The effect of short-term and long-term coronavirus quarantine on physical performance and injury incidence in high-level soccer

The effect of short-term and long-term coronavirus quarantine on physical performance and injury incidence in high-level soccer

by | Jun 8, 2020 | Injuries, Performance, Soccer

Summary of several aspects considered in the paper recently published in the Journal Soccer & 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/LocationExperts
Muscle – HamstringsAceña, Campos, Sala, Torreño, Owen
Muscle – QuadricepsAceña, Campos, Jiménez Rubio, Sala, Torreño, Owen
Muscle – AdductorsCampos, Sala, Owen
Muscle – CalfJiménez Rubio, Owen
Groin painSala
TendinopathiesSala
JointsGranero
HerniasOwen
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)

  • Akenhead, R., & Nassis, G. P. (2016). Training Load and Player Monitoring in High-Level Football: Current Practice and Perceptions. International Journal of Sports Physiology and Performance, 11(5), 587–593.
  • Andrzejewski, M., Chmura, P., Konefał, M., Kowalczuk, E., & Chmura, J. (2017). Match outcome and sprinting activities in match play by elite German soccer players. The Journal of Sports Medicine and Physical Fitness, 58(6), 785–792.
  • Bradley, P. S., Archer, D. T., Hogg, B., Schuth, G., Bush, M., Carling, C., & Barnes, C. (2016). Tier-specific evolution of match performance characteristics in the English Premier League: it’s getting tougher at the top. Journal of Sports Sciences, 34(10), 980–987.
  • Bradley, P. S., & Noakes, T. D. (2013). Match running performance fluctuations in elite soccer: Indicative of fatigue, pacing or situational influences? Journal of Sports Sciences, 31(15), 1627–1638.
  • Brito, J., Hertzog, M., & Nassis, G. P. (2016). Do Match-Related Contextual Variables Influence Training Load in Highly Trained Soccer Players? Journal of Strength and Conditioning Research, 30(2), 393–399.
  • Carling, C., Lacome, M., McCall, A., Dupont, G., Le Gall, F., Simpson, B., & Buchheit, M. (2018). Monitoring of Post-match Fatigue in Professional Soccer: Welcome to the Real World. Sports Medicine, 48(12), 2695–2702.
  • Curtis, R. M., Huggins, R. A., Benjamin, C. L., Sekiguchi, Y., Adams, W. M., Arent, S. M., … Casa, D. J. (2019). Contextual Factors Influencing External and Internal Training Loads in Collegiate Menʼs Soccer. Journal of Strength and Conditioning Research, 1.
  • Gabbett, T. J. (2016). The training—injury prevention paradox: should athletes be training smarter and harder? British Journal of Sports Medicine, 50(5), 273–280.
  • Malone, J., Di Michele, R., Morgans, R., Burgess, D., Morton, J., & Drust, B. (2015). Seasonal training-load quantification in elite English premier league soccer players. International Journal of Sports Physiology and Performance, 10(4), 489–497.
  • Malone, S., Owen, A. L., Mendes, B., Hughes, B., Collins, K., & Gabbett, T. J. (2017). High-speed running and sprinting as an injury risk factor in soccer: Can well-developed physical qualities reduce the risk? Journal of Science and Medicine in Sport, 21(3), 257–262.
  • Martín-García, A., Gómez Díaz, A., Bradley, P. S., Morera, F., & Casamichana, D. (2018). Quantification of a professional football team’s external load using a microcycle structure. Journal of Strength and Conditioning Research, 32(12), 3511–3518.
  • Owen, A. L., Djaoui, L., Newton, M., Malone, S., & Mendes, B. (2017). A contemporary multi-modal mechanical approach to training monitoring in elite professional soccer. Science and Medicine in Football, 3938(July), 1–6.
  • Rago, V., Rebelo, A., Krustrup, P., & Mohr, M. (2019). Contextual Variables and Training Load Throughout a Competitive Period in a Top-Level Male Soccer Team. Journal of Strength and Conditioning Research, (25), 1.

Berni Guerrero-Calderón

S&C Coach | Rehab Therapist | Sport Scientist

If you have any doubt, do not hesitate to leave your comment. If you liked the post, share it on social media!

All the information of this post has been retrieved from the paper published in Soccer & Society Journal.

The Hamstring muscle complex injuries: types and classification

The Hamstring muscle complex injuries: types and classification

by | Jun 8, 2020 | Injuries, Sport

This article aims to provide a conceptual clarification, classification and basic knowledge about one of the most common injuries in sport: the hamstring injury.

