Sweat Rate Research Articles

Developing a test device to analyze heat transfer combined with radiant exposure and continuous liquid sweating through thermal protective clothing

Human perspiration significantly affects heat and mass transfer in clothing systems and absorbs thermal energy on the skin, especially in radiant exposure and high-intensity work. However, few testing devices simulate human sweating for assessing heat transfer under thermal radiation exposure. Thus, a test device that could realistically simulate specific sweat rates was developed to evaluate the influence of continuous sweating on thermal protective performance (TPP). The TPP of single-layer fabrics at dry (No-sweating) and three constant sweating rates was studied based on the calibrated tester. It was indicated that the new testing apparatus effectively evaluated fabrics’ dry and wet thermal protective properties. Furthermore, compared to continuous sweating, the traditional pre-wet method may overestimate the TPP of the single-layer fabric depending on sweating rates. The continuous sweat rates played a dual role in the second-degree burn time and absorbed thermal energy, which is related to the moisture management performance of fabrics. The research provides an effective method to characterize the TPP of materials under continuous sweating/wetting, which will help optimize clothing performance and update relative standards.

Evaluation of fatigue in young female adults due to repeated exposure to heat in summer and cold in winter.

The magnitude of fatigue (MF) from psychological and physiological responses during repeated exposure to heat in summer and during repeated exposure to cold in winter was evaluated to test two hypotheses on fatigue models. The first hypothesis is that exposure time (ET, min) would be a factor determining the MF and the second hypothesis is that the same fatigue models as a function of the number of exposure repetitions (NR) could be applied to both repeated exposure to heat in summer and cold in winter. In summer, eight young adult female subjects with clothing insulation (Icl, clo) of 0.3 clo first stayed in the control room at 26 ℃ for 15min, moved to the main testing room at 30 ℃ for 25min, 33°C for 15min, or 36 ℃ for 10min, and then returned to the control room. The product of air temperature difference (ΔTa, ℃) and ET was designed to be almost equal among these latter three conditions. The exposure was repeated five times. In winter, the same female subjects with Icl of 0.84 clo first stayed in the control room at 24 ℃ for 15min, moved to the main testing room at 18 ℃ for 30min, 15 ℃ for 20min, or 12 ℃ for 15min, and then returned to the control room. Again, the product of ΔTa and ET was designed to be equal among these latter three conditions. The exposure was repeated four times. The scores of subjective fatigue feeling (SFF) and salivary amylase value (SAV) were recorded when the subjects returned to the control room. Tympanic temperature, skin temperatures and local sweat rates (Sw, mg/cm2/min) at chest, forearm, front thigh, and front shin, and ECG were continuously monitored, except for Sw in the winter experiment. In the summer experiment, the SFF showed a threshold value at ΔTa = 4 ℃ but continuously increased with NR at ΔTa = 7 ℃ and 10 ℃. It was not correlated with ECG variables, but was positively correlated with SAV (R2 = 0.50) and the mean Sw (R2 = 0.76) at ΔTa = 7 ℃ and 10 ℃. In the winter experiment, the SFF showed a threshold value at ΔTa = - 6 ℃ but continuously increased with NR at ΔTa = - 9 ℃ and - 12 ℃. It was correlated with SAV at ΔTa = - 9 ℃ (R2 = 0.77) and score of LF: HF ratio at ΔTa = - 6 ℃ and - 9 ℃ (R2 = 0.49). It was confirmed that ET may be related to the MF and that different fatigue models may be applied dependent on ΔTa during repeated exposure to heat in summer and during repeated exposure to cold in winter. Thus, the two hypotheses were verified.

Influences of moisture management performance and continuous sweat rate on heat transfer through firefighting clothing under radiant exposure

Human continuous sweating can adjust the thermal protective performance (TPP) of clothing for firefighters by controlling moisture distribution and transfer, which can provide extra thermal protection or injury. To accurately evaluate the heat transfer performance, a calibrated sweat simulant sensor was applied to investigate the influence of moisture management performance (MMP) of materials on the TPP under continuous sweating at a low-level thermal radiative intensity of 8.5 kW/m2. The results revealed that the dual role of continuous sweating on the TPP depended on sweat rate, fabric layers, material properties of the inner layer, and exposure time. The MMP could reduce the heat transfer performance at a high sweat rate for prolonged work, leading to a maximum decrease of absorbed thermal energy up to 16.93% and 49.03% for single and multi-layer fabrics, respectively. The second-degree skin burn occurred in half of the exposure process, and the skin burn time was reduced by up to 5.57% for multi-layer fabrics with good MMP due to the limited increase in thermal conductivity during initial exposure. This study provides a more comprehensive understanding of accurately assessing thermal damage and offers some guidance for selecting the inner layer materials of firefighting protective clothing for various firefighting conditions.

