Latest research in football - week 17 - 2018

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 Assessing Repeated-Sprint Ability in Division I Collegiate Women Soccer Players
Reference: J Strength Cond Res. 2018 Apr 26. doi: 10.1519/JSC.0000000000002527. [Epub ahead of print]
Authors: Lockie RG, Liu TM, Stage AA, Lazar A, Giuliano DV, Hurley JM, Torne IA, Beiley MD, Birmingham-Babauta SA, Stokes JJ, Risso FG, Davis DL, Moreno MR, Orjalo AJ
Summary: Repeated-sprint ability (RSA) is a key component of soccer, and is the capacity to repeatedly produce near-maximal to maximal sprints with short recovery periods. Repeated-sprint ability has received little analysis in collegiate women soccer players. The purpose of this study was to investigate relationships between RSA and tests of soccer-specific performance. Nineteen players from the same Division I collegiate women's soccer team were recruited. The RSA test consisted of six 20-m sprints completed on 15-second cycles. The measurements taken were total time (TT) and percent decrement (PD; percent change from first to last sprint). Subjects also completed tests of: lower-body strength (1 repetition maximum [1RM] back squat); jump performance (vertical and standing long jumps); linear (0-5, 0-10, and 0-30 m sprint intervals) and change-of-direction (505 from each leg) speed; and soccer-specific fitness (Yo-Yo intermittent recovery test level 1 [YYIRT1]). Pearson's correlations (p ≤ 0.05) were used to calculate relationships between RSA TT and PD with the performance tests. Total time exhibited significant relationships with the 0-10 (r = 0.50) and 0-30 m (r = 0.71) sprint intervals, and the left-leg 505 (r = 0.57). However, lower-body strength measured by the 1RM back squat and jump performance did not relate to TT. Percent decrement correlated only with the left-leg 505 (r = 0.53) and no other performance test. This included the YYIRT1, although both PD and YYIRT1 performance are limited by fatigue. The results from this study indicated that faster linear sprinting speed could positively influence RSA in Division I collegiate women soccer players.

#2 EEG alpha activity during imagining creative moves in soccer decision-making situations
Reference: Neuropsychologia. 2018 Apr 24. pii: S0028-3932(18)30166-0. doi: 10.1016/j.neuropsychologia.2018.04.025. [Epub ahead of print]
Authors: Fink A, Rominger C, Benedek M, Perchtold CM, Papousek I, Weiss EM, Seidel A, Memmert D
Summary: This study investigated task-related changes of EEG alpha power while participants were imagining creative moves in soccer decision-making situations. After presenting brief video clips of a soccer scene, participants had to imagine themselves as the acting player and to think either of a creative/original or an obvious/conventional move (control condition) that might lead to a goal. Performance of the soccer task generally elicited comparatively strong alpha power decreases at parietal and occipital sites, indicating high visuospatial processing demands. This power decrease was less pronounced in the creative vs. control condition, reflecting a more internally oriented state of information processing characterized by more imaginative mental simulation rather than stimulus-driven bottom-up processing. In addition, more creative task performance in the soccer task was associated with stronger alpha desynchronization at left cortical sites, most prominently over motor related areas. This finding suggests that individuals who generated more creative moves were more intensively engaged in processes related to movement imagery. Unlike the domain-specific creativity measure, individual's trait creative potential, as assessed by a psychometric creativity test, was globally positively associated with alpha power at all cortical sites. In investigating creative processes implicated in complex creative behavior involving more ecologically valid demands, this study showed that thinking creatively in soccer decision-making situations recruits specific brain networks supporting processes related to visuospatial attention and movement imagery, while the relative increase in alpha power in more creative conditions and in individuals with higher creative potential might reflect a pattern relevant across different creativity domains.

