#1 Emergence of Exploratory, Technical and Tactical Behavior in Small-Sided Soccer Games when Manipulating the Number of Teammates and Opponents
Reference: PLoS One. 2016 Dec 22;11(12):e0168866. doi: 10.1371/journal.pone.0168866. eCollection 2016.
Authors: Torrents C, Ric A, Hristovski R, Torres-Ronda L, Vicente E, Sampaio J
Download link: http://journals.plos.org/plosone/article/file?id=10.1371/journal.pone.0168866&type=printable
Summary: The effects that different constraints have on the exploratory behavior, measured by the variety and quantity of different responses within a game situation, is of the utmost importance for successful performance in team sports. The aim of this study was to determine how the number of teammates and opponents affects the exploratory behavior of both professional and amateur players in small-sided soccer games. Twenty-two professional (age 25.6 ± 4.9 years) and 22 amateur (age 23.1 ± 0.7 years) male soccer players played three small-sided game formats (4 vs. 3, 4 vs. 5, and 4 vs. 7). These trials were video-recorded and a systematic observation instrument was used to notate the actions, which were subsequently analyzed by means of a principal component analysis and the dynamic overlap order parameter (measure to identify the rate and breadth of exploratory behavior on different time scales). Results revealed that a higher the number of opponents required for more frequent ball controls. Moreover, with a higher number of teammates, there were more defensive actions focused on protecting the goal, with more players balancing. In relation to attack, an increase in the number of opponents produced a decrease in passing, driving and controlling actions, while an increase in the number of teammates led to more time being spent in attacking situations. A numerical advantage led to less exploratory behavior, an effect that was especially clear when playing within a team of seven players against four opponents. All teams showed strong effects of the number of teammates on the exploratory behavior when comparing 5 vs 7 or 3 vs 7 teammates. These results seem to be independent of the players' level.


#2 Assessment of myocardial function in elite athlete's heart at rest - 2D speckle tracking echocardiography in Korean elite soccer players
Reference: Sci Rep. 2016 Dec 22;6:39772. doi: 10.1038/srep39772.
Authors: Eun LY, Chae HW
Download link: www.nature.com/articles/srep39772.pdf
Summary: The purpose of this study was to investigate Korean elite soccer players' myocardial function using the conventional and advanced speckle tracking imaging to compare the difference with the normal controls. We used 2D echocardiography speckle tracking echocardiography (STE) to evaluate LV regional strain in 29 elite soccer players compared to 29 age-matched healthy controls. Conventional, tissue Doppler, and STI echocardiography was performed, for strain at base and apex, rotation and torsion. There is no difference in longitudinal strain (-17.6 ± 1.8 vs -17.3 ± 2.9, p = ns), and basal radial strain. However, the significant increases were noticed in basal circumferential strain (-17.5 ± 2.6 vs -15.5 ± 8.9, p = 0.05), apical radial strain (33.1 ± 20.5 vs 22.5 ± 19.4, p = 0.02), and apical circumferential strain in soccer players (-21.4 ± 4.8 vs -16.8 ± 7.6, p = 0.005). Soccer players showed the higher rotation at base (-3.9 ± 1.9 vs -2.6 ± 3.2, p = 0.03), and apex (6.98 ± 2.62 vs 6.21 ± 3.81, p = 0.05), higher torsion (10.9 ± 3.7 vs 8.8 ± 6.3, p = 0.05). In conclusion, the elite soccer players' heart demonstrated the unique ventricular adaptation. These alterations could benefit the cardiovascular adjustment to exercise without much loss of myocardial energy expenditure.


#3 "There is soccer but we have to watch": the embodied consequences of rhetorics of inclusion for South African children with cerebral palsy
Reference: J Community Appl Soc Psychol. 2015 Nov-Dec;25(6):474-486. doi: 10.1002/casp.2225. Epub 2015 Jan 19.
Authors: Bantjes J, Swartz L, Conchar L, Derman W
Download link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5166572/pdf/nihms799944.pdf
Summary: Twenty years after the advent of democracy in South Africa (SA), there have been some successes in the achievement of greater equality, access and inclusion for many persons with disabilities. The move towards inclusive education may, however, have had unanticipated embodied consequences for people positioned discursively as included, but who in fact may in some respects be further marginalised than they had been under apartheid. We describe ethnographic research conducted in a special needs school in SA to explore the lived experiences of children with cerebral palsy and their involvement in physical activity. Our study shows how inclusive educational practices in SA have impeded involvement in sport for some children with motor impairments because of resource limitations and other historic reasons. This paper raises important questions about the role of community psychology in recognising, naming and contributing to action around injustices, which may be hard to see but which can have profound effects on the lives and bodies of those who experience exclusion.


#4 Game-profile-based Training in Soccer: A New Field Approach
Reference: J Strength Cond Res. 2016 Dec 8. doi: 10.1519/JSC.0000000000001768. [Epub ahead of print]
Authors: Iacono AD, Martone D, Cular D, Milic M, Padulo J
Summary: The aim of the study was to profile and compare the time-motion, physiological, and neuromuscular responses of both national youth league (NYL) and UEFA Youth League (UYL) matches with those of an experimental game-profile-based training (GPBT) protocol. Time-motion traits and physiological, perceptual, and neuromuscular responses were investigated in 24 male soccer players across 14 matches and 6 GPBT training sessions, for a total of 420 samples. The GPBT had a greater influence on time-motion traits and perceptual responses than the NYL and UYL matches (all p< 0.001). No significant GPBT vs. matches differences were found for mean heart rate (%HR) or BLa (F= 1.228, p= 0.304 and F= 0.978, p= 0.385, respectively). Finally, the GPBT protocol led to greater impairment of the neuromuscular explosive performances when compared to those of the post-match scores (SJ: F= 19.991, p< 0.001; CMJ: F= 61.703, p< 0.001). Results identified the GPBT protocol as characterized by relatively greater high-intensity workloads than official NYL and UYL matches, requiring increased demanding efforts. In light of these outcomes, the GPBT protocol can be considered an advantageous training method for elite soccer players, capable of stimulating the physical effort and physiological capabilities required during a match. This approach is favorable when designing a training intervention according to the principle of sport specificity, as it is based on the specific metabolic demands.


