Authors: Emmanouil Smpokos, Antonios Tsikakis, Ricardo Peres, Vangelis Lappas, Pedro Caravela,  Paulo Oliveira, Manolis Linardakis  and the ‘Olympiacos FC Academy Research Group’

Corresponding Author:
Emmanouil Smpokos
E-mail: msbokos@edu.med.uoc.gr or manosmpok@yahoo.gr (Dr. E. Sbokos)
Phone number: 0030 6945233315
Fax number: 0030 2155308859

Emmanouil Smpokos, PhD/MSc, is the senior physiologist at the Research and Development Department, Olympiacos Academy Football Club, Piraeus, Greece and fitness coach of the U-19; Antonios Tsikakis is the fitness coach at the Department in U-17 ; Ricardo Peres is the Technical Director and the Head coach of the U-19 of Olympiacos FC Academy ; Vangelis Lappas is the head of Goalkeepers’ Department and the Goalkeeper coach of the U-19 team of Olympiacos FC Academy; Pedro Caravela is the Head of the Scouting Department and assistant coach of U-19 team of Olympiacos FC Academy; Paulo Oliveira is assistant coach of Olympiacos FC Academy ; Manolis Linardakis, PhD/MSc, is Biostatistician at Department of Social Medicine, Faculty of Medicine, University of Crete, Heraklion, Greece.  

Physical performance of youth football (soccer) players playing in European and National Leagues’ matches

ABSTRACT

The current study assessed the physical performance of youth Greek football (soccer) players between the Union of European Football Associations (UEFA) Youth and National Leagues’ matches. This effort was based on 271 measurements of nine physical/motor activities recruited from 25 players with a mean age of 18.4 (±1.2 years) during August 2017 and January 2018 from official-matches of UEFA Youth (n=6) and National Leagues (n=16). Measurements were recruited using Global-Positioning-System Technology-(GPS) and differences were assessed through analysis of covariance. 56.0% of the players were 18.0+ years old, 52.0% were midfielders, and 56.5% of players’ participations were recorded in full time (90.0+ minutes). Between the two competitions of UEFA Youth and National Leagues’ matches, it has been found that there is significant difference only in mean number of decelerations (71.4 vs. 61.7, respectively, p=0.010). High mean levels of total distance-(TD), very high-intensity-speed-running-distance-(VHS), maximal-sprinting-speed-distance-(MS), high-speed-running-(HSR), distance/time-(D/T), sprints, number of accelerations and maximum-velocity-(Vmax) were noticed as well as in UEFA Youth Leagues’ matches but did not differed significantly in relation to counterparts (p>0.05). The researchers observed that youth football players displayed similar efforts in all matches maintaining a high level of physical performance, without separating the matches according to the competition, due to the educational behavior adopted within the football academy of the club.

Keywords: GPS, youth, motor skills, football, match analysis

INTRODUCTION

Modern association football (soccer) is characterized by highly dynamic and acyclical game movements, interspersed with frequent bouts of high-speed movements and a number of high variability of actions, players’ motor, and mental preparation as well as technical-tactical skills monitoring all these actions using time-motion analysis (TMA) (1,2,26). The number of studies on match running performance has exponentially increased over the current decade in youth football (soccer) populations, providing information that could aid the development of physical conditioning programs (26). Most of theprofessional football academies are seeking to optimize the early detection and physical development of their young football players according to age and playing position (27). The match-running performance of elite male youth football players has been extensively described that the elite youth footballers cover 9-12 Km during an official match, of which 1.5-3.3 Km is high-intensity running (HIR) (24). In a study conducted in youth population (aged 17 years) of elite football players it was found that they have covered 5-7 km during an official match, of which approximately 15% (0.4-1.5 km) with high-intensity activities and the ability to perform in intermittent fitness tests was related to the total distance (TD) covered, as well as with the distance covered in high intensity activities (6,7).

Nevertheless while some information is available about the physical and physiological demands of highly trained young footballers during match play (3-5,30), little is known about whether those physical capacities change during official matches in domestic and European competitions. Although many studies have reported significant correlation between field or laboratory test results and running performance during football matches suggesting that individual physical capacities can account for match-related performance (6,15,20), none to current knowledge, has compared performance between deferent official competitions. In this case and among other factors, an important point is the youth athletes’ motivation of participation that could be affecting their performance (23,31).

With this in mind, the aim of the present study was to assess the measurements of physical performance of youth Greek football (soccer) players playing in UEFA (Union of European Football Associations) Youth and National Leagues’ matches.

Material and Methods

Subjects

The study is based on data collected from 16 Greek Youth National League team’s matches and six UEFA Youth leagues’ matches during the football season 2017/2018. Data were collected for half of an annual season spanning 24 weeks, from August 27th, 2017 to January 14th, 2018.

