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.
The Warm-Up (WU) is an activation or preparatory activity aimed to enhance the physical predisposition before the activity and reduce the injury risks. Therefore, the development of an adequate Warm-Up in soccer is of paramount importance. Although WU is focused on physical contents, the match WU also aims to get a technical and mental readiness of players to compete.
Main objectives for WU:
Increase the intra-muscular temperature.
Increase the blood-flow.
Increase the metabolic reactions (cardiorespiratory system, heart rate).
Muscle activation.
Increase the nerve conductance rate.
The WU is indicative of its physiological and physical benefits (1,2).
According to the WU timing in competition, we can differentiate between Pre-Match WU (WU), just before the match starting (Re-WU) and half-time WU (HT-WU).
In this article, I am going to make specific con concise considerations about the most important points considered in the research to help build your own match WU. However, there are not many studies that establish the progression of WU contents, excepting the FIFA prevention programs (3).
What does the research say?
General considerations of WU
Prolonged WU routine has been shown to be non-beneficial (1).
Mean time: 30.8 min (15-45’).
90% of practitioners recommended a WU of ≤ 25 min.
The increases in heart rate (HR) and core temperature result in an increase in the blood flow, increase sensitivity of nerve receptors, and may subsequently explain partly the improvement in muscle performance enhancement.
The research suggests that 5–10 min at 40–70% of VO2max is sufficient to improve short, intermediate and long-term performance (1).
Short-duration high-intensity (HI) activity is beneficial for WU: enhance explosive muscular performance by increasing central nervous system activity (4).
However, >23 min HI-WU may induce fatigue: increase thermoregulation and the energy sources depletion.
Changes of directions (CODs) and plyometrics enhance explosive strength performance.
Stretching:
The static stretching decreases acute physical performance in soccer players: strength, vertical jump, slalom, dribbling and speed; and also, physiological outcomes (HR, core temperature).
Post-Activation Potentiation (PAP) increases the jump and sprint performance.
PAP should be program individualized by player as there is variability in recovery time by player.
WU using heavy resistance exercises (e.g. 15” of 5RM Squat) can significantly increase repeated-sprint performance and vertical jump (5).
The eccentric exercises are not recommended because induce muscle damage.
The FIFA 11+ prevention program shows an increase in jump, sprint and balance performance (3).
In addition, the FIFA 11+ program reduces the top four most prevalent soccer injuries: hamstring (60%), hip/groin (41%), knee (48%) and ankle (32%) injury.
The small-sided games (SSG) also improve performance (neuromuscular activation) and can be introduced in the WU.
The acquisition of specific motor skills can facilitate the transfer of cognitive process in subsequent tasks.
Specific considerations for Re-WU
Many practitioners recommend an additional WU of 3 min just before start the match, between WU ending and match starting (2).
A prolonged sedentary period after the WU might negate many of the physiological benefits associated with WU:
Towlson et al. (2) showed rapid decline in sprinting (5%) and jumping (13%) performance when players had a 10 min passive rest interval after a typical WU.
The level of play did not moderate the effectiveness of active Re-WU (5).
Specific considerations for HT-WU
Traditional passive half-time period during soccer match causes temporary impairment in the players’ physical performance capacity.
In Half time the muscle temperature declines 1.5-2 ºC.
An active Re-WU reduced the negative impact induced by passive half-time practices both in physiological (HR, core temperature) or performance outcomes (jump, sprint, distance covered).
3-min HT-WU elicit significant improvements in sprinting and jumping performance (6).
The HT-WU elicit performance benefits during the initial stages of the second half.
HR immediately increases following the HT-WU.
The most important responses in HT-WU are to increase blood-flowto muscles and muscle temperature increase.
The HT-WU might enhance the players’ concentration and focus for performance.
The Whole-body vibration (WBV) techniques might be appropriate as a short-duration, low-intensity and practical dose of WBV is also ergogenic for sprint and power performance and maintained eccentric hamstring peak torque, potentially reducing the risk of injury.
In addition, it is a good activation manner as it can be done in the dressing room.
Use of vibration platforms in Sevilla FC (Spanish First Division)
Conclusions
A successful match WU regimen for soccer players should contain either dynamic stretching exercise and PAP (time, reps, RM).
