Plateau in Core Temperature during Shorter but Not Longer Work/Rest Cycles in Heat.

This study compared physiological responses to two work/rest cycles of a 2:1 work-to-rest ratio in a hot environment. In a randomized crossover design, fourteen participants completed 120 min of walking and rest in the heat (36.3 ± 0.6 °C, 30.2 ± 4.0% relative humidity). Work/rest cycles were (1) 40 min work/20 min rest [40/20], or (2) 20 min work/10 min rest [20/10], both completing identical work. Core temperature (Tc), skin temperature (Tsk), heart rate (HR), nude body mass, and perception of work were collected. Comparisons were made between trials at equal durations of work using three-way mixed model ANOVA. Tc plateaued in [20/10] during the second hour of work (p = 0.93), while Tc increased in [40/20] (p < 0.01). There was no difference in maximum Tc ([40/20]: 38.08 ± 0.35 °C, [20/10]: 37.99 ± 0.27 °C, p = 0.22) or end-of-work Tsk ([40/20]: 36.1 ± 0.8 °C, [20/10]: 36.0 ± 0.7 °C, p = 0.45). End-of-work HR was greater in [40/20] (145 ± 25 b·min-1) compared to [20/10] (141 ± 27 b·min-1, p = 0.04). Shorter work/rest cycles caused a plateau in Tc while longer work/rest cycles resulted in a continued increase in Tc throughout the work, indicating that either work structure could be used during shorter work tasks, while work greater than 2 h in duration may benefit from shorter work/rest cycles to mitigate hyperthermia.

Effects of palm cooling on thermoregulatory-related and subjective indicators during exercise in a hot environment.

Palm cooling is a simple and easily implemented intervention strategy during exercise. We aimed to examine the effects of bilateral palm cooling before and during exercise on thermoregulatory-related and subjective indicators in a hot environment. Ten active men (age: 21 ± 1 years; height 172.2 ± 5.7 cm; weight 67.4 ± 7.2 kg) underwent three experimental trials at the same time of the day, consisting of palm cooling with 12°C (ICE12°C), palm cooling with 0°C (ICE0°C) where vasoconstriction is supposed to occur, and control (CON) trials. After 30 min rest at ambient temperature, participants performed 20 min exercise at 33°C, 60% relative humidity. Rectal temperature, skin temperature, rate of perceived exertion, heart rate, local sweat rate, oxygen uptake, carbon dioxide production, and respiratory exchange ratio did not differ between the trials. Thermal sensation and comfort were lower in the ICE12°C and ICE0°C trials than in the CON trial, but the ICE0°C trial showed a longer duration of cold sensation than the ICE12°C trial. Palm cooling at 12°C and 0°C improved thermal sensation and thermal comfort during exercise in a hot environment, although there was no effect on core body temperature, sweating, and cardiorespiratory function. Bilateral palm cooling at 12°C and 0°C improve subjective indicators during exercise in a hot environment and these effects are slightly greater at 0°C than at 12°C cooling, while having no effect on thermoregulatory-related indicators. These results suggest that bilateral palm cooling at lower temperatures may safely reduce the perception of warmth during exercise in a hot environment.

Nanowired Delivery of Cerebrolysin with Mesenchymal Stem Cells Attenuates Heat Stress-Induced Exacerbation of Neuropathology Following Brain Blast Injury.

