Energy system requirements of soccer player. Correlation between game analysis and aerobic/anaerobic power test

Riccardo Proietti Ph D
Consulente scientifico Omegawave (www.omegawave.com),e Bayern di Monaco.
 
Autore di pubblicazioni varie e di due libri/video "Forza e velocita' nel calcio" e "Potenza aerobica e resistenza alla velocita' nel calcio"  edizioni Prhomos.
Ha svolto la sua professione sia come prep atletico che come responsabile della valutazione funzionale e metodologica nell FC Empoli, Al Jazira football club (Emirati Arabi), Nazionale Austriaca, Grasshopper Zurigo e in altre squadre professioniste. 

Needs Analyses -The Physical Demand Profile of High-Performance Soccer

Before programming the training process it has to be decided what abilities or qualities and what physical characteristics a player has to develop. This is
done by examining the needs of the athlete’s event – in this case by examining what abilities and qualities are needed for the game of soccer. By examining the game of soccer and what is involved in its execution, we amass information to help us make decisions about what qualities we would like to see in the players. Understanding what qualities and what physical characteristics are necessary for soccer also help to determine what tests should be selected to evaluate the athlete’s fitness level. This means that in a second step, it has to be examined how the particular player compares to the needs of the game. The choice of tests must be specific to the physiological characteristics that are analyzed to be critical components of performance. Specificity must include the energy systems used and the muscle actions that are sports specific. Validity of the test is reduced if it does not include the sports specific action of the game. The physical and physiological demands of soccer on its participants become more pronounced as the level of competition increases (Junge et al., 2000).
Therefore, understanding the energy system(s) involved in soccer will help to determine what kind of volume, intensity and rest/recovery are necessary in a players training. By developing the correct energy system(s), training will be conduced in a way that is designed to enhance the player’s performance. Analyzing the energy system(s) involved will allow to focus on what is important during training and competition.
Determining which muscles are involved in the game will help to prioritize what needs to be developed during a conditioning program. Analyzing these specific muscles will help to determine if the players have the qualities soccer requires.
Speed of movement is an other important concept to understand. Training players with predominantly slow exercises will result in their being slow in the match. However, if players are wanted to be fast and explosive, they have to be trained in this manner.
Therefore it is necessary to analyze the physical demand profile of highperformance soccer. With the knowledge of the physical demands of a given activity, it is possible to scientifically design and develop more efficient training
and physical conditioning methods. In contrast to other sports that predominantly use either anaerobic or aerobic metabolic pathways, success in soccer depends upon a combination of speed, agility, power, strength, endurance, skill, flexibility as well as on technical and tactical knowledge. It appears that the physical aspects of soccer have become more and more important in recent years, not only to cope with the physiological demands in soccer but also to be able to maintain the technical standard throughout the match. Without an improvement of the physical preparation level, one cannot expect an improvement in technical and tactical skill, the body’s work output, or the speed of execution of exercises.

Energy System Requirements of Soccer Players

In the past many researchers have addressed the metabolic demands imposed on soccer players during competitive and friendly matches. These analyses have demonstrated, that the majority of the body’s physiological systems are stressed during the course of a soccer game and often also by a strenuous training program. These include metabolic energy systems, the musculoskeletal system and perhaps also the nervous and immune system. It is widely documented, that the aerobic system is the main source of energy provision in soccer match-play where players have to sustain a high rate of work for a period of at least 90 minutes. However, soccer is characterised by an intermittent activity profile with high-intensity anaerobic efforts superimposed on a background of aerobic activity. This varying intensity places high metabolic demands on the energy delivery pathways Thompson et al.1999; Drust et al., 2000; Thompson et al., 2001). In this high intensity intermittent sport, many other factors such as speed, power, strength, agility, flexibility and anaerobic capacity all combine with aerobic capacity also contribute to a successful game.
Previous studies have demonstrated, that the higher the fitness level of the soccer player, the more frequently the player is capable of high intensity phases of play -and that a high level of fitness from all players in a team helps to allow for a high work rate and maintenance of good technique
throughout a match (Smaros, 1980; Dowsen et al, 2002; Edwards et al., 2003).
From the metabolic point of view, soccer is classified as an alternating aerobic/anaerobic engagement sport. In fact, it alternates high intensity phases of play and phases in which the player carries out active recovery. During an intermittent exercise, well-trained athletes can regularly make use of the system of oxygen transport without creating high lactate levels in the muscles and in the blood. Even if there are differences depending on the player’s position -time and motion analyses of soccer matches demonstrate, that soccer players may cover as much as 10-12 km (see table 1) during a match lasting 90 minutes (actual playing time 55-62 minutes), involving a combination of high-intensity sprinting, prolonged running at more moderate speeds and periods of walking (FIFA, 1989; Meyer et al., 2000; Tumilty 2000. The highest distances covered by an individual player are reported to be about 14 km (Ekblom, 1986; Bangsbo, 1993). Therefore aerobic endurance must play an important role in the team performance. It is interesting to note, that recreational players cover about the same distance per unit of time as professional players do and that the mean distance for the first and second halves are about the same (Ekblom, 1986).






