Solar Radiation Exposure Has Diurnal Effects on Thermoregulatory Responses During High-Intensity Exercise in the Heat Outdoors

The fan cooling vest use reduces thermal and perceptual strain during outdoor exercise in the heat on a sunny summer day

The fan cooling vest is coming into very common use by Japanese outdoor manual workers. We examined that to what extent using this vest reduces thermal strain and perception during outdoor exercise in the heat on a sunny summer day. Ten male baseball players in high school conducted two baseball training sessions for 2-h with (VEST) or without (CON) a commercially available fan cooling vest on a baseball uniform. These sessions commenced at 10 a.m. on separate days in early August. The fan airflow rate attached the vest was 62 L·s-1. Neither ambient temperature (Mean ± SD: VEST 31.9 ± 0.2°C; CON 31.8 ± 0.7°C), wet-bulb globe temperature (VEST 31.2 ± 0.4°C; CON 31.4 ± 0.5°C) nor solar radiation (VEST 1008 ± 136 W·m-2; CON 1042 ± 66 W·m-2) was different between trials. Mean skin temperature (VEST 34.5 ± 1.1°C; CON 35.1 ± 1.4°C), infrared tympanic temperature (VEST 38.9 ± 0.9°C; CON 39.2 ± 1.2°C), heart rate (VEST 127 ± 31 bpm; CON 139 ± 33 bpm), body heat storage (VEST 140 ± 34 W·m-2; CON 160 ± 22 W·m-2), thermal sensation (- 4-4: VEST 0 ± 2; CON 3 ± 1) and rating of perceived exertion (6-20: VEST 11 ± 2; CON 14 ± 2) were lower in VEST than CON (all P < 0.05). Total distance measured with a global positioning system (VEST 3704 ± 293 m; CON 3936 ± 501 m) and body fluid variables were not different between trials. This study indicates that the fan cooling vest use can reduce thermal strain and perception during outdoor exercise in the heat on a sunny summer day. Cooling with this vest would be effective to mitigate thermal risks and perceptual stress in athletes and sports participants under such settings.

Effects of 4 weeks of whole-body vibration training on energy expenditure during deep squats of male well-trained students

From the perspective of energy expenditure, this study investigated the effects of whole-body vibration training on the energy metabolism of deep squats with different weights. Twenty-two healthy male college students with sports experiences were selected and randomly assigned to perform resistance exercise vibration (REV) or resistance exercise (RE) with varying loads two times per week for 4 weeks. Oxygen uptake and heart rate were measured before, during, and after exercises using a gas analyzer, and energy expenditure was calculated. The results showed the following: 1) the oxygen uptake and energy expenditure of the REV group were significantly higher than those of the RE group during and 30 min after exercise (p < 0.01), respectively, and the excess post-exercise oxygen consumption (EPOC) was also significantly higher than that of the RE group (p < 0.01). 2) Changes in the oxygen uptake and energy expenditure were stable with increasing exercise in both vibration and non-vibration conditions. There was no difference in energy expenditure per unit of body mass versus additional energy per kilogram of body weight (p > 0.05). 3) No significant differences in changing exercise intensity were observed in the REV group compared to those in the RE group during the adjacent incremental load phases of △ (40%-0%) and △ (80%-40%) of load during and 30 min after exercise (p > 0.05). Our results suggest that 1) vibration training can increase energy expenditure during low-intensity training and excess post-exercise oxygen consumption, and improve the exercise intensity. 2) The effects on energy expenditure were the same for both weight-bearing and non-weight-bearing deep squats, up to 40% of body mass.