Versatile sweat bioanalysis on demand with hydrogel-programmed wearables

Wearable sweat bioanalysis is promising for non-invasive diagnostics of diseases. However, collection of representative sweat samples without disturbing daily life and wearable bioanalysis of targets that are clinically significant are still challenging. In this work, we report on a versatile method for the sweat bioanalysis. The method is based on a thermoresponsive hydrogel which can imperceptibly absorb slowly secreted sweat without stimulation such as heat or sport exercise. The wearable bioanalysis is accomplished by programmed electric heating of hydrogel modules to 42°C to release absorbed sweat or preloaded reagents into a microfluidic detection channel. Using our method, not only one-step detection of glucose but also multi-step immunoassay of cortisol is accomplished within 1 h, even at a very low sweat rate. Our test results are also compared with those obtained with conventional blood samples and stimulated sweat samples to evaluate the applicability of our method to non-invasive clinical practice.

Carbohydrate, but not fat, oxidation is reduced during moderate-intensity exercise performed in 33 vs. 18°C at matched heart rates.

Exposure to environmental heat stress increases carbohydrate oxidation and extracellular heat shock protein 70 (HSP70) concentrations during endurance exercise at matched absolute, external work rates. However, a reduction in absolute work rate typically occurs when unacclimated enduranceathletes train and/or compete in hot environments. We sought to determine the effect of environmental heat stress on carbohydrate oxidation rates and plasma HSP70 expression during exercise at matched heart rates (HR). Ten endurance-trained, male cyclists performed two experimental trials in an acute, randomised, counterbalanced cross-over design. Each trial involved a 90-min bout of cycling exercise at 95% of the HR associated with the first ventilatory threshold in either 18 (TEMP) or 33°C (HEAT), with ~ 60% relative humidity. Mean power output (17 ± 11%, P < 0.001) and whole-body energy expenditure (14 ± 8%, P < 0.001) were significantly lower in HEAT. Whole-body carbohydrate oxidation rates were significantly lower in HEAT (19 ± 11%, P = 0.002), while fat oxidation rates were not different between-trials. The heat stress-induced reduction in carbohydrate oxidation was associated with the observed reduction in power output (r = 0.64, 95% CI, 0.01, 0.91, P = 0.05) and augmented sweat rates (r = 0.85, 95% CI, 0.49, 0.96, P = 0.002). Plasma HSP70 and adrenaline concentrations were not increased with exercise in either environment. These data contribute to our understanding of how moderate environmental heat stress is likely to influence substrate oxidation and plasma HSP70 expression in an ecologically-valid model of endurance exercise.

Serum, interstitialand sweat ATP in humans exposed to heat stress: Insights into roles of ATP in the heat loss responses.

Hyperthermia increases intravascular adenosine triphosphate (ATP) and is associated with greater hyperthermia-induced cutaneous vasodilation. Hyperthermia may also increase skin interstitial fluid ATP thereby activating cutaneous vascular smooth muscle cells and sweat glands. We evaluated the hypothesis that whole-body heating would increase skin interstitial fluid ATP, and this response would be associated with an increase in cutaneous vasodilation and sweating. Nineteen (8 females) young adults underwent whole-body heating using a water-perfusion suit to increase core temperature by ~1°C during which time cutaneous vascular conductance (CVC, ratio of laser-Doppler blood flow to mean arterial pressure) and sweat rate (ventilated capsule technique) were measured at four forearm skin sites to minimize between-site variations. Dialysate from the skin sites were collected via intradermal microdialysis. Heating increased serum ATP, CVC, and sweat rate (all p ≤ 0.031). However, heating did not modulate dialysate ATP (median, baseline vs. end-heating: 2.38 vs. 2.70 nmol/ml) (p = 0.068), though the effect size was moderate (Cohen's d = 0.566). While the heating-induced increase in CVC was not correlated with changes in serum ATP (r = 0.439, p = 0.060), we observed a negative correlation (rs = -0.555, p = 0.017) between dialysate ATP and CVC. We did not observe a significant correlation between the heating-induced sweating and serum, dialysate, or sweat ATP (rs = 0.091 to -0.322, all p ≥ 0.222). Altogether, we showed that passive heating increases ATP in blood and possibly skin interstitial fluid, with the latter potentially blunting cutaneous vasodilation. However, ATP does not appear to modulate sweating.