Superimposed on this background of running and walking activities there are several other movement patterns like jumping, dribbling, tackling shooting as well as rapid changes in speed and direction.
Match analyses provide some insight into the physical demands of soccer in terms of distance covered, both absolutely and at different intensities. These observations also provide information about the work-to-rest ratios, number of physical contacts, time spent in possession of the ball, number of tackles, headers and other activity modes increasing energy expenditure.
A recent match analysis done by Rienci and co-workers 2000 showed, that there are about 1431±206 different actions with and without a ball within a single match. This study also showed, that on average activities of a player change every four seconds within a game (Rienci et al., 2000).
According to Withers et al., (1982) 26.3% of total play time is made up of phases of walk, 64.6% of slow runs, 18.9% of quick runs and sprints, and 1.1% of phases of possession of the ball. In (1985) Mayhew and Wenger established that during his game a soccer player walks 46.6%, runs slowly 38%, runs quickly or sprints 11.3% and stands without moving 2.3% of total playing time. During a match, soccer players perform different types of physical activities, ranging from standing still to maximum speed runs, the intensity of which may change at any given time. However, intensity parameters are not exactly defined in these papers.
According to J. Bangsbo (1996), the types of runs during a soccer match (for a total length of 8-12 kilometers) can be expressed as follows, keeping in mind, however, that both the total distance covered and the intensity of the runs are extremely variable with regard to the physical conditioning level and the player’s position. Walk: 4 km/h (distance covered: about 3,400 meters), jogging: 8 km/h (distance covered: about 3,200 meters), low speed run: 12 km/h (distance covered: about 2,500 meters), moderate speed run: 16 km/h (distance covered: about 1,700 meters), high speed run: 21 km/h (distance covered: about 700 meters), and sprint 30 km/h (distance covered: about 400 meters) – see figure 4.



Match analyses using ProZone System (UEFA official system)

A recent, match analyses by Proietti, (2003) was used to analyze three top teams in the English Premier League (participating in the Champions League) and three top teams of the United Arabic Emirates playing in the Asian Cup. In this study different intensities of walking/running during match-play were analyzed in 47 players using a “ProZone System” (34 Roundhay Rd., Leed 34003200250017007004004 km/h8 km/h12 km/h16 km/h21 km/h30 km/hDistance covered during the game with different intensities Distance covered during the game with different intensities mmmmmm
LS7 1LY /UK). The results of this investigation are summarized in (table 2-17 previously unpublished). The first table summarizes mean values and other descriptive data of distance covered with different intensities. As shown in this overview players in average covered 10374± 1070 meters during the analyzed matches with a range from 8476 to 12692 meters.













Soccer frequently is called a “multiple sprint sport”. However, the average number of sprints in this investigation mentioned above is 14.3 ± 6.1(range: 327). Like in other investigations, sprints covered with highest speed are rarely longer than 20 meters in distance (Reilly et al., 1976; Winkler, 1985; Bangsbo et al., 1991; Müller et al., 1996; Müller et al., 1998). In average these more or less frequent sprints last about 2 seconds, corresponding to an average distance of 17 meters (Bangsbo et al., 1991).



























Table 5,9,13,17 can be used as a physical valuation index for the different metabolic system involved in a soccer game. This is the first study which reports an accurate analyses concerning the objective way to investigate the real game performance for the different player position .The three groups show some statistically significant differences regarding the types of run.The data are below reported.

