Infrared Thermography in Exercise Physiology: The Dawning of Exercise Radiomics

Response of infrared thermography related parameters to (non-)sport specific exercise and relationship with internal load parameters in individual and team sport athletes-a systematic review

Introduction

Monitoring internal load is crucial for athletes but often requires invasive methods for muscle-related parameters, limiting practicality. Infrared thermography (IRT) related parameters might overcome this limitation. This systematic review aimed to examine the available literature on the response of IRT related parameters to (non-)sport specific exercise and reveal relationships with internal load parameters in athletic populations.

Methods

Four scientific databases were systematically searched (February 2024) with keywords related to IRT, load, and sports disciplines. Risk of bias was evaluated using QUADAS-2. Main inclusion criteria for studies were i) reporting of IRT related parameters and other internal load parameters prior/post (non-)sport specific exercise ii) inclusion of least Tier 2 athletes ≥ 18 years. After identifying n = 10,538 studies, 13 articles (n = 231 participants) were included.

Results

Following (non-)sport specific exercise in athletic populations, the majority of relevant studies showed a decrease in IRT related parameters within 15 min, while studies showed an increase in IRT related parameters following 30 min, 24 h, 48 h, and 72 h after exercise cessation. Relationships between alterations in IRT related parameters and other internal load parameters are inconsistent across the literature.

Conclusion

While the majority of studies show an increase in IRT related parameters following (non-)sport specific exercise, relationships with other internal load parameters and underlying physiological mechanisms evoking IRT related alterations are not conclusively revealed in athletic populations. Future research needs to assess the relationship of IRT related parameters especially with inflammatory parameters in athletic populations following (non-)sport specific exercise. Practitioners might assess IRT related parameters in conjunction with other load parameters.

Effects of pre-exercise glycerol supplementation on dehydration, metabolic, kinematic, and thermographic variables in international race walkers

BACKGROUND

Due to the increase in global temperature, it is necessary to investigate solutions so that athletes competing in hot conditions can perform in optimal conditions avoiding loss of performance and health problems. Therefore, this study aims to evaluate the effect of pre-exercise glycerol supplementation during a rectangular test at ambient temperature mid (28.2ºC) on dehydration variables in international race walkers.

METHODS

Eight international male race walkers (age: 28.0 years (4.4); weight: 65.6 kg (6.6); height: 180.0 cm (5.0); fat mass: 6.72% (0.66); muscle mass: 33.3 kg (3.3); VO2MAX: 66.5 ml · kg-1·min-1 (1.9)) completed this randomized crossover design clinical trial. Subjects underwent two interventions: they consumed placebo (n = 8) and glycerol (n = 8) acutely, before a rectangular test where dehydration, RPE, metabolic, kinematic, and thermographic variables were analyzed before, during and after the test.

RESULTS

After the intervention, significant differences were found between groups in body mass in favor of the placebo (Placebo: -2.23 kg vs Glycerol: -2.48 kg; p = 0.033). For other variables, no significant differences were found.

CONCLUSION

Therefore, pre-exercise glycerol supplementation was not able to improve any dehydration, metabolic, kinematic, or thermographic variables during a rectangular test at temperature mid in international race walkers. Possibly, a higher environmental temperature could have generated a higher metabolic and thermoregulatory stress, generating differences between groups like other previous scientific evidence.

Assessment of alternative metrics in the application of infrared thermography to detect muscle damage in sports

Objective.The association between muscle damage and skin temperature is controversial. We hypothesize that including metrics that are more sensitive to individual responses by considering variability and regions representative of higher temperature could influence skin temperature outcomes. Here, the objective of the study was to determine whether using alternative metrics (TMAX, entropy, and pixelgraphy) leads to different results than mean, maximum, minimum, and standard deviation (SD) skin temperature when addressing muscle damage using infrared thermography.Approach.Thermal images from four previous investigations measuring skin temperature before and after muscle damage in the anterior thigh and the posterior lower leg were used. The TMAX, entropy, and pixelgraphy (percentage of pixels above 33 °C) metrics were applied.Main results.On 48 h after running a marathon or half-marathon, no differences were found in skin temperature when applying any metric. Mean, minimum, maximum, TMAX, and pixelgraphy were lower 48 h after than at basal condition following quadriceps muscle damage (p< 0.05). Maximum skin temperature and pixelgraphy were lower 48 h after than the basal condition following muscle damage to the triceps sural (p< 0.05). Overall, TMAX strongly correlated with mean (r= 0.85) and maximum temperatures (r= 0.99) and moderately with minimum (r= 0.66) and pixelgraphy parameter (r= 0.64). Entropy strongly correlates with SD (r= 0.94) and inversely moderately with minimum temperature (r= -0.53). The pixelgraphy moderately correlated with mean (r= 0.68), maximum (r= 0.62), minimum (r= 0.58), and TMAX (r= 0.64).Significance.Using alternative metrics does not change skin temperature outcomes following muscle damage of lower extremity muscle groups.

The influence of static and dynamic warm-up on knee temperature: infrared thermography insights before and after a change of direction exercise

Introduction

Infrared thermography is gaining attention in the field of sports medicine and performance. This study investigated the effects of static and dynamic warm-ups and a 90° change of direction (COD) exercise on the thermal response of the knee.

Methods

Thermograms were collected using the FlIR E54 Imaging Camera from 85 healthy young adults, 46 men and 39 women, aged 20-31 years. The participants were divided in two groups, static and dynamic warm-up. Four thermograms were taken: baseline (T0), warm-up (T1), COD (T2), and rest (T3). Four regions of interest (ROIs) of the knee were analyzed: anterior upper half (AUH), anterior lower half (ALH), posterior upper half (PUH), and posterior lower half (PLH). Mixed ANOVA with the Bonferroni-Holm test and independent t-test were used for pairwise comparison and to spot differences between the right and left knees at T1 and T2 and at T0 between men and women, respectively.

Results

The mixed ANOVA was significant for time points (p< 0.001) in all the ROIs and for the stretching/temperature interaction with different levels of significance. The t-test results for the right and left knees at T1 and T2 were not significant. The temperature in the static warm-up group followed a decrease at T1, a subsequent decrease at T2, and a recovery similar to the baseline at T3, in the ALH in men and women and in the PUH only in men.

Conclusion

Static stretching was more suitable for preparing the knee for the COD exercise than the dynamic one in terms of the thermal response.

