For a long time, endurance training in soccer was based on improving physiological parameters. This methodology comes from athletics and only aims to improve the cardiorespiratory system, differentiating physical and technical-tactical training. However, soccer has evolved toward a holistic training methodology considers together the physical and technical-tactical aspects in task design. In this regard, it is of great importance that S&C coaches know how to organize the physical load within the coaches’ tactical objectives. Such Seirul.lo established: the aim is not to enhance a specific physical parameter; players must be able to withstand the physical demands required by the game system itself and that of the opponent.
Therefore, soccer endurance should not be exclusively considered for improving physiological parameters. Although it is not our premise, it is essential to have knowledge of physiological values such as heart rate (HR) or VO2max of our players. These parameters are referred to the intensity of the exercise. The following is a brief summary of the traditional methodology of endurance training using tables.
Pallarés & Morán-Navarro (2012) established training zones based on the improvement of cardiorespiratory capacity:
Endurance training zones in soccer (Pallarés & Morán-Navarro, 2012, modified by Guerrero-Calderon)
Pallarés & Morán-Navarro (2012) also established endurance training methods for these zones:
Endurance training methods in soccer (Pallarés & Morán-Navarro, 2012, modified by Guerrero-Calderon)
Conclusions
Although I have written about the traditional approach of endurance training in this post and it is essential to know how soccer affects the players’ cardiorespiratory system, it is a decontextualized training method and, therefore, inadequate, as it does not represent the real demands of soccer. The current endurance training methodology should consider the following items:
Specificity
Technical skills
Playing style
Opponents
Decision taking
If you want me to talk about training methodology from an integrated approach in future posts, leave a comment or share on social networks.
References
Guerrero-Calderón, B., Klemp, M., Morcillo, J. A., & Memmert, D. (2021). How does the workload applied during the training week and the contextual factors affect the physical responses of professional soccer players in the match? International Journal of Sports Science & Coaching, 16(4), 994–1003. https://doi.org/10.1177/1747954121995610
Pallarés, J., & Morán-Navarro, R. (2012). Methodological Approach To the Cardiorespiratory Endurance Training. Journal of Sport and Health Research, 4(2), 119–136.
Slettaløkken, G., & Rønnestad, B. R. (2014). High-Intensity Interval Training Every Second Week Maintains VO2max in Soccer Players During Off-Season. Journal of Strength and Conditioning Research, 28(7), 1946–1951.
Solé, J. (2002). Entrenamiento de la Resistencia en los Deportes de Equipo. In Apuntes Master Alto Rendimiento Deportes de Equipo. Byomedic System.
Small-Sided Games (SSGs) is one of the most common training methods in soccer at all level or ages; from elite teams to children, as it allows to develop the technic and tactics (TT) such as situations of numerical superiority, defensive retreat or third man play, among others, keeping the physical objectives programmed in that training session (1). However, it should be noted that practitioners need a good knowledge of SSGs in order to properly carry out these tasks adapted to coach’s objectives (2). A good teamwork and communication between the technical staff are essential. In addition, the S&C Coach must hold good knowledge of TT elements.
Benefits of SSGs
SSGs allow to train with the ball and achieve an exercise intensity of 95% of maximum heart rate (HRmax), which has been shown to improve the soccer-specific endurance, develop the specific muscle-groups involved in game, improve the TT elements in the specific conditions of game, and keep an effective transfer to the game (1–6). Therefore, SSG seem an effective task to combine the behaviors and motor patterns, the cohesion of the team in addition to aerobic training (1).
Design of SSGs
Pitch area
Increasing the playing area dimensions means an increase of HR, lactate concentration (La-) and RPE. This is caused to the greater area per player, with player having more space to move. Thus, larger SSGs is used in training to maintain high-intensity (HI) throughout exercise.
On the other hand, there are also differences in number of shots to goal, rebounds and passes between smaller and bigger game-area. In addition, lower number of assists, steals and turnover are found in big game pitches.
Big game area vs smaller game area
The greater the space, the greater intensity. Larger pitches involve covering a greater HI distance, speed-running and sprint frequency; whereas smaller pitches involve a greater number of accelerations, decelerations or changes of direction (4), in addition to a greater number of TT actions.
On the other hand, work-to-rest ratios are lower in the smallest areas. The work-to-rest ratio was only >1 on medium and large pitches, which indicates that activity prioritizes over recovery (4).
Number of players
The fewer number of players, higher HR, La- and RPE.
