Latest research in football - week 24 - 2019

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 Assessment of a Nutrition Intervention on the Nutrition Knowledge, of Adolescent Soccer Academy Players
Reference: Curr Dev Nutr. 2019 Jun 13;3(Suppl 1). pii: nzz050.P16-044-19. doi: 10.1093/cdn/nzz050.P16-044-19. eCollection 2019 Jun.
Authors: Ray S, Mounce CD, Gonzalez-Rodenas J, Prieto MS, Brannan R
Summary: National surveys found that adolescents in America often fail to meet dietary recommendations probably due to lack of nutrition knowledge, giving rise to chronic diseases such as obesity, coronary heart diseases and type 2 diabetes. Knowledge about sports nutrition is considered essential for adolescent athletes to have healthy eating habits. It would help maximize their performance. The aim of the study was to assess the nutrition knowledge of adolescent soccer players pre and post a nutrition education intervention. A study was conducted on the youth academy level soccer players (n = 21) from three age groups (U19, U17, U15), to determine their nutrition knowledge using a validated Nutrition Knowledge Questionnaire. From the completed questionnaire, on factors like energy refueling, hydration, supplements and protein, a knowledge score was calculated for each athlete ranging from 0 (0%) to 16 (100%). The players participated in a nutrition education intervention for 5 months, consisting of monthly nutritional education newsletters, electronic handouts and one-hour nutrition lesson in the form of jeopardy game and nutrition education workshop for the players and their parents. Following the intervention, they filled out the same questionnaire again. From their responses, pre- and post-intervention, we found that at baseline, nutrition knowledge was highest in the U19 team as 44% of the responses were correct, lesser for the U17 team (25%) and least for the U15 team (6%). However, the intervention only produced a 6% increase in nutrition knowledge in the U19 while the intervention produced a 19% increase in the U17 team and a 44% increase in the U15 team. There was significant improvement in the category under supplements which asked whether it was better to get vitamins and minerals from supplements than from foods (P = 0.002). There was no significant difference in improvement of protein knowledge after the intervention in any group. The study shows that the nutrition education intervention was most effective for the younger players. Overall, more nutrition education, especially in the area of proteins, would be required for these players to increase their nutrition knowledge so that they know the type of food they should select and understand the importance of healthy eating.

#2 Evolution of technical activity in various playing positions, in relation to match outcomes in professional soccer
Reference: Biol Sport. 2019 Jun;36(2):181-189. doi: 10.5114/biolsport.2019.83958. Epub 2019 Apr 25.
Authors: Konefał M, Chmura P, Zając T, Chmura J, Kowalczuk E, Andrzejewski M
Summary: The study presented below aimed to examine the position-specific evolution of technical activity among soccer players and how it is related to match outcomes over three consecutive domestic seasons in Germany's Bundesliga. The research was based on a sample of 13,032 individual match observations of 556 soccer players during the 2014/2015, 2015/2016 and 2016/2017 seasons. These players were classified into five positional roles: central defenders (CD), full-backs (FB), central midfielders (CM), wide midfielders (WM) and forwards (F). The activity of the players was analysed using the Impire AG motion analysis system. Our study indicates that over the course of the three seasons: 1) the total numbers of shots by CMs decreased in the case of won or drawn matches; 2) the number of passes by CD players increased in matches won, and by CM and WM players in matches won, drawn and lost, whereas percentage pass accuracy increased at the CM position in won and drawn matches; 3) players at each position engaged in a substantially smaller number of duels, no matter what the match outcome, while the percentage of encounters won in subsequent seasons decreased among CD, and increased among WM in matches won and at F positions in both won and drawn matches. This research clearly shows that the evolution of technique among professional soccer players is heading in the direction of increased accuracy, with a simultaneous stabilisation of, or even a decline in, the number of activities engaged in.