Short-term effects of 448 kilohertz radiofrequency stimulation on plantar fascia measured by quantitative ultrasound elastography and thermography on active healthy subjects: an open controlled clinical trial

Objective: This study is an open clinical trial. The aim of this study was to show the changes that occur in the viscoelastic properties of the plantar fascia (twenty healthy volunteers) measured by SEL and the changes in the plantar fascia temperature measured by thermography after the application of a 448 kHz capacitive resistive monopolar radiofrequency (CRMR) in active healthy subjects immediately after treatment and at the 1-week follow-up.

Methods: Furthermore, to analyze if an intervention with 448 kHz CRMR in the plantar fascia of the dominant lower limb produces a thermal response in the plantar fascia of the non-dominant lower limb. The final objective was to analyze the level of association between the viscoelastic properties of the PF and the temperature before and after the intervention with 448 kHz CRMR.

Results: Our results showed that a temperature change, which was measured by thermography, occurred in the plantar fascia after a single intervention (T0-T1) and at the 1-week follow up (T1-T2).

Conclusion: However, no changes were found in the viscoelastic properties of the plantar fascia after the intervention or at the 1-week follow up. This is the first study to investigate changes in both plantar fascia viscoelastic properties and in plantar fascia temperature after a radiofrequency intervention.

Respiratory muscles's thermographic analysis in asthmatic youth with and without bronchospasm induced by eucapnic voluntary hyperpnea

OBJECTIVE

To compare the thermographic pattern of regions of interest (ROI) of respiratory muscles in young asthmatics with and without bronchospasm induced by eucapnic voluntary hyperpnea (EVH).

MATERIALS AND METHODS

Cross-sectional study carried out with 55 young (55% male and 45% females) aged 12.5 ± 3.3 years, divided in nine nonasthmatics, 22 asthmatics without exercise-induced bronchospasm compatible response (EIB-cr) and 24 asthmatics with EIB-cr. The diagnosis of EIB was given to subjects with a fall in forced expiratory volume in the first second (FEV1) ≥ 10% compared to baseline. Thermographic recordings of respiratory muscles were delimited in ROI of the sternocleidomastoid (SCM), pectoral, and rectus abdominis intention area. Thermal captures and FEV1 were taken before and 5, 10, 15 and 30 min after EVH.

RESULTS

Twenty-four (52.1%) of asthmatics had EIB-cr. There was a decrease in temperature at 10 min after EVH test in the SCM, pectoral and rectus abdominis ROIs in all groups (both with p < 0.05). There was a decrease in temperature (% basal) in asthmatic with EIB-cr compared to nonasthmatics in the rectus abdominis area (p < 0.05).

CONCLUSION

There was a decrease in temperature in the ROIs of different muscle groups, especially in asthmatics. The greater drop in FEV1 observed in individuals with EIB-cr was initially associated with a decrease in skin temperature, with a difference between the nonasthmatics in the abdominal muscle area. It is likely that this decrease in temperature occurred due to a temporary displacement of blood flow to the most used muscle groups, with a decrease in the region of the skin evaluated in the thermography.

Knee temperature remains abnormal in patients successfully treated with anterior cruciate ligament reconstruction: An infrared thermography analysis

Purpose

The aim of this study was to evaluate if the operated knee environment remains abnormal in patients successfully treated with anterior cruciate ligament reconstruction (ACL-R).

Methods

Thirty asymptomatic patients were enrolled (28 men, 2 women, age 28.6 ± 6.54 years, body mass index: 24.9 ± 3.0 kg/m2) and evaluated at 42.2 ± 12.5 months after surgery. Patients were assessed with patient-reported outcome measurements and with a triaxial accelerometer. The temperature of the knees as well as four regions of interest were evaluated with an infrared thermographic camera FLIR T1020 (FLIR® Systems) according to a standardised protocol including a baseline evaluation and further evaluations immediately after exercise and after 5, 10 and 20 min. The temperature of the ACL-R knee was compared to that of the contralateral healthy knee for the purpose of the study.

Results

The mean temperature of the knee was higher (p = 0.010) for the ACL-R knees (31.4 ± 1.4°C) compared to the healthy knees (31.1 ± 1.6°C), as well as for the patellar area (p = 0.005), the lateral area (p = 0.016) and the medial area (p = 0.014). The analysis of the response to the exercises of the ACL-R knees showed similar trends to the healthy knees but higher temperature values at all time points (p < 0.05). Patients who underwent ACL-R with concomitant meniscal treatment showed higher knee temperatures compared to ACL-R knees without concomitant meniscal treatment after 5 (p = 0.047), 10 (p = 0.027) and 20 min (p = 0.048).

Conclusions

The temperature of asymptomatic knees previously treated with ACL-R is higher than the contralateral healthy knee, both at rest and after exercise, with a further increase in knees that underwent both ACL-R and meniscal treatment. These results suggest an inflammatory state persisting years after the surgery, which could predispose to the early onset of knee degeneration.

Level of Evidence

III, Case-control study.

Exploring the correlation of skin temperature and body composition in athletes undergoing exhaustive physical exercise

During strenuous exercise, skin temperature (Tsk) plays an essential role in thermoregulatory processes. As indicated in the literature, its response might be influenced by body composition, among other factors. Hence, the objectives of this investigation were to determine whether there is a correlation between selected body components, specifically fat tissue and muscle tissue, and Tsk during graded exercise and recovery in athletes, and to identify which body component exhibits the strongest correlation with Tsk. Participants were grouped according to their aerobic capacity (VO2max/kg). A significant main effect was observed for the test stages (p < .001, η2 = 0.71), with Tsk decreasing from the start of the exercise, significantly decreasing at 12 km/h-1 (p < .001), and then increasing after exercise, especially within the first 5 min of recovery. Weak and non-significant effect for group/stage interaction was detected (p = .374, η2 = 0.03). A significant negative correlation was found between Tsk and both total tissue fat [%] (-0.51 < r < -0.63, p < .001) and lower limb tissue fat [%] (-0.50 < r < -0.71, p < .001) across all test stages. The correlation between Tsk and BMI was inconsistent, appearing only during the first stage of exercise and throughout recovery. No correlation was observed between Tsk and skeletal muscle mass, appendicular lean soft tissue, or relative skeletal muscle index. Endurance running to exhaustion leads to a progressive decrease in the Tsk of the lower extremity, followed by rewarming during recovery. The observed inverse correlation between adipose tissue and Tsk, along with the distinct temperature trends in groups with varying levels of fat tissue, could imply that the skin and subcutaneous tissue complex may play a more intricate role in thermal energy exchange beyond its insulating function. This implies a multifaceted involvement of these tissues in thermoregulation.