Inkjet-Printed Soft Intelligent Medical Bracelet for Simultaneous Real-Time Sweat Potassium (K+), Sodium (Na+), and Skin Temperature Analysis

Truly wearable, fully flexible, multi-parametric sweat analysis with soft and socially discrete packaging offers tremendous potential to enable the next generation of non-invasive digital biomarkers analysis. Several examples of miniaturized potentiometric ion selective electrodes (ISE) have been proposed. However, several challenges remain unsolved concerning their long-term stability due to variations in physical sweat parameters. We hypothesize that the simultaneous monitoring of such parameters (e.g., skin-surface temperature, sweat rate, and pH) may pave the way for accurate and robust sweat biomarker analysis. Therefore, we propose a flexible multiparameter sensory interface fabricated on Kapton polyimide (PI) foil with high-resolution inkjet printing using silver nanoparticles (AgNPs). A facile controlled drop-casting of a custom synthesized ion-selective membrane ensures the selectivity of the biosensing. Next, we interfaced the fabricated sensory array with a custom-designed compact flexible biosignals conditioning embedded system, which enables system calibration, data processing, and wireless data transmission to a smartphone device. Later, we validate the proposed system in simultaneous sweat multi-ion (K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> and Na <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ) and skin-surface temperature recording. After that, we characterize the system by embedding the smart medical bracelet in a soft microfluidic platform to mimic <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> analysis on the body. Overall, the reported results represent the fundamental evidence proof for the development of the wearable multimodal sweat parameter analyzer.

Occupational Heat Stress and Kidney Health in Salt Pan Workers

Work in heat affects millions of workers. Although kidney function in agricultural workers is increasingly researched, nonagricultural studies are scarce. In coastal salt pans, the absence of occupational exposures to pesticides and other toxicants allows assessment of heat stress alone. Seven Indian salt pans were surveyed from 2017 to 2020. Job-specific workload was assessed. Heat stress was characterized as exceeding the wet bulb globe temperature (WBGT)-threshold limit value (TLV) for high and moderate workloads. Preshift and postshift heart rates (HRs), tympanic temperatures, and urine specific gravity (USG) were measured for 352 workers, as were sweat rates (SwR), serum creatinine (SCr), serum uric acid, and urine dipstick. Estimated glomerular filtration rate (eGFR; ml/min per 1.73 m2) was computed. Heat-strain symptoms were assessed using questionnaires. The mean WBGT was 30.5 ± 1.3 °C (summer) and 27.8 ± 1.9 °C (winter). Water intake during the workday was low, median was one Litre, and most workers (87%) exceeded the TLV for heat stress. Dehydration-related symptoms were frequent in those with high-heat stress, as were cross-shift increases in temperature (≥1°C; 15%), a high USG (≥1.020; 28%), and a high SwR (≥1 l/h; 53%). An eGFR of 60 to 89 ml/min per 1.73 m2 was observed in 41% of all workers examined, and 7% had eGFR below 60 ml/min per 1.73 m2. The odds ratio for eGFR<90 ml/min per 1.73 m2 in workers exceeding the TLV, compared to workers below this limit, adjusted for age and gender was 2.9 (95% CI: 1.3-6.4). Workplace interventions to prevent heat stress and dehydration in the salt pans and other at-risk industries are urgently required. The findings strengthen the notion that high-heat stress and limited hydration is a risk factor for kidney dysfunction.

