Thermographic imaging in physical activity and sports: methodology and specific responses

Field: Health Professions (Health Sciences)

Introduction: The importance of using infrared thermography (IRT) to measure skin temperature (tsk) is increasing in health and disease situations. Recently, its use has been growing especially in sports and exercise medicine; however, no consensus guideline exists to address the methods for collecting data in such situations. This lack of standardization and control of the intervening variables in the IRT data collection is commonly attributed as a source of bias, and can in most cases influence the results. Additionally, given the possible influence of individual factors on skin temperature response recorded by IRT, it is hard to identify if changes in tsk are due to thermoregulatory adjustments of the body, such as sweating and increased peripheral blood flow, or if these changes rely on anthropometrical or physiological parameters. However, the literature about this is scarce and needs new studies.
Objectives: This thesis was divided into two studies with complementary objectives. The aim of the first study was to develop a checklist for the collection of tsk using IRT in sports and exercise medicine. The aim of the second study was to analyze the tsk response in judokas after a specific incremental test and to determine if anthropometric and physiological measures can be explained by the variation in mean tsk.
Methods: In the first study, it was carried out a Delphi study to set a checklist based on consensus agreement from leading experts in the field. Panelists (n = 24) representing the areas of sport science (n=8; 33%), physiology (n=7; 29%), physiotherapy (n=3; 13%) and medicine (n=6; 25%), from 13 different countries completed the Delphi process. An initial list of 16 points was proposed which was rated and commented on by panelists in three rounds of anonymous surveys following a standard Delphi procedure. In the second study, it was analyzed a total of 23 male judo athletes (age: 20.1 ± 4.7 yrs, height: 173.1 ± 8.1 cm; body mass: 71.7 ± 8.1 kg) who performed a specific incremental judo test. Skin temperature evaluations were collected in 26 regions of interest (ROI), and the mean tsk was calculated using an equation including ten of them. The time points before the test (pre-test), immediately after (0 min), and after 5, 10 and 15 min of the test were established to measure the tsk, mean tsk, auricular temperature (tau), and blood lactate. Additionally, the VO2peak was measured during the specific judo test via gas analyzer.
Results: In the first study, the results of the Delphi produced the checklist entitled “Thermographic Imaging in Sports and Exercise Medicine (TISEM)” which is a proposal to standardize the collection and analysis of tsk data using IRT. In the second study, the athletes completed a mean of 7.0 ± 1.0 stages of the test, 95% CI [6.2; 7.1]. The VO2peak achieved was 48.7 ± 5.3 ml.kg-1.min-1, 95% CI [46.4; 51.0]. Compared to pre-test values, only the forehead significantly decreased 5 min after the test (p < .05). The posterior right arm and posterior left arm remained increased 10 min after the test (p < .05). After 15 min, 19 of the 26 ROIs analyzed significantly decreased (p < .05). Among all tested models of linear regression, only two were significant, the difference of tsk 5 min compared to pre-test (F1, 21=16.49, p = .001) and the difference of tsk 10 min compared to pre-test, to predict lactate concentration at the end of the test (F1, 21=9.30, p = .006).
Conclusions: This thesis has provided a checklist with 15 items directed at standardizing the assessment of tsk using IRT for a wide array of end-users including practitioners, sports scientists, exercise physicians, medical professionals and others. This checklist is not limited to this setting, and may also be used in others fields such occupational medicine and public health. It is intended that the TISEM can also be applied to evaluate bias in thermographic studies, and to guide practitioners in the use of this technique. Additionally, based on the analysis of the second study of this thesis, it was concluded that 5 min after the test the judokas present a higher tau and a higher tsk in seven ROIs, and the tsk decreases 15 min after the test in 19 of the considered ROIs. The variation in mean skin temperature is not related to anthropometric measures. Only the variation of mean tsk 5 min and 10 min after the test compared to pre-test values is associated with blood lactate at the end of the test.