The rehabilitation program and RTP process of Hamstring strain injury in soccer

The rehabilitation program and RTP process of Hamstring strain injury in soccer

In a previous post, it was made a conceptual clarification and classification of the types of hamstring injuries (muscular or tendinous), differentiated by severity (go to post). This post aims to specifically summarized the rehabilitation program and RTP process of Hamstring strain injury in soccer, differentiate the phases of treatment and knowing the main injury mechanisms for hamstring strain injuries with the final objective of to be able to program a recovery and progressive return to play (RTP) process with our soccer players, based on the scientist knowledge (mainly systematic reviews and meta-analysis).

Injury incidence

The hamstring injury is the most common injury in soccer, with an injury rate of 12% of total injuries (1). In addition, the reinjury rate in soccer is high (12-33%) which, in most cases, probably indicates inadequate rehabilitation programmes and/or premature return to football (2). Of these recurrences, 59% occur within the first month after RTP. Therefore, it is of paramount importance to design an appropriate rehabilitation programme and timing to optimize the RTP process. However, to date there are not validated RTP criteria to facilitate hamstring injury management (3).

Main injury mechanisms (4,5)

  • Sprinting activity
    • During the latter part of swing phase, decelerating knee extension (changing from functioning eccentrically to concentrically). 
  • Stretching actions 
    • Actions of large joint excursions (high kicks, quick stretching movements, …) 

Etiological factors (4)

Non-modifiable risks (internal)

  • Older age
  • Black or aboriginal ethnic origin
  • Injury history
  • Level of sport
  • Timing

Modifiable risk factors (external)

  • Muscular imbalances (low hamstring-quadriceps ratio)
  • Poor flexibility
  • Fatigue (muscles are able to absorb less energy before reaching the degree of stretch that causes injuries)
  • Psychological state

Phases of Hamstring strain injury treatment (4)

Phase I (acute): 1-7 days

  • RICE
  • Goal: control hemorrhaging and minimise inflammation and pain.
  • NSAIDs are accepted. Controversy with appropiate timing: 3-7 days after injury.
  • Early motion exercise is important to prevent or decrease adhesion within the connective tissue.
    • Active knee flexion and extension exercises (ice post-training) 
    • Exercises must be Pain-free.

Phase II (subacute): day 3 to > 3 weeks

  • This phase begins when the signs of inflammation (swelling, heat, redness, and pain) begin to resolve.
  • Continue muscle action to prevent atrophy and promote healing. 
    • Concentric strength exercises (when the athlete has achieved full ROM without pain).
    • Multiple joint angle, submaximal isometric contraction.
    • Decrease the intensity with pain.
  • Other cardiovascular activities: biking, swimming.

Phase III (remodelling): 1-6 weeks

  • Stretching exercise to avoid the loss of flexibility in hamstring (characteristic feature of hamstring strains due to pain, inflammation, and connective tissue scar formation).
  • Eccentric exercises (always after concentric exercise are begun because eccentric contractions cause greater forces).
  • the eccentric exercises are delayed until the injured muscle is well regenerated.

Phase IV (functional): 2 weeks to 6 months

  • Goal: RTP without reinjury.
  • Increase hamstring strength and flexibility to the normal values for the individual player (before injury).
  • Pain-free running activities (from jogging at low intensity to running and finally sprinting). 
  • Pain-free participation in soccer-specific activities (best indicator of readiness to RTP).
  • Return to competition before this time may result in recurrent or more severe injury.

Phase V (return to competition): 3 weeks to 6 months

  • When the athlete has returned to competition, the goal is to avoid reinjury. 
  • Focus: maintaining stretching and strengthening.

Main training tasks

Generally, the rehabilitation program and RTP process of hamstring strain injury in soccer should be based on hamstrings strengthening mainly through eccentric training; the Core stability training; and the sprinting activity, focused on accelerations and high-intensity actions, becoming the most important training subjects in the last phases of RTP as it is a predominant type of activity in soccer.

  • Eccentric contractions
  • Core stability
  • Running activity (sprint and acelerations)
  • Soccer-specific actions.