No intensity changes have been found when teams play with unequal number of players, excepting with the inclusion of floaters players, who attain much higher intensity than other players.
Choosing the appropriate number of players, several authors recommend using a reduced number of players and alternating equal and unequal number of players.
Relationship between the pitch area and number of players
The intensity of game is highly affected by the interaction between the pitch area and the number of players and it is considered a critical factor for an appropriate SSG design. The interpersonal playing area (IPA) arise from this relationship. IPA is defined as the available game area for each player into the total game area. Increasing the IPA might be useful to increase the intensity of SSG (3). Contrary, reducing the IPA results in a reduction of playing area and the time available for the task, so the decision-making process and technical execution should be faster.
4v4 SSGs
4v4 SSGs are considered the most appropriate game format (1,3). Caro et al. (3) concluded in its study with elite soccer players belonging to the Spanish First Division that 4v4 SSGs should be played in smaller spaces for a better recreation of match situations, and in addition these should be wider than longer. Also, the author found differences in the playing space depending to the area of the field where these actions take place. 4v4 game situations are played on reduced spaces for areas close to the goals while they are played in open spaces in the central areas. Caro et al. (3) proposed areas of 15x17m or 17x20m. However, the areas should be adapted to the level and age of players.
It should be noted that only 10v10 SSGs allow players to obtain similar running distances covered in match (2). The higher number of players, the higher distance per minute. Therefore, Lacome et al. (2) recommend 4v4 SSGs for strength-oriented training sessions and 10v10 SSGs for endurance-oriented training sessions.
Rules modification
Number of touches, man marking and presence of goalkeepers affect the physiological, technical and tactical responses of players, so they should be considered to modify the intensity. The free play rule produced greater number of duels, lower number of sprints and high-intensity running, and preserved the effectiveness of TT actions compared to 1-2 touches SSG. On the other hand, there are more intense actions when combining the offensive and defensive playing situations together than in isolation.
Presence of Goalkeepers (GK)
Including small goals in SSGs increase the motivation of players. The presence of GK in these tasks might modify the intensity of SSG. There are opposite results in the literature at present; several authors showed an increase in the %HRmax and others found a reduction. Therefore, coaches should avoid to include GK in SSGs and only use small goals to keep a high motivation of players and consequently higher intensity of training.
Coach Encouragement
The direct involvement and supervision of coach leads to an improvement of task intensity in addition to a higher adherence of players to the training.
Duration of SSGs
There are not clear conclusions about the appropriate time of SSGs due to the scarce literature analysing the effect of time duration on the physiological responses of soccer players. However, a systematic review did not show different physiological responses between continuous and intermittent training methods (1). Both methods can be used effectively to produce adaptations for soccer-specific endurance and coaches may alternate between the two in SSGs. However, it should be noted that other factors can affect the exercise intensity. Nonetheless, Fanchini et al. (7) concluded that 4-minute series may be a positive stimulus for SSGs.
Casamichana & Castellano (4) consider the variable ‘distance per minute’ the most representative intensity marker for this kind of HI tasks.
Differences with Competition
SSGs show greater distance per minute and high-intensity activity in all positions compared to competition, showing higher HRmax, La- and RPE. Also, SSGs show a greater number of duels and ball losses, in addition to a lower percentage of successful passes and total possessions (1).
Differences between positions
The SSGs show different physical demands relative to the playing position. Therefore, the intensity of the task should be programmed according to the specific demands of each role throughout modifying the rules, including floaters players, etc.
SSGs vs traditional intervallic-training methods
No differences on physiological responses have been found between SSGs and traditional intervallic-training methods. It is logically understood that the magnitude of response normally depends of the intensity, frequency and duration of training, as well as the total duration of training program and conditioning of players.
SSGs seem lightly more demanding than traditional approaches, which may lead to an improvement of the cardiorespiratory capacity of players. The increased responses can be caused by the higher motivation and enthusiasm of player for SSGs.
Conclusions
SSGs are an effective training method to develop the aerobic capacity of players and obtaining an appropriate readiness to real situations occurring in match.
The conditioning training should not be exclusively based on SSGs.
It is of paramount importance to keep an elevated motivation of players in training sessions.
A reduced IPA results in faster decision-making process and technical executions.
4v4 SSGs is the most effective training format. However, 10v10 SSGs allow better simulation of match physical demands.
Contact injuries seem to most prevalent injuries of this kind of tasks.
Practical applications
It is recommended to vary the SSGs training formats (number of players, pitch size, etc) over the season phases to obtaining the adequate training stimuli (intensity).