#5 Changes in dynamic balance and hip-strength after an eight-week conditioning program in NCAA Division I Female soccer (Football) athletes
Reference: Int J Sports Phys Ther. 2016 Dec;11(7):1054-1064.
Authors: Ness BM, Comstock BA, Schweinle WE
Download link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5159630/pdf/ijspt-11-1054.pdf
Summary: Lower extremity injury commonly affects female soccer athletes. Decreased dynamic balance and hip strength are identified risk factors for lower extremity injury. Little is known about how these factors adapt to a training stimulus in this population. The purpose of the study was to retrospectively investigate changes in lower extremity dynamic balance and isometric hip strength in Division I collegiate female soccer athletes after participating in an eight-week strength and conditioning program. As part of a standard testing battery, soccer athletes completed athletic performance pre- and post-testing separated by an eight-week off-season conditioning program consisting of overall strength and technical skill development. Testing included lower extremity dynamic balance assessment through the Star Excursion Balance Test (SEBT) and isometric hip abduction and external rotation (ER) strength testing, normalized to limb length and percent body mass, respectively. Athletes rested for one week prior to post-testing. Seventeen healthy Division I female soccer athletes (age: 18.8 ± 0.9 years, height: 1.7 ± 0.06 m, mass: 68.0 ± 8.2 kg) completed the protocol. Significant improvements in SEBT composite reach distance were observed in the dominant (DOM) (3.6 ± 4.8%, 95% CI: 1.1 to 6.0) and nondominant (NDOM) (4.8 ± 6.1%, 95% CI: 1.7 to 7.9) limbs. Significant improvements in DOM hip ER strength (2.4 ± 2.3%, 95% CI: 1.3 to 3.6) and DOM SEBT anterior reach (2.1 ± 2.8%, 95% CI: 0.6 to 3.5) were observed. Large effect sizes were observed for DOM and NDOM hip ER strength gains (0.87 - 1.0), while small-moderate effect sizes were noted for the anterior reach direction (0.40 - 0.66). Further, DOM hip ER strength gains were significantly associated with DOM anterior reach performance improvements (r2 = 0.37, p<.01). DOM hip ER strength gains appear to be associated with improved lower extremity dynamic balance on the ipsilateral limb for the SEBT anterior reach direction in collegiate, Division I female soccer athletes after an eight-week conditioning program. Future investigations should prospectively investigate intervention strategies to modify lower extremity injury risk factors in this population.


#6 Analysis of Gauntlet Test Performance and Injury Risk in Intercollegiate Division I Female Soccer (Football) Players: A Retrospective Study
Reference: J Sport Rehabil. 2016 Dec 19:1-21. [Epub ahead of print]
Authors: Ness BM, Zimney K, Schweinle WE
Summary: Injury risk factors and relevant assessments have been identified in women's soccer athletes. Other tests assess fitness, e.g. the Gauntlet Test (GT). However, little empirical support exists for the utility of the GT to predict time loss injury. The aim of the study was to examine the GT as a predictor of injury in intercollegiate Division I female soccer athletes. 71 female division I soccer athletes (age 19.6 ± 1.24, BMI 23.0 ± 2.19) participated in this study. GT, demographic, and injury data was collected over three consecutive seasons. GT trials were administered by coaching staff each pre-season. Participation in team-based activities (practices, matches) was restricted until a successful GT trial. Soccer-related injuries that resulted in time loss from participation were recorded. 71 subjects met the inclusion criteria, with 12 lower body time loss injuries sustained. Logistic regression models indicated that with each unsuccessful GT attempt, the odds of sustaining an injury increased by a factor of 3.5 (P < .02). The Youden index was 2 GT trials for success, at which sensitivity = .92 and specificity = .46. For successive GT trials before success (1, 2, or 3), the predicted probabilities for injury were .063, .194, and .463. The GT appears to be a convenient and predictive screen for potential lower body injuries among female soccer athletes in this cohort. Further investigation into the appropriate application of the GT for injury prediction is warranted given the scope of this study.


#7 Construct validity of tests that measure kick performance for young soccer players based on cluster analysis: exploring the relationship between coaches rating and actual measures
Reference: J Sports Med Phys Fitness. 2016 Dec 16. [Epub ahead of print]
Authors: Vieira LH, DE Andrade VL, Aquino RL, Moraes R, Barbieri FA, Cunha SA, Bedo BL, Santiago PR
Summary: The main aim of this study was to verify the relationship between the classification of coaches and actual performance in field tests that measure the kicking performance in young soccer players, using the K--means clustering technique. Twenty--three U--14 players performed eight tests to measure their kicking performance. Four experienced coaches provided a rating for each player as follows: 1--poor, 2--below average, 3--average, 4--very good, 5-excellent as related to three parameters (i.e. accuracy, power and ability to put spin on the ball). The scores interval established from k--means cluster metric was useful to originating five groups of performance level, since ANOVA revealed significant differences between clusters generated (p < 0.01). Accuracy seems to be moderately predicted by the penalty kick, free kick, kicking the ball rolling and Wall Volley Test (0.44 ≤ r ≤ 0.56), while the ability to put spin on the ball can be measured by the free kick and the corner kick tests (0.52 ≤ r ≤ 0.61). Body measurements, age and PHV did not systematically influence the performance. The Wall Volley Test seems to be a good predictor of other tests. Five tests showed reasonable construct validity and can be used to predict the accuracy (penalty kick, free kick, kicking a rolling ball and Wall Volley Test) and ability to put spin on the ball (free kick and corner kick tests) when kicking in soccer. In contrast, the goal kick, kicking the ball when airborne and the vertical kick tests exhibited low power of discrimination and using them should be viewed with caution.


