Latest research in football - week 35 - 2015

As previous literature updates, we have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:


#1 Influence of body composition on vertical jump performance according with the age and the playing position in football players
Reference: Nutr Hosp. 2015 Jul 1;32(1):299-307. doi: 10.3305/nh.2015.32.1.8876. [Article in Spanish]
Authors: Chena Sinovas M, Pérez-López A, Álvarez Valverde I, Bores Cerezal A, Ramos-Campo DJ, Rubio-Arias JÁ, Valadés Cerrato D
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Summary: Body composition and vertical jump are two factors in the multifactorial approach to talent identification in soccer with implication on performance monitorization and injury rehabilitation. The aim of this study was to describe the anthropometric attributes and vertical jump performance in young soccer players based on their playing position. Four hundred and thirty-four young soccer players from 7 to 25 years (13.4 ± 3.45 yrs; 156 ± 17 cm; 47.9 ± 15.4 kg), who trained 3 days/week for 1.5 hours/ day, took part in the study. All were split up based on their age or soccer category (U9, U11, U13, U15, U17, U25) and playing position (goalkeeper, defenders, midfielders and forwards). Then, body composition was measure using the anthropometric method and vertical jump performance was analysed by three vertical jump test Squat Jump (SJ), Counter-movement Jump (CMJ) and Abalakov Jump (CMJA). Significant differences among playing positions were mainly detected in categories U13, U15 and U25. Goalkeepers from U13 category reported a significantly higher fat free mass, appendicular lean body mass, area of the thigh and area of the calf (P < 0.05). While, defenders from U25 category showed a significantly greater vertical jump performance compared to midfielders for SJ, midfielders and forwards for CMJ and all playing position for CMJA (P < 0.05). In addition to biological age and muscle mass development, playing position should be taken into consideration as a relevant variable in the utilization of body composition and vertical jump performance as talent detection factors.

#2 Adaptation and validation in Spanish of the Group Environment Questionnaire (GEQ) with professional football players
Reference: Psicothema. 2015 Aug;27(3):261-8. doi: 10.7334/psicothema2014.247.
Authors: Leo FM, González-Ponce I, Sánchez-Oliva D, Pulido JJ, García-Calvo T
Summary: This investigation presents two studies with the goal of adapting and validating a short version of the Group Environment Questionnaire in the Spanish sport context with professional players. Study 1 used a sample of 377 male soccer players aged between 18 and 39 years ( M = 24.51, SD = 3.73), in a preliminary study using exploratory factor analysis. Study 2 used a sample of 604 professional male and female athletes, ages between 15 and 38 years ( M = 24.34, SD = 4.03). The data analyzed were collected at three moments of the season. For each measurement, we developed seven first- and second-order structures that were analyzed with confirmatory factor analysis. Study 1 indicated appropriate factorial validity (&gt; .60) and internal consistency (&gt; .70), with only Item 3 presenting a low factor loading (.11), so its drafting was modified in the next study. Study 2 revealed that the Spanish version of the GEQ has high levels of internal consistency (&gt; .70) and acceptable fit index values in its original four first-order factor structure in all three measurements ( &#967;2/df = 4.39, CFI = .95, IFI = .95, RMSEA = .07, SRMR = .04, AIC = 271.09). Discriminant validity (from r = .45 to r = .72) and concurrent validity (from r = .21 to r = .60) also presented appropriate values. Lastly, we conducted analysis of invariance, confirming that the models established in the different measurements were invariant. The short 12-item adaptation of the GEQ to Spanish is a valid and reliable instrument to measure team cohesion in professional male and female soccer players.

