Latest research in football - week 9 - 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 An assessment of the nutritional intake of soccer referees
Reference: J Int Soc Sports Nutr. 2015 Feb 7;12:8. doi: 10.1186/s12970-015-0068-9. eCollection 2015.
Authors: Martínez Reñón C, Collado PS
Summary: The present study aims to analyze the eating habits and attitudes of a group of soccer referees and linesmen. A nutritional study was undertaken of thirty-five soccer referees (aged between 18 and 50) refereeing at different levels, from the Spanish national third division down to the provincial second division. Through the use of a 3-day food diary and 24-hour recall, this study analyzed the intake and distribution of macro- and micro-nutrients and of dietary fiber consumed on different types of day (normal, training, and match days). There were no significant differences in calorie intake related to the three types of day (normal, training, and match days). This was true both of overall amounts (2371.1 kcal, 2479.7 kcal, and 2368.4 kcal, respectively) and amounts per unit of body weight (32.4 kcal/kg, 33.9 kcal/kg, and 32.4 kcal/kg, respectively). In respect of macro-nutrient intake, more specifically carbohydrates, the subjects consumed a diet with an insufficient amount of carbohydrates: 279 g, as against the 371 g (REC1) or 540 g (REC2) recommended according to physical activity levels. Slight increases were observed on game days, but were not statistically significant. Consideration of micro-nutrients showed that the quantities of three vitamins (B6, B12, and C) consumed were above the recommended amounts. However, this was not an issue, since the figures related to water-soluble vitamins. Finally, the amounts of minerals (Ca, Mg, and Fe) and fiber consumed were close to recommended values, regardless of the type of day being considered. This study found that the group of referees investigated consumed a diet that did not have sufficient calories from carbohydrates, in view of their occupation. This poor nutritional status might interfere with the development of their sporting performance and ultimately increase the risk of injury. This implies a need to design and implement a diet and to introduce educational programs on nutrition for these sportspeople.

#2 Cognitive representations and cognitive processing of team-specific tactics in soccer
Reference: PLoS One. 2015 Feb 25;10(2):e0118219. doi: 10.1371/journal.pone.0118219. eCollection 2015.
Authors: Lex H, Essig K, Knoblauch A, Schack T
Download link:
Summary: Two core elements for the coordination of different actions in sport are tactical information and knowledge about tactical situations. The current study describes two experiments to learn about the memory structure and the cognitive processing of tactical information. Experiment 1 investigated the storage and structuring of team-specific tactics in humans' long-term memory with regard to different expertise levels. Experiment 2 investigated tactical decision-making skills and the corresponding gaze behavior, in presenting participants the identical match situations in a reaction time task. The results showed that more experienced soccer players, in contrast to less experienced soccer players, possess a functionally organized cognitive representation of team-specific tactics in soccer. Moreover, the more experienced soccer players reacted faster in tactical decisions, because they needed less fixations of similar duration as compared to less experienced soccer players. Combined, these experiments offer evidence that a functionally organized memory structure leads to a reaction time and a perceptual advantage in tactical decision-making in soccer. The discussion emphasizes theoretical and applied implications of the current results of the study.

#3 Quantification and analysis of offensive situations in different formats of sided games in soccer
Reference: J Hum Kinet. 2014 Dec 30;44:193-201. doi: 10.2478/hukin-2014-0125. eCollection 2014.
Authors: Garcia JD, Román IR, Calleja-González J, Dellal A
Download link:
Summary: There has been a lot of research that enabled soccer to improve: its technique, tactics and strategy through analysis and training. Nevertheless, players' need to interact with each other turns any defending or attacking situation into complex solutions with a wide range of variables to be considered, in which the player is never isolated and must make the move that has the most positive impact on play. Fifty-four sided games played in three different formats (5v5, 7v7 and 9v9) and with two age groups (U9 and U14) were filmed at three soccer clubs in Spain in order to identify the most relevant attacking moves, from a technical and tactical perspective. This study used the observational method; it is descriptive and is applied through well-prepared systematic quantitative observation in a natural environment. A key part of the method involved viewing the match recordings and logging moves that had been categorised beforehand. Cohen's Kappa analysis showed that the results for the most representative variables presented a substantial degree of concordance (0.61-0.80). The results show that there were significant variations depending on the game format, and the following study will present a description and analysis of the aspects that had considerable influence on attacking moves in different formats of sided games (5v5, 7v7 and 9v9). The study also presents various practical applications for the area of training and analysing both youth and professional soccer.