PAP should be program individualized by player.
WU should include short periods of HI.
The FIFA 11+ program elicits gains in strength performance and potential benefits for injuries preventions.
There are negative effects of passive half time, which may induce to a higher injury risk (7).
5RM- or SSGs exercises for WU may increase specific performance of players.
The WBV might be appropriate for HT-WU and causes acute improvement in reactive strength.
It is necessary to consider the time demands and situational factors during the half time periods.
The WU has to be adapted for the playing style.
The weather (hot or cold) will affect the required WU duration.
Practical Applications
This is the structure of Traditional team-sport WU retrieved from the research:
6 min general activities
High-knees, butt-kicks and body-weight squats; performed at medium intensity (sub-maximal velocity).
9 min specific movements
Back and forth sprinting, lateral skipping and CODs; performed at high intensity (maximal velocity).
6 min ball-control activities
Dribbling, passing and run-throughs; performed at high intensity.
Recovery: 1×60 sec and 2×30 sec passive recovery periods interspersed within the routine.
However, this is a basic and not very precise WU. The research has not still established a practice guideless showing an adequate timing progression of different qualities and develop an adequate warm-up in soccer. On the other hand, it is logically understood that all players have individualized needs and requirements (e.g. for previous injuries).
The WU programs should include the next contents (personal opinion):
General mobility (dynamic stretching, basic movements)
Specific movements
Coordination and SAQ
PAP
Technical skills
Specific HI activity (SSG)
Punctual tactical aspects
Accelerations and short speed
The development of an adequate Warm-Up in soccer is of paramount importance for both improve the players’ performance and reduce the injury risk. Therefore, it is important to pay special attention in this content.
You can find below is a detailed WU which has been used in the past. It is important to know the team’s playing style or the individual characteristics, among others.
You need to be subscribed to this website to download the Warm-Up.
References
Zois J, Bishop DJ, Ball K, Aughey RJ. High-intensity warm-ups elicit superior performance to a current soccer warm-up routine. J Sci Med Sport. 2011; 14(6): 522–8.
Towlson C, Midgley AW, Lovell R. Warm-up strategies of professional soccer players: practitioners’ perspectives. J Sports Sci. 2013; 31(13): 1393–401.
Thorborg K, Krommes KK, Esteve E, Clausen MB, Bartels EM, Rathleff MS. Effect of specific exercise-based football injury prevention programmes on the overall injury rate in football: A systematic review and meta-analysis of the FIFA 11 and 11+ programmes. Br J Sports Med. 2017; 51(7): 562–71.
Abade E, Sampaio J, Gonçalves B, Baptista J, Alves A, Viana J. Effects of different re-warm up activities in football players’ performance. Ardigò LP, editor. PLoS One. 2017; 12(6): e0180152.
Hammami A, Zois J, Slimani M, Russel M, Bouhlel E. The efficacy and characteristics of warm-up and re-warm-up practices in soccer players: A systematic review. J Sports Med Phys Fitness. 2018; 58(1–2): 135–49.
Fashioni E, Langley B, Page RM. The effectiveness of a practical half-time re-warm-up strategy on performance and the physical response to soccer-specific activity. J Sports Sci. 2020; 38(2): 140–9.
Lovell R, Midgley A, Barrett S, Carter D, Small K. Effects of different half-time strategies on second half soccer-specific speed, power and dynamic strength. Scand J Med Sci Sport. 2013; 23(1): 105–13.
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.
Summary of several aspects considered in the paper recently published in the JournalSoccer & Society. (click on the image to go the website)
Guerrero-Calderón B (2020) The effect of short-term and long-term coronavirus quarantine on physical performance and injury incidence in high-level soccer, Soccer & Society. DOI: 10.1080/14660970.2020.1772240
With this article, I have managed to gather the opinion of international soccer experts on the effect of short- (ST) and long-term (LT) QRT on physical performance and injury incidence in high-level soccer players, using open-ended questions in order to encourage the expression of unrestricted opinion. In this way, the text aims to provide the reader, whether strength & conditioning coach (S&C), physiotherapist, children’s coach or sport enthusiastic, from a practical perspective with a compilation and relationship of knowledge to understand how the coronavirus quarantine may affect the physical performance of high-level players based on the extensive experience and broad careers of conditioning area professionals in top-level soccer teams around the world together with the knowledge provided by research.