The higher intensity is obtained reducing the number of players and increasing the pitch size.
The coach encouragement and feedback during SSGs are effective to increase the intensity of game.
The suitability of using GK on SSGs is unclear. However, the presence of GK in bigger playing areas could motivate players and therefore increase the intensity of task.
4vs4 SSGs seem the most effective game format.
Manipulating some rules such increasing the number of players, number of touches or the type of marking can increase the intensity of SSGs and adapt it to the specific demands of each playing position.
References
Halouani J, Chtourou H, Gabbett TJ, Chaouachi A, Chamari K. Small-sided games in team sports training: a brief review. J Strength Cond Res. 2014; 28(12): 3594–618.
Lacome M, Simpson BM, Cholley Y, Lambert P, Buchheit M. Small-Sided Games in Elite Soccer: Does One Size Fit All? Int J Sports Physiol Perform. 2018; 13(5): 568–76.
Caro O, Zubillaga A, Fradua L, Fernandez-Navarro J. Analysis of Playing Area Dimensions in Spanish Professional Soccer: Extrapolation to the Design of Small-Sided Games With Tactical Applications. J strength Cond Res. 2019; 1–7.
Casamichana D, Castellano J. Time–motion, heart rate, perceptual and motor behaviour demands in small-sides soccer games: Effects of pitch size. J Sports Sci. 2010; 28(14): 1615–23.
Silva B, Garganta J, Santos R, Teoldo I. Comparing tactical behaviour of soccer players in 3 vs. 3 and 6 vs. 6 small-sided games. J Hum Kinet. 2014; 41(1): 191–202.
Beenham M, Barron DJ, Fry J, Hurst HH, Figueirdo A, Atkins S. A Comparison of GPS Workload Demands in Match Play and Small-Sided Games by the Positional Role in Youth Soccer. J Hum Kinet. 2017; 57: 129–37.
Fanchini M, Azzalin A, Castagna C, Schena F, Mccall A, Impellizzeri FM. Effect of Bout Duration on Exercise Intensity and Technical Performance of Small-Sided Games in Soccer. J Strength Cond Res. 2011; 25(2): 453–8.
If you have any doubt, do not hesitate to leave your comment. If you liked the post, share it on social media!
This article has been made based on the references showed, other studies reviewed but not showed and according to the experience and knowledge of the author. In this way, it may include subjective ideas and opinions not contrasted in the research.
Physical load monitoring has advance significantly during the last century (1). Sport is become more demanding and it is more difficult to win. There is a need of keeping a good physical capacity of athletes to withstand the high competition demands: both improve performance and decrease the injury risk. The position of Sport Scientist (SS) is becoming more required to supply the work of technical staff (coaches and S&C Coaches) in the field through the load analysis provided by players. Thus, the role of SS involves the analysis of internal- and external load parameters throughout different tests and monitoring methods and tools and compare and interpret the results with the research to provide coach a detailed report of athletes’ physical performance. However, there are several doubts about how the training load may affect the physical performance of high-level athletes.
It should be noted that the main objective of SS is to provide a detailed and practical report interpreting the athletes’ physical performance taking into account the scientist literature so the coach can easily use and solve his doubts. Therefore, the provided information should be clear and summarized, avoiding long and tedious reports and adapted to the coach requirements: digital vs paper format, quantitative vs qualitative, tables or graphs, among others.
3 most important step to make an adequate report (2)
Appropriate analysis and understanding of data. Using the right variables and statistical tests. They have to be useful to answer the questions that are asked by coaches.
Provide attractive reports through a good presentation and visualization: creativity (using colors, diagrams, tables, etc).
Good communication skills and attitude to efficiently deliver the reports to coaches (this is the most important point for the author).
The SS must provide ‘good knowledge’ to assess the performance of athletes, the competition plan and load monitoring (3). It is useful to compare the obtained data with current scientific knowledge. However, the SS must develop intervention strategies that facilitate the S&C coaches work. It should be noted that they can never have access to all the information relevant to a given problem. Therefore, the decision making should be based on a practical and flexible interpretation of data; either quantitatively and qualitatively.
The decision making in load monitoring: ‘Green, amber or red light?’
Knowing the physical state of players to withstand the competition demands showing their ‘level’ of readiness simulating the lights of traffic-lights (4) might be a good way to assess the physical capacity of athletes and how they are assimilating the load providing coaches an easier way to take decisions relative to the possible risks to assume for using a determinate player in competition or reprogramming the training load. Thus, the physical performance and injury risk relationship should be added and, logically, individualized. The main goal of the traffic-light system is providing coaches a ‘visual’ and rapidly interpreted method to facilitate the decision making.