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.

Global trends and performances of infrared imaging technology studies on acupuncture: a bibliometric analysis

Objectives

To summarize development processes and research hotspots of infrared imaging technology research on acupuncture and to provide new insights for researchers in future studies.

Methods

Publications regarding infrared imaging technology in acupuncture from 2008 to 2023 were downloaded from the Web of Science Core Collection (WoSCC). VOSviewer 1.6.19, CiteSpace 6.2.R4, Scimago Graphica, and Microsoft Excel software were used for bibliometric analyses. The main analyses include collaboration analyses between countries, institutions, authors, and journals, as well as analyses on keywords and references.

Results

A total of 346 publications were retrieved from 2008 to 2023. The quantity of yearly publications increased steadily, with some fluctuations over the past 15 years. "Evidence-Based Complementary and Alternative Medicine" and "American Journal of Chinese Medicine" were the top-cited journals in frequency and centrality. China has the largest number of publications, with the Shanghai University of Traditional Chinese Medicine being the most prolific institution. Among authors, Litscher Gerhard from Austria (currently Swiss University of Traditional Chinese Medicine, Switzerland) in Europe, was the most published and most cited author. The article published by Rojas RF was the most discussed among the cited references. Common keywords included "Acupuncture," "Near infrared spectroscopy," and "Temperature," among others. Explore the relationship between acupoints and temperature through infrared thermography technology (IRT), evaluate pain objectively by functional near-infrared spectroscopy (fNIRS), and explore acupuncture for functional connectivity between brain regions were the hotspots and frontier trends in this field.

Conclusion

This study is the first to use bibliometric methods to explore the hotspots and cutting-edge issues in the application of infrared imaging technology in the field of acupuncture. It offers a fresh perspective on infrared imaging technology research on acupuncture and gives scholars useful data to determine the field's hotspots, present state of affairs, and frontier trends.

Inspiratory muscles pre-activation in young swimmers submitted to a tethered swimming test: effects on mechanical, physiological, and skin temperature parameters

Inspiratory muscles pre-activation (IMPA) has been studied to improve subsequent performance in swimming. However, the effects of IMPA on various parameters in swimmers are still unknown. Therefore, this study aimed to investigate the effects of IMPA on the mechanical parameters, physiological responses, and their possible correlations with swimming performance. A total of 14 young swimmers (aged 16 ± 0 years) underwent a 30-s all-out tethered swimming test, preceded or not by IMPA, a load of 40% of the maximal inspiratory pressure (MIP), and with a volume of 2 sets of 15 repetitions. The mechanical (strength, impulse, and fatigue index) and physiological parameters (skin temperature and lactatemia) and the assessment of perceived exertion and dyspnea were monitored in both protocols. The IMPA used did not increase the swimming force, and skin temperature, decrease blood lactate concentration, or subjective perception of exertion and dyspnea after the high-intensity tethered swimming exercises. Positive correlations were found between mean force and blood lactate (without IMPA: r = 0.62, P = 0.02; with IMPA: r = 0.65, P = 0.01). The impulse was positively correlated with blood lactate (without IMPA: r = 0.71, P < 0.01; with IMPA: r = 0.56, P = 0.03). Our results suggest that new IMPA protocols, possibly with increased volume, should be developed in order to improve the performance of young swimmers.

Response of skin temperature, blood ammonia and lactate during incremental exercise until exhaustion in elite athletes

The study aimed to evaluate the lower limb skin temperature (Tsk) and blood concentrations of lactate (LA) and ammonia (NH3) during exercise and recovery. Eleven elite sprint athletes (25 ± 3.4 yrs) and 11 elite endurance athletes (24.45 ± 5.4 yrs) performed an incremental running test until exhaustion. Body composition was estimated using the DXA method. Thermograms of the anterior and posterior surfaces of the lower limbs were recorded at rest, before each test stage (every 3 min, starting from 10 km h-1 and increasing by 2 km h-1), and in the 5th, 10th, 15th, 20th, and 30th minute of recovery. Endurance athletes had a higher maximum oxygen uptake than sprint athletes (5.0 ± 0.7 vs 4.3 ± 0.4 l·kg-1, p = 0.018), lower percentage of lean content (79 ± 2 vs 83 ± 2%, p < 0.001), and a higher percentage of fat content in the lower limbs (17 ± 2 vs 12 ± 2%, p < 0.001). In both groups, a significant decrease in Tsk was observed compared to resting value (endurance athletes-31.5 ± 0.6 °C; sprint athletes-32.3 ± 0.6 °C), during exercise (p < 0.001) and rewarming during recovery (p < 0.001). However, endurance athletes had a lower Tsk than sprint athletes at the exhaustion point (30.0 ± 1.1 vs 31.6 ± 0.8 °C, p < 0.05) and the pattern of change in Tsk differed between groups (p < 0.001). Tsk in the endurance athletes group decreased throughout the exercise protocol and returned more rapidly to initial values during recovery, while Tsk in the sprint group stabilised between moderate intensity and exhaustion, recovering more slowly after exercise. Both LA (endurance athletes-max 10.2 ± 1.5; sprint athletes-max 10.1 ± 1.4 mmol⋅L-1, p < 0.001) and NH3 (endurance athletes-max 75.6 ± 11.5; sprint athletes-max 76.7 ± 9.0 mmol⋅L-1, p < 0.001) increased during exercise and decreased during recovery (p < 0.001). During exercise, lower levels and slower increases in LA were observed during exercise in the endurance athletes' group (p < 0.05). A negative correlation was revealed between Tsk and fat percentage (r = -0.43 to -0.71, p < 0.05). Tsk was positively correlated with LA during recovery (r = 0.43 to 0.48, p < 0.05), and negatively during recovery (r = -0.45 to -0.54, p < 0.05). Differences between groups in maximum aerobic capacity, the pattern of change in Tsk, and the correlation between Tsk and LA suggest that individuals who decrease less Tsk during exercise and higher Tsk during recovery are those with better aerobic capacity. In addition, athletes with less body fat dissipate heat from their tissues more efficiently.