#8 Quantifying Inter-Segmental Coordination during the Instep Soccer Kicks
Reference: Int J Exerc Sci. 2016 Nov 1;9(5):646-656. eCollection 2016.
Authors: Li Y, Alexander M, Glazebrook C, Leiter J
Download link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5154722/pdf/ijes_09_05_646.pdf
Summary: In order to generate a high ball speed in soccer, the inter-segmental coordination of the kicking leg is critical. The purpose of this study was to quantify the coordination between the thigh and shank movement in the sagittal plane during instep kicks. Eleven female soccer players were video recorded using a high-speed (80 Hz) video camera during penalty kicks. Hip, knee and ankle joint centers of the right leg were digitized, and the movement was analyzed using Dartfish TeamPro (6.0). The thigh and shank segment angles were generated, and the coordination was quantified using the cross-correlation and the vector coding method. Four coordination patterns were defined based on coupling angles: in-phase, anti-phase, thigh-phase and shank-phase. The time spent in each coordination pattern was analyzed. The cross-correlation coefficient was positive for all the participants, indicating that the two segments rotated with similar patterns. Based on the vector coding method, we observed dominant coordination patterns of shank-phase and in-phase during the backswing and forward swing phase, respectively. We hope the outcomes of our study could provide a better understanding of soccer kicking coordination and benefit training young soccer players. Future studies may use the methodology and outcomes in the present study to investigate the coordination of different levels of players to better understand the process of skill acquisition.


#9 Meta-analytical review of the effects of football heading
Reference: Br J Sports Med. 2016 Dec 21. pii: bjsports-2016-096276. doi: 10.1136/bjsports-2016-096276. [Epub ahead of print]
Authors: Kontos AP, Braithwaite R, Chrisman SP, McAllister-Deitrick J, Symington L, Reeves VL, Collins MW
Summary: The objective of this study was to provide a meta-analysis examining the effects of football heading. Combinations of the key terms were entered into the following electronic database search engines: Cochrane Libraries, PyscARTICLE, PyscINFO, PubMed, ProQuest, SPORTDiscus and Web of Science on 7 July 2016. The following inclusion criteria were used to determine eligibility for studies: (1) the study examined and reported on soccer athletes; (2) the population's age, sex and sport position was described; (3) cognitive function, symptoms, balance or other outcomes were quantitatively measured; (4) football heading exposure was quantitatively measured between at least two groups and (5) the study was written in the English language after December 1979. The literature search process identified 467 unique studies. After applying exclusion criteria, 28 studies remained. Included studies had a total of 2288 participants (female participants =933, male participants =1355), aged 13-70 years. The overall results of random effects modelling of football heading were found to be inconclusive across all outcomes, groups and time points. No moderating variables related to methodological, sample or study characteristics were supported in the analysis; age was a potential moderating variable. We provide the first meta-analytical review of football heading effects aggregated from multiple studies and extended findings from a recent systematic review of the effects of football heading. Our analysis indicates no overall effect for heading a football on adverse outcomes.


#10 Traditional vs. sport-specific vertical jump tests: reliability, validity, and relationship with the legs strength and sprint performance in adult and teen soccer and basketball players
Reference: J Strength Cond Res 31(1): 196–206, 2017
Authors: Rodríguez-Rosell, D, Mora-Custodio, R, Franco-Márquez, F, Yáñez-García, JM, González-Badillo, JJ
Summary: The vertical jump is considered an essential motor skill in many team sports. Many protocols have been used to assess vertical jump ability. However, controversy regarding test selection still exists based on the reliability and specificity of the tests. The main aim of this study was to analyze the reliability and validity of 2 standardized (countermovement jump [CMJ] and Abalakov jump [AJ]) and 2 sport-specific (run-up with 2 [2-LEGS] or 1 leg [1-LEG] take-off jump) vertical jump tests, and their usefulness as predictors of sprint and strength performance for soccer (n = 127) and basketball (n = 59) players in 3 different categories (Under-15, Under-18, and Adults). Three attempts for each of the 4 jump tests were recorded. Twenty-meter sprint time and estimated 1 repetition maximum in full squat were also evaluated. All jump tests showed high intraclass correlation coefficients (0.969–0.995) and low coefficients of variation (1.54–4.82%), although 1-LEG was the jump test with the lowest absolute and relative reliability. All selected jump tests were significantly correlated (r = 0.580–0.983). Factor analysis resulted in the extraction of one principal component, which explained 82.90–95.79% of the variance of all jump tests. The 1-LEG test showed the lowest associations with sprint and strength performance. The results of this study suggest that CMJ and AJ are the most reliable tests for the estimation of explosive force in soccer and basketball players in different age categories.


