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INTRODUCTION We tested the hypothesis that people with multiple sclerosis (MS) who experience heat sensitivity voluntarily engage in cool-seeking behavior during exercise to a greater extent than healthy controls. METHODS In a 27.0°C ± 0.2°C, 41% ± 2% RH environment, seven participants with relapsing-remitting MS who exhibited heat sensitivity and seven healthy controls completed two randomized trials cycling for 40 min (EX) at 3.5 W·kg-1 metabolic heat production, followed by 30 min recovery (REC). In one trial, participants were restricted from engaging in cooling (CON). In the other trial, participants voluntarily pressed a button to receive 2 min of ~2°C water perfusing a top (COOL). Mean skin and core temperatures and mean skin wettedness were recorded continuously. Total time in cooling provided an index of cool-seeking behavior. RPE, total symptom scores (MS only), and subjective fatigue (MS only) were recorded every 10 min. RESULTS Core temperature (+0.5°C ± 0.1°C) and skin wettedness (+0.53 ± 0.02 a.u.) increased but were not different between groups or trials at end exercise (P = 0.196) or end recovery (P = 0.342). Mean skin temperature was reduced in COOL compared with CON at end exercise (P ≤ 0.002), with no differences between groups (P ≥ 0.532). MS spent more total time in cooling during EX (MS, 13 ± 3 min; healthy, 7 ± 4 min; P < 0.001) but not REC (MS, 2 ± 1 min; healthy, 0 ± 1 min; P = 0.496). RPE was greater at end exercise in MS (P = 0.001). Total symptom scores increased during exercise (P = 0.005) but was not different between trials (P = 0.321), whereas subjective fatigue was not attenuated in the cooling trial (P = 0.065). CONCLUSION Voluntary cooling is augmented in MS but does not consistently mitigate perceptions of heat-related symptoms or subjective fatigue.

Skin grafting following a burn injury attenuates/abolishes sweat production within grafted areas. It is presently unknown whether the thermoregulatory consequences of skin grafting depend on anatomical location.Purpose: To test the hypothesis that a simulated burn injury on the torso will be no more or less detrimental to core temperature control than on the limbs during uncompensable exercise-heat stress.Methods: Nine non-burned individuals (7 males, 2 females) completed the protocol. On separate occasions, burn injuries of identical surface area (0.45 ± 0.08 m2 or 24.4% ± 4.4% of total body surface area) were simulated on the torso or the arms/legs using an absorbent, vapor-impermeable material that impedes sweat evaporation in those regions. Participants performed 60 min of treadmill walking at 5.3 km·h-1 and a 4.1% ± 0.8% grade, targeting 6 W·kg-1 of metabolic heat production in 40.1°C ± 0.2°C and 19.6% ± 0.6% relative humidity conditions. Rectal temperature, heart rate, and perceptual responses were measured.Results: Rectal temperature increased to a similar extent with simulated injuries on the torso and limbs (condition-by-time interaction: P = 0.86), with a final rectal temperature 0.9 ± 0.3°C above baseline in both conditions. No differences in heart rate, perceived exertion, or thermal sensation were observed between conditions (condition-by-time interactions: P ≥ 0.50).Conclusion: During uncompensable exercise-heat stress, sized-matched simulated burn injuries on the torso or limbs evoke comparable core temperature, heart rate, and perceptual responses, suggesting that the risk of exertional heat illness in such environmental conditions is independent of injury location.

The objective of this study was to assess biothermal conditions in the selected Polish health resorts for specific forms of climatic therapy. We calculated Universal Thermal Climate Index (UTCI) for ten-year period (2008- 2017) and then added adjustment terms, taking into account changes in metabolic rates during various physical activities from resting to vigorous exercise. The adjusted UTCI values increased with rising activity, implying that warmer parts of the year were unsuitable for intensive forms of climatotherapy. These results demonstrate that the UTCI adjustment procedure provides well-balanced assessments of bioclimatic conditions for the purpose of climatic treatment considering the level of activity

The intensity of environmental heat stress during a marathon race increases the runner's metabolic heat production. Based on series of participatory studies and interview sessions with 100 respondents among runners, the contributing factors to this homeostatic imbalance risk are the excessive amount of body-water deficit from extensive sweating, and the rapid increase of cardiovascular and thermal strain while running. In addition, environmental factors such as humidity, the increase of air temperature, wind speed and solar radiation contribute to the marathon runner's low performance during running with the paucity of cooling strategy that results in the increase of core body temperature with symptoms of exertional heat illness. This paper elucidates the integration of the statistical and theoretical studies of exertional heat illness and the human physiological responses complementing with the product design context. The integration demonstrates the synchronisation of design thinking process within the ergonomics ergosystem framework to develop the appropriate prototype design for marathon runners. As outcome, this research has successfully developed a running suit as its design proposal to minimise exertional heat illness risk and promote the runner's safety, wellbeing and performance in the heat.