Prior heat exposure diminishes upper-body endurance work capacity and maximal arm and leg strength in young men

Workers often experience heat exposure before manual labour. This study investigated whether prior heat exposure diminished upper-body endurance work capacity and maximal isokinetic arm and leg strength in young men. Ten male participants completed two trials in a climatic chamber maintained at 25°C with 50% relative humidity. The two trials required them to complete a 30-min pre-exercise water-immersion at either 40°C (HOT) to provoke an approximately 1°C rise in rectal temperature (T_re) or 36°C (CON) to maintain a normal T_re. Pre- and post-immersion and following arm-cranking, isokinetic maximal voluntary contraction (MVC) torque was assessed for the elbow flexors and knee extensors. During arm-cranking, time to exhaustion was measured using arm crank ergometry at 60% peak oxygen uptake. Electromyography was recorded from the elbow flexors and knee extensors to calculate the integrated electromyography. T_re at post-immersion was higher in HOT (Mean ± SD, 38.1 ± 0.3°C) than CON (37.1 ± 0.3°C; P < 0.01). Time to exhaustion was less in HOT (41 ± 13 min) than CON (52 ± 12 min; P < 0.01). Isokinetic MVC torque in the elbow flexors and knee extensors was lower in HOT than CON (both P < 0.05). The integrated electromyography of the elbow flexors and knee extensors were lower in HOT than CON (both P < 0.05). This study indicates that a 1°C rise in T_re by prior heat exposure reduces time to exhaustion during arm-cranking and isokinetic MVC torque of the elbow flexors and knee extensors. Workers should be careful about reductions in upper-body endurance work capacity and maximal arm and leg strength when exposed to heat before manual labour.

Evaluation of thermoregulation of horses (Equus caballus) submitted to two methods of post-exercise cooling, in hot and humid climate conditions, in the Eastern Amazon

In Brazil, the study on equine thermoregulation has not shown considerable advances, moreover, in the Amazon, this is a little explored aspect. This study aims to evaluate the thermoregulation of horses submitted to two methods of post-exercise cooling, in the climatic conditions of the Eastern Amazon. The experiment was conducted at Centro Hipico, Ananindeua, Para, for 15 days. Ten male horses, castrated of the Brazilian breed, aged 13 years and with an average weight of 482.3 kg were used. Equestrianism, which was exercised with pre-established protocol in the arena and track, for 30 min. After the exercise, the animals were divided into two groups for application of the treatments, which were two cooling methods, such as a bath with water at room temperature (about 25°C) and a hiper cooling method (6-9°C). During the experimental period, air temperature (AT) and relative humidity (RH) data were recorded and the Temperature and Humidity Index (THI) was calculated. Data from the rectal temperature (RT), heart rate (HR), respiratory rate (RR) and Body surface temperature (BST) of the animals were also measured at three moments: before exercise, after exercise and after applying the cooling methods. The adaptability index used was the Benezra Thermal Comfort Index (BTCI). The BST was performed with the help of infrared thermograph, which were the left side of the neck, thorax, rump, and right side to the armpi, before the exercise, after the exercise and after applying the cooling methods. The statistical design was completely randomized. Analysis of variance was performed using the GLM Procedure of SAS 9.1.3. After the application of the cooling techniques in the animals, the AT and THI were higher and the highest RH values were found before the exercise (87.21%). The highest RT, RR, HR, BST, and BTCI values were observed after exercise. There was no significant dierence (P > 0.05) between cooling methods. There was a highly significant and positive correlation (P < 0.01) between all physiological variables (RT, RR, HR, and BST) and the Iberian Index with AT and THI and negative with RH (P < 0.01), thus demonstrating the influence of the environment on the thermoregulation of animals. It is concluded the evaluation of stress, welfare and thermoregulation of horses submitted to two methods of post-exercise cooling, in the climatic conditions of the Eastern Amazon, demonstrated that the studied cooling methods showed to reduce the rectal temperature, the respiratory rate, the heart rate and the body surface temperature with equal efficiency. However, in terms of practical ease of use, the room temperature water cooling method has proven to be more practical.

