Evidence of heat sensitivity in people with Parkinson's disease.

Examining how heat affects people with Parkinson's disease is essential for informing clinical decision-making, safety, well-being, and healthcare planning. While there is evidence that the neuropathology associated with Parkinson's disease affects thermoregulatory mechanisms, little attention has been given to the association of heat sensitivity to worsening symptoms and restricted daily activities in people with this progressive disease. Using a cross-sectional study design, we examined the experiences of people diagnosed with Parkinson's disease in the heat. Two-hundred and forty-seven people completed an online survey (age: 66.0 ± 9.2 years; sex: male = 102 (41.3%), female = 145 (58.7%)), of which 195 (78.9%) reported becoming more sensitive to heat with Parkinson's disease. Motor and nonmotor symptoms worsened with heat in 182 (73.7%) and 203 (82.2%) respondents, respectively. The most commonly reported symptoms to worsen included walking difficulties, balance impairment, stiffness, tremor, fatigue, sleep disturbances, excess sweating, difficulty concentrating, and light-headedness when standing. Concerningly, over half indicated an inability to work effectively in the heat, and nearly half reported that heat impacted their ability to perform household tasks and social activities. Overall, heat sensitivity was common in people with Parkinson's disease and had a significant impact on symptomology, day-to-day activities and quality of life.

Hot water immersion acutely reduces peripheral glucose uptake in young healthy males: An exploratory crossover randomized controlled trial.

Whether glucose concentration increases during heat exposure because of reduced peripheral tissue uptake or enhanced appearance is currently unknown. This study aimed to report glucose concentrations in both capillary and venous blood in response to a glucose challenge during passive heating (PH) to assess whether heat exposure affects glucose uptake in healthy males. Twelve healthy male participants completed two experimental sessions, where they were asked to undertake an oral glucose tolerance test (OGTT) whilst immersed in thermoneutral (CON, 35.9 (0.6) °C) and hot water (HWI, 40.3 (0.5) °C) for 120 min. Venous and capillary blood [glucose], rectal temperature, and heart rate were recorded. [Glucose] area under the curve for HWI venous (907 (104) AU) differed from CON venous (719 (88) AU, all P < 0.001). No other differences were noted (P > 0.05). Compared with CON, HWI resulted in greater rectal temperature (37.1 (0.3) °C versus 38.6 (0.4) °C, respectively) and heart rate (69 (12) bpm versus 108 (11) bpm, respectively) on cessation (P < 0.001). An OGTT results in similar capillary [glucose] during hot and thermoneutral water immersion, whereas venous [glucose] was greater during HWI when compared with CON. This indicates that peripheral tissue glucose uptake is acutely reduced in response to HWI. Abbreviations: AUC: Area under the curve; CON: Thermoneutral immersion trial; HWI: Hot water immersion trial; OGTT: Oral glucose tolerance test; PH: Passive heating; T-msk: Mean skin temperature; Trec: Rectal temperature.

Climate Change Effects on the Predicted Heat Strain and Labour Capacity of Outdoor Workers in Australia.

Global heating is subjecting more of the planet to longer periods of higher heat stress categories commonly employed to determine safe work durations. This study compared predicted worker heat strain and labour capacity for a recent normal climate (1986-2005) and under commonly applied climate scenarios for the 2041-2080 period for selected Australian locations. Recently published heat indices for northern (Darwin, Townsville, and Tom Price) and south-eastern coastal and inland Australia locations (Griffith, Port Macquarie, and Clare) under four projected climate scenarios, comprising two representative concentration pathways (RCPs), RCP4.5 and RCP8.5, and two time periods, 2041-2060 and 2061-2080, were used. Safe work durations, before the threshold for core temperature (38.0 °C) or sweat loss (5% body mass) are attained, were then estimated for each scenario using the predicted heat strain model (ISO7933). The modelled time to threshold core temperature varied with location, climate scenario, and metabolic rate. Relative to the baseline (1986-2005), safe work durations (labour capacity) were reduced by >50% in Port Macquarie and Griffith and by 20-50% in northern Australia. Reaching the sweat loss limit restricted safe work durations in Clare and Griffith. Projected future climatic conditions will adversely impact the predicted heat strain and labour capacity of outdoor workers in Australia. Risk management strategies must adapt to warming conditions to protect outdoor workers from the deleterious effects of heat.