#4 Analysis of speed performance in soccer by a playing position and a sports level using a laser system
Reference: J Hum Kinet. 2014 Dec 30;44:143-53. doi: 10.2478/hukin-2014-0120. eCollection 2014.
Authors: Ferro A, Villacieros J, Floría P, Graupera JL
Download link:
Summary: The purpose of this study was to determine the kinematic variables that identify the quality of velocity in soccer players at different competitive levels and playing positions. This study had two independent variables: 1) a competitive level (competitive and non-competitive players); and 2) a playing position, with four levels (central defenders, wide defenders/midfielders, central midfielders and forwards). Forty-two soccer players took part in a 30 m sprint-test, which was measured using a laser sensor-type 1 (LDM301-Jenoptik) at 2000 Hz. Absolute and relative times, average velocities and absolute and relative maximum velocities over 10 m sections were analyzed at 200 Hz with BioLaserSport(®). There were no significant differences in average velocity between competitive and non-competitive players; however, the former reached a greater maximum velocity in the 10-20 m section. Average velocity in the 0-10 m section identified specificity among playing positions in competitive players. The forwards were the fastest followed by the central midfielders, the wide defenders/midfielders and the central defenders. No differences were found among the non-competitive players. Average velocity over the 0-10 meter section may be an important indicator when assigning a playing position for competitive players. These results support the use of more accurate systems, such as a laser system, to identify soccer players' speed qualities (including maximum velocity) during short sprints.

#5 Short-term effects of complex training on agility with the ball, speed, efficiency of crossing and shooting in youth soccer players
Reference: J Hum Kinet. 2014 Nov 12;43:105-12. doi: 10.2478/hukin-2014-0095. eCollection 2014.
Authors: Cavaco B, Sousa N, Dos Reis VM, Garrido N, Saavedra F, Mendes R, Vilaça-Alves J
Summary: Complex training (CXT) is the result of a combination of strength and plyometric exercises in the same session. This method has recently been used in the preparation of athletes of different sports. The aim of the present study was to observe the acute effects of a CXT program of 6 weeks: i) on agility with the ball, sprinting and the efficiency of crossing and shooting in youth soccer players; ii) and the influence of the number of CXT sessions per week (one vs. two). Sixteen youth male soccer players were randomly divided into three groups: a group that performed one weekly CXT session (GCT1, n = 5, age: 13.80 ± 0.45 years); or a group that performed two weekly CXT sessions (GCT2, n = 5, age: 14.20 ± 0.45 years); or a control group that did not perform the CTX (n = 6, age: 14.20 ± 0.84 years). All groups maintained their regular soccer training sessions. No significant interactions were found between GCT1 and GCT2 in all variables. Significant statistical differences were identified (F = 1139, p = 0.02, μp (2) = 0531) in the pre-test versus post-test, for both experimental groups, in shot effectiveness. In conclusion, the CXT program proved to be an effective method in boosting abilities and motor skills associated with soccer among young athletes, particularly in increasing shot effectiveness.

#6 Soccer practice and functional and social performance of men with lower limb amputations
Reference: J Hum Kinet. 2014 Nov 12;43:33-41. doi: 10.2478/hukin-2014-0087. eCollection 2014.
Authors: Monteiro R, Pfeifer L, Santos A, Sousa N
Download link:
Summary: Practicing sports together with rehabilitative treatment improves the development of motor, social and emotional abilities of lower limb amputees. The aim of this study was to compare the functional and social performance of individuals with lower limb amputations between those who played soccer and those who did not engage in any sports activities. A total of 138 individuals participated in the study and were divided into two groups: soccer players (n = 69, 34 ± 8.1 years) and non-athletes (n = 69, 38 ± 8.9 years). A checklist, based on the International Classification of Functioning, Disability and Health, was used. Data were analyzed using the Chi-square and Mann-Whitney tests. The soccer players group showed significantly better performance than the non-athletes group in most items of body function, body structure, occupational performance components and daily activities (p < 0.001 for all), and also in some important items of social and environment factors (p < 0.001 for all). The results strongly suggest that amputee soccer significantly improves the functional and social performance in individuals with lower limb amputations.

