DOI: https://doi.org/10.21203/rs.3.rs-2046162/v1
Background: This study aims to evaluate the effectiveness of newly designed evaporative cooling short pants (ECSP) in decreasing physiological and perceptual heat strain under hot/dry laboratory conditions.
Methods: At the first, an evaporative cooling short pants was designed. Then, to evaluate this cooling garment, 12 healthy men participated in the test. The subjects performed the test at two stages, including test with regular pants and test with ECSP. During each stage, the physiological and perceptual parameters, including heart rate, local temperature in thighs, ear temperature, sweat rate, thermal sensation, sweat sensation, and thermal comfort, were measured every 5 minutes for 60 minutes.
Results: The results showed that use of the cooling short pants compared to regular pants could not significantly decrease the parameters of heart rate (P=0.547), ear temperature (P=0.487), sweat rate (P=0.368), local and general sweat sensation (P=0.632) and (P=0.368) respectively. However, use of this garment significantly decreased the mean value of local temperature in thighs by 3 °C (P=0.002), local and general thermal sensation of body by 1.4 (P=0.002) and 0.4 (P=0.006), respectively and increased the mean values of local and general thermal comfort by 1.2 (P=0.003) and 0.7 (P=0.002), respectively.
Conclusion: The results revealed that designed evaporative cooling short pants reduced local temperature in thighs and had positive effect on controlling the perceptual heat strain.
Heat is one of the harmful factors in work environments, which may have originated from a process or caused by the climatic conditions of the region [1, 2]. If the heat stress exceeds the allowable limits, it can lead to disorders such as heat rash, muscle cramps, heat weakness, severe sweating, heatstroke, and decreased efficiency [3, 4].
When the internal body temperature remains in the acceptable range (nearly 37 ± 1°C), the necessary conditions are provided for the human body to function normally and healthily, as well as, the condition for cellular and biochemical reactions to occur correctly and completely. This is the case when a person is in an environment free of any thermal stress. In such environment, the human body is considered in the situation of thermal homeostasis [5]. Due to the existence of several occupations and industries whose conditions may result in an increase in body temperature by more than 1°C and lead to heat strain. There are various solutions for decreasing the heat strain, such as technical solutions, administrative measures, and using personal cooling garments. However, if it is not possible to use engineering and management solutions in some conditions, it is useful to exploit personal cooling garments for cooling the body [6].
One major problem in melting industries is that lower parts of the body are more exposed to heat, especially the upper part of the lower limbs. This leads to heat rash and infertility. Heat rash or intertrigo is a type of inflammatory lesion (dermatitis) of the skin surface that occurs in the folded parts of the body. Intertrigo can usually cause itching, bumps, and pain. Certain areas that are more exposed to it are the inner thighs and genitals, armpits, chest, and lower abdomen. Sweaty skin is susceptible to infections [7]. Sweating in the pelvic area will cause dissatisfaction as well as reduced job performance. Normally, the temperature of the testicles in the scrotum is 1 to 2°C lower than the internal body temperature. Therefore, an increase in testicular temperature can negatively affect the process of spermatogenesis. Exposure to hot work environments (baker, welder, casting workers) can disrupt the internal temperature of the scrotum and lead to an increase in testicular temperature [8, 9]. There are many reports available regarding workers' reproductive health exposed to high temperatures, for instance, researchers have observed a high prevalence of pathological sperm among workers in the ceramic industry [10]. Therefore, use of the cooling short pants can be useful in decreasing the temperature of this body region.
Concerning reports and frequent dissatisfaction of workers working in hot process industries, and the problems related to lower limb warming such as intertrigo and its consequences, the requisite need to reduce skin surface temperature in this area, which decreases the stimulation of sweat glands and secondary problems, is a major concern. Therefore, this study was conducted to design and sew evaporative cooling short pants with evaporative mechanism and evaluate their performance.
This experimental study consisted of two phases of designing and sewing evaporative cooling short pants and evaluating the effectiveness of the cooling short pants.
In evaporative cooling clothing, water evaporation causes the clothing texture to cool, hence, the contact between the skin and this clothing reduces the skin temperature. These short pants were made of three layers based on their cooling pattern. The outer layer is made of a breathable and light-colored fabric and the middle layer is made of non-woven fibers containing highly water-absorbent Polyacrylamide crystals, which does not have toxic, corrosive, and flammable properties and it is in charge of water storage in the middle layer. Also, because the lower areas, especially the pelvic areas, are prone to skin diseases and complications caused by moisture, the inner layer is made of waterproof fabric to prevent the user's body from getting wet. Based on the design of these short pants, by utilizing elastic stretch straps, the short pants can stick to the skin in the stated areas (Fig. 1).
