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.
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.
This article summarizes one of the most used physiological parameters for internal-load monitoring in soccer: the heart rate (HR).
As we know, soccer is an intermittent sport characterized by alternating recovery periods with aerobic or anaerobic random active-cycles (AC) (1). Different actions like fights, accelerations, jumps or changes of directions, among others, may be made on these ACs, which are regulated by Autonomous Nervous System (ANS) to provide active responses of sympathetic nature. However, adequate levels of parasympathetic activity in recovery periods is useful to recover between HI bouts or ACs. Thus, many authors conclude that HR monitoring is an adequate method to assess the physical capacity or the fatigue (2–8) and enables an indirect estimation of the aerobic cost, but no the anaerobic (9).
In recent years almost all studies have analysed and monitored the HR based on the maximum HR (HRmax) to define the physiological profiles of soccer players. However, the use of the reserve HR percentage (%HRres) provides more accurate results (10). The formula was established by Karvonen et al. (11):
Due to the calculation of %HRres takes into account the biorhythm variations and consequently allows to compare the players HR on different activities or training sessions.
HR in competition
After an extensive review of the literature, I collected the main HR values:
HR mean: 165 to 175 ppm (10).
Intensity range of HR: 80-90% HRmax (12,13).
37% of match total time: ranges of 70-80% and 80-90% HRmax (14).
The research does not show differences on these values among categories or levels. However, the age, sex and physical capacity of players should be related with the HR as it may be show different recovery time between high-intensity efforts. For instance, the %HRmax of players may be higher if they have a low physical level.
Accumulated fatigue
It is important to analyse and interpret the HR of players’ on the different match halves as the intensity (expressed as %HRmax) is lower in the second half than the first due to the accumulated fatigue during the match (14). The author found that the players are less time on ranges of 85-90% HRmax and more time on lower intensity ranges (75-85% HRmax) on the second half. In addition, players have different mean HR according to the position, playing style or individual characteristics (15). Therefore, several authors conclude that the HRmax is not the best parameter to evaluate the soccer-activity intensity as it not considers the different HR responses (10). Although two players attain the same HRmax, they may show different HRrest, which it will elicit different responses in the match.
HR analysis by playing position
Midfielders usually show the highest HR values and central defenders the lowest as a result of the tactical function of each position in the modern game (10). From a technical-tactical approach, midfielders are involved in both offensive and defensive actions and therefore need greater aerobic capacity to withstand theif continuous participation in the game (13). Nonetheless, as mentioned above the playing style developed by the team or the individual characteristics will affect the players’ HR responses.
Maximal oxygen consumption(VO2max)
The HR values are closely related with the VO2max. The mean intensity of professional soccer player is among 70-80% VO2max during the match (13). So, the VO2max of top-level soccer players is 52-68 ml · kg-1 · min-1 (16).
However, we have to take into account that the type of recovery (active or passive) and effort during a short-duration intermittent activity like soccer will modify the HR response. Although the accelerations, decelerations or CODs greatly affect the HR, his analysis does not reflect the anaerobic metabolism changes (10). Other factors as hormonal activity, environment conditions or playing surface may also alter the HR pattern and no affect the VO2max equally.
Heart Rate Variability (HRV)
The importance of analysing HRV in an intermittent sport such as soccer has increased in recent years for a deepen evaluation of recovery HR with different types of stimuli. Therefore, HRV may be very useful for detecting overtraining symptoms (2–4,6).
Conclusions
HR is an adequate monitoring parameter to monitor the internal load in soccer players (especially the HRres). However, it can be inaccurate to quantify the training load.
HRmean: 165-175 ppm.
HR ranges in competition: 70-80% and 80-90% HRmax.
VO2max: 52-68 ml · kg-1 · min-1 (70-80%).
HR must be interpreted individually by player.
HR must be analysed separately in the different halves of match (fatigue).