A Systematic Review of Post-Work Core Temperature Cooling Rates Conferred by Passive Rest.

Physical work increases energy expenditure, requiring a considerable elevation of metabolic rate, which causes body heat production that can cause heat stress, heat strain, and hyperthermia in the absence of adequate cooling. Given that passive rest is often used for cooling, a systematic search of literature databases was conducted to identify studies that reported post-work core temperature cooling rates conferred by passive rest, across a range of environmental conditions. Data regarding cooling rates and environmental conditions were extracted, and the validity of key measures was assessed for each study. Forty-four eligible studies were included, providing 50 datasets. Eight datasets indicated a stable or rising core temperature in participants (range 0.000 to +0.028 °C min-1), and forty-two datasets reported reducing core temperature (-0.002 to -0.070 °C min-1) during passive rest, across a range of Wet-Bulb Globe Temperatures (WBGT). For 13 datasets where occupational or similarly insulative clothing was worn, passive rest resulted in a mean core temperature decrease of -0.004 °C min-1 (-0.032 to +0.013 °C min-1). These findings indicate passive rest does not reverse the elevated core temperatures of heat-exposed workers in a timely manner. Climate projections of higher WBGT are anticipated to further marginalise the passive rest cooling rates of heat-exposed workers, particularly when undertaken in occupational attire.

Sex-based differences in body core temperature response across repeat work bouts in the heat.

OBJECTIVE: To investigate the effects of repeated work bouts in the heat on peak body core temperature and to explore sex-based differences in body core temperature responses. METHODS: Fourteen males and fifteen females performed four work bouts (two heavy and two moderate, alternating) in 32.5 °C Wet Bulb Globe Temperature (WBGT), each separated by 30-min seated rest in 28.0 °C WBGT. Participants wore a military combat uniform with body armour and helmet (10 kg load) during the work bouts, removing the vest and helmet during recovery periods. RESULTS: Body core temperature elevation over time was faster in the first compared with subsequent work bouts of each intensity. Body core temperature elevation was similar between males and females during the first heavy work bout, then remained significantly lower in females for the reminder of the trial. CONCLUSIONS: Contrary to the assumed progressive elevation in strain, but in agreement with recent literature, a gradual reduction in heat storage in subsequent exercise bouts prevented a cumulative increase in heat strain in the conditions tested.

Heat Stress Management in the Military: Wet-Bulb Globe Temperature Offsets for Modern Body Armor Systems.

OBJECTIVE: The aim of this study was to model the effect of body armor coverage on body core temperature elevation and wet-bulb globe temperature (WBGT) offset. BACKGROUND: Heat stress is a critical factor influencing the health and safety of military populations. Work duration limits can be imposed to mitigate the risk of exertional heat illness and are derived based on the environmental conditions (WBGT). Traditionally a 3°C offset to WBGT is recommended when wearing body armor; however, modern body armor systems provide a range of coverage options, which may influence thermal strain imposed on the wearer. METHOD: The biophysical properties of four military clothing ensembles of increasing ballistic protection coverage were measured on a heated sweating manikin in accordance with standard international criteria. Body core temperature elevation during light, moderate, and heavy work was modeled in environmental conditions from 16°C to 34°C WBGT using the heat strain decision aid. RESULTS: Increasing ballistic protection resulted in shorter work durations to reach a critical core temperature limit of 38.5°C. Environmental conditions, armor coverage, and work intensity had a significant influence on WBGT offset. CONCLUSION: Contrary to the traditional recommendation, the required WBGT offset was >3°C in temperate conditions (<27°C WBGT), particularly for moderate and heavy work. In contrast, a lower WBGT offset could be applied during light work and moderate work in low levels of coverage. APPLICATION: Correct WBGT offsets are important for enabling adequate risk management strategies for mitigating risks of exertional heat illness.

