Thermography for skin temperature evaluation during dynamic exercise: a case study on an incremental maximal test in elite male cyclists

Exercise-induced changes in lower limbs skin temperature against plasma ATP among individuals with various type and level of physical activity

The objective of the study was to examine the lower limbs skin temperature (TSK) changes in response to exhaustive whole-body exercise in trained individuals in reference to changes in plasma adenosine triphosphate (ATP). Eighteen trained participants from distinct sport type ‒ endurance (25.2 ± 4.9 yr) and speed-power (25.8 ± 3.1 yr), and 9 controls (24,9 ± 4,3 yr) ‒ were examined. Lower limbs TSK and plasma ATP measures were applied in parallel in response to incremental treadmill test and during 30-min recovery period. Plasma ATP kinetics were inversely associated to changes in TSK. The first significant decrease in TSK (76-89% of V˙ O2MAX) occurred shortly before a significant plasma ATP increase (86-97% of V˙ O2MAX). During recovery, TSK increased, reaching pre-exercise values (before exercise vs. after 30-min recovery: 31.6 ± 0.4 °C vs. 32.0 ± 0.8 °C, p = 0.855 in endurance; 32.4 ± 0.5 °C vs. 32.9 ± 0.5 °C, p = 0.061 in speed-power; 31.9 ± 0.7 °C vs. 32.4 ± 0.8 °C, p = 0.222 in controls). Plasma ATP concentration did not returned to pre-exercise values in well trained participants (before exercise vs. after 30-min recovery: 699 ± 57 nmol l-1 vs. 854 ± 31 nmol l-1, p < 0.001, η2 = 0.961 and 812 ± 35 nmol l-1 vs. 975 ± 55 nmol l-1, p < 0.001, η2 = 0.974 in endurance and speed-power, respectively), unlike in controls (651 ± 40 nmol l-1 vs. 687 ± 61 nmol·l-1, p = 0.58, η2 = 0.918). The magnitude of TSK and plasma ATP response differed between the groups (p < 0.001, η2 = 0.410 for TSK; p < 0.001, η2 = 0.833 for plasma ATP). We conclude that lower limbs TSK change indirectly corresponds to the reverse course of plasma ATP during incremental exercise and the magnitude of the response depends on the level of physical activity and the associated to it long-term metabolic adaptation.

Relationship between aerobic fitness and lower limb skin temperature during cycling exercise testing among well-trained athletes and nonathletes: a cross-sectional study

Background

During prolonged physical exercise, the skin plays an important role in thermoregulation by dissipating heat to maintain core temperature. Moreover, thermal variation may be influenced by the physical fitness level of an individual. The aim of the present study was to determine the relationship between aerobic fitness and lower limb skin temperature during graded cycling exercise testing in well-trained athletes and nonathletes.

Methods

Twelve trained athletes (mean ± SD maximal oxygen consumption [VO2max], 52.44 ± 4.5 ml/kg/min) and 12 nonathletes (VO2max, 36.95 ± 4.9 ml/kg/min) participated in this study. The regional skin temperature over the lower limbs was monitored continuously during incremental exercise testing using a thermal camera, and cardio-respiratory parameters were assessed and recorded using a metabolic analyzer (K5, COSMED, Rome, Italy).

Results

The mean skin temperature of athletes at a high intensity of exercise was 27.23 ± 0.3 °C while that of nonathletes was 29.03 ± 0.44 °C, a difference that was statistically significant (p < 0.05). A negative correlation was observed between skin temperature and cardiovascular parameters (VO2max and heart rate) in athletes, while no such correlation was found among nonathletes.

Conclusion

The present study demonstrated a negative correlation between oxygen consumption and lower limb skin temperature in athletes, while the correlation was poor in nonathletes. This suggests that physical fitness level may influence the pattern of alterations in lower limb skin temperature, which supports the hypothesis that athletes exhibit better heat dissipation mechanisms than nonathletes.

