Latest research in football - week 51 - 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 Pre-Practice Hydration Status in Soccer (Football) Players in a Cool Environment
Reference: Medicina (Kaunas). 2018 Dec 5;54(6). pii: E102. doi: 10.3390/medicina54060102.
Authors: Kiitam U, Voitkevica L, Timpmann S, Pontaga I, Ereline J, Unt E, Ööpik V
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Summary: Only a few studies have reported the pre-practice hydration status in soccer players (SPs) who train in a cool climate. The primary purpose of this study was to examine the hydration status of male semiprofessional SPs immediately before their regular training session in winter. The secondary purpose was to compare the urinary indices of the hydration status of Estonian and Latvian SPs. Pre-training urine samples were collected from 40 Estonian (age 22.1 ± 3.4 years, soccer training experience 13.7 ± 3.9 years) and 41 Latvian (age 20.8 ± 3.4 years, soccer training experience 13.3 ± 3.0 years) SPs and analyzed for urine specific gravity (USG). The average outdoor temperature during the sample collection period (January⁻March) was between -5.1 °C and 0.2 °C (Estonia) and -1.9 °C and -5.0 °C (Latvia). Results: The average pre-training USG of Estonian and Latvian SPs did not differ (P = 0.464). Pooling the data of Estonian and Latvian SPs yielded a mean USG value of 1.021 ± 0.007. Hypohydration (defined as a USG ≥ 1.020) was evident altogether in fifty SPs (61.7%) and one of them had a USG value greater than 1.030. Estonian and Latvian SPs do not differ in respect of USG and the prevalence of pre-training hypohydration is high in this athletic cohort. These findings suggest that SPs as well as their coaches, athletic trainers, and sports physicians should be better educated to recognize the importance of maintaining euhydration during the daily training routine in wintertime and to apply appropriate measures to avoid hypohydration.

#2 Injury Risk and Injury Burden Are Related to Age Group and Peak Height Velocity Among Talented Male Youth Soccer Players
Reference: Orthop J Sports Med. 2018 Dec 11;6(12):2325967118811042. doi: 10.1177/2325967118811042. eCollection 2018 Dec.
Authors: Bult HJ, Barendrecht M, Tak IJR
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Summary: The relationship between injury risk (IR) in age groups and periods around peak height velocity (PHV) remains unclear. PHV is defined as the moment of the largest increase in body height. The purpose was to investigate injury risk and injury burden as functions of growth velocity (periods around PHV) and chronological age groupings (under 12 years [U12] to U19) in talented youth male soccer players. Cohort study; Level of evidence, 2. A total of 170 players from the youth academy of a Dutch soccer club (highest professional league: Eredivisie) were observed for 1 to 3 seasons. Injuries, exposure, PHV age, and chronological age were registered. The injury incidence density (IID) and injury burden per 1000 hours of soccer participation, with 95% CIs, were calculated for 5 PHV periods and 7 age groups. These were compared with the overall cohort results using incidence ratios (IRs) and burden ratios (BRs) with 95% CIs. The mean age at PHV was 14.4 ± 0.65 years (range, 12.8-16.5 years). The mean IID for the total cohort was 8.34 injuries per 1000 hours (95% CI, 7.71-9.02). Compared with the overall mean, a significantly higher IID was found for PHV period 4+5 (IR, 1.31 [95% CI, 1.00-1.71]; P = .049) and for the U15 group (IR, 1.49 [95% CI, 1.24-1.79]; P < .001). The overall injury burden was 58.37 injury days per 1000 hours (95% CI, 56.66-60.13). In PHV period 4+5, the injury burden was significantly higher (BR, 1.53 [95% CI, 1.39-1.68]; P < .001) when compared with the overall mean. Also, compared with the overall mean, the injury burden was higher in the U16 (BR, 1.48 [95% CI, 1.39-1.58]; P < .001), U15 (BR, 1.28 [95% CI, 1.19-1.38]; P < .001), and U17 groups (BR, 1.21 [95% CI, 1.13-1.31]; P < .001). Talented young soccer players were more prone to injuries during the 6 months after PHV (31% above overall mean) as well as in the U15 group (49% above overall mean). Based on the higher injury burden in the U16 (48%), U15 (28%), and U17 (21%) groups, we suggest that research on injury risk factors and preventive measures should primarily target these age groups. Additional interventions based on PHV may be of limited value from a screening perspective. Further research is needed on the interaction between age groups and PHV periods.