Determining behavioural-based risk to SLODs of urban public open spaces: Key performance indicators definition and application on established built environment typological scenarios

A behavioural-based approach can be used to assess how users’ reactions to surrounding environmental conditions can alter the urban Built Environment (BE) risk to Slow Onset Disasters (SLODs). Public Open Spaces (POSs) in the BE are relevant scenarios, due to micro-climate-related stress, users’ vulnerabilities (e.g., age, health frailty) and exposure time. Simulation methods can support behavioural-based risk-assessment, but results are generally site-specific. Performing analysis on BE Typologies (BETs) can improve robustness, since BETs represent archetypes from real-world scenarios. This work adopts a behavioural-based approach to evaluate time-dependant users’ risks of POSs in different BETs due to SLODs-related stress (i.e., heat, air pollution). UTCI and AQI values are mapped within each BET. Users’ distributions are then calculated depending on thermal acceptability correlations. Key Performance Indicators are developed associating users’ distribution to SLODs effects on health (i.e., sweat rate, water loss; health affection rate probability). The approach is applied to Italian BETs, under one relevant climate, rating their heat and air pollution risks. Results suggest critical conditions for toddlers. In detail, about 2-hour high heat exposure could result in dehydration, while 1-hour exposure to low NO2 concentration could result in +1% mortality probability. This approach could potentially support decision-makers on BE risk-assessment.

Fluid balance during physical work in the heat is not modified by the menstrual cycle when fluids are freely available.

We tested the hypothesis that women may be more at risk of becoming dehydrated during physical work in the heat in the early follicular phase (EF), compared with the late follicular (LF) and mid-luteal (ML) phases of the menstrual cycle when allowed free access to drink. Twelve healthy, eumenorrheic, unacclimated women (26 ± 5 yr) completed three trials (EF, LF, and ML phases) involving 4 h of exposure to 33.8 ± 0.8 °C, 54 ± 1% relative humidity. Each hour, participants walked on a treadmill for 30 min at a rate of metabolic heat production of 338 ± 9 W. Participants drank a cool, flavor-preferred non-caloric sport drink ad libitum. Nude body weight was measured pre- and post-exposure, and percent changes in body weight loss were interpreted as an index of changes in total body water. Total fluid intake and urine output were measured and sweat rate was estimated from changes in body mass corrected for fluid intake and urine output. Fluid intake was not different between phases (EF: 1,609 ± 919 mL; LF: 1,902 ± 799 mL; ML: 1,913 ± 671; P = 0.202). Total urine output (P = 0.543) nor sweat rate (P = 0.907) differed between phases. Percent changes in body mass were not different between phases (EF: -0.5 ± 0.9%; LF: -0.3 ± 0.9%; ML: -0.3 ± 0.7%; P = 0.417). This study demonstrates that the normal hormonal fluctuations that occur throughout the menstrual cycle do not alter fluid balance during physical work in the heat.NEW & NOTEWORTHY The effect of the menstrual cycle on fluid balance during physical work in the heat when fluids are freely available is unknown. This study demonstrates that fluid balance is not modified in women across three distinct phases of the menstrual cycle during physical work in the heat These results indicate that when women have free access to cool fluid during physical work in the heat, they respond similarly across all three phases to maintain fluid homeostasis across the menstrual cycle.

Non-Invasive Multiparametric Approach To Determine Sweat-Blood Lactate Bioequivalence.

Many sweat-based wearable monitoring systems have been recently proposed, but the data provided by those systems often lack a reliable and meaningful relation to standardized blood values. One clear example is lactate, a relevant biomarker for both sports and health sectors, with a complex sweat-blood bioequivalence. This limitation decreases its individual significance as a sweat-based biomarker. Taking into account the insights of previous studies, a multiparametric methodology has been proposed to predict blood lactate from non-invasive independent sensors: sweat lactate, sweat rate, and heart rate. The bioequivalence study was performed with a large set of volunteers (>30 subjects) in collaboration with sports institutions (Institut Nacional d'Educació Física de Catalunya, INEFC, and Centre d'Alt Rendiment, CAR, located in Spain). A neural network algorithm was used to predict blood lactate values from the sensor data and subject metadata. The developed methodology reliably and accurately predicted blood lactate absolute values, only adding 0.3 mM of accumulated error when compared to portable blood lactate meters, the current gold standard for sports clinicians. The approach proposed in this work, along with an integrated platform for sweat monitoring, will have a strong impact on the sports and health fields as an autonomous, real-time, and continuous monitoring tool.

Predicting the body core temperature of recreational athletes at the end of a 10 km self-paced run under environmental heat stress.