Thermographic Changes following Short-Term High-Intensity Anaerobic Exercise

Current studies report thermographic changes following aerobic or resistance exercise but not short, vigorous anaerobic exercise. Therefore, we investigated body surface temperature changes using thermal imaging following a short session of anaerobic exercise. We studied three different regions of interest (ROIs): the legs, chest, and forehead. Thermal imaging for each participant was performed before and immediately after completing a Wingate anaerobic test and every minute during a 15 min recovery period. Immediately after the test, the maximum temperature was significantly higher in all ROIs (legs, p = 0.0323; chest, p = 0.0455; forehead, p = 0.0444) compared to pre-test values. During the recovery period, both legs showed a significant and continuous temperature increase (right leg, p = 0.0272; left leg, p = 0.0382), whereas a non-significant drop was noted in the chest and forehead temperatures. Additionally, participants with a lower anaerobic capacity exhibited a higher delta increase in surface leg temperature than participants with higher anaerobic capacities, with a minimal change in surface leg temperature. This is the first study to demonstrate body surface temperature changes following the Wingate anaerobic test. This temperature increase is attributed to the high anaerobic mechanical power outputs achieved by the leg muscles and the time taken for temperature reduction post-exercise.

Acute physiological responses to a pyramidal exercise protocol and the associations with skin temperature variation in different body areas

This study aimed to examine the skin temperature (Tsk) variations in five regions of interest (ROI) to assess whether possible disparities between the ROI's Tsk could be associated with specific acute physiological responses during cycling. Seventeen participants performed a pyramidal load protocol on a cycling ergometer. We synchronously measured Tsk in five ROI with three infrared cameras. We assessed internal load, sweat rate, and core temperature. Reported perceived exertion and calves' Tsk showed the highest correlation (r = -0.588; p < 0.01). Mixed regression models revealed that the heart rate and reported perceived exertion were inversely related to calves' Tsk. The exercise duration was directly associated with the nose tip and calf Tsk but inversely related to the forehead and forearm Tsk. The sweat rate was directly related to forehead and forearm Tsk. The association of Tsk with thermoregulatory or exercise load parameters depends on the ROI. The parallel observation of the face and calf Tsk could indicate simultaneously the observation of acute thermoregulatory needs and individual internal load. The separate Tsk analyses of individual ROI appear more suitable to examine specific physiological response than a mean Tsk of several ROI during cycling.

An exploratory, intra- and interindividual comparison of the deep neural network automatically measured calf surface radiation temperature during cardiopulmonary running and cycling exercise testing: A preliminary study

Non-invasive and contactless infrared thermography (IRT) measurements have been claimed to indicate acute neural, cardiovascular, and thermoregulatory adaptations during exercise. Due to challenging comparability, reproducibility, and objectivity, investigations considering different exercise types and intensities, and automatic ROI analysis are currently needed. Thus, we aimed to examine surface radiation temperature (T_sr) variations during different exercise types and intensities in the same individuals, ROI, and environmental conditions. Ten healthy, active males performed a cardiopulmonary exercise test on a treadmill in the first week and on a cycling ergometer the following week. Respiration, heart rate, lactate, rated perceived exertion, the mean, minimum, and maximum T_sr of the right calf (CT_sr (°C)), and the surface radiation temperature pattern (CP_sr) were explored. We executed two-way rmANOVA and Spearman's rho correlation analyses. Across all IRT parameters, mean CT_sr showed the highest association to cardiopulmonary parameters (E.g., oxygen consumption: r_s = -0.612 (running); -0.663 (cycling); p < .001). A global significant difference of CT_sr was identified between all relevant exercise test increments for both exercise-types (p < .001; η²_p = .842) and between both exercise-types (p = .045; η²_p = .205). Differences in CT_sr between running and cycling significantly appeared after a 3-min recovery period, whereas lactate, heart rate, and oxygen consumption were not different. High correlations between the CT_sr values extracted manually and the CT_sr values processed automatically by a deep neural network were identified. The applied objective time series analysis enables crucial insights into intra- and interindividual differences between both tests. CT_sr variations indicate different physiological demands between incremental running and cycling exercise testing. Further studies applying automatic ROI analyses are needed to enable the extensive analysis of inter- and intraindividual factors influencing the CT_sr variation during exercise to allow determine the criterion and predictive validity of IRT parameters in exercise physiology.

