Sedilla and Maeda ﻿
Journal of Physiological Anthropology(2022) 41:35
https://doi.org/10.1186/s40101-022-00308-x

Open Access

SHORT REPORT

Autonomic thermoregulatory responses
and subjective thermal perceptions
upon the initiation of thermal behavior
among resting humans in hot and humid
environment
Keneth B. Sedilla1*   and Takafumi Maeda2,3

Abstract
Background: While thermoregulatory behavior is critical for maintaining homeostasis, our knowledge of behavioral
thermoeffectors in humid heat is limited compared to the control of autonomic thermoeffectors. The predictions thatthe frequency and duration of intensified humid heat events are expected to increase in the coming years underline
this shortcoming. Therefore, this study aims to elucidate the activation of autonomic thermoregulatory responses andsubjective thermal perceptions upon deciding to initiate thermal behavior in a hot and humid environment.
Methods: Ten young male adults participated in an experimental trial where local cooling was permitted at any time
during the behavioral assessment during passive exposure to humid heat. The air temperature and relative humidity were kept at 33◦C and 80%, respectively. Skin temperatures, core body temperature (Tcore), and skin blood flow
(forearm, upper arm, and upper back) were obtained 120 s preceding thermal behavior. Local sweat rate (forearm andupper arm) and subjective thermal perceptions (neck and whole-body) upon thermal behavior initiation were also
recorded.
Results: Mean skin temperature ( T sk ) and Tcore increased prior to thermal behavior initiation (p = 0.002; p = 0.001). An
increase in mean body temperature ( T body ) was also observed (p < 0.001). However, the initiation of thermal behavior
is not preceded by an increase in skin blood flow (p ≥ 0.154) and local sweat rate (p ≥ 0.169). An increase in thermal
discomfort and skin wetness perception was observed (p ≤ 0.048; p ≤ 0.048), while thermal sensation did not differ
from the baseline (p ≥ 0.357).
Conclusion: These findings suggest that when given the opportunity to behaviorally thermoregulate in a hot andhumid environment, changes in skin blood flow and sweat rate are not required for thermal behavior to be initiatedin resting humans. Moreover, an increase in T sk and Tcore, which appears to cause an increase in thermal discomfort,
precedes thermal behavior. In addition, an increase in T body leading up to thermal behavior initiation was observed,
suggesting that changes in T body rather than T sk and Tcore alone mediate thermal behavior in humid heat. Collectively,*Correspondence: sedilla.keneth.004@s.kyushu-u.ac.jp
1
Department of Design (Human Science International Course), Graduate
School of Design, Kyushu University, 4‑9‑1 Shiobaru, Minami‑ku,
815‑8540 Fukuoka, Japan
Full list of author information is available at the end of the article© The Author(s) 2022. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which
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mmons.​org/​publi​cdoma​in/​zero/1.​0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.

Sedilla and Maeda ﻿Journal of Physiological Anthropology(2022) 41:35

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the results of this study appear to support the hypothesis that the temporal recruitment of autonomic thermoeffectors follows an orderly manner based on their physiological cost.
Keywords: Behavioral thermoregulation, Autonomic responses, Subjective responses, Hot and humid environment

Background
When humans are subjected to heat stress, the temperature gradient between the skin and the environment isreduced, causing a decrease in heat dissipation rate [1].
As a result, the body becomes heavily dependent on
evaporative cooling via sweating to facilitate heat loss [2].
However, evaporative heat loss decreases when humidity rises due to a reduced water vapor pressure gradient
between the ambient air and the skin’s surface [1]. Such
hot and humid condition significantly affects thermal
comfort [3] and elevates skin temperature (Tsk ) and core
body temperature (Tcore) [4].
Thermal behavior has long been recognized as our firstline of defense against uncompensable heat stress [5, 6].
Behavioral thermoeffectors have been postulated to alleviate the autonomic strain by preventing the rise in Tcore
and thereby minimizing the requirement to activate cutaneous vasodilation and sweating [7]. While it is criticalfor homeostasis, our understanding of behavioral thermoregulation is limited compared to the substantial workon autonomic thermoregulation.
Recent studies on behavioral thermoregulation in resting humans have utilized paradigms that permit thermal behavior while continuously measuring autonomic
responses along with subjective thermal perceptions
upon initiating thermal behavior [5, 8–13]. Schlader
et al. [5, 8, 9, 11, 13] conducted several studies using the
shuttle-box thermoregulatory model that permits passive movement between a cold room (air temperature[Tair ]: 7–17 ◦ C, relative humidity [RH]: 31–50%) and awarm room (Tair : 40–45◦ C, RH: 10–47%), when they feel“too cool” or “too warm”. They found that neither sweating nor shivering is required to initiate thermal behavior[8]. It has also been reported that thermal behavior ispreceded by small changes in skin blood flow (SkBF) andoccurs prior to a substantial increase in SkBF and sweating during heat exposure or an increase in metabolicheat production during cold exposure [14]. Furthermore,
Schlader et al. [5] suggest that thermal behavior is elicitedby subjective thermal perceptions caused by changes inmean Tsk ( Tsk ) and Tcore. These findings, taken together,suggest that autonomic thermoeffectors are recruited ina systematic and coordinated manner relative to their
physiological costs [10].
While the previous literature has advanced our understanding of human behavioral thermoregulation, its
mechanisms and modulators under extreme thermal

