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.