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The objective of our study was to assess the impact of heat stress on hydration and cognition among outdoor workers in hot environment. Area heat stress assessments were measured using Quest Temp WBGT monitor. Sweat rate for dehydration and reaction time for acute cognitive processing were recorded using standard procedures. Heat stress measurements ranged from 23.8 °C – 42 °C. More than 50 % of the workers had high sweat rate (>1.2 L/h) when exposed to high environmental temperatures. Positive correlation was obtained between WBGT, sweat rate and reaction time which indicates that hyperthermia has an impact on neural network processing. Heart rate and reaction time also increased with rise in WBGT and heavy physical activity. There was impairment of cognitive functions (reaction time) under heat stress conditions. Hence, reaction time can be used to assess the short-term impact of heat stress on neural modulation and will help to plan effective intervention strategies to reduce morbidity and mortality among workers. [ABSTRACT FROM AUTHOR]

Objectives: The ACSM recommends drinking to avoid loss of body mass >2% during exercise to avert compromised performance. Our study aimed to assess the level of dehydration in elite runners following a city marathon in a tropical environment.Design: Prospective cohort design.Methods: Twelve elite runners (6 males, 6 females; age 24-41 y) had body mass measured to the nearest 0.01kg in their race attire immediately before and after the 2017 Standard Chartered Singapore Marathon 2017. Body mass change was corrected for respiratory water loss, gas exchange, and sweat retained in clothing, and expressed as % of pre-race mass (i.e. % dehydration).Results: Data are expressed as means±SD (range). Dry bulb temperature and humidity were 27.9±0.1°C (27.4-28.3°C) and 79±2% (73-82%). Finish time was 155±10min (143-172min). Male runners finishing positions ranged from 2-12 out of 7627 finishers, whilst female runners placed 1-8 out of 1754 finishers. Body mass change (loss) and % dehydration for all runners were 2.5±0.5kg (1.8-3.5kg) and 4.6±0.9% (3.6-6.8%). Male runners experienced body mass loss of 2.8±0.5kg and 4.9±1.2% while females experienced body mass loss of 2.1±0.2kg and 4.3±0.6%.Conclusions: Despite experiencing dehydration (4.6% body mass loss) two-fold higher than current fluid replacement guidelines recommend (≤2%), elite male and female runners performed successfully and without medical complication in a hot weather marathon. [ABSTRACT FROM AUTHOR]

This study investigated the separate and combined effects of skin cooling and cold fluid ingestion on the alleviation of heat strain when wearing protective firefighting clothing at an air temperature of 30°C with 50%RH. A vest with the dual functions of cooling and providing sports drink supply (1.2% body mass) was developed. Eight males participated in the following four conditions: control [CON], drinking only [DO], cooling only [CO], and both cooling and drinking [CD]. The results showed that rectal (Tre), mean skin temperature (Tsk) and heart rate (HR) during recovery were lower for CD than for CON (p<0.05), while no significant differences between the four conditions were found during exercise. CO significantly reduced mean Tsk and HR and improved thermal sensation, whereas DO was effective for relieving thirst and lowering HR in recovery. In summary, the combined effect of skin cooling and fluid ingestion was synergistically manifested in Tre, Tsk and thermal sensation in recovery. Practitioner Summary: The present results provide data on a novel vest that contributes to alleviating firefighters' heat strain. Because a cooling vest after melting may be a burden for firefighters, this study indicates a practical way to reduce the additional weight load of the vest by drinking the melted fluid of the cooling packs. [ABSTRACT FROM AUTHOR]

Abstract Quantification of physiological state is a key issue for human physiological safety in high temperature environments. In this study, the fuzzy comprehensive evaluation method is introduced into the physiological state evaluation in indoor high temperature environments. Five physiological parameters (skin temperature, rectal temperature, heart rate, systolic pressure and sweat rate) are selected as the evaluation indexes, then the membership functions of the evaluation indexes are proposed to determine their membership degrees related to the evaluation grades. Based on the sensitivity analysis method, the sensitivity weights of above physiological parameters are determined. Then a comprehensive evaluation model for quantifying the physiological state is established. And physiological state score (PSS) is proposed to rank the safety level of the physiological state. Finally, the evaluation model is applied and verified in a case study. The results indicate that the weights of each physiological index change with the ambient temperature. The weights of the skin temperature and the rectal temperature account for a relatively large proportion, ranging from 81.8% to 88.5%. The safety levels ranked by the physiological state score are similar to the heat strain levels ranked by the physiological strain index values. The comparison results demonstrate the effectiveness and reliability of the proposed approach. The application of fuzzy comprehensive evaluation and sensitivity analysis provides a new scientific method for quantifying the human physiological state. This study can provide guidance for the physiological state evaluation and safety protection of relevant people in indoor high temperature environments. Highlights • Human physiological state in indoor high temperature environments is quantified. • Sensitivity analysis method is adopted to obtain the dynamic weights of parameters. • The weights of each physiological index change with the ambient temperature. • The weights of skin temperature and rectal temperature account for a major proportion. • The case study verifies the reasonability and scientificness of the proposed method. [ABSTRACT FROM AUTHOR]