Objective: To verify the thermoregulatory and perceptual responses of obese and lean girls, either fit or unfit, exercising in the heat at a similar rate of metabolic heat production per unit body mass. Methods: A total of 34 pubescent girls were allocated in four groups: 12 obese fit, 9 obese unfit, 5 lean fit, and 8 lean unfit. The obese groups (13.2 ± 1.4 years, 40.5% ± 5.8% fat by DXA) differed in their aerobic fitness (V˙O2peak 76.0 ± 8.1 vs. 56.6 ± 5.8 mL.kg muscle mass-1.min-1), as well as the lean groups (13.1 ± 1.6 years, 24.0% ± 4.8% fat) (V˙O2peak 74.5 ± 2.9 vs. 56.2 ± 5.0 mL.kg muscle mass-1 min-1). Girls cycled two bouts of 25 min with a 10 min rest in between, at ∼5.4 W.kg-1 in the heat (36 °C and 40% relative humidity) and they were kept euhydrated. Rectal and skin temperatures and heart rate were measured every 5 min. Perceptual responses were evaluated throughout the exercise. Results: Initial rectal temperature was higher in the obese subjects compared to the lean subjects (37.5 ± 0.3 and 37.2 ± 0.3 °C). No difference was observed among the girls whom were obese (eight fit or unfit) and lean (also fit or unfit) throughout the exercise in rectal temperature (37.6 ± 0.2, 37.5 ± 0.3, 37.5 ± 0.3, 37.4 ± 0.3 °C, respectively), skin temperature (34.8 ± 0.8, 35.1 ± 1.0, 34.4 ± 0.9, 35.2 ± 0.9 °C), and heart rate (128 ± 18; 118 ± 12, 130 ± 16, 119 ± 16 beats min-1). No differences were observed in perceptual responses among groups. Conclusion: Regardless of the adiposity or aerobic fitness, pubescent girls had similar thermoregulatory and perceptual responses while cycling in the heat at similar metabolic heat production. Resumo Objetivo: Verificar as respostas termorregulatórias e perceptivas de meninas obesas e magras, com alta e baixa aptidão aeróbica, exercitando-se no calor com produção metabólica de calor similar por massa corporal. Métodos: Um total de 34 meninas púberes foram alocadas em quatro grupos: 12 obesas com alta aptidão aeróbica, 9 obesas com baixa aptidão aeróbica, 5 magras com alta aptidão aeróbica e 8 magras com baixa aptidão aeróbica. Os grupos obesos (13,2 ± 1,4 anos, 40,5% ± 5,8% de gordura por DXA) diferiram em sua aptidão aeróbica (V˙O2peak 76,0 ± 8,1 vs. 56,6 ± 5,8 mL.kg de massa muscular-1.min-1), bem como os grupos magros (13,1 ± 1,6 anos, 24,0% ± 4,8% de gordura) (V˙O2peak 74,5 ± 2,9 vs. 56,2 ± 5,0 mL.kg de massa muscular-1min-1). As meninas pedalaram duas sessões de 25 minutos com descanso de 10 minutos entre as sessões, a ∼5,4 W.kg-1 no calor (36∘C e 40% de umidade relativa) e foram mantidas hidratadas. As temperaturas retal e cutânea e a frequência cardíaca foram medidas a cada 5 minutos. As respostas perceptivas foram avaliadas durante o exercício. Resultados: A temperatura retal inicial foi maior nas meninas obesas em comparação com as magras (37,5 ± 0,3 e 37,2 ± 0,3 °C). Não houve diferença entre as meninas obesas (com alta aptidão aeróbica ou não) e magras (também com alta aptidão aeróbica ou não) durante todo o exercício em relação à temperatura retal (37,6 ± 0,2; 37,5 ± 0,3; 37,5 ± 0,3; 37,4 ± 0,3 °C; respectivamente), temperatura da pele (34,8 ± 0,8; 35,1 ± 1,0; 34,4 ± 0,9; 35,2 ± 0,9 °C), e frequência cardíaca (128 ± 18; 118 ± 12, 130 ± 16, 119 ± 16 batimentos.min-1). Não foram observadas diferenças nas respostas perceptivas entre os grupos. Conclusão: Independentemente da adiposidade ou do condicionamento aeróbico, as meninas púberes tiveram respostas termorregulatórias e perceptivas semelhantes, enquanto pedalavam no calor com uma produção metabólica de calor similar.

Adenosine triphosphate (ATP) regeneration by substrate-level phosphorylation is a general feature of cancer metabolism, even under normoxic conditions (aerobic glycolysis). However, it is unclear why cancer cells prefer inefficient aerobic glycolysis over the highly efficient process of oxidative phosphorylation for ATP regeneration. To investigate the metabolic principles underlying aerobic glycolysis, we performed13C-metabolic flux analysis of 12 cultured cancer cell lines and explored the metabolic constraints required to reproduce the results usingin silicometabolic simulations. We found that the measured flux distribution can be reproduced by maximizing the ATP consumption in the flux balance analysis considering a limitation of metabolic heat dissipation (enthalpy change). It suggests that aerobic glycolysis may be preferable because metabolic heat production during one mol of ATP regeneration by aerobic glycolysis was less than that produced by oxidative phosphorylation (OXPHOS). Consistent with the simulation, OXPHOS inhibition induced metabolic redirection to aerobic glycolysis while maintaining the intracellular temperature. Furthermore, the dependency on aerobic glycolysis was partly alleviated upon culturing at low temperatures. Our data suggest that metabolic thermogenesis is an important factor in understanding aerobic glycolysis in cancer cells and that an advantage of aerobic glycolysis is the reduction in metabolic heat generation during ATP regeneration.

Blood glucose (BG) concentration monitoring is essential for controlling complications arising from diabetes, as well as digital management of the disease. At present, finger-prick glucometers are widely used to measure BG concentrations. In consideration of the challenges of invasive BG concentration measurements involving pain, risk of infection, expense, and inconvenience, we propose a noninvasive BG concentration detection method based on the conservation of energy metabolism. In this study, a multisensor integrated detection probe was designed and manufactured by 3D-printing technology to be worn on the wrist. Two machine-learning algorithms were also applied to establish the regression model for predicting BG concentrations. The results showed that the back-propagation neural network model produced better performance than the multivariate polynomial regression model, with a mean absolute relative difference and correlation coefficient of 5.453% and 0.936, respectively. Here, about 98.413% of the predicted values were within zone A of the Clarke error grid. The above results proved the potential of our method and device for noninvasive glucose concentration detection from the human wrist.