Personal interpretation and practical applications
HR is useful to establish individualized references-values of cardiorespiratory capacity of each player for knowing if they are physically prepared to withstand the competition demands. In addition, depending on the values obtained, individualized training sessions (differentiated from group-sessions) might be made if are necessary for players.
HR is NOT useful to quantify the training load in which all kind of actions and efforts take place: sprints, CODs, jumps, collisions, fights, …
Whenever the HR is used as a parameter it will be for the performance of some specific tests without ball and/or evaluating the cardiorespiratory capacity of players (e.g., establish the anaerobic threshold).
References
Ravé G, Fortrat J-O. Heart rate variability in the standing position reflects training adaptation in professional soccer players. Eur J Appl Physiol. 2016; 116(8): 1575–82.
Proietti R, di Fronso S, Lucas AP, Bortoli L, Robazza C, Fabio YN, et al. Heart rate variability discriminates competitive levels in professional soccer players. J strength Cond Res. 2017; 31(6): 1719–25.
Boullosa DA, Abreu L, Nakamura FY, Muñoz VE, Domínguez E, Leicht AS. Cardiac autonomic adaptations in elite Spanish soccer players during preseason. Int J Sports Physiol Perform. 2013; 8(4): 400–9.
Naranjo J, De la Cruz B, Sarabia E, De Hoyo M, Dominguez-Cobo S. Two New Indexes for the Assessment of Autonomic Balance in Elite Soccer Players. Int J Sports Physiol Perform. 2015; 10(4): 452–7.
Task Force of The European Society of Cardiology and The North American Society of Pacing and Electrophysiology. Heart rate variability, standards of measurement, physiological interpretation, and clinical use. Eur Heart J. 1996; 17: 354–81.
Naranjo J, De la Cruz B, Sarabia E, De Hoyo M, Domínguez-Cobo S. Heart Rate Variability: a Follow-up in Elite Soccer Players Throughout the Season. Int J Sports Med [Internet]. 2015; 36(11): 881–6.
Mourot L, Bouhaddi M, Perrey S, Cappelle S, Henriet M-T, Wolf J-P, et al. Decrease in heart rate variability with overtraining: assessment by the Poincaré plot analysis. Clin Physiol Funct Imaging. 2004; 24(1): 10–8.
Buchheit M, Racinais S, Bilsborough JC, Bourdon PC, Voss SC, Hocking J, et al. Monitoring fitness, fatigue and running performance during a pre-season training camp in elite football players. J Sci Med Sport. 2013; 16(6): 550–5.
Bangsbo J, Mohr M, Krustrup P. Physical and metabolic demands of training and match-play in the elite football player. J Sports Sci. 2006; 24(7): 665–74.
Alexandre D, da Silva CD, Hill-Haas S, Wong DP, Natali AJ, De Lima JRP, et al. Heart rate monitoring in soccer: interest and limits during competitive match play and training, practical application. J strength Cond Res. 2012; 26(10): 2890–906.
Karvonen MJ, Kentala E, Mustala O. The effects of training on heart rate; a longitudinal study. Ann Med Exp Biol Fenn. 1957; 35(3): 307–15.
Bangsbo J, Nørregaard L, Thorsø F. Activity profile of competition soccer. Can J Sport Sci. 1991; 16(2): 110–6.
Stølen T, Chamari K, Castagna C, Wisløff U. Physiology of soccer: an update. Sports Med. 2005; 35(6): 501–36.
Helgerud J, Engen LC, Wisloff U, Hoff J. Aerobic endurance training improves soccer performance. Med Sci Sports Exerc. 2001 Nov; 33(11): 1925–31.
Suarez-Arrones L, Torreño N, Requena B, Sáez De Villarreal E, Casamichana D, Barbero-Alvarez JC, et al. Match-play activity profile in professional soccer players during official games and the relationship between external and internal load. J Sports Med Phys Fitness. 2015; 55(12): 1417–22.
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.
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.
Last comments