Interpretation of the traffic lights for decision making (Figure 2):
GREEN: things should continue as per normal.
AMBER: suggests caution. It may suppose a risk if left unattended.
RED: alarm. Action is required.
Figure 2. Players’ readiness expressed in different colors. (Robertson, Bartlett & Gastin. 2017)
This evaluation method of traffic light might be differentiated depending of what it wants to evaluate: physical performance or injury risks; using parameters or variables that can be adapted to the specific objective. Nonetheless, the final purpose is knowing what players are ready to compete (green light). Therefore, I personally consider that this relationship should include both a good fitness of player and low risk of injury. On the other hand, the differentiation by colors might be used to assess anything more visual and easier.
What coaches need from Sport Scientist (1):
A way to evaluate athlete potential
A way to evaluate an athlete’s current status
A way to evaluate how an athlete is responding to a training program
A way to measure progress, that is translatable into performance
Foster (1) highlight the subjective perception of effort provided by players due to the large correlation between internal and external load (2).
Statistical analysis
The statistical analysis or tests performed by SS will vary depending of what they want to calculate. It is logically understood that the results must be reliable and valid, in addition to practical application for training programming.
Traditional null hypothesis significance testing (NHST) based on p-values has always been used. However, the author considers it an inappropriate test for this kind of sample due to the low number of players into the team and to answer the questions that arise from the field. The magnitude-based inference (MBI) is an innovate and relevant method which facilitates his clinical interpretation.
The MBI proposed by Batterham (5) is based on two simple concepts:
Changes/differences in any variable are systematically compared to a typical threshold representative of a smallest important or meaningful change.
Not all changes are worthwhile. Is the change longer than the SWC? How many times greater? Small, moderate, large or very large. (SWC: small-worthwhile change)
Instead of a classic ‘yes or no’ type response (NHST), the probabilities for these changes/differences to be ‘real’ (greater than the SWC) are reported.
More precisely: both quantitatively and qualitatively changes.
The percentage change and associated qualitative interpretations are generally set a priori: <1% (almost certainly not); 1-5% (very unlikely); 5-25% (probably not); 25-75% (possible); 75-95% (likely); 95-99 (very likely); >99% (almost certain).
Final decisions can be translated into plain language when chatting with coaches
The duties of Sport Scientist (1–4):
Reports:
Simple and precise.
Horizontal text.
Remove extra decimals and ‘noise’.
Images better than written text: VISUAL.
Use different colors (fast and better interpretation).
Highlight the main results.
Add plots and tables.
Selection of appropriate variables and metrics.
Summarize the data.
The results must answer the questions of coaches and adapting to their needs.
Develop a database.
Improve the integration of different multidisciplinary areas.
Support the results with scientist knowledge.
Conclusions
The role of SS is still not fully established in sport, even in top-level. Although it may seem illogical due to the high number of tools and methods for load monitoring and management, in addition to the high demands in high-level, there is controversy regarding the SS’ tasks and despite of this role is well established in many staffs and there is an increasing number of clubs which are incorporating this role into the staff, I personally believe that there is still a long way to go as practitioners (in the field) work still far away from sport scientists possibly due to an inadequate analysis and management of data.
As aforementioned, the data must be interpreted and adapted to answer the questions of coaches and provide practical application before delivery to facilitate the work of practitioners and therefore focus on practice. So, SS should not only be limited to analyse the workload and deliver a excel sheet with multitude of ‘raw’ data to coaches and S&C coaches so that they have to find out the adequate load and why. The SS should interpret the data, take decisions and deliver precise and easily and fast understood reports adapted to the specific requirements from technical staff.
As we can see in Figure 2 retrieved from Robertson (4), using different colors simulating the traffic lights according to the level of readiness of player may be an easy and precise method. Foster (1) concludes that currently the great number of evaluation and monitoring tools may be a problem for coaches as the cannot manage all of them, so it is of paramount importance to summarize the data. ‘More is not better’.
Finally, creating an area of investigation and development (I+D) within the clubs can be very useful to improve and progress the analysis of specific physical or technical-tactical performance.
References
Foster C, Rodriguez-Marroyo JA, de Koning JJ. Monitoring Training Loads: The Past, the Present, and the Future. Int J Sports Physiol Perform. 2017; 1–24.
Buchheit M. Want to see my report coach? Sports science reporting in the realworld. Aspetar Sport Med J. 2017; 6: 36–43.