Blast brain injury (bBI) following explosive detonations in warfare is one of the prominent causes of multidimensional insults to the central nervous and other vital organs injury. Several military personnel suffered from bBI during the Middle East conflict at hot environment. The bBI largely occurs due to pressure waves, generation of heat together with release of shrapnel and gun powders explosion with penetrating and/or impact head trauma causing multiple brain damage. As a result, bBI-induced secondary injury causes breakdown of the blood-brain barrier (BBB) and edema formation that further results in neuronal, glial and axonal injuries. Previously, we reported endocrine imbalance and influence of diabetes on bBI-induced brain pathology that was significantly attenuated by nanowired delivery of cerebrolysin in model experiments. Cerebrolysin is a balanced composition of several neurotrophic factors, and active peptide fragment is capable of neuroprotection in several neurological insults. Exposure to heat stress alone causes BBB damage, edema formation and brain pathology. Thus, it is quite likely that hot environment further exacerbates the consequences of bBI. Thus, novel therapeutic strategies using nanodelivery of stem cell and cerebrolysin may further enhance superior neuroprotection in bBI at hot environment. Our observations are the first to show that combined nanowired delivery of mesenchymal stem cells (MSCs) and cerebrolysin significantly attenuated exacerbation of bBI in hot environment and induced superior neuroprotection, not reported earlier. The possible mechanisms of neuroprotection with MSCs and cerebrolysin in bBI are discussed in the light of current literature.

Co-administration of Nanowired Oxiracetam and Neprilysin with Monoclonal Antibodies to Amyloid Beta Peptide and p-Tau Thwarted Exacerbation of Brain Pathology in Concussive Head Injury at Hot Environment.

Environmental temperature adversely affects the outcome of concussive head injury (CHI)-induced brain pathology. Studies from our laboratory showed that animals reared at either cold environment or at hot environment exacerbate brain pathology following CHI. Our previous experiments showed that nanowired delivery of oxiracetam significantly attenuated CHI-induced brain pathology and associated neurovascular changes. Military personnel are the most susceptible to CHI caused by explosion, blasts, missile or blunt head trauma leading to lifetime functional and cognitive impairments affecting the quality of life. Severe CHI leads to instant death and/or lifetime paralysis. Military personnel engaged in combat operations are often subjected to extreme high or low environmental temperature zones across the globe. Thus, further exploration of novel therapeutic agents at cold or hot ambient temperatures following CHI are the need of the hour. CHI is also a major risk factor for developing Alzheimer's disease by enhancing amyloid beta peptide deposits in the brain. In this review, effect of hot environment on CHI-induced brain pathology is discussed. In addition, whether nanodelivery of oxiracetam together with neprilysin and monoclonal antibodies (mAb) to amyloid beta peptide and p-tau could lead to superior neuroprotection in CHI is explored. Our results show that co-administration of oxiracetam with neprilysin and mAb to AßP and p-tau significantly induced superior neuroprotection following CHI in hot environment, not reported earlier.

Nanowired Delivery of Mesenchymal Stem Cells with Antioxidant Compound H-290/51 Reduces Exacerbation of Methamphetamine Neurotoxicity in Hot Environment.

Military personnel are often exposed to hot environments either for combat operations or peacekeeping missions. Hot environment is a severe stressful situation leading to profound hyperthermia, fatigue and neurological impairments. To avoid stressful environment, some people frequently use methamphetamine (METH) or other psychostimulants to feel comfortable under adverse situations. Our studies show that heat stress alone induces breakdown of the blood-brain barrier (BBB) and edema formation associated with reduced cerebral blood flow (CBF). On the other hand, METH alone induces hyperthermia and neurotoxicity. These effects of METH are exacerbated at high ambient temperatures as seen with greater breakdown of the BBB and brain pathology. Thus, a combination of METH use at hot environment may further enhance the brain damage-associated behavioral dysfunctions. METH is well known to induce severe oxidative stress leading to brain pathology. In this investigation, METH intoxication at hot environment was examined on brain pathology and to explore suitable strategies to induce neuroprotection. Accordingly, TiO2-nanowired delivery of H-290/51 (150 mg/kg, i.p.), a potent chain-breaking antioxidant in combination with mesenchymal stem cells (MSCs), is investigated in attenuating METH-induced brain damage at hot environment in model experiments. Our results show that nanodelivery of H-290/51 with MSCs significantly enhanced CBF and reduced BBB breakdown, edema formation and brain pathology following METH exposure at hot environment. These observations are the first to point out that METH exacerbated brain pathology at hot environment probably due to enhanced oxidative stress, and MSCs attenuate these adverse effects, not reported earlier.

