Latest research in football - week 50 - 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 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
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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
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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
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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
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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
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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.

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