Heat of sorption induced by sweating affects thermoregulatory responses during heat load

Abstract

To investigate the effects of heat of sorption per se induced by sweating on thermoregulatory responses in clothed subjects, two experiments were carried out. In experiment 1 [ambient temperature (Ta) 27.2 degrees C, 50% relative humidity (r.h.)], seven female subjects immersed their lower-legs in a water bath at a temperature raised between 35-41 degrees C during 70 min wearing garments made for the experiment of either 100% cotton (C) or 100% polyester (P). Skin blood flow at the forearm was significantly greater in C than in P (P < 0.05). The increase of mean skin temperature (Tsk) and clothing surface and clothing microclimate temperatures were significantly higher in C than that of P after the onset of sweating (P < 0.05). Furthermore, these responses were accompanied by warmer and more uncomfortable sensations in C than in P despite a lower rectal temperature in C compared with P and identical mean body temperature in both sets of garments. In experiment 2, to simulate the clothing microclimate after the onset of sweating, C and P garments were exposed in the climate chamber to r.h. raised from 50% to 95% at a constant Ta of 27.2 degrees C. The clothing surface temperature rose by 2.2 degrees C for C and by 0.5 degree C for P after the increase of r.h. These results clearly showed a more marked increase in heat of sorption in C than in P. These results indicated that the heat of sorption per se after the onset of an increasing clothing microclimate vapour pressure, mimicking the onset of sweating, enhanced thermoregulatory responses such as skin blood flow, (Tsk) and subjective voting in C.

Effects of humid heat exposure in later sleep segments on sleep stages and body temperature in humans

“…Heat of sorption is produced by absorption of human sweat as well as increased ambient RH (Tanaka et al 2001). In subjects who are awake, heat of sorption increases mean and chest Tsk, and skin blood flow while suppressing an increase in Tre (Tanaka et al 2001) and local sweat rate (Ha et al 1995), accompanied by greater perceived warmth and discomfort (Tanaka et al 2001). Further study is needed to clarify whether heat of sorption during sleep has a significant physiological role in reducing thermal stress or perceived warmth or discomfort rather increase wakefulness.…”

Wear trial assessment of layer structure effects on vapor permeability and condensation in a cold weather clothing ensemble

“…Materials were deliberately selected from non-hygroscopic materials to prevent the influence of heat absorption of the fibers; the heat is considerable and sufficient to alter the condensation mechanism as well as the heat and moisture transfer characteristics of the clothing system. 20,21 Before any testing was conducted, all of the test garments except the jacket were laundered and air dried to remove any finishing chemicals in the textiles. After each trial, the garments were laundered and stored in a conditioned room (t a ¼ 25 AE 2 C, rh ¼ 50 AE 5%) for the next trial.…”

Effects of ventilation design on thermal comfort performance and breast displacement for sports bras

“…According to previous research, 10,23,61 the sports bra with (significantly) lower values in T s and H s at all or most of the five time points was considered to be (significantly) better in thermal comfort performance than other sports bras. In addition, the average value of T s and H s of five time points was also compared if there was no significant difference between two sports bras at any time point.…”

“…(2020) found that the bouncing breast movements might create extra airflows through the bra cup neckline, which swiftly promoted sweat evaporation during exercise at the upper-center front cup. 23 Besides, the heat-reduction mastectomy bra with ventilation holes and breast prosthesis with a hollow inner air chamber demonstrated better thermal and moisture control, resulting in lower body temperature and lower humidity increment during excise. 24 This suggests the possibility that the thermal comfort performance of the sports bra can be improved through ventilation design.…”

“…(2020) suggested the possibility that the thermal comfort performance of sports bras could be improved through ventilation design. 23 However, most studies on the thermal comfort of sports bras were addressing the effect of different fabrics, 7–10 whereas the effect of ventilation design on heat loss during exercise has yet to be investigated. In addition, the improvement of thermal comfort performance should not be at the cost of the reduction of support performance, which was regarded as one of the most important functions of sports bras.…”