#3 Influence of warm-up duration on perceived exertion and subsequent physical performance of soccer players
Reference: Biol Sport. 2019 Jun;36(2):125-131. doi: 10.5114/biolsport.2019.81114. Epub 2019 Jan 11.
Authors: Yanci J, Iturri J, Castillo D, Pardeiro M, Nakamura FY
Summary: The aim of this study was to analyse the effects of three warm-up protocols with different durations in semiprofessional soccer players. Fifteen semi-professional soccer players performed three warm-up protocols (Wup25min: 25 min, Wup15min: 15 min and Wup8min: 8 min duration) on three different days. Before (pre-test) and after (post-test) each warm-up protocol, the players' physical performance (sprint, vertical jump and change of direction) was evaluated and all the players were asked to respond to the subjective scale of readiness to play a match. Also, after completing each warm-up protocol, all players responded to the rating of perceived exertion (RPE) scale. Although all protocols significantly improved the feeling of players being prepared to play the game (p<0.05 or p<0.01), after performing the Wup25min protocol the players performed worse in the 10 m sprint (p<0.01) and in the 20 m sprint (p<0.05). However, the Wup8min protocol significantly improved performance in both the 10 m sprint (p<0.05) and the 20 m sprint (p<0.05). In addition, with the Wup25min protocol players stated a higher perceived exertion (RPE) (p < 0.05) than in the Wup15min and Wup8min protocols. The Wup8min protocol was the only one that improved the acceleration ability of the soccer players in this study.

#4 Sprint force-velocity profiles in soccer players: impact of sex and playing level
Reference: Sports Biomech. 2019 Jun 21:1-11. doi: 10.1080/14763141.2019.1618900. [Epub ahead of print]
Authors: Devismes M, Aeles J, Philips J, Vanwanseele B
Summary: This study aimed to assess potential differences in force-velocity (Fv) profiles in both male and female soccer players of different playing levels. One hundred sixty three soccer players (63 women and 100 men) competing from the Regional to the National Belgian league were recruited. The participants performed two maximal 60-m sprints monitored via a 312 Hz laser. For each participant, the theoretical maximal force (F0) and velocity (v0), maximal power (Pmax), maximal ratio of force (RF) and the slope of the Fv profile (Sfv) were computed. Male players in the highest competition level showed higher values for all the Fv variables compared to lower level groups (Effect size range: 1.01-1.97). Higher Pmax and v0 were observed in the female players of highest competition level compared to all other groups (ES range: 1.09-1.48). Female players showed more negative Sfv than male players (ES = 1.11), which suggests that male players' Fv profile is more velocity-oriented compared to female players. This study shows that the determinants of sprint performance increase with soccer playing level in both men and women, but that the contribution of each variable varies with sex.

#5 Vague Posterior Knee Discomfort in a Soccer Player: A Case Report
Reference: Am J Phys Med Rehabil. 2019 Jun 17. doi: 10.1097/PHM.0000000000001248. [Epub ahead of print]
Authors: Schroeder A, Onishi K
Summary: A 24-year-old male soccer player presented with a 7-year history of left posterior knee "looseness." Evaluation 7 years ago, at the time of initial injury, revealed atraumatic ACL and PCL sprains. On re-presentation, the patient described the pain as a constant, dull ache, 3/10, but his biggest complaint was this feeling of "instability" and "looseness" where his knee would "buckle" 3-4 times a week. Physical exam was positive for grade 1 posterior drawer and grade 1 posterior sag signs. Reverse KT-1000 testing showed a 3 mm side-to-side difference. Sonographic evaluation confirmed MRI findings of PCL laxity and buckling and a small cystic lesion abutting the posteromedial margin of the distal 1/3 of the PCL. After a trial of physical therapy, the patient elected to undergo experimental injection of dextrose hyperosmolar solution. This resulted in resolution of the cyst and reverse KT-1000 measurements improved to a side-to-side difference of 1 mm. The patient's subjective feeling of "looseness" and "instability" resolved by 7 weeks.

#6 Physical performance metrics in elite soccer: do power and acceleration metrics provide insight into positional demands and match-related fatigue in the 4-3-3 system?
Reference: J Sports Med Phys Fitness. 2019 Jun 19. doi: 10.23736/S0022-4707.19.09772-X. [Epub ahead of print]
Authors: Filetti C, Ruscello B, Ascenzi G, Di Mascio M, D'ottavio S
Summary: The aim of this study was to quantify power and acceleration metrics in elite soccer matches to gain an insight into positional demands and match-related fatigue patterns. Elite players (n = 212, observations = 522) were analysed during 50 matches of the Italian Serie A using a semi-automatic tracking system (K-Sport, Montelabbate, PU, Italy - Stats, Leeds, UK) during the 2015/16 season. A principal component analysis (PCA) was performed to find the latent variables that better explain the huge amount of data collected; an ANOVA was performed to find differences among positional roles and a mixed factorial analysis of mixed data (FAMD) was carried out to investigate the patterns of fatigue over time. Power and Acceleration were defined as the latent variables out of the 19 investigated that provided most of the variance (90.39%); significant differences among roles were found (p<0.05; Effect Size (ES) as ω2>0.14) and significant patterns of fatigue (p<0.05) with a moderate to large ES were observed over time in some of the key performance indicators. The data demonstrate that there are implications for developing power and acceleration in training sessions and assessing these components during a game. With the introduction of 'live streaming' of GPS data, the movement patterns could be observed in real time, and interchanges could be made before the onset of fatigue and before evident reductions in performance might be observed.

