The role of tracking systems in modern soccer

During the last 20 years, there has been a marked increase in the number of publications investigating the use of tracking systems on measuring player’s physical performance and match/training load. The background for this has been two-fold: (1) to examine the physical performance of player’s during matches, (2) and to optimize match- and training load, in order to increase fitness and freshness, and prevent overuse injuries.

This article is a fully translated version of the original article written in Norwegian, published in the main Norwegian soccer coach magazine “The Soccer Coach” (“Fotballtreneren”).

An innovation within soccer has been the introduction of modern tracking systems. These systems give the coaching staff and sport scientists loads of information on the physical activity of player’s. This can be compared to the dashboard of a car; the information of the car’s movement, performance and possible errors makes us aware of the car’s condition. In a similar way could sport tracking systems give us information on the player’s physical activities.

More and more clubs are today using GPS-based or local positioning systems. Examples of these tracking systems are manufactures such as STATSports, Catapult Sports or ZXY Sport Tracking. The small chips that gather information on player’s movements are either worn in a sports bra at the upper back, or in a belt around the waist. These chips measure movements such as running distance, speed and acceleration. In addition, other external camera systems are used during games to quantify the player’s movement patterns.

The use of such technology sounds and looks good. The question is what to do with all this information about player’s movements, how can one use such data, and to what extent can it benefit player’s and coaching staff to gather such considerable amount of data?

Physical performance during games

To understand the use of sport tracking systems it is important to be acquainted with the physical activity during matches. Studies have for a long time measured physical performance during games for total distances covered at different speed thresholds. Several studies show that soccer player’s at elite level cover between 10-14km per game, with about 800m of high-speed running and 300m of sprints (1).

During recent years, the physical activity in soccer has evolved, with more actions at higher velocities. The gameplay is to a larger extent characterized with short periods of rapid changes in pace and intensity. Elite players are today extremely good at repeating high-intensity actions, and this seems to be an important physical quality for success in soccer. The number of high-intensity actions has seen a marked increase in Premier League over the recent years, and the lengths of these actions are shorter (2). This underlines the importance of speed and power for soccer players.

A consequence of a more intense gameplay is higher mechanical load to musculature during games. More intense actions lead to more eccentric muscle contractions when decelerating. This large eccentric load can lead to structural damages to musculature, increasing the recovery time after matches. It has been shown that sprint performance, maximal strength for knee extensors and flexors, and vertical jump performance could be reduced up to 72 hours post-game, indicating that the ability to perform maximal actions is reduced and that player’s are fatigued (3). Muscular fatigue over time is often linked to increased risk of injuries.

The challenge with running distance as a solely measure of physical performance

Studies that have been published since the introduction of sport tracking systems have often focused on total distances covered at higher velocities, which can indicate how much physical work is done at higher intensities. The reason for using high-intensity running as a marker of load is to quantify the activity that will increase muscular fatigue, since physical activity at higher intensities will demand more energy, thus increase fatigue at a faster rate.

However, recent research has shown that physical workload measured through different velocities doesn’t necessarily give a correct picture of the physical demands of training and match (4, 5). We know that soccer includes several other movements that are important for success. These actions, like accelerations, decelerations, change of direction and jumps are movements that are physical demanding and require a significant amount of energy. Such movements have shown to be underestimated when workload is measured by predefined locomotor categories.

An example of a positional role that is underestimated from the traditional approach is the central defender, who generally have significantly less distance covered at higher velocities. Based on this, central defenders will seem to do significantly less work compared to all other positional roles. However, their main job is to counter and stop the attack of the other team. This work primarily includes short accelerations and decelerations, change of directions, jumps and tackles; movements that constitute a great load even at lower velocities. These movement will to a large extent be registered as low-intensity work, due to the fact that these movements rarely exceeds the predefined limits for high-intensity running.

Due to these weaknesses from positional data alone, modern tracking systems can with larger precision quantify different non-linear movements, through sensors such as accelerometer, gyrometer and magnetometer.

Examples on the possible use of tracking systems in training

Modern tracking systems give several opportunities in training. With information on movement patterns for various exercises or training drills, the coaching staff could choose exercises or drills based on which movements they want to overload. For example could one drill stimulate more accelerations, decelerations and change of directions, and one drill stimulate more runs at higher velocities. The coaching staff could also quantify drills that constitute low workload. In addition, the coaching staff could assess the speed and force of actions.

With regular collection of player data, the coaching staff and sport scientists could establish individual thresholds for physical performance at various training drills. This quantifies the “regular” performance of each player, giving each player their own activity profile. An individual profile would give a better overview of the physical work for each practice or over time, and the workload could be individually adjusted. Such objective data is an important development in monitoring physical progress throughout training.

Quantifying the workload for each player is an important development within soccer fitness and sport science. A soccer team has several different player types. Some players are natural runners with excellent stamina, and can tolerate a high workload. Other players are explosive and quick, and should not do the same workload as the runners. The same workload given to two different player types could be more demanding for one player, and explosive and quick players could require more time to recover, especially after intense training sessions.