Infrared thermal imaging-based skin temperature response during cupping at two different negative pressures

Cupping therapy can relieve muscle fatigue and pain after exercise by increasing blood flow at the treatment site, which may lead to dynamic changes of the local skin temperature. This study aimed to analyze the effect of cupping on local skin temperature under two different negative pressures using infrared thermography (IRT). Cupping therapy was performed on the forearms of 22 healthy subjects using the negative pressures of − 0.03 and − 0.04 MPa. IRT was used to record the dynamic changes in skin temperature before, during, and after cupping. Both cupping pressures induced a non-linear skin temperature response: temperature decreased first and then increased during cupping, while it first increased and then decreased after cupping. A significant difference was noted between the two negative pressure groups in the maximum temperature increment after cupping (P < 0.001). Compared with the basal temperature before cupping, the maximum increase in skin temperature after cupping in the − 0.03 and − 0.04 MPa groups was 0.92 and 1.42 °C, respectively. The findings of this study can lay the foundation evaluating the curative effect of cupping based on IRT and provide an objective reference for selecting the cupping negative pressure.

Preliminary study of thermal density distribution and entropy analysis during cycling exercise stress test using infrared thermography

Considerable differences related to the results of temperature changes acquired during exercise exist, and in many cases, these lead to poor correlation with physiological variables. In this preliminary study we investigated the temperature changes and the temperature distribution (entropy) of the torso during a graded cycling exercise stress test using thermal imaging and studied the correlation between the increase in pulmonary ventilation (VE) and the changes in the surface temperature of the anterior torso during exercise. Thermal images of the anterior torso were captured every 30 s during the exercise, while the resistance was gradually increased every minute until exhaustion. The thermal images were processed to obtain a mean temperature in the regions of interest (ROI) (chest, forehead, and abdomen). We also developed an algorithm to calculate the distribution of temperature and texture (entropy) within each ROI. No changes were found in absolute temperatures. However, the entropy of the chest surface area increased significantly throughout the exercise test, compared with baseline temperature at rest. This increase in entropy was significantly correlated with exercise duration and intensity (p < 0.001). Furthermore, a high correlation between the increase in VE and chest entropy during exercise was detected (r = 0.9515). No correlations were found between the increase in entropy and the abdomen or the forehead compared with the VE. The non-invasive IR thermal imaging during graded exercise, combined with advanced image processing, successfully correlates surface thermography with exercise duration and pulmonary ventilation.

Towards Exercise Radiomics: Deep Neural Network-Based Automatic Analysis of Thermal Images Captured During Exercise

Infrared thermography is increasingly applied in sports science due to promising observations regarding changes in skin's surface radiation temperature ( T_sr) before, during, and after exercise. The common manual thermogram analysis limits an objective and reproducible measurement of T_sr. Previous analysis approaches depend highly on expert knowledge and have not been applied during movement. We aimed to develop a deep neural network (DNN) capable of automatically and objectively segmenting body parts, recognizing blood vessel-associated T_sr distributions, and continuously measuring T_sr during exercise. We conducted 38 cardiopulmonary exercise tests on a treadmill. We developed two DNNs: body part network and vessel network, to perform semantic segmentation of 1 107 855 captured thermal images. Both DNNs were trained with 263 training and 75 validation images. Additionally, we compare the results of a common manual thermogram analysis with these of the DNNs. Performance analysis identified a mean IoU of 0.8 for body part network and 0.6 for vessel network. There is a high agreement between manual and automatic analysis (r = 0.999; p 0.001; T-test: p = 0.116), with a mean difference of 0.01 ^C (0.08). Non-parametric Bland Altman's analysis showed that the 95% agreement ranges between -0.086 ^C and 0.228 ^C. The developed DNNs enable automatic, objective, and continuous measurement of T_sr and recognition of blood vessel-associated T_sr distributions in resting and moving legs. Hence, the DNNs surpass previous algorithms by eliminating manual region of interest selection and form the currently needed foundation to extensively investigate T_sr distributions related to non-invasive diagnostics of (patho-)physiological traits in means of exercise radiomics.