The cooling mechanism of these short pants includes steps beginning with immersing the shorts in ordinary water (20–25°C) for 5 minutes, then, they are taken out of the water and extra water is removed by squeezing the short pants. Finally, two leggings are added to the wet short pants using a zipper to turn it into pants. In the end, they are ready to wear (Fig. 2).
With regard to the number of participants according to the articles of Hadid et al. (with 12 participants), Selkrik et al. (with 15 participants), and Bennett et al. (with 12 participants) [11–13] who examined the performance of cooling vests, 12 men were volunteered to attend in the study considering the inclusion criteria. Inclusion criteria comprises having a normal body mass index (BMI) (18.5–25), no history of cardiovascular, pulmonary, neuromuscular, and musculoskeletal diseases, epilepsy, seizures, diabetes, not taking blood pressure medications and drugs affecting heart rate, not consuming coffee, caffeine, and alcohol 12 hours prior to the test and the criteria for termination also involved an increase in heart rate of more than 180 beats per minute and a core temperature above 39°C [14, 15]. The mean ± SD values of age, body mass, and height in the participants were 23.6 ± 3.9 years, 83.1 ± 11, 11.8 kg and 183.9 ± 4.3 cm, respectively.
Demographic information including age, height, and weight were gathered by a researcher made questionnaire. After explaining objectives of the study to the participants, the requisite training was taught and the voluntary informed consent form was completed by them. The subjects performed the test at two stages, including test with the regular pants (CON) (70% polyester and 30% linen fibers) and test with the evaporative cooling short pants (ECSP) while both of these garments used separately and they stayed in direct contact with skin. In each stage, firstly, subjects were asked to rest in the restroom (24°C) for 20 minutes in a comfortable temperature mode. Afterward, they entered the climatic chamber and started the test. In the test, the participants were asked to sit on a chair for 30 minutes and then walk on a treadmill (3km/h, 0%) for 30 minutes (Fig. 3).
During each stage, the physiological parameters of heart rate, local thigh temperature, ear temperature, and sweat rate, and also perceptual parameters of thermal sensation, sweat sensation, and thermal comfort were measured on two local scales in the pelvis and the entire body. Moreover, the thermal acceptability and the intensity of perceived exertion were measured. The stated parameters (except sweat rate) were measured every 5 minutes for 60 minutes in each stages. After the stage 1 (in the test with regular pants), the subject left the chamber and rested for 20 minutes to return to a normal state of physiological and perceptual parameters and entered to the chamber again for the stage 2 (in the test with ECSP) (Fig. 4). To measure sweat rate, individuals' weight was calculated before entering and after leaving the climatic chamber. the climatic chamber was with dimensions of 4×3 meters and had 2.8-meter height. Within the chamber, the average dry temperature was 39.9°C, wet temperature was 26°C, globe temperature was 38.9°C, the WBGT temperature index was 29.6°C and the relative humidity was 42.5%. Table 2 shows the value of microclimate indicators in two stages of the test. All sessions were performed at the same time of day avoid the confounding influence of circadian variability on the outcome measures.
Wet-bulb globe temperature (WBGT) Index, globe temperature, natural wet bulb temperature, dry-bulb temperature, and relative humidity were measured with the Microtherm Heat Stress WBGT kit (Casella CEL HB3279-04). Local thigh temperature, ear temperature, and heart rate were measured by using Dual Temp Biofeedback thermometer, Microlife IR 120 (non-contact thermometer), and Microlife OXY 300 Pulse Oximeter Fingertip, respectively. Individual weighing was calculated by using a Hamilton digital scale with an accuracy of 0.1 kg. Additionally, perceptual indices including thermal sensation, sweat rate, thermal comfort, thermal acceptability, and perceived exertion were recorded using the Likert scale (Table 1)[16–19].