Thermoregulation during Field Exercise in Horses Using Skin Temperature Monitoring

Hyperthermia and exertional heat illness (EHI) are performance and welfare issues for all exercising horses. Monitoring the thermoregulatory response allows for early recognition of metabolic heat accumulation during exercise and the possibility of taking prompt and effective preventative measures to avoid a further increase in core body temperature (Tc) leading to hyperthermia. Skin temperature (Tsk) monitoring is most used as a non-invasive tool to assess the thermoregulatory response pre- and post-exercise, particularly employing infrared thermographic equipment. However, only a few studies have used thermography to monitor skin temperature continuously during exercise. This commentary provides an overview of studies investigating surface skin temperature mainly by infrared thermography (IRT) during exercise. The scientific evidence, including methodologies, applications, and challenges associated with (continuous) skin temperature monitoring in horses during field exercise, is discussed. The commentary highlights that, while monitoring Tsk is straightforward, continuous Tsk alone does not always reliably estimate Tc evolvement during field exercise. In addition, inter-individual differences in thermoregulation need to be recognized and accounted for to optimize individual wellbeing. With the ongoing development and application of advanced wearable monitoring technology, there may be future advances in equipment and modeling for timely intervention with horses at hyperthermic risk to improve their welfare. However, at this point, infrared thermographic assessment of Tsk should always be used in conjunction with other clinical assessments and veterinary examinations for a reliable monitoring of the welfare of the horse.

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.

Thermal resting pattern and acute skin temperature response to exercise in older adults: Role of cardiorespiratory fitness

BACKGROUND

Infrared thermography is a growing area of interest in sports science due to the potential of skin temperature (Tsk) measurements to provide valuable information from rest to exercise. However, limited research exists on Tsk in older adults and the impact of factors such as sex and cardiorespiratory fitness (CRF) on Tsk. This study aims to investigate Tsk at rest and after acute exercise in older adults and assess whether sex or CRF influences Tsk.

METHODS

Ninety-two participants (41 women, 68.48 ± 3.01 years) were examined with a thermographic camera in a conditioned room (23.02 ± 3.01 °C) at rest and after a graded protocol. The Tsk of 25 regions of interest (ROIs) were extracted and analysed.

RESULTS

Men had higher overall Tsk at rest in 76% of ROIs, showing significant differences (p < 0.010) in six specific ROIs, independent of CRF. Both sexes had similar Tsk responses after graded exercise, with increases in distal parts (1.06 ± 0.50 °C), decreases in proximal parts (-0.62 ± 0.42 °C), and stable central Tsk (0.23 ± 0.59 °C). Increases in lower limb Tsk were significantly associated with CRF in men and women (β = 0.438, p = 0.001, and β = 0.535, p < 0.001, respectively), explaining 17% and 27% of the variance, respectively.

CONCLUSIONS

This study demonstrates a sex-specific effect on resting Tsk in older adults, suggesting that sex-specific Tsk patterns should be considered when analysing Tsk in this population. Additionally, the association between increases in lower limb Tsk and CRF suggests that Tsk could be a promising predictor of CRF in older adults.

Association between physical demands, skin temperature and wellbeing status in elite football players

The demanding nature of elite football requires players to be closely monitored to ensure optimal performance and minimize injury risk. This study aimed to evaluate the relationship between physical demands, skin temperature, and well-being status in 30 elite football players over a 12-week competitive period. Thermography assessments, weekly Well-being questionnaires, and daily training and match load recordings were used to gather data. Results indicated that along the microcycles there was a decrease in high-intensity accelerations and decelerations distance completed, while maintaining other high-intensity actions. Furthermore, it was found that high-intensity movements contribute to the generation of thermal asymmetries in the thighs; the adductor thermal asymmetry showed a positive relationship with stress and muscle soreness, the knee thermal asymmetry had a positive relationship with fatigue and a negative relationship with rest and quality of rest, and finally the hamstrings muscles exhibited significant differences between the thermal asymmetry groups, with the high asymmetry completing less high intensity actions than the low asymmetry group. In conclusion, this study highlights the interconnections between physical demands, skin temperature, and well-being in elite football players and provides valuable insights for coaches and trainers in their efforts to optimize performance and health.

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.

Joint Response to Exercise Is Affected by Knee Osteoarthritis: An Infrared Thermography Analysis

Infrared thermography can be used to evaluate the inflammation characterizing the joint environment of OA knees, but there is limited evidence on the response to physical exercise. Identifying the response to exercise of OA knees and the influencing variables could provide important information to better profile patients with different knee OA patterns. Sixty consecutive patients (38 men/22 women, 61.4 ± 9.2 years) with symptomatic knee OA were enrolled. Patients were evaluated with a standardized protocol using a thermographic camera (FLIR-T1020) positioned at 1 m with image acquisition of an anterior view at baseline, immediately after, and at 5 min after a 2-min knee flexion-extension exercise with a 2 kg anklet. Patients' demographic and clinical characteristics were documented and correlated with the thermographic changes. This study demonstrated that the temperature response to exercise in symptomatic knee OA was affected by some demographic and clinical characteristics of the assessed patients. Patients with a poor clinical knee status presented with a lower response to exercise, and women showed a greater temperature decrease than men. Not all evaluated ROIs showed the same trend, which underlines the need to specifically study the different joint subareas to identify the inflammatory component and joint response while investigating knee OA patterns.

Body surface profile in ambient and hot temperatures during a rectangular test in race walker champions of the World Cup in Oman 2022

There is current interest in infrared thermography as a method to assess changes in body surface temperature to determine thermoregulatory mechanisms, especially in endurance sports. The aim of this study was to evaluate the effect of two environmental temperatures (17 and 28°C) on body surface temperature in different anterior and posterior aspects of the body during a rectangular test in international walkers of the Spanish National Team. Three international walkers performed a rectangular test, where body temperature was measured at rest, and after the 5th, 10th and 15th run using an infrared thermographic camera in room temperatures at 17 and 28°C. In addition, oxygen consumption was measured simultaneously. ANOVA detected a group × time interaction in the chest and abdomen (right and left), left back and right calf (p = < 0.05), with a trend in the right hamstring (p = 0.053) when comparing 17°C and 28°C. ANOVA detected no significant group × time interaction (p = 0.853) but there was a significant group effect (p = 0.022). The eleven degrees increase in ambient temperature (17 to 28°C) produces changes in almost all anatomical zones, but not homogeneously in international walkers during a rectangular test. This indicates that metabolic and blood flow changes are different depending on the anatomical zone measured.