Water consumption patterns impact hydration markers in males working in accordance with the National Institute for Occupational Safety and Health recommendations.

The impact of water consumption bolus volume and frequency on hydration biomarkers during work in the heat is unknown. In a randomized, crossover fashion, eight males consumed either 500 mL of water every 40 min or 237 mL of water every 20 min during 2 hr of continuous walking at 6.4 kph, 1.0% grade in a 34 °C/30% relative humidity environment, followed by 2 hr of rest. Hydration biomarkers and variables were assessed pre-work, post-work, and after the 2 hr recovery. There were no differences in body mass between trials at any time point (all p > 0.05). Percent change in plasma volume during work was not different when 237 mL of water was repeatedly consumed (-1.6 ± 8.2%) compared to 500 mL of water (-1.3 ± 3.0%, p = 0.92). Plasma osmolality was maintained over time (p = 0.55) with no difference between treatments (p = 0.21). When consuming 500 mL of water repeatedly, urine osmolality was lower at recovery (205 ± 108 mOsmo/L) compared to pre-work (589 ± 95 mOsmo/L, p < 0.01), different from repeatedly consuming 237 mL of water which maintained urine osmolality from pre-work (548 ± 144 mOsmo/L) through recovery (364 ± 261 mOsmo/L, p = 0.14). Free water clearance at recovery was greater with repeated consumption of 500 mL of water (1.2 ± 1.0 mL/min) compared to 237 mL of water (0.4 ± 0.8 mL/min, p = 0.02). Urine volume was not different between treatments post-work (p = 0.62), but greater after 2 hr of recovery when repeatedly consuming 500 mL of water compared to 237 mL (p = 0.01), leading to greater hydration efficiency upon recovery with repeated consumption of 237 mL of water (68 ± 12%) compared to 500 mL (63 ± 14%, p = 0.01). Thirst and total gastrointestinal symptom scores were not different between treatments at any time point (all p > 0.05). Body temperatures and heart rate were not different between treatments at any time point (all p > 0.05). Drinking larger, less frequent water boluses or drinking smaller, more frequent water boluses are both reasonable strategies to promote adequate hydration and limit changes in body mass in males completing heavy-intensity work in the heat.

Cold water immersion of the hand and forearm during half-time improves intermittent exercise performance in the heat.

The present study aimed to investigate the effect of cold water immersion of the hand and forearm during half-time (HT) on intermittent exercise performance and thermoregulation by imitating intermittent athletic games in the heat. In a randomized crossover design, 11 physically active men performed the first half (first and second block) and second half (third and fourth block) intermittent cycling exercise protocol, which consisted of a 5-s maximal power pedalling (body weight × 0.075 kp) every minute separated by 25-s of unloaded pedalling and rest (30 s) in the heat (33°C, 50% relative humidity). The two-halves were separated by a 15-min HT. During HT, the participants were assigned to the CON (sedentary resting) or COOL (immersion of hands and forearms in cold water at 15-17°C) condition. The mean power output in the second half was significantly greater (third and fourth block: p < 0.05) in the COOL than in the CON condition. Moreover, there was a significant decrease in the rectal (0.54 ± 0.17°C, p < 0.001) and mean skin (1.86 ± 0.34°C, p < 0.05) temperatures of the COOL condition during HT. Furthermore, the heart rate (16 ± 7 bpm, p < 0.05) and skin blood flow (40.2 ± 10.5%, p < 0.001) decreased at the end of HT in the COOL condition. In the second half, thermal sensation was more comfortable in the COOL condition (p < 0.001). Cold water immersion of the hand and forearm during HT improved physiological and reduced perceived heat stress. Moreover, it prevented a reduction in intermittent exercise performance in the second half.

Association between physiological and perceptual heat strain while wearing stab-resistant body armor.