#11 Influence of rest intervals after assisted sprinting on bodyweight sprint times in female collegiate soccer players
Reference: J Strength Cond Res 31(1): 88–94, 2017
Authors: Nealer AL, Dunnick DD, Malyszek KK, Wong MA, Costa PB, Coburn JW, Brown LE
Summary: Speed is a crucial element an athlete must possess to be successful. In soccer, the ability to accelerate faster than your opponent can result in being first to reach a ball on a breakaway or stopping a counter attack. A unique way to train explosive movements is to evoke postactivation potentiation (PAP) in the working muscles. Traditionally, an overload stimulus with a long rest period is used, but a model using an overspeed stimulus with shorter rest periods is less understood. Therefore, the purpose of this study was to determine the acute effects of varied rest intervals after assisted sprinting on bodyweight sprint time. Twenty-four female soccer players were split into 2 groups: recreational (n:11; age:20 ± 1.67 year; ht:162.30 ± 4.35 cm; mass:61.02 ± 8.78 kg) and collegiate athletes (n:13; age:19.76 ± 0.83 year; ht:166.85 ± 5.98 cm; mass:61.23 ± 3.77 kg). All participants attended 5 separate sessions, performed a dynamic warm up, then executed one 20 m sprint (with 5 m splits) at 30% bodyweight assistance (BWA). They then rested for 30 seconds, 1, 2, or 4 minutes in random order, followed by one bodyweight sprint with no BWA. Baseline sprint times were measured without BWA on the initial session of testing. Results revealed no difference in sprint time for the full 20 m distance in either group. However, sprint time was significantly decreased for the 0–5 m split only for the athletes after 1 minute (1.15 ± 0.06 second) and 2 minute (1.16 ± 0.06 second) rest compared with baseline (1.21 ± 0.04 second). Therefore, trained athletes should rest 1 or 2 minutes after 30% BWA supramaximal sprinting for increased bodyweight sprint speed.

#1 Time series of ground reaction forces following a single leg drop jump landing in elite youth soccer players consist of four distinct phases
Reference: Gait Posture. 2016 Sep 4;50:137-144. doi: 10.1016/j.gaitpost.2016.09.002. [Epub ahead of print]
Authors: Fransz DP, Huurnink A, de Boode VA, Kingma I, van Dieën JH
Summary: The single leg drop jump landing test may assess dynamic and static balance abilities in different phases of the landing. However objective definitions of different phases following landing and associated reliability are lacking. Therefore, we determined the existence of possible distinct phases of single leg drop jump landing on a force plate in 82 elite youth soccer players. Three outcome measures were calculated over moving windows of five sizes: center of pressure (COP) speed, COP sway and horizontal ground reaction force (GRF). Per outcome measure, a Factor Analysis was employed with all windows as input variables. It showed that four factors (patterns of variance) largely (>75%) explained the variance across subjects/trials along the 12s time series. Each factor was highly associated with a distinct phase of the time series signal: dynamic (0.4-2.7s), late dynamic (2.5-5.0s), static 1 (5.0-8.3s) and static 2 (8.1-11.7s). Intra-class correlations (ICC) between trials were lower for the dynamic phases (0.45-0.68) than for the static phases (0.60-0.86). The COP speed showed higher ICC's (0.63-0.86) than COP sway (0.45-0.61) and GRF (0.57-0.71) for all four phases. In conclusion, following a drop jump landing unique information is available in four distinct phases. The COP speed is most reliable, with higher reliability in the static phases compared to the dynamic phases. Future studies should assess the sensitivity of information from dynamic, late dynamic and static phases.


#2 Big data and tactical analysis in elite soccer: future challenges and opportunities for sports science
Reference: Springerplus. 2016 Aug 24;5(1):1410. doi: 10.1186/s40064-016-3108-2. eCollection 2016.
Authors: Rein R, Memmert D
Download link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4996805/pdf/40064_2016_Article_3108.pdf
Summary: Until recently tactical analysis in elite soccer were based on observational data using variables which discard most contextual information. Analyses of team tactics require however detailed data from various sources including technical skill, individual physiological performance, and team formations among others to represent the complex processes underlying team tactical behavior. Accordingly, little is known about how these different factors influence team tactical behavior in elite soccer. In parts, this has also been due to the lack of available data. Increasingly however, detailed game logs obtained through next-generation tracking technologies in addition to physiological training data collected through novel miniature sensor technologies have become available for research. This leads however to the opposite problem where the shear amount of data becomes an obstacle in itself as methodological guidelines as well as theoretical modelling of tactical decision making in team sports is lacking. The present paper discusses how big data and modern machine learning technologies may help to address these issues and aid in developing a theoretical model for tactical decision making in team sports. As experience from medical applications show, significant organizational obstacles regarding data governance and access to technologies must be overcome first. The present work discusses these issues with respect to tactical analyses in elite soccer and propose a technological stack which aims to introduce big data technologies into elite soccer research. The proposed approach could also serve as a guideline for other sports science domains as increasing data size is becoming a wide-spread phenomenon.


#3 Ankle Injury Prevention Programs for Soccer Athletes Are Protective: A Level-I Meta-Analysis
Reference: J Bone Joint Surg Am. 2016 Sep 7;98(17):1436-43. doi: 10.2106/JBJS.15.00933.
Authors: Grimm NL, Jacobs JC Jr, Kim J, Amendola A, Shea KG
Download link: http://jbjs.org/content/jbjsam/98/17/1436.full.pdf
Summary: Soccer has one of the highest rates of ankle injury in sports for both males and females. Several injury prevention programs have been developed to address this concern. The purposes of this study were to conduct a meta-analysis of ankle injury prevention programs for soccer players, assess the heterogeneity among the studies, and evaluate the reported effectiveness of the prevention programs. A systematic search of the literature was conducted in PubMed (MEDLINE), Embase, CINAHL (Cumulative Index to Nursing and Allied Health), and the Cochrane Central Register of Controlled Trials (CENTRAL) database. Studies were limited to clinical investigations of injury prevention programs specific to the ankle in soccer players. Title, abstract, and full-text review were utilized to identify articles that met the inclusion criteria. The Cochrane Q test and I(2) index were independently used to assess heterogeneity among the studies. Sensitivity analyses were performed to assess heterogeneity. The pooled risk difference was calculated by random-effects models with use of the DerSimonian-Laird method. Publication bias was assessed with a funnel plot and Egger weighted regression technique. Ten studies met the inclusion criteria as randomized controlled trials. A total of 4,121 female and male soccer athletes were analyzed for ankle injuries. Significant heterogeneity was found among studies of ankle injury prevention (p = 0.002), with an I(2) index of 65.2%. For studies of ankle injury prevention programs, the risk ratio was 0.60 (95% confidence interval, 0.40 to 0.92) and a significant reduction in the risk of ankle injury was found in the prevention group (p = 0.002). No evidence of publication bias was found among the included studies. This meta-analysis of studies regarding ankle injury prevention programs identified a significant reduction in the risk of ankle injury. Future high-quality research designs with a low risk of bias are necessary to further evaluate the effectiveness of specific exercises and the optimal timing and age at intervention for the prevention of ankle injuries in the athletic soccer player.