#7 Monitoring Fatigue During the In-Season Competitive Phase in Elite Soccer Players
Reference: Int J Sports Physiol Perform. 2015 Feb 24. [Epub ahead of print]
Authors: Thorpe RT, Strudwick AJ, Buchheit M, Atkinson G, Drust B, Gregson W.
Summary: The purpose of the study was to quantify the relationship between daily training load and a range of potential measures of fatigue in elite soccer players during an in-season competitive phase (17-days). Total high-intensity running distance (THIR), perceived ratings of wellness (fatigue, muscle soreness, sleep quality), counter-movement jump height (CMJ), post-exercise heart rate recovery (HRR) and heart rate variability (Ln rMSSD) were analysed during an in-season competitive period (17 days). General linear models were used to evaluate the influence of daily fluctuation in THIR distance on potential fatigue variables. Fluctuations in fatigue (r=-0.51; large; P<0.001), Ln rMSSD (r=-0.24; small; P=0.04), and CMJ (r=0.23; small; P=0.04) were significantly correlated with fluctuations in THIR distance. Correlations between variability in muscle soreness, sleep quality and HRR and THIR distance were negligible and not statistically significant. Perceived ratings of fatigue and heart rate variability were sensitive to daily fluctuations in THIR distance in a sample of elite soccer players. Therefore, these particular markers show particular promise as simple, non-invasive assessments of fatigue status in elite soccer players during a short in-season competitive phase.

#8 Peak Match Speed and Maximal Sprinting Speed in Young Soccer Players: Effect of Age and Playing Position
Reference: Int J Sports Physiol Perform. 2015 Feb 24. [Epub ahead of print]
Authors: Al Haddad H1, Simpson BM, Buchheit M, Di Salvo V, Mendez-Villanueva A.
Summary: In this study we assessed the relationship between peak match speed (PMS) and maximal sprinting speed in regard to age and playing positions. Maximal sprinting speed and absolute PMS (PMSAbs) were collected from 180 male youth soccer players (U13 to U17, 15.0 ± 1.2 yrs, 161.5 ± 9.2 cm and 48.3 ± 8.7 kg). The fastest 10-m split over a 40-m sprint was used to determine maximal sprinting speed. PMSAbs was recorded using a global positioning system and was also expressed as a percentage of maximal sprinting speed (PMSRel). Sprint data were compared between age groups and between playing positions. Results showed that regardless of age and playing positions, faster players were likely to reach higher PMSAbs and possibly lower PMSRel. Despite a lower PMSAbs compared with older groups (e.g., 23.4 ± 1.8 vs. 26.8 ± 1.9 km/h for U13 and U17, respectively, ES= 1.9 90% confidence limits (1.6;2.1)), younger players reached a greater PMSRel (92.0±6.3% vs. 87.2±5.7% for U13 and U17, respectively, ES= -0.8 90% CL (-1.0; -0.5)). Playing position also affected PMSAbs and PMSRel, as strikers were likely to reach higher PMSAbs (e.g., 27.0 ± 2.7 vs. 23.6 ± 2.2 km/h for strikers and central midfielder, respectively, ES= 2.0 (1.7;2.2)) and PMSRel (e.g., 93.6 ± 5.2% vs. 85.3 ± 6.5% for striker and central midfielder, respectively, ES= 1.0 (0.7;1.3)) compared with all other positions. Present findings confirm that age and playing positions affect the absolute and relative intensity of speed-related actions during matches.

#9 An interval kicking progression for return to soccer following lower extremity injury
Reference: Int J Sports Phys Ther. 2015 Feb;10(1):114-27.
Authors: Arundale A, Silvers H, Logerstedt D, Rojas J, Snyder-Mackler L.
Download link:
Summary: The majority of all soccer injuries affect the lower extremities. Regardless of whether the injured limb is an athlete's preferred kicking or stance leg, a lower extremity injury may affect their ability to impact the ball. Sport-specific biomechanical progressions to augment loading and gradually reintroduce a player to the demands of sport have been developed for upper extremity sports such as baseball, softball, tennis, and golf. Generalized return to soccer progressions have also been published in order to assist clinicians in safely returning athletes to sport; however, there are no specific progressions for the early stages of kicking designed to introduce stance leg loading and kicking leg impact. Thus, the purpose of this clinical commentary was to review the existing literature elucidating the biomechanics of kicking a soccer ball and propose a progressive kicking program to support clinicians in safely returning their soccer athletes to the demands of sport. The interval kicking program (IKP) describes clinical guidelines for readiness to begin a kicking program as well as possible readiness to return to sport measures. The program is performed on alternate days integrating therapeutic exercise and cardiovascular fitness. The IKP gradually introduces a player to the loading and impact of kicking. The progression increases kicking distance (using the markings of a soccer field as a guide), volume, and intensity and uses proposed soreness rules, effusion guidelines, and player feedback in order to assist clinicians in determining readiness for advancement though the stages. The IKP also recommends utility of specific tests and measures to determine readiness for return to sport. Gradual reintroduction to sport specific demands is essential for a safe return to soccer. This return to sport progression provides a framework integrating injury specific therapeutic exercise, cardiovascular fitness, and the return to kicking progression, to assist clinicians in initiating an athletes' return to soccer.

The Training Manager -