Latest research in football - week 8 - 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 Psychological Characteristics in Talented Soccer Players - Recommendations on How to Improve Coaches' Assessment
Reference: Front Psychol. 2018 Feb 5;9:41. doi: 10.3389/fpsyg.2018.00041. eCollection 2018.
Authors: Musculus L, Lobinger BH
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Summary: Psychological characteristics, including personality traits and psychological skills, have been shown to be relevant predictors of soccer performance. In research, general and sport specific standardized self-report questionnaires have been applied in psychological diagnostics of sports talent. However, with regard to the assessment of psychological characteristics of talented soccer players, a gap between research and practice is apparent. While soccer clubs often ask their coaches to assess their players on self-designed, unevaluated scouting sheets, research widely neglects expert coaches' and clubs' perspectives on relevant performance characteristics. As we believe that expert coaches' assessments could be a valid predictor of a player's current performance and future success, we provide recommendations on how to improve coaches' assessment of psychological characteristics. As the quality of the assessment of psychological characteristics is crucial, we provide recommendations on how to ensure the central diagnostic standards: objectivity, reliability, and validity in talent assessment. Further, we argue that assessing psychological characteristics should combine self ratings of players and external ratings of coaches in talent development. Sport psychologists should assist clubs and coaches in improving the diagnostics of psychological characteristics as well as in embedding psychological diagnostics and interventions in the talent development process.

#2 Influence of biological maturity on the match performance of 8 to 16 year old elite male youth soccer players
Reference: J Strength Cond Res. 2018 Feb 14. doi: 10.1519/JSC.0000000000002510. [Epub ahead of print]
Authors: Goto H, Morris JG, Nevill ME
Summary: The aim of this study was to examine the influence of biological maturity on match performance in elite youth male soccer players. The participants were 80 Premier League Academy outfield players (8-16 years old). Biological maturity was determined by calculating estimated chronological age at peak height velocity. The U9 and U10 squads played 6-a-side and the U11-U16 squads played 11-a-side inter-academy matches. All matches were analyzed using a 1 Hz Global Positioning System (SPI elite, GPSport, Australia) with squad specific speed zones which were calculated based on 5 m flying sprint speed in the last 5 m of 10 m sprint test. In the U9/U10s, earlier maturers were given a longer pitch time by coaches (∼4 min per match, p = 0.029) and covered a greater total distance (∼9%, ∼400 m, p = 0.037) and a greater distance by walking (∼13%, ∼100 m, p = 0.024) and jogging (∼12%, ∼200 m, p = 0.014) during a match compared to later maturers. In the U13/U14s, earlier maturers covered a greater distance per hour of a match by high speed running compared to later maturers (∼25%, ∼130 m, p = 0.028) and spent a longer percentage of time in high speed running during a match compared to later maturers (3.4% vs. 2.7%, p = 0.034). Thus, coaches should take care to provide all players with a similar pitch-time and should be aware in the talent identification and development process, particularly with the U13/U14 age group, that maturity can influence high speed match running performance.

#3 Detection of Spatiotemporal Asymmetry in Pro Level Soccer Players
Reference: J Strength Cond Res. 2018 Mar;32(3):798-804. doi: 10.1519/JSC.0000000000001811.
Authors: Knudsen NS, Andersen TB
Summary: Several papers have focused on change of direction (COD) asymmetry investigated through standardized tests, and used this information to provide some spatiotemporal insight during games. The aim of this study was to investigate asymmetry in the reachable areas of the players through actual position data from soccer games. Sixteen professional players from the Danish Superliga participated in this study, but 5 were excluded because of lack of participation throughout the investigated games. The reachable areas of the players were investigated at varying sprint velocities (1-7 m·s) and within varying time intervals (0.5-4 seconds). The analysis found 7 players having spatiotemporal asymmetries in their reachable areas (0.5-3%) and shift of center of reachable area (4-29 cm). Four players (LB, RB, DM, and CF) had spatiotemporal asymmetries that could be attributed to COD and thus physiological asymmetries, whereas 3 players (LCB, LW, and RW) had spatiotemporal asymmetries that might be caused by their position or by use of tactic. This type of asymmetry was named a tactical spatiotemporal asymmetry. Coaches with knowledge about spatiotemporal asymmetries can use these actively in their tactical approach using the players' asymmetries in synergy, using opponents' asymmetries or improving the existing postgame spatiotemporal analyzing tools.