Another important aspect is how tracking systems could be used when a player is recovering from injury. Previous injury is the biggest risk marker for a new or recurring injury, and this is often caused by players returning to training and match before fully recovered. A player could look ready at practice, but isn’t necessarily fit enough to meet the high physical demands of the match. With the use of tracking systems, the coaching staff could look at the physical performance of the player before injury, and compare this to the recovery period. This could give better evidence if the player’s physical performance is comparable to the physical performance before injury, and if the player can optimally perform the different movements that are important during games. A soccer match is more demanding than training, and it’s therefore important to know that a player is fully fit in order to perform maximally during games to reduce risk of injury and optimise performance.

Injury risk reduction and publications as evidence for practical use

Several teams that have used tracking systems daily have reported through media that they have reduced the risk of injuries.

A technology company producing tracking devices and firmware, Catapult Sports, have in an interview with crunchdatanews.com said that some clubs in American College Football have reduced muscle injuries with up to 88%. In addition, the Toronto Raptors using the same tracking system was the least injured team in NBA in 2013-2014 season (fastcompany.com).

The soccer club Seattle Sounders reported in an interview with citworld.com that they over the last seasons reduced the number of muscle injuries from 498 in 2012, to 214 in 2014, after introducing tracking system monitoring during training.

There have been published some scientific articles that supports the use of tracking systems in optimizing training load in soccer, and if these systems could identify overloaded players and prevent injuries. A recent study from Australian Soccer found that GPS-parameters had an association with injuries in soccer, where injured players had higher meters per minute and lower body load in the weeks preceding injury, compared to seasonal average (6).

Others studies have shown that parameters from tracking systems have a high correlation with player’s subjective response to training, which indicates that training load based on data from tracking systems is in line with the body’s response to training (7). In addition, a study from Australian Rules Football has shown a relationship between neuromuscular fatigue and different movements registered by tracking systems during training, with a likely tendency that fatigued player’s ran more at slower speed, and with less change of directions and accelerations (8).

The results from these studies show that modern tracking systems give additional and valuable information regarding player’s match and training load. However, for a better understanding of the relationship between tracking systems and workload, more research is needed to establish the validity of these systems in reducing injury risk and predict injuries.

Conclusion

Based on the physiological and biomechanical foundation for using tracking system in movement analysis, in addition to the recent studies published, it is likely that these systems could contribute significantly to quantify workload and reduce injuries in modern soccer. Small marginal differences exist between the best soccer teams, hence optimally trained soccer players are important for performance and success. A high training load to increase physical condition is often balancing on a fine line regarding overtraining and overuse injuries, and additional and valid information on player load could contribute to individually adjust training load.

A well-trained soccer player will have reduced risk of injury. Studies have shown that injuries to players could affect team performance, and injured players will also cost clubs a considerable amount of money. Hence, tracking systems could contribute to save unnecessary expenses to injuries.

However, the use of tracking systems requires staff with the ability and knowledge to extract information, interpret the information and communicate the most important information with the coaches in order to take advantage of the additional data. Regular monitoring therefore requires additional staff that can make practical use of the data.

The use of modern tracking systems, and how to utilize these systems in training, will continue to develop. Due to the increased physical demands of the game, and the need to individually adjust training load to optimize physical performance and reduce risk of injuries, modern tracking systems will continue to be a central part of workload monitoring in a team setting. One should not underestimate the coach’s understanding, logical opinion and interpretation of the game, but modern tracking systems could give a deeper and improved understanding of movements and load during training and match. Soccer is not science, but science could contribute to improve performance in soccer.

 

References

 

  1. Bradley PS, Sheldon W, Wooster B, Olsen P, Boanas P, Krustrup P. High-intensity running in English FA Premier League soccer matches. Journal of sports sciences. 2009;27(2):159-68.
  2. Barnes C, Archer DT, Hogg B, Bush M, Bradley PS. The evolution of physical and technical performance parameters in the English Premier League. International journal of sports medicine. 2014;35(13):1095-100.
  3. Nedelec M, McCall A, Carling C, Legall F, Berthoin S, Dupont G. Recovery in soccer: part I – post-match fatigue and time course of recovery. Sports Med. 2012;42(12):997-1015.
  4. Osgnach C, Poser S, Bernardini R, Rinaldo R, di Prampero PE. Energy cost and metabolic power in elite soccer: a new match analysis approach. Medicine and science in sports and exercise. 2010;42(1):170-8.
  5. Gaudino P, Iaia FM, Alberti G, Strudwick AJ, Atkinson G, Gregson W. Monitoring Training in Elite Soccer Players: Systematic Bias between Running Speed and Metabolic Power Data. International journal of sports medicine. 2013;34(11):963-8.
  6. Ehrmann FE, Duncan CS, Sindhusake D, Franzsen WN, Greene DA. GPS and Injury Prevention in Professional Soccer. Journal of strength and conditioning research / National Strength & Conditioning Association. 2015.
  7. Scott BR, Lockie RG, Knight TJ, Clark AC, Janse de Jonge XA. A comparison of methods to quantify the in-season training load of professional soccer players. International journal of sports physiology and performance. 2013;8(2):195-202.
  8. Cormack SJ, Mooney MG, Morgan W, McGuigan MR. Influence of neuromuscular fatigue on accelerometer load in elite Australian football players. International journal of sports physiology and performance. 2013;8(4):373-8.

 

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