Short-Term Skin Temperature Responses to Endurance Exercise: A Systematic Review of Methods and Future Challenges in the Use of Infrared Thermography

BACKGROUND

Body temperature is often assessed in the core and the skin. Infrared thermography has been used to measure skin temperature (Tsk) in sport research and clinical practice. This study aimed to explore the information reported to date on the use of infrared thermography to detect short-term Tsk responses to endurance exercise and to identify the methodological considerations and knowledge gaps, and propose future directions.

METHOD

A web search (PubMed, Science Direct, Google Scholar, and Web of Science) was conducted following systematic review guidelines, and 45 out of 2921 studies met the inclusion criteria (endurance sports, since 2000, English, full text available).

RESULTS

A total of 45 publications were extracted, in which most of the sample were runners (n = 457, 57.9%). Several differences between IRT imaging protocols and ROI selection could lead to potential heterogeneity of interpretations. These particularities in the methodology of the studies extracted are widely discussed in this systematic review.

CONCLUSIONS

More analyses should be made considering different sports, exercise stimuli and intensities, especially using follow-up designs. Study-derived data could clarify the underlying thermo physiological processes and assess whether Tsk could be used a reliable proxy to describe live thermal regulation in endurance athletes and reduce their risk of exertional heat illness/stroke. Also more in-depth analyses may elucidate the Tsk interactions with other tissues during exercise-related responses, such as inflammation, damage, or pain.

Quantitative assessment of Bell's palsy-related facial thermal asymmetry using infrared thermography: A preliminary study

The temperature distribution of normal human skin is symmetrical. Facial paralysis generally changes this thermal symmetry. The aim of this study is to analyze facial thermal asymmetry during the early onset of Bell's palsy, and to assess the feasibility of the diagnosis of early-onset Bell's palsy using infrared thermography (IRT). Fifteen subjects with Bell's palsy and 15 healthy volunteers were considered in this study. The infrared thermal images of the front, left, and right sides of all the subjects were collected and analyzed. Each group of facial thermograms was divided into 16 symmetrical regions of interest (ROIs) with respect to the left and right sides. Three different temperature difference calculation methods were used to express the degree of thermal symmetry between the left- and right-side ROIs, namely, the mean temperature difference (ΔT_roi), maximum temperature difference (ΔT_max), and minimum temperature difference (ΔT_min). Among the facial ROIs, there were significant differences in the thermal symmetries of the frontal region, medial canthus region, and infraorbital region between subjects with and without Bell's palsy (p < 0.05). Based on the results, ΔT_roi was more effective than the other two methods for the diagnosis of early-onset Bell's palsy. The area under the ROC curve (AUC) of ΔT_roi in the infraorbital region was 0.818; and the sensitivity and specificity were 0.867 and 0.800, respectively. Subjects with early-onset Bell's palsy exhibited thermal asymmetry on the left and right sides of their faces. The diagnosis of early-onset Bell's palsy using IRT is therefore necessary. Nevertheless, more effective thermal symmetry analysis methods will be investigated further in future research.

Regions of interest selection and thermal imaging data analysis in sports and exercise science: a narrative review

OBJECTIVE

Infrared thermography (IRT) is a non-invasive, contactless and low-cost technology that allows recording of the radiating energy that is released from a body, providing an estimate of its superficial temperature. Thanks to the improvement of infrared thermal detectors, this technique is widely used in the biomedical field to monitor the skin temperature for different purposes (e.g. assessing circulatory diseases, psychophysiological state, affective computing). Particularly, in sports and exercise science, thermography is extensively used to assess sports performance, to investigate superficial vascular changes induced by physical exercise, and to monitor injuries. However, the methods of analysis employed to treat IRT data are not standardized, and hence introduce variability in the results.

APPROACH

This review focuses on the methods of analysis currently used for thermal imaging in sports and exercise science.

MAIN RESULTS

Firstly, the procedures employed for the selection of regions of interest (ROIs) from anatomical body districts are reviewed, paying attention also to the potentialities of morphing algorithms to increase the reproducibility of thermal results. Secondly, the statistical approaches utilized to characterize the temperature frequency and spatial distributions within ROIs are investigated, showing their strengths and weaknesses. Moreover, the importance of employing tracking methods to analyze the temporal thermal oscillations within ROIs is discussed. Thirdly, the capability of employing procedures of investigation based on machine learning frameworks on thermal imaging in sports science is examined.