• JOG 2-4 m/s Midfield 4328 m > Forwards 3508 m (p .00)
• RUN 4-6 m/s Midfield 1766m > Forwards 1360m (p .01) Midfield 1766m > Defender 1480m (p .03)
• HSR 6-7 m/s Midfield 640m > Forwards 506m (p .05)
• TDIST Midfield 10944 m > Forwards 9774 m (p .00) Midfield 10944 m > Defender 10286 m (p .03)
• TDISTBP Midfield 3986 m > Forwards 3594 m (p .03) Midfield 3986 m > Defender 3439 m (p .00)
• TDISTWBP Midfield 3757 m > Forwards 3251 m (p .05) Defender 3818 m > Forwards 3251 m (p .03)
• HIBP Forwards 378 m > Defender 226 m (p .04)
Midfield 343 m > Defender 226 m (p .00)
• HIWBP Defender 437 m > Forwards 278 m (p .02)
• SPRBP Midfield 99 m > Defender 54 m (p .02) Forwards 101 m > Defender 54 m (p .04)

One of the factors that may account for the difference between the three groups is that the Midfield seems to be involve in all the tactical movement like the other player but as a linking player they run more compare to the majority.Nevertheless all midfield include the outfield must be mobile, capable of covering ground quickly to contest possession, play the ball, or support team-mates in defense and attack.They may need to sustain runs and recover quickly to move into positions supporting the player on the ball or maintain defensive lines.Some significant correlation (p <.05) are reported between the different tipes of run as RUN 4-6 m/s (r.91), JOG 2-4 m/s (r.90), HSR 6-7 m/s (r.68), HIT >6 m/s (r.58), Walk 0-2 m/s (r -.44) and the TDIST.While there is no meaningful difference between amateur and professional players as far as the total amount of work is concerned, there is a big difference between them in the percentage of work carried out at maximum intensity. The higher the division, the higher the intensity (Bangsbo et al., 1991; Bangsbo, 1996; Müller & Lorenz, 1996; Williams et al., 1999). Evidence for an increased work intensity during contemporary soccer has been shown by Williams at al., (1999) in their quantitative analyses of matches played in the 1991-1992 and the 1997-1998 seasons. Objective match statistics were presented to highlight the major changes in the game that have occurred in this short period of time. Findings indicate that the game has changed markedly during the intervening period. Contemporary matches include more runs with the ball, more passes, dribbles and crosses which suggest a significant increase in the “tempo” of the game. In order to cope with these demands, players must react quickly to continually changing game situations. Speed of movement is therefore an essential characteristic for successful performance in contemporary professional soccer. Anyway to understand the effective metabolic profile involve in soccer game is necessary to analyse second by second the real behaviour of the
players.Thank to the match analyses Pro Zone system Proietti 2003 report the following data (table 18-23) of three professional player of U.A.E soccer League.


















