Latest research in football - week 36 - 2016

#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.