SIGNIFICANCE

Finally, some proposals to improve the standardization and the reproducibility of IRT data analysis are provided, in order to facilitate the development of a common database of thermal images and to improve the effectiveness of IRT in sports science.

Lactate Concentration Is Related to Skin Temperature Variation After a Specific Incremental Judo Test

ABSTRACT

Gomes Moreira, D, José Brito, C, de Almeida Ferreira, JJ, Bouzas Marins, JC, López Díaz de Durana, A, Couceiro Canalejo, J, Butragueño Revenga, J, and Sillero-Quintana, M. Lactate concentration is related to skin temperature variation after a specific incremental judo test. J Strength Cond Res 35(8): 2213-2221, 2021-This study aimed to analyze the skin temperature (tsk) response in judokas after a specific incremental test and to determine whether anthropometric and physiological measures can be explained by the variation in mean tsk. A total of 23 male judo athletes (age: 20.1 ± 4.7 years; height: 173.1 ± 8.1 cm; and body mass: 71.7 ± 8.1 kg) performed a specific incremental judo test. Skin temperature evaluations were collected in 26 regions of interest (ROIs), and the mean tsk was calculated using an equation including 10 of them. The time points before the test (pre-test), immediately after (0 minutes), and after 5, 10, and 15 minutes of the test were established to measure the tsk, mean tsk, auricular temperature (tau), and blood lactate (LAC). The athletes completed a mean of 7.0 ± 1.0 stages of the test, 95% confidence interval (CI; 6.2-7.1). The V̇o2peak achieved was 48.7 ± 5.3 ml·kg-1·min-1, 95% CI (46.4-51.0). Compared with pre-test values, only the forehead significantly decreased 5 minutes after the test (p < 0.05). The posterior right arm and posterior left arm remained increased 10 minutes after the test (p < 0.05). After 15 minutes, 19 of the 26 ROIs analyzed were significantly decreased (p < 0.05). Among all tested models of linear regression, only 2 were significant, the difference of tsk 5 minutes compared with pre-test (F1, 21 = 16.49, p = 0.001) and the difference of tsk 10 minutes compared with pre-test, to predict LAC concentration at the end of the test (F1, 21 = 9.30, p = 0.006). We concluded that 5 minutes after the test, the judokas present a higher tau and a higher tsk in 7 ROIs, and the tsk decreases 15 minutes after the test in 19 of the considered ROIs. The variation of mean tsk 5 and 10 minutes after the test compared with pre-test values is associated with blood LAC at the end of the test.

Non-obstructive monitoring of muscle fatigue for low intensity dynamic exercise with infrared thermography technique

Surface electromyography (sEMG) has been widely used in evaluating muscle fatigue among athletes where electrodes are attached on the skin during the activity. Recently, infrared thermography technique (IRT) has gain popularity and shown to be another preferred method in monitoring and predicting muscle fatigue non-obstructively. This paper investigates the correlation between surface temperature and muscle activation parameters obtained using both IRT and sEMG methods simultaneously. Twenty healthy subjects were required to perform a repetitive calf raise exercise with various loads attached around their ankle for 3 min to induce fatigue on the targeted gastrocnemius muscles. Average temperature and temperature difference information were extracted from thermal images, while root mean square (RMS) and median frequency (MF) were extracted from sEMG signals. Spearman statistical analysis performed shows that there is a significant correlation between average temperature with RMS and between temperature difference with MF values at p<0.05. While ANOVA test conducted shows that there is significant impact of loads on RMS and MF where F=12.61 and 3.59, respectively, at p< 0.05. This study suggested that skin surface temperature can be utilized in monitoring and predicting muscle fatigue in low intensity dynamic exercise and can be extended to other dynamic exercises.