Twenty-five youth football players (13 midfielders; 5 defenders; 4 forwards, and 3 wingbacks with the mean age of 18.4 years (±1.2 years) competing in the first division of the U-19 Greek football league were analyzed in the present study. Their total measurements were 271 retrieving from 22 matches. Their weight was measured on calibrated digital scales (Seca 861; Seca, Hamburg, Germany) to the nearest 0.1 kg and height was measured to the nearest 0.5 cm with a wall mounted stadiometer (Seca 225; Seca), without shoes. Body mass index (BMI) was calculated as weight divided by height, squared (kg·m-2). The player’s field position, kicking leg, matches’ outcome, matches and measurements and minutes playing per match were also recorded. The study was approved by the institutional ethics board and written informed consent was obtained for each participant or their parents at the beginning of the season, who agreed to participate in the research (29).

Physical/motor activity measurements

Each match was monitored using a computerized semi-automatic video match analysis image recognition system (data were supplied by Viper pod 2, STATSport, Belfast, UK). The data systematically analyzed using proprietary software to provide an interactive coaching and analysis tool that provided a comprehensive data on each individual (17). Match data collection for this study was carried out at the football club’s official stadium and both home and away stadiums, respectively (28).

Each player’s physical activity, during each match, was monitored using portable global positioning system (GPS) units (Viper pod 2, STATSports, Viper Belfast, UK). This device provides position velocity and distance data at 10Hz. Each player wore a special adjustable neoprene harness which enables this device to be fitted to the upper part of his back (i.e. between the left and right scapula). All devices were activated 30 minutes before data collection to allow acquisition of satellite signals, and synchronize the GPS clock with the satellite’s atomic clock (21). GPS data were downloaded after every match and analyzed using the respective software package (Viper PSA software, STATSport, Belfast, UK). In order to avoid inter-unit error, players wore the same GPS device for each game (3,18). The players’ external load that were selected for analysis included total distance covered (TD; km), relative total distance: distance/time (meters/minutes) (D/T), maximum sprint velocity reached (Vmax) (m/s), and high speed categories were used: Very High Speed running (VHS; from 19.8 to 25.2km/h) and Maximal Speed-Sprint (MS;>25.2km/h) or High Speed Running (zone 5 + zone 6) (HSR;>19.8km/h, in meters) (10,18). A sprint was defined as a running exercise lasting at least 1 sec at the speed of at least 25.2km/h (>7 m/s). Acceleration activity was measured on the basis of the change in GPS speed data and was defined as a change in speed for a minimum period of 0.5 s with a maximum acceleration in the period at least 0.5 m·s-2. The acceleration was considered finished when the player stopped accelerating. The classification of accelerations by zone is based on the maximum acceleration reached in the acceleration period. The same approach was used with regard to deceleration. The load and intensity measures were identified as total number of accelerations or decelerations (>2 m·s-2) and accelerations/min or decelerations/min, respectively. In addition, the “dynamic stress load” was calculated as the total of the weighted impacts. Impacts were weighted using convex-shaped function (approximately a cubic function), an approach similar to the one used in the speed intensity calculation, with the key concept being that an impact of 4g is more than twice as hard on the body as an impact of 2g. The weighted impacts were totaled and finally scaled to give more workable values expressed in arbitrary units (AU). The load and intensity measures were identified as Dynamic Stress Load (DSL) (2). Both speed intensity and dynamic stress load were calculated automatically using a custom algorithm included in the proprietary software provided by the manufacturers (Viper Version 1.2, STATSports, Belfast, UK). High Metabolic Load Distance (HML; distance covered >25.5 W·kg-1) was used as measure of movement intensity (12). The HML distance measure combines the energy cost of all constant velocity running above 5.5m·s-1 and acceleration and deceleration activity over 2 m·s-2 during intermittent running (9,25). Players who did not get into HSR zones because of covering short, sharp distances were given credit in their HML score since the intensity of the work could be greater (28).

Statistical Analysis

Data were analyzed using the SPSS software (IBM SPSS Statistics for Windows, Version 25.0. Armonk, NY: IBM Corp). Distributions of descriptive characteristics of the 25 youth football players were estimated. Multivariate analysis of covariance (mancova) was performed to assess the differences of physical/motor activity measurements between the two groups (measurements came from UEFA Youth League and National Youth League). Effect size (η2) and heterogeneity of comparisons were also estimated (based on Levene’s test). Age, body mass index, players’ position, kicking leg, minutes playing per match, and matches’ outcome were used as covariates. Finally, the percentage differences of physical/motor activity measurements were graphically illustrated.  