Thermography and rasterstereography as a combined infrared method to assess the posture of healthy individuals

The demand for noninvasive methods to assess postural defections is increasing because back alterations are more common among the healthy population. We propose a combined infrared method of rasterstereography and thermography to assess the back without harmful effects. This study aims to provide reference data on rasterstereography and thermography to evaluate the back of a healthy population and to further study the correlation between these two methods. This cross-sectional research involved 175 healthy individuals (85 males and 90 females) aged 22 to 35 years. There is a large Cohen's d effect size in the cervical depth (males = 43.77 ± 10.96 mm vs. females = 34.29 ± 7.04 mm, d = 1.03), and in the lumbar lordosis angle (males = 37.69 ± 8.89° vs. females = 46.49 ± 8.25°, d = - 1.03). The back temperature was different for gender in the cervical area (males = 33.83 ± 0.63 °C vs. females = 34.26 ± 0.84 °C, d = - 0.58) and dorsal area (males = 33.13 ± 0.71 °C vs. females = 33.59 ± 0.97 °C, d = - 0.55). Furthermore, in the female group there was a moderate correlation of lumbar temperature with lumbar lordosis angle (r = - 0.50) and dorsal temperature with shoulders torsion (r = 0.43). Males showed a moderate correlation for vertebral surface rotation RMS with cervical (r = - 0.46), dorsal (r = - 0.60), and lumbar (r = - 0.50) areas and cervical temperature with shoulders obliquity (r = 0.58). These results highlight a possible correlation between rasterstereography and thermography, which may elucidate the underlying mechanics of spinal alterations and thermal muscle response. Our findings may represent reference data for other studies using noninvasive methods to assess postural alterations.

Effect of Whole-, Upper-, and Lower-Body High-Intensity Rowing Exercise on Skin Temperature Measured by Thermography

Purpose: Despite the growing works analyzing exercise-induced thermoregulatory adjustments through thermography, the skin temperature (Tsk) response of the same muscle groups underwent to different exercise demands has not been investigated. This study analyzed the behavior of Tsk of the same muscle groups when exercised with different demands in rowing. Methods: Eighteen men underwent three performance tests on a rowing ergometer: whole-body 2,000 m test (RT_WB), upper-body (RT_UB), and lower-body (RT_LB) tests. In each condition, thermograms were recorded before (pre), immediately after test (post), and at 10 (REC₁₀), 20 (REC₂₀), and 30 (REC₃₀) minutes post-exercise recovery. Tsk was measured at the pectoral (control body region), upper back, quadriceps, brachial biceps, and forearm. Results: Pectoral-Tsk reduced comparably in response to all testing conditions (p < .05). Upper back-Tsk decreased post (p < .001) and returned to baseline in the RT_UB (REC₁₀, p = 1.0) and RT_WB (REC₃₀, p = .128), while remained reduced in the RT_LB (p < .001). Quadriceps-Tsk reduced post (p < .05) and returned to baseline in the RT_WB and RT_LB at REC₁₀ (p = 1.0), remaining reduced in the RT_UB during recovery (p < .05). Regarding the upper limbs, Tsk increased more markedly in the RT_UB versus RT_WB during the recovery period (p < .05); in the RT_LB, biceps-Tsk remained below baseline over time (p < .05), whereas the forearm-Tsk was restored at REC₁₀ (p = 1.0). Conclusion: Manipulating the muscle groups involved in rowing alters the Tsk response within equal ROI. Exercise-induced Tsk changes can reflect local hemodynamic and thermoregulatory adjustments.

Infrared thermography for the evaluation of adolescent and juvenile idiopathic scoliosis: A systematic review

INTRODUCTION

Adolescent and Juvenile Idiopathic Scoliosis are a three-dimensional spine deformity characterized by a muscle alteration of the convex and concave sides of the scoliosis, which can be evaluated with different non-invasive and radiation-free methods such as infrared thermography. The objective of the present review is to assess infrared thermography as a potential method to evaluate alterations of the scoliosis.

MATERIALS AND METHODS

A systematic review was performed by collecting articles from PubMed, Web of Science, Scopus, and Google Scholar, published from 1990 to April 2022, on the use of infrared thermography to evaluate adolescent and juvenile idiopathic scoliosis. Relevant data were collected in tables, and the primary outcomes were discussed narratively.

RESULTS

Of the 587 articles selected, only 5 were in line with the objective of this systematic review and were eligible for the inclusion criteria. The findings of the selected articles corroborate the applicability of infrared thermography as an objective method to assess the thermal differences of the muscles between the convex and concave sides of scoliosis. The overall quality of the research was uneven in the reference standard method and assessment of measures.

CONCLUSION

Infrared thermography is providing promising results to discriminate thermal differences in scoliosis evaluation, albeit there are still some concerns about considering it as a diagnostic tool for scoliosis evaluation because specific recommendations for collecting data are not met. We propose additional recommendations to existing guidelines to perform thermal acquisition to reduce errors and provide the best results to the scientific community.

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.

Validating within-limb calibrated algorithm using a smartphone attached infrared thermal camera for detection of arthritis in children

OBJECTIVES

To determine the impact of physical activity on temperature after within-limb calibration (TAWiC) measures and their reproducibility. To determine if thermal imaging from a smartphone attached thermal camera is comparable to thermal imaging using a handheld thermal camera for detection of arthritis in children.

METHODS

Children without symptoms were enrolled to the "asymptomatic exercise cohort", and received infrared imaging, using a standard handheld camera, after initial resting period, after activity, and after second resting period. Children seen in the rheumatology clinic with knee pain were enrolled into the "symptomatic knee pain cohort" and received imaging with both the smartphone-attached and handheld cameras before a routine clinical exam. TAWiC was defined as the temperature differences between joint and ipsilateral mid-tibia as the main readout for arthritis detection.