#3 Inter-season variability in isokinetic strength and poor correlation with nordic hamstring eccentric strength in football players
Reference: Scand J Med Sci Sports. 2018 Apr 25. doi: 10.1111/sms.13201. [Epub ahead of print]
Authors: van Dyk N, Witvrouw E, Bahr R
Summary: In elite sport, the use of strength testing to establish muscle function and performance is common. Traditionally, isokinetic strength tests have been used, measuring torque during concentric and eccentric muscle action. A device that measures eccentric hamstring muscle strength while performing the Nordic hamstring exercise is now also frequently used. The study aims to investigate the variability of isokinetic muscle strength over time, e.g. between seasons, and the relationship between isokinetic testing and the new Nordic hamstring exercise device. All teams (n=18) eligible to compete in the premier football league in Qatar underwent a comprehensive strength assessment during their periodic health evaluation at Aspetar Orthopaedic and Sports Medicine Hospital in Qatar. Isokinetic strength was investigated for measurement error, and correlated to Nordic hamstring exercise strength. Of the 529 players included, 288 players had repeated tests with one/two seasons between test occasions. Variability (measurement error) between test occasions was substantial, as demonstrated by the measurement error (approximately 25Nm, 15%), whether separated by one or two seasons. Considering hamstring injuries, the same pattern was observed among injured (n=60) and uninjured (n=228) players. A poor correlation (r=0.35) was observed between peak isokinetic hamstring eccentric torque and Nordic hamstring exercise peak force. The strength imbalance between limbs calculated for both test modes were not correlated (r=0.037). There is substantial intraindividual variability in all isokinetic test measures, whether separated by one or two seasons, irrespective of injury. Also, eccentric hamstring strength and limb-to-limb imbalance were poorly correlated between the isokinetic and Nordic hamstring exercise tests. This article is protected by copyright. All rights reserved.

#4 Variability of activity profile during medium-sided games in professional soccer
Reference: J Sports Med Phys Fitness. 2018 Apr 24. doi: 10.23736/S0022-4707.18.08376-7. [Epub ahead of print]
Authors: Rago V, Silva JR, Mohr M, Barreira D, Krustrup P, Rebelo AN
Summary: In Southern European countries it is very frequent to perform medium-sized games (MSG) as last training drill. We analyzed the individual variability and changes in activity patterns during MSG throughout the preseason. Activity profile during MSGs (10v10+goalkeepers, duration: 10-min, field length: 50 m, width: 90 m, area per player: 204.5 m2) was quantified using a GPS in 14 professional male players (6 defenders, 5 midfielders 5 and attackers). Inter-individual variability was higher for high-intensity (HIR), very-high speed (VHS), maximum acceleration (Accmax) and maximum deceleration (Decmax) distance (CV=25.2 to 43.3%), compared to total distance (TD), total acceleration (Acctot) and total deceleration (Dectot) distance (CV= 8.3 to 18.3 %). Defenders showed higher variability in TD, HIR, VHS, Acctot and Dectot (ES= 1.30 to 11.28) compared to the other field positions, whereas attackers showed higher variability in HIR, VHS Accmax and Decmax (ES=-4.92 to 2.07) than other the field positions. Variability in TD regularly increased (ES= -2.13 to -0.91) towards the end of the preseason, while HIR and VHS variability tended to increase over the 3rd and the 4th preseason week (ES=-0.94 to -3.05). However, the behavior of variability across the preseason period was more unpredictable for Acctot and Dectot, both decreasing in the 3rd week (ES= 0.70 to 1.20), while Decmax increased in the 4th week (ES=-0.91±0.59). During MSGs, individual variability of activity differs among field positions, and tends to increase with either speed or acceleration intensity, underlining the need of an individualized approach for training load monitoring.

#5 Landing Kinematics in Elite Male Youth Soccer Players of Different Chronologic Age and Stage of Maturation
Reference: J Athl Train. 2018 Apr 25. doi: 10.4085/1062-6050-493-16. [Epub ahead of print]
Authors: Read PJ, Oliver JL, De Ste Croix MBA, Myer GD, Lloyd RS
Summary: Despite the high frequency of knee injuries in athletes, few researchers have studied the effects of chronologic age and stage of maturation on knee-joint kinematics in male youth soccer players. The aim was to use a coach-friendly screening tool to examine knee-valgus scores for players of different ages and at different stages of maturation. A total of 400 elite male youth soccer players aged 10 to 18 years categorized by chronologic age and stage of maturation based on their years from peak height velocity (PHV) participated in the study. Knee valgus was evaluated during the tuck-jump assessment via 2-dimensional analysis. Frontal-plane projection angles were subjectively classified as minor (<10°), moderate (10°-20°), or severe (>20°), and using these classifications, we scored knee valgus in the tuck jump as 0 ( no valgus), 1 ( minor), 2 ( moderate), or 3 ( severe). A trend toward higher valgus scores was observed in the younger age groups and the pre-PHV group. The lowest frequency of no valgus occurred in the U18 and post-PHV groups. The highest percentages of severe scores were in the U13 and pre-PHV groups for the right limb. Knee-valgus scores were lower for both lower extremities in the U18 group than in all other age groups ( P < .001) except the U16 group. Scores were lower for the post-PHV than the pre-PHV group for the right limb ( P < .001) and both pre-PHV and circa-PHV groups for the left limb ( P < .001). Noteworthy interlimb asymmetries were evident in the U14, U15, and circa-PHV groups. Reductions in knee valgus with incremental age and during the later stages of maturation indicated that this risk factor was more prevalent in younger players. Interlimb asymmetry may also emerge around the time of the peak growth spurt and early adolescence, potentially increasing the risk of traumatic injury.