#4 Effects of far infrared rays emitting clothing on recovery after an intense plyometric exercise bout applied to elite soccer players: a randomized double-blind placebo-controlled trial
Reference: Biol Sport. 2016 Sep;33(3):277-83. doi: 10.5604/20831862.1208479. Epub 2016 Jul 2.
Authors: Loturco I, Abad C, Nakamura FY, Ramos SP, Kobal R, Gil S, Pereira LA, Burini F, Roschel H, Ugrinowitsch C, Tricoli V
Download link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4993144/pdf/JBS-33-1208479.pdf
Summary: The aim was to investigate the effects of far infrared (FIR) ray emitting clothes on indirect markers of exercise-induced muscle damage and physical performance recovery after a plyometric bout applied to soccer players. Twenty-one male players (18.9±0.6 years; 70.8±5.01 kg; 178.3±0.06 cm) performed 100 drop-jumps. Six hours after the bout, athletes put on FIR clothes (FIR) (density of 225 g·m(-2), 88% far infrared rays emitting polyamide 66 Emana yarn (PA66) fibre, 12% Spandex, emissivity of 0.88 and power emitted of 341 W/m2µm at 37°C in the 5-20 µm wavelength range, patent WO 2009/077834 A2) (N = 10) or placebo clothes (PLA) (N = 11). Mid-thigh circumferences, creatine kinase (CK), and delayed-onset muscle soreness (DOMS) were assessed before, immediately after and 24, 48, and 72 h after the bout. Squat (SJ) and countermovement jump (CMJ) heights were measured before and at 24, 48, and 72 h after, while 1RM leg press (maximum strength) was measured before and at 72 h after the plyometrics. No differences between groups were found in mid-thigh circumferences, SJ, CMJ or 1RM. CK increased significantly 24 h after the plyometrics in comparison to before (p < 0.05) in both groups. PLA showed significant DOMS increases at 24, 48, and 72 h, while FIR showed significant increases at 24 and 48 h (p < 0.05). DOMS effect sizes were greater in FIR (moderate at 48 h, ES = 0.737 and large at 72 h, ES = 0.844), suggesting that FIR clothes may reduce perceived DOMS after an intense plyometric session performed by soccer players.


#5 The Hoff circuit test is more specific than an incremental treadmill test to assess endurance with the ball in youth soccer players
Reference: Biol Sport. 2016 Sep;33(3):263-8. doi: 10.5604/20831862.1201913. Epub 2016 May 11.
Authors: Zagatto AM, Papoti M, Da Silva A, Barbieri RA, Campos EZ, Ferreira EC, Loures JP, Chamari K
Download link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4993142/pdf/JBS-33-1201913.pdf
Summary: The assessment of aerobic endurance is important for training prescription in soccer, and is usually measured by straight running without the ball on a track or treadmill. Due to the ball control and technical demands during a specific soccer test, the running speeds are likely to be lower compared to a continuous incremental test. The aim of the present study was to compare the heart rate (HR), rating of perceived exertion (RPE) and speeds corresponding to 2.0 mmol∙L(-1), 3.5 mmol∙L(-1), lactate threshold (Dmax method) and peak lactate determined in the laboratory and in the Hoff circuit soccer-specific test. Sixteen soccer players (16±1 years) underwent two incremental tests (laboratory and Hoff circuit tests). The speeds were significantly higher in the treadmill test than on the Hoff circuit (2.0 mmol∙L(-1): 9.5±1.2 and 8.1±1.0 km∙h(-1); 3.5 mmol∙L(-1): 12.0±1.2 and 10.2±1.1 km∙h(-1); Dmax: 11.4±1.4 and 9.3±0.4 km∙h(-1); peak lactate: 14.9±1.6 and 10.9±0.8 km∙h(-1)). The HR corresponding to 3.5 mmol∙L-1 was significantly higher on the Hoff circuit compared to the laboratory test (187.5±18.0 and 178.2±17.6 bpm, respectively; P <0.001), while the RPE at the last incremental stage was lower on the Hoff circuit (P < 0.01). The speeds during the Hoff specific soccer test and the HR corresponding to 2.0 mmol∙L(-1), 3.5 mmol∙L(-1) and Dmax/threshold were different compared with the laboratory test. The present study shows that it is possible to assess submaximal endurance related variables specifically in soccer players.