Aerobic metabolism in soccer

A professional soccer player should ideally be able to maintain a high level of intensity throughout the whole game. Some studies however, have shown a reduction in distance covered, a lower fractional work intensity, reduced maximal heart rate, reduced sugar levels, and reduced lactate levels in the second half of games compared with the first half (Douglas, 1993; Helgerud et al., 2001).
There have been several attempts to determine the aerobic contribution to metabolism by measuring oxygen uptake (VO2) during match play (Covell et al., 1965; Durin et al., 1967; Kawakami et al., 1992; Ogushi et al., 1993). However, data obtained is probably not representative of oxygen uptake during match-play because, since measurement procedure interferes with normal play (Bangsbo, 1994). Information about the aerobic energy expenditure during soccer can also be obtained from continuous heart rate measurement during the match. Based on individual relationship between heart rate and VO2 during a standardized exercise protocol in the laboratory the heart rate determinations for each player during match-play can be transformed to oxygen uptake (Bangsbo, 1994). By such estimations mean values of about 75% VO2 max have been obtained. (Reilly & Thomas, 1979; Ekblom, 1986; Bangsbo, 1994). However, Bangsbo, (1994) speculates that this value of 75% is overestimating (emotional and thermal stress) the mean relative workload and this author believes that the real value might be close to 70% VO2 max corresponding to an energy production of 1360 kcal for a person weighing 75kg with a maximum oxygen uptake of 60 ml/kg/min. Mean heart rate during soccer match-play have been found to be in a range from 165-175 beats / minute (Figure 5) with values usually being slightly higher during the first half of the game (for review see Tschan et al., 2001). According to Smodlaka (1978) this heart rate is close to 85% of maximum theoretical heartbeat for long periods of play. Similar values have been described also by Ekblom at al. (1986). Rhode & Esperson (1988) showed that for 63% of the game heart rate was in a range between 73 and 92% of maximum heart rate – 26% of match-play heart rate was higher than 92% and only 11% of the playing time heart rate was bellow 73% of HRmax.
In a research on professional soccer players, Baron, et al (1986) pointed out that the anaerobic threshold is about 78% (± 6.9) of maximum VO2, thus confirming above mentioned findings. Other more recent study by Reilly (1994) or Helgerud et al., (2001) also showed that the average work intensity, measured as percent of maximal heart rate, during a 90 minute match is close to lactate threshold, or 80-90% of the maximal heart rate. This means that during a soccer match an alternating aerobic/anaerobic metabolic system takes place, in relation to intense technical-tactical situations.






It has to be pointed out that expressing intensity as an average over 90 minutes could result in a substantial loss of specific information. Indeed, as mentioned above, soccer matches have periods and situations of highintensity where accumulation of lactate takes place. Therefore the players need periods of lower intensity to remove lactate from the working muscles (figure 6).




In determining aerobic endurance, VO2 max is considered the most important element. Other important elements are lactate threshold (a higher lactate threshold theoretically means, that a player is able to maintain a higher average intensity in an activity without accumulation of lactate) and running economy (cardiovascular efficiency). Several studies have determined the VO2 max for male elite adult players, and mean values in a range between 55 and 65 ml kg min have been reported with few individual values over 70 ml kg min (Bangsbo, 1994; Chin et al., 1992; Dowson et al., 2002; Ekblom, 1986; Tschan et al., 2001; Tumilty 2000; Wisloff et al., 1998). Reviewing available VO2 max values of the last decade (see table 23) of international elite teams show that this magnitude did not change significantly compared with values from the 1980s. Although several studies observed higher VO2 max values of elite players of top class teams compared to lower ranked teams other studies failed to show any relation which indicates that
this variable is not crucial for good performance in soccer (Bangsbo & Michalsik, 2002; Dowson et al, 2002).






Several studies have determined the VO2 max for male elite players, based on their positional role within the team (Di Salvo et al., 1998; Di Salvo et al., 2001; Bangsbo et al., 2002). However, most of these studies failed to evaluate significant differences between different position (exception goal keepers) see figure 7.








Anaerobic metabolism in soccer
As already mentioned soccer in contrast to other sports taps into both aerobic and anaerobic metabolism. Anaerobic energy production is extremely important, in soccer as it provides energy at a very high rate during periods of intense exercise in a match. The concentration of lactate in the blood is frequently used as an indicator of anaerobic lactacid energy production in soccer. High level of lactic acid in the blood of soccer players during a match, with peaks of 12 mmol/l, (average values: 3-8 mmol/l) are evidence of the high intensity of some fractions of play (for review see Tschan et al., 2001). Explosive actions (sprint with quick change of direction, jumps, tackles, kicks) mainly require an anaerobic-alactacid metabolism and are repeated with remarkable frequency during a match, and making up about 15-20% of total playing time. When explosive actions are spaced very closely, there is a shift from aerobic to anaerobic metabolism and this accounts for the high accumulation of lactic acid during a match-play. Soccer requires intermittent physical activity in which sequences of actions requiring a variety of skills of varying intensities are strung together (Cometti et al., 2001). The exercise pattern is characterized by repeated short duration
bouts of high intensity exercise interspersed with longer periods of lower intensity exercise and passive recovery (Balsom et al., 2001). Although the total duration of high intensity exercise performed during a multiple sprint sport only accounts for a very small proportion of the total game time, such periods are most often instrumental in determining the outcome of the game. Many activities in soccer require forceful and explosive bursts of energy including tackling, jumping, kicking, turning and changing pace. The power output during such activities is critical in determining the overall success of performance (Strudwick et al, 2002). In order to cope with the physical requirements for elite soccer match-play, it is important that the players have a high level of speed, agility, muscular strength and anaerobic power.