Real-time measurement method for the skin temperature of the human arm via large lateral shearing interferometry

This paper presents a real-time measurement method for the skin temperature of the human arm. In this method, the air temperature close to the arm skin is measured via large lateral shearing interferometry, thus avoiding the possible influences of the different physical characteristics of different people, while maintaining the advantages of optical measurement, including its noncontact, noninvasive, and rapid features. The method captures the real-time fringe patterns generated using a parallel-sided plate when a collimated laser light beam transfers through the air surrounding the arm to be measured. Additionally, the phase difference distribution caused by the temperature difference is calculated in combination with the background fringe patterns. The phase difference in the light close to the arm skin is then estimated via a linear fitting method. Accordingly, based on the size parameters of the arm cross section and the ambient temperature monitored in real time, the air temperature close to the arm skin, which is considered equal to the arm skin temperature, is determined while considering the heat conduction effect. Experimental measurements of the temperature of human arm skin were conducted using the proposed method, and the axillary temperatures of the same person before and after the experiments were also measured using an electronic thermometer and a mercury thermometer. Good agreements were found, verifying the reliability of the proposed method. Moreover, based on this method, the possibility for the construction of a real-time body temperature measurement system is also discussed.

Effect of Exercise on Athletes Performing in Fencing Uniforms: Methodology and Preliminary Results of the Use of Infrared Thermography to Detect the Thermal Behaviour of Fencers

In recent times, infrared thermography has been often applied to sport science, in order to evaluate athletes’ performance in relation to their thermal behaviour. As there is a lack of studies for the sport of fencing, this paper aims to provide preliminary results showing the thermal behaviour of fencers of different competitive level and to provide a methodology for its assessment. In particular, thermal images were acquired before, during and after the training, as well as the metabolic rate and the rate of perceived exertion, for eight fencers with different competitive levels (international/national/veteran). Results showed that in moderate environments there was any correlation between the environmental parameters and temperature trend on athletes’ bodies, while competitive level and thermal behaviour were connected. The presence of thermal asymmetries was also detected. In general, from these preliminary results, professional athletes presented the same temperature trend. Therefore, further studies should be carried out in order to investigate these findings on a larger sample of elite athletes, as their thermal response may be important for improving their performance.

Bilateral asymmetry of skin temperature is not related to bilateral asymmetry of crank torque during an incremental cycling exercise to exhaustion

Although moderate relationships (|r| ∼ 0.5) were reported between skin temperature and performance-related variables (e.g., kinetic), it remains unclear whether skin temperature asymmetry reflects muscle force imbalance in cycling. Therefore, the aim of this study was to assess whether a relationship exists between kinetic and thermal asymmetry during a fatiguing exercise. Ten elite cyclists were enrolled and tested on a maximal incremental cycling test. Peak crank torques of both legs were obtained at the initial and final workload. Likewise, bilateral skin temperatures were recorded before and after exercise. Asymmetric indexes were also calculated for kinetic (AIK) and skin temperature (AIT) outcomes. The bilateral peak crank torques showed a larger difference at the final compared to the initial workload (p < 0.05) of the incremental exercise. Conversely, the bilateral skin temperature did not show any differences at both initial and final workload (p > 0.05). Additionally, trivial relationships were reported between AIK and AIT (-0.3 < r < 0.2) at the initial and final workload. The obtained results showed that changes in bilateral kinetic values did not reflect concurrent changes in bilateral skin temperatures. This finding emphasizes the difficulty of associating the asymmetry of skin temperature with those of muscle effort in elite cyclists. Lastly, our study also provided further insights on thermal skin responses during exhaustive cycling exercise in very highly-trained athletes.

Relationship between foot eversion and thermographic foot skin temperature after running

The main instruments to assess foot eversion have some limitations (especially for field applications), and therefore it is necessary to explore new methods. The objective was to determine the relationship between foot eversion and skin temperature asymmetry of the foot sole (difference between medial and lateral side), using infrared thermography. Twenty-two runners performed a running test lasting 30 min. Skin temperature of the feet soles was measured by infrared thermography before and after running. Foot eversion during running was measured by kinematic analysis. Immediately after running, weak negative correlations were observed between thermal symmetry of the rearfoot and eversion at contact time, and between thermal symmetry of the entire plantar surface of the foot and maximum eversion during stance phase (r=-0.3 and p=0.04 in both cases). Regarding temperature variations, weak correlations were also observed (r=0.4 and p<0.05). The weak correlations observed in this study suggest that skin temperature is not related to foot eversion. However, these results open interesting future lines of research.