#3 Association of Soccer and Genu Varum in Adolescents
Reference: Trauma Mon. 2015 May;20(2):e17184. doi: 10.5812/traumamon.17184. Epub 2015 May 25.
Authors: Asadi K, Mirbolook A, Heidarzadeh A, Mardani Kivi M, Emami Meybodi MK, Rouhi Rad M
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Summary: Genu varum is a physical deformity marked by bowing of the leg. One of the risk factors of this musculoskeletal alignment is stress on the knee joint such as with exercise. Since the evaluation of genu varum has not been widely studies, this study was conducted to examine the association between genu varum and playing soccer. Between Septembers 2010-2012, 750 soccer players and 750 non-soccer players 10-18 years of age were included in the study. A questionnaire of data including age, height, weight, body mass index (BMI), years of soccer participation, the average time of playing soccer per week, previous trauma to the lower limbs, history of any fractures of the knee, previous hospitalizations, and the distance of joint lines between the knees was assessed for all subjects. Chi-square, student t-test, and one-way ANOVA were used for statistical analysis by SPSS v.19.0 software. In all tests, a P value of less than 0.05 was construed as statistically significant. Both soccer players and controls had genu varum. However, the incidence of genu varum was higher in the soccer players (P = 0.0001) and it was more prevalent in the 16-18 year age group (P = 0.0001). The results revealed a statistically significant association between the degree of practices and the prevalence of genu varum (P = 0.0001). Moreover, previous trauma to the knees and practicing in load-bearing sports led to an increase in the degree of genu varum (P = 0.0001). There was a higher incidence of genu varum in soccer players than in control adolescents; the stress and load imposed on the knee joint led to more severe genu varum.

#4 Regular- and postseason comparisons of playing time and measures of running performance in NCAA Division I women soccer players
Reference: Appl Physiol Nutr Metab. 2015 Sep;40(9):907-17. doi: 10.1139/apnm-2014-0560. Epub 2015 May 6.
Authors: Wells AJ, Hoffman JR, Beyer KS, Hoffman MW, Jajtner AR, Fukuda DH, Stout JR
Summary: The management of playing time in National Collegiate Athletic Association (NCAA) soccer athletes may be a key factor affecting running performance during competition. This study compared playing time and running performance between regular-season and postseason competitions during a competitive women's soccer season. Nine NCAA Division I women soccer players (age, 21.3 ± 0.9 years; height, 170.3 ± 5.7 cm; body mass, 64.0 ± 5.8 kg) were tracked using portable GPS devices across 21 games during a competitive season (regular season (n = 17); postseason (n = 4)). Movements on the field were divided into operationally distinct thresholds defined as standing/transient motion, walking, jogging, low-speed running, moderate-speed running, high-speed running, sprinting, low-intensity running, and high-intensity running. A significant increase in minutes played (+17%, p = 0.010) was observed at postseason compared with the regular season. Concomitant increases in time spent engaged in low-intensity running (LIR: +18%, p = 0.011), standing/transient motion (+35%, p = 0.004), walking (+17%, p = 0.022), distance covered while walking (+14%, p = 0.036), and at low intensity (+11%, p = 0.048) were observed. Performance comparisons between the first and second half within games revealed a significant decrease (p ≤ 0.05) in high-speed and high-intensity runs during the second half of the postseason compared with the regular season. Changes in minutes played correlated significantly with changes in absolute time spent engaged in LIR (r = 0.999, p < 0.001), standing/transient motion (r = 0.791, p = 0.011), walking (r = 0.975, p = 0.001), jogging (r = 0.733, p = 0.025), distance covered while walking (r = 0.898, p < 0.001) and low-intensity activity (r = 0.945, p < 0.001). Negative correlations were observed between minutes played and absolute time sprinting (r = -0.698, p = 0.037) and distance covered sprinting (r = -0.689, p = 0.040). Results indicate that additional minutes played during the postseason were primarily performed at lower intensity thresholds, suggesting running performance during postseason competitions may be compromised with greater playing time in intercollegiate women's soccer.