RTP criteria

To date, no consensus on RTP-criteria for hamstring strain injuries has been validated yet. The following criteria are the most important according to different systematic reviews and meta-analyses (3–10): 

  • Muscle strength 
    • Isokinetic dynamometry: Concentric, eccentric.
    • Manual assessment of isometric knee flexor strength
    • H:Q ratio ≥ 0.55
    • Limb strength imbalance (LSI) <10% – comparing with the uninjured leg and data before injury. 
  • Flexibility (complete ROM)
  • Complete pain-free
    • Pain-free sprinting
    • Pain-free palpation
  • Player’s confidence 
  • Functional soccer-specific performance
    • Sprint
    • Single-leg triple hops
  • Medical clearance
  • Askling H-test 
  • Capacity to train with the team normally (no pain or discomfort)

Figure 1 shows the coding of criteria for RTP after hamstring strain injury retrieved from the systematic review of Van der Horst (3).

Figure 1. Coding of criteria for RTP after hamstring strain injury. Retrieved from van Der Horst et al. (3).


  • There is a high percentage of reinjury for hamstring strain injury in soccer.
  • There is a need to established a consensus RTP-criteria and recovery program for hamstring strain injuries. 
  • The Askling H-test shows lower percentage of reinjury, but the recovery time is longer.

For a detailed description of the rehabilitation program and RTP process of Hamstring strain injury in soccer, please refer to the studies cited.


  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. Askling CM, Tengvar M, Thorstensson A. Acute hamstring injuries in Swedish elite football: a prospective randomised controlled clinical trial comparing two rehabilitation protocols. Br J Sports Med. 2013; 47(15): 953–9.
  3. van der Horst N, van de Hoef S, Reurink G, Huisstede B, Backx F. Return to Play After Hamstring Injuries: A Qualitative Systematic Review of Definitions and Criteria. Sport Med. 2016; 46(6): 899–912.
  4. Petersen J, Hölmich P. Evidence based prevention of hamstring injuries in sport. Br J Sports Med. 2005; 39(6): 319–23. 
  5. Askling CM, Nilsson J, Thorstensson A. A new hamstring test to complement the common clinical examination before return to sport after injury. Knee Surgery, Sport Traumatol Arthrosc. 2010; 18(12): 1798–803. 
  6. Zambaldi M, Beasley I, Rushton A. Return to play criteria after hamstring muscle injury in professional football: a Delphi consensus study. Br J Sports Med. 2017; 51(16): 1221–6.
  7. Hickey JT, Timmins RG, Maniar N, Williams MD, Opar DA. Criteria for Progressing Rehabilitation and Determining Return-to-Play Clearance Following Hamstring Strain Injury: A Systematic Review. Sport Med. 2017; 47(7): 1375–87. 
  8. Maniar N, Shield AJ, Williams MD, Timmins RG, Opar DA. Hamstring strength and flexibility after hamstring strain injury: A systematic review and meta-analysis. Br J Sports Med. 2016; 50(15): 909–20. 
  9. Mendiguchia J, Martinez-Ruiz E, Edouard P, Morin JB, Martinez-Martinez F, Idoate F, et al. A Multifactorial, Criteria-based Progressive Algorithm for Hamstring Injury Treatment. Med Sci Sports Exerc. 2017; 49(7): 1482-1492.
  10. Brukner P, Nealon A, Morgan C, Burgess D, Dunn A. Recurrent hamstring muscle injury: applying the limited evidence in the professional football setting with a seven-point programme. Br J Sports Med. 2014; 48(11): 929–38.

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.

Small-Sided Games in soccer: Physical or technical-tactical training?

Small-Sided Games in soccer: Physical or technical-tactical training?


Small-Sided Games (SSGs) is one of the most common training methods in soccer at all level or ages; from elite teams to children, as it allows to develop the technic and tactics (TT) such as situations of numerical superiority, defensive retreat or third man play, among others, keeping the physical objectives programmed in that training session (1). However, it should be noted that practitioners need a good knowledge of SSGs in order to properly carry out these tasks adapted to coach’s objectives (2). A good teamwork and communication between the technical staff are essential. In addition, the S&C Coach must hold good knowledge of TT elements.

Benefits of SSGs

SSGs allow to train with the ball and achieve an exercise intensity of 95% of maximum heart rate (HRmax), which has been shown to improve the soccer-specific endurance, develop the specific muscle-groups involved in game, improve the TT elements in the specific conditions of game, and keep an effective transfer to the game (1–6). Therefore, SSG seem an effective task to combine the behaviors and motor patterns, the cohesion of the team in addition to aerobic training (1).

Design of SSGs

Pitch area

Increasing the playing area dimensions means an increase of HR, lactate concentration (La-) and RPE. This is caused to the greater area per player, with player having more space to move. Thus, larger SSGs is used in training to maintain high-intensity (HI) throughout exercise.