#3 Anthropometry, Physical and Movement Features, and Repeated-sprint Ability in Soccer Players
Reference: Int J Sports Med. 2018 Dec 17. doi: 10.1055/a-0781-2473. [Epub ahead of print]
Authors: Campa F, Semprini G, Júdice PB, Messina G, Toselli S
Summary: This study aimed to evaluate the associations of anthropometry, functional movement patterns (FMP) and physical performance characteristics with repeated-sprint ability (RSA) in male youth soccer players. Thirty six athletes (ages 16.6±0.5 years, BMI 22.0±1.3 kg/m2) completed the RSA test and other physical tests including countermovement jump with (CMJA) and without the help of arms (CMJ), 10-m and 20-m straight-line sprints, Yo-Yo Intermittent Recovery Test Level 1 (Yo-Yo), and functional movement screen (FMS). In addition, a battery of anthropometric variables was measured. RSA performance components such as best time (BT), mean time (MT) and sprint decrement were calculated. Results showed that measures of physical performance derived from horizontal plane in 10-m and 20-m sprints, were more strongly associated (p<0.01) with RSA performance than those obtained with CMJ or CMJA (p<0.05). High correlations (p<0.01) were found between MT, BT and Yo-Yo distance (r=-0.79, r=-0.67, respectively), as well as with FMS scores (r=-0.68, r=-0.58, respectively). Anthropometric measures, such as fat mass, upper fat area, thigh fat area, calf muscle area, and endomorphy were associated with RSA components (p<0.05). Predictors for the RSA performance identified in the stepwise multivariate analysis included Yo-Yo distance, time in sprints, FMP, and calf muscle area.

#4 Do male and female soccer players differ in helping? A study on prosocial behavior among young players
Reference: PLoS One. 2018 Dec 17;13(12):e0209168. doi: 10.1371/journal.pone.0209168. eCollection 2018.
Authors: Van Lange PAM, Manesi Z, Meershoek RWJ, Yuan M, Dong M, Van Doesum NJ
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Summary: Acting prosocially can be quite challenging in one of the most salient intergroup contexts in contemporary society: Soccer. When winning is the ultimate goal, balancing self-interest with helping a fellow player in distress can be a tough decision; yet it happens. To date, we know little about what motivates soccer players to offer such help in the heat of the game. We propose that sex and what is at stake will matter in such prosocial dilemma situations. A pilot study (N = 107) indicated that female players may be more likely to help than male players, but this difference was only observed when the players are close to scoring position rather than far away from the goal (midfield). The main study (N = 366) finds that young soccer players show elevated inclinations to help in low-stakes situations, for example when their team is winning or when the outcome of the game seems pretty much decided. Contrariwise, helping intentions decline in high-stakes situations, for example when one's own team is losing, when one is close to a scoring position in the offense (rather than at the midfield), or when the outcome of the game is still uncertain. Furthermore, female players show somewhat greater inclinations to help than their male counterparts. The current data point at some differences for male and female soccer players, albeit small in effect size. In contrast, we conclude that especially quick cost-benefit judgments regarding the stakes can play a major role in decisions to help or not to help another player on the soccer field.

#5 Internal and External Loads in Training Week Before the Competition in U19 High-Level Soccer Players
Reference: J Strength Cond Res. 2018 Dec 14. doi: 10.1519/JSC.0000000000002975. [Epub ahead of print]
Authors: Martín-López Á, Mendes RS, Castillo-Rodríguez A
Summary: Nowadays, the information about the load in training sessions (TRs) and the relationship of these TRs with official competition are necessary to gain the sport success in soccer. The aim of this study was to quantify the different loads in TRs according to days before the competition (P-4, P-2, and P-1) on soccer players U19 based on their playing position and their sport success. Twenty-four male Spanish high-level players (age: 16.5 ± 0.5 years; height: 1.69 ± 0.04 m; and body mass: 63.0 ± 6.3 kg) participated in the study. They were grouped according to their playing position: external defenders, internal defenders (ID), external midfielders, internal midfielders (IM), and forwards (FO). To conduct the study, global positioning system technology was used, and a 1-way analysis of variance and Pearson correlation were performed. The main results revealed that the highest physical and physiological responses in the TRs were shown by ID, IM, and players without sport success (p < 0.05), and during P-2. In addition, sport success is predicted by the mean heart rate (R = 0.33; p < 0.001). As conclusion, players covering central positions in the playing field performed higher physical and physiological demands than players covering exterior or forward positions. Furthermore, physical and physiological responses during the TRs P-2 may be similar to the responses produced in competition match and are notably different depending on the sport success of the soccer player.

