Gonçalo Trindade, Sports Scientist at Clube Desportivo Nacional, has been collecting data in his team during the seasons 2020/2021 (using a GPS tracker) and 2021/2022 (using a combination of technologies, including thermography) with the aim of discovering the relevance in his players’ musculoskeletal injury incidence.
Regardless of whether directly or indirectly, an injury has an important cost for the team. Eliakim et al. (2020) investigated the economic costs of injuries in the football teams of the Premier League. The results were outstanding: more than €53 million in losses, divided into: wages of players that are not playing, TV rights, place in the championship and rights of national and international leagues. You can read more about this topic in the previous article.
This is why reducing the injury rate of professional football players has gained more and more attention in recent years. Among the technologies and methodologies that aim to decrease the amount of injuries, thermography is usually highlighted thanks to its scientific results. The fields it is more frequently used are injury prevention, diagnosis support, injury follow-up, and internal load monitoring.
Thermography can also be used in high-performance football teams with other complementary objectives, such as monitoring muscle damage in football players (de Andrade et al. 2017) and assessing the relationship with lower limb strength before and after a competitive season (Rodrigues Júnior et al. 2019). Actually, it has been proven that a combination of strength training and a thermography protocol in a football team, can decrease the number of injuries from 23 to 14 when early year rates were compared to late year (Menezes et al. 2018).
Moreover, researchers such as Matheus Fontes (Dias, V. 2017), Ana Carolina Côrte (Côrte et al. 2019) and Pedro Gómez (Gómez-Carmona et al. 2020) have shown that the implementation of thermography during a pre-season or a season may result in an important reduction of muscle injuries, ranging from 63-74%.
The main objectives of this study were:
In an experimental design, 28 professional football players of the same team in Portugal (age: 27.5 ± 4.2 years, height: 1.8 ± 0.5 m, body mass: 75.9 ± 6.0 kg and BMI: 23.1 ± 1.5 kg/m2) were included in the study. Furthermore, 15 players participated in both seasons.
During the 2020/2021 season, only one technology, a GPS tracker, was used on a daily basis. All players had a JOHAN V4 GPS Sports Tracking system (Johan Sports®, The Netherlands), a wearable GPS tracker, during the training. It collected data, such as distance covered, top speed, number and distance of sprints and other external training load parameters. For Tim J. Gabbett (2016) the sudden and excessive increases in training loads are related to non-traumatic, soft-tissue injuries, hence, likely to be prevented. However, the appropriate training protects against injuries. This is why it is so important to monitor both internal and external training load, by calculating the acute:chronic workload ratio. Recording acute and chronic training loads, allows practitioners to establish the individual state of fitness (lower than average risk of injury) or fatigue (higher than average risk of injury).
During the 2021/2022 season, a combination of sports technologies was used to have a wider perspective of the training load the players had. The same GPS tracker and tracking platform were used for this new season. In addition to it, thermography, a wellness questionnaire and neuromuscular assessments were made with the next frequencies, also represented in Figure 1:
Figure 1. Description of the assessment performed in the protocol followed by the players in an usual week during the 2021/2022 season (MD: match day)
GPS data was collected and analyzed every training session, as well as a wellness questionnaire, totalizing 5 tests per week (from MD+1 to MD-1). Wellness questionnaire is one of the most studied, simple and inexpensive means for monitoring an athlete’s training load (Halson et al. 2014), in order to better know his degree of fatigue, quality of recovery and readiness before the next training (Mateus et al. 2021).
The neuromuscular tests consisted of the adductor squeeze strength test (Smart Groin Test, Neuro Excellence®, Portugal) and the nordic hamstring symmetry test (Smart Nordic Trainer, Neuro Excellence®, Portugal). In the squeeze test the players made three maximal isometric hip adduction contractions lasting 5 seconds, interspersed by 3 min rest intervals (Sousa et al. 2022). The maximal pressure (squeeze) value displayed on the dynamometer dial was recorded during each of the three test trials (Moreno-Pérez et al. 2019). The neuromuscular tests were performed once a week, to detect if there were imbalances in the adductors and hamstrings muscles. The players who did not play or played less than 30’ were tested on MD-4. Only the players who actually played more than 60’ were tested on MD-3.