The Biologically Relevant Coordination Chemistry of Iron and Nitric Oxide: Electronic Structure and Reactivity.

Nitric oxide (NO) is an important signaling molecule that is involved in a wide range of physiological and pathological events in biology. Metal coordination chemistry, especially with iron, is at the heart of many biological transformations involving NO. A series of heme proteins, nitric oxide synthases (NOS), soluble guanylate cyclase (sGC), and nitrophorins, are responsible for the biosynthesis, sensing, and transport of NO. Alternatively, NO can be generated from nitrite by heme- and copper-containing nitrite reductases (NIRs). The NO-bearing small molecules such as nitrosothiols and dinitrosyl iron complexes (DNICs) can serve as an alternative vehicle for NO storage and transport. Once NO is formed, the rich reaction chemistry of NO leads to a wide variety of biological activities including reduction of NO by heme or non-heme iron-containing NO reductases and protein post-translational modifications by DNICs. Much of our understanding of the reactivity of metal sites in biology with NO and the mechanisms of these transformations has come from the elucidation of the geometric and electronic structures and chemical reactivity of synthetic model systems, in synergy with biochemical and biophysical studies on the relevant proteins themselves. This review focuses on recent advancements from studies on proteins and model complexes that not only have improved our understanding of the biological roles of NO but also have provided foundations for biomedical research and for bio-inspired catalyst design in energy science.

Nitric oxide and heme-NO stimulate superoxide production by NADPH oxidase 5.

Nitric oxide (NO) is a ubiquitous cell signaling molecule which mediates widespread and diverse processes in the cell. These NO dependent effects often involve activation (e.g. NO binding to the heme group of soluble guanylyl cyclase for cGMP production) or inactivation (e.g. S-nitrosation) of protein targets. We studied the effect of NO and heme-NO on the transmembrane signaling enzyme NADPH oxidase 5 (NOX5), a heme protein which produces superoxide in response to increases in intracellular calcium. We found that treatment with NO donors increases NOX5 activity through heme-dependent effects, and that this effect could be recapitulated by the addition of heme-NO. This work adds to our understanding of NOX5 regulation in the cell but also provides a framework for understanding how NO could cause widespread changes in hemeprotein activity based on different affinities for heme v. heme-NO, and helps explain the opposing roles NO plays in activation and inactivation of hemeprotein targets.

Comparison of two mathematical models for predicted human thermal responses to hot and humid environments.

PURPOSE: We compared the accuracy and design of two thermoregulatory models, the US Army's empirically designed Heat Strain Decision Aid (HSDA) and the rationally based Health Risk Prediction (HRP) for predicting human thermal responses during exercise in hot and humid conditions and wearing chemical protective clothing. METHODS: Accuracy of the HSDA and HRP model predictions of core body and skin temperature (Tc, Ts) were compared to each other and relative to measured outcomes from eight male volunteers (age 24 ± 6 years; height 178 ± 5 cm; body mass 76.6 ± 8.4 kg) during intermittent treadmill marching in an environmental chamber (air temperature 29.3 ± 0.1 °C; relative humidity 56 ± 1%; wind speed 0.4 ± 0.1 m∙s-1) wearing three separate chemical protective ensembles. Model accuracies and precisions were evaluated by the bias, mean absolute error (MAE), and root mean square error (RMSE) compared to observed data mean ± SD and the calculated limits of agreement (LoA). RESULTS: Average predictions of Tc were comparable and acceptable for each method, HSDA (Bias 0.02 °C; MAE 0.18 °C; RMSE 0.21 °C) and HRP (Bias 0.10 °C; MAE 0.25 °C; RMSE 0.34 °C). The HRP averaged predictions for Ts were within an acceptable agreement to observed values (Bias 1.01 °C; MAE 1.01 °C; RMSE 1.11 °C). CONCLUSION: Both HSDA and HRP acceptably predict Tc and HRP acceptably predicts Ts when wearing chemical protective clothing during exercise in hot and humid conditions.