Establishing proper policies regarding the recognition and prevention of equine heat stress becomes increasingly important, especially in the face of global warming. To assist this, a detailed view of the variability of equine thermoregulation during field exercise and recovery is essential. 13 endurance horses and 12 trotter horses were equipped with continuous monitoring devices [gastrointestinal (GI) pill, heartrate (HR) monitor, and global positioning system] and monitored under cool weather conditions during four endurance rides over a total of 80 km (40 km loops) and intense trotter track-based exercise over 1,540 m. Recordings included GI temperature (Tc), speed, HR and pre- and post-exercise blood values. A temperature time profile curve of Tc was constructed, and a net area under the curve was calculated using the trapezoidal method. Metabolic heat production and oxygen cost of transport were also calculated in endurance horses. Maximum Tc was compared using an independent samples t-test. Endurance horses (mean speed 14.1 ± 1.7 km h–1) reached mean maximum Tc (39.0 ± 0.4°C; 2 × 40 km in 8 horses) during exercise at 75% of completion of Tc exercise and Tc returned to baseline within 60 min into recovery. However, the mean Tc was still 38.8 ± 0.4°C at a HR of 60 bpm which currently governs “fit to continue” competition decisions. Trotters (40.0 ± 2.9 km h–1) reached a comparable mean max Tc (38.8 ± 0.5°C; 12 horses) always during recovery. In 30% of trotters, Tc was still >39°C at the end of recovery (40 ± 32 min). The study shows that horses are individuals and thermoregulation monitoring should reflect this, no matter what type of exercise is performed. Caution is advised when using HR cut-off values to monitor thermal welfare in horses since we have demonstrated how Tc can peak quite some time after finishing exercise. These findings have implications for training and management of performance horses to safeguard equine welfare and to maximize performance.

The metabolic heat production of modern pigs has increased by an average of 16%, compared with sows of 30 years ago. Therefore, it is likely that temperature recommendations require updating to meet the needs of modern pigs. The objective of this study was to evaluate whether different reproductive stages of sows altered thermal preference and if current recommendations required updating. Twenty multiparous sows (3.4 ± 1.2 parity) in different reproductive stages (nonpregnant: n = 7; mid-gestation: 58.5 ± 5.68 d, n = 6; and late-gestation: 104.7 ± 2.8 d, n = 7) were tested. Thermal preference was individually tested, and sows could freely choose a temperature, using a thermal gradient between 10.4 and 30.5 °C. Sows were given 24 h to acclimate to the thermal apparatus. Before testing began, sows were given daily feed allotment and returned to the apparatus. Video from the 24-h test period was used to record sow behavior (time spent inactive), posture (upright and sternal and lateral lying), and location using instantaneous scan samples every 15 min. Data were analyzed using PROC MIXED procedure in SAS 9.4. A cubic regression model was used to calculate the sow’s most preferred temperature based on the location, or temperature, in which they spent the most time. The preference range was calculated using peak temperature preference ±SE for each sow. The reproductive stage altered where sows spent their time within the thermal gradient (P < 0.01). Late-gestation sows preferred cooler temperatures (14.0 °C) than mid-gestation (14.8 °C; P < 0.01) and nonpregnant sows (14.8 °C; P < 0.01). In summary, sow thermal preferences were within the lower half of the current recommended range (10 to 25 °C). This indicates that temperatures at the higher end of the recommended range could be uncomfortable to sows and that the thermal comfort zone of sows may be narrower than recommendations indicate.

NEW FINDINGS What is the central question of this study? Black-African descendants are thought, by some, to possess genotypic adaptations conducive to survival in hot climates. We therefore assessed whether Canadian residents of black-African descent display enhanced whole-body total heat loss (evaporative plus dry heat exchange) in comparison to Caucasian Canadians during exercise eliciting matched heat-loss requirements in dry heat. What is the main finding and its importance? Neither whole-body total heat loss nor body heat storage differed significantly between groups, irrespective of the exercise intensity. Our findings indicate that genotypic adaptations associated with ethnicity do not appreciably modify whole-body heat exchange during exercise-heat stress. ABSTRACT Ethnicity has long been thought to modulate thermoregulatory function; however, an evaluation of whole-body heat exchange in men of black-African descent and Caucasian men (white-European descendants), born and raised in the same climate, during exercise eliciting matched heat-loss requirements remained unavailable. We therefore used direct calorimetry to assess whole-body total heat loss (evaporative plus dry heat exchange) in young (18-30 years of age), second-generation (or higher) black-African (n = 11) and Caucasian (n = 11) men. Participants performed three 30 min bouts of semi-recumbent cycling at fixed metabolic heat productions (and therefore matched heat-loss requirements between groups) of 200 (light), 250 (moderate) and 300 W m-2 (vigorous), each followed by 15 min recovery, in dry heat (40°C, ∼13% relative humidity). Across all exercise bouts, dry (P = 0.435) and evaporative (P = 0.600) heat exchange did not differ significantly between groups. As such, total heat loss during light, moderate and vigorous exercise was similar between groups (P = 0.777), averaging [mean (SD)] 177 (10), 217 (13) and 244 (20) W m-2 in black-African men and 172 (13), 212 (17) and 244 (17) W m-2 in Caucasian men. Accordingly, body heat storage across all exercise bouts (summation of metabolic heat production and total heat loss) was also similar between the black-African [568 (142) kJ] and Caucasian groups [623 (124) kJ; P = 0.356]. We demonstrated that, when assessed in young, second-generation (or higher) black-African and Caucasian men during exercise eliciting matched heat-loss requirements in dry heat, ethnicity did not significantly modulate whole-body dry and evaporative heat exchange or the resulting changes in total heat loss and body heat storage.

Although the severity of a burn injury is often associated with the percentage of total body surface area burned (%TBSA), the thermoregulatory consequences of a given %TBSA injury do not account for the interactive effects of body morphology and metabolic heat production (H(prod)). PURPOSE: Using a simulated burn injury model to mimic the detrimental effect of a 40% TBSA injury on whole-body evaporative heat dissipation, core temperature response to exercise in physiologically uncompensable conditions between morphologically-disparate groups were examined at (i) an absolute H(prod) (watts, W), and (ii) a mass-specific H(prod) (watts per kilogram of body mass, W·kg(−1)). METHODS: Healthy, young, non-burned individuals of small (SM, n = 11) or large (LG, n = 11) body size cycled for 60 min at 500 W or 5.3 W·kg(−1) of H(prod) in 39°C and 20% relative humidity conditions. A 40% burn injury was simulated by affixing a highly absorbent, vapor-impermeable material across the torso (20% TBSA), arms (10% TBSA), and legs (10% TBSA) to impede evaporative heat loss in those regions. RESULTS: While the elevation in core temperature was greater in SM compared to LG at a H(prod) of 500 W (SM: 1.69 ± 0.26°C, LG: 1.05 ± 0.26°C, P < 0.01), elevations in core temperature were not different at a H(prod) of 5.3 W·kg(−1) between groups (SM: 0.99 ± 0.32°C, LG: 1.05 ± 0.26°C, P = 0.66). CONCLUSION: These data suggest that among individuals with a 40% TBSA burn injury, a smaller body size leads to exacerbated elevations in core temperature during physical activities eliciting the same absolute H(prod) (non-weight-bearing tasks) but not activities eliciting the same mass-specific H(prod) (weight-bearing tasks).