|
Thermal Sensation |
Sweat Sensation |
Thermal Comfort |
Thermal Acceptability |
Perceived Exertion |
|||||
|---|---|---|---|---|---|---|---|---|---|
|
Score |
Scale |
Score |
Scale |
Score |
Scale |
Score |
Scale |
Score |
Scale |
|
0 |
Neutral |
0 |
Dry |
0 |
Very uncomfortable |
0 |
Not acceptable |
1 |
Very light activity |
|
1 |
Slightly warm |
1 |
Slight wet |
1 |
Uncomfortable |
1 |
Acceptable |
2–3 |
Light activity |
|
2 |
Warm |
2 |
Wet |
2 |
Slightly uncomfortable |
- |
- |
4–5 |
Moderate activity |
|
3 |
Hot |
3 |
Very wet |
3 |
Slightly comfortable |
- |
- |
6–7 |
Vigorous activity |
|
4 |
Very Hot |
4 |
Sweating |
4 |
Comfortable |
- |
- |
8–9 |
Very hard activity |
|
5 |
Intolerably hot |
- |
- |
5 |
Very comfortable |
- |
- |
10 |
Max effort |
|
Microclimate indicators |
CON |
ESCP |
|---|---|---|
|
WBGT (°C) |
29.3 ± 1.4 |
29.9 ± 1.1 |
|
Dry Temperature (°C) |
39.7 ± 0.5 |
39.9 ± 0.4 |
|
Wet Temperature (°C) |
25.9 ± 0.9 |
26.1 ± 1.2 |
|
Globe Temperature (°C) |
38.7 ± 0.7 |
39.1 ± 0.7 |
|
Humidity (%) |
42.7 ± 2.7 |
42.3 ± 2.9 |
The data were analysed using SPSS Version 26.0 software. Shapiro-Wilk test was used to check the normality of data distribution and paired t-test was used for normal data distribution and Wilcoxon signed-rank test was used for otherwise.
The mean values of heart rate in the test with CON and ECSP were 85.5 ± 14 and 84.7 ± 12.5 beats per minute, respectively. while the distribution of data was normal, the statistical test revealed that mean heart rate was not significantly different in these two conditions (P = 0.547).
Figure 5 illustrates the changes in heart rate during the test in the CON and ECSP.
The average values of ear temperature in the test with CON was 36.9 ± 0.3°C and 36.9 ± 0.4°C in the test with ECSP. Statistical analysis depicted that the data distribution was normal and the differences between the mean ear temperature was not significantly noticeable in the two conditions (P = 0.487).
The results of measuring ear temperature in the CON and ECSP was not significant during the experiment (Fig. 5), and the maximum value of it did not exceeds 37.1°C.
The mean temperature of the right and left thighs was 35.3 ± 0.7°C in the test with CON and it was 32.3 ± 1°C in ECSP. Since the distribution of data was not normal, using statistical tests, it was concluded that the difference between the mean skin temperature in the CON and ECSP was significant (P = 0.002).
Figure 5 shows that after using the cooling short pants, when the person is sitting (from the beginning of the test till the 30th minute) and in the treadmill phase (the 35th minute till the end of the test), the temperature in both thighs declined by 2.4°C and 3.3°C, respectively.
Thermal sensation, which was scored based on the Likert scale by the subjects, was examined in two ways: local thermal sensation in the thigh area and the general thermal sensation in the body. The mean value of local thermal sensation in the CON was 1.7 ± 0.9, and the ECSP was 0.5 ± 0.3, and with an abnormal distribution of data, statistical analysis showed that the difference was significant (P = 0.002). Also, the mean values of general thermal sensation in the CON was 2.3 ± 0.7, and the ECSP was 1.9 ± 0.6. Also, with the normal distribution of data, the statistical test showed that this difference was significant (P = 0.006).
The changes in both local and general scales illustrated that thermal sensation reduced significantly after using cooling short pants (Figs. 6).
Sweat sensation was also scored on a Likert scale by the subjects and was evaluated as local sweat sensation in the thighs and general sweat sensation in the body. The mean of local sweat sensation in the CON was 1.5 ± 0.7 and it was 1.7 ± 0.7 in the ECSP, and with normal distribution of data, the difference was not significant (P = 0.368). Also, the mean values of general sweating in the body in the CON was 2 ± 0.8 and 1.9 ± 0.7 in the ECSP, and with an abnormal distribution of data, statistical analysis showed that this difference in values was not significant (P = 0.632). Based on the weight of subjects before and after the tests, the average sweat rate in both cases was equally measured to 500 grams of sweat per hour with ECSP and with regular pants conditions.
Figures 6 shows the changes in sweat sensation both locally and generally during the test with CON and ECSP.