Utilizing Drones to Restore and Maintain Radio Communication During Search and Rescue Operations.

INTRODUCTION: The ability of rescuers to maintain contact with incident command (IC) and each other is a critical component of search and rescue (SAR) operations. When rescuers lose radio communication with operation leaders, the effectiveness of operations may be substantially affected. This often occurs owing to the limitations of standard communications equipment in difficult terrain or when victims are beyond line-of-sight. This study investigates the viability of using an aerial drone-repeater system configuration to restore and maintain radio communications between IC and deployed rescuers. METHODS: SAR operators in Southern Utah identified 10 areas where radio communication is compromised during live rescue operations. Trained SAR personnel were deployed to these areas in a mock exercise. After confirmed loss of communication, a repeater-equipped aerial drone was piloted 122 m above IC to restore communication. Once restored, communication was assessed at regular intervals for the duration of the mock deployment. RESULTS: In all 10 areas tested, communication was successfully restored. In all cases, once communication was restored, no additional loss of radio contact occurred. The time between communication loss and restoration across the 10 scenarios was 6.5±1.1 (4.4-9.3) min (mean±SD with range). CONCLUSIONS: This method of restoring radio communication among SAR personnel could drastically improve the ability to assist victims and help mitigate the risks faced by rescuers. SAR leaders should be made aware of the useful applications of drones during SAR operations, especially in instances where communication is compromised.

Monitoring heat strain: the effect of sensor type and location on single-site and mean skin temperature during work in the heat.

PURPOSE: Elevations in skin temperature and heat strain reduce tolerance to work in the heat. This study assessed agreement between mean (eight sites) and single-site skin temperature, measured by a conductive or infrared sensor, during exercise in the heat. METHODS: Twelve males (age: 24.2 ± 3.7 years; height: 180 ± 6.5 cm; body mass: 82.9 ± 9.5 kg; body fat: 16.0 ± 6.5%) volunteered to participate in two trials. Thirty minutes of seated rest was followed by 60 min of treadmill walking (4.5 km·h-1, 1%) inside an environmental chamber (35.5 ± 0.2 °C dry bulb, 50.7 ± 2.5% relative humidity) wearing either an athletic (ATH: t-shirt, shorts, shoes) or a chemical protective ensemble (CPE: ATH plus coverall and respirator). Skin temperature was measured on the axilla with a conductive sensor (Tsk-C) and an infrared sensor (Tsk-I) and compared to mean skin temperature ([Formula: see text] 8-site conductive sensors). Rectal temperature and heart rate were measured and used to calculate the adaptive physiological strain index (aPSI). RESULTS: Skin temperature on the chest, scapula, and thigh showed acceptable agreement with [Formula: see text] (mean difference < 0.5 °C and limits of agreement ± 1.0 °C) in both ATH and CPE. Skin temperature on the axilla overestimated [Formula: see text] in ATH (Tsk-C: 1.5 ± 0.8 °C; Tsk-I: 2.2 ± 1.2 °C) and CPE (Tsk-C: 1.1 ± 0.9 °C; Tsk-I: 1.8 ± 1.1 °C). Significant differences (p < 0.001) were observed in aPSI using Tsk-I (ATH: 5.7 ± 1.0, CPE: 8.3 ± 1.1) and Tsk-C (ATH: 5.4 ± 1.0, CPE 7.8 ± 1.0) compared to [Formula: see text] (ATH: 5.2 ± 1.0, CPE: 7.4 ± 1.0). CONCLUSION: The overestimate of mean skin temperature had a significant influence on the aPSI, which has important implications for real-time monitoring and risk management of personnel working in hot environments.