Robertson S. Man & machine: Adaptive tools for the contemporary performance analyst. J Sports Sci. 2020; 00(00): 1–9.
Robertson S, Bartlett JD, Gastin PB. Red, Amber, or Green? Athlete Monitoring in Team Sport: The Need for Decision-Support Systems. Int J Sports Physiol Perform. 2017; 12(Suppl 2): S2-73-S2-79.
Batterham AM, Hopkins WG. Making Meaningful Inferences About Magnitudes. Int J Sports Physiol Perform. 2006; 1(1): 50–7.
If you have any doubt, do not hesitate to leave your comment. If you liked the post, share it on social media!
This article has been made based on the references showed, other studies reviewed but not showed and according to the experience and knowledge of the author. In this way, it may include subjective ideas and opinions not contrasted in the research.
The load monitoring in team sports has evolved greatly in recent years and there are currently many methods and tools for training and match load quantification and evaluation aimed to improve the training process, the competition performance and reduce the injury risks. It can be evaluated the internal or external load; physiological and biomechanical; objectively- or subjectively-based; the volume or intensity; pre-, intra- or post- training; and quantify different locomotion parameters (e.g. total distance covered at different speed ranges or the acceleration and deceleration events); the energy expenditure; the heart rate analysis; blood lactate; muscle contractile capacity; muscular asymmetries; hidratation state; sleep quality; muscle temperature; body composition, etc. throughout the use of GPS devices, video-tracking, accelerometers, blood analysis, dynamometers, tensyomiography, etc. A myriad of evaluation tools and devices that are impossible to carry out all of them.
The practitioners of each club have to decide what the monitoring systems and devices to evaluate players. It is logically understood there are daily monitoring systems, like time-motion analysis trough GPS; weekly analysis like heart rate variability (HRV); and others analysis with lower frequency as the spirometry.
Monitoring purpose
As afore mentioned, the main purpose of load monitoring and evaluation in team-sport is facilitate the training process to improve the performance and reduce the injury risks. Therefore, it cannot be: ‘I quantify and assess everything, I do nothing’. The practitioner is not better if measures more parameters. The good practitioner must be able to use the available tools correctly to keep an optimized performance of players. Obviously, in high-level a great number of parameters must be evaluated to keep a good fitness of players in all facets. Therefore, it is important to understand:
WHAT do we want to know? WHEN? And maybe more important, FOR WHAT?
What do we want to know and when?
High-level is very demanding, with a congested competition schedule and it is of paramount importance to keep a good physical capacity of players to avoid increasing the injury incidence. Therefore, the load monitoring and evaluation in team sports must be very precise for knowing exactly what parameters we are managing and how.
An important consideration to work with sportsmen is that we must ‘disturb’ them as little as possible and try to use the monitoring tools that interfere less in their usual practice. Athletes must be focused exclusively on train and compete in the best possible way. Therefore, invasive methods (e.g. blood analysis) should be performed eventually. In addition, many athletes will not want to carry out on a regular basis. Logically there are a recommended frequency or timing for each monitoring tool or test. Although there are parameters that may be more interesting than others, the evaluations or tests that we can make more often will be those that are less annoying for athletes.
For what?
We must not forget that the final purpose of load monitoring and evaluation in high-level team sports is to win. Thus, practitioners must keep an optimal physical performance and reduce the injury risks of athletes. In this way, a certain load parameter can be assessed or monitored either when the training session or task goal is the performance optimization, injury prevention or during an injury recovery process.
However, it is important to know exactly what we are monitoring or assessing the parameter for. If we are monitoring the time-motion through GPS devices; why are we assessing a certain parameter? What values do I want to attain? How these attained values may affect the players’ physical performance? How will affect to my consequent decision taking? There is a recent study about how to manage the decision taking in the monitoring process and how the sport scientist can support this process (1). This is an interesting topic for discussion that will be soon posted on the Blog. For instance, the evaluation of players’ body composition with anthropometry.
The literature shows that the adequate body-fat percentage should not be higher than 10-12% (2–4) because it will negatively affect the players’ performance such as shorter high-intensity running distance or the early onset of fatigue, among others, which will consequently increase the injury risk. If the body-fat of player is higher than 10-12%, the player will undergo an extra training program in addition to a specific nutritional plan to reduce the body-fat percentage. It is more difficult to find people with a lower percentage than the benchmark but lower values than 3-5% might be dangerous. With this example, I know exactly what I want to measure, what values I am looking for, and how I will act accordingly.