Thermal strain indices have been developed to assess the risk level of heat strain on workers in occupational settings. To date, no comprehensive study has validated these indicators. The present study aims to investigate the validity of eighteen empirical heat stress indices in predicting the physiological parameters of workers under various occupational and environmental conditions. This cross-sectional study was conducted with 201 male employees working in warm environments. First, Individual and background information was collected. After participants had rested for 30 min, their heart rate and tympanic temperature were measured. People then returned to their workplace and started their routine work. At the end of 90 min, workers' heart rate and tympanic temperature were measured again. Additionally, researchers estimated their metabolic rate and clothing thermal insulation. Environmental parameters were also collected including dry temperature, wet temperature, globe temperature, relative humidity and air flow speed at 30, 60 and 90 min time points. Additional information was recorded to calculate environmental indicators. Then, the values of each of the environmental indicators were calculated. Finally, the validity of each index was evaluated under these different conditions. Results showed that highest regression coefficients with tympanic temperature were CET (0.6822), TSI (0.6697), WBGT (0.6692), and ESI (0.6415) indices, respectively. The greatest regression coefficients with heart rate belonged to TSI (0.4687), OT (0.4545), CET (0.4449), and Teq (0.4449) indices, respectively. Based on these results, the highest diagnostic accuracies of ROC curves for tympanic temperature were related to indices of WBGT, CET, and HI with AUC of 0.913, 0.912, and 0.910, respectively. In total, the results showed that the two indices of WBGT and CET have the strongest validity among the empirical indices. However, each of these empirical indices has the best accuracy under specific conditions. Therefore, the development of new indices is required for the precise assessment of heat strain under various conditions. • WBGT and CET have the best validity among the empirical indices. • Globe temperature and Total metabolism have the highest correlation with tympanic temperature and heart rate, respectively. • Highest regression coefficients with tympanic temperature and heart rate assigned to CET and TSI, respectively. [ABSTRACT FROM AUTHOR]

During the COVID-19 pandemic, many health care workers (HCWs) were required to perform medical tasks in outdoor settings while wearing medical protective clothing. Although personal protective equipment (PPE) is virus-resistant, it can impair the heat dissipation of HCWs. Hence, HCWs face significant heat stress risks while working outdoors. There is an urgent need to find effective ways to reduce heat stress in order to protect the health and safety of HCWs who wear personal protective equipment. In this study, the applicability of two ice-bag cooling vests (ICVs) with varying cooling areas for HCWs wearing PPE was evaluated. Based on the effects of the two ICVs on the thermal comfort of HCWs working outdoors, a cooling strategy for HCWs wearing PPE in outdoor environments was demonstrated. In addition, the gender difference in cooling demand was examined. Eighteen participants took part in the outdoor field study. The results indicated that using ice-bag cooling vests could reduce sweat loss by 27.3–39.4 % (0.09–0.13 kg) and the mean skin temperature by 0.25–0.95 °C. Cooling the back is more effective than cooling the abdomen in reducing overall thermal sensation. The area of discomfort corresponds to the area of sweating. Sweating is an important factor influencing the comfort of HCWs. ICVs could provide some comfort relief for 15–30 min. Gender differences in thermal sensation disappear after 30 min of exposure. The ICVs are recommended for use in future emergency situations. The findings of this study are beneficial to the health and safety of outdoor-working HCWs wearing personal protective equipment. • Ice-bag cooling vests could reduce sweat loss by 27.3–39.4 %. • Ice-bag cooling vests could reduce mean skin temperatures by 0.25–0.95 °C. • Back cooling is more effective than abdomen in reducing thermal sensation. • Ice-bag vests extended HCW thermal comfort by 15–30 min. • Gender differences in thermal sensation vanished after 30 min of exposure. [ABSTRACT FROM AUTHOR]