Is there any correlation between game analysis and aerobic – anerobic power tests?

Proietti (2002) reported a significant correlation between the aerobic power (Synthesis test 1999) and the high speed running (> 21.6 km/h) during a soccer game (table 24,25,26).Further correlation was found also with the anaerobic sprint power (Rast test 1996).The tests explanation and protocol are below reported.


Synthesis test (Proietti R. 1999)


Objective: this test was set up to meet the need to have a test
• that could measure metabolic properties in conditions of intermittent work in the field;
• that could approximate the soccer player’s kind of run from the biomechanical standpoint;
• that could provide information on the fitness level and that, without special machines (except for the heart rate meter), could enable the coach to customize the physical conditioning work loads by measuring the athlete’s maximum heart rate.
Equipment: heart rate meters. Performance: the test is comprised of eleven 20-meter sprints, with 20-second recovery periods between sprints, plus an 8-minute run at maximum speed over a 20-40-60-80-100-meter long shuttle track. In the last minute of the run, the athlete should be urged to carry out a maximum sprint in order to reach exhaustion and maximum heart rate.
There are significant positive correlations between the results obtained here and the results obtained in the Canadian version of the Leger test (p.< 0.05; r.0.95), and the Mongnoni-test (p < 0.05 and r.0.85) they show that the subjects who have a high maximum VO2 can run longer distances during the 8-minute run. Also, there is significant correlation between the maximum heart rate measured at the end of this test and the maximum heart rate measured in the Leger test (p.< 0.05; r.0.90). Results: aerobic power is calculated by the following formula: V02max = (meters run in the 8-min. run x 0.01635) + 27.353 Anaerobic threshold = (meter x 0.00705) + 1.7592






The Running-based Anaerobic Sprint Test (RAST) has been developed at the University of Wolverhampton as a sports-specific anaerobic test. It is similar to the Wingate anaerobic 30 cycle Test (WANT) in that it provides coaches with measurements on peak power, average power and minimum power along with a fatigue index. The tests differ with regard to specificity and cost of administration. The Wingate test is more specific for cyclists, whereas the RAST provides a test that can be used with athletes where running forms the basis for movement. The WANT necessitates the use of a cycle ergometer and computer which are not available for all coaches. The RAST requires only a stopwatch and a calculator for some simple computations. The RAST provides a more specific test of anaerobic performance in running-based sports.
The Running-based Anaerobic Sprint Test
Prior to the test each athlete is weighed. They then need to warm up for a period of five to 10 minutes followed by a three to five minute recovery. The RAST is a six by 35m dis-continuous sprint. Each sprint represents a maximal effort with 10 seconds allowed between each sprint for turnaround. The time
taken for each sprint should be recorded to the nearest hundredth of a second (the greater the accuracy the better). To perform the test accurately there will need to be two timers, one to time each run, the other to time the 10-second turnarounds. The athlete must sprint at maximum speed through the line each time. The arrangement for administration of the test can be seen in the diagram below. The next sprint starts from the opposite end of the measured track. The time between each run is designed to allow the athlete to return to the start line after running through the line, to record the time and reset the watch. The total running time is close to 30 seconds, making the test comparable with the WANT. At the end of the test the coach will have six times which can be used, along with body weight, to calculate maximal, minimal and average power outputs along with a fatigue index.
Example results and calculations
Power output for each sprint is found using the following formulas (Harman, 1995): The result from the first sprint of one athlete (with a body weight of 74 kilograms and a first sprint of 4.79 seconds) at the University of Wolverhampton can be seen below. The power output for the athlete's first run was therefore 825 watts. The power output for each of the other five sprints can be seen in the table below (having been calculated in exactly the same way) From these power outputs the same measures as for the WANT can be easily found. Maximal power is the highest output, which in this case is the first sprint; 825 watts and minimum power the lowest output which is the final sprint; 376 watts. The average power is found by adding each of the outputs and dividing by 6 (the number of sprints); 3666/6 = 611 watts. The fatigue index is found by taking the minimum power away from the maximal power and then dividing by the total time for the sprints; (Max -Min 825 -376 = 449), (Time 32.2) (Fatigue index = 449/32.2 = 14 watts/sec). The results can also be displayed on a graph and used to compare with previous results or other athletes.
Explanation of the results
Maximal/Peak Power Output: is a measure of highest power output. The range in scores in our research has been between 1054 and 676 watts. It provides information about strength and maximal sprint speed.