Effect on physical performance
Due to the forecast of a congested competition calendar after QRT, it will be necessary to optimize players’ physical performance to withstand the high physical demands of high-level soccer. The experts reported that individualized home training programs (HTP) have been developed for all players during QRT, in addition to specific nutrition plans. Nonetheless, despite the fact that all players are expected to act professionally and perform their HTPs, coinciding with the research, experts consider that there will be an irremediable physical performance decrease in the ST and, consequently, an increase in risk factors (RFs). The experts considered that the QRT will lead to negative changes in body composition in ST (Torreño & Owen), decrease in cardiorespiratory capacity of players (Aceña) and decrease in the capacity to generate strength, especially in soccer-specific muscle contractions and effort (Campos, Jiménez Rubio & Djaoui).
Injury incidence
In line with the literature, all the experts agreed that muscular injuries will be the most prevalent. Dr. Owen believes that most injuries will occur on reactive actions during turns. For Dr. Torreño, the main RF will be the loss of muscle mass and strength. Table 1 shows the most common muscular injuries considered by experts.
Injury/Location
Experts
Muscle – Hamstrings
Aceña, Campos, Sala, Torreño, Owen
Muscle – Quadriceps
Aceña, Campos, Jiménez Rubio, Sala, Torreño, Owen
Muscle – Adductors
Campos, Sala, Owen
Muscle – Calf
Jiménez Rubio, Owen
Groin pain
Sala
Tendinopathies
Sala
Joints
Granero
Hernias
Owen
Table 1. Most recurrent injuries according to experts.
Lluis Sala believes that different injuries will occur when the team returns to training and when competition begins: as soon as teams resume training, the flexor and adductor hip injuries, in addition with overuse injuries such as tendinopathy and groin pain. On the other hand, once competition starts and due to the congested match schedule, teams will increase the incidence rate of muscle injuries, without betting on a specific area. Based on the research, I believe overuse injuries RF on adductors muscles and groin pain will be high from the second or third week onwards if there is not enough preparation time to progressively increase the load before the start of competition.
Similarly, Ángel Aceña suggests two possible scenarios that might change the injury epidemiology: if the team does not have enough preparation time before returning to competition the hamstrings strain will be the most prevalent injuries; if, on the contrary, the teams can provide 3-4 weeks of preparation, the excessive training load may cause a greater number of quadriceps strain injuries.
Several experts agreed that there is a need for in-depth knowledge and exhaustive and individualized daily monitoring of players to adapt training and match load in order to identify the players best prepared for competition (Torreño, Jiménez Rubio, Granero, Sala & Djaoui). For Ángel Aceña & Dr. Torreño the biggest challenge for teams will not be to restore fitness capacity, but to cope with a very congested match calendar which will complicate players’ recovery process. Therefore, load individualization, together with the control and dosage of minutes of play together with rotation of player will be key elements in load management for S&C Coaches (Aceña, Campos, Owen & Granero), especially for teams also competing at international level, e.g. UEFA Champions League or Europa League (Jiménez Rubio).
Physical performance & injury risk relationship
Figure 1 shows a subjective interpretation of the relationship between physical performance, workload bearing capacity and injury risk, differentiating the periods before QRT (pre-IR) and when retraining after QRT (post-IR). At first, it is important to note that a greater workload does not necessarily means better physical performance. However, it is well known that high-level soccer requires excellent physical capacity of players in order to cope with the demands of competition (Bradley et al., 2016). Therefore, players with good fitness (represented by the PP line) will be able to withstand very high loads with lower risk of injury. When the workload is increased to improve physical performance, there is a ‘relative point’ of load, which currently cannot be known since there are many contributing factors such as accumulated load (S. Malone, Owen, Mendes, et al., 2017), locomotion activity and intensity (Martín-García, Gómez Díaz, Bradley, Morera, & Casamichana, 2018; Owen, Djaoui, Newton, Malone, & Mendes, 2017), mood and sleep quality (Carling et al., 2018), previous fatigue (Bradley & Noakes, 2013) or contextual factors (Andrzejewski, Chmura, Konefał, Kowalczuk, & Chmura, 2017; Brito, Hertzog, & Nassis, 2016; Curtis et al., 2019; Rago, Rebelo, Krustrup, & Mohr, 2019), among others, in which there is an exponential increase in injury. In addition, rapid or excessive load increases may involve a substantially increased RF.