environments remain unknown. Furthermore, thesestudies have utilized experimental paradigms by which
thermal behavior in resting humans is examined in a
dry heat environment. To our knowledge, the subjective thermal perceptions and the temporal recruitmentof autonomic thermoeffectors preceding thermal behavior in a hot and humid environment have not been formally examined. The predictions that the frequency andduration of intensified humid heat events are expected
to increase in the coming years [15] underline thisshortcoming.
Therefore, this study aims to provide insights into
human behavioral thermoregulation in a hot and humid
environment. Moreover, this study aimed to test whether
the systematic recruitment of autonomic thermoeffectors
holds true in hot and humid conditions. Since evaporative heat loss is impeded in humid heat, Tsk and Tcore arelikely to be substantially elevated. Thus, we hypothesizedthat changes in Tsk and Tcore precede thermoregulatory behavior. However, we expect that there will be nochanges in SkBF and local sweat rate (LSR) leading up toand upon thermal behavior initiation.

Methods
Subjects

Ten young male adults participated in this study. The
subjects’ characteristics were as follows: age, 23 ± 2
years; height, 171.5 ± 5.1 cm; weight, 64.9 ± 7.8 kg; bodysurface area, 1.76 ± 0.11 m2; percent body fat, 14.07 ±
4.51%. All subjects were physically or recreationallyactive and not taking any medications. The Montreal
Cognitive Assessment (MoCA) [16] was used to ensurethat the subjects did not have any mild cognitive impairment (MoCA score: 29 ± 1). The subjects were free fromany known cardiovascular, respiratory, or neurologicaldiseases. All the subjects abstained from alcoholic drinks
and vigorous exercise for 24 h and did not consume any
food or caffeine for at least 2 h before the experiment.
Each subject was fully informed of the experimental
procedures and possible risks before obtaining written
informed consent. Experimental testing was conductedfrom winter to spring in Fukuoka, Japan (the average outdoor temperature on the day and time of the experimental trials was 16 ± 4 ◦C). Within the month leading up to
the experimental testing, none of the participants had
performed any training in particularly hot environments.
This study was approved by the Ethics Committee of theSedilla and Maeda ﻿Journal of Physiological Anthropology(2022) 41:35

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Graduate School of Design, Kyushu University (approval
number 394).

dorsal surface of the proximal third of the left forearm(SkBFfa ), on the left upper arm (SkBFua ), and on theupper back (SkBFub).
LSR was obtained by securing a plastic capsuleinfused with dry silica gel on the dorsal surface of theright forearm (LSRfa ) and upper arm (LSRua ) with adoughnut-shaped double-sided medical tape (Nihon
Kohden Corp., Japan). The plastic capsule has a circular opening at the bottom, covering 1 cm2 of the skin.
The LSR was calculated by taking the difference in massof the plastic capsule (with silica gel) between the postand pre-application (measured in triplicate), dividing by the surface area covered by the plastic capsuleand the duration of application, yielding values in mg
min−1 cm−2 . Throughout the experimental trial, LSRfa
and LSRua were measured at a 5-min interval and linear interpolation was used to determine the LSRs at thetime when thermal behavior was first initiated.
The participants used subjective scales [18, 19] to rate
their thermal sensation (TS), skin wetness perception(SW), and thermal comfort (TC) on their dorsal neckand across their whole body at the time when thermal
behavior was first initiated. Subjective thermal perceptions were also recorded every 5 min throughout theexperimental trial.

