Latest research in football - week 20 - 2016

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 MRI of the knees in asymptomatic adolescent soccer players: A case-control study
Reference: J Magn Reson Imaging. 2016 Jun 2. doi: 10.1002/jmri.25329. [Epub ahead of print]
Authors: Matiotti SB, Soder RB, Becker RG, Santos FS, Baldisserotto M
Summary: The purpose of the study was to determine the range of asymptomatic abnormal findings in adolescent soccer players at 3.0T MRI of the knee. In all, 87 knees of asymptomatic 14-17-year-old male adolescents were evaluated at 3T, using a standardized examination protocol comprising four sequences: two fat-suppressed T2 -weighted fast spin-echo sequences (T2 FSE), in the sagittal (repetition time / echo time [TR/TE], 5.300/71, echo train length [ETL] 17) and coronal planes (TR/TE, 4234/70, ETL 17), one fat-suppressed proton density (PD) sequence in the axial plane (TR/TE, 2.467/40, ETL 9), and one T1 -weighted spin-echo (T1 SE) sequence in the sagittal plane (TR/TE, 684/12.5). Soccer players (46 knees) were paired with controls (41 knees) by age and weight. Bone marrow, articular cartilage, meniscus, tendons, ligaments, fat pad abnormalities, and joint fluid were assessed. One or more abnormalities were detected in 31 knees (67.4%) in the soccer player group, compared to 20 knees (48.8%) in the control group. The prevalence of bone marrow edema was higher in the soccer group (19 knees, 41.3%) than in the control group (3 knees, 7.3%), P = 0.001. Other abnormalities found in this sample (joint effusion, cartilage lesions, tendinopathy, ganglion cysts, and infrapatellar fat pat edema) were not significantly different between the two study groups. Asymptomatic adolescents had a high prevalence of abnormal findings on knee imaging, especially bone marrow edema. This prevalence was higher among soccer players.

#2 Current Approaches to Tactical Performance Analyses in Soccer Using Position Data
Reference: Sports Med. 2016 Jun 1. [Epub ahead of print]
Authors: Memmert D, Lemmink KA, Sampaio J
Summary: Tactical match performance depends on the quality of actions of individual players or teams in space and time during match-play in order to be successful. Technological innovations have led to new possibilities to capture accurate spatio-temporal information of all players and unravel the dynamics and complexity of soccer matches. The main aim of this article is to give an overview of the current state of development of the analysis of position data in soccer. Based on the same single set of position data of a high-level 11 versus 11 match (Bayern Munich against FC Barcelona) three different promising approaches from the perspective of dynamic systems and neural networks will be presented: Tactical performance analysis revealed inter-player coordination, inter-team and inter-line coordination before critical events, as well as team-team interaction and compactness coefficients. This could lead to a multi-disciplinary discussion on match analyses in sport science and new avenues for theoretical and practical implications in soccer.

#3 Assessment of skeletal age on the basis of DXA-derived hand scans in elite youth soccer
Reference: Res Sports Med. 2016 Jun 1:1-12. [Epub ahead of print]
Authors: Romann M, Fuchslocher J
Summary: Physical performance is highly dependent on maturity. Therefore, consideration of maturity is recommended in the talent identification process. To date, skeletal age (SA) is assessed using X-ray scans. However, X-rays are associated with a 10-fold higher radiation compared to dual-energy X-ray absorptiometry (DXA). The aim of the study was to validate SA assessments in male soccer players with the DXA technique. Paired X-ray and DXA scans of the left hand of 63 Swiss U-15 national soccer players were performed. SA assessments were performed twice by two blinded raters using Tanner and Whitehouse' reference technique. Intrarater and interrater reliability as well as agreement between both techniques were tested. Intrarater and interrater reliabilities were excellent. Bland-Altman plots showed that SA assessments between X-ray and DXA differed by -0.2 years and 95% limits of agreement were ±0.6 years. Therefore, DXA offered a replicable method for assessing SA and maturity in youth soccer players.