#6 The team's influence on physical and technical demands of elite goalkeepers in LaLiga: a longitudinal study in professional soccer
Reference: Res Sports Med. 2018 Dec 16:1-15. doi: 10.1080/15438627.2018.1555755. [Epub ahead of print]
Authors: Serrano C, Paredes-Hernández V, Sánchez-Sánchez J, Gallardo-Pérez J, Da Silva R, Porcel D, Colino E, García-Unanue J, Gallardo L
Summary: This study examined physical and technical demands and the influence of the team's level on elite goalkeepers' performance during six consecutive seasons in Spanish Professional Soccer League. The goalkeepers' performance data were obtained by analyzing a total of 3,874 matches using a multiple-camera computerized tracking system. The physical and technical match variables registered were: distance traveled; distance Sprinted and the number of sprints; total number of passes; successful passes; pass percentage; recovered balls; lost balls; ratio lost balls: recovered balls, and number of saves. The results showed that the number of saves made has shown a significant reduction (p < 0.001). When comparing between the teams' level, the goalkeepers of the worst classified teams showed a greater distance traveled by sprint (+3.72 m, IC95%: 1.00-6.44, ES: 0.41, p = 0.008). In conclusion, the results the influence of the team's level on the technical and physical parameters of the goalkeepers during the last six seasons

#7 Intra-seasonal variation of injury patterns among German Bundesliga soccer players
Reference: J Sci Med Sport. 2018 Dec 6. pii: S1440-2440(18)30449-3. doi: 10.1016/j.jsams.2018.12.001. [Epub ahead of print]
Authors: Leventer L, Eek F, Lames M
Summary: High fluctuations in injury-risk during the playing season in soccer have been reported. As seasons are structured in periods with homogenous loads and intensities, we investigated injury-risk over season periods, contrarily to previous studies adopting a month-based approach. Incidence-rate ratios (IRRs) for match and training injuries were compared across six consecutive seasons of German Bundesliga, divided into six periods each: Pre-season (PS), winter-break (WB), quarter 1-4: (Q1-Q4). Significant variations in injury-risk were observed for match and training injuries. IRRs in matches was 1.30 (95% CI: 1.11-1.53) times higher in Q3 and 1.53 (95% CI: 1.31-1.78) higher in Q4 compared to Q1. For training injuries, IRR peaked in Q1 and Q3 followed by a marked decrease in each subsequent quarter. Compared to Q4, IRR was 1.62 (95% CI: 1.40-1.86) times higher during Q3 and 1.78 (95% CI: 1.53-2.07) times higher in Q1. IRR was significantly higher in the competitive season compared to pre-season across match (IRR: 2.00, 95% CI: 1.30-3.00) and training (IRR: 1.27, 95% CI: 1.11-1.43) injuries. The increased match IRRs later during the season indicate that, in practice, coaches should consider putting even more emphasis on recovery in the last part of the season. Moreover, training injuries seem to indicate a carry-over effect. Further studies need to investigate how training during preparatory phases can be implemented in a way that prevents injuries during the competitive season.