Experimental design and procedures

Subjects arrived at the laboratory euhydrated (urine specific gravity: 1.05 ± 0.03) and wore short-sleeve T-shirts
and shorts (0.13 clo). Following instrumentation in theadjacent room with Tair at 25 ◦ C and 50% RH, subjects
were transferred to the climatic chamber and assumed
a seated position on a standard upright cycle ergometerwith custom-made footstools and armrests. Throughout
the experiment, the climatic chamber’s Tair and RH were
fixed at 33 ◦ C and 80%, respectively.
The experimental trial lasted 60 min and was separated
into two phases: baseline measurement (which occurred
within the first 5 minutes of the experiment) and behavioral assessment. At any time during the behavioral
assessment phase, subjects were allowed to use a portable cooler (IPC-221N, Iris Ohyama Inc., Japan) with acustom-built tubing system that delivers cool air (∼ 6 ms−1) to the dorsal part of their neck. They were specifically instructed to use the portable cooler to keep theirneck at a thermally comfortable temperature throughout
the experiment. This local-cooling behavioral paradigm,
in which cooling is permitted to maintain local thermal
comfort [14], was adopted and modified from those of
Schlader et al. [10]. In our study, the initiation of thermal
behavior was defined as the decision to use and/or adjust
the temperature of the portable cooler. All subjects wereallowed to watch nature and ecology documentaries (i.e.,“Our Planet”) throughout the experiment.
Measurements

Tcore and all Tsk (including the dorsal neck temperature[Tneck ]) were recorded every 1 s using a data logger (LT8A, Gram Corporation, Japan; precision: ± 0.01◦C). In
this study, aural temperature served as an indicator of
Tcore and was measured with earplug-type thermistor(Nikkiso-Thermco. Ltd., Japan; maximum precision: ±0.01 ◦ C within 30–40 ◦ C temperature range). Tsk was
obtained as the weighted average of ten skin thermistors (LT-ST08-12, Gram Corporation, Japan; precision:± 0.01 ◦ C) attached to the following locations: forehead,
upper back, chest, upper arm, forearm, hand, abdomen,thigh, lower leg, and instep [17], while mean body temperature ( Tbody ) was calculated as 0.9 × Tcore + 0.1 × Tsk[9].
SkBF was measured every 0.01 s (then averaged to 1s) with a laser Doppler flowmeter using a contact-type
disk probe (Omegaflo FLO-C1, Omegawave Co., Ltd,
Japan; time constant: 1 s) at three locations: on the

Data analysis

In this study, our data analysis focused exclusively on
the subject’s initial thermal behavior, which occurred
when they turned on the portable cooler for the
first time. The analysis of the subsequent behavioral
responses was not included in this study.
Temperature and SkBF data were analyzed at baseline (5-min average) and 120, 90, 60, and 30 s (all 30 s
averages) immediately before the initiation of thermal
behavior. These data were also reported as a percent
change (%) from 120 s preceding thermal behavior,
which enabled the identification of changes in these
physiological measurements (adopted from Schlader
et al. [8]). LSR data and subjective thermal perceptions
were analyzed at baseline and at the time when thethermal behavior was first initiated. All temperatureand SkBF data were analyzed using one-way repeatedmeasures ANOVA. Data were assessed for approximation to a normal distribution and sphericity. Where
appropriate, post hoc Bonferroni adjusted pair-wisecomparisons were made. A paired t-test was used toanalyze all LSR data, while related Wilcoxon signedrank test was used to analyze subjective thermal perceptions. Data were analyzed using SPSS v. 28.0. A
priori statistical significance was set at p ≤ 0.05, and alldata were presented as mean ± SD.

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Results
Two subjects did not use the portable cooler throughout the experimental trial. The average time before theinitiation of thermal behavior was 12.0 ± 10.0 min (n= 8), and the individual latency before the initiation ofthermal behavior was 6.5, 6.1, 35.3, 6.4, 8.1, 6.1, 11.9,
and 15.5 min, respectively.

Both TCbody and TCneck were different from baseline (p≤ 0.048; Fig. 4c).