#5 Cortical thinning in former professional soccer players
Reference: Brain Imaging Behav. 2015 Aug 19. [Epub ahead of print]
Authors: Koerte IK, Mayinger M, Muehlmann M, Kaufmann D, Lin AP, Steffinger D, Fisch B, Rauchmann BS, Immler S, Karch S, Heinen FR, Ertl-Wagner B, Reiser M, Stern RA, Zafonte R, Shenton ME
Summary: Soccer is the most popular sport in the world. Soccer players are at high risk for repetitive subconcussive head impact when heading the ball. Whether this leads to long-term alterations of the brain's structure associated with cognitive decline remains unknown. The aim of this study was to evaluate cortical thickness in former professional soccer players using high-resolution structural MR imaging. Fifteen former male professional soccer players (mean age 49.3 [SD 5.1] years) underwent high-resolution structural 3 T MR imaging, as well as cognitive testing. Fifteen male, age-matched former professional non-contact sport athletes (mean age 49.6 [SD 6.4] years) served as controls. Group analyses of cortical thickness were performed using voxel-based statistics. Soccer players demonstrated greater cortical thinning with increasing age compared to controls in the right inferolateral-parietal, temporal, and occipital cortex. Cortical thinning was associated with lower cognitive performance as well as with estimated exposure to repetitive subconcussive head impact. Neurocognitive evaluation revealed decreased memory performance in the soccer players compared to controls. The association of cortical thinning and decreased cognitive performance, as well as exposure to repetitive subconcussive head impact, further supports the hypothesis that repetitive subconcussive head impact may play a role in early cognitive decline in soccer players. Future studies are needed to elucidate the time course of changes in cortical thickness as well as their association with impaired cognitive function and possible underlying neurodegenerative process.

#6 Effect of Practicing Soccer Juggling With Different Sized Balls Upon Performance, Retention and Transfer to Ball Reception
Reference: Motor Control. 2015 Aug 12. [Epub ahead of print]
Authors: Raastad O, Aune TK, van den Tillaar R
Summary: The aim of this study was to investigate if making the skill acquisition phase more difficult or easier would enhance performance in soccer juggling, and if this practice has a positive inter-task transfer effect to ball reception performance. Twenty-two adolescent soccer players were tested in juggling a soccer ball and in the control of an approaching ball at a pre-, post and retention test. The participants were randomly divided in a small ball size and bigger ball size training group that both trained four times per week for six weeks. At the post and retention test both groups enhanced performance in soccer juggling test with no difference between groups and no increase in ball reception performance at these tests. It was concluded that about intra task transfer and retention of soccer juggling skills, it does not matter if you increase (small balls) or decrease the difficulty (larger balls) when using the same amount of practice time within the skill acquisition phase in soccer juggling. In addition that for ball juggling and ball reception (inter task) these two tasks differ too much in afferent information and movement characteristics that no positive transfer between these two skills no positive inter-task transfer can be expected.

#7 Strength training in soccer with a specific focus on highly trained players
Reference: Sports Med Open. 2015;1(1):1. Epub 2015 Apr 2.
Authors: Silva JR, Nassis GP, Rebelo A
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Summary: Data concerning the physical demands of soccer (e.g., activity pattern) suggest that a high level of performance requires well-developed neuromuscular function (NF). Proficient NF may be relevant to maintain and/or increase players' short- (intense periods of soccer-specific activity; accelerations, decelerations, and sprinting) and long-term performance during a match and throughout the season. This review examines the extent to which distinct modes of strength training improve soccer players' performance, as well as the effects of concurrent strength and endurance training on the physical capacity of players. A selection of studies was performed in two screening phases. The first phase consisted of identifying articles through a systematic search using relevant databases, including the US National Library of Medicine (PubMed), MEDLINE, and SportDiscus. Several permutations of keywords were utilized (e.g., soccer; strength; power; muscle function), along with the additional scanning of the reference lists of relevant manuscripts. Given the wide range of this review, additional researchers were included. The second phase involved applying six selection criteria to the articles. After the two selection phases, 24 manuscripts involving a total sample of 523 soccer players were considered. Our analysis suggests that professional players need to significantly increase their strength to obtain slight improvements in certain running-based actions (sprint and change of direction speed). Strength training induces greater performance improvements in jump actions than in running-based activities, and these achievements varied according to the motor task [e.g., greater improvements in acceleration (10 m) than in maximal speed (40 m) running movements and in non-squat jump (SJ) than in SSC-based actions (countermovement jump)]. With regard to the strength/power training methods used by soccer players, high-intensity resistance training seems to be more efficient than moderate-intensity resistance training (hypertrophic). From a training frequency perspective, two weekly sessions of strength training are sufficient to increase a player's force production and muscle power-based actions during pre-season, with one weekly session being adequate to avoid in-season detraining. Nevertheless, to further improve performance during the competitive period, training should incorporate a higher volume of soccer-specific power-based actions that target the neuromuscular system. Combined strength/power training programs involving different movement patterns and an increased focus on soccer-specific power-based actions are preferred over traditional resistance exercises, not only due to their superior efficiency but also due to their ecological value. Strength/power training programs should incorporate a significant number of exercises targeting the efficiency of stretch-shortening-cycle activities and soccer-specific strength-based actions. Manipulation of training surfaces could constitute an important training strategy (e.g., when players are returning from an injury). In addition, given the conditional concurrent nature of the sport, concurrent high-intensity strength and high-intensity endurance training modes (HIT) may enhance a player's overall performance capacity. Our analysis suggests that neuromuscular training improves both physiological and physical measures associated with the high-level performance of soccer players.

