Physical preparation of the U16 soccer

As a sports osteopath, many sports patients, especially soccer players, are seen in my practice. Osteopathy is a wonderful profession, a real passion for me which allows me to prevent injuries, to relieve or even treat a patient. But osteopathy alone is not enough, whatever the patient's level and physical condition.
The treatment of a sports patient must therefore be multidisciplinary for prophylaxis but also to optimize the return of the injured player.

It was therefore essential for me to try to understand and master as much as possible the field of physical preparation. The goal is to be able to optimize the physical condition of the player, based on my knowledge as a sports carer, so that he does not get injured, or in case of injury, to accelerate his return and avoid recurrences. I therefore chose to apply for the University Diploma of Physical Trainer in order to optimize the care of my patients but also the collaborative work between the technical and medical teams. 

For the training course, I chose to work with the soccer club of Savigny le Temple, with which I already work. I chose, as a study group, the team of under 16 years (U16) composed of 20 boys.

Not being an expert in soccer, I had to learn quickly, especially about the specificity of the positions and what this meant for the physical preparation. 

This 2019-2020 year has been marked by strikes and especially the coronavirus (Covid-19) with its containment, which has completely disrupted training and the sports season.

Soccer, also called soccer in English-speaking countries, is one of the most practiced sports in the world with 265 million players according to FIFA(1) in 2006 and 2,198,256 licensees including 184,037 women according to the French Football Federation(2).

Soccer is a team sport in which two teams of eleven players compete on a field for a 90-minute match, divided into two 45-minute halves(3).

The tactical aspect of the game is paramount and must allow a team to put the ball in the opposing goals defended by the opposing team whose goalkeeper is allowed to touch the ball with his hands. This action (scoring) is very difficult because only 2% of the attacks lead to a goal against 80% in Basketball(3).

Only the feet, head and any area of the body other than the arms are allowed to be in contact with the ball(3).

Physical preparation is at the heart of the success of the game, it must allow the footballer to remain as efficient as possible and physical skills alone are no longer enough.

According to Vigne G (2011)(4) Stolen et al (2005), Reilly et al (2000), the physical qualities needed are endurance, strength, speed and coordination. The physical preparation of the soccer player has long been based on endurance, but as Gilles Cometti presents, the practice of soccer requires explosive actions allowed by the fast fibers(5). It is therefore essential to work on explosiveness and speed and to repeat these actions.

But to this must be added the mastery of technique, the mental, the intelligence of the game, the psychomotricity.

Playing time has evolved in recent years from 54.58 minutes in 1990 to 68 minutes in 2000(6) and 56.07 minutes in 2002, despite the fact that the amount of action remains the same or even increases. The efforts are more rapid, it is necessary to adapt the physical capacities of the players.

According to Vigne (2010), an amateur player spends 50 to 55 minutes of effective play and this time increases to an average of 73.62 for a professional player(7). 

Playing distances vary depending on the position, the system of play, the opponent, and whether or not the player has the ball.

The video tracking system appeared in the 1970's and has been very strongly developed since then. It has allowed a precise analysis of the players' activity during the games (distance covered, types of movement, etc.). 

Mohr et al in 2003 showed that high level footballers perform more high intensity running than amateur footballers(8). Physical preparation has a very important role to play in enabling the player to have endurance for high intensity running. It has become necessary to work on speed and explosiveness.

According to Castagna in 2005, a footballer sprints on average every 90 seconds, over a period of 2-4 seconds(8). Sprinting then represents between 1 and 11% of the total distance covered during a match, i.e. between 0.5 and 3% of the actual playing time(9).

In soccer, there are different positions for different players:

• Front left
• Front center
• Front right
• Left midfield
• Middle center
• Right middle
• Right or left side rear
• Central defender
• Guardian

During a match, defenders show less intensity than midfielders, fullbacks and forwards. Fatigue seems to occur towards the end of the match as well as temporarily during the match according to Mohr et al(8).

O'Donoghue(10) highlighted in 2002 that over a 15-minute analysis period :

• An attacker performs 31 sprints of about 3.2 seconds with an average recovery time of 28 seconds.
• A midfielder performs 32 sprints with an average duration of 3.2 seconds with about 27 seconds of recovery.
• A defender performs 28 sprints with an average duration of 3.1 seconds and an average recovery time of 32 seconds(10).

Dellal et al evaluated, in 2010, the distance traveled at high intensitý defined as between 21 to 24 km/h and sprinting defined as greater than 24 km/h in an offensive and a defensive situation(11). They show that the distance covered by the player is different depending on the position and the situation:

• Players in defensive situations achieve a greater distance during defensive phases of play than during offensive phases, and vice versa.
• There were no significant differences between the environments.

The time of possession of the ball varies according to the authors. We find:

• According to Bangsbo (1994), a player has the ball in his possession for about 1.3 minutes(13).
• According to Dellal et al (2010 and 2011), this possession time ranges from 44 to 75 seconds(11,14). 
• According to Carling (2010), this time lasts on average 1.1 seconds(15).