Body temperatures

At all time intervals preceding thermal behavior, T core
was higher than baseline (p ≤ 0.042; Fig. 1a) except
for the 120–90-s interval (p = 0.059), whereas the %
from 120 to 90 s before thermal behavior in T core wasincreasing (p = 0.001). Likewise, both Tsk and Tbody
were higher than baseline preceding thermal behavior(p ≤ 0.05; Fig. 1b and c) and elicited an increasing trend
in the % from 120 to 90 s immediately before thermal
behavior (p ≤ 0.002). T neck did not differ between baseline (p ≥ 0.089; Fig. 1d) but was increasing in the %
from 120 to 90 s immediately before thermal behavior(p < 0.001).
Skin blood flow

SkBFfa did not differ from baseline at all time intervals
preceding thermal behavior (p = 0.148; Fig. 2a). The %
from 120 s preceding initiation of thermal behavior in
SkBFfa did not change (p = 0.238). Similarly, both SkBFua
and SkBFub were not different from baseline (p ≥ 0.177;
Fig. 2b and c), and there were no changes in the % from
120 to 90 s immediately before thermal behavior (p ≥0.154).
Local sweat rate

LSRfa at the time when thermal behavior was initiated
was not different from baseline (p = 1.00; Fig. 3). Similarly, the same results were observed for LSRua (p =0.169).
Subjective thermal perceptions

Subjects felt “warm” at the time when thermal behavior was initiated, and it was not different from baseline(TSbody : p = 0.071; Fig. 4a). Furthermore, subjects felt
“slightly warm” in their neck region at thermal behavior
initiation, and it did not differ from baseline (TSneck : p= 0.357). Subjects perceived their neck region (SWneck )and their whole body (SWbody ) “slightly wet” at the time
when thermal behavior was initiated (p ≤ 0.048; Fig. 4b),and both differed from the baseline. For TCbody and
TCneck , subjects felt “slightly uncomfortable” at baseline
but felt “uncomfortable” at thermal behavior initiation.

Discussion
In support of our hypothesis, this study demonstrates anincrease in Tsk and Tcore upon the initiation of thermal
behavior. Likewise, an increase in Tbody were observed
preceding initial thermal behavior. However, it is not preceded by an increase in SkBF and LSR, indicating thatchanges in skin blood flow and sweating are not required
for the initiation of thermal behavior in a hot and humid
environment. Furthermore, changes in SW and TC wereobserved upon thermal behavior initiation.
Autonomic and subjective responses upon the initiationof thermal behavior

In resting humans, Schlader et al. [8] have reported thatbehavioral responses are primarily driven by signals arising from changes in Tsk and not in Tcore. The present
study, however, found that both Tsk and Tcore increased
prior to the initiation of thermal behavior. In addition,
the results showed that Tcore and Tsk were higher thanbaseline at nearly all time points leading up to thermal
behavior initiation. Thus, it is possible that both the absolute values and the changes in Tcore and Tsk influence thedecision to thermoregulate behaviorally. We were notable to uncover the related mechanisms of these findings
in our study design. Thus, further research is required todetermine whether the absolute temperature or the rateof increase in temperature influences thermal behavior or a combination of both. We have also observed anincrease in Tbody immediately before thermal behavior.
These findings suggest that in hot and humid environments, both Tsk and Tcore appear to be important thermal inputs in signaling a subjective, conscious increasein thermal discomfort, which subsequently induces thermal behavior. Furthermore, our results corroborate priorfindings [20] that changes in Tbody , rather than Tsk alone,
mediate thermal behavior initiation. These results are notsurprising given the previously demonstrated significant
correlation between Tsk and thermal discomfort [5].
Thermal behavior has also been reported to be preceded by slight changes in SkBF and occurs before thesignificant increase in SkBF and sweating during heat
exposure [8]. Similarly, this study demonstrated the same
results where marginal increase in SkBF precede thermal
behavior activation. Moreover, no changes were observedin LSRs at the point when thermal behavior was initiated.
From these results, it can be postulated that changes inskin blood flow and sweat rate are not required to initiate
thermal behavior in hot and humid environments.
Humidity is a significant limiting factor in the evaporation of perspiration in humid heat [21]. It has beenSedilla and Maeda ﻿Journal of Physiological Anthropology(2022) 41:35