Muscle function

The Hamstrings is a biarticular muscle group; It is the main knee flexor and is one of the hip join extensors. In addition, it also provides medial and lateral stability to the knee (1). 

Figure 1. The hamstring muscle complex

Anatomy

The hamstrings muscle complex (Figure 1) are composed by:

  • Semimembranosus (SM)
  • Semitendinosus (ST)
  • Biceps femoris (BF)
    • Long head (BFlh)
    • Short head (BFsh)

The muscle origin and insertion of each of the hamstring complex are presented in Table 1.

MuscleOriginInsertion
SMischial tuberosityproximal medial tibia
STischial tuberosity (joint tendon with BFlh) proximal anteromedial tibia, forming the Pes Anserinus complex together with the sartorius and gracilis muscles
BFlhischial tuberosity (joint tendon with ST)External tuberosity fibula
BFshlinea aspera, lateral intermuscular septum, and condyloid ridge of the posterior femurExternal tuberosity fibula
Table 1. Anatomy of hamstring muscles complex

Classification of Hamstring injuries

The hamstring may be injured in the muscle, tendon or in the ischial tuberosity. Therefore, the injuries are also classified according to the affected area:

  • Proximal injury (ischial origin): tendinosis, partial tendon tear, or complete tendon tear with or without avulsed osseous fragment. 
  • Distal injury: involves the distal tendons or insertion of the tendons in a similar fashion.
  • Central hamstring injury: involve muscle usually at the proximal or distal musculotendinous junction. There are the most common injuries.

Muscular injuries

On the muscle belly or musculotendinous junction, the hamstring muscle injuries are the most common injuries in soccer (2–4). Ekstrand et al. (4) found in their study with elite soccer players that these injuries represent the 12% of total injuries during the season and the sprinting and/or accelerations and decelerations actions are the greatest injury mechanisms. In addition, a recent systematic review showed a mean percentage of reinjury of 22.9% (2).

Muscular injury classification according to the severity:

Grade 0

  • Discomfort sensation caused by overloading or contractures. DOMS. 
  • Slight fiber structural-damage. Edema (but non hematoma).
  • Prognosticated recovery time: 1-5 days.

Grade I

  • Muscle strain (microtear) of the muscle fibers. Edema.
  • It mostly occurs at the musculotendinous junction, and more often in the proximal area. 
  • Higher reinjury incidence compared with others grades (5).
  • Healing: RICE and adequate training program.
  • Prognosticated recovery time: 1-2 weeks (6).

Grade II

  • Partial macroscopic muscle fiber disruption.
  • Edema and immediate functional impotence after the injury.
  • Prognosticated recovery time: 3-4 weeks (6).

Grade III

  • Complete disruption of the myotendinous unit, often with retraction and a gap between the torn ends.
  • It necessitates prompt surgical correction. Delayed reattachment is associated with loss of full function and therefore increased morbidity. 
  • Prognosticated recovery time: ≥ 3-4 weeks (6).

There are different grades of severity based on recovery time (4):

  • Minimal injury: 1-3 days
  • Mild injury: 4-7 days
  • Moderate injury: 8-28 days
  • Severe injury: >28 days

Tissue damage

However, the injury normally comprises a spectrum of tissue damage (i.e. different grades and areas) and not only in a single grade injury (1). On the other hand, there are factors which increases the recovery time: presence of injury to the BF, the cross-sectional area (as a percentage score), the length of the injury, and injury outside the musculotendinous junction.

Tendon injuries

Although it is less common, tendons may also avulse from their distal insertions or proximal origins with or without an associated avulsed osseous fragment.

  • Tendinosis (chronic injury caused by an accumulation of small tears in the tendon that have failed to heal properly over the time).
  • Partial tear
  • Complete tear

Besides, the ischiatic tuberosity (muscle origin) injuries may be described according to a three-tiered method:

  • Enthesopathic change (osseous area where the tendon is attached).
  • Avulsion < 2 cm displacement of an osseous fragment 
  • Avulsion > 2 cm displacement of an osseous fragment (normally requires surgical intervention)

The causes of enthesopathic changes may be due to a contusion, osteomyelitis (bone infection), or a more aggressive though rare process such as neoplasm (abnormal formation of new tissue of a tumoral, benign or malignant nature) should be considered with marrow signal change. In addition, they may be associated with a thickening of the cortical area of the bone or periostitis.