#7 The Effect of a Four-Month Training Program on Body Fat and Pulmonary Parameters of Young Soccer Players
Reference: Iran J Public Health. 2019 Feb;48(2):353-354.
Authors: Sermaxhaj S
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#8 Relation of injuries and psychological symptoms in amateur soccer players
Reference: BMJ Open Sport Exerc Med. 2019 Apr 24;5(1):e000522. doi: 10.1136/bmjsem-2019-000522. eCollection 2019.
Authors: Jansen P, Lehmann J, Fellner B, Huppertz G, Loose O, Achenbach L, Krutsch W
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Summary: The first main goal of this study was to investigate the prevalence of depression and anxiety as well as self-compassion in a heterogeneous sample of male amateur soccer players. The second main goal of this study was the examination of the relationship between injuries and psychological factors in amateur soccer players. Players were recruited from German amateur soccer clubs of the fourth to seventh league. 419 soccer players with the mean age of 22.88 years participated in the psychological and the injury assessment at the beginning of the season and at the end, 9 months later. For the psychological assessment, depression and anxiety rate as well as self-compassion was analysed. Furthermore, the frequencies of injuries were registered. The results showed that players of the highest amateur league, the fourth league in German soccer, showed significantly higher anxiety values than players from a lower league (p=0.013). There were no differences in depression values dependent on the league. Furthermore, players who suffered from an injury before the start of the season demonstrated higher anxiety values (p=0.027). This result was independent of the respective league. The results of this study demonstrate that even in higher amateur soccer the anxiety level of the players varies between soccer players of different leagues. Because an injury before the start of the season influenced the anxiety level, a psychological treatment during injury should be considered.

#9 Professional soccer player with an in-game ankle injury
Reference: Skeletal Radiol. 2019 Jun 16. doi: 10.1007/s00256-019-03253-6. [Epub ahead of print]
Authors: Iqbal A, McLoughlin E, Botchu R, James SL
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#10 Comparison of knee sonography and pressure pain threshold after anterior cruciate ligament reconstruction with quadriceps tendon versus hamstring tendon autografts in soccer players
Reference: Acta Orthop Traumatol Turc. 2019 Jun 12. pii: S1017-995X(18)30300-6. doi: 10.1016/j.aott.2019.04.012. [Epub ahead of print]
Authors: Martin-Alguacil JL, Arroyo-Morales M, Martin-Gómez JL, Lozano-Lozano M, Galiano-Castillo N, Cantarero-Villanueva I
Summary: The aim of this study was to compare the pressure pain threshold and muscle architecture after an anatomic single bundle reconstruction with quadriceps tendon and hamstring tendon autografts of the anterior cruciate ligament in competitive soccer players. We hypothesized that both procedures will obtain similar outcomes. Fifty-one participants were enrolled in this secondary analysis of a randomized controlled trial and were categorised into two groups: quadriceps tendon (QT) group (23 men and 3 women; mean age 18.7 ± 3.6; BMI 23.0 ± 2.2) or hamstring tendon (HT) group (16 men and 9 women; mean age 19.2 ± 3.6 BMI 23.5 ± 3.5). Both groups followed the same rehabilitation staged protocol. Pressure pain threshold (PPT), as a measure of perceived pain, was obtained in several points of quadriceps and hamstring muscles. Ultrasound imaging measurements were obtained in quadriceps tendon and knee cartilage thickness. Four measurements were taken in this study: baseline, 1, 3, 6, and 12 months after the anterior cruciate ligament (ACL) reconstruction. The analysis of PPT did not find significant differences in both groups × interaction time in the points evaluated: epicondyle (QT = 421.1 ± 184.1 vs HT = 384.7 ± 154.1 kPa), vastus lateralis (QT = 576.2 ± 221.3 vs HT = 560.1 ± 167.7 kPa), vastus medialis (QT = 544.7 ± 198.8 vs HT = 541.1.1 ± 181.77 kPa), patellar tendon (QT = 626.3 ± 221.1 vs HT = 665.0 ± 205.5 kPa), QT (QT = 651.1 ± 276.9 vs HT = 660.0 ± 195.2 kPa). (QT = 667.8 ± 284.7 vs HT = 648.2 ± 193.4 kPa) injured knee (all P > 0.05). The results of ultrasound imaging did not show significant differences in both groups × interaction time in the thickness of the QT (QT = 9.9 ± 2.4 vs HT = 9.4 ± 1.7 kPa) and patellar cartilage (QT = 3.2 ± 0.6 vs HT = 3.2 ± 0.4 kPa) (P > 0.05). A QT autograft produces similar results to a HT autograft in ACL reconstructions in terms of pressure pain threshold and ultrasound muscle architecture during the 1-year follow-up.