Thermal strain is greater in the late afternoon than morning during exercise in the gym without airflow and air conditioning on a clear summer day

Introduction

There are no reports examining the time-of-day effect on team training sessions in the gym without airflow and air conditioning on thermal strain in the summer heat. We investigated this effect during badminton training sessions on a clear summer day.

Methods

Nine male high school badminton players (Mean ± SD; age 17.1 ± 0.6 y, height 171 ± 4 cm, body mass 59 ± 7 kg) completed two 2.5-h badminton training sessions in the gym without airflow and air conditioning. The training sessions were started at 0900 h (AM) and 1600 h (PM) on separate days in August. Skin temperatures (chest, triceps, thigh, calf), infrared tympanic temperature, heart rate, thermal sensation and rating of perceived exertion were recorded at rest and at regular intervals during the sessions.

Results

Indoor and outdoor environmental heat stress progressively increased in AM and decreased in PM during the sessions. Ambient temperature (AM 30.1 ± 0.9°C; PM 33.2 ± 1.0°C: P < 0.001) and wet-bulb globe temperature (AM 28.1 ± 0.5°C; PM 30.0 ± 0.9°C: P = 0.001) during the sessions in the gym were higher in PM than AM. Mean skin temperature (AM 34.2 ± 1.0°C; PM 34.7 ± 0.7°C: P < 0.001), infrared tympanic temperature (AM 37.8 ± 0.5°C; PM 38.1 ± 0.4°C: P = 0.001) and thermal sensation (AM 2.7 ± 1.4; PM 3.3 ± 1.0: P < 0.001) during the sessions were higher in PM than AM. Body heat storage (AM 159 ± 30 W·m^-2; PM 193 ± 30 W·m^-2: P < 0.05) was greater in PM than AM. There were no time-of-day differences in the average heart rate (AM 75 ± 4% age-predicted maximal heart rate; PM 76 ± 5 age-predicted maximal heart rate: P = 0.534), body mass loss (AM 0.6 ± 0.3 kg; PM 0.8 ± 0.2°C: P = 0.079), the volume of water ingested (AM 1.5 ± 0.1 L; PM 1.6 ± 0.3 L: P = 0.447) and rating of perceived exertion (AM 16 ± 2; PM 16 ± 3: P = 0.281).

Conclusions

This study indicates greater thermal strain in PM trial than in AM trial during team training sessions in the gym without airflow and air conditioning on a clear summer day. Therefore, athletes and coaches of indoor sports should perceive that athletes may be exposed to a greater risk for thermal strain in the late afternoon from 1600 h than in the morning from 0900 h during the sessions in the gym under these conditions.

Comparison of the effects of high and low levels of solar radiations on exercise capacity in hot outdoor environments

BACKGROUND

High solar radiation from the sun in the heat outdoor may be impaired exercise capacity. This study aimed to compare the effects of different levels of solar radiation on exercise capacity and evaluate skin temperature responses in the heat.

METHODS

Seven male participants performed cycling exercise at 60% of their maximal oxygen uptake until volitional exhaustion in hot outdoor environments (approximately 33-35°C, 40-50% relative humidity) under both clear sky (high solar radiation trial: 1062±50 W/m²) and under thick clouds (low solar radiation trial: 438±52 W/m²).

RESULTS

The time to exhaustion of the participants was shorter in the high solar radiation trial (32.0±12.4 min) than in the low solar radiation trial (39.2±18.0 min: P=0.045). Mean skin temperature was significantly higher in the high solar radiation trial than that in the low solar radiation trial (P<0.05); however, the rectal temperature did not differ significantly between the two trials. The high solar radiation trial had narrower core-to-skin temperature gradient, greater the body heat gain from the sun, and higher rating of perceived exertion than the low solar radiation trial.

CONCLUSIONS

These results indicate that high solar radiation during outdoor exercise in the heat causes a greater increase in skin temperature and body heat gain from the sun than low solar radiation and consequently impairs exercise capacity.