We compared the effectiveness of 5 heated hypothermia wrap systems.Physiologic and subjective responses were determined in 5 normothermic subjects (1 female) for 5 heated hypothermia wraps (with vapor barrier and chemical heat sources) during 60 min of exposure to a temperature of -22°C. The 5 systems were 1) user-assembled; 2) Doctor Down Rescue Wrap; 3) hypothermia prevention and management kit (HPMK); 4) MARSARS Hypothermia Stabilizer Bag; and 5) Wiggy's Victims Casualty Hypothermia Bag. Core and skin temperature, metabolic heat production, skin heat loss, and body net heat gain were determined. Subjective responses were also evaluated for whole body cold discomfort, overall shivering rating, overall temperature rating, and preferential ranking.The Doctor Down and user-assembled systems were generally more effective, with higher skin temperatures and lower metabolic heat production; they allowed less heat loss, resulting in higher net heat gain (P0.05). HPMK had the lowest skin temperature and highest shivering heat production and scored worse than the other 4 systems for the "whole body cold discomfort" and "overall temperature" ratings (P0.05).The user-assembled and Doctor Down systems were most effective, and subjects were coldest with the HPMK system. However, it is likely that any of the tested systems would be viable options for wilderness responders, and the choice would depend on considerations of cost; volume, as it relates to available space; and weight, as it relates to ability to carry or transport the system to the patient.

ObjectivesTo provide a rationale for minimum water temperature rules for elite and subelite marathon swim racing and highlight factors that make individuals vulnerable to excessive cooling during open water swimming.Methods12 lean competitive swimmers swam for up to 2 hours, three times in different water temperatures between 14°C and 20°C, wearing standard swimming costumes and hats. Rectal temperature (Tre), oxygen consumption, perception of cold and performance were measured.ResultsIn 16°C, half the swimmers did not complete a 2-hour swim; four became (or were predicted to become) hypothermic within 2 hours. In 18°C, three-quarters completed the swim; three became (or were predicted to become) hypothermic. In 20°C, one swimmer was predicted to become hypothermic in under 2 hours. The mean linear rate of fall of Trewas greater in 16°C (−1.57°C/hour) than 18°C (−1.07°C/hour) (p=0.03). There was no change in swimming performance during the swims or between conditions. Most of the cooling rate could be explained by metabolic heat production and morphology for both 16°C (R2=0.94, p2=0.82, preand perception of thermal sensation (r=0.25, p=0.13), and there was a weak correlation between Treand thermal comfort (r=0.32, p=0.04).ConclusionWe recommend that 16°C and 18°C water are too cold for elite marathon swim racing. FédérationInternationale de Natation rules were changed in 2017 to make wetsuits compulsory below 18°C and optional below 20°C.

This study tested the hypothesis that females rely on thermal behavior to a greater extent during and after exercise, relative to males.In a 24°C ± 1°C; (45% ± 10% RH) environment, 10 males (M) and 10 females (F) (22 ± 2 yr) cycled for 60 min (metabolic heat production: M, 117 ± 18 W·m; F, 129 ± 21 W·m), followed by 60-min recovery. Mean skin and core temperatures, skin blood flow and local sweat rates were measured continually. Subjects controlled the temperature of their dorsal neck to perceived thermal comfort using a custom-made device. Neck device temperature provided an index of thermal behavior and mean body temperature provided an index of the stimulus for thermal behavior. Data were analyzed for total area under the curve for exercise and recovery time points. To further isolate the effect of exercise on thermal behavior during recovery, data were also analyzed the minute mean body temperature returned to preexercise levels within a subject.There were no sex differences in metabolic heat production (P = 0.71) or body temperatures (P ≥ 0.10) during exercise. Area under the curve for neck device temperature during exercise was greater for F (-98.4°C·min ± 33.6°C·min vs -64.5°C·min ± 47.8°C·min, P = 0.04), but did not differ during recovery (F, 86.8°C·min ± 37.8°C·min; M, 65.6°C·min ± 35.9°C·min; P = 0.11). In M, mean skin (P = 0.90), core (P = 0.70) and neck device (P = 0.99) temperatures had recovered by the time that mean body temperature had returned to preexercise levels. However, in F, neck device temperature (P = 0.04) was reduced while core temperature remained elevated (P0.01).Females use thermal behavior during exercise to a greater extent than M. During recovery, thermal behavior may compensate for elevated core temperatures in F despite mean body temperatures returning to preexercise levels.

Horticultural crops have a low tolerance to dehydration. In this paper, we show that the reversible electroporation (200 monopolar, rectangular pulses of 50 µs pulse duration, 760 µs between pulses and nominal field strength of 650 V/cm) of Thai basil leaves followed by 24 h resting before hot air drying at 40 °C enhanced the survivability of the tissues at certain levels of dehydration (moisture ratio = 0.2 and 0.1). However, this increased survival was rather limited. Through measurements of metabolic heat production during resting, rehydration kinetics, respiration and photosynthesis of the rehydrated leaves, we show that resting after the application of a reversible pulse-electric field (PEF) may allow a phase of hardening that has a protective effect on the cells, thus decreasing damage during the subsequent drying phase. Increased preservation of cell vitality would be associated with a more turgid and fresh-like rehydrated product, as cells would have the capacity to retain the rehydration water.