In this study, we explored the association between physiological and perceptual heat strain while wearing stab-resistant body armor (SRBA). Human trials were performed on ten participants in warm and hot environments. Physiological responses (core temperature, skin temperature, and heart rate), and perceptual responses (thermal sensation vote, thermal comfort vote, restriction of perceived exertion (RPE), wetness of skin, and wetness of clothing) were recorded throughout the trials, and subsequently, the physiological strain index (PSI), and perceptual strain index (PeSI) were calculated. The results indicated that the PeSI showed a significant moderate association with the PSI, and was capable of predicting PSI for low (PSI = 3) and high (PSI = 7) levels of physiological strain with the areas under the curves of 0.80 and 0.64, respectively. Moreover, Bland-Altman analysis indicated that the majority of the PSI ranged within the 95% confidence interval, and the mean difference between PSI and PeSI was 0.14 ± 2.02 with the lower 95% limit and upper 95% limit being -3.82 to 4.10, respectively. Therefore, the subjective responses could be used as an indicator for predicting physiological strain while wearing SRBA. This study could provide fundamental knowledge for the usage of SRBA, and the development of physiological heat strain assessment.

Effects of Mdivi-1 on Extending the Golden Treatment Time following Hemorrhagic Shock in Hot Environment in Rats.

It is found that a hot environment aggravates hemorrhagic shock-induced internal environment and organ dysfunction. Meanwhile mitochondria show over-fission. Whether inhibition of mitochondrial fission benefits from the early treatment of hemorrhagic shock under a hot environment is unclear. An uncontrolled hemorrhagic shock model in rats is used, and the effects of mitochondrial fission inhibitor mdivi-1 on mitochondrial function, organ function, and survival rate of rats are measured. The results show that 0.1-3 mg/kg mdivi-1 antagonizes hemorrhagic shock-induced mitochondrial fragment. In addition, mdivi-1 improves mitochondrial function, and alleviates hemorrhagic shock-induced oxidative stress and inflammation under a hot environment. Further studies show that 0.1-3 mg/kg Mdivi-1 reduces blood loss, and maintains a mean artery pressure (MAP) of 50-60 mmHg before bleeding-stops after hemorrhagic shock, compared with single Lactate Ringer's (LR) resuscitation. Notably, 1 mg/kg of Mdivi-1 extends the time of hypotensive resuscitation to 2-3 h. During 1 or 2 h of ligation, Mdivi-1 prolongs survival time and protects vital organ function by rescuing mitochondrial morphology and improving mitochondrial function. These results suggest Mdivi-1 is suitable for the early treatment of hemorrhagic shock under a hot environment and can extend the golden treatment time to 2-3 hour for hemorrhagic shock under a hot environment.

Development of a Core Body Thermometer Applicable for High-Temperature Environment Based on the Zero-Heat-Flux Method.

Monitoring core body temperature (CBT) allows observation of heat stress and thermal comfort in various environments. By introducing a Peltier element, we improved the zero-heat-flux core body thermometer for hot environments. In this study, we performed a theoretical analysis, designed a prototype probe, and evaluated its performance through simulator experiments with human subjects. The finite element analysis shows that our design can reduce the influence of external temperature variations by as much as 1%. In the simulator experiment, the prototype probe could measure deep temperatures within an error of less than 0.1 °C, regardless of outside temperature change. In the ergometer experiment with four subjects, the average difference between the prototype probe and a commercial zero-heat-flux probe was +0.1 °C, with a 95% LOA of -0.23 °C to +0.21 °C. In the dome sauna test, the results measured in six of the seven subjects exhibited the same trend as the reference temperature. These results show that the newly developed probe with the Peltier module can measure CBT accurately, even when the ambient temperature is higher than CBT up to 42 °C.

A Single Dose of Ibuprofen Impacts IL-10 Response to 164-km Road Cycling in the Heat.