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Fig. 1 a Tcore, b T sk, c T body , and d Tneck at baseline and 120, 90, 60, and 30 s immediately before thermal behavior (left panels) and the % fromthe 120–90-s interval preceding thermal behavior (right panels). All values are reported as means ± SD, n = 8. ∗Different from baseline (p ≤ 0.05). 1
Different from 120–90-s interval (p ≤ 0.024). 2Different from 90–60-s interval (p ≤ 0.02). 3Different from 60–30-s interval (p ≤ 0.029). ∗∗The one-way
repeated measures ANOVA is significant; however, post hoc analysis indicates that all 30-s intervals prior to thermal behavior initiation are notdifferent from the baseline (p ≥ 0.089). The p-values for one-way repeated measures ANOVA are notedSedilla and Maeda ﻿Journal of Physiological Anthropology(2022) 41:35

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Fig. 2 a SkBFfa, b SkBFua, and c SkBFub at baseline and 120, 90, 60, and 30 s immediately before thermal behavior (left panels) and the % fromthe 120–90-s interval preceding thermal behavior (right panels). All values are reported as means ± SD, n = 8. The p-values for one-way repeatedmeasures ANOVA are noted

proposed that perceived changes in ambient humidity and absolute skin wetness influence thermal comfort[22]. In this study, some of the generated sweat drips
from the body due to the high level of humidity. The subjects perceived “slight skin wetness” upon thermal behavior initiation. Thus, we speculate that the accumulated
non-evaporated sweat on the skin exacerbates thermal
discomfort. It is possible that in the current paradigm, theautonomic thermoeffector end-organ responses (increasein body temperatures and skin wetness) are sensed via
known afferent signaling pathways and interpreted asthermal discomfort, which ultimately stimulates behavior [23]. Unfortunately, we were not able to measure theactual skin wetness during the experimental trial, so wecannot speculate the degree of its potential role in thermal behavior initiation. Nevertheless, such a relationshipappears to be probable.
Recruitment of thermoeffectors

Recent studies have found that thermal behavior reduces the need for autonomic thermoeffector

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Fig. 3 Paired t-test results for LSRfa and LSRua at baseline (BL) and at the time when thermal behavior was initiated (TB). All values are reported asmeans ± SD, n = 8. The p-values for paired t-tests are noted

Fig. 4 Boxplot representation and related Wilcoxon signed-rank test results for a TS, b SW, and c TC at baseline (BL) and at the time when thermal
behavior was initiated (TB). 1TS subjective scale [18] (to the nearest 0.5 units; 1 = cold, 2 = cool, 3 = slightly cool, 4 = neutral, 5 = slightly warm,
6 = warm, 7 = hot). 2 SW subjective scale [19] (to the nearest 0.5 units; 1 = very dry, 2 = dry, 3 = slightly dry, 4 = neutral, 5 = slightly wet, 6 =wet, 7 = very wet). 3 TC subjective scale [18] (to the nearest 0.5 units; 1 = comfortable, 2 = slightly comfortable, 3 = uncomfortable, 4 = very
uncomfortable). ∗The median of differences is significantly different (p ≤ 0.048). The p-values for related Wilcoxon signed-rank test are noted (n = 8)

activation, enabling body temperature regulation withminimal impact on the regulation of other biological systems [10, 14]. Schlader et al. [14] hypothesizedthat autonomic thermoeffector activation is sensed
and recruited in an orderly manner to stimulate thermal behavior and that autonomic thermoeffectorsthat do not consume many physiological resources areactivated before the more resource-consuming thermoeffectors. Collectively, our findings that the initiation of thermal behavior is preceded by an increase in
Tsk and T core and that changes in SkBF and LSR are
not required in thermal behavior activation appear
to support the orderly recruitment of autonomic
thermoeffectors.