#6 Team Dynamics, Running, and Skill-Related Performances of Brazilian U11 to Professional Soccer Players During Official Matches
Reference: J Strength Cond Res. 2018 Apr 26. doi: 10.1519/JSC.0000000000002577. [Epub ahead of print]
Authors: Palucci Vieira LH, Aquino R, Moura FA, Barros RML, Arpini VM, Oliveira LP, Bedo BLS, Santiago PRP
Summary: Analyses of movements during soccer competition have been used previously to help develop conditioning programs. However, this has not been extensively studied in youth populations. Therefore, the purposes of this study were to examine (1) dynamics of collective tactical movements, (2) running, and (3) skill-related performances during soccer matches disputed by children to senior players. A total of 120 Brazilian players in the age groups U11, U13, U15, U17, U20, and professional (PRO) were monitored during official competition matches (N = 12). Using semiautomatic video-based tracking (30 Hz), match running variables including total distance traveled, average speed, maximum sprint speed, and high-intensity activities were evaluated. Tactical metrics were computed as team surface area, spread, and median frequency. Through notational analysis, technical skills such as involvements with the ball, passes, ball touches, duels, and goal attempts were also recorded. One-way analysis of variance and magnitude-based inferences were used to detect differences between ages. Although the average speed, team surface area, and spread tended to present stabilized increases from the U15 (e.g., U15 > U13 > U11), maximal sprinting speed (PRO > U17 > U15, U13, U11) and percentage at very high-intensity activities (U20 > PRO, U17 > U15 > U13 > U11) demonstrated continuous gains. Median frequencies were higher in the younger groups (U13, U15, U17 > U20, PRO), although the percentage of successful passes was higher in the older groups (PRO > U17, U15 > U13, U11). We concluded that Brazilian U11 to PRO players present different performance profiles for running, collective movement dynamics, and technical skills, and that the rate of development regarding these components varies. Coaches should be aware of these differences to select and adapt training content for each age group.

#7 New Tool to Control and Monitor Weighted Vest Training Load for Sprinting and Jumping in Soccer
Reference: J Strength Cond Res. 2018 Apr 26. doi: 10.1519/JSC.0000000000002580. [Epub ahead of print]
Authors: Carlos-Vivas J, Freitas TT, Cuesta M, Perez-Gomez J, De Hoyo M, Alcaraz PE
Summary: The purpose of this study was to develop 2 regression equations that accurately describe the relationship between weighted vest loads and performance indicators in sprinting (i.e., maximum velocity, Vmax) and jumping (i.e., maximum height, Hmax). Also, this study aimed to investigate the effects of increasing the load on spatio-temporal variables and power development in soccer players and to determine the "optimal load" for sprinting and jumping. Twenty-five semiprofessional soccer players performed the sprint test, whereas a total of 46 completed the vertical jump test. Two different regression equations were developed for calculating the load for each exercise. The following equations were obtained: % body mass (BM) = -2.0762·%Vmax + 207.99 for the sprint and % BM = -0.7156·%Hmax + 71.588 for the vertical jump. For both sprinting and jumping, when the load increased, Vmax and Hmax decreased. The "optimal load" for resisted training using weighted vest was unclear for sprinting and close to BM for vertical jump. This study presents a new tool to individualize the training load for resisted sprinting and jumping using weighted vest in soccer players and to develop the whole force-velocity spectrum according to the objectives of the different periods of the season.