On the other hand, there are also differences in number of shots to goal, rebounds and passes between smaller and bigger game-area. In addition, lower number of assists, steals and turnover are found in big game pitches. 

Big game area vs smaller game area

The greater the space, the greater intensity. Larger pitches involve covering a greater HI distance, speed-running and sprint frequency; whereas smaller pitches involve a greater number of accelerations, decelerations or changes of direction (4), in addition to a greater number of TT actions.

On the other hand, work-to-rest ratios are lower in the smallest areas. The work-to-rest ratio was only >1 on medium and large pitches, which indicates that activity prioritizes over recovery (4).

Number of players

The fewer number of players, higher HR, La- and RPE.

No intensity changes have been found when teams play with unequal number of players, excepting with the inclusion of floaters players, who attain much higher intensity than other players. 

Choosing the appropriate number of players, several authors recommend using a reduced number of players and alternating equal and unequal number of players.

Relationship between the pitch area and number of players

The intensity of game is highly affected by the interaction between the pitch area and the number of players and it is considered a critical factor for an appropriate SSG design. The interpersonal playing area (IPA) arise from this relationship. IPA is defined as the available game area for each player into the total game area. Increasing the IPA might be useful to increase the intensity of SSG (3). Contrary, reducing the IPA results in a reduction of playing area and the time available for the task, so the decision-making process and technical execution should be faster.

4v4 SSGs

4v4 SSGs are considered the most appropriate game format (1,3). Caro et al. (3) concluded in its study with elite soccer players belonging to the Spanish First Division that 4v4 SSGs should be played in smaller spaces for a better recreation of match situations, and in addition these should be wider than longer. Also, the author found differences in the playing space depending to the area of the field where these actions take place. 4v4 game situations are played on reduced spaces for areas close to the goals while they are played in open spaces in the central areas. Caro et al. (3) proposed areas of 15x17m or 17x20m. However, the areas should be adapted to the level and age of players.

It should be noted that only 10v10 SSGs allow players to obtain similar running distances covered in match (2). The higher number of players, the higher distance per minute. Therefore, Lacome et al. (2) recommend 4v4 SSGs for strength-oriented training sessions and 10v10 SSGs for endurance-oriented training sessions.

Rules modification

Number of touches, man marking and presence of goalkeepers affect the physiological, technical and tactical responses of players, so they should be considered to modify the intensity. The free play rule produced greater number of duels, lower number of sprints and high-intensity running, and preserved the effectiveness of TT actions compared to 1-2 touches SSG. On the other hand, there are more intense actions when combining the offensive and defensive playing situations together than in isolation.

Presence of Goalkeepers (GK)

Including small goals in SSGs increase the motivation of players. The presence of GK in these tasks might modify the intensity of SSG. There are opposite results in the literature at present; several authors showed an increase in the %HRmax and others found a reduction. Therefore, coaches should avoid to include GK in SSGs and only use small goals to keep a high motivation of players and consequently higher intensity of training.

Coach Encouragement

The direct involvement and supervision of coach leads to an improvement of task intensity in addition to a higher adherence of players to the training. 

Duration of SSGs

There are not clear conclusions about the appropriate time of SSGs due to the scarce literature analysing the effect of time duration on the physiological responses of soccer players. However, a systematic review did not show different physiological responses between continuous and intermittent training methods (1). Both methods can be used effectively to produce adaptations for soccer-specific endurance and coaches may alternate between the two in SSGs. However, it should be noted that other factors can affect the exercise intensity. Nonetheless, Fanchini et al. (7) concluded that 4-minute series may be a positive stimulus for SSGs.

Casamichana & Castellano (4) consider the variable ‘distance per minute’ the most representative intensity marker for this kind of HI tasks.

Differences with Competition

SSGs show greater distance per minute and high-intensity activity in all positions compared to competition, showing higher HRmax, La- and RPE. Also, SSGs show a greater number of duels and ball losses, in addition to a lower percentage of successful passes and total possessions (1).

Differences between positions

The SSGs show different physical demands relative to the playing position. Therefore, the intensity of the task should be programmed according to the specific demands of each role throughout modifying the rules, including floaters players, etc.

SSGs vs traditional intervallic-training methods 

No differences on physiological responses have been found between SSGs and traditional intervallic-training methods. It is logically understood that the magnitude of response normally depends of the intensity, frequency and duration of training, as well as the total duration of training program and conditioning of players. 