This study aims to determine the optimal cooling intervention of a newly designed hybrid cooling vest. 10 males participated in three random experiments, i.e., cooling vest worn during exercise and recovery (ALL-COOL), cooling vest worn during passive recovery (REC-COOL) and control (CON) in a climatic chamber controlled at 37 °C temperature, 60% relative humidity, 0.3 m/s air velocity, and 450 W/m 2 solar radiation to simulate the summer working environment of construction sites. The work–rest protocol was adopted to compare the effectiveness of ALL-COOL and REC-COOL. Physiological (core temperature, skin temperature, and heart rate) and perceptual (ratings of perceived exertion, thermal sensation, and wetness sensation) parameters were measured during the entire heat exposure. The cooling vest worn during exercise improved thermal comfort but did not alleviate heat strain or prolong work duration, as shown by the significant reduction in skin temperature and thermal sensation in ALL-COOL compared with CON (p < 0.05; d = 0.53–0.95, moderate to large effect). The cooling vest used during recovery largely hastened thermoregulatory and cardiovascular strain recovery, as indicated by the significant reduction of body core temperature and heart rate (p < 0.01; d = 0.82–1.04, large effect). Findings implied that post-exercise cooling by the cooling vest can be an appropriate and practical countermeasure in reducing body heat strain in construction sites where repeated bouts of construction work are required. [ABSTRACT FROM AUTHOR]

Electric fans are proposed to mitigate indoor heat stress during heatwaves. Fan cooling threshold temperatures were determined by biophysical models. However, such models could only account for sweating adjustment and disregarded evident cardiovascular impairment in older adults. This study demonstrated the contribution of cardiovascular function adjustment to core temperature responses. Results revealed that focusing just on sweating adjustment greatly underestimated the actual heat stress experienced by older adults. It is not recommended to use biophysical models to determine the threshold temperature of electric fan use for older adults during heatwaves because cardiovascular adjustment was not possible. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the effects of head hair on thermoregulatory responses when cooling the head under heat stress. Eight young males participated in six experimental conditions: normal hair (100-130 mm length) and cropped hair (5 mm length) with three water inlet temperatures of 10, 15, and 20°C. The head and neck of subjects were cooled by a liquid perfused hood while immersing legs at 42°C water for 60 min in a sitting position at the air temperature of 28°C with 30% RH. The results showed that heat removal from the normal hair condition was not significantly different from the cropped hair condition. Rectal and mean skin temperatures, and sweat rate showed no significant differences between the normal and cropped hair conditions. Heat extraction from the head was significantly greater in 10°C than in 15 or 20°C cooling (p<0.05) for both normal and cropped hair, whereas subjects preferred the 15°C more than the 10 or 20°C cooling regimen. These results indicate that the selection of effective cooling temperature is more crucial than the length of workers' hair during head cooling under heat stress, and such selection should be under the consideration of subjective perceptions with physiological responses. [ABSTRACT FROM AUTHOR]

Elderly indoors can be subject to considerable heat strain during heat waves. We investigated if a short indoor acclimation (HA) program leads to improved resilience to heat. Although full HA takes about ten days, the main changes occur in the first days, leading to reduced heat strain with similar stress. This study investigates changes after 3 days HA in 8 elderly (>75 y) and 8 young (20–30 y) females. The pre-test (Monday) and post-test (Friday) was a 20-min 50 W cycle exercise test in 35 °C/40% relative humidity (RH); the indoor preparation program or HA consisting of one hour exercise in the same climate aimed at reaching a gastrointestinal temperature ( T gi ) of 38 °C. HA did not result in any changes in T gi , mean skin temperature, heart rate, weight loss or thermal sensation. The elderly felt more fatigued but evaporated 28% less sweat than the young group during the tests. We conclude that 3-day HA for one hour daily is insufficient to cause physiological benefits in young and elderly females. [ABSTRACT FROM AUTHOR]

Heat strain may cause heat-related illness and reduce work efficiency as well as represent individual differences. To simulate individualized physiological responses of the human body to various conditions, an individualized predicted heat strain (IPHS) model accounting for individual difference factors including height, weight, gender, and age was proposed based on the widely used predicted heat strain (PHS) model. Subsequently, the IPHS model was validated against the PHS model and human trials (total, 3 cases, 9 conditions, and 51 subjects) from the literature. The results indicated that the maximal difference between simulations and measurements in terms of the core temperature, mean skin temperature, and sweating loss was no more than 1.0 °C, 1.6 °C, and 10 g respectively, for all cases. Specifically, an excellent prediction performance of the IPHS model was found, with a lower maximal difference for the core temperature (PHS: 0.98 °C vs. IPHS: 0.55 °C) and sweating loss (PHS: 335.7 g vs. IPHS: 8.9 g) in Case 1. The maximal difference for core temperature was only 0.59 °C under high metabolism (320 W/m2) conditions in Case 2. Furthermore, the prediction performance of the IPHS model varied with the environment and gender. The proposed model performed better on steady-state skin temperature simulations for women than for men in Case 3. It was concluded that the proposed model can predict individualized core temperature, mean skin temperature, and sweating loss with acceptable accuracy for the studied cases. The proposed model can provide insights into personalized heat management and occupational safety protection. • An individualized predicted heat strain model (IPHS) was proposed. • The IPHS model can predict core temperature, skin temperature, and sweating loss. • The IPHS model improved prediction performance than the PHS model. • The prediction accuracy of the IPHS model varied with environments and gender. [ABSTRACT FROM AUTHOR]