Therefore, the training-free period of QRT will cause a deficit (represented by the grey shaded area) of the capacity to cope with greater loads (Gabbett, 2016) and increase the RF (represented by the left yield RF curve shift [post-RF]). A progressive load increase will help players to attain greater capacity to cope with the workload thus reducing load deficit caused by QRT and consequently improving the physical performance and decreasing the injury RF (flattening and right-shift of the curve, from post-IR to pre-IR). To minimize the left-shift of the curve and therefore produce a smaller load deficit that players are able to cope without an exponential increase in RF, players should maintain an adequate strength capacity during QRT, mainly in the lower limbs, to mitigate the muscle damage that will occur when they return to training (Torreño).
Figure 1. Subjective representation of the relationship between physical performance (PP), workload bearing capacity and injury risks before (pre-IR) and after (post-IR) quarantine. (WL1: maximum PP without an exponential IR increase before quarantine; WL2: maximum PP without an exponential IR increase when players returning to training after quarantine).
Return to training
There are several opinions regarding the starting point after QRT: an initial workload about 50-60% (Dr. Owen); start with the ‘minimum dose of effective training-load’ and build a progressive adaptation (Aceña & Jiménez Rubio); and other experts consider that players’ physical capacity should be tested as soon as training resumes (Djaoui, Jiménez Rubio & Sala).
On the other hand, several experts considered that group training sessions after QRT should be completely contextualized with respect to the game from the beginning by integrating the conditional goals into the tasks to improve game pace (Torreño & Campos). Therefore, in addition to improving players’ physical performance by generating new and game-specific muscle adaptations, the injury RF will be reduced and recovery process will improve due to the positive relationship between players’ capacity to generate strength and the reduction of post-match muscle damage markers (Akenhead & Nassis, 2016; J. Malone et al., 2015; Owen et al., 2017). However, players should undertake individualized training sessions that complement the team training in order to enhance possible weaknesses and facilitate the recovery process.
Long-term affectation
There are many doubts about how the QRT will affect LT (Jiménez Rubio, Granero, Sala, Torreño & Djaoui). For Dr. Jiménez Rubio, the current focus is on assessing how the QRT period has affected players in order to design the applicable individualized training programs for preventing ST injuries. Afterwards, different training contexts may be handled to prevent LT injuries. Finally, the players psychological state will be of paramount importance (Granero, Djaoui & Jiménez Rubio).
Conclusions & Recommendations
The QRT will highly negative affect the players’ physical capacity. In addition, it is also expected a reduction on the technical-tactical performance and game pace due to the decontextualization of QRT period.
All the participating experts are in agreement with the need to dispose a minimum of 3 training weeks before start to compete.
It will be necessary to dose the minutes of play by player and carry out the timely substitutions. In this sense, it might be interesting to be able to exceptionally perform a greater number of substitutions during the match.
Pre-QRT player data should not be used as reference values (e.g., accumulated load).
HTPs should mainly focus on HIT and strength and power training.
It is very important to include the eccentric training into the strength program of QRT to reduce the muscle damage when returning to training.
According to experts, hamstring and quadriceps strains will be the most prevalent injuries. In addition, overused injuries in adductors muscles and groin pain may also have high injury rate if there are rapid load increases.
The main injury RF will be the lack of specific-soccer locomotion activity (high-intensity, sprints, accelerations and decelerations) and ball hitting during QRT.
The role of technical staff will be decisive in the workload management to cope a congested competitive calendar.
Some experts consider that the psychological state and mood of players will be affected due to players will be under very significant strain.
Acknowledgments
I sincerely thank the physical performance and injuries experts collaborating in this study; Ángel Aceña, Dr. Campos, Dr. Jiménez Rubio, Paulino Granero, Lluis Sala, Dr. Torreño, Dr. Djaoui and Dr. Owen; for their excellent contributions and exchange of knowledge and broad work experience in elite-level soccer.
References(only in this post)
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