SSGs seem lightly more demanding than traditional approaches, which may lead to an improvement of the cardiorespiratory capacity of players. The increased responses can be caused by the higher motivation and enthusiasm of player for SSGs.


  • SSGs are an effective training method to develop the aerobic capacity of players and obtaining an appropriate readiness to real situations occurring in match.
  • The conditioning training should not be exclusively based on SSGs.
  • It is of paramount importance to keep an elevated motivation of players in training sessions.
  • A reduced IPA results in faster decision-making process and technical executions.
  • 4v4 SSGs is the most effective training format. However, 10v10 SSGs allow better simulation of match physical demands.
  • Contact injuries seem to most prevalent injuries of this kind of tasks.

Practical applications

  • It is recommended to vary the SSGs training formats (number of players, pitch size, etc) over the season phases to obtaining the adequate training stimuli (intensity).
  • The higher intensity is obtained reducing the number of players and increasing the pitch size.
  • The coach encouragement and feedback during SSGs are effective to increase the intensity of game.
  • The suitability of using GK on SSGs is unclear. However, the presence of GK in bigger playing areas could motivate players and therefore increase the intensity of task.
  • 4vs4 SSGs seem the most effective game format.
  • Manipulating some rules such increasing the number of players, number of touches or the type of marking can increase the intensity of SSGs and adapt it to the specific demands of each playing position.


  1. Halouani J, Chtourou H, Gabbett TJ, Chaouachi A, Chamari K. Small-sided games in team sports training: a brief review. J Strength Cond Res. 2014; 28(12): 3594–618.
  2. Lacome M, Simpson BM, Cholley Y, Lambert P, Buchheit M. Small-Sided Games in Elite Soccer: Does One Size Fit All? Int J Sports Physiol Perform. 2018; 13(5): 568–76.
  3. Caro O, Zubillaga A, Fradua L, Fernandez-Navarro J. Analysis of Playing Area Dimensions in Spanish Professional Soccer: Extrapolation to the Design of Small-Sided Games With Tactical Applications. J strength Cond Res. 2019; 1–7.
  4. Casamichana D, Castellano J. Time–motion, heart rate, perceptual and motor behaviour demands in small-sides soccer games: Effects of pitch size. J Sports Sci. 2010; 28(14): 1615–23.
  5. Silva B, Garganta J, Santos R, Teoldo I. Comparing tactical behaviour of soccer players in 3 vs. 3 and 6 vs. 6 small-sided games. J Hum Kinet. 2014; 41(1): 191–202. 
  6. Beenham M, Barron DJ, Fry J, Hurst HH, Figueirdo A, Atkins S. A Comparison of GPS Workload Demands in Match Play and Small-Sided Games by the Positional Role in Youth Soccer. J Hum Kinet. 2017; 57: 129–37.
  7. Fanchini M, Azzalin A, Castagna C, Schena F, Mccall A, Impellizzeri FM. Effect of Bout Duration on Exercise Intensity and Technical Performance of Small-Sided Games in Soccer. J Strength Cond Res. 2011; 25(2): 453–8.

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.

Evaluation of agility as a fundamental physical quality in soccer

Evaluation of agility as a fundamental physical quality in soccer

The concept of agility

The agility is an essential physical quality in soccer to achieve a quick start to action, change of direction (COD) and short-distance running (1,2). Along with accelerations and maximum speed, agility is one of the most important specific qualities in soccer (3). 

Agility: rapid whole-body movement with change of speed or direction in response to a stimulus (4).

Agility consists of two main components: 

  • Change of direction (COD)
  • Perceptual and decision-making factors.

Performance factors associated to agility

Perceptive and cognitive factors

This factor is of paramount importance in soccer. The reaction time to stimuli could be the predictor of agility time (5). Players with inappropriate decision-makings and long reaction times show higher injury risks (they will be able to avoid fewer collisions, sprained ankles on landings after an aerial fight, etc). In addition, any action involves a prior decision-making process.

Motor pattern

Essential element of CODs ability (4). The presence of decision-making into the action negatively affect the running speed when making the step to change direction, so foot position pattern differs from previously programmed. Reaction time is very important. 

Physical factors

The principal purpose of an agility action is re-direction the whole-body in the same direction as fast as possible (6). Several authors have showed a direct relationship between agility tests and jump and sprint performance (2). This author found that players who obtained higher jump height (CMJ and SJ) and lower sprint time showed greater agility. However, other authors did not find such correlation (7).