In this study, thermal comfort was also scored on a Likert scale by the subjects and the feeling of local thermal comfort in the thighs area and the general thermal comfort in the body were examined. The mean of local thermal comfort in the CON was 2.9 ± 1.2 and 4.1 ± 0.7 in the ECSP, and with an abnormal distribution of data, the statistical test demonstrated that this difference was significant (P = 0.003). Also, the mean values of general thermal comfort in the CON and ECSP were 2.5 ± 1.2 and 3.2 ± 1, respectively. With the normal distribution of data, the statistical test showed that this difference was significant (P = 0.002).
According to the Figs. 6, the changes in thermal comfort sensation both in the thighs area and in the whole body improved significantly using the ECSP.
Thermal acceptability was expressed based on the Likert scale with two scores of 0 and 1 for heat unacceptability and heat acceptance, respectively. The mean for the CON was 0.9 ± 0.3 and 1 ± 0 for the ECSP, while the distribution of data was abnormal using statistical tests, it was found that this difference was not significant (P = 0.144).
The mean perceived exertion was 1.6 ± 0.8 for the CON and 1.8 ± 0.8 for the ECSP, given the non-normality of the data, the statistical test showed that this difference was not significant (P = 0.385).
Figure 7 shows the changes in subjects' values for perceived exertion during the test in the two conditions with CON and with ECSP.
According to the results of the current study, which was conducted to evaluate the performance of evaporative cooling short pants on physiological and perceptual parameters in hot and dry laboratory conditions. No significant difference was observed in heart rate values during the experiment (with cooling short pants or with regular work pants). However, the average heart rate experienced a decrease after using ECSP compared to regular pants. This relative reduction is more significant in the treadmill stage (the 35th minute to the end of the test) and the maximum reduction occurred in the 45th and 50th minute at 4 beats per minute fewer than regular work pants. Local skin temperature of the thighs was significantly reduced by using ECSP at all intervals of the test. The highest average temperature recorded was 35.6°C in the 30th minute with regular work pants, as opposed to 32.2°C for subjects wearing ECSP at the same time, which indicates a 3.4°C decrease in thigh temperature.
The results of mean heart rate and skin temperature are consistent with the study of Radovan M. Karkalic et al. (2015). In their study, while, the trend of changes in mean heart rate increased in both cases, with regular clothing, and with evaporative cooling vests during the experiment, after utilizing the evaporative cooling vests, the heart rate decreased significantly and the maximum difference of 11 beats per minute was recorded in the last minutes of the final stage. Also, in the case of using a lower temperature cooling vest (mean 0.8 ± 0.02°C) at two measuring points in the trunk area, a direct relationship was observed between the effects of this vest and skin temperature reduction [20]. In the study conducted by Eijsvogels et al. (2014), skin temperature was significantly lower during the experiment using the evaporative cooling vest compared to control conditions. Heart rate initially did not differ between conditions with and without vests and increased significantly during the experiment in both conditions, and the difference between the two control modes and with the cooling vest was 3 beats per minute, which was not statistically significant [21].
In the present study, the mean ear temperature showed an increase in both experimental conditions, and its maximum value was 37.1°C in the 50th minute of the test with CON and in the 55th minute of the test with ECSP. No significant difference was observed, probably due to low body coverage of the short pants (Fig. 5). These results are in contradiction with the study of J Procter (2017). The results of his study showed that wearing an evaporative cooling vest reduced core body temperature during the experiment. In his experiment, in both cases with the evaporative cooling vest and without it, the trend of deep body temperature changes was increasing, and its maximum for the condition with the vest was recorded 36.13 ± 0.40°C and for the condition without it, was measured 37.14 ± 0.58°C, and the difference in values was significant [22]. The difference in the results of the core body temperature is probably due to the choice of rectal temperature over the ear temperature, which is a better representative of the core body temperature and shows its changes more accurately. In addition to that, the difference in load of work during his study in which subjects started their cycling activity with 100W power and then added to its intensity gradually by the rate of 20W power per minute till the end of the test, however, in our study, subjects at each stage spent half of the test time sitting and the other half walking on a treadmill with light load of work (speed 3 km/h and zero-degree incline).
In the study of Eijsvogels et al. (2014), the core body temperature did not change significantly after the use of the evaporative cooling vest. In addition, the rate of increase in core temperature and its maximum was not different between the two control groups (39.1 ± 0.5°C and 1.5 ± 0.4°C) and the cooling vest (39.0 ± 0.3°C and 1.4 ± 0.4°C), which is consistent with the results of the present study [21].