RESULTS

A comprehensive overview of the studied samples and their characteristics is given in Table 1. Fifty-six percent of the youth footballers (n=14) had mean age of 18.0+ years, body weight 71.2kg, height 1.77cm, and BMI 22.6kgŸm-2. The majority of the players were midfielders (52%) followed by defenders (20%), forwards (16%), and wingbacks (12%). Furthermore, with regard to the match outcome the team had succeeded 59.1% wins or 27.3% defeats while 16 youth footballers had theirdominant kicking leg as the right one and six had their dominant as the left leg. One-hundred and fifty three or 56.5% of players’ participations were recorded in full time (90.0+ minutes) of the 22 matches.

Table 1. Characteristics of 25 youth Greek football players and matches of the current study. 

    N %
Age, years 18.0+ 14 56.0
  mean±stand. dev. [min, max] 18.4±1.2 [16.8, 21.8]
Weight, kg mean±stand. dev. 71.2±5.5
Height, m mean±stand. dev. 1.77±0.06
Body Mass Index, kgŸm-2 mean±stand. dev. 22.6±1.1
Players’ position defenders 5 20.0
  wingbacks 3 12.0
  midfielders 13 52.0
  forwards 4 16.0
Kicking leg right 16 64.0
  left 6 24.0
  both 3 12.0
Matches’ outcome win 13 59.1
  draw 3 13.6
  defeat 6 27.3
Matches and measurements† UEFA youth league 6 (72)
  National league 16 (199)
Minutes playing per match 90.0+ 153 56.5
  mean±stand. dev. 72.1±27.6

Body measurements were obtained at the beginning of the season 2017/2018.

† The 271 measurements of physical/motor activities were obtained during the 27th August 2017 and 14th January 2018 retrieving from 22 matches.

Analytical differences in physical/motor activities of the 25 youth players between the two competitions of UEFA Youth and National Youth leagues’ matches are presented in Table 2.Between the nine physical/motor activities measurements, it has been found significant difference only in mean number of decelerations (71.4 vs. 61.7, respectively or difference -9.7; p=0.010). High mean levels of TD, VHS, MS, HSR, D/T, sprints, number of accelerations and Vmax were noticed in UEFA Youth Leagues’ matches but did not differed significantly in relation to counterparts (p>0.05).

Table 2. Differences in physical/motor activities of youth Greek football players in the season 2017/18 which playing in European and National leagues’ matches.

  Players participation in      
UEFA Youth
League,n=6		 National Youth
League, n=16 		     
measurements 72 199    
         
  marginal means (stand. errors) Difference p-value η2
Total Distance, TD, meters 9,391 (366) 8,806 (206) -585 0.187 0.007
Very high-intensity speed running distance, VHS, meters (sprinting or speed 19.8-25.2 km/h) 408.1 (22.1) 379.0 (12.9) -29.1 0.282 0.005
Maximal sprinting speed running distance, MS, meters (sprinting or speed >25.2 km/h) 95.2 (8.5) 82.7 (4.9) -12.4 0.230 0.006
High Speed Running, HSR, meters (running speed >19.8 km/h) 505.0 (28.6) 464.3 (16.1) -40.7 0.239 0.005
Distance/Time, D/T, meters/minutes 99.5 (1.4) 97.9 (0.8) -1.7 0.315 0.004
Sprints, number 35.3 (1.8) 32.5 (1.0) -2.8 0.193 0.006
Accelerations >2m/s2,n 54.1 (2.5) 52.4 (1.4) -1.7 0.577 0.001
Decelerations >2m/s2,n 71.4 (3.1) 61.7 (1.7) -9.7 0.010 0.025
Maximum velocity (Vmax),m/s 8.33 (0.08) 8.24 (0.04) -0.09 0.346 0.004

Analysis of covariance (Levene’s test was used for testing heterogeneity). Age, body mass index, players’ position, kicking leg, minutes playing per match and matches’ outcome were used as covariates. 

Figure 1presents the percentage differences in nine physical/motor activities of youth footballers of National in relation to European leagues’ matches. The higher percentage difference is showed for decelerations (-13.9%) as it was only founded significantly (p=0.010).

Figure 1. Percentage differences inphysical/motor activities of youth Greek football players of National in relation to European leagues’ matches.

Figure 1

TD; total distance; VHS, Very High Speed running; MS, Maximal Speed-Sprint;  HSR, High Speed Running; D/T, total distance:time

Discussion

In the current study and for the first time, the researchers investigated the physical/motor activities of youth Greek football players playing in UEFA Youth and National Leagues’ matches using GPS monitors. The main finding was that between the two competitions there was no significant difference in nine physical/motor activities with exception to the number of decelerations.