RESULTS

The asymptomatic exercise cohort demonstrated notable changes in absolute and TAWiC temperatures collected by thermal imaging after physical activity, and temperatures did not consistently return to pre-activity levels after a second period of rest. The 95th TAWiC from anterior view were, resting one -0.1 C (0.5), activity -0.7 C (0.5), resting two -0.2 C (0.6) (resting 1 vs resting 2, p-value = 0.13). In the symptomatic knee pain cohort, the smartphone attached and handheld thermal cameras performed similarly in regards to detection of joint inflammation and evaluation of joint temperature using the TAWiC algorithm, with high sensitivity of 80% (55.2-100.0%) and specificity of 84.2% (76.0-92.4%) in the anterior knee view when compared with the gold standard joint exam performed by a pediatric rheumatologist. The mean 95th TAWiC temperature difference between the two cameras was -0.1 C (-0.1 to 0.0) (p = 0.0004).

CONCLUSIONS

This study showed continued validity of the TAWiC algorithm across two distinct thermal camera platforms and demonstrates promise for improved accessibility and utility of this technology for arthritis detection.

A review of non-invasive sensors and artificial intelligence models for diabetic foot monitoring

Diabetic foot complications have multiple adverse effects in a person's quality of life. Yet, efficient monitoring schemes can mitigate or postpone any disorders, mainly by early detecting regions of interest. Nowadays, optical sensors and artificial intelligence (AI) tools can contribute efficiently to such monitoring processes. In this work, we provide information on the adopted imaging schemes and related optical sensors on this topic. The analysis considers both the physiology of the patients and the characteristics of the sensors. Currently, there are multiple approaches considering both visible and infrared bands (multiple ranges), most of them coupled with various AI tools. The source of the data (sensor type) can support different monitoring strategies and imposes restrictions on the AI tools that should be used with. This review provides a comprehensive literature review of AI-assisted DFU monitoring methods. The paper presents the outcomes of a large number of recently published scholarly articles. Furthermore, the paper discusses the highlights of these methods and the challenges for transferring these methods into a practical and trustworthy framework for sufficient remote management of the patients.

The use of thermal imaging for monitoring the training progress of professional male sweep rowers

This study assesses the thermal profile of the skin in highly trained rowers and investigates the relationship between resting skin temperature (Ts) and the muscle peak torque (PT) measured in statics at the beginning (autumn) and the end (spring) of the preparatory period. Ten professional male sweep rowers, members of the Polish national rowing team, were investigated. A thermal imaging camera was used to analyze the Ts. The PT of the muscles involved in the rowing cycle were measured isometrically. No significant temperature asymmetries were found, except in front of arms after exercise in the spring (p = 0.0228). In contrast, the PT test in the autumn confirmed the significant asymmetry of the knee joint extensors (p = 0.0192). In spring compared to autumn, Ts in many areas of the body were slightly higher, as was PT of underlying muscles. Significant correlations between resting Ts and PT of the underlying muscles were found. Thermal imaging makes it possible to observe changes in skin temperature and symmetry before and after exercise. At this stage, it does not appear to be a method that, without supporting of other methods such as those assessing muscle function, will allow monitoring of training progress.

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.

Is Continuous Monitoring of Skin Surface Temperature a Reliable Proxy to Assess the Thermoregulatory Response in Endurance Horses During Field Exercise?

Hyperthermia is a performance and welfare issue for exercising horses. The thermoregulatory stressors associated with exercise have typically been estimated by responses in the laboratory. However, monitoring surface skin temperature (T sk ) coincident with core temperature (T c ) has not previously been investigated in horses exercising in the field. We investigated the suitability of monitoring surface T sk as a metric of the thermoregulatory response, and simultaneously investigated its relationship with T c using gastrointestinal (GI) temperature. We evaluated T sk in 13 endurance horses competing during four endurance rides over 40 km (n = 1) or a total of 80 km (n = 12) distance. Following each 40-km loop, the horses were rested for 60 min. T sk and T c were continuously recorded every 15 s by an infrared thermistor sensor located in a modified belt and by telemetric GI pill, respectively, and expressed as mean ± SD. The net area under the curve (AUC) was calculated to estimate the thermoregulatory response to the thermal load of T sk over time (°C × minutes) using the trapezoidal method. The relationship between T sk and T c was assessed using scatterplots, paired t-test or generalized linear model ANOVA (delta T sk ) (n = 8). Ambient temperature ranged from 6.7°C to 18.4°C. No relationship was found between T sk and T c profiles during exercise and recovery periods, and no significant difference between delta T sk results was detected when comparing exercise and rest. However, time to maximum T sk (67 min) was significantly reduced compared to T c (139 min) (p = 0.0004) with a significantly lesser maximum T sk (30.3°C) than T c (39°C) (p = 0.0002) during exercise. Net AUC T sk was 1,164 ± 1,448 and -305 ± 388°C × minutes during periods of exercise and recovery, respectively. We conclude that T sk monitoring does not provide a reliable proxy for the thermoregulatory response and horse welfare, most probably because many factors can modulate T sk without directly affecting T c . Those factors, such as weather conditions, applicable to all field studies can influence the results of T sk in endurance horses. The study also reveals important inter-individual differences in T sk and T c time profiles, emphasizing the importance of an individualized model of temperature monitoring.

Effects of Unilateral Muscle Fatigue on Thermographic Skin Surface Temperature of Back and Abdominal Muscles—A Pilot Study

The present study aimed to assess the effects of asymmetric muscle fatigue on the skin surface temperature of abdominal and back muscles. The study was based on a pre-post/follow-up design with one group and included a total of 41 subjects (22 male, 19 female; age, 22.63 ± 3.91; weight, 71.89 ± 12.97 kg; height, 173.36 ± 9.95). All the participants were asked to perform side bends in sets of 20 repetitions on a Roman chair until complete exhaustion. The pre-, post- and follow-up test (24 h after) skin surface temperatures were recorded with infrared thermography. Subjective muscle soreness and muscle fatigue were analyzed using two questionnaires. The results of the post hoc tests showed that skin temperature was statistically significantly lower in the post-tests than in the pre- and follow-up tests, but no meaningful differences existed between the pre- and follow-up tests. Asymmetric side differences were found in the post-test for the upper and lower areas of the back. Differences were also noted for the front in both the upper and lower areas. No thermographic side asymmetries were found at the pre- or follow-up measurement for either the back or the front. Our results support the potential of using thermographic skin surface temperature to monitor exercise and recovery in athletes, as well as its use in rehabilitational exercise selection.