What is the central question of this study? The aim was to identify the factors predicting the body core temperature of athletes at the end of a 10km self-paced run in a hot environment. What is the main finding and its importance? Hyperthermia in athletes subjected to self-paced running depends on several factors, highlighting the integrated control of core temperature during exercise under environmental heat stress. Five of the seven variables that significantly predicted core temperature are not invasive and, therefore, practical for use outside the laboratory environment: heart rate, sweat rate, wet-bulb globe temperature, running speed and maximal oxygen consumption. Measurement of body core temperature (Tcore ) is paramount to determining the thermoregulatory strain of athletes. However, standard measurement procedures of Tcore are not practical for extended use outside the laboratory environment. Therefore, determining the factors that predict Tcore during a self-paced run is crucial for creating more effective strategies to minimize the heat-induced impairment of endurance performance and reduce the occurrence of exertional heatstroke. The aim of this study was to identify the factors predicting Tcore values attained at the end of a 10km time trial (end-Tcore ) under environmental heat stress. Initially, we extracted data obtained from 75 recordings of recreationally trained men and women. Next, we ran hierarchical multiple linear regression analyses to understand the predictive power of the following variables: wet-bulb globe temperature, average running speed, initial Tcore , body mass, differences between Tcore and skin temperature (Tskin ), sweat rate, maximal oxygen uptake, heart rate and change in body mass. Our data indicated that Tcore increased continuously during exercise, attaining 39.6±0.5°C (mean±SD) after 53.9±7.5min of treadmill running. This end-Tcore value was primarily predicted by heart rate, sweat rate, differences between Tcore and Tskin , wet-bulb globe temperature, initial Tcore , running speed and maximal oxygen uptake, in this order of importance (β power values corresponded to 0.462, -0.395, 0.393, 0.327, 0.277, 0.244 and 0.228, respectively). In conclusion, several factors predict Tcore in athletes subjected to self-paced running under environmental heat stress. Moreover, considering the conditions investigated, heart rate and sweat rate, two practical (non-invasive) variables, have the highest predictive power.

Digital Companion for Elders in Tracking Health and Intelligent Recommendation Support using Deep Learning

Ambient assisted living (AAL) facilitates the daily routines of elderly people, particularly those who have clinical difficulties or physical limitations. The latest technologies like distributed compuring,internet of things (IoT) and machine learning pave the ground for the creation of an effective automated tracker which aids elder citizens to live independently. The suggested system is attempted to design a wearable that monitors the blood glucose level through sweat. To achieve high accuracy, the proposed system uses ambient sensing and deep learning based techniques. It places a strong emphasis on calculating the health index by taking into account numerous disease-related characteristics or vitals such as heart rate, blood pressure, SpO2, blood glucose level, respiration rate, sweat rate, uric acid, and temperature. From the wearable device designed the vital signs are gathered, further environmental sensors and camera fixed around the person continually monitors the behavioral pattern along with physiological signals. This ensures the improved accuracy of health state prediction from its conventional models in place. The key advantage of this device is that it may be held and operated anyplace without interrupting their day-to-day tasks because the device is to be cheap, reliable and speedy.

Fluid Balance, Sodium Losses and Hydration Practices of Elite Squash Players during Training.

Elite squash players are reported to train indoors at high volumes and intensities throughout a microcycle. This may increase hydration demands, with hypohydration potentially impairing many key performance indicators which characterise elite squash performance. Consequently, the main aim of this study was to quantify the sweat rates and sweat [Na+] of elite squash players throughout a training session, alongside their hydration practices. Fourteen (males = seven; females = seven) elite or world class squash player's fluid balance, sweat [Na+] and hydration practices were calculated throughout a training session in moderate environmental conditions (20 ± 0.4 °C; 40.6 ± 1% RH). Rehydration practices were also quantified post-session until the players' next training session, with some training the same day and some training the following day. Players had a mean fluid balance of -1.22 ± 1.22% throughout the session. Players had a mean sweat rate of 1.11 ± 0.56 L·h-1, with there being a significant difference between male and female players (p < 0.05), and a mean sweat (Na+) of 46 ± 12 mmol·L-1. Players training the following day were able to replace fluid and sodium losses, whereas players training again on the same day were not. These data suggest the variability in players hydration demands and highlight the need to individualise hydration strategies, as well as training prescription, to ensure players with high hydration demands have ample time to optimally rehydrate.