Evaporative heat dissipation is a key aspect of avian thermoregulation in hot environments. We quantified variation in avian thermoregulatory performance at high air temperatures (Ta) using published data on body temperature (Tb), evaporative water loss (EWL) and resting metabolic rate (RMR) measured under standardized conditions of very low humidity in 56 arid-zone species. Maximum Tb during acute heat exposure varied from 42.5±1.3°C in caprimulgids to 44.5±0.5°C in passerines. Among passerines, both maximum Tb and the difference between maximum and normothermic Tb decreased significantly with body mass (Mb). Scaling exponents for minimum thermoneutral EWL and maximum EWL were 0.825 and 0.801, respectively, even though evaporative scope (ratio of maximum to minimum EWL) varied widely among species. Upper critical limits of thermoneutrality (Tuc) varied by >20°C and maximum RMR during acute heat exposure scaled to Mb0.75 in both the overall data set and among passerines. The slope of RMR at Ta>Tuc increased significantly with Mb but was substantially higher among passerines, which rely on panting, compared with columbids, in which cutaneous evaporation predominates. Our analysis supports recent arguments that interspecific within-taxon variation in heat tolerance is functionally linked to evaporative scope and maximum ratios of evaporative heat loss (EHL) to metabolic heat production (MHP). We provide predictive equations for most variables related to avian heat tolerance. Metabolic costs of heat dissipation pathways, rather than capacity to increase EWL above baseline levels, appear to represent the major constraint on the upper limits of avian heat tolerance.

Temperature is an important environmental factor governing the ability of organisms to grow, survive and reproduce. Thermal performance curves (TPCs), with some caveats, are useful for charting the relationship between body temperature and some measure of performance in ectotherms, and provide a standardized set of characteristics for interspecific comparisons. Endotherms, however, have a more complicated relationship with environmental temperature, as endothermy leads to a decoupling of body temperature from external temperature through use of metabolic heat production, large changes in insulation and variable rates of evaporative heat loss. This has impeded our ability to model endothermic performance in relation to environmental temperature as well as to readily compare performance between species. In this Commentary, we compare the strengths and weaknesses of potential TPC analogues (including other useful proxies for linking performance to temperature) in endotherms and suggest several ways forward in the comparative ecophysiology of endotherms. Our goal is to provide a common language with which ecologists and physiologists can evaluate the effects of temperature on performance. Key directions for improving our understanding of endotherm thermoregulatory physiology include a comparative approach to the study of the level and precision of body temperature, measuring performance directly over a range of body temperatures and building comprehensive mechanistic models of endotherm responses to environmental temperatures. We believe the answer to the question posed in the title could be ‘yes’, but only if ‘performance’ is well defined and understood in relation to body temperature variation, and the costs and benefits of endothermy are specifically modelled.

INTRODUCTION Exercise thermoregulation studies typically control for time of day. The present study assessed whether circadian rhythm independently alters time-dependent changes in core temperature and sweating during exercise at a fixed rate of metabolic heat production (Hprod) during the wake period. METHODS Ten men (26 ± 2 yr, 76.6 ± 6.3 kg, 1.95 ± 0.10 m2) cycled for 60 min in three combinations of ambient temperature and Hprod (23°C-7.5 W·kg-1, 33°C-5.5 W·kg-1, and 33°C-7.5 W·kg-1) at two times of day (a.m.: 0800 h, p.m.: 1600 h). Rectal temperature (Tre), local sweat rate, and whole-body sweat losses were measured. RESULTS Absolute Tre was lower at baseline in a.m. versus p.m. for all three conditions (a.m.: 36.8°C ± 0.2°C, p.m.: 37.0°C ± 0.2°C, P 0.22) and not different at 60 min between a.m. and p.m. for 23°C-7.5 W·kg-1 (a.m.: 0.83°C ± 0.14°C, p.m.: 0.75°C ± 0.20°C; P = 0.20), 33°C-5.5 W·kg-1 (a.m.: 0.51°C ± 0.14°C, p.m.: 0.47°C ± 0.14°C; P = 0.22), and 33°C-7.5 W·kg-1 (a.m.: 0.77°C ± 0.20°C, p.m.: 0.73°C ± 0.21°C; P = 0.80). The change in local sweat rate was unaffected by time of day (P > 0.16) and not different at 60 min in 23°C-7.5 W·kg-1 (a.m.: 0.67 ± 0.20 mg·cm-2·min-1, p.m.: 0.62 ± 0.21 mg·cm-2·min-1; P = 0.55), 33°C-5.5 W·kg-1 (a.m.: 0.59 ± 0.13 mg·cm-2·min-1, p.m.: 0.57 ± 0.12 mg·cm-2·min-1; P = 0.65), and 33°C-7.5 W·kg-1 (a.m.: 0.91 ± 0.19 mg·cm-2·min-1, p.m.: 0.84 ± 0.15 mg·cm-2·min-1; P = 0.33). Whole-body sweat loss was not different between a.m. and p.m. for 23°C-7.5 W·kg-1 (a.m.: 579 ± 72 g, p.m.: 579 ± 96 g; P = 0.99), 33°C-5.5 W·kg-1 (a.m.: 558 ± 48 g, p.m.: 555 ± 83 g; P = 0.89), and 33°C-7.5 W·kg-1 (a.m.: 796 ± 72 g, p.m.: 783 ± 75 g; P = 0.31). CONCLUSIONS The change in core temperature and sweating throughout a 60-min exercise bout in 23°C and 33°C were unaffected by circadian rhythm during the wake period when exercise intensity was prescribed to elicit comparable rates of Hprod, suggesting that scheduling thermoregulatory exercise trials for the same time of day is unnecessary.