#4 Capture of Time-Loss Overuse Soccer Injuries in the National Collegiate Athletic Association's Injury Surveillance System, 2005-2006 Through 2007-2008
Reference: J Athl Train. 2018 Feb 21. doi: 10.4085/1062-6050-191-16. [Epub ahead of print]
Authors: Roos K, Kucera K, Golightly Y, Myers JB, Rosamond W, Marshall SW
Summary:  Overuse injuries are reported to account for nearly 50% of sports injuries and, due to their progressive nature and the uncertainty regarding date of onset, are difficult to define and categorize. Comparing the capture rates of overuse injuries between injury-surveillance systems and medical records can clarify completeness and determinants of how overuse injuries are represented in injury-surveillance data. The objective was to estimate the capture rate of time-loss medical-attention overuse injuries in men's and women's soccer in the National Collegiate Athletic Association Injury Surveillance System (NCAA ISS) compared with medical records maintained by certified athletic trainers and assess the differences in completeness of capture and factors contributing to those differences. Fifteen NCAA institutions provided NCAA ISS and medical record data from men's and women's soccer programs from 2005-2006 through 2007-2008. National Collegiate Athletic Association men's and women's soccer players participated in this study.  Time-loss medical-attention overuse injuries were defined as injuries with an overuse mechanism of injury in the NCAA ISS or medical records. Capture rates were calculated as the proportion of total overuse injuries classified as having overuse mechanisms in the NCAA ISS and the NCAA ISS and medical records combined. The NCAA ISS captured 63.7% of the total estimated overuse mechanisms of injury in men's and women's soccer players. The estimated proportion of overuse injury mechanisms captured by both the NCAA ISS and medical records was 37.1%. The NCAA ISS captured more overuse injury mechanisms in men's soccer than in women's soccer (79.2% versus 45.0%, χ2 = 9.60; P = .002) athletes.  From 2005-2006 through 2007-2008, the NCAA ISS captured only two thirds of time-loss medical-attention overuse mechanisms of injury in men's and women's soccer players. Future researchers should consider supplementing injury-surveillance data with a clinical record review to capture the burden of these injuries.

#5 Is the technical performance of young soccer players influenced by hormonal status, sexual maturity, anthropometric profile, and physical performance?
Reference: Biol Sport. 2017 Dec;34(4):305-311. doi: 10.5114/biolsport.2017.69817. Epub 2017 Sep 20.
Authors: Moreira A, Massa M, Thiengo CR, Rodrigues Lopes RA, Lima MR, Vaeyens R, Barbosa WP, Aoki MS
Summary: The aim of this study was to examine the influence of hormonal status, anthropometric profile, sexual maturity level, and physical performance on the technical abilities of 40 young male soccer players during small-sided games (SSGs). Anthropometric profiling, saliva sampling, sexual maturity assessment (Tanner scale), and physical performance tests (Yo-Yo and vertical jumps) were conducted two weeks prior to the SSGs. Salivary testosterone was determined by the enzyme-linked immunosorbent assay method. Technical performance was determined by the frequency of actions during SSGs. Principal component analyses identified four technical actions of importance: total number of passes, effectiveness, goal attempts, and total tackles. A multivariate canonical correlation analysis was then employed to verify the prediction of a multiple dependent variables set (composed of four technical actions) from an independent set of variables, composed of testosterone concentration, stage of pubic hair and genitalia development, vertical jumps and Yo-Yo performance. A moderate-to-large relationship between the technical performance set and the independent set was observed. The canonical correlation was 0.75 with a canonical R2 of 0.45. The highest structure coefficient in the technical performance set was observed for tackles (0.77), while testosterone presented the highest structure coefficient (0.75) for the variables of the independent set. The current data suggest that the selected independent set of variables might be useful in predicting SSG performance in young soccer players. Coaches should be aware that physical development plays a key role in technical performance to avoid decision-making mistakes during the selection of young players.