#4 Analysis of Injury Incidences in Male Professional Adult and Elite Youth Soccer Players: A Systematic Review
Reference: J Athl Train. 2016 May 31. [Epub ahead of print]
Authors: Pfirrmann D, Ingelfinger P, Simon P, Tug S
Summary: The incidence of injury for elite youth and professional adult soccer players is an important concern, but the risk factors for these groups are different. The purpose of the study was to summarize and compare the injury incidences and injury characteristics of male professional adult and elite youth soccer players. We searched MEDLINE and Web of Science using the search terms elite, international, European, soccer, football, injury, injuries, epidemiology, incidence, prevalence, not female, not American football, and not rugby. We also used the search terms professional for studies on professional adult soccer players and high-level, soccer academy, youth, adolescent, and young for studies on elite youth soccer players. Eligible studies were published in English, had a prospective cohort design, and had a minimum study period of 6 months. To ensure that injury data were assessed in relationship to the athlete's individual exposure, we included only studies that reported on injuries and documented exposure volume. Two independent reviewers applied the selection criteria and assessed the quality of the studies. A total of 676 studies were retrieved from the literature search. Eighteen articles met the inclusion criteria: 6 for elite youth and 12 for professional adult soccer players. Injury rates were higher for matches than for training for both youth and adult players. Youth players had a higher incidence of training injuries than professionals. Efforts must be made to reduce the overall injury rate in matches. Therefore, preventive interventions, such as adequately enforcing rules and focusing on fair play, must be analyzed and developed to reduce match-related injury incidences. Reducing training injuries should be a particular focus for youth soccer players.

#5 Effects Of Two Warm-Up Programs On Balance And Isokinetic Strength In Male High School Soccer Players
Reference: J Strength Cond Res. 2016 May 25. [Epub ahead of print]
Authors: Ghareeb DM, McLaine AJ, Wojcik JR, Boyd JM.
Summary: One of the most common warm-up programs utilized to prevent injury in soccer, FIFA11+, integrates aerobic, strength, and balance. The purpose of this study was to compare FIFA11+ to a new warm-up program (NWP) on balance and isokinetic strength of the quadriceps and hamstrings at 60, 180, and 300 degrees per second in male high school soccer players. Participants at one school (n=17) performed the NWP before practice for six weeks during one soccer season while participants at another school (n =17) performed FIFA11+. There were no differences at baseline. At posttest, players in NWP significantly improved (p< 0.01) in Overall Stability Index Balance, Anterior/Posterior Index Balance, and Medial Lateral Index with large effect sizes (ES) > 1.3. No changes were seen in FIFA11+. Isokinetic strength peak torque increased at 60 degrees per second in quadriceps and hamstrings dominant and nondominant legs NWP (p< 0.01, ES 0.59 to 1.02) and in hamstrings in FIFA11+ (p <0.05, ES 0.32 to 0.40). At 180 degrees per second NWP improved peak torque (p < 0.01, ES 0.74 to 0.90) except hamstrings in the non-dominant leg, while FIFA11+ showed improvements across all muscle groups (p <0.01), but with smaller ES 0.25 to 0.84. Both programs improved isokinetic peak torque at 300 degrees per second except hamstrings in the non-dominant leg in NWP, although ES were higher in NWP (ES 0.60 to 1.03) than FIFA11+ (ES 0.31 to 0.42). The NWP appears to be effective for soccer conditioning by improving balance and isokinetic strength.

#6 Acute Achilles Paratendinopathy following Major Injury of the Crural Fascia in a Professional Soccer Player: A Possible Correlation?
Reference: Case Rep Orthop. 2016;2016:1830875. doi: 10.1155/2016/1830875. Epub 2016 May 8.
Authors: Mattiussi G, Turloni M, Baldassi PT, Moreno C
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Summary: The anatomy and mechanical properties of the Crural Fascia (CF), the ubiquitous connective tissue of the posterior region of the leg, have recently been investigated. The most important findings are that (i) the CF may suffer structural damage from indirect trauma, (ii) structural changes of the CF may affect the biomechanics of tissues connected to it, causing myofascial pain syndromes, and (iii) the CF is in anatomical continuity with the Achilles paratenon. Consistent with these points, the authors hypothesize that the onset of acute Achilles paratendinopathy may be related to histological and biomechanical changes of the CF. Case Presentation. A professional male football player suffered an isolated injury of the CF, interposed between the soleus and medial gastrocnemius (an atypical site of injury) with structural connective integrity of the muscles. After participating in the first official match, two and a half months after the trauma, he has unexpectedly demonstrated the clinical picture of acute Achilles paratendinopathy in the previously injured limb. Conclusions. Analysis of this case suggests that the acute Achilles paratendinopathy may be a muscle injury complication from indirect trauma of the calf muscle, if a frank and extensive involvement of the CF were to be ascertained.