Infrared cameras overestimate skin temperature during rewarming from cold exposure.

OBJECTIVE: The primary aim of this study was to assess the accuracy of an infrared camera and that of a skin thermistor, both commercially available. The study aimed to assess the agreement over a wide range of skin temperatures following cold exposure. METHODS: Fifty-two males placed their right hand in a thin plastic bag and immersed it in 8 °C water for 30 min whilst seated in an air temperature of 30 °C. Following hand immersion, participants removed the bag and rested their hand at heart level for 10 min. Index finger skin temperature (Tsk) was measured with a thermistor, affixed to the finger pad, and an infrared camera measured 1 cm distally to the thermistor. Agreement between the infrared camera and thermistor was assessed by mean difference (infrared camera minus thermistor) and 95% limits of agreement analysis, accounting for the repeated measures over time. The clinically significant threshold for Tsk differences was set at ±0.5 °C and limits of agreement ±1 °C. RESULTS: As an average across all time points, the infrared camera recorded Tsk 1.80 (SD 1.16) °C warmer than the thermistor, with 95% limits of agreement ranging from -0.46 °C to 4.07 °C. CONCLUSION: Collectively, the results show the infrared camera overestimated Tsk at every time point following local cooling. Further, measurement of finger Tsk from the infrared camera consistently fell outside the acceptable level of agreement (i.e. mean difference exceeding ±0.5 °C). Considering these results, infrared cameras may overestimate peripheral Tsk following cold exposure and clinicians and practitioners should, therefore, adjust their risk/withdrawal criteria accordingly.

Model Complexes Elucidate the Role of the Proximal Hydrogen-Bonding Network in Cytochrome P450s.

Cytochrome (Cyt) P450s are an important class of enzymes with numerous functions in nature. The unique reactivity of these enzymes relates to their heme b active sites with an axially bound, deprotonated cysteine (a "cysteinate") ligand (chemically speaking a thiolate). The heme-thiolate active sites further contain a number of conserved hydrogen-bonds (H-bonds) to the bound cysteinate ligand, which have been proposed to tune and stabilize the Fe-S bond. In this work, we present the low-temperature preparation of five ferric heme-thiolate nitric oxide (NO) model complexes that contain one tunable hydrogen-bond to the bound thiolate ligand. We show that the presence of a H-bond has a dramatic effect in stabilizing the thiolate ligand against direct reaction with NO. This observation reinforces the important protective role of H-bonds in Cyt P450s. We further demonstrate that H-bond strength tunes thiolate donor strength, which, in turn, controls the N-O and Fe-NO stretching frequencies and hence, bond strengths. We observe a direct correlation between the Fe-NO and N-O stretching frequencies, indicative of a thiolate σ-trans effect (interaction). Here, very small changes in H-bond strength lead to a surprisingly large effect on the FeNO unit. This result implies that subtle changes in the Cys-pocket of a Cyt P450 can strongly affect reactivity. Importantly, using the Fe-NO/N-O correlation established here, the thiolate donor strength in heme-thiolate enzyme active sites and model complexes can be quantified in a straightforward way, using NO as a probe. This spectroscopic correlation provides a quantitative measure of the thiolate's "push" effect, which is important in O2-activation (Compound I formation) in Cyt P450s in general.

Electron Paramagnetic Resonance Spectroscopy as a Probe of Hydrogen Bonding in Heme-Thiolate Proteins.