The purpose of this study was to examine the changes in metabolic heat production (Hprod), evaporative heat loss (Hevap), and dry heat loss (Hdry), following heat acclimatization (HAz) and heat acclimation (HA). Twenty-two male endurance athletes (mean ± standard deviation; age, 37 ± 12 y; body mass, 73.4 ± 8.7 kg; height, 178.7 ± 6.8 cm; and VO2max, 57.1 ± 7.2 mL·kg−1·min−1) completed three trials (baseline; post-HAz; and post-HA), which consisted of 60 min steady state exercise at 59 ± 2% velocityVO2max in the heat (ambient temperature [Tamb], 35.2 ± 0.6 °C; relative humidity [%rh] 47.5 ± 0.4%). During the trial, VO2 and RER were collected to calculate Hprod, Hevap, and Hdry. Following the baseline trial, participants completed self-directed outdoor summer training followed by a post-HAz trial. Then, five days of HA were completed over eight days in the heat (Tamb, 38.7 ± 1.1 °C; %rh, 51.2 ± 2.3%). During the HA sessions, participants exercised to maintain hyperthermia (38.50 °C and 39.75 °C) for 60 min. Then, a post-HA trial was performed. There were no differences in Hprod between the baseline (459 ± 59 W·m−2), post-HAz (460 ± 61 W·m−2), and post-HA (464 ± 55 W·m−2, p = 0.866). However, Hevap was significantly increased post-HA (385 ± 84 W·m−2) compared to post-HAz (342 ± 86 W·m−2, p = 0.043) and the baseline (332 ± 77 W·m−2, p = 0.037). Additionally, Hdry was significantly lower at post-HAz (125 ± 8 W·m−2, p = 0.013) and post-HA (121 ± 10 W·m−2, p < 0.001) compared to the baseline (128 ± 7 W·m−2). Hdry at post-HA was also lower than post-HAz (p = 0.049). Hprod did not change following HAz and HA. While Hdry was decreased following HA, the decrease in Hdry was smaller than the increases in Hevap. Adaptations in body heat exchange can occur by HA following HAz.

PURPOSE It is often assumed that a person with a higher mean skin temperature (Tsk) will sweat more during exercise. However, it has not yet been demonstrated whether Tsk describes any individual variability in whole-body sweat rate (WBSR) independently of the evaporative requirement for heat balance (Ereq). METHODS One hundred forty bouts of 2-h treadmill walking completed by a pool of 21 participants (23 ± 4 yr, 174 ± 8 cm, 76 ± 11 kg, 1.9 ± 0.2 m) under up to nine conditions were analyzed. Trials employed varying rates of metabolic heat production (Hprod; 197-813 W), and environmental conditions (15°C, 20°C, 25°C, 30°C; all 50% relative humidity), yielding a wide range of Ereq (86-684 W) and Tsk values (26.9°C-34.4°C). RESULTS The individual variation observed in WBSR was best described using Ereq (in watts; R = 0.784) as a sole descriptor, relative to Ereq (in watts per meter squared; R = 0.735), Hprod (in watts; R = 0.639), Hprod (in watts per meter squared; R = 0.584), ambient air temperature (Ta) (R = 0.263), and Tsk (R = 0.077; all, P < 0.001). A multiple stepwise linear regression included only Ereq (in watts; adjusted R = 0.784), with Tsk not significantly correlating with the residual variance (P = 0.285), independently of Ereq (in watts). Hprod (in watts) had similar predictive strength to Ereq (in watts) at a fixed air temperature, explaining only 5.2% at 30°C, 4.9% at 25°C, 2.7% at 20°C, and 0.5% at 15°C (all, P < 0.001) less variance in WBSR compared with Ereq. However, when data from all ambient temperatures were pooled, Hprod alone was a markedly worse predictor of WBSR than Ereq (R = 0.639 vs 0.784; P < 0.001). CONCLUSIONS Ereq (in watts) explained approximately four-fifths of the individual variation in WBSR over a range of ambient temperatures and exercise intensities, whereas Tsk did not explain any residual variance independently of Ereq.

The aim of this paper is to propose a new non-invasive methodology to estimate thermogenesis in newborns with perinatal asphyxia (PA) undergoing therapeutic hypothermia (TH). Metabolic heat production (with respect to either a neonate’s body mass or its body surface) is calculated from the newborn’s heat balance, estimating all remaining terms of this heat balance utilising results of only non-invasive thermal measurements. The measurement devices work with standard equipment used for therapeutic hypothermia and are equipped with the Global System for Mobile Communications (GSM), which allows one to record and monitor the course of the therapy remotely (using an internet browser) without disturbing the medical personnel. This methodology allows one to estimate thermogenesis in newborns with perinatal asphyxia undergoing therapeutic hypothermia. It also offers information about instantaneous values of the rate of cooling together with values of remaining rates of heat transfer. It also shows the trend of any changes, which are recorded during treatment. Having information about all components of the heat balance one is able to facilitate comparison of results obtained for different patients, in whom these components may differ. The proposed method can be a new tool for measuring heat balance with the possibility of offering better predictions regarding short-term neurologic outcomes and tailored management in newborns treated by TH.

The parameter of human body metabolic rates has been popularly used for the prediction of human heat stress in hot environments. However, most modules use the fixed and estimated metabolic heat production. The aim of this study is to develop the prediction of personal heat stress in dynamic working environments. Based on the framework of the predicted heat stress (PHS) model in ISO 7933, a heart rate-based PHSHR model has been developed using the time-based heart rate index, which is suitable for prediction in situations where metabolic rates are dynamic and there are inter-individual variations. The infinitesimal time unit Δti, has been introduced into the new PHSHR model and all the terms used in the PHS model related to metabolic rates are thus redefined as the function of real-time heart rates. The PHSHR has been validated under 8 experimental combined temperature-humidity conditions in a well-controlled climate chamber. The feature of the PHSHR model is being able to calculate dynamic changes in body metabolism with exposure time. It will be useful to the identification of potential risks of individual workers so to establish an occupational working environment health and safety protection mechanism by means of simultaneous monitoring of workers' heart rates at the personal levels, using advanced sensor technology.