Infrared Thermography in Wound Care, Surgery, and Sports Medicine: A Review

For many years, the role of thermometry was limited to systemic (core body temperature) measurements (e.g., pulmonary catheter) or its approximation using skin/mucosa (e.g., axillary, oral, or rectal) temperature measurements. With recent advances in material science and technology, thermal measurements went beyond core body temperature measurements and found their way in many medical specialties. The article consists of two primary parts. In the first part we overviewed current clinical thermal measurement technologies across two dimensions: (a) direct vs. indirect and (b) single-point vs. multiple-point temperature measurements. In the second part, we focus primarily on clinical applications in wound care, surgery, and sports medicine. The primary focus here is the thermographic imaging modality. However, other thermal modalities are included where relevant for these clinical applications. The literature review identified two primary use scenarios for thermographic imaging: inflammation-based and perfusion-based. These scenarios rely on local (topical) temperature measurements, which are different from systemic (core body temperature) measurements. Quantifying these types of diseases benefits from thermographic imaging of an area in contrast to single-point measurements. The wide adoption of the technology would be accelerated by larger studies supporting the clinical utility of thermography.

Effect of fatigue strength exercise on anterior thigh skin temperature rewarming after cold stress test

Although dynamic thermography skin temperature assessment has been used in medical field, scientific evidence in sports is scarce. The aim of the study was to assess changes in anterior thigh skin temperature in response to a cold stress test after a strength exercise fatiguing protocol. Ten physically active adults performed a familiarization session and two strength exercise sessions, one with dominant and the other with non-dominant lower limb. Participants performed bouts of 10 concentric and eccentric contractions of leg extensions in an isokinetic device until reaching around 30% of force loss. Infrared thermographic images were taken at baseline conditions and after the fatigue level from both thighs after being cooled using a cryotherapy system. ROIs included vastus medialis, rectus femoris, adductor and vastus lateralis. Skin temperature rewarming was assessed during 180s after the cooling process obtaining the coefficients of the following equation: ΔSkin temperature = β₀ + β_{1 *} ln(T), being β₀ and β₁ the constant and slope coefficients, respectively, T the time elapsed following the cold stress in seconds, and ΔSkin temperature the difference between the skin temperature at T respect and the pre-cooling moment. Lower β₀ and higher β₁ were found for vastus lateralis and rectus femoris in the intervention lower limb compared with baseline conditions (p < 0.05 and ES > 0.6). Adductor only showed differences in β₀ (p = 0.01 and ES = 0.92). The regressions models obtained showed that β₀ and β₁ had a direct relationship with age and muscle mass, but an inverse relationship with the number of series performed until 30% of fatigue (R² = 0.8). In conclusion, fatigue strength exercise results in a lower skin temperature and a faster thermal increase after a cold stress test.

Association of Innate and Acquired Aerobic Capacity With Resilience in Healthy Adults: Protocol for a Randomized Controlled Trial of an 8-Week Web-Based Physical Exercise Intervention

BACKGROUND

Physical activity alleviates chronic stress. The latest research suggests a relationship between resilience and physical fitness. Beneficial adaptations of the hypothalamic-pituitary-adrenal axis, sympathetic nervous system, endocannabinoid system, and tryptophan pathway, which are induced by an active lifestyle, are considered to be conducive to resilience. However, detailed knowledge on the molecular link between the effects of acute and chronic physical exercise and improved resilience to stress in humans is missing. Moreover, the relationship between innate and acquired aerobic capacity and resilience is poorly understood.

OBJECTIVE

The aim of this study is to implement a human exercise intervention trial addressing the following main hypotheses: a high innate aerobic capacity is associated with high resilience to stress, and web-based physical exercise training improves aerobic capacity of physically inactive adults, which is accompanied by improved resilience. In this setting, we will analyze the relationship between resilience parameters and innate and acquired aerobic capacity as well as circulating signaling molecules.

METHODS

A total of 70 healthy, physically inactive (<150 minutes/week of physical activity) adults (aged 18-45 years) will be randomly assigned to an intervention or control group. Participants in the intervention group will receive weekly training using progressive endurance and interval running adapted individually to their remotely supervised home training performance via web-based coach support. A standardized incremental treadmill exercise test will be performed before and after the intervention period of 8 weeks to determine the innate and acquired aerobic capacity (peak oxygen uptake). Before and after the intervention, psychological tests and questionnaires that characterize parameters implicated in resilience will be applied. Blood and saliva will be sampled for the analysis of cortisol, lactate, endocannabinoids, catecholamines, kynurenic acid, and further circulating signal transducers. Statistical analysis will provide comprehensive knowledge on the relationship between aerobic capacity and resilience, as well as the capacity of peripheral factors to mediate the promoting effects of exercise on resilience.

RESULTS

The study was registered in October 2019, and enrollment began in September 2019. Of the 161 participants who were initially screened via a telephone survey, 43 (26.7%) fulfilled the inclusion criteria and were included in the study. Among the 55% (17/31) of participants in the intervention group and 45% (14/31) of participants in the control group who completed the study, no serious adverse incidents were reported. Of 43 participants, 4 (9%) withdrew during the program (for individual reasons) and 8 (19%) have not yet participated in the program; moreover, further study recruitment was paused for an indeterminate amount of time because of the COVID-19 pandemic.

CONCLUSIONS

Our study aims to further define the physiological characteristics of human resilience, and it may offer novel approaches for the prevention and therapy of mental disorders via an exercise prescription.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/29712.

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.

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.

A simplified approach to describe the mean skin temperature variations during prolonged running exercise

Skin blood flow and skin temperature play a fundamental role in the thermoregulatory processes and are expected to largely change in response to a prolonged running exercise. The skin temperature changes have been documented in the literature, mainly through infrared thermographic measurements performed before, after, and, in a limited number of studies, during the exercise. After an initial reduction probably ascribed to skin vasoconstriction, the further skin temperature modifications with time, measured in reference papers during a steady and prolonged run, do not show a common behaviour, probably due to different exercise intensities and environmental conditions reported in these studies. This research aimed to develop a simplified method for describing the skin temperature changes during running exercise through the theoretical solutions of the dynamic energy balance of the human body in the early and late time periods, i.e., close to the onset and the end of exercise. These two asymptotic solutions for the skin temperature, having a largely dissimilar trend, collide at a time instant likely associated with the switch from skin vasoconstriction to vasodilation. Examples of application of the proposed method, based on the intersection of asymptotes, were provided. It was also demonstrated its capability to interpret the experimental skin temperature variations with time for constant-load running exercises reported in the literature under different levels of exercise intensity and environmental conditions.