Purpose: The purpose was to determine the effect of a single-dose prophylactic ibuprofen use before a 164-km road cycling event in high ambient temperature on the circulating cytokine and leukocyte responses. Methods: Twenty-three men (53 ± 8 y, 172.0 ± 22.0 cm, 85.1 ± 12.8 kg, 19.6 ± 4.4% body fat) completed a 164-km self-paced recreational road cycling event in a hot, humid, sunny environment (WBGT = 29.0 ± 2.9°C) after consuming 600 mg of ibuprofen (n = 13) or a placebo (n = 10). Blood samples were obtained one to two hours before (PRE) and immediately after (POST) the event, and analyzed for concentrations of circulating cytokines interleukins (IL)-1ß, IL-2, IL-4, IL-5, IL-6, IL-7, IL-8, IL-10, IL-12, IL-13, GM-CSF, IFN-γ, and TNF-α and leukocytes (total leukocytes, granulocytes, monocytes, and lymphocytes). Results: Event completion time was 400.2 ± 74.8 min. Concentrations of all cytokines (except IL-1ß, IL-2, IL-5, IL-12, GM-CSF, and IFN-γ) and of all leukocyte subsets increased from PRE to POST. Ibuprofen ingestion attenuated the increase in IL-10 (86% increase with Ibuprofen; 270% increase with placebo). Conclusions: Consuming 600 mg of Ibuprofen prior to a 164-km road cycling event in a hot-humid environment attenuates exercise-induced increases in the concentration of the anti-inflammatory cytokine IL-10, but does not alter the effect of the exercise event on concentrations of other circulating cytokines or leukocyte subset concentrations.

Identification of Glu-D1 Alleles and Novel Marker-Trait Associations for Flour Quality and Grain Yield Traits under Heat-Stress Environments in Wheat Lines Derived from Diverse Accessions of Aegilops tauschii.

Heat stress during grain filling is considered one of the major abiotic factors influencing wheat grain yield and quality in arid and semi-arid regions. We studied the effect of heat stress on flour quality and grain yield at moderate and continuous heat stress under natural field conditions using 147 lines of wheat multiple synthetic derivatives (MSD) containing Aegilops tauschii introgressions. The study aimed to identify the marker-trait associations (MTAs) for the quality traits and grain yield under heat-stress conditions and identify stress-resilient germplasm-combining traits for good flour quality and grain yield. The MSD lines showed considerable genetic variation for quality traits and grain yield under heat-stress conditions; some lines performed better than the recurrent parent, Norin 61. We identified two MSD lines that consistently maintained relative performance (RP) values above 100% for grain yield and dough strength. We found the presence of three high-molecular-weight glutenin subunits (HMW-GSs) at the Glu-D1 locus derived from Ae. tauschii, which were associated with stable dough strength across the four environments used in this study. These HMW-GSs could be potentially useful in applications for future improvements of end-use quality traits targeting wheat under severe heat stress. A total of 19,155 high-quality SNP markers were used for the genome-wide association analysis and 251 MTAs were identified, most of them on the D genome, confirming the power of the MSD panel as a platform for mining and exploring the genes of Ae. tauschii. We identified the MTAs for dough strength under heat stress, which simultaneously control grain yield and relative performance for dough strength under heat-stress/optimum conditions. This study proved that Ae. tauschii is an inexhaustible resource for genetic mining, and the identified lines and pleiotropic MTAs reported in this study are considered a good resource for the development of resilient wheat cultivars that combine both good flour quality and grain yield under stress conditions using marker-assisted selection.

Do the National Institute for Occupational Safety and Health recommendations for working in the heat prevent excessive hyperthermia and body mass loss in unacclimatized males?