Finally, high-grade muscle, tendon, and chronic osseous avulsion injuries can lead to muscular atrophy over time (1).

I will post another publication about the recommendations and training program of hamstring injury treatment.

References

  1. Hancock CR, Sanders TG, Zlatkin MB, Clifford PD, Pevsner D. Flexor femoris muscle complex: grading systems used to describe the complete spectrum of injury. Clin Imaging. 2009; 33(2): 130–5.
  2. Pfirrmann D, Herbst M, Ingelfinger P, Simon P, Tug S. Analysis of injury incidences in male professional adult and elite youth soccer players: A systematic review. J Athl Train. 2016; 51(5): 410–24. 
  3. Dupont G, Nedelec M, McCall A, McCormack D, Berthoin S, Wisløff U. Effect of 2 soccer matches in a week on physical performance and injury rate. Am J Sports Med. 2010; 38(9): 1752–8. 
  4. Ekstrand J, Hägglund M, Waldén M. Injury incidence and injury patterns in professional football: The UEFA injury study. Br J Sports Med. 2011;45(7):553–8. 
  5. Petersen J, Hölmich P. Evidence based prevention of hamstring injuries in sport. Br J Sports Med. 2005;39(6):319–23. 
  6. Revista AMEF. Asociación Española de Médicos de Equipos de Fútbol. 2007.

Berni Guerrero-Calderón

S&C Coach | Rehab Therapist | Sport Scientist 

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 injury epidemiology in soccer

The injury epidemiology in soccer

by | Jun 8, 2020 | Injuries, Soccer, Sport

This article aims to provide a summarized analysis and a guideless of injury epidemiology in soccer.

Soccer is an interaction sport characterized by the alternance of high-intensity actions, thus implying a high injury incidence (1,3). In recent years there has been an increased physical demands in competition, being more aggressive and requiring better physical preparation of players to withstand the match demands (4,5). In addition, considering the high number of matches in high-level soccer during the season, playing two matches per week over a long period of season (a total of 60-70 matches), it is logically understood the augmented injury risk of players in soccer practice (1,3). In this way, although several authors showed that a recovery time of 72 to 96 hours between two matches is sufficient to maintain the level of physical performance, it is not enough time to maintain a low injury rate (6). On the other hand, the player age, training load (TL), level of competition and training standard are some of the main injury risk factors (3). 

The systematic review and meta-analysis performed by Pfirrmann et al. (3) with high-level junior and senior soccer players, it has been shown a total injury incidence of 2.0 to 19.4 injuries per 1000 hours of practice in junior players; and  2.5 to 9.4 injuries per 1000 hours of practice in professional senior soccer players, with the higher injury incidence found in competition. In the same way, Ekstrand et al. (1) accounted a total of 50 injuries per season by team, that’s 2 injuries by player. 57% of these injuries are in match whereas a 43% are in training sessions.

Main conclusions

Retrieved from the bibliography reviewed relative to the epidemiological analysis in soccer are:

  • There are more injuries in match than in training sessions. 
  • The most common injuries are the muscle strain, ligament sprain and contusion.
  • Muscular injuries account for 30% of all injuries.
  • The most common body location is the thigh in both junior and senior soccer players. The following most common were the knee, the ankle and the hip/groin. In addition, this injury pattern is not affected by the player age.
  • Thigh strains represent the 17% of injury incidence and 7 of 10 injuries are in hamstrings.
    • Hamstrings strain: 12% 
    • Quadriceps strain: 5% 
  • Other injuries:
    • Adductor pain/strain: 9%
    • Ankle sprain: 7%
    • Medial collateral knee ligament (MCL): 5%
  • The high risk of hamstring strain reflects the high intensity of professional soccer.
  • Overuse injuries account for 27 to 33% of the injury incidence. These injuries are caused by a repetitive stress without sufficient time to undergo the natural regenerative process. 
  • 2/3 of injuries are trauma injuries: 81% in match and 59% in training. 
  • Severe injuries, which accompany longer recovery process and RTP, occurred more often during matches.
  • Most common severe injuries: 
    • Hamstring strain (12%)
    • MCL knee sprain (9%)
    • Quadriceps strain (7%)
    • Adductor pain/strain (6%)
  • 21% of all injuries are due to foul play: ankle sprain (15%), knee sprain (9%) and thigh contusion (10%).
  • Head injury: 2%.
  • Fractures represent only a small percentage of all injuries.
  • In young soccer players, the most severe injuries occurred in the range age between 14 to 16 years. 
  • Reinjury (R-in):
    • The injury risk factors (RF) are 4 to 7 times higher for soccer players previously injured.
    • Ekstrand et al. accounted the R-in incidence for 12% of injury incidence in professional soccer players. However, there are differences in the research (9-30%) which author attributes for a better medical support in elite clubs. 
    • R-in causes longer absences than new injuries.
    • Junior players had lower reinjury rate.
    • R-in are more common during training than match.
    • These injuries are overuse injuries.
  • There are differences in the injury incidence according to the season period.
    • Preseason (few matches, high training volume)
      • Overuse injuries (e.g., groin pain)
      • Quadriceps strain. 
    • Competitive period (many matches, high intensity)
      • Traumatic injuries, hamstring strain (previously commented)
    • Injury incidence increases towards the end of each half of play (fatigue).
    • The injury incidence during matches is influenced by the playing position: midfield players and defenders were the most at-risk groups*.