#5 Expression analysis of selected classes of circulating exosomal miRNAs in soccer players as an indicator of adaptation to physical activity
Reference: Biol Sport. 2017 Dec;34(4):331-338. doi: 10.5114/biolsport.2017.69820. Epub 2017 Sep 1.
Authors: Domanska-Senderowska D, Jastrzębski Z, Kiszalkiewicz J, Brzezianski M, Pastuszak-Lewandoska D, Radziminki L, Brzezianska-Lasota E, Jegier A
Summary: Recently studies have shown that, depending on the type of training and its duration, the expression levels of selected circulating myomiRNAs (c-miR-27a,b, c-miR-29a,b,c, c-miR-133a) differ and correlate with the physiological indicators of adaptation to physical activity. To analyse the expression of selected classes of miRNAs in soccer players during different periods of their training cycle. The study involved 22 soccer players aged 17-18 years. The multi-stage 20-m shuttle run test was used to estimate VO2 max among the soccer players. Samples serum were collected at baseline (time point I), after one week (time point II), and after 2 months of training (time point III). The analysis of the relative quantification (RQ) level of three exosomal myomiRNAs, c-miRNA-27b, c-miR-29a, and c-miR-133, was performed by quantitative polymerase chain reaction (qPCR) at three time points - before the training, after 1 week of training and after the completion of two months of competition season training. The expression analysis showed low expression levels (according to references) of all evaluated myomiRNAs before the training cycle. Analysis performed after a week of the training cycle and after completion of the entire training cycle showed elevated expression of all tested myomiRNAs. Statistical analysis revealed significant differences between the first and the second time point in soccer players for c-miR-27b and c-miR-29a; between the first and the third time point for c-miR-27b and c-miR-29a; and between the second and the third time point for c-miR-27b. Statistical analysis showed a positive correlation between the levels of c-miR-29a and VO2 max. Two months of training affected the expression of c-miR-27b and miR-29a in soccer players. The increased expression of c-miR-27b and c-miR-29 with training could indicate their probable role in the adaptation process that takes place in the muscular system. Possibly, the expression of c-miR-29a will be found to be involved in cardiorespiratory fitness in future research.

#6 The Impact of Soccer Match Play on the Muscle Damage Response in Youth Female Athletes
Reference: Int J Sports Med. 2018 Feb 23. doi: 10.1055/s-0044-101147. [Epub ahead of print]
Authors: Hughes JD, Denton K, S Lloyd R, Oliver JL, De Ste Croix M
Summary: Post-match assessment of creatine kinase (CK) activity and delayed-onset muscle soreness (DOMS) are common markers of exercise-induced muscle damage and recovery status in soccer players. These responses have not been examined in youth female players. This study examined the effect of competitive match play on CK activity and DOMS in elite youth players. Thirty-four elite female players, divided into three chronological age groups (U13, n=11; U15, n=10; U17 n=12). Players completed baseline testing for CK and DOMS that was repeated immediately (for DOMS), 80, 128 and 168 h post-competitive match play for CK. Significant time effects were reported for CK (P=0.006) and DOMS (P<0.01). Significant differences between baseline and 168 h post-match were reported for CK (P<0.01), with significant group differences between the U13 and U17 groups for CK (P<0.01). All parameters returned to baseline in U17s at 168 h, but increased CK was evident for U13s and U15s at 168 h. In conclusion, seven days may be insufficient for biochemical recovery in youth female athletes. Therefore, monitoring strategies to assess muscle damage between training and match play should be considered to track recovery and potentially reduce muscular injury risk.