#11 Positional demands for various-sided games with goalkeepers according to the most demanding passages of match play in football
Reference: Biol Sport. 2019 Jun;36(2):171-180. doi: 10.5114/biolsport.2019.83507. Epub 2019 Mar 14.
Authors: Martin-Garcia A, Castellano J, Diaz AG, Cos F, Casamichana D
Summary: The main aim was to determine the differences between four training games and competitive matches (CM) according to position and compared to the most demanding passages (MDP) of competitive match play. Global Positioning System data were obtained from 21 football players belonging to the reserve squad of a Spanish La Liga club during the 2015/16 season. The training games were small-sided games (SSGs) with 5 and 6 and large-sided games with 9 and 10 outfield players per team. The players were categorized based on positional groups: full back (FB), central defender (CD), midfielder (MF), offensive midfielder (OMF), and forward (FW). The variables recorded were the distance covered (DIS), DIS at high speed (HSR; >19.8 km·h-1), DIS at sprint (SPR; >25.2 km·h-1), high metabolic load distance (HMLD; >25.5 W·kg-1) all in m·min-1, average metabolic power (AMP; W·kg-1) and number of high-intensity accelerations (ACC; >3 m·s-2) and decelerations (DEC; <-3 m·s-2), both in n·min-1. The MDP was analysed using a rolling average method for AMP as a criterion variable, where maximal values were calculated for time windows of 5 and 10 minutes of CM and after that compared with the training game formats. As the SSG format increases, all the rest of the variables increase and the number of cases with significant interposition differences also increases (effect size [ES]: DIS: 0.7-2.2; HSR: 0.7-2.1; SPR: 0.8-1.4; HMLD: 0.9-2.0; AMP: 0.8-1.9; ACC: 0.8-1.7; DEC: 0.5-1.7). The large-sided game 10v10 + 2 goalkeepers over-stimulates sprint values relative to MDP (all: 121.0% of MDP, ES=0.5-1.8). This study provides useful information for coaching staff on the heightened impact of different training game formats on physical load, considering positional differences in relation to the MDP of competitive match play.

#12 Relative pitch area plays an important role in movement pattern and intensity in recreational male football
Reference: Biol Sport. 2019 Jun;36(2):119-124. doi: 10.5114/biolsport.2019.81113. Epub 2019 Jan 11.
Authors: Pantelić S, Rađa A, Erceg M, Milanović Z, Trajković N, Stojanović E, Krustrup P, Randers MB
Summary: Recreational football has been shown to be an effective health-promoting activity, but it is still unclear how changes in game formats affect external and internal load. The aim of this study was therefore to evaluate the effect of area per player in recreational small-sided football games. Ten recreational active male football participants (mean±standard deviation, age: 20.1±1.1 years; height: 182.2±7.4 cm; body mass: 75.9±9.8 kg) completed two sessions comprising 2x20 min of 5v5 football with 80 and 60 m2 per player, during which heart rate (HR) and movement pattern were measured. In 80 m2, mean HR (167±9 vs. 160±10 b.p.m., P<0.001, ES=0.70) and peak HR (192±8 vs. 188±9 b.p.m., P=0.041, ES=0.50) were significantly higher than in 60 m2. Percentage playing time with HR >90%HRpeak was higher in 80 m2 than 60 m2 (45±14 vs. 29±16%, P=0.004, ES=1.07). Moreover, a higher number of sprints (8.0±4.8 vs. 3.0±1.3, P=0.014, ES=1.41) and a greater distance in the highest speed zones (>13, >16 and >20 km·h1) were covered in 80 m2 than 60 m2. Peak running speed was also higher in 80 m2 (24.3±1.7 vs. 22.3±1.4 km·h-1, P=0.011, ES=1.27), whereas no statistically significant differences were found in total distance covered, player load, or the acceleration-deceleration profiles. In conclusion, the internal and external loading was higher for recreationally active male football players when playing on a pitch with 80 m2 area per player compared to 60 m2.

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