#8 Injury prevention and return to play strategies in elite football: no consent between players and team coaches
Reference: Arch Orthop Trauma Surg. 2018 Apr 20. doi: 10.1007/s00402-018-2937-6. [Epub ahead of print]
Authors: Loose O, Achenbach L, Fellner B, Lehmann J, Jansen P, Nerlich M, Angele P, Krutsch W
Summary: Injuries are a common problem in football. To improve prevention strategies, the players' (p) and coaches' (c) views need to be disclosed as they have a strong impact on return to play decisions. The aim of this study is to reveal current opinions with regard to injury prevention and return to play strategies to introduce new strategies in elite football. In a retrospective data analysis of elite salaried football players (n = 486) and team coaches (n = 88), a detailed investigation by means of a standardized questionnaire was carried out. In a preseason period of the 2015/16 season and as part of a large interventional research project in elite salaried German football, a request about players' and team coaches' knowledge and opinions was performed. Topics such as injury prevention, return to play after injuries, the importance of screening tests, general problems of injuries in football, or the decision-making in terms of prevention and return to play in elite football were investigated. The study revealed a high interest in injury prevention and screening tests among players and coaches (p 82.5%; c 99.1%). The participants of the study reported warm-up exercises (p 76.4%; c 74.7%), regeneration training (p 54.1%; c 56.3%), and core stability (p 53.8; c 70.1%) as the most important prevention methods, but the additional investigation of the teams' current daily training routine showed that the transfer is incomplete. Coaches are more familiar with scientific published warm-up programs like FIFA 11 + than players (42.5 vs. 12.6; p < 0.001). Knee injuries (p 90.7%; c 93.1%) and ACL injuries in particular were reported as the most severe and common problem in elite football. Players and coaches expressed different attitudes concerning return to play decisions. While players want to decide themselves (81.4%), team coaches consult medical advice ahead of the decision of return to play after injuries (83.5%; p < 0.001). Decisions against the doctor's recommendation are often made by both groups (p 64.4% vs. c 87.1%; p < 0.001). The basic knowledge of prevention and injuries is sufficient in elite football, but the transfer from theoretical knowledge to practical routine is suboptimal. The study also shows possibilities to improve the prevention process and communication between players, coaches, doctors, and physiotherapists, while there is no consent between players and coaches regarding return to play decision.

#9 Dynamics of submaximal effort soccer instep kicking
Reference: J Sports Sci. 2018 May 1:1-8. doi: 10.1080/02640414.2018.1470216. [Epub ahead of print]
Authors: Nunome H, Inoue K, Watanabe K, Iga T, Akima H
Summary: During a soccer match, players are often required to control the ball velocity of a kick. However, little information is available for the fundamental qualities associated with kicking at various effort levels. We aimed to illustrate segmental dynamics of the kicking leg during soccer instep kicking at submaximal efforts. The instep kicking motion of eight experienced university soccer players (height: 172.4 ± 4.6 cm, mass: 63.3 ± 5.2 kg) at 50, 75 and 100% effort levels were recorded by a motion capture system (500 Hz), while resultant ball velocities were monitored using a pair of photocells. Between the three effort levels, kinetic adjustments were clearly identified in both proximal and distal segments with significantly different (large effect sizes) angular impulses due to resultant joint and interaction moments. Also, players tended to hit an off-centre point on the ball using a more medial contact point on the foot and with the foot in a less upright position in lower effort levels. These results suggested that players control their leg swing in a context of a proximal to distal segmental sequential system and add some fine-tuning of the resultant ball velocity by changing the manner of ball impact.

#10 Periodic Health Examination and Injury Prediction in Professional Football (Soccer): Theoretically, the Prognosis is Good
Reference: Sports Med. 2018 Apr 27. doi: 10.1007/s40279-018-0928-y. [Epub ahead of print]
Authors: Hughes T, Sergeant JC, van der Windt DA, Riley R, Callaghan
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Summary: In professional soccer and other elite sports, medical and performance screening of athletes (also termed periodic health examination or PHE) is common practice. The purposes of this are: (1) to assist in identifying prevalent conditions that may be a threat to safe participation, (2) to assist in setting benchmark targets for rehabilitation or performance purposes and (3) to assist clinicians in determining which athletes may be at risk of future injury and selecting appropriate injury prevention strategies to reduce the perceived risk. However, when using PHE as an injury prevention tool, are clinicians seeking to identify potential causes of injury or to predict future injury? This Current Opinion aims to examine the conceptual differences between aetiology and prediction of injury while relating these areas to the capabilities of PHE in practice. We also introduce the concept of prognosis-a broader approach that is closely related to prediction-and why this may have greater applicability to PHE of professional athletes.

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