Authors: Patel MN, Rund DA, Howe WB
Summary: In brief when a football player has a brief suspected head or neck injury, when and how to remove the football helmet become critical issues. Protocols differ; however, the National Collegiate Athletic Association guidelines, which state that the helmet should only be removed on the field under very special circumstances, are appropriate. An understanding of the technologically advanced design and tight fit of modern football helmets will help guide medical personnel through each step of the helmet removal process.

#6 Flexibility as a Predictor of Knee Injuries in College Football Players
Reference: Phys Sportsmed. 1982 Jul;10(7):93-97. doi: 10.1080/00913847.1982.11947274.
Authors: Moretz JA, Walters R, Smith L.
Summary: In brief The ligamentous laxity testing scores and knee injuries of football players from three colleges were compared and statistically analyzed. Since no correlation was found between laxity test scores and knee injuries, the tests have no apparent predictive value.

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