Purpose Heart failure (HF) patients seem to exhibit altered thermoregulatory responses during exercise in the heat. However, the extent to which these responses are altered due to physiological impairments independently of biophysical factors associated with differences in metabolic heat production (H-prod), evaporative heat balance requirements (E-req), and/or body size is presently unclear. Therefore, we examined thermoregulatory responses in 10 HF patients and 10 age-matched controls (CON) similar in body size during exercise at a fixed rate of H-prod and therefore E-req in a 30 degrees C environment.Methods Rectal temperature, local sweat rate, and cutaneous vascular conductance were measured throughout 60 min of cycle ergometry. Whole-body sweat rate was estimated from pre-post nude body weight corrected for fluid intake.Results Despite exercising at the same rate of H-prod (HF, 338 43 W; CON, 323 +/- 31 W; P = 0.25), the rise in rectal temperature was greater (P < 0.01) in HF (0.81 degrees C +/- 0.16 degrees C) than in CON (0.49 degrees C +/- 0.27 degrees C). In keeping with a similar E-req (HF, 285 +/- 40 W; CON, 274 +/- 28 W; P = 0.35), no differences in whole-body sweat rate (HF, 0.45 +/- 0.11 Lh(-1); CON, 0.41 +/- 0.07 Lh(-1); P = 0.38) or local sweat rate (HF, 0.96 +/- 0.17 mgcm(-2)min(-1); CON, 0.79 +/- 0.15 mgcm(-2)min(-1); P = 0.50) were observed between groups. However, the rise in cutaneous vascular conductance was lower in HF than in CON (HF, 0.83 +/- 0.42 aumm Hg-1; CON, 2.10 +/- 0.79 aumm Hg-1; P < 0.01). In addition, the cumulative body heat storage estimated from partitional calorimetry was similar between groups (HF, 154 +/- 106 kJ; CON, 196 +/- 174 kJ; P = 0.44).Conclusions Collectively, these findings demonstrate that HF patients exhibit a blunted skin blood flow response, but no differences in sweating. Given that HF patients had similar body heat storage to that of CON at the same H-prod, their greater rise in core temperature can be attributed to a less uniform internal distribution of heat between the body core and periphery.

The recruitment of thermoeffectors, including thermoregulatory behavior, relative to changes in body temperature has not been quantified in humans. We tested the hypothesis that changes in skin blood flow, behavior, and sweating or metabolic rate are initiated with increasing changes in mean skin temperature (Tskin) in resting humans. While wearing a water-perfused suit, 12 healthy young adults underwent heat (Heat) and cold stress (Cold) that induced gradual changes in Tskin. Subjects controlled the temperature of their dorsal neck to their perceived thermal comfort. Thus neck skin temperature provided an index of thermoregulatory behavior. Neck skin temperature (Tskin), core temperature (Tcore), metabolic rate, sweat rate, and nonglabrous skin blood flow were measured continually. Data were analyzed using segmental regression analysis, providing an index of thermoeffector activation relative to changes in Tskin. In Heat, increases in skin blood flow were observed with the smallest elevations in Tskin ( P < 0.01). Thermal behavior was initiated with an increase in Tskin of 2.4 ± 1.3°C (mean ± SD, P = 0.04), while sweating was observed with further elevations in Tskin (3.4 ± 0.5°C, P = 0.04), which coincided with increases in Tcore ( P = 0.98). In Cold, reductions in skin blood flow occurred with the smallest decrease in Tskin ( P < 0.01). Thermal behavior was initiated with a Tskin decrease of 1.5 ± 1.3°C, while metabolic rate ( P = 0.10) and Tcore ( P = 0.76) did not change throughout. These data indicate that autonomic and behavioral thermoeffectors are recruited in coordination with one another and likely in an orderly manner relative to the comparative physiological cost.

We tested the hypotheses that older adults with cardiovascular co-morbidities will demonstrate greater changes in body temperature and exaggerated changes in blood pressure before initiating thermal behavior. We studied twelve healthy younger adults (Younger, 25 ± 4 y) and six older adults (‘At Risk’, 67 ± 4 y) taking prescription medications for at least two of the following conditions: hypertension, type II diabetes, hypercholesterolemia. Subjects underwent a 90-min test in which they voluntarily moved between cool (18.1 ± 1.8°C, RH: 29 ± 5%) and warm (40.2 ± 0.3°C, RH: 20 ± 0%) rooms when they felt ‘too cool’ (C→W) or ‘too warm’ (W→C). Mean skin and intestinal temperatures and blood pressure were measured. Data were analyzed as a change from pretest baseline. Changes in mean skin temperature were not different between groups at C→W (Younger: +0.2 ± 0.8°C, ‘At Risk’: +0.7 ± 1.8°C, P = 0.51) or W→C (Younger: +2.7 ± 0.6°C, ‘At Risk’: +2.9 ± 1.9°C, P = 0.53). Changes in intestinal temperature were not different at C→W (Younger: 0.0 ± 0.1°C, ‘At Risk’: +0.1 ± 0.2, P = 0.11), but differed at W→C (-0.1 ± 0.2°C vs. +0.1 ± 0.3°C, P = 0.02). Systolic pressure at C→W increased (Younger: +10 ± 9 mmHg, ‘At Risk’: +24 ± 17 mmHg) and at W→C decreased (Younger: −4 ± 13 mmHg, ‘At Risk’: -23 ± 19 mmHg) to a greater extent in ‘At Risk’ (P ≤ 0.05). Differences were also apparent for diastolic pressure at C→W (Younger: −2 ± 4 mmHg, ‘At Risk’: +17 ± 23 mmHg, P < 0.01), but not at W→C (Younger Y: +4 ± 13 mmHg, ‘At Risk’: −1 ± 6 mmHg, P = 0.29). Despite little evidence for differential control of thermal behavior, the initiation of behavior in ‘at risk’ older adults is preceded by exaggerated blood pressure responses.