#8 Changes in injury incidences and causes in Swiss amateur soccer between the years 2004 and 2015
Reference: Swiss Med Wkly. 2018 Dec 15;148:w14690. doi: smw.2018.14690. eCollection 2018 Dec 3.
Authors: Gebert A, Gerber M, Pühse U, Faude O, Stamm H, Lamprecht M
Summary: Injury prevention in amateur soccer has been promoted in recent years, but only a few studies have addressed long-term changes in injury incidence in amateur soccer. However, better knowledge of changes with respect to injury incidences and causes could make an important contribution to improving prevention strategies. The aim of this study was to investigate the long-term development of injury incidence in Swiss amateur soccer with respect to level of play, injury causes and injury characteristics. A representative sample of about 1000 Swiss amateur soccer coaches was interviewed by telephone in 2004, 2008 and 2015. They were asked to recall their last game and to report details on all injuries. For every injury, the coaches were asked to remember injury characteristics and causes. The same procedure was repeated for all games that took place during the previous 4 weeks. Additionally, all training injuries in the previous 4 weeks were recorded in detail. The incidence of game injuries decreased between the years 2004 and 2008 from 15.1 (95% confidence interval [CI] 14.2&ndash;16.0) to 13.3 (95% CI 12.4&ndash;14.2) injuries per 1000 hours, and increased between the years 2008 and 2015 to 16.5 (95% CI 15.5&ndash;17.4) injuries per 1000 hours. Between 2004 and 2015, the rate of contact injuries during games increased by 19.1%. The incidence of foul play injuries in games increased by 25.5% between 2008 and 2015. The rise in total training injury incidence between the years 2004 (2.4, 95% CI 2.2&ndash;2.7) and 2015 (2.9, 95% CI 2.6&ndash;3.1) was caused by a 22.2% higher rate of noncontact injuries. During the same period, game and training injury incidences increased across all amateur soccer leagues without exception, but these changes did not reach statistical significance. In 2015, the incidence of injuries leading to medical attention was higher than in 2004 (game 20.0%, training 37.5%). There is evidence that injury incidence in Swiss amateur soccer has increased in past years. &nbsp.

#9 The Effect of Block Versus Daily Undulating Periodization on Strength and Performance in Adolescent Football Players
Reference: Int J Sports Physiol Perform. 2018 Dec 20:1-25. doi: 10.1123/ijspp.2018-0609. [Epub ahead of print]
Authors: Gavanda S, Geisler S, Quittmann OJ, Schiffer T
Summary: Muscle mass, strength and power are important factors for performance. To improve these characteristics, periodized resistance training is used. However, there is no consensus regarding the most effective periodization model. Therefore the purpose of this study was to compare the effects of block (BLOCK) versus daily undulating periodization (DUP) on body composition, hypertrophy, strength, performance and power in adolescent American football players. Forty-seven subjects participated in this study (M±SD age = 17±0.8 years; strength training experience = 0.93±0.99 years). Pre- and post-measurements consisted of body mass (BM), fat mass (FMkg), body fat percentage (relFM), fat-free mass (FFM), muscle mass (MM) and muscle thickness of the M. vastus lateralis (VL), M. rectus femoris (RF) and M. triceps brachii (TB), one repetition maximum (1-RM) back squat (BS) and bench press (BP), countermovement jump (CMJ), estimated peak power from vertical jump performance (Wpeak), medicine ball put (MBP) and 40 yd sprint. Subjects were randomly assigned in either the BLOCK or DUP group prior to the 12 week intervention period consisting of 3 full-body sessions per week. Both groups displayed significantly higher BM (p<0.001), relFM (p=0.005), FFM (p<0.001), MM (p<0.001), RF (p<0.001), VL (p<0.001), TB (p<0.001), BS (p<0.001), BP (p<0.001), CMJ (p<0.001), Wpeak (p<0.001) and significant lower sprint times (p<0.001) following twelve weeks of resistance training with no difference between groups. Resistance training was effective to increase muscle mass, strength, power and performance in adolescent athletes. BLOCK and DUP affect anthropometric measures and physical performance equally.

#10 Transfer market activities and sportive performance in European first football leagues: A dynamic network approach
Reference: PLoS One. 2018 Dec 19;13(12):e0209362. doi: 10.1371/journal.pone.0209362. eCollection 2018.
Authors: Matesanz D, Holzmayer F, Torgler B, Schmidt SL, Ortega GJ
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Summary: Professional football is a globalized game in which players are the most valuable assets for clubs. In this study, we explore the evolution of the football players' transfer network among 21 European first leagues between the seasons 1996/1997 and 2015/2016. From a topological point of view, we show that this network achieved an upper limit expansion around season 2007/2008, thereafter becoming more connected and dense. Using a machine learning approach based on Self-Organizing Maps and Principal Component Analysis we confirm that European competitions, such as the UEFA Champions League or UEFA Europa League, are indeed a "money game" where the clubs with the highest transfer spending achieve better sportive performance. Some clubs' transfer market activities also affect domestic performance. We conclude from our findings that the relationship between transfer spending and domestic or international sportive performance might lead to substantial inequality between clubs and leagues, while potentially creating a virtuous (vicious) circle in which these variables reinforce (weaken) each other.

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