#7 Sprint and jump performances do not determine the promotion to professional elite soccer in Spain, 1994-2012
Reference: J Sports Sci. 2016 May 30:1-7. [Epub ahead of print]
Authors: Martinez-Santos R, Castillo D, Los Arcos A
Summary: The aims of this study are (a) to describe the evolution of neuromuscular performance over an 18 year period within a Spanish elite reserve team; (b) to check if there were any relation between the playing position and sprint and jump performances and (c) to look into the alleged impact of this factor on the top playing level attained by the soccer players. We considered the physical tests (5 m and 15 m sprint times and countermovement jump (CMJ) height) made by 235 players enrolled in the reserve team of the Club from 1994 to 2012 and the highest competitive-level they achieved: Spanish first (n = 39) and second divisions (n = 36) and semi-professional (n = 160). Furthermore, the players were classified according to their playing positions. The main findings were a very-likely/most-likely lower neuromuscular performance (ES = 0.48-0.68, small to moderate) in the last six-season term (2006-2012) than in the first term (1994-2000); possibly/very-likely lower performances in sprinting and CMJ (ES = 0.22-0.55, small) by central defenders (CDs) and midfielders than by other playing positions; very-likely better performances in sprinting and jumping by first and second divisions central defenders than by semi-professional central defenders (ES = 0.90-1.02, moderate). Sprint and jump performances are not a relevant physical parameter to promote to the top level of soccer in Spain except for one in six of the playing positions: CDs.

#8 The Anatomy of the Global Football Player Transfer Network: Club Functionalities versus Network Properties
Reference: PLoS One. 2016; 11(6): e0156504
Authors: Liu XF, Liu YL, Lu XH, Wang QX, Wang TX
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Summary: Professional association football is a game of talent. The success of a professional club hinges largely on its ability of assembling the best team. Building on a dataset of player transfer records among more than 400 clubs in 24 world-wide top class leagues from 2011 to 2015, this study aims to relate a club's success to its activities in the player transfer market from a network perspective. We confirm that modern professional football is indeed a money game, in which larger investment spent on the acquisition of talented players generally yields better team performance. However, further investigation shows that professional football clubs can actually play different strategies in surviving or even excelling this game, and the success of strategies is strongly associated to their network properties in the football player transfer network.

#9 Quantifying Explosive Actions in International Women's Soccer.
Reference: Int J Sports Physiol Perform. 2016 Jun 13. [Epub ahead of print]
Authors: Meylan CM, Trewin J, McKean K.
Summary: The aims of the current study were to examine the external validity of inertial based parameters (inertial movement analysis; IMA) to detect multi-planar explosive actions during maximal sprinting, change of direction (COD) and to further determine its reliability, set appropriate magnitude bands for match analysis and assess its variability during international women's soccer matches. Twenty U20 female soccer players, wearing GPS units with a built-in accelerometer, completed three trials of a 40-m sprint and a 20-m sprint with a change of direction to the right or left at 10-m. Further, thirteen women's national team players (157 files; 4-27 matches per player) were analyzed to ascertain match-to-match variability. Video synchronization indicated IMA signal was instantaneous with explosive movement (acceleration/deceleration/COD). Peak GPS velocity during the 40-m sprint showed similar reliability (CV = 2.1%) to timing gates, but increased pre- and post-COD (CV = 4.5-13%). IMA variability was greater at the start of sprints (CV = 16-21%) compared to pre- and post-COD (CV = 13-16%). IMA threshold for match analysis was set at 2.5m.s-2 by subtracting one standard deviation from the mean IMA during sprint trials. IMA match variability (CV = 14%) differed from high-speed GPS metrics (35-60%). Practitioners are advised that timing lights should remain the gold standard for monitoring sprint and acceleration capabilities of athletes. However, IMA indicates a reliable method to monitor between match explosive actions and assess changes due to various factors such as congested schedule, tactics, heat or altitude.