A NOMOGRAM FOR PREDICTING PATIENTS WITH SEVERE HEATSTROKE

ABSTRACT

Background: No predictive models are currently available to predict poor prognosis in patients with severe heatstroke. We aimed to establish a predictive model to help clinicians identify the risk of death and customize individualized treatment. Methods: The medical records and data of 115 patients with severe heatstroke hospitalized in the intensive care unit of Changzhou No. 2 People's Hospital between June 2013 and September 2019 were retrospectively analyzed for modeling. Furthermore, data of 84 patients with severe heatstroke treated at Jintan No. 1 People's Hospital from June 2013 to 2021 were retrospectively analyzed for external verification of the model. We analyzed the hematological parameters of the patients recorded within 24 h of admission, which included routine blood tests, liver function, renal function, coagulation routine, and myocardial enzyme levels. Risk factors related to death in patients with severe heatstroke were screened using Least Absolute Shrinkage and Selection Operator regression. The independent variable risk ratio for death was investigated using the Cox univariate and multivariate regression analyses. The nomogram was subsequently used to establish a suitable prediction model. A receiver operating characteristic curve was drawn to evaluate the predictive power of the prediction model and the Acute Physiology and Chronic Health Evaluation (APACHE II) score. In addition, decision curve analysis was established to assess the clinical net benefit. The advantages and disadvantages of both models were evaluated using the integrated discrimination improvement and Net Reclassification Index. A calibration curve was constructed to assess predictive power and actual conditions. The external data sets were used to verify the predictive accuracy of the model. Results: All independent variables screened by Least Absolute Shrinkage and Selection Operator regression were independent risk factors for death in patients with severe heatstroke, which included neutrophil/lymphocyte ratio, platelet (PLT), troponin I, creatine kinase myocardial band, lactate dehydrogenase, human serum albumin, D-dimer, and APACHE-II scores. On days 10 and 30, the integrated discrimination improvement of the prediction model established was 0.311 and 0.364 times higher than that of the APACHE-II score, respectively; and the continuous Net Reclassification Index was 0.568 and 0.482 times higher than that of APACHE-II, respectively. Furthermore, we established that the area under the curve (AUC) of the prediction model was 0.905 and 0.918 on days 10 and 30, respectively. Decision curve analysis revealed that the AUC of this model was 7.67% and 10.67% on days 10 and 30, respectively. The calibration curve showed that the predicted conditions suitably fit the actual requirements. External data verification showed that the AUC on day 10 indicated by the prediction model was 0.908 (95% confidence interval, 82.2-99.4), and the AUC on day 30 was 0.930 (95% confidence interval, 0.860-0.999). Conclusion: The survival rate of patients with severe heatstroke within 24 h of admission on days 10 and 30 can be effectively predicted using a simple nomogram; additionally, this nomogram can be used to evaluate risks and make appropriate decisions in clinical settings.

The use of sun-shade on safe heat exposure limit on a sunny summer day: a modelling study in Japan

Sustainable methods are required to reduce the risks of thermal strain and heat-related illness without exacerbating greenhouse gas emissions. We investigated the effects of sun-shade use on safe heat exposure limit on a sunny summer day using historical climate data in Japan. We simulated a heat-acclimatised person standing at rest (metabolic heat production, 70 W·m^-2) and during light work (100 W·m^-2) on an asphalt pavement in the sun and sun-shade. Japan has three Köppen climate regions: tropical, temperate and cold. We analysed one city in the tropical region (24°N), three cities in the temperate region (31°N, 35°N and 39°N) and one city in the cold region (40°N). Hourly data were collected from 7 AM to 6 PM, June to September, from 2010 to 2019. The day with the longest daylight hours and the greatest solar radiation intensity was used for analysis. With sun-shade (a white polyester tarpaulin/awning), ambient temperature, global solar radiation and ground surface temperature were assumed to be 0.5°C, 45% and 6°C lower than in the sun, respectively. Sun-shade use eliminated the days with at least 1 hour exceeding safe heat exposure limit at rest in all cities. The same was observed for light work in the temperate and cold cities, although the tropical city had 2 days exceeding safe heat exposure limit during the decade. Sun-shade use on a sunny summer day can be an effective and sustainable method to reduce heat exposure hazard at rest and during light work in tropical, temperate and cold climate regions.