*However, although a there are authors showing differences between playing positions, a recent systematic review did not find enough evidence to provide general considerations of injury incidence by position (7). Only goalkeepers show lower injury incidence.  

Table 1 shows a visual guideless of injury epidemiology in soccer.

Elite Youth Soccer PlayersProfessional Adults Soccer Players
Total Injury IncidenceFrom 2.0 to 19.4 injuries per 1000 h(+ severe on match and 14-16y than older adolescents)From 2.5 to 9.4 injuries per 1000 h(the majority were moderate severity and ≤ 1 week)
Incidence on MatchFrom 9.5 to 48.7 injuries per 1000 hFrom 8.7 to 65.9 injuries per 1000 h
Incidence on TrainingFrom 3.7 to 11.1 injuries per 1000 hFrom 1.4 to 5.8 injuries per 1000 h
Match-Training relationshipMatch >x5 than TrainingHigher during matches53% on match, 47% training
Most common injury typesStrains, sprains and contusions2/3 Traumatic – 1/3 overuse (*Prevention plans)Strains, sprains and contusions
Most frequently injured body partThigh – HamstringsThigh – Hamstrings (strains)
Most frequently injury–Hamstrings strain*Quadriceps injury = Longer absence
Others injuriesAnkle, knee, groin, lower limb*Fractures: small % but major injuryGroin, knee, ankle*Fractures: small % but major injury
ReinjurySprains (42.9%) and strains (22.9%)15.3% of all injuries
+40% recovery time than initial injury2/3 or 63% were overuse injuries
Most common during training16% of Hamstring injuries
Overuse injuriesNeeds + recovery time
Table 1. Guideless of injury epidemiological analysis in both junior and senior professional soccer players retrieved from the systematic review and meta-analysis by Pfirrmann et al. (2016)

References

  1. Ekstrand J, Hägglund M, Waldén M. Injury incidence and injury patterns in professional football: The UEFA injury study. Br J Sports Med. 2011;45(7):553–8. 
  2. Guerrero-Calderón B. The effect of short-term and long-term coronavirus quarantine on physical performance and injury incidence in high-level soccer. Soccer Soc. 2020 Jun 7;00(00):1–11.
  3. Pfirrmann D, Herbst M, Ingelfinger P, Simon P, Tug S. Analysis of injury incidences in male professional adult and elite youth soccer players: A systematic review. J Athl Train. 2016;51(5):410–24. 
  4. Bradley PS, Archer DT, Hogg B, Schuth G, Bush M, Carling C, et al. Tier-specific evolution of match performance characteristics in the English Premier League: it’s getting tougher at the top. J Sports Sci [Internet]. 2016 May 18 [cited 2017 Jan 29];34(10):980–7.
  5. Carling C. Interpreting physical performance in professional soccer match-play: Should we be more pragmatic in our approach? Sport Med. 2013;43(8):655–63. 
  6. Dupont G, Nedelec M, McCall A, McCormack D, Berthoin S, Wisløff U. Effect of 2 soccer matches in a week on physical performance and injury rate. Am J Sports Med. 2010;38(9):1752–8. 
  7. Della Villa F, Mandelbaum BR, Lemak LJ. The Effect of Playing Position on Injury Risk in Male Soccer Players: Systematic Review of the Literature and Risk Considerations for Each Playing Position. Am J Orthop (Belle Mead NJ). 2018;47(10).

Berni Guerrero-Calderón

S&C Coach | Rehab Therapist | Sport Scientist 

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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