Dellal et al showed in 2010 that the number of ball possessions varies between 38 and 57 with a number of touches between 1.87 and 2.23 per possession(11).

Carling's observations in 2010 are similar with an average number of possessions of 47 and an average number of touches of 1 to 2.2 times per possession(15). 

Carling also shows that when in possession of the ball, a player travels an average of 191 metres, distributed according to intensity(15) :

• 34% at speeds over 19.1 km/h ;
• 26% between 14.1 and 19 km/h ;
• 12% between 11.1 and 14 km/h ;
• 28% for a speed lower than 11km/h.

The tactical set-up corresponds to the placement of the players on the field, so there is a tactical and spatial component. The players are placed on the device according to their position but Bradley et al showed, in 2010, significant differences on the athletic component of the players according to the tactical device used(16).

There are different tactical devices but the three most used are:

• 4-4-2 " diamond or square " tactical device
• 4-3-3" tactical setup 
• 4-5-1" tactical system 

Also included are:

• 5-3-2" tactical system
• 3-5-2" tactical system
• 5-4-1" tactical device

Bradley et al analyzed, in 2011, the total distance traveled as a function of the playing position and the tactical setup used(17). Their findings include:

The result is that defenders cover more distance in a "4-4-2" set-up, i.e. 10452 metres, than in a "4-3-3" set-up (10073 metres) or in a "4-5-1" set-up (10123 metres). 

Defenders travel 11% more distance at high intensitý in a "4-4-2" setup (2454 meters) than in a "4-5-1" system (2207 meters) (17).

The tactical arrangement "4-4-2" seems to be more physically demanding for the defenders than the arrangements "4-3-3" and "4-5-1".

Attackers travel between 28 and 32% more distance at high intensitý in a "4-3-3" setup (2988 meters) than in "4-4-2" (2250 meters) and "4-5-1" (2333 meters).

Attackers cover more distance at very high intensity in "4-3-3" (1155 meters) than in "4-5-1" (870 meters)(17).

The tactical arrangement "4-3-3" seems to be more physically demanding for the strikers than the arrangements "4-4-2" and "4-5-1".

No significant differences were found for the environments(17).

The average heart rate (HR) is estimated to be 160 beats/minute representing between 80 to 90% of the maximum HR(18).

In 1992, Mombaerts highlighted the alternation of play and rest sequences during a match. His studies show that more than 50% of the play sequences are less than or equal to 15 seconds in duration and that the average rest time is 15 seconds(19).

30% of the game sequences in a match alternate with 15 seconds of play and then 15 seconds of rest and 25% of the game sequences alternate 7 seconds of play and 15 seconds of rest(19).

Orendurff show in 2010 that 90% of the races are distributed as follows:

• 43% of the efforts last less than 6 seconds; 
• 23% between 6 and 9 seconds; 
• 13% between 9 and 12 seconds;
• 9% between 12 and 15 seconds(20). 

And that 90 of the recovery periods are divided as follows:

• 53% of recoveries are less than 6 seconds;
• 22% between 6 and 9 seconds;
• 9% between 9 and 12 seconds ;
• 5% between 12 and 15 seconds(20). 

Between 1000 and 1400 short duration actions (between 2 and 4 seconds) are performed by a player during a match18 and about 220 at high intensity(8). These actions appear to have a recurrence every 4 to 6 seconds according to Bangsbo(21) and according to Strudwick and Reilly, a player would perform a high intensity ruń every 60 seconds and a sprint every 4 minutes(22).

The actions are multiple and diverse:

• Acceleration;
• Rapid decelerations;
• Management changes;
• Sprint;
• Tackles;
• Jumps ;
• Strikes(23). 

There are several energy channels that allow the action of the muscle:

• The aerobic pathway: this pathway allows the synthesis of ATP through the degradation of glucose or fatty acids from adipose tissue (via beta-oxidation and glycolysis). For glucose, the first part of degradation is identical to anaerobic glycolysis, in fact pyruvate is formed from glucose. This pyruvate will enter the mitochondria and will allow the aerobic part, that is to say the set of reactions that require oxygen. This part allows the release of 36 additional ATP molecules (i.e. 38 in total) from a glucose molecule: Glucose + 6 O2 + 38 ADP -> 6 CO2 + 6 H20 + 38 ATP. This pathway therefore has a much greater capacity than the anaerobic pathways. The disadvantage is that the start-up of this pathway is very long to provide energy unlike the other two. We say that the aerobic pathway is the pathway of endurance because of its high capacity and low power.
   