#10 Braking characteristics during cutting and pivoting in female soccer players.
Reference: J Electromyogr Kinesiol. 2016 May 24;30:46-54. doi: 10.1016/j.jelekin.2016.05.006. [Epub ahead of print]
Authors: Jones PA, Herrington L, Graham-Smith P.
Summary: Most biomechanical studies into changing direction focus on final contact (FC), whilst limited research has examined penultimate contact (PEN). The aim of this study was to explore the kinematic and kinetic differences between PEN and FC of cutting and pivoting in 22 female soccer players (mean±SD; age: 21±3.1years, height: 1.68±0.07m, mass: 58.9±7.3kg). Furthermore, the study investigated whether horizontal force-time characteristics during PEN were related to peak knee abduction moments during FC. Three dimensional motion analyses of cutting and pivoting on the right leg were performed using Qualysis 'Proreflex' infrared cameras (240Hz). Ground reaction forces (GRF) were collected from two AMTI force platforms (1200Hz) to examine PEN and FC. Both manoeuvres involved significantly (P<0.05) greater knee joint flexion angles, peak horizontal GRF, but lower average horizontal GRF during PEN compared to FC. Average horizontal GRF during PEN (R=-0.569, R2=32%, P=0.006) and average horizontal GRF ratio (R=0.466, R2=22%, P=0.029) were significantly related to peak knee abduction moments during the FC of cutting and pivoting, respectively. The results indicate PEN during pre-planned changing direction helps reduce loading on the turning leg where there is greater risk of injuries to knee ligaments.

#11 The delivery of injury prevention exercise programmes in professional youth soccer: Comparison to the FIFA 11.
Reference: J Sci Med Sport. 2016 Jun 1. pii: S1440-2440(16)30087-1. doi: 10.1016/j.jsams.2016.05.007. [Epub ahead of print]
Authors: O'Brien J, Young W, Finch CF
Summary: Injury prevention exercise programmes for amateur soccer have gained considerable attention, but little is known about their relevance and adaptability to professional soccer settings. The first aim of this study was to evaluate the delivery and content of injury prevention exercise programmes used by professional youth soccer teams, compared to the industry standard injury prevention exercise programme for soccer, the Fédération Internationale de Football Association's FIFA 11+. The second aim was to document specific challenges to implementing injury prevention exercise programmes in this context. The participants were soccer coaches, fitness coaches and physiotherapists (n=18) from four teams in a professional youth soccer academy. Each team's chosen injury prevention exercise programmes were observed weekly across an entire soccer season (160 sessions). The delivery and content of the programmes were documented on a standardised worksheet and compared to the FIFA 11+. Specific implementation challenges were recorded. Fitness coaches were the primary deliverers of injury prevention exercise programmes, with support from physiotherapists. Multiple delivery formats and locations were employed, along with the extensive use of equipment. Across all injury prevention exercise programme sessions, a median of one FIFA 11+ exercise was performed in its original form and a further four in a modified form. Implementation challenges included poor staff communication, competing training priorities and heavy game schedules. Although the basic components of the FIFA 11+ hold relevance for professional youth male teams, the delivery and content of injury prevention exercise programmes require considerable tailoring for this context. Recognising this will inform the development of improved, context-specific injury prevention exercise programmes, along with corresponding strategies to enhance their implementation.

#12 Exercise Intensity during Power Wheelchair Soccer.
Reference: Arch Phys Med Rehabil. 2016 Jun 8. pii: S0003-9993(16)30239-8. doi: 10.1016/j.apmr.2016.05.012. [Epub ahead of print]
Authors: Barfield JP, Newsome L, Malone LA
Summary: The purpose of this study was to determine exercise intensity during power wheelchair soccer (PWS) among a sample of persons with mobility impairments. Thirty participants with severe mobility impairments (MAge = 29.40 ± 15.51 yrs, MBMI = 24.11 ± 6.47, MPower Soccer Experience = 7.91 ± 3.93 yrs, MDisability Sport Experience = 12.44 ± 9.73 yrs) were recruited from multiple PWS teams. Portable metabolic carts were used to collect oxygen consumption data during resting (REST) and gameplay (GAME) conditions. Average VO2 (expressed in METs) for REST and GAME and rate of perceived exertion (RPE) for GAME were used as outcome measures. VO2 increased from 1.35 ± 0.47 METs at REST to 1.81 ± 0.65 METs during GAME. This 34% increase in exercise intensity was significant (p < .01) and supported by a mean perceived exertion score of approximately 13 (Somewhat Hard). Although not able to sustain an intensity associated with reduced secondary disease risk (i.e., 3 METs), the documented light-intensity exercise in the current study surpassed an intensity threshold associated with improved functional capacity and performance of daily living activities (i.e., 1.5 METs).

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