The National Institute for Occupational Safety and Health recommendations for work in the heat suggest workers consume 237 mL of water every 15-20 min and allow for continuous work at heavy intensities in hot environments up to 34 °C and 30% relative humidity. The goal was to determine whether the National Institute for Occupational Safety and Health recommendations prevented core temperature from exceeding 38.0 °C and greater than 2% body mass loss during heavy-intensity work in the heat. Eight males consumed 237 mL of water every 20 min during 2 hr of continuous heavy-intensity walking (6.4 kph, 1% grade) in a 34 °C/30% relative humidity environment, in accordance with the National Institute for Occupational Safety and Health recommendations. Projected core temperature and percent body mass loss were calculated for 4 and 8 hr of continuous work. Core temperature rose from baseline (36.8 ± 0.3 °C) to completion of 2 hr of work (38.1 ± 0.6 °C, p < 0.01), with two participants reaching the 38.0 °C threshold. Projected core temperatures remained elevated from baseline (p < 0.01), did not change from 2 to 4 hr (38.1 ± 0.7 °C, p > 0.99) and 4 to 8 hr (38.1 ± 0.8 °C, p > 0.99), respectively, and one participant exceeded 38.0 °C at 4 to 8 hr. There was no change in body mass loss over time (p > 0.99). During 2 hr of continuous heavy-intensity work in the heat, 75% of participants did not reach 38 °C core temperature and 88% did not reach 2% body mass loss when working to National Institute for Occupational Safety and Health recommendations.

Environmental enrichment in dairy goats in a semi-arid region: Thermoregulatory and behavioral responses.

This study aimed to evaluate the effect of environmental enrichment on the thermoregulatory and behavioral responses of goats raised in semi-arid conditions. 12 Saanen goats lactating, aged between 2 and 4 years, clinically healthy with a mean body weight of 31.4 ± 1.65 kg and body condition score between 2.0 and 2.5 were used. The types of enriched environments used were: 1) without environmental enrichment (control); 2) classical music;3) PET plastic bottles with corn;4) suspended tires;5) logs of wood; and 6) all objects simultaneously. The air temperature, black globe tempeature and humidity index, and radiant heat load were higher (P < 0.05) during treatment with all objects simultaneously. The respiratory rate (RR) was higher (P = 0.001) in the control treatment compared to those with environmental enrichment. The rectal temperature (RT) was higher in the control and acoustic groups (P < 0.05), however it was lower with all objects. The coat surface temperature (CST) was higher (P < 0.01) in the control group and lower in the treatment with music, tires, logs of wood, PET bottles and all objects. The behaviors lying down, drinking water, urination, ruminating while standing, and defecating were similar (P > 0.05) between treatments. The first two discriminant functions were significant (F1 and F2: P < 0.001) and discriminated 93.40% of the data variation. A static pattern was observed in the classification of goats in their group of origin for thermoregulatory and behavioral responses when a single type of enrichment was used with the formation of two more groups: (i) goats which had access to all enrichments simultaneously; and (ii) the control group. The offer of the diversity of various objects for environmental enrichment positively contributed to the thermoregulatory and behavioral responses, thereby providing well-being to the animals.

A potential wearable solution for preventing heat strain in workplaces: The cooling effect and the total evaporative resistance of a ventilation jacket.

The increase in average seasonal temperatures has an impact in the occupational field, especially for those sectors whose work activities are performed outdoors (agricultural, road and construction sectors). Among the adaptation measures and solutions developed to counteract occupational heat strain, personal cooling garments represent a wearable technology designed to remove heat from the human body, enhancing human performance. This study aims to investigate the effectiveness and the cooling power of a specific cooling garment, i.e. a ventilation jacket, by quantifying the evaporative heat losses and the total evaporative resistance both when worn alone and in combination with a work ensemble, at three adjustments of air ventilation speed. Standardised "wet" tests in a climatic chamber were performed on a sweating manikin in isothermal conditions considering three clothing ensembles (single jacket, work ensemble and a combination of both) and three adjustments of fan velocity. Results showed a significant increase (p < 0.001) in evaporative heat loss values when the fan velocity increased, particularly within the trunk zones for all the considered clothing ensembles, showing that fans enhanced the dissipation by evaporation. The cooling power, quantified in terms of percent changes of evaporative heat loss, showed values exceeding 100% when fans were on, in respect to the condition of fans-off, for the trunk zones except for the Chest. A significant (p < 0.01) decrease (up to 42.3%) in the total evaporative resistance values of the jacket, coupled with the work ensemble, was found compared to the fans-off condition. Results confirmed and quantified the cooling effect of the ventilation jacket which enhanced the evaporative heat losses of the trunk zones, helping the body to dissipate heat and showing the potential for a heat adaptation measure to be developed.