• The anaerobic pathway:
  • Anaérobie alactique : cette filière ne nécessite pas d’oxygène et ne produit pas d’acide lactique. Elle utilise l’ADP formée par la dégradation de l’ATP pour re-synthétiser de l’ATP grâce à la phosphocréatine (PC) : (PC + ADP <=> ATP + C). La puissance de cette filière est très élevée mais sa capacité est très faible. Schématiquement, on dit que c’est la filière des efforts courts et intenses.
  • Anaerobic lactic: this pathway does not require oxygen and works through the breakdown of glucose (anaerobic glycolysis: Glucose + ADP to Pyruvate + 2 ATP + H2O to Lactate). The activation time of this pathway is short, a few seconds. It can be sustained for up to 20 minutes.

Howald's curve explains the sequence of intervention of the different energy channels during an effort.

The average aerobic load during a match is estimated to be 75% of VO2 max (80% of maximum heart rate (HR)(23). 

Explosiveness is defined as the time it takes to reach the greatest possible force. It is therefore the ability to reach the greatest force in the least amount of time.

Power is different from explosiveness. Indeed, the power imposes a movement whereas the explosiveness can be produced in isometry.

It is therefore possible to be explosive without being powerful, however being explosive favors the expression of power.

Weightlifting allows for the expression of explosive strength and plyometrics allows for the development of greater power. 

The word "pliometry" comes, according to Wilt, from the Greek "plethyein" which means to increase and the word "isometry" which means the same length.

A plyometric action is defined, according to Gilles Cometti, as the action of a muscle in tension subjected to a phase of muscular lengthening (eccentric phase) followed by a phase of muscular shortening (concentric phase) and this in the same movement. 

This stretch-shortening cycle requires, according to Komi and Gollhofer, 1997(24) :

• A "pre-activation" of the muscles before the eccentric phase;
• A fast and short eccentric phase;
• An immediate transition between the stretching (eccentric) and shortening (concentric) phases (24).

In 1966, Bosco showed the effectiveness of plyometric work thanks to the action of two components:

• The myotatic reflex: this is a muscular contraction in reaction to its own stretching, bringing into play an autonomous defense loop. This muscle contraction is mediated by a receptor, the neuromuscular spindle, a type 1a sensitive pathway, the synapse between the sensory neuron and the alpha motor neuron. This was demonstrated by Schmidtbleicher in 1985(25).
• The muscular elastic component: This component is explained by the Hill diagram (modified by Shorten, 1987). It is composed of two elastic components:
  • Serial elastic component: it is responsible for the muscular action. It is composed of two parts:
    • Active portion: actin and myosin bridges.
    • Passive portion located in the tendons;
  • Parallel elastic component: it is constituted by the membranes and muscular envelopes and does not intervene in the efficiency of the action of the muscle.

According to Gilles Cometti, plyometric work allows :

• The development of forces greater than the maximum voluntary force (= 1.5 x voluntary force) ;
• Decrease of inhibitions on the myotatic reflex;
• Golgi receptor threshold increase;
• Improving the sensitivity of the neuromuscular spindle; 
• Decreased coupling time;
• Increased muscle stiffness. 

Plyometric training is composed of 4 main stages according to COMETTI in 201226 :  

• Horizontal plyometrics: for example, there is work with skipping rope, jumps with jointed feet, uni-podal, alternating feet, jumps with hoops, leaping strides, etc.
• Concentric strength training: for example, seated bench work, standing bench work, etc.
• Counter Movement Jump (CMJ) plyometrics: e.g. CMJ work, fixed arm CMJ, free arm CMJ, sequence of several CMJ, etc. 
• Vertical plyometrics: e.g. hurdle work (varying the height of the hurdles), box jump or low jump, etc.

Speed is the ability to move as fast as possible. It is the ratio between length and time (Speed = Length/time). Speed is a neuromuscular quality that allows us to perform high intensity motor actions in a minimum amount of time.

Speed depends on three factors, according to Zatsiorsky(27):  

• Reaction time;
• Gestural speed;
• Gestural frequency: this also depends on 3 elements:
  • • Agonist/Antagonist Strength;
    • The ability to alternate muscle contraction and relaxation;
    • The ability to increase the pace.

"Strength is the ability to move a mass (one's own body, the opponent's body, or an accessory), in other words, to overcome or oppose resistance through muscular work." according to Meusel28.

The force is broken down into 3 subparts: 

• Maximum force: this is the greatest force that the muscular and nervous systems are capable of producing during a maximum voluntary contraction. 
• Speed force or explosive force: according to Meusel, "Speed-force is the capacity for high-speed movements against submaximal resistance(28)."
• Strength endurance or strength endurance: again according to Meusel, "The more strength endurance is developed, the better we can train speed strength and maximum strength(28). Strength endurance corresponds to the ability to maintain the same level of strength over a given period of time or the ability to limit decreases in strength due to muscle fatigue. 

I would like to thank all the team of the Savigny-le-Temple Football Club (coaches, children, parents) for their kindness and the great welcome I received and especially Nicolas Nevejans, coach with whom I had the pleasure to collaborate all this year. I particularly thank the U16 that I followed throughout the year for their investment and this, despite the rebounds of the year 2019-2020.

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