#8 Injuries in male versus female soccer players: epidemiology of a nationwide study
Reference: Acta Orthop Belg. 2015 Jun;81(2):289-95.
Authors: Mufty S, Bollars P, Vanlommel L, Van Crombrugge K, Corten K, Bellemans J.
Summary: The aim of this study is to analyse soccer injuries on a national scale over one decade and to compare injury rates by gender. Detailed injury data obtained from the Royal Belgian Football Association from seasons 1999-2000 and 2009-2010 were recorded and gender differences in incidences of injuries, type of injury, affected body part and timing of injury were compared. A significant decrease in injuries from 7.56 to 5.96 injuries per 100 players was seen (p < 0.0001). Overall male players sustained more cont usions, fractures, joint dislocations and musculotendinous injuries than female players. Proportionally, females sustained more severe injuries than men (p < 0.0001). Significantly more injuries where sustained during competition in both males and females. The number of injuries in male and female soccer players has decreased over the past decade. A higher injury rate was seen in men but proportionally, females sustained more severe injuries.

#9 Sleep Hygiene and Recovery Strategies in Elite Soccer Players
Reference: Sports Med. 2015 Aug 15. [Epub ahead of print]
Authors: Nédélec M, Halson S, Delecroix B, Abaidia AE, Ahmaidi S, Dupont G.
Summary: In elite soccer, players are frequently exposed to various situations and conditions that can interfere with sleep (e.g., playing night matches interspersed with 3 days; performing activities demanding high levels of concentration close to bedtime; use of products containing caffeine or alcohol in the period preceding bedtime; regular daytime napping throughout the week; variable wake-up times or bedtime), potentially leading to sleep deprivation. We outline simple, practical, and pharmaceutical-free sleep strategies that are coordinated to the constraints of elite soccer in order to promote sleep. Sleep deprivation is best alleviated by sleep extension; however, sleep hygiene strategies (i.e., consistent sleep pattern, appropriate napping, and active daytime behaviors) can be utilized to promote restorative sleep. Light has a profound impact on sleep, and sleep hygiene strategies that support the natural environmental light-dark cycle (i.e., red-light treatment prior to sleep, dawn-simulation therapy prior to waking) and prevent cycle disruption (i.e., filtering short wavelengths prior to sleep) may be beneficial to elite soccer players. Under conditions of inordinate stress, techniques such as brainwave entrainment and meditation are promising sleep-promoting strategies, but future studies are required to ascertain the applicability of these techniques to elite soccer players. Consuming high-electrolyte fluids such as milk, high-glycemic index carbohydrates, some forms of protein immediately prior to sleep, as well as tart cherry juice concentrate and tryptophan may promote rehydration, substrate stores replenishment, muscle-damage repair and/or restorative sleep. The influence of cold water immersion performed close to bedtime on subsequent sleep is still debated. Conversely, the potential detrimental effects of sleeping medication must be recognized. Sleep initiation is influenced by numerous factors, reinforcing the need for future research to identify such factors. Efficient and individualized sleep hygiene strategies may consequently be proposed.