The New Balance Falmouth Road Race held in Falmouth, Massachusetts, U.S. is a short distance race (11.26 km) that is well-known for high rates of exertional heat stroke (EHS). Previous research has documented the increased EHS rates with hotter and more humid weather conditions, yet did not explore the influence of race pacing on EHS risk. In this study, we leverage 15 years of data to investigate if runners who experienced an EHS moderate their average paces based on weather conditions and if there is a difference in average race pace between participants who experienced an EHS and other runners. Results indicate that runners who experience an EHS do not appear to reduce their average pace with increasing WBGT warning flag categories. In addition, runners who suffer an EHS run at a faster average pace than others, even when controlling for age, gender, race performance, and starting time WBGT. This suggests the important role of metabolic heat production as a risk factor of EHS. Since race pacing is a modifiable risk factor, our findings support the need for race organizers to actively encourage runners to adjust race pacing based on weather conditions.

Endothermic animals regulate body temperature by balancing metabolic heat production and heat exchange with the environment. Heat dissipation is especially important during and immediately after demanding activities such as flapping flight, the most energetically expensive mode of locomotion. As uninsulated appendages, bird bills present a potential avenue for efficient heat dissipation. Puffins possess large bills and are members of the bird family with the highest known flight cost. Here, we used infrared thermography to test whether wild tufted puffins (Fratercula cirrhata) use their bills to dissipate excess heat after energetically-expensive flight. Both bill surface temperature and the proportion of total heat exchange occurring at the bill decreased with time since landing, suggesting that bills are used to dissipate excess metabolic heat. We propose that bill size in puffins may be shaped by opposing selective pressures that include dissipating heat after flight and conserving heat in cold air and water temperatures.

Many ideas have been put forward for the adaptive value of the cassowary casque; and yet, its purpose remains speculative. Homeothermic animals elevate body temperature through metabolic heat production. Heat gain must be offset by heat loss to maintain internal temperatures within a range for optimal performance. Living in a tropical climate, cassowaries, being large bodied, dark feathered birds, are under thermal pressure to offload heat. We tested the original hypothesis that the casque acts as a thermal window. With infrared thermographic analyses of living cassowaries over an expansive range of ambient temperatures, we provide evidence that the casque acts as a thermal radiator, offloading heat at high temperatures and restricting heat loss at low temperatures. Interestingly, at intermediate temperatures, the casque appears thermally heterogeneous, with the posterior of the casque heating up before the front half. These findings might have implications for the function of similar structures in avian and non-avian dinosaurs.

Caenorhabditis elegans is one of the most attractive model organisms in biomedical research for understanding human diseases and for drug testing at a whole-organism level, since many biological pathways and genes have been conserved between itself and humans. The nematode is sufficiently complex so that complex biological questions can be addressed, yet the organism is still simple enough to be used in high-content in vivo assays. In this work, we present new microfluidic and MEMS-based tools enabling the characterization of C. elegans worms and embryos in vivo. In a first part of this thesis, we measured the metabolic heat production of small C. elegans larval populations using a custom nanocalorimetric system. Our system is based on microfabricated Si thermopile sensors which are integrated with PDMS microfluidic chips. In addition to versatile fluidic manipulation of samples on-chip, our microfluidic approach allows confining worm populations close to the Si sensor surface, thus enabling high sensitivity of the assays. Our results indicate an increase of the heat production per worm body volume from the L2 to the L3 larval stages, and a significant decrease from the L3 to the L4 stages. Additionally, we investigated the metabolic heat production of the larval populations during maximal respiratory capacity after treatment with a mitochondrial uncoupling agent. Depending on the larval stage, inducing uncoupled respiration causes an increase of the metabolic heat production ranging from 55% up to 95% with respect to untreated worms. Our experiments demonstrated that nanocalorimetry is a direct and highly-sensitive technique that can be combined with other analytical methods to open the way to a more holistic understanding of fundamental biological processes. In a second study, we present a new microfluidic worm culture system with integrated luminescence-based sensing of the on-chip oxygen concentration for measuring the oxygen uptake of C. elegans worms. The microfluidic chip was fabricated in OSTE+ to allow reliable measurement of the dissolved oxygen and the fabrication of high-resolution microstructures down to the &m-range. Our microfluidic approach allows confining a single nematode from the L4 stage in a culture chamber over a time span of up to 7 days. An automated protocol for feeding and for performing oxygen consumption rate (OCR) measurements during the worm development was applied. We found an increase of OCR values from the L4 stage to the adult worm, and a continuous decrease as the worm ages. In addition, we performed a C. elegans metabolic assay using a mitochondrial uncoupling agent, which increased OCR by a factor of ¿ 2 when compared to basal respiration rates. Treatment with sodium azide inhibited mitochondrial respiration and returned OCR values to zero. The biomechanical properties of the C. elegans embryonic eggshell are largely unknown. In a third study, we developed a new method to study its mechanical properties. In our work, we use cellular force microscopy (CFM), a technique that combines micro-indentation with high-resolution force sensing approaching that of atomic force microscopy, to quantitatively study the mechanical properties of the eggshell of living C. elegans embryos. ...

The exoskeleton as functional wearable equipment has been increasingly used in working environments. However, the effects of wearing an exoskeleton on human thermal responses are still unknown. In this study, 10 male package handlers were exposed to 10 °C (COLD) and 25 °C (TEMP) ambient temperatures while performing a 10 kg lifting task (LIFTING) and sedentary (REST) both with (EXO) and without the exoskeleton (WEXO). Thermal responses, including the metabolic rate and mean skin temperature (MST), were continuously measured. Thermal comfort, thermal sensation and sweat feeling were also recorded. For LIFTING, metabolic heat production is significant decrease with the exoskeleton support. The MST and thermal sensation significantly increase when wearing the exoskeleton, but thermal discomfort and sweating are only aggravated in TEMP. For REST, MST and thermal sensation are also increased by the exoskeleton, and there is no significant difference in the metabolic rate between EXO and WEXO. The thermal comfort is significantly improved by wearing the exoskeleton only in COLD. The results suggest that the passive exoskeleton increases the local clothing insulation, and the way of wearing reduces the “pumping effect”, which makes a difference in the thermal response between COLD and TEMP. Designers need to develop appropriate usage strategies according to the operative temperature.