Every thermography assessment was performed after an acclimation period of 10-15 min in underwear in an acclimatized room (20-24 ºC), respecting the requirements described in the TISEM consensus (Moreira et al. 2019) and confirmed by a questionnaire before. The data collection included taking thermal images with a thermographic camera FLIRT 540-EST (FLIR® Systems, Sweden) 464 × 348 pixels of resolution, thermal range from 15°C to 45°C, spectral range of 7.5-14 m, accuracy of 2% (±0.3 °C) and a high thermal sensitivity (<0,04ºC / <40mK at 30 ºC). Before the data collection, the camera was auto calibrated and it was switched on at least half an hour before, in accordance with the influence factors related by Marins et al. (2015). For the healthy players, the thermal data was collected before the first and last training sessions of the week. Injured athletes did thermography every 48 hours.
In the analysis process, the coefficient of variation metric, very common in advanced thermographic analysis, was used. It is defined as the ratio of the standard deviation to the mean temperature of a region of interest and shows the extent of variability in relation to the mean. Thanks to it, we could observe that the players experienced an increase or decrease in their global temperature 24h after the match, depending on the nature of their fatigue. As recommended by Thorpe (2021), and explained in this article, the players who had a global hot behavior, should use cooling strategies (i.e.: cold water immersion), while the players who had a decrease in their skin temperature should use heating strategies (i.e.: diathermy), in order to minimize their fatigue and optimize their recovery.
If wellness questionnaires, GPS data and values in the strength tests were below what the staff intended, the athlete was evaluated with thermography. Also, terrain changes were also considered, as whenever the training changed locations, thermography assessment was postponed to the next day.
During the 2020-2021 season, only a GPS tracker was used to monitor muscle imbalances, but there was no injury prevention protocol. A total of 26 muscle injuries were registered, as follows: hamstring (16), adductors (6), rectus femoris (3), calves (1). These injuries implied a total of 505 days out for the players.
At the end of the season 2021-2022, the total number of muscle injuries was 9, being hamstring (4), adductors (3), rectus femoris (2), calves (0). The players were injured and not playing for 167 days during the season. Figure 2 shows a summary of this data:
Figure 2. Summary of the registered injuries and total days off during the seasons 2020-2021 and 2021/2022.
When both seasons are compared, a difference of -17 muscle injuries was found, which means a 65% reduction in muscle injuries. Counting the days out, there was a difference of -338 days, which means a 67% reduction in days out for the whole team. Comparing the 15 players who participated in both seasons, it was found that in the 2020-2021 season 13 muscle injuries (263 days out) were registered whereas only 4 (68 days out) were found in the 2021-2022 season, which reflects a decrease of 69% in muscle injuries and 74% in days out.
When a player suffered an injury, we immediately followed the development of the injury through thermography, performing the follow-up in order to reduce times and improve decision-making in the process of return to play through multi-technology combination. However, a clinical examination was necessary to confirm the injury. All the information was shared with the physiotherapists to optimize the treatment, hence we evaluated the athletes with thermography every 48 hours.
In figure 3, you can see a player of the team with a muscle injury in his left hamstring region. From the thermogram we can appreciate a significant hypothermic difference in the injured region. The mean asymmetry metric confirms this difference (asymmetry: 0.46 ºC middle region of the posterior thigh; 0.82 ºC internal region). The coefficient of variation metric adds more specific information, flagging the middle region as cooler than usual (-1). In addition, the right side, without any injury, appears to have a hot profile, since the player's biomechanics have been affected during the recovery process, increasing the temperature of a large part of the regions of the healthy side:
Figure 3. Example of a player injured in the hamstring region of his left leg. Mean asymmetry and coefficient of variation metrics confirm the severity of the injury.
On average, in the 2020-2021 season the time of a muscle injury recovery was 26 days (from the injury day to the return-to-play day). The next season, this time was 18 days on average, which means a decrease of 8 days (-31%). We can explain this optimization in the recovery process largely due to the various data we had that allowed us to get the player to train and play safely without having any recurrence. Besides, those injuries had a lesser severity.
Thermography is a useful complementary tool that assists an injury prevention protocol in a professional football team, combining its assessments with other tests like neuromuscular, wellness questionnaire and GPS tracker. One only technology may have an impact in injury incidence, but the combination of different technologies is key to obtaining excellent results.
By creating an injury reduction protocol, in which different technologies are combined, the players’ performance is optimized, more players are available to train and play, post-game recovery can be individualized according to the thermal response and injury recovery times and medical department costs are drastically reduced. It is also important to mention that teamwork is essential, namely in helping the coach to improve his training methodology.
de Andrade Fernandes, A., Pimenta, E.M., Moreira, D.G. et al. Skin temperature changes of under-20 soccer players after two consecutive matches. Sport Sci Health 13, 635–643 (2017).