#10 Cooperation Improves Success during Intergroup Competition: An Analysis Using Data from Professional Soccer Tournaments
Reference: PLoS One. 2015 Aug 27;10(8):e0136503. doi: 10.1371/journal.pone.0136503.
Authors: David GK, Wilson RS
Summary: The benefit mutually gained by cooperators is considered the ultimate explanation for why cooperation evolved among non-relatives. During intergroup competition, cooperative behaviours within groups that provide a competitive edge over their opposition should be favoured by selection, particularly in lethal human warfare. Aside from forming larger groups, three other ways that individuals within a group can cooperate to improve their chances of gaining a mutual benefit are: (i) greater networking, (ii) contributing more effort, and (iii) dividing labour. Greater cooperation is expected to increase the chances of gaining a group benefit by improving proficiency in the tasks critical to success-yet empirical tests of this prediction using real-world cases are absent. In this study, we used data derived from 12 international and professional soccer competitions to test the predictions that: 1) greater levels of cooperative behaviour are associated with winning group contests, 2) the three forms of cooperation differ in relative importance for winning matches, 3) competition and tournament-type affect the levels of cooperation and shooting proficiency in matches, and 4) greater levels of networking behaviour are associated with increased proficiency in the most critical task linked with winning success in soccer-shooting at goal. Winners were best predicted by higher shooting proficiency, followed by greater frequencies of networking interactions within a team but unexpectedly, fewer networking partners and less division of labour. Although significant variation was detected across competitions and tournament-types, greater levels of networking behaviour were consistently associated with increased proficiency in shooting at goal, which in turn was linked with winning success. This study empirically supports the idea that intergroup competition can favour cooperation among non-relatives.

#11 Mental Fatigue Impairs Soccer-Specific Physical and Technical Performance
Reference: Med Sci Sports Exerc. 2015 Aug 27. [Epub ahead of print]
Authors: Smith MR, Coutts AJ, Merlini M, Deprez D, Lenoir M, Marcora SM
Summary: The purpose of the study was to investigate the effects of mental fatigue on soccer-specific physical and technical performance. This investigation consisted of two separate studies. Study 1 assessed the soccer-specific physical performance of 12 moderately-trained soccer players using the Yo-Yo Intermittent Recovery Test, Level 1 (Yo-Yo IR1). Study 2 assessed the soccer-specific technical performance of 14 experienced soccer players using the Loughborough Soccer Passing and Shooting Tests (LSPT, LSST). Each test was performed on two occasions and preceded, in a randomized, counter-balanced order, by 30-min of the Stroop task (mentally fatiguing treatment) or 30-min of reading magazines (control treatment). Subjective ratings of mental fatigue were measured before and after treatment, and mental effort and motivation were measured after treatment. Distance run, heart rate (HR) and ratings of perceived exertion (RPE) were recorded during the Yo-Yo IR1. LSPT performance time was calculated as original time plus penalty time. LSST performance was assessed using shot speed, shot accuracy and shot sequence time. Subjective ratings of mental fatigue and effort were higher following the Stroop task in both studies (P < 0.001), while motivation was similar between conditions. This mental fatigue significantly reduced running distance in the Yo-Yo IR1 (P < 0.001). No difference in HR existed between conditions, while RPE was significantly higher at iso-time in the mental fatigue condition (P < 0.01). LSPT original time and performance time were not different between conditions, however penalty time significantly increased in the mental fatigue condition (P = 0.015). Mental fatigue also impaired shot speed (P = 0.024) and accuracy (P < 0.01), while shot sequence time was similar between conditions. Mental fatigue impairs soccer-specific running, passing, and shooting performance.

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