Small-sided games (SSG)

SSG is a very complete exercise that improves both decision-making and movement speed. However, there is controversy in the literature about its suitability as there are different demands among positions. Furthermore, it is unlikely that players perceive, decide and act on an SSG as they would on the soccer-11 field (8).


Sporis, Milanovic & Vucetic (9) analyse the reliability and validity of different soccer agility tests. The authors highlight the important to perform the test simulating the real conditions (with football shoes and on the specific surface), to avoid different ground contact forces.

The most used agility tests (9):

Agility tests. Retrieved from Sporis, Jukic, Milanovic, & Vucetic, 2010.

Differences between positions

Different tests are recommended according to the specific functions and demands required for each position: 

  • Defenders: T-Test (longer backward running)
  • Central-midfielder: s180º/SBD (more CODs and higher frequency)
  • Attackers: S4x5 (similar movements)

Types of stimuli

Different types of stimuli (EE) are used in agility tests with high reliability: light-EE, video-EE and human-EE. Human-EE show are the most reliable and also are much closer to ‘real situation’ (10).

  • Light-EE: the player has to react and perform the precise movement or COD when a light is turned on.
  • Video-EE: the player has to react to an EE presented on screen.
  • Human-EE: the player acts depending of other player (e.g. reaction to player’s movement).

However, the research is increasing to validate test much closer to real soccer situations; with the ball, decision-makings, more players or unexpected EE. 


Finally, agility consists in change direction fast and easy. By training agility, balance and coordination players will be able to move and change direction faster while keeping a good body control and balance. So for improving agility, athletes have to train power, balance, speed and coordination (9). In addition, it is of paramount importance to include perceptive and decision-making process in training (7). The authors advise to use training drills with a series of visual stimuli, where players have to react and change direction repeatedly and have more directional alternatives and running directions. Therefore, SSGs are a recommended training exercise. 


  1. Lloyd RS, Oliver JL, Radnor JM, Rhodes BC, Faigenbaum AD, Myer GD. Relationships between functional movement screen scores, maturation and physical performance in young soccer players. J Sports Sci. 2014; 33(1): 11–9.
  2. Negra Y, Chaabene H, Hammami M, Amara S, Sammoud S, Mkaouer B, et al. Agility in Young Athletes: Is It a Different Ability From Speed and Power? J strength Cond Res. 2017; 31(3): 727–35.
  3. Little T, Williams A. Specificity of acceleration, maximum speed, and agility in professional soccer players. J Strength Cond Res. 2005; 19(1): 76–8. 
  4. Sheppard JM, Young WB. Agility literature review: Classifications , training and testing. J Sports Sci. 2006; 37–41. 
  5. Scanlan A, Humphries B, Tucker PS, Dalbo V. The influence of physical and cognitive factors on reactive agility performance in men basketball players. J Sports Sci. 2014; 32(4): 367–74.
  6. Lyle MA, Valero-Cuevas FJ, Gregor RJ, Powers CM. Lower extremity dexterity is associated with agility in adolescent soccer athletes. Scand J Med Sci Sports. 2015; 25(1): 81–8.
  7. Matlák J, Tihanyi J, Rácz L. Relationship Between Reactive Agility and Change of Direction Speed in Amateur Soccer Players. J strength Cond Res. 2016; 30(6): 1547–52.
  8. Young W, Rogers N. Effects of small-sided game and change-of-direction training on reactive agility and change-of-direction speed. J Sports Sci. 2014; 32(4): 307–14.
  9. Sporis G, Jukic I, Milanovic L, Vucetic V. Reliability and factorial validity of Agility Tests for Soccer players. J Strength Cond Res. 2010; 24(3): 679–86. 
  10. Paul DJ, Gabbett TJ, Nassis GP. Agility in Team Sports: Testing, Training and Factors Affecting Performance. Sport Med. 2016; 46(3): 421–42.

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 role of Sport Scientist in team sport at present: searching the right physical load

The role of Sport Scientist in team sport at present: searching the right physical load

The role of Sport Scientist

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.


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.


  1. 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.
  2. Buchheit M. Want to see my report coach? Sports science reporting in the realworld. Aspetar Sport Med J. 2017; 6: 36–43. 
  3. Robertson S. Man & machine: Adaptive tools for the contemporary performance analyst. J Sports Sci. 2020; 00(00): 1–9.
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Berni Guerrero-Calderón

S&C Coach | Rehab Therapist | Sport Scientist

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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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