Based on the results of the present study it can be concluded that in terms of physical/motor activities of youth football players who compete in any competition (Domestic or European league matches) had displayed similar performance in all matches. This could be explained by a great number of factors affecting football players’ performance. Studies have shown that apart from the primary contribution of players’ motor skills their match performance is also greatly affected by the lack of soccer motivation, the technical-tactical skills, game strategy, efficiency of decision-making processes, personality traits, or probably due to the educational behavior adopted within the academy in that footballers arenot to separate the matches according to importance of thecompetition (8,11,16,31). However, there is still a gap in the literature to be able to draw conclusions about the comparison of motor activities of youth footballers in two different competitions. Searching the literature, there has not been a study found that investigated the differences between motor skill activities in youth footballers between different competitions. The majority of studies employed field testing procedures, such as linear speed (13,14,22) as a means to determine age-specific or individualized speed thresholds (26). In a study performed on a professional Greek footballers (soccer) teamit demonstrated the changes in all types of tested motor skills in official matches in Domestic National and European championships (28). The seasonal variations of the study that were investigated during the three periods of the season 2016/17 (1st period was the pre-season to the 1/3 of the Greek Super League, the 2nd period was the 2/3 of the Championship, and the 3rd was the last part 3/3 of the Championship) separated by approximately 14 matches in each period as in our study (16 National Youth League matches). In terms of endurance skills the youth team displayed almost the same TD in UEFA Youth League match play compared with the professional footballers (1st period of the season) (9391m vs 9806m).

Another study carried out between two German Bundesliga teams analyzed the effects of endurance and speed skills on their teams’ final standing in the league table (19). The study showed that the players from the second team (despite being ranked lower in the league table than the first team) attained better scores in all types of tested motor skills than the players from the first team (19).

One of the limitations of the study was the data of the present study focusing in physical performance only considered for the first half of the entire season because they lost the qualification for the knockout stage in the third round of the competition. Therefore, studies dealing with an entire full season or more consecutive seasons are needed to better comprehend the in match related physical parameters. This study is also reflective of one team only (albeit one of the top league teams) and hence may not represent the customary official match demands of other domestic league teams that may be influenced by different coaching philosophies (28). Moreover, most of the youth footballers, in contrary with the professional players, are attending schools, and they were not recorded (through daily activity questionnaire), which could limit the participation of the players in theteam’s official and training obligations.

CONCLUSIONS

Based on the obtained results, high mean levels of all types of nine physical/motor activities were noticed between the two competitions (UEFA Youth & National Leagues’ matches) although no significant differences were observed with the exception in number of decelerations. We observed that youth football players displayed similar efforts in all matches maintaining a high level of physical performance, without separating the matches according to the competition importance a process of educational philosophy adopted within the Academy of the Club. However, motivating distinction, personal or collective, enhances competition among athletes and teams participating in similar competitions. While academies constantly invest in the search and development new talented athletes, with improved skills and better performance in their physical condition.     

APPLICATIONS IN SPORT

Young footballers seem to put equal efforts in the participating competitions without distinguishing their significance and this may be explained due to a variety of factors influencing their performance, including their personal abilities, the technical-tactical skills, game strategy, efficiency of decision-making processes, personality traits, or probably due to the educational behavior adopted within the football (soccer) academy.

Technical staff of the Academies should be educators, teachers, and parents simultaneously. Training of young athletes, cannot include only improvement of physical condition or soccer techniques learning.  Primarily, technical staff should focus on developing the personality of the young in total, reporting and consolidating basic principles and values, such as emulation, good cooperation, and behavior towards fellow athletes and trainers, synergy, and respect. Especially in sports since ancient times the dogma of “a healthy mind in a healthy body” is emphasized (in Latin “mens sana in corpore sano” or in Ancient Greek “νοῦς ὑγιής ἐν σώματι ὑγιεῖ” – https://www.encyclopedia.com) and hence the technical staff, taking advantage of the constantly good physical condition, can mold and develop the mental virtues of the youth, the correct non-competitive and competitive thinking and behavior. Critical thinking needs to constantly accompany young athletes, to take care of their body and that of their peers and opponents, to behave with caution and respect in every game or training, avoiding conflict or reactions that put in danger their physical and mental health. Technical staff must empower young athletes and their abilities, avoiding potential injuries that could constitute impediments to their physical and athletic development.

ACKNOWLEDGMENTS

The authors would like to extend their gratitude to all players who participated in this study. The ‘Olympiacos FC Academy Research Group’ include: Nikolaos Kolokythas, Athanasios Rossidis, Anastasios Lazarou, Dimitrios Kalogerakos, Emmanouil Askounis, Nikolaos Katsikostas, Ariel Ibagaza, Aristeidis Kyriazis, Dimitrios Mavrogennidis, Nikolaos Topoliatis, Iakovos Chatziraptis.

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