The value of the exertional heat stroke score for the prognosis of patients with exertional heat stroke

OBJECTIVE

This study aims to evaluate the exertional heat stroke score (EHSS) system for the prognosis of exertional heat stroke (EHS) patients.

METHODS

Forty-two EHS patients who had been treated in our hospital between January 2017 and December 2019 were divided into two groups according to their prognosis, a survival group and a non-survival group. All the patients had received comprehensive EHS treatment after admission, and their EHSS parameters were collected within 24 h of admission, including body temperature, hepatorenal function, and coagulation function. A retrospective comparative evaluation was made of the effectiveness of the EHSS, the Acute Physiology and Chronic Health Evaluation II (APACHE II) and the Sequential Organ Failure Assessment (SOFA) in making an EHS prognosis.

RESULTS

Among 42 patients, 28 patients were treated successfully and discharged from the hospital, 5 were given a poor prognosis, and 9 died, amounting to a fatality rate of 21.42%. Univariate analysis showed that within 24 h of admission, the differences were statistically significant (p < 0.05) in the comparison of the following factors: lactate concentration, platelets, prothrombin time, fibrinogen, troponin, aspartate aminotransferase, total bilirubin, urinary creatinine, acute gastrointestinal injury, temperature, and Glasgow coma score. However, no statistically significant difference in blood pH was observed between the two groups of patients (p = 0.117). The EHSS, APACHE II, and SOFA scores of the survival group were significantly lower than those of the non-survival group (p < 0.001). The area under the receiver operating characteristic curve of the EHSS, APACHE II and SOFA scores were the area under the curve (AUC) _EHSS = 0.96 (0.901, 0.990), AUC _{Apache II} = 0.895 (0.802, 0.950), and AUC _SOFA = 0.884 (0.837, 0.964), respectively. Thus, the EHSS diagnostic efficacy of the survival group was significantly higher than that of the other two scores. In addition, the sensitivity and specificity of EHSS were higher than those of the APACHE II and SOFA scores.

CONCLUSION

The EHSS has a good diagnostic efficacy for the prognosis of EHS patients and is significantly higher than that of the APACHE II and SOFA scores. This finding provides a theoretical basis for further increasing the rescue success rate of EHS patients and improving their prognostic quality of life.

Cooling Between Exercise Bouts and Post-exercise With the Fan Cooling Jacket on Thermal Strain in Hot-Humid Environments

This study investigated the effects of cooling between exercise bouts and post-exercise with a commercially available fan cooling jacket on thermal and perceptual responses during and following exercise in hot-humid environments. Ten male athletes completed two 30 min cycling bouts at a constant workload (1.4 watts⋅kg^-1 of body mass) with a 5 min recovery period in between. Exercise was followed by a 10 min recovery period. In an environmental chamber (33°C, 65% relative humidity), participants performed two trials with (FCJ) or without (CON) the fan cooling jacket on a T-shirt during the 5 min inter-exercise and 10 min post-exercise recovery periods. Mean, chest and upper arm skin temperatures, and thermal sensation and comfort were lower in FCJ than CON trial during and following exercise (P < 0.05). Thigh and calf skin temperatures, infrared tympanic temperature and heart rate were lower in FCJ than CON trial during the experimental trials (P < 0.05). The rates of fall in mean, chest and upper arm skin temperatures, infrared tympanic temperature and thermal sensation and comfort were faster in FCJ than CON trial during both recovery periods (P < 0.05). There were faster rates of fall in thigh and calf skin temperatures and heart rate in FCJ than CON trial during the post-exercise recovery period (P < 0.05). No difference was observed between trials in the rating of perceived exertion (P > 0.05). This study indicates that cooling between exercise bouts and post-exercise with the fan cooling jacket would effectively mitigate thermal strain and perception/discomfort during and following exercise in hot-humid environments. This garment would reduce whole-body skin temperature quickly while promoting falls in lower-body as well as upper-body skin temperatures.