Excretion of Ni, Pb, Cu, As, and Hg in Sweat under Two Sweating Conditions.

Physiologists have long regarded sweating as an effective and safe means of detoxification, and heavy metals are excreted through sweat to reduce the levels of such metals in the body. However, the body can sweat through many means. To elucidate the difference in the excretion of heavy metals among sweating methods, 12 healthy young university students were recruited as participants (6 men and 6 women). Sweat samples were collected from the participants while they were either running on a treadmill or sitting in a sauna cabinet. After they experienced continuous sweating for 20 min, a minimum of 7 mL of sweat was collected from each participant, and the concentrations of nickel (Ni), lead (Pb), copper (Cu), arsenic (As), and mercury (Hg) were analyzed. The results demonstrated that the sweating method affected the excretion of heavy metals in sweat, with the concentrations of Ni, Pb, Cu, and As being significantly higher during dynamic exercise than during sitting in the sauna (all p < 0.05). However, the concentrations of Hg were unaffected by the sweating method. This study suggests that the removal of heavy metals from the body through dynamic exercise may be more effective than removal through static exposure to a hot environment.

Effects of different external cooling placements prior to and during exercise on athletic performance in the heat: A systematic review and meta-analysis.

Background: Nowadays, many high-profile international sport events are often held in warm or hot environments, hence, it is inevitable for these elite athletes to be prepared for the challenges from the heat. Owing to internal cooling may cause gastrointestinal discomfort to athletes, external cooling technique seems to be a more applicable method to deal with thermal stress. Central cooling mainly refers to head, face, neck and torso cooling, can help to reduce skin temperature and relieve thermal perception. Peripheral cooling mainly refers to four limbs cooling, can help to mitigate metabolic heat from muscular contrac to effectively prevent the accumulation of body heat. Hence, we performed a meta-analysis to assess the effectiveness of different external cooling placements on athletic performance in the heat Methods: A literatures search was conducted using Web of Science, MEDLINE and SPORTDiscus until September 2022. The quality and risk of bias in the studies were independently assessed by two researchers. Results: 1,430 articles were initially identified (Web of Science = 775; MEDLINE = 358; SPORTDiscus = 271; Additional records identified through other sources = 26), 60 articles (82 experiments) met the inclusion criteria and were included in the final analysis, with overall article quality being deemed moderate. Central cooling (SMD = 0.43, 95% CI 0.27 to 0.58, p < 0.001) was most effective in improving athletic performance in the heat, followed by central and peripheral cooling (SMD = 0.38, 95% CI 0.23 to 0.54, p < 0.001), AND peripheral cooling (SMD = 0.32, 95% CI 0.07 to 0.57, p = 0.013). For the cooling-promotion effects on different sports types, the ranking order in central cooling was ETE (exercise to exhaustion), TT (time-trial), EWT (exercise within the fixed time or sets), IS (intermittent sprint); the ranking order in peripheral cooling was EWT, TT, ETE and IS; the ranking order in central and peripheral cooling was ETE, IS, EWT and TT. Conclusion: Central cooling appears to be an more effective intervention to enhance performance in hot conditions through improvements of skin temperature and thermal sensation, compared to other external cooling strategies. The enhancement effects of peripheral cooling require sufficient re-warming, otherwise it will be trivial. Although, central and peripheral cooling seems to retain advantages from central cooling, as many factors may influence the effects of peripheral cooling to offset the positive effects from central cooling, the question about whether central and peripheral cooling method is better than an isolated cooling technique is still uncertain and needs more researchs to explore it.