The article discusses the impact of climate change to the productivity of the workers in harvesting rice in India. It highlights the effect of heat exposure to the workers including high risk of heat stroke and limit work productivity. It notes that heat exposure contributes to the impairment of human physiological function and health.

The article provides information on a study to determine the validity of infrared tympanic membrane temperature for the assessment of heat strain of workers in hot environments. In the study the thermodynamics of infrared tympanic temperature was compared with rectal temperature under the various environmental conditions. The study concludes that using infrared tympanic temperature is valid as a thermal index in evaluating the heat strain of workers wearing impermeable protective coveralls.

Heatwaves are one of the most dangerous natural hazards causing more than 166,000 deaths from 1998–2017. Their frequency is increasing, and they are becoming more intense. Electric fans are an efficient, and sustainable solution to cool people. They are, for most applications, the cheapest cooling technology available. However, many national and international health guidelines actively advise people not to use them when indoor air temperatures exceed the skin temperature, approximately 35 °C. We used a human energy balance model, to verify the validity of those recommendations and to determine under which environmental (air temperature, relative humidity, air speed and mean radiant temperature) and personal (metabolic rate, clothing) conditions the use of fans would be beneficial. We found that current guidelines are too restrictive. Electric fans can be used safely even if the indoor dry-bulb temperature exceeds 35 °C since they significantly increase the amount of sweat that evaporates from the skin. The use of elevated air speeds (0.8 m/s) increases the critical operative temperature at which heat strain is expected to occur by an average of 14 °C for relative humidity values above 22 %. We also analyzed the most extreme weather events from 1990 to 2014 recorded in the 115 most populous cities worldwide, and we determined that in 93 of them the use of fans would have been beneficial. We developed a free, open-source, and easy-to-use online tool to help researchers, building practitioners, and policymakers better understand under which conditions electric fans can be safely used to cool people. [Display omitted] • Electric fans can safely be used even if the air temperature is higher than 35 °C. • Electric fans can cool people even when air temperature exceeds skin temperature. • Health guidelines should not discourage people from using fans during heatwaves. • Health guidelines regarding the use of electric fans should be reviewed. • Our open-source tool calculates humidity-dependent temperature thresholds. [ABSTRACT FROM AUTHOR]

Summary: This study examined the effects of active warm up on thermoregulatory responses and intermittent-sprint cycle performance in hot conditions (35.5±0.6°C, RH 48.7±3.4%). Eight trained males performed a 36-min, intermittent-sprint test (IST) after no (WUP 0), 10-min (WUP 10) or 20-min warm up (WUP 20). The IST contained 2-min blocks consisting of a 4-s sprint, 100s active recovery and 20s passive rest. Twice during the IST, there was a repeated-sprint bout (RSB) comprising five, 2-s sprints separated by ∼20s. There were no significant differences between trials for mean work (3870±757 versus 4028±562 versus 3804±494Jsprint−1), peak power (W) or work decrement (%). However, mean work was significantly less in RSB2 than RSB1 for WUP 20 only (P <0.05). Plasma lactate was significantly higher after active warm up (WUP 20=WUP 10>WUP 0; P <0.05), but not significantly different between conditions following either RSB. Rectal temperature (T re) was significantly higher after active warm up (37.0±0.3 versus 37.3±0.3 versus 37.7±0.1°C for WUP0, WUP10 and WUP20, respectively) and throughout the IST. The longer active warm up resulted in a greater increase in T re and was associated with a decrease in short-term repeated-sprint ability (with incomplete recovery), but not prolonged, intermittent-sprint performance in the heat. As active warm up did not improve performance (<40min), team-sport athletes may minimise changes in T re (and the likelihood of heat illness) by avoiding excessive warm up when competing in the heat. [Copyright &y& Elsevier]

The article examines the effects of different types of personal cooling equipment (PCE) on the alleviation of heat strain during red pepper harvest simulated in a climatic chamber in Korea. The study shows that rectal temperature (Tre) is effectively maintained under 38°C by wearing PCE. The study suggests that heat strain of farm workers can be eliminated by the combination of the cooling vest, a scarf and a brimmed hat.