Alkali metals (Na, K) doped ZnO/CuO composite films for real-time tracking of sweat loss

Real-time sweat rate monitoring provides clinically proper directives for preventive medicine and disease diagnosis. This research represents an attempt to develop a semiconductor-based nanostructured sensor for monitoring sweat rate using a ZnO/CuO composite thin film. A series of alkali metals (sodium, Na; potassium, K) doped ZnO/CuO composite samples were fabricated on soda lime glass substrates by the Successive Ionic Layer Adsorption and Reaction method. The sweat solution sensing response characterization exhibited promising sensing behavior under room conditions. The Na- and K-doped samples showed a pronounced response at low and high concentrations of the sweat solution. While the undoped composite film responds to the high concentration sweat solution (117.90 mM) with a sensitivity of 4.10, this value increases up to 9.15 for the 2.0% Na-doped samples. In addition, the response time shortens from 6 s to 4 s for 2.0% Na substitutions. Pristine, 2.0% Na and 2.0% K-substituted ZnO/CuO composites exhibit great linearity with linear regression ranges, R2, of 0.958, 0.971, and 0.984, respectively. We concluded that doping of ZnO/CuO composites with alkali metals Na and K is a good candidate for real-time tracking of sweat loss as biological evidence.

Influence of topical capsaicin cream on thermoregulation and perception during acute exercise in the heat

PurposeDetermine if topical capsaicin, a transient receptor potential vanilloid heat thermoreceptor activator, alters thermoregulation and perception when applied topically prior to thermal exercise. MethodsTwelve subjects completed 2 treatments. Subjects walked (1.6 m s−1, 5% grade) for 30 min in the heat (38 °C, 60% relative humidity) with either a capsaicin (0.025% capsaicin) or control cream applied to the upper (shoulder to wrist) and lower (mid-thigh to ankle) limbs covering ∼50% body surface area. Skin blood flow (SkBF), sweat (rate, composition), heart rate, temperature (skin, core), and perceived thermal sensation were measured prior to and during exercise. ResultsThe relative change in SkBF was not different between treatments at any time point (p = 0.284). There were no differences in sweat rate between the capsaicin (1.23 ± 0.37 L h−1) and control (1.43 ± 0.43 L h−1, p = 0.122). There were no differences in heart rate between the capsaicin (122 ± 38 beats·min−1) and control (125 ± 39 beats·min−1, p = 0.431). There were also no differences in weighted surface (p = 0.976) or body temperatures (p = 0.855) between the capsaicin (36.0 ± 1.7 °C, 37.0 ± 0.8 °C, respectively) and control (36.0 ± 1.6 °C, 36.9 ± 0.8 °C, respectively). The capsaicin treatment was not perceived as hotter than the control treatment until minute 30 of exercise (2.8 ± 0.4, 2.5 ± 0.5, respectively, p = 0.038) ConclusionsTopical capsaicin application does not alter whole-body thermoregulation during acute exercise in the heat despite perceiving the treatment as hotter late in exercise.

Short-term heat acclimation protocols for an aging population: Systematic review.

Elderly and sedentary individuals are particularly vulnerable to heat related illness. Short-term heat acclimation (STHA) can decrease both the physical and mental stress imposed on individuals performing tasks in the heat. However, the feasibility and efficacy of STHA protocols in an older population remains unclear despite this population being particularly vulnerable to heat illness. The aim of this systematic review was to investigate the feasibility and efficacy of STHA protocols (≤twelve days, ≥four days) undertaken by participants over fifty years of age. Academic Search Premier, CINAHL Complete, MEDLINE, APA PsycInfo, and SPORTDiscus were searched for peer reviewed articles. The search terms were; (heat* or therm*) N3 (adapt* or acclimati*) AND old* or elder* or senior* or geriatric* or aging or ageing. Only studies using primary empirical data and which included participants ≥50 years of age were eligible. Extracted data includes participant demographics (sample size, gender, age, height, weight, BMI and [Formula: see text]), acclimation protocol details (acclimation activity, frequency, duration and outcome measures taken) and feasibility and efficacy outcomes. Twelve eligible studies were included in the systematic review. A total of 179 participants took part in experimentation, 96 of which were over 50 years old. Age ranged from 50 to 76. All twelve of the studies involved exercise on a cycle ergometer. Ten out of twelve protocols used a percentage of [Formula: see text] or [Formula: see text] to determine the target workload, which ranged from 30% to 70%. One study-controlled workload at 6METs and one implemented an incremental cycling protocol until Tre was reached +0.9°C. Ten studies used an environmental chamber. One study compared hot water immersion (HWI) to an environmental chamber while the remaining study used a hot water perfused suit. Eight studies reported a decrease in core temperature following STHA. Five studies demonstrated post-exercise changes in sweat rates and four studies showed decreases in mean skin temperature. The differences reported in physiological markers suggest that STHA is viable in an older population. There remains limited data on STHA in the elderly. However, the twelve studies examined suggest that STHA is feasible and efficacious in elderly individuals and may provide preventative protection to heat exposures. Current STHA protocols require specialised equipment and do not cater for individuals unable to exercise. Passive HWI may provide a pragmatic and affordable solution, however further information in this area is required.