Minimum Power Output: reveals the lowest power output achieved and allows the calculation of fatigue index. The range in scores has been between 674 and 319 watts.

Average/Mean Power Output: gives an indication of an athlete's ability to maintain power over time. The higher this score the better the athlete's ability to maintain anaerobic performance.

Fatigue Index: indicates the rate at which power output declines for an athlete. The higher this rate the lower his or her ability to maintain power over the six runs. This can provide the coach with information about the athlete's anaerobic capacity or endurance. With a high fatigue index the athlete may need to focus on improving his or her lactate tolerance and this could be a focus of training.

Table 24 Descriptive statistics of aerobic power level and most important phases during the game (all players)





Conclusion
Various types of measurement have been conducted to evaluate specific aspects of the physical performance of soccer players.Several measurement obtained in the laboratory such as vo2 max and power output during maximal running, may give a general picture of the physical capacity of the player.Such test do not give a complete measure of performance in soccer.Instead, game analysis provide a better measure of performance in soccer.Neverthless, it has to be recognized that no single method may allow for a representative assessment of a player' s physical performnce during a soccer match.It seems that there are many characteristic that are required for play at top level in contemporary football.A success is dependent on how individuals are knitted together into a competent unit, the combination of physiological characteristics may vary from player to player.Nevertheless it is possible to generalize on physiological characteristics of specialists in this sport.Leg muscle composition is not extreme, the fiber type distribution favoring fast movements but demonstrating histochemical properties of aerobically trained athletes.This leads us to assume that intermittent training, which set running speeds corresponding to lactate concentrations between 4 and 8 mmol/l within a hearbeat range between 90-95% of max , have a conditioning effect both on aerobic/anaerobic power (Proietti R.1997). In soccer training, these exercises should be carried out in a linked way, with few seconds of recovery between the various fractions of the run, as it often happens in a match (Proietti R.1999; Colli R., Introini E, Bosco C.1997). Besides, as Evertsen F., Medbo J.I., Jebens E., Gjovaag T.F. 1999 pointed out, it is vital that the intensity of the work be comprised between 80-90% of the maximum VO2, that is, around the anaerobic threshold. In fact, the tested athletes improved their performance, and there was also a significant 6% (p.<0.02) increase of SDH enzyme (present in type I and IIa fibers), while the concentration of PFK (present in IIa and IIb fibers) decreased by 10% (p.=0.02). We should not forget that the activity of these enzymes in fundamental from the physiological standpoint, as they catalyze the chemical reactions that control energy metabolism during physical activity. More exactly, SDH enables the pyruvic
acid, which is the by-product of the aerobic combustion of sugars, to be oxidized, while PFK catalyzes the reaction that starts from glycogen to produce pyruvic acid. In other words, conditioning based on intermittent exercises enables the athlete to bear high intensity work, drawing fully on the aerobic system, and less on the lactacid system. Therefore, it is highly recommended that soccer training sessions include all those exercises made up of pliometric jump, combined with a sprint in the last part of the exercise, if possible. In fact, it is better to combine the two exercises because while jumps improve intramuscular coordination, sprints improve intermuscular coordination. The main objective of pliometric physical conditioning is to increase the ability to accelerate. Sensory physiological mechanisms are also relevant considerations in the make-up of football players.It is likely that central factors in deciding the timing of game-related movement, supported by sufficiently well-developed muscular strength, motor coordination, and oxygen trasport mechanisms to implement the decisions, are the keys to successful football play.

Acknowledgments
I am grateful to Univ. Prof. Dr. Ramon Baron, Univ. Ass. Mag. Dr. Harald Tschan (Sport University of Vienna) and Jamie Atherton (ProZone football analyst ) for their valuable comments.
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