The mean value of local thermal sensation at the beginning and at the end of the experiment for the ECSP (0 and 0.5 (Neutral), respectively) and for the CON (0.8 (Neutral) and 2.3 (Warm)) as well as the average value of general thermal sensation was reported at the beginning and at the end of the test for the ECSP (1.5 (Slightly warm) and 2.4 (Warm), respectively) and also for the CON (2 and 2.8 (Warm)), which demonstrated a significant effect of ECSP on the thermal sensation in both local and general scales (Fig. 6).
The mean value of local and general thermal comfort for the ECSP were recorded (2.9 and 2.5 (Slightly uncomfortable), respectively) and for the ECSP were measured (4.1 (Comfortable) and 3.2 (Slightly comfortable), respectively). These changes also significantly indicate the effectiveness of ECSP on thermal comfort (Fig. 6).
When the ECSP were used, the average local sweat sensation increased by 0.2 points, probably due to the nature of the ECSP, which themselves need to be wet to function. Therefore, these short pants may cause a slight moisture sensation in the area covered by them. But the average sweat sensation in the whole body with ECSP decreased by 0.1, which indicates a feeling of less moisture in the whole body, however, changes in sweat sensation in both local and general scales were not significant.
Zhao et al. (2015), Who studied the effect of two cooling vests on thermal comfort in 8 female students, found that when they used the cooling vest, they felt cooler on both the trunk and whole-body scales, in a way that they scored 0.5 in 50 minutes (Slightly cool) which meant feeling cooler and more comfortable. Cooling vests also improved thermal comfort in the trunk area and the whole body, specifically, more efficacy was observed in the trunk area, which is related to the coverage of this area by the cooling vest. They also found that the sense of wet skin all over the body and in the torso increased with continued exercise and reduced by using cooling vests, however, this difference was not considerable [23]. The results of their study regarding all three indices confirmed the results of using ECSP.
In the study of Luomala MJ et al. (2012), Which examined the performance of 7 cyclists wearing a cooling vest, it was found that after using the cooling vest, their thermal sensation and thermal comfort improved during the test, which is in line with the results of the present study. Perceived exertion also decreased after using the cooling vest, also, at its maximum level decreased by 2 points from 18 (Very hard) to 16 (Hard) during the experiment [24]. However, the present study showed different results concerning perceived exertion, so that, its upward trend and its maximum value was recorded 3 (Light activity), with ECSP, in the 55th minute, but in general, its changes were not significant (Fig. 7). Probably due to the light load of work subjects, the effect of ECSP on the process of changes in perceived exertion intensity was not tangible. Thermal acceptability improved after using ECSP during the experiment and its mean decreased by 0.1 compared to regular pants, but the changes were not significant.
As a limitation of the current study, the subjects refused and did not express their consent to measure their rectal temperature, ear temperature was measured instead.
The present study results showed that using evaporative cooling short pants in hot and dry conditions of the climatic chamber resulted in thigh temperature reduction and improved the perceptual indices of the subjects. Given the effectiveness of this garment in controlling local heat strain, it is proposed that the effectiveness of this garment with other cooling clothing are evaluated in the next studies. Also, it is suggested that in future research, the functionality of these evaporative cooling short pants should be investigated within the industries and in more real-life conditions.
Acknowledgements
We would like to acknowledge the Isfahan University of Medical Sciences for supporting our study and we would like to express my deep and sincere gratitude and appreciation from the volunteers who cooperate in the research and those who helped and assisted us during the research.
Author contributions
S.MR and H.D Conception and design of study. S.MR acquisition of data. S.MR and H.D analysis and/or interpretation of data. S.MR Drafting the manuscript. S.MR and H.D revising the manuscript critically for important intellectual content. S.MR approval of the version of the manuscript to be published.
Conflict of interest
The authors declare they do not have any conflicts of interest.
Consent to participate
The participants gave their written informed consent to participate in the study.
Funding
This research was funded by Isfahan University of Medical Sciences.
Data availability
Data and material will be provided upon reasonable request.
Disclosure statement
No potential conflict of interest was reported by the authors.
Ethical approval
The code of ethics in research was obtained IR.MUI.RESEARH.REC1400.019 and evaluated by Vice-chancellor in Research Affairs Medical University of Isfahan.
Consent for publication
Not applicable.