Effects of heat exposure on the thermoregulatory responses of young children

The purpose of this study was to determine whether young children's thermoregulation during heat exposure varies with age and body size. A total of 34 young children (aged 6 months–8 years)–18 boys and 16 girls–participated in the study. They were divided into five groups according to age (<1 year, 1 year, 2–3 years, 4–5 years, and 8 years). The participants sat for 30 min in a 27°C, 50% rh room, then moved to a 35°C, 70% rh room and remained seated for at least 30 min. They then returned to the first 27°C room and remained stationary for 30 min. Rectal temperature (Tre) and skin temperature (Tsk) were continuously recorded, and the amount of whole-body sweat rate (SR) was measured. Local SR of the back and upper arm were collected with filter paper to calculate local sweating volume, and Na + concentration was measured later. The smaller the age, the significantly greater the increase in Tre. There was no significant difference in the amount of whole-body SR and the increase in Tsk during the heating among the five groups. Furthermore, there was no significant difference in whole-body SR per increase in Tre during heating between the five groups, but a significant difference was found in back local SR per increase in Tre with age. Difference in local SR between upper arm and back was observed at age 2 years and above, and difference in Na+ concentrations in sweat was observed at age 8 years. The development of thermoregulatory responses with growth was observed. The results indicate that the thermoregulatory response is disadvantaged by immature mechanisms and small body size in younger children.

Skin-Interfaced Superhydrophobic Insensible Sweat Sensors for Evaluating Body Thermoregulation and Skin Barrier Functions.

Monitoring sweat rate is vital for estimating sweat loss and accurately measuring biomarkers of interest. Although various optical or electrical sensors have been developed to monitor the sensible sweat rate, the quantification of the insensible sweat rate that is directly related to body thermoregulation and skin barrier functions still remains a challenge. This work introduces a superhydrophobic sweat sensor based on a polyacrylate sodium/MXene composite sandwiched between two superhydrophobic textile layers to continuously measure sweat vapor from insensible sweat with high sensitivity and rapid response. The superhydrophobic textile on a holey thin substrate with reduced stiffness and excellent breathability allows the permeation of sweat vapor, while preventing the sensor from being affected by the external water droplets and internal sensible sweat. Integrating the insensible sweat sensor with a flexible wireless communication and powering module further yields a standalone sensing system to continuously monitor insensible sweat rates at different body locations for diverse application scenarios. Proof-of-concept demonstrations on human subjects showcase the feasibility to continuously evaluate the body's thermoregulation and skin barrier functions for the assessment of thermal comfort, disease conditions, and nervous system activity. The results presented in this work also provide a low-cost device platform to detect other health-relevant biomarkers in the sweat (vapor) as the next-generation sweat sensor for smart healthcare and personalized medicine.

Tape‐Free, Digital Wearable Band for Exercise Sweat Rate Monitoring

AbstractMonitoring sweat secretion rate is essential for uncovering underlying physical conditions like hyperhidrosis, mental stress, and neural disorders. Often, flexible microfluidic sweat rate monitoring devices use tape as a means of attachment to the skin to tightly seal the collection area. While these single‐use, adhesive‐backed devices have lightweight and thin interfaces for mounting on the skin, their form factor complicates their potential integration with available commercial wearables, such as smartwatches. Here, a tape‐free device, consisting of a 3D‐printed sweat collector with a concave surface that is strapped onto the skin to form an effective seal, is presented. The materials, structure, and dimensions of the sweat collector are optimized for conformal device‐to‐skin contact and efficient capture of sweat. The collector is interfaced with a fluidic microchannel with embedded electrodes for continuous digital monitoring of sweat rate. Long‐term exercise‐induced local sweat rate from multiple body locations in both multi‐subject and longitudinal studies is measured, depicting the correlation between the measured sweat profile and total body fluid loss. The simple installation procedure and reusability of this tape‐free device make it a good candidate for integration with the band of a watch.