Investigation of factors affecting the rate of changes in endurance exercise performance by pre-cooling with ice slurry / 体力科学

To investigate the factors affecting the rate of improvement in endurance exercise performance following pre-cooling with ice slurry, we focused on individual physical characteristics and thermoregulatory capacity. Twenty-four healthy adults (12 males and 12 females) ingested 7.5g kg-1 of either ice slurry at -1°C (ICE) or control water at 20°C (CON) before cycling at 55% VO2max and continued cycling until the rectal temperature reached 38.5°C or untill exhaustion in a hot environment (controlled at 38°C, 40% relative humidity). The relationship between the rate of improvement in exercise performance and physical characteristics and thermoregulatory factors (changes in rectal temperature, the rate of rectal temperature increase, whole body sweat loss, mean metabolic heat production, and heat storage) was investigated. No correlation was noted between the rate of improvement in exercise performance and physical characteristics and heat storage. On the other hand, the rate of improvement in exercise performance showed significant correlations with changes in rectal temperature (r = -0.497), the rate of rectal temperature increases during exercise (r = -0.784), whole body sweat loss (r = 0.407), and mean metabolic heat production (r = -0.436). The rate of inhibition of sweating and the rate of increase in metabolic heat production by ice slurry ingestion during exercise have been suggested to be related to the rate of improvement in exercise performance. On the other hand, there was no relationship between body composition or VO2max and the rate of improvement in exercise performance.

Comparison of sweating components during endurance exercise under the same load in a hot environment and in a neutral thermal environment / 体力科学

Sweat contains electrolytes (minerals), therefore, it is necessary to consider its loss through sweat in the fluid replacement strategy in sports. The purpose of this study was to compare the concentration of components in sweat, such as electrolytes (minerals), when endurance exercise is performed in hot and neutral thermal environments. Eight men cycled for 60 min at 55% VO2peak under two envitonment conditions: a hot environment (WetBulb Globe Temperature (WBGT): 29.0±0.2℃; Heat) and a neutral thermal environment (WBGT: 20.5±0.2℃; Con). During exercise, sweat loss, core temperature, and heart rate (HR) were measured, and sweat from the chest, back, and thigh was collected. The core temperature, sweat loss, and HR increased significantly in Heat. The sweat electrolyte concentration was significantly higher in Heat than in Con only for Na. Regarding the amount of electrolyte loss from sweat, Na and K showed a significantly higher value than Con in Heat in comparison of each region, and the total loss amount of three regions in Cu also had a significantly higher value than Con in Heat. In addition, there was no difference in the concentration of Ca and Cu between the regions, but there was a significant difference in the amount of loss. It was concluded that even if there was no difference in the electrolyte concentration in sweat, the amount of electrolyte loss increased in K and Cu in a hot environment, and that there was a site difference in the amount of loss in Ca and Cu.

Climate Warming and Occupational Heat and Hot Environment Standards in Thailand.

BACKGROUND: During the period 2001 to 2016, the maximum temperatures in Thailand rose from 38-41oC to 42-44oC. The current occupational heat exposure standard of Thailand issued in 2006 is based on wet bulb globe temperature (WBGT) defined for three workload levels without a work-rest regimen. This study examined whether the present standard still protects most workers. METHODS: The sample comprised 168 heat acclimatized workers (90 in construction sites, 78 in foundries). Heart rate and auditory canal temperature were recorded continuously for 2 hours. Workplace WBGT, relative humidity, and wind velocity were monitored, and the participants' workloads were estimated. Heat-related symptoms and signs were collected by a questionnaire. RESULTS: Only 55% of the participants worked in workplaces complying with the heat standard. Of them, 79% had auditory canal temperature ≤ 38.5oC, compared with only 58% in noncompliant workplaces. 18% and 43% of the workers in compliant and noncompliant workplaces, respectively, had symptoms from heat stress, the trend being similar across all workload levels. An increase of one degree (C) in WBGT was associated with a 1.85-fold increase (95% confidence interval: 1.44-2.48) in odds for having symptoms. CONCLUSION: Compliance with the current occupational heat standard protects 4/5 of the workers, whereas noncompliance reduces this proportion to one half. The reasons for noncompliance include the gaps and ambiguities in the law. The law should specify work/rest schedules; outdoor work should be identified as an occupational heat hazard; and the staff should include occupational personnel to manage heat stress in establishments involving heat exposure.