#6 Assessment of hydration status of elite young male soccer players with different methods and new approach method of substitute urine strip
Reference: J Int Soc Sports Nutr. 2016 Sep 2;13(1):34. doi: 10.1186/s12970-016-0145-8. eCollection 2016.
Authors: Ersoy N, Ersoy G, Kutlu M
Download link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5010764/pdf/12970_2016_Article_145.pdf
Summary: The purpose of the study is to determine and compare the hydration status with different methods and determine fluid intake, dehydration percentages and sweat rate of 26 young male soccer players (15 ± 1.2 years) before an important competition. More specifically, the study aims at validating the urine strip and advising the players to use it as an easy and practical method. Measurements of urine analysis were taken from the urine sample of the participants before breakfast and conducted for 3 consecutive days before the competition. Hydration status was assessed through analysis of urine color, urine specific gravity (USG) (laboratory, strip, refractometry), and osmolality. The players' dehydration percentages and sweat ratio were calculated. The average values for all samples were 3 ± 1 for color, and 1.021 ± 4 g/cm(3) for USG (laboratory), and 1.021 ± 3 g/cm(3) for USG (strip), and 1.021 ± 4 for USG (refractometry), and 903 ± 133 mOsm/kg for osmolality. USG (strip) was highly correlated with USG (laboratory), USG (refractometry) (r = 0.8; P < 0.01) and osmolality (r = 0.7; P < 0.01), and moderately correlated with urine color (r = 0.4; P < 0.05). The mean dehydration percentage and sweat rate of the soccer players were observed as 0.5 % and 582.3 ± 232.0 mL/h, respectively. We found that youth soccer players are under a slight risk of dehydration under moderate weather conditions. As indicated by the research results, determination of hydration status of athletes must be taken into account more carefully under moderate and hot weather conditions. In addition, hydration methods were compatible with one another as measured in this study.


#7 Spontaneous Intracranial Hypotension Following Soccer Game: Potential Role of MRI in The Treatment Response
Reference: Turk Neurosurg. 2015 Sep 21. doi: 10.5137/1019-5149.JTN.15549-15.0. [Epub ahead of print]
Authors: Acar T, Gölen MK, Gölen M.
Download link: http://www.turkishneurosurgery.org.tr/pdf/JTNEPUB_15549_online.pdf


#8 Agility profile in sub-elite under-11 soccer players: is SAQ training adequate to improve sprint, change of direction speed and reactive agility performance?
Reference: Res Sports Med. 2016 Sep 3:1-10. [Epub ahead of print]
Authors: Trecroci A, Milanović Z, Rossi A, Broggi M, Formenti D, Alberti G
Summary: The purpose of this study was to examine the effects of speed, agility and quickness (SAQ) training on acceleration (5 and 20 m), change of direction speed (CODS) and reactive agility in preadolescent soccer players. Thirty-five participants (age = 10.57 ± 0.26, body mass = 36.78 ± 5.34 kg, body height = 1.42 ± 0.05 m), randomly assigned to experimental (EG, n = 20) and control groups (CG, n = 15), completed a 12-week training intervention, 2 day/week. A significant interaction was found in 5-m sprint (P < 0.05, part η2 = 0.117) and reactive agility (P < 0.01, part η2 = 0.248) between EG and CG. In both groups, 20-m sprint time improved significantly (P < 0.05, effect size = 0.3-0.4) while performance on CODS remained unchanged after 12 weeks. These findings indicated that SAQ training could positively affect cognitive skills and initial sprint acceleration through the middle childhood, offering useful guidance to soccer coaches.


#9 Offensive strategies in the European Football Championship 2012
Reference: Percept Mot Skills. 2016 Sep 8. pii: 0031512516667455. [Epub ahead of print]
Authors: Sgrò F, Aiello F, Casella A, Lipoma M
Download link: http://pms.sagepub.com/content/early/2016/09/07/0031512516667455.full.pdf+html
Summary: The aim of this study was to identify the independent and interactive effects of possession strategy, pitch location, and game period on the offensive actions performed by the winning teams in the 2012 European Football Championship. The non-clinical magnitude-based inferences method was used to interpret the true effect of the performance indicators on the response variable. The offensive team possessions were grouped into winning (n = 2035) and losing (n = 2071). The winning teams performed offensive processes mainly using the possession play strategy (OR: 0.75, very likely negative effect of the direct play). When the analysis included the pitch location, negative interaction effect was found for the direct play, which ended up in the central path (OR: 0.70, very likely negative effect). On the contrary, the direct play in the second half of the match seemed to produce an effect on the probability of the winning teams performing offensive processes (OR: 1.59, most likely positive effect). The results of multivariate analyses showed that the offensive team possession profiles required a careful investigation because the possession strategy changed under the conjoint effect of pitch location and game period.


#10 Interseason variability of a functional movement test, the 9+ screening battery, in professional male football players
Reference: Br J Sports Med. 2016 Sep 6. pii: bjsports-2016-096570. doi: 10.1136/bjsports-2016-096570. [Epub ahead of print]
Authors: Bakken A, Targett S, Bere T, Eirale C, Farooq A, Tol JL, Whiteley R, Witvrouw E, Khan KM, Bahr R
Summary: The Nine Plus screening battery test (9+) is a functional movement test intended to identify limitations in fundamental movement patterns predisposing athletes to injury. However, the interseason variability is unknown.
The aim of the study was to examine the variability of the 9+ test between 2 consecutive seasons in professional male football players. Asymptomatic Qatar Star League players (n=220) completed the 9+ at the beginning of the 2013 and 2014 seasons. Time-loss injuries in training and matches were obtained from the Aspetar Injury and Illness Surveillance Program. No intervention was initiated between test occasions. A significant increase in the mean total score of 1.6 points (95% CI 1.0 to 2.2, p<0.001) was found from season 1 (22.2±4.1 (SD)) to season 2 (23.8±3.3). The variability was large, as shown by an intraclass correlation coefficient (ICC) of 0.24 (95% CI 0.11 to 0.36) and a minimal detectable change (MDC) of 8.7 points. Of the 220 players, 136 (61.8%) suffered a time-loss injury between the 2 tests. There was an improvement in mean total scores in the injured (+2.0±0.4 (SE), p<0.001) group but not in the uninjured group (+0.9±0.5, p=0.089). The variability from season 1 to season 2 was large both in the injured (ICC 0.25, 0.09 to 0.40, MDC 8.3) and uninjured (ICC 0.24, 0.02 to 0.43, MDC 9.1) groups. The 9+ demonstrated substantial intraindividual variability in the total score between 2 consecutive seasons, irrespective of injury. A change above 8 points is necessary to represent a real change in the 9+ test between seasons.


