Infrared thermography has proven to be a non-invasive and effective tool for monitoring physical performance and preventing injuries in high-performance athletes. Specifically, this method allows for the identification of thermal asymmetries, which can serve as early indicators of muscle imbalances or injury risk. However, one of the recurring challenges in the use of thermography in sports is the need to follow strict acclimatization protocols before taking images, as suggested by the TISEM (Thermographic Imaging in Sports and Exercise Medicine) consensus. This protocol recommends a 10-minute acclimatization period in a controlled environment to stabilize physiological responses before conducting thermal evaluations.
This pilot study, conducted with an elite youth football team, was designed to evaluate the influence of acclimatization on thermography patterns in different body regions, with particular focus on thermal differences and asymmetries between contralateral areas. Over a four-week period, thermography sessions were conducted at three different times: immediately after arrival (0 minutes of acclimatization), after 5 minutes, and after 10 minutes of acclimatization. The room temperature was maintained at 20°C with a relative humidity of 50%.
For this study, a total of 26 youth football players from Spain's top youth division were included. The players underwent thermographic evaluations four times per week over a four-week competitive period, aiming to observe how acclimatization conditions influenced the thermal patterns of different muscle groups.
The imaging procedure followed the standards of the TISEM protocol regarding camera configuration and environmental conditions, although with modifications in the acclimatization process. Thermal images were captured at three distinct times: immediately upon arrival at the facility, after 5 minutes of acclimatization, and after 10 minutes of acclimatization in a room with controlled temperature and humidity. The images were always taken at the same time of day (9:00 am) to ensure that players were in similar physiological conditions, having eaten breakfast but not showered or engaged in intense exercise before the sessions.
The thermal camera used was a FLIR T435bx, placed 3 meters away from the players, with a resolution of 320 × 240 pixels and thermal sensitivity of 0.04°C. This distance was chosen to capture a complete image of the lower limbs, allowing for both anterior and posterior views. Thermal images were taken of 44 regions of interest (ROI) in the lower limbs, divided between the thigh, knee, tibia, ankle, and foot on the anterior view; and the hamstrings, popliteal area, calves, Achilles tendon, and foot on the posterior view.
Each session consisted of two thermal images per player for each of the three acclimatization moments (0, 5, and 10 minutes), one for the anterior part and another for the posterior part of the lower limbs. The images were analyzed using ThermoHuman software, which automatically segmented the regions of interest and calculated average, minimum, and maximum temperatures for each ROI, as well as thermal asymmetry between contralateral regions.
One of the most relevant findings of this study was that acclimatization has a significant impact on the evaluation of the hamstrings. The data showed that, when comparing the three evaluation moments, thermal asymmetry in the hamstrings decreased noticeably after 10 minutes of acclimatization. This suggests that initial temperature differences between the hamstrings could be related to external factors, such as sedentary posture or prior activity before arriving at the facility.
The study hypothesizes that the prolonged sitting posture to which players are subjected before testing may generate vascular compression in the hamstrings, increasing initial thermal asymmetry. As players acclimate to the controlled environment during the first 10 minutes, these asymmetries tend to disappear, indicating that acclimatization may be crucial for obtaining accurate data in this specific muscle region.
In contrast, the results for other body regions, such as the anterior thigh, knee, calf, and ankle, did not show significant differences in thermal asymmetries after the acclimatization period. Despite exposure to controlled temperatures during the same period, most muscles did not present significant variations in thermal asymmetry. This suggests that, for these body regions, acclimatization does not seem to be a critical factor, and thermographic evaluation could be performed without strictly adhering to the 10-minute period recommended by the TISEM protocol.
This study highlights key points for the application of thermography:
With this article, we would like to pay special tribute to the first author of this study, Carlos Majano López, who passed away on July 20, 2024. Carlos, within the framework of his doctoral thesis on thermography, made significant contributions to the field of thermography applied to sports. We deeply appreciate his work and the close relationship he always provided us. Rest in peace.
Majano, C., García-Unanue, J., Fernández-Cuevas, I., Escamilla-Galindo, V., Alonso-Callejo, A., Gallardo, L., & Felipe, J. L. (2024). Assessment of the acclimatization influence on thermography patterns in youth football players: a pilot study. Journal of Thermal Analysis and Calorimetry, 1-10.
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.