Despite utilizing a common cofactor binding motif, hemoproteins bearing a cysteine-derived thiolate ligand (heme-thiolate proteins) are involved in a diverse array of biological processes ranging from drug metabolism to transcriptional regulation. Though the origin of heme-thiolate functional divergence is not well understood, growing evidence suggests that the hydrogen bonding (H-bonding) environment surrounding the Fe-coordinating thiolate influences protein function. Outside of X-ray crystallography, few methods exist to characterize these critical H-bonding interactions. Electron paramagnetic resonance (EPR) spectra of heme-thiolate proteins bearing a six-coordinate, Fe(III) heme exhibit uniquely narrow low-spin (S = 1/2), rhombic signals, which are sensitive to changes in the heme-thiolate H-bonding environment. To establish a well-defined relationship between the magnitude of g-value dispersion in this unique EPR signal and the strength of the heme-thiolate H-bonding environment, we synthesized and characterized of a series of six-coordinate, aryl-thiolate-ligated Fe(III) porphyrin complexes bearing a tunable intramolecular H-bond. Spectroscopic investigation of these complexes revealed a direct correlation between H-bond strength and g-value dispersion in the rhombic EPR signal. Using density functional theory (DFT), we elucidated the electronic origins of the narrow, rhombic EPR signal in heme-thiolates, which arises from an Fe-S pπ-dπ bonding interaction. Computational analysis of the intramolecularly H-bonded heme-thiolate models revealed that H-bond donation to the coordinating thiolate reduces thiolate donor strength and weakens this Fe-S interaction, giving rise to larger g-value dispersion. By defining the relationship between heme-thiolate electronic structure and rhombic EPR signal, it is possible to compare thiolate donor strengths among heme-thiolate proteins through analysis of low-spin, Fe(III) EPR spectra. Thus, this study establishes EPR spectroscopy as a valuable tool for exploring how second coordination sphere effects influence heme-thiolate protein function.

Nitric Oxide Generation On Demand for Biomedical Applications via Electrocatalytic Nitrite Reduction by Copper BMPA- and BEPA-Carboxylate Complexes.

Intravascular (IV) catheters are essential devices in the hospital that are used to monitor a patient's blood and for administering drugs or nutrients. However, IV catheters are also prone to blood clotting at the point of insertion and infection by formation of robust bacterial biofilms on their surface. Nitric oxide (NO) is ideally suited to counteract both of these problems, due to its antimicrobial properties and its ability to inhibit platelet activation/aggregation. One way to equip catheters with NO releasing properties is by electrocatalytic nitrite reduction to NO by copper complexes in a multi-lumen configuration. In this work, we systematically investigate six closely related Cu(II) BMPA- and BEPA-carboxylate complexes (BMPA = bis-(2-methylpyridyl)amine); BEPA = bis-(2-ethylpyridyl)amine), using carboxylate groups of different chain lengths. The corresponding Cu(II) complexes were characterized using UV-Vis, EPR spectroscopy, and X-ray crystallography. Using detailed cyclic voltammetry (CV) and bulk electrocatalyic studies (with real-time NO quantification), in aqueous buffer, pH 7.4, we are able to derive clear reactivity relations between the ligand structures of the complexes, their Faradaic efficiencies for NO generation, their turnover frequencies (TOFs), and their redox potentials. Our results show that the complex [Cu(BEPA-Bu)](OAc) is the best catalyst with a high Faradaic efficiency over large nitrite concentration ranges and the expected best tolerance to oxygen levels. For this species, the more positive redox potential suppresses NO disproportionation, which is a major Achilles heel of the (faster) catalysts with the more negative reduction potentials.

Indices of physiological strain for firefighters of the Australian Defence Forces.