#11 Mechanical Player Load™ using trunk-mounted accelerometry in football: Is it a reliable, task- and player-specific observation?
Reference: J Sports Sci. 2016 Sep 6:1-8. [Epub ahead of print]
Authors: Barreira P, Robinson MA, Drust B, Nedergaard N, Raja Azidin RM, Vanrenterghem J
Summary: The aim of the present study was to examine reliability and construct convergent validity of Player Load™ (PL) from trunk-mounted accelerometry, expressed as a cumulative measure and an intensity measure (PL · min-1). Fifteen male participants twice performed an overground football match simulation that included four different multidirectional football actions (jog, side cut, stride and sprint) whilst wearing a trunk-mounted accelerometer inbuilt in a global positioning system unit. Results showed a moderate-to-high reliability as indicated by the intra-class correlation coefficient (0.806-0.949) and limits of agreement. Convergent validity analysis showed considerable between-participant variation (coefficient of variation range 14.5-24.5%), which was not explained from participant demographics despite a negative association with body height for the stride task. Between-task variations generally showed a moderate correlation between ranking of participants for PL (0.593-0.764) and PL · min-1 (0.282-0.736). It was concluded that monitoring PL® in football multidirectional actions presents moderate-to-high reliability, that between-participant variability most likely relies on the individual's locomotive skills and not their anthropometrics, and that the intensity of a task expressed by PL · min-1 is largely related to the running velocity of the task.

Players market values
The report shows Messi as the player with the hightest value (216 mio Euros) followed by Christiano Ronaldo (114 mio Euros), Suarez, Hazard and Neymar. The list furthermore closes with number 60 Jerome Boateng from Bayern Munich with an estimated value of 23.7-27.5 mio Euros. Interestingly, the players with an value of over 50 mio Euros are exclusively offensive players and players employed by English and Spanish clubs are over-represented in the ranking, as well as footballers under the contract with Barcelona.

Question arise whether these values are accurate or not? The report indicates that the correlation between the reported and estimated transfer fees explained 76%.

Club assets
Ranking of clubs (players) asset are as followed:

• Barcelona (593 mio Euros)
• Real Madrid (488 mio Euros)
• Bayern Munich (400 mio Euros)
• Manchester City (386 mio Euros)
• Chelsea (385 mio Euros)
• Liverpool (373 mio Euros)
• ……
• Juventus (282 mio Euros first in Serie A)
• Paris SG (278 mio Euros first in French division)

Club performance
The report also indicated club performances, showing small statistics such as Barcelona as the club with the least shots conceded per match.
Others were:

• Juventus – least shots conceded from inside the box
• Juventus – highest number of shots on target needed by opposition to score
• Atletico Madrid – hightest number of passess before shots on target by opposition
• Bayern Munich – most passess per match (739)
• Bayern Munich – most passes in the opposition zone (437)
• Paris St. Germain – most passes in own half
• Paris St. Germain – most passes before shots on goal (43.9)
• Real Madrid - most number of shots per match (19.6)
• Real Madrid – most shots on target per match (7.9)
• Barcelona and ManCity – least shots to score (6.4)

Other statistics were with regards to best players and club demographics.

You can download and extract of the report HERE.

Lets pretend physical attributes are a major factor, we would then assume that the more successful team is superior in those factors. Is that the case? Probably not, however, I would like to give some thoughts about differences in players in different levels of competition and furthermore if players within the same level of competition differ with regards to physical and/or physiological variables.

Significant differences were seen between top-class (UEFA Champions League players) compared to Danish National players in performance parameters (high-intensity running and sprints during matches) and YYIRT level 1 performance (9 - see references below). Sprint and repeated sprint performance was significant different between different levels of play in Portugal, with the higher the level of play, the faster the players, who also inherent greater sprint endurance (1). The Literature also suggests physiological and performance differences in Serbian national league players compared to Serbian amateurs from 3rd division (11). The professional players had a higher VO2max, better jumping performance and greater estimated percentage of fast twitch muscle fibers. Furthermore, Swedish national players experience greater strength compared to other professional and amateur players (10), in addition national players had better proprioception/balance ability (12) compared to lower level players.

Knee flexor strength and 10-meter sprint were also significant different in French professional players compared to amateur players (2), with the professional players experiencing greater strength and higher running speed. However, the amateurs had significantly greater peak torque in the knee extension in low speed.

Investigation in female footballers showed differences in anthropometric variables between recreational 3rd division female players in Spain compared with Primera division female footballers. The lower level players showed greater body mass, more fat and less muscle percentage (16). Starter showed superior sprint and maximal aerobic velocity compared to non-starters (8) in New Zealand international female football players. Furthermore, eccentric strength discriminated between starters and non-starters in female NCAA Division I soccer players (5).

Youth national players showed superior performance in strength measures, jump and sprint performance to sub-elite and recreational players (4), despite no significant differences in anthropometry.

As a result, it seems that there are (some) differences in physical and/or physiological parameters between players in different levels of competition and between starters and non-starters.

However, I doubt that the physical performances were the only variables that differed. So what about the technical and tactical aspects. Well with regards to only the technical and tactical aspects I was not able to provide some literature, however, there were differences in French international players vs. amateur players with regards to the influence of the physical component on the technical and tactical aspect. For example, there are differences in performance parameters (successful passes, RPE, greater amount of loss of ball possession, less distance coverage in sprint and high-intensity running) between the two groups in SSG (3), which shows only that players from the higher level perform better (more connected passes), with less effort (RPE), are more efficient (fever loss of ball possession) and perform more repeatedly at a higher pace.

