Injury prevention with thermography in football: the most recent results
Injury prevention in high-performance football is imperative, as it is one of the hardest difficulties the football teams need to lead with. An important part of the team’s budget is lost every year due to injured players. Thermography appears as a complementary tool that may drastically decrease the incidence of musculoskeletal injuries in high-performance football teams.
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:
- To measure different biometric aspects of the players thanks to a technology combination for injury prevention, especially by adding thermography, neuromuscular tests and a wellness questionnaire to their daily testing.
- To quantify the difference of injuries and days out between two consecutive seasons.
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:
- MD: Match Day
- MD+1: Day Off
- MD+2: GPS tracker, wellness questionnaire and thermography
- MD-4: GPS tracker, wellness questionnaire, neuromuscular assessment (only the players who did not play or played less than 30’)
- MD-3: GPS tracker, wellness questionnaire, neuromuscular assessment (only the players who played more than 60’)
- MD-2: GPS tracker, wellness questionnaire
- MD-1: GPS tracker, wellness questionnaire and thermography
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:
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.
The injuries that actually occurred
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:
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.
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