High levels of exertion and physiological strain are the leading cause of fireground injuries. The Physiological Strain Index (PSI) provides a rating of strain based on body core temperature and heart rate; however, it may underestimate the strain of workers in protective clothing as skin temperature may be elevated. This study aimed to examine the relationship between the PSI and an Adaptive Physiological Strain Index (aPSI) that incorporates skin temperature, among firefighters wearing protective clothing. Nine male firefighters of the Australian Defence Force volunteered to participate. Participants conducted scenario-based activities while wearing turnout gear and breathing apparatus. Working in teams of four, participants would respond to a situation around and within a small building with several rooms that could be filled with smoke, however, no live fire was present. Heart rate, gastrointestinal temperature, and skin temperature were monitored throughout work and rehabilitation. Physiological strain was estimated via the PSI and aPSI. Absolute peak PSI and aPSI ratings were significantly different during work (PSI: 7.3 ± 1.6; aPSI 8.2 ± 2.0; p < 0.001). The aPSI produced higher ratings of physiological strain, >0.5 above PSI, progressively from a moderate level of strain (>6). The aPSI may provide a more accurate indication of a level of "maximal strain" for encapsulated workers than the original PSI, coincident with the occupational limits for body core temperature of 38.0 °C for general occupational groups, or 38.5 °C for selected and acclimatised personnel.

Ballet and Contemporary Dance Injuries When Transitioning to Full-Time Training or Professional Level Dance: A Systematic Review.

This systematic review examines the relationship between injury and two stages of a dancer's career development: when transitioning to full-time training and to a professional dance company. The findings are discussed in relation to managing transitioning loads with regard to injury prevention. Six electronic databases (PubMed, Embase, CINAHL, SPORTDiscus, Scopus, and Performing Arts Periodicals Database) were searched from inception to July 2018, inclusive of English language peer reviewed studies investigating injury in pre-professional and professional ballet and contemporary dancers. Seventeen studies met the inclusion criteria. "Limited" evidence revealed that dancers transitioning to professional ballet had a significantly higher rate of time-loss injuries per exposure hour relative to established professionals, whereas transitioning professional contemporary dancers had a significantly lower rate of both medical-attention and time-loss injuries. "Limited" evidence also showed a decreased rate and trend toward lower prevalence rates for time-loss injuries per exposure hour for transitioning ballet students and an increased rate of medical-attention injury in a combined cohort of transitioning ballet and contemporary dance students. Thus, this review provides some evidence that injuries tend to occur as dancers are transitioning to full-time ballet or contemporary dance training or to professional careers.

Validity of a noninvasive estimation of deep body temperature when wearing personal protective equipment during exercise and recovery.

BACKGROUND: Deep body temperature is a critical indicator of heat strain. However, direct measures are often invasive, costly, and difficult to implement in the field. This study assessed the agreement between deep body temperature estimated from heart rate and that measured directly during repeated work bouts while wearing explosive ordnance disposal (EOD) protective clothing and during recovery. METHODS: Eight males completed three work and recovery periods across two separate days. Work consisted of treadmill walking on a 1% incline at 2.5, 4.0, or 5.5 km/h, in a random order, wearing EOD protective clothing. Ambient temperature and relative humidity were maintained at 24 °C and 50% [Wet bulb globe temperature (WBGT) (20.9 ± 1.2) °C] or 32 °C and 60% [WBGT (29.0 ± 0.2) °C] on the separate days, respectively. Heart rate and gastrointestinal temperature (TGI) were monitored continuously, and deep body temperature was also estimated from heart rate (ECTemp). RESULTS: The overall systematic bias between TGI and ECTemp was 0.01 °C with 95% limits of agreement (LoA) of ±0.64 °C and a root mean square error of 0.32 °C. The average error statistics among participants showed no significant differences in error between the exercise and recovery periods or the environmental conditions. At TGI levels of (37.0-37.5) °C, (37.5-38.0) °C, (38.0-38.5) °C, and > 38.5 °C, the systematic bias and ± 95% LoA were (0.08 ± 0.58) °C, (- 0.02 ± 0.69) °C, (- 0.07 ± 0.63) °C, and (- 0.32 ± 0.56) °C, respectively. CONCLUSIONS: The findings demonstrate acceptable validity of the ECTemp up to 38.5 °C. Conducting work within an ECTemp limit of 38.4 °C, in conditions similar to the present study, would protect the majority of personnel from an excessive elevation in deep body temperature (> 39.0 °C).