Côrte AC, Pedrinelli A, Marttos A. Infrared thermography study as a complementary method of screening and prevention of muscle injuries: pilot study. BMJ Open Sport & Exercise Medicine 2019;5:e000431.
Danilo Gomes Moreira, Joseph T. Costello, Ciro J. Brito, Jakub G. Adamczyk, Kurt Ammer, Aaron J.E. Bach, Carlos M.A. Costa, Clare Eglin, Alex A. Fernandes, Ismael Fernández-Cuevas, José J.A. Ferreira, Damiano Formenti, Damien Fournet, George Havenith, Kevin Howell, Anna Jung, Glen P. Kenny, Eleazar S. Kolosovas-Machuca, Matthew J. Maley, Arcangelo Merla, David Pascoe, Jose I. Priego-Quesada, Robert G. Schwartz, Adérito R.D. Seixas, James Selfe, Boris G. Vainer and Manuel Sillero-Quintana. Thermographic imaging in sports and exercise medicine: a Delphi study and consensus statement on the measurement of human skin temperature, Journal of Thermal Biology, 2017; 69:155-162.
Dias, V. (2017). DNA mineiro: projeto inovador impulsiona retorno de time de Portugal à Liga Europa. Retrieved 15/06/2022, from https://toqdiletra.blogspot.com/2017/05/dna-mineiro-projeto-inovador-impulsiona-retorno-de-time-de-portugal-a-liga-europa.html
Eliakim E, Morgulev E, Lidor R, et al Estimation of injury costs: financial damage of English Premier League teams’ underachievement due to injuries BMJ Open Sport & Exercise Medicine 2020;6:e000675.
Gabbett TJ. The training-injury prevention paradox: should athletes be training smarter and harder? Br J Sports Med. 2016 Mar;50(5):273-80.
Gómez-Carmona P, Fernández-Cuevas I, Sillero-Quintana M, Arnaiz-Lastras J, Navandar A. Infrared Thermography Protocol on Reducing the Incidence of Soccer Injuries. J Sport Rehabil. 2020 Nov 1;29(8):1222-1227. doi: 10.1123/jsr.2019-0056. Epub 2020 Mar 17. PMID: 32188790.
Halson SL. Monitoring training load to understand fatigue in athletes. Sports Medicine, 2014;44(2):139-147.
Marins J, Fernández-Cuevas I, Arnaiz Lastras J, Fernandes A, Sillero Quintana M. Applications of infrared thermography in sports. A review. Int J Med Sci Phys Act Sport. 2015;15(60):805-24.
Mateus N, Gonçalves B, Felipe JL, Sánchez-Sánchez J, Garcia-Unanue J, Weldon A, Sampaio J. In-season training responses and perceived wellbeing and recovery status in professional soccer players. PLoS One. 2021 Jul 14;16(7):e0254655.
Menezes P, Rhea MR, Herdy C, Simão R. Effects of Strength Training Program and Infrared Thermography in Soccer Athletes Injuries. Sports (Basel). 2018 Nov 19;6(4):148.
Moreno-Pérez V, Travassos B, Calado A, Gonzalo-Skok O, Del Coso J, Mendez-Villanueva A. Adductor squeeze test and groin injuries in elite football players: A prospective study. Phys Ther Sport. 2019 May;37:54-59.
Rodrigues Júnior JL, Duarte W, Falqueto H, Andrade AGP, Morandi RF, Albuquerque MR, de Assis MG, Serpa TKF, Pimenta EM. Correlation between strength and skin temperature asymmetries in the lower limbs of Brazilian elite soccer players before and after a competitive season. J Therm Biol. 2021 Jul;99:102919.
Sousa C, Marques DL, Calado AM, Pacheco A, Almeida-Marinho D, Cardoso-Marques M, Travassos F (2022). Validity and Reliability of the Smart Groin Trainer for Measuring Hip Adduction Strength. Journal of Human Kinetics,82(1) 51-59.
Thorpe, R. T. (2021) Post-exercise Recovery: Cooling and Heating, a Periodized Approach. Front. Sports Act. Living 3:707503.
ThermoHuman has had the support of the Funds of the European Union and the Community of Madrid through the Operational Programme on Youth Employment. Likewise, ThermoHuman within the framework of the Export Initiation Program of ICEX NEXT, had the support of ICEX and the co-financing of the European Regional Development Fund (ERDF).
Thermohuman has received funding from the Centre for the Development of Industrial Technology (CDTI), in participation with the European Regional Development Fund (ERDF), for the R+D activities involved in creating a new tool, based on thermography, for the prediction and prevention of rheumatoid arthritis. See project detail.