Combined effects of solar radiation and airflow on endurance exercise capacity in the heat

This study investigated the combined effects of different levels of solar radiation and airflow on endurance exercise capacity and thermoregulatory responses during exercise-heat stress. Ten males cycled at 70% peak oxygen uptake until exhaustion in an environmental chamber (30°C, 50% relative humidity). Four combinations of solar radiation and airflow were tested (800 W⋅m^-2 and 10 km⋅h^-1 [High-Low], 800 W⋅m^-2 and 25 km⋅h^-1 [High-High], 0 W⋅m^-2 and 10 km⋅h^-1 [No-Low], and 0 W⋅m^-2 and 25 km⋅h^-1 [No-High]). Participants were exposed to solar radiation by a ceiling-mounted solar simulator (Metal halide lamps) and the headwind by two industrial fans. Time to exhaustion was shorter (p < 0.05) in High-Low (mean ± SD; 35 ± 7 min) than the other trials and in High-High (43 ± 6 min) and No-Low (46 ± 9 min) than No-High (61 ± 9 min). There was an interaction effect in total (dry + evaporative) heat exchange which was less in High-Low and High-High than No-Low and No-High, and in No-Low than No-High (all p < 0.001). Core temperature, heart rate and thermal sensation were higher in high (High-Low and High-High) than no (No-Low and No-High) solar radiation trials and in lower (High-Low and No-Low) than higher (High-High and No-High) airflow trials (p < 0.05). Mean skin temperature and rating of perceived exertion were higher in high than no solar radiation trials (p < 0.05). This study indicates that combining high solar radiation and lower airflow have negative effects on thermoregulatory and perceptual strain and endurance exercise capacity than when combining high solar radiation and higher airflow and combining no solar radiation and lower/higher airflow during exercise-heat stress.

Greater thermoregulatory strain in the morning than late afternoon during judo training in the heat of summer

Purpose

The time-of-day variations in environmental heat stress have been known to affect thermoregulatory responses and the risk of exertional heat-related illness during outdoor exercise in the heat. However, such effect and risk are still needed to be examined during indoor sports/exercises. The current study investigated the diurnal relationships between thermoregulatory strain and environmental heat stress during regular judo training in a judo training facility without air conditioning on a clear day in the heat of summer.

Methods

Eight male high school judokas completed two 2.5-h indoor judo training sessions. The sessions were commenced at 09:00 h (AM) and 16:00 h (PM) on separate days.

Results

During the sessions, indoor and outdoor heat stress progressively increased in AM but decreased in PM, and indoor heat stress was less in AM than PM (mean ambient temperature: AM 32.7±0.4°C; PM 34.4±1.0°C, P<0.01). Mean skin temperature was higher in AM than PM (P<0.05), despite greater dry and evaporative heat losses in AM than PM (P<0.001). Infrared tympanic temperature, heart rate and thermal sensation demonstrated a trial by time interaction (P<0.001) with no differences at any time point between trials, showing relatively higher responses in these variables in PM compared to AM during the early stages of training and in AM compared to PM during the later stages of training. There were no differences between trials in body mass loss and rating of perceived exertion.

Conclusions

This study indicates a greater thermoregulatory strain in the morning from 09:00 h than the late afternoon from 16:00 h during 2.5-h regular judo training in no air conditioning facility on a clear day in the heat of summer. This observation is associated with a progressive increase in indoor and outdoor heat stress in the morning, despite a less indoor heat stress in the morning than the afternoon.