On the other hand, I personally believe that it is of paramount important to explain player the reason for they are been monitored or assessed and make them understand that it is to improve their physical performance.
The following are the most commonly used monitoring parameters in team sports, the assessment method, goal and tools required to carry them out, differentiating between internal and external load parameters.
Internal load
Table 1 list the most commonly used internal-load monitoring parameters in the research.
Parameter
Device/tool
Monitoring/test
Goal
Considerations
Heart rate
HR monitor
On training tasks or specific tests.
Assessing the cardiorespiratory capacity, intensity, fatigue
HR reserve is more accurate than HRmax
HR Variability
HR monitor
Test: once a week before training
Detect fatigue and overtraining
Fasting state
Post-activity
CR10 Börg Scale
30’ post-training
Players’ subjective effort perception
RPE-TL (RPE x min of session)Acute:chronic workload ratio
There is more variability to monitor the external load in team sports according to the specific sport as it will depend of the kind of locomotion, the game-field size or the demanded efforts, among others. The external-load parameters most common are:
Analysis of locomotion activity
Tools: GPS or video-tracking
Frequency: daily (during the activity)
Objectives: knowing the type of efforts of athletes (distances covered, type of actions, etc).
Considerations: take into account the positional and individualized differences, contextual variables.
Strength and muscular power
Tools: dynamometer, RM, power test, etc.
Frequency: daily/periodic
Objectives: quantify the developed strength by player in different tasks.
Considerations: take into account the positional and individualized differences, contextual variables.
Conclusions
Today there are many tools and load assessing methods for sportsmen. Although this article shows some of the most commonly used load parameters in high-level team sports, each practitioner should choose the most adequate methods and tools for him and players according to his needs, knowledge and possibilities. As a S&C coach who I admire and has worked on some of the world best soccer teams once said:
‘The best S&C Coach is able to doing his job properly ‘undetected’, passing unnoticed.’
Very insightful words. ‘Do a proper job’ is referred to program and manage the training load to optimize the players’ performance and decrease the injury rate.
Personally, I believe that the S&C Coach should not want to be protagonist, because HE IS NOT. The player is the protagonist. The S&C Coach work by and for the athlete and the good professional is who get to keep players available to the coach in every match with an optimized physical condition and confidence ready for competition. Therefore, the S&C Coach prepare players to train in the best conditions and the coach then decides the most adequate players for each match. Finally, it is necessary to keep a good collaboration and communication between all the staff (technical-tactical, physical, medical) to achieve ‘harmony’ in the training process of athletes.
References
Robertson S. Man & machine: Adaptive tools for the contemporary performance analyst. J Sports Sci. 2020; 00(00): 1–9.
Fernández Paneque S, Alvero Cruz JR. La Producción Científica En Cineantropometría: Datos De Referencia De Composición Corporal Y Somatotipo the Scientific Production in Kinanthropometry : Reference Data of Body Composition and Somatotype. Arch Med Del Deport. 2006; XXIII(111): 17–35.
Foster C, Florhaug JA, Franklin J, Gottschall L, Hrovatin LA, Parker S, et al. A new approach to monitoring exercise training. J strength Cond Res. 2001; 15(1): 109–15.
Owen AL, Forsyth JJ, Wong DP, Dellal A, Connelly SP, Chamari K. Heart Rate–Based Training Intensity and Its Impact on Injury Incidence Among Elite-Level Professional Soccer Players. J Strength Cond Res. 2015; 29(6): 1705–12.
Roca A. El proceso de entrenamiento en el fútbol. Metodología de trabajo en un equipo profesional (FC Barcelona). Preparación futbolística. Barcelona, España: MC Sports; 2008. 1–72 p.
González-Boto R, Salguero A, Tuero C, Márquez S, Kellmann M. SPANISH ADAPTATION AND ANALYSIS BY STRUCTURAL EQUATION MODELING OF AN INSTRUMENT FOR MONITORING OVERTRAINING: THE RECOVERY-STRESS QUESTIONNAIRE (RESTQ-SPORT). Soc Behav Personal an Int J. 2008; 36(5): 635–50.
Note: although not many studies have been referenced in the text, all written content has been developed based on years of scientist reading about the subject matter.
If you have any doubt, do not hesitate to leave your comment. If you liked the post, share it on social media!
This article has been made based on the references showed, other studies reviewed but not showed and according to the experience and knowledge of the author. In this way, it may include subjective ideas and opinions not contrasted in the research.
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