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.

Is skin temperature associated with muscle recovery status following a single bout of leg press?

Objective. The measurement of skin temperature using infrared thermography has gained a lot of attention in sport and science since it might be related to the recovery process following high intensity, potentially damaging exercise. This study investigated the time course of the skin temperature response and the muscle recovery status following a resistance training session involving leg press exercise.Approach. Fourteen young male college students (19.9 ± 1.7 years, 176 ± 6 cm, 66.1 ± 7.6 kg, 21.1 ± 1.8 kg.m^-2) performed one session involving 10 sets, of 10 repetition maximum each (RM), of unilateral leg press 45° exercise, performed to momentary muscle failure, with 2 min rest between sets. Perceived recovery, mean and maximum thigh skin temperatures, thigh muscle thickness, maximal isometric strength, muscle soreness, and horizontal jump performance were measured pre, 24, 48, and 72 h following exercise.Main results. The exercise protocol resulted in significant reduction in isometric strength, horizontal jump performance, and perceived recovery (p < 0.05). There was also a significant (p < 0.05) increase in muscle thickness and muscle soreness. With exception of jump performance, that recovered at 48 (p > 0.05), recovery parameters did not recover up to 72 h post-exercise (p > 0.05). Surprisingly, skin temperatures were not altered throughout the entire 72 h post-exercise period (p > 0.05). No significant positive correlation was found between skin temperatures and muscle thickness. Additionally, only one out of 16 correlation coefficients showed significant (r = -0.56,p = 0.036) inverse association between skin temperature and isometric strength.Significance. In conclusion, thigh skin temperature remains unaffected up to 72 h following a leg press exercise, and the time course response of thigh skin temperature was not associated with recovery status.

Thermographic assessment of the immediate and short term-effects of blood flow restriction exercise on Achilles tendon skin temperature

OBJECTIVES

To determine the thermal patterning of the Achilles tendon following bodyweight resistance exercise with and without blood-flow restriction (BFR).

DESIGN

Cross-sectional.

SETTING

Research laboratory.

PARTICIPANTS

Twelve asymptomatic recreational runners (Age: 37 ± 10, Height: 169 ± 20, Mass: 73.8 ± 13.4).

MAIN OUTCOME MEASURES

Thermograms were taken pre and post exercise with and without a BFR cuff on separate legs. BFR cuff pressure was set at 80% maximal arterial occlusion pressure determined using doppler via the tibial artery. Linear mixed-effects models were used to assess the effect of BFR and time post-exercise on skin-temperature (Tskin).

RESULTS

A lower Tskin was seen following BFR exercise at the tendon insertion (P = 0.002), but not at the free tendon (P = 0.234), or the musculotendinous junction (P = 0.933). A significant effect of time upon changes in Tskin was observed in both BFR and non-BFR groups (P = 0.002). No interaction of time and BFR were observed on changes in Tskin (P = 0.726).

CONCLUSION

Region specific changes in Tskin were found, with greater and longer reductions observed at the insertion of the Achilles following BFR exercise before returning to baseline. These findings could have implications for the programming of BFR exercise on tendon health. Future research should observe for differences between symptomatic and healthy tendons.

Influence of infrared camera model and evaluator reproducibility in the assessment of skin temperature responses to physical exercise

Infrared thermography (IRT) has been gaining in popularity in clinical and scientific research due to the increasing availability of affordable infrared cameras. This study aims to determine the similarity of measurement performance between three models of IRT camera during assessment of skin temperature before and after physical exercise. Three models of FLIR thermographic cameras (E60bx, Flir-One Pro LT, and C2) were tested. Thermal images were taken of the foot sole, anterior leg, and anterior thigh from 12 well-trained men, before and after a 30-min run on a treadmill. Image files were blinded and processed by three evaluators to extract the mean, maximum, and standard deviation of skin temperature of the region of interest. Time for data processing and rate of perceived effort was also recorded. Data processing was slower on the E60bx (CI95% E60 vs C2 [0.2, 2.6 min], p = 0.02 and ES = 0.6); vs. Flir-One [0.0, 3.4 min], p = 0.03 and ES = 0.6) and was associated with lower effort perception (E60 3.0 ± 0.1 vs. Flir-One 5.6 ± 0.2 vs C2 7.0 ± 0.2 points; p < 0.001 and ES > 0.8). The C2 and Flir-One cameras underestimated the temperature compared with the E60. In general, measuring mean temperature provided higher camera and examiner intra-class correlations than maximum and standard deviation, especially before exercise. Moreover, post exercise mean skin temperatures provided the most consistent values across cameras and evaluators. We recommend the use of mean temperature and caution when using more than one camera model in a study.

Skin Temperature in Master Long-Distance Runners-Results From a Field Study at the 2018 World Master Athletics Championships

Older people and athletes show impairments in thermoregulation, but this has not yet been studied during a running competition. The aim of the study was to assess (1) whether there are age-related differences in skin temperature during the last stage of a race in well-trained master athletes and (2) to what extent such differences are related to running speed and sex. To investigate this, we used thermography to measure maximum skin temperatures of the head, legs and hands of participants of the 2018 World Master Athletics (WMA) Championships when they were approximately 9,600 m into a 10,000-m road race. Of the 813 runners, 404 were analyzed (142 women, 262 men) including athletes of age groups 35 to 85. All ≥70-year-old athletes completed the race; all 16 non-finishers were younger. The hand temperature was lower than that of the head and legs (p < 0.001). Stepwise regression revealed that head ( R adj 2 = 0.143; p < 0.001) and hand temperature decreased with increasing speed ( R adj 2 = 0.092; p < 0.001). Sex was the most important determinant of leg skin temperature ( R adj 2 = 0.054; p < 0.001), men having higher leg temperatures than women, with a small negative contribution of speed ( R adj 2 increased to 0.069). In conclusion, higher running speed is associated with lower skin temperatures, and leg skin temperature is lower in women than men. The absence of an age effect on skin temperature suggests that there is no impairment in heat dissipation in well-trained older athletes.