#7 Age-Related Differences in Functional Hamstring/Quadriceps Ratio Following Soccer Exercise in Female Youth Players: An Injury Risk Factor
Reference: Pediatr Exerc Sci. 2018 Feb 27:1-7. doi: 10.1123/pes.2017-0034. [Epub ahead of print]
Authors: De Ste Croix M, Priestley A, Lloyd R, Oliver J
Summary: Fatigue negatively alters dynamic knee control, and the functional hamstring/quadriceps ratio (H/QFUNC) plays an important role in stabilizing the joint. The aim of this study was to investigate the influence of soccer-specific exercise on H/QFUNC in under (U) 13-, U15-, and U17-year-old female soccer players. A total of 36 female players performed concentric and eccentric actions of the hamstrings at 60°, 120°, and 180°/s before and after an age group-specific field-based soccer protocol. H/QFUNC was determined in the first 30° of knee flexion. Significant angle × velocity (P = .001) and time × angle (P = .033) interaction effects were found indicating a lower H/QFUNC with increased movement velocity at 0°-10° as opposed to greater knee flexion angles. Fatigue-related effects were only evident near full knee extension. Probabilistic inferences indicated that changes in H/QFUNC were generally unclear in U13s, likely detrimental in U15s, and very likely beneficial in U17s. Altered muscular control following soccer-specific exercise is age dependent with players' 1-year post-peak height velocity at greatest risk of injury. Injury prevention and screening need to be age and maturation appropriate, should consider the effects of fatigue, and include movements near full extension.

#8 Discovery of a Sweet Spot on the Foot with a Smart Wearable Soccer Boot Sensor That Maximizes the Chances of Scoring a Curved Kick in Soccer
Reference: Front Physiol. 2018 Feb 13;9:63. doi: 10.3389/fphys.2018.00063. eCollection 2018.
Authors: Fuss FK, Duking P, Weizman Y
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Summary: This paper provides the evidence of a sweet spot on the boot/foot as well as the method for detecting it with a wearable pressure sensitive device. This study confirmed the hypothesized existence of sweet and dead spots on a soccer boot or foot when kicking a ball. For a stationary curved kick, kicking the ball at the sweet spot maximized the probability of scoring a goal (58-86%), whereas having the impact point at the dead zone minimized the probability (11-22%). The sweet spot was found based on hypothesized favorable parameter ranges (center of pressure in x/y-directions and/or peak impact force) and the dead zone based on hypothesized unfavorable parameter ranges. The sweet spot was rather concentrated, independent of which parameter combination was used (two- or three-parameter combination), whereas the dead zone, located 21 mm from the sweet spot, was more widespread.

#9 Anterior cruciate ligament ruptures in German elite soccer players: Epidemiology, mechanisms, and return to play
Reference: Knee. 2018 Feb 22. pii: S0968-0160(18)30031-0. doi: 10.1016/j.knee.2018.01.010. [Epub ahead of print]
Authors: Schiffner E, Latz D, Grassmann JP, Schek A, Thelen S, Windolf J, Schneppendahl J, Jungbluth P
Summary: Anterior cruciate ligament ruptures (ACLRs) are severe sports-related injuries with significant consequences for affected players and teams. This study aims to identify the epidemiology and injury-related lay-off after ACLR in professional male soccer players from the first-division German Bundesliga. Exposure times and incidence of anterior cruciate ligament ruptures were collected during 7.5 consecutive seasons using two media-based registers. A total of 72 total ACLRs were registered in 66 different players with an incidence of 0.040 per 1000h of exposure (95% CI 0.009-0.12). On average there were 9.6 ACLRs per season and 0.53 per team and season. The mean age of players affected was 24 (standard deviation±3.6) years. The number of ACLRs recorded per season fluctuated during the period observed. Goalkeepers are significantly (P<0.05) less prone to suffer an ACLR compared to outfield players. Understanding ACLR loading mechanisms, knowing risk factors for the injury and mean off time after ACLR are essential information for the coach, the medical staff, the elite soccer players, the insurance and team managers. Our results are in accordance with reports based on information from medical team staff. Therefore, our analysis of ACLR based on media sources may serve as an alternative for injury reports in elite soccer. The information of this study may be helpful for the medical staff taking care of professional soccer players and for orthopedic surgeons performing ACL reconstructions in this patient population.

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