As it seems differences between levels are not only seen in the physical aspects but also in technical (and maybe tactical) elements. However, (and unfortunately) it is unresolved if the superior skills are just because the players in the higher competition level are just more skilled or maybe if the physical capacities (or also the delayed/lesser fatigue) influenced the skills. It seems established that fatigue from football match activity affects skill performance (15). Muscle fatigue influenced technical outcome/passing ability measured with the Loughborough Soccer Passing Test in college soccer players (7) and youth players form an Italian professional football team (13). However, the decline in passing ability was less in fitter players (13). There were also differences between successful teams and non-successful teams in the technical and physical aspects of Italian Serie A teams (14), with the more successful teams showing fewer decline in physical variables (such as total distance covered with the ball and high-intensity running with the ball) and also technical variables (such as successful short passes and dribblings and shots on goal) from the 1st to the 2nd half in a match.

Another quite interesting study investigated the role of stress, skill and fatigue on penalty outcome in FIFA World Cups. The study states that psychological stress seemed to be a greater factor, compared to skill and fatigue, in penalty outcomes (6).

In my opinion, the higher the level of competition the lower the importance of physical components (between teams). Well I have not worked on an UEFA Champions League level, but from my impressions it seems that physical fitness sets the foundation to be able to play at this level, but it is NOT a decisive component (obviously with the exception of having a Christiano Ronaldo finishing a counterattack after an opposition corner for a 2:1 win). Basically if the player is not fit (however this is defined), the player cannot play. If he/she is, then its more a matter of other qualities/individual class (technical, tactical, psychological aspects under high Champion League match speed) the player can add to the team.

Coaches of teams in “lower” divisions need to decide through measurements, experience or game analysis if the physical fitness is sufficient to compete on their level successfully. Due to the analysis the coaches can then decide if technical and/or tactical and/or psychological aspects of the game are “more” decisive compared to their players physical fitness and train appropriately/dominantly one or the others.

References
1. Abrantes, C., Macas, V., and Sampaio, J. Variation in football players' sprint test performance across

different ages and level of competition. J. Sci. Med. Sport. 3: 44-49, 2004.

2. Cometti, G., Maffiuletti, N.A., Pousson, M., Chatard, J.C., and Maffulli, N. Isokinetic strength and

anaerobic power of elite, subelite and amateur French soccer players. Int. J. Sports. Med. 22: 45-51, 2001.

3. Dellal, A., Hill-Haas, S., Lago-Penas, C., and Chamari, K. Small-sided games in soccer: Amateur vs.

professional players' physiological responses, physical, and technical activities. J. Strength. Cond. Res. 25: 2371-2381, 2011.

4. Gissis, I., Papadopoulos, C., Kalapotharakos, V., Sotiropoulos, A., Komsis, G., and Manolopoulos, E.

Strength and speed characteristics of elite, subelite, and recreational young soccer players. Res. Sports. Med. 14: 205-214, 2006.

5. Jenkins, N.D., Hawkey, M.J., Costa, P.B., Fiddler, R.E., Thompson, B.J., Ryan, E.D., Smith, D.,

Sobolewski, E.J., Conchola, E.C., Akehi, K., and Cramer, J.T. Functional hamstrings: quadriceps ratios in elite women's soccer players. J. Sports. Sci. 31: 612-617, 2013.

6. Jordet, G., Hartman, E., Visscher, C., and Lemmink, K.A. Kicks from the penalty mark in soccer: the

roles of stress, skill, and fatigue for kick outcomes. J. Sports. Sci. 25: 121-129, 2007.

7. Lyons, M., Al-Nakeeb, Y., and Nevill, A. Performance of soccer passing skills under moderate and

high-intensity localized muscle fatigue. J. Strength. Cond. Res. 20: 197-202, 2006.

8. Manson, S.A., Brughelli, M., and Harris, N.K. Physiological characteristics of international female soccer

players. J. Strength. Cond. Res. 28: 308-318, 2014.

9. Mohr, M., Krustrup, P., and Bangsbo, J. Match performance of high-standard soccer players with special

reference to development of fatigue. J. Sports. Sci. 21: 519-528, 2003.

10. Oberg, B., Moller, M., Gillquist, J., and Ekstrand, J. Isokinetic torque levels for knee extensors and knee

flexors in soccer players. Int. J. Sports. Med. 7: 50-53, 1986.

11. Ostojic, S.M. Elite and nonelite soccer players: Preseasonal physical and physiological characteristics.

Res. Sports. Med. 12: 143-150, 2004.

12. Paillard, T., Noe, F., Riviere, T., Marion, V., Montoya, R., and Dupui, P. Postural performance and

strategy in the unipedal stance of soccer players at different levels of competition. J. Athl. Training. 41: 172-176, 2006.

13. Rampinini, E., Impellizzeri, F.M., Castagna, C., Azzalin, A., Ferrari Bravo, D., and Wisloff, U. Effect of

match-related fatigue on short-passing ability in young soccer players. Med. Sci. Sports. Exerc. 40: 934-942, 2008.

14. Rampinini, E., Impellizzeri, F.M., Castagna, C., Coutts, A.J., and Wisloff, U. Technical performance

during soccer matches of the Italian Serie A league: effect of fatigue and competitive level. J. Sci. Med. Sports. 12: 227-233, 2009.

15. Russell, M., Benton, D., and Kingsley, M. The effects of fatigue on soccer skills performed during a

soccer match simulation. Int. J. Sports. Physiol. Perform. 6: 221-233, 2011.

16. Sedano, S., Vaeyens, R., Philippaerts, R.M., Redondo, J.C., and Cuadrado, G. Anthropometric and

anaerobic fitness profile of elite and non-elite female soccer players. J Sports Med Phys Fitness 49: 387-394, 2009.

Very interesting, however the questions (to me) still exists if continuity precedes success or vice versa with regards to coaches. The article gives some insight for players, however, I believe it would be very interesting to see some coaches and their attrition as well, as it is easier to change the coach instead of a couple of players.