Sedilla and Maeda ﻿Journal of Physiological Anthropology(2022) 41:35

Considerations and perspectives

In this study, several methodological considerations warrant attention. First, our findings are constrained by themethodology employed herein. For instance, throughout the experimental trial, the climatic chamber’s Tairand RH were fixed at 33 ◦ C and 80%, respectively. Thus,
whether our results would have been the same if we had
used different Tair and RH in simulating hot and humid
environments remains unknown. Moreover, skin bloodflow measurements were localized to the forearm, upper
arm, and upper back, while sweat rate was measured in
the forearm and upper arm. During heat exposure, variations in skin blood flow and sweat rate are known tooccur across the body. Therefore, it is unknown whether
our findings can be extended to other body measurementsites, such as those with glabrous skin. Also, it is essential
to note that local sweat rate data at the thermal behavior initiation were estimated using linear interpolation, so
they might not have been entirely accurate. Furthermore,
we did not control for the time of day of the experimental
trials. Second, we did not perform an a priori power analysis in determining sample size. However, our primarymeasurement variables, such as Tcore, Tsk , Tbody , andTneck , which show statistically significant changes leading up to the initiation of thermal behavior, all reacheda statistical power of at least 96.78%. Lastly, the present
study utilized only male subjects. Given that sex modulates autonomic and subjective responses, sex-relateddifferences in behavioral thermoregulation appear likely.
Therefore, formal comparisons between male and female
subjects are warranted.

Conclusion
This study demonstrates that when given the opportunity to behaviorally thermoregulate in a hot and humid
environment, changes in skin blood flow and an increasein sweat rate are not required for thermal behavior to be
initiated in resting humans. Furthermore, an increase in
Tsk and Tcore, which appears to cause an increase in thermal discomfort, precedes the decision to thermoregulate
behaviorally. In addition, an increase in Tbody leading up
to thermal behavior initiation was observed, suggesting thatchanges in Tbody rather than Tsk and Tcore alone mediate
thermal behavior in humid heat. Altogether, these findings
suggest that the orderly recruitment of autonomic thermoeffectors holds true in hot and humid conditions.
Nonetheless, to the best of our knowledge, this is thefirst study of its sort. Thus, this study can be considered apreliminary step in understanding the control of humanbehavioral thermoregulation in hot and humid environments. We believe that knowledge regarding the mechanisms and modulators of thermal behavior in humid heat

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is essential in light of forecasts that the frequency andduration of intense humid heat will rise in the coming
years.
Abbreviations
Tair: Air temperature; RH: Relative humidity; Tsk: Skin temperature; Tcore: Core bodytemperature; Tsk: Mean skin temperature; Tbody: Mean body temperature;
Tneck: Neck temperature; SkBFfa: Forearm skin blood flow; SkBFua: Upper arm
skin blood flow; SkBFub: Upper back skin blood flow; LSRfa: Forearm local sweat rate;
LSRua: Upper arm local sweat rate; TSbody: Whole-body thermal sensation;
TSneck: Neck thermal sensation; TCbody: Whole-body thermal comfort;
TCneck: Neck thermal comfort; SWbody: Whole-body skin wetness perception;
SWneck: Neck skin wetness perception; %: Percent change; BL: Baseline; TB:
Thermal behavior.
Acknowledgements
We would like to express our gratitude to all our participants for their voluntary
contribution to this study. We would also like to acknowledge Mr. Yasuhiko
Maeda (technical staff of the Research Center for Human Environmental
Adaptation), Ms. Jiang Ruhan, Ms. Zhuang Ruijia, Ms. Lizbeth A. Mariano, andMr. Keita Shiragami for their assistance in conducting the experiments.
Authors’ contributions
Keneth B. Sedilla (KS) and Takafumi Maeda (TM) conceived and designed theresearch. KS conducted the experiments, analyzed the data, and wrote themanuscript. TM edited the manuscript and provided critical feedback. All
authors read and approved the final manuscript.
Funding
Not applicable.
Availability of data and materials
All datasets used and/or analyzed in this study are available from the corresponding authors on reasonable request.

Declarations
Ethics approval and consent to participate
This study was approved by the Ethics Committee of the Graduate School of
Design, Kyushu University (Approval No. 394). All the participants were fully
informed of the experimental procedures and possible risks before obtaining
written informed consent.
Consent for publication
Not applicable.
Competing interests
The authors declare that they have no competing interests.
Author details
1
Department of Design (Human Science International Course), Graduate Schoolof Design, Kyushu University, 4‑9‑1 Shiobaru, Minami‑ku, 815‑8540 Fukuoka,
Japan. 2 Department of Human Life Design and Science, Faculty of
Design, Kyushu University, 4‑9‑1 Shiobaru, Minami‑ku, 815‑8540 Fukuoka,
Japan. 3 Physiological Anthropology Research Center, Faculty of Design,
Kyushu University, 4‑9‑1 Shiobaru, Minami‑ku, 815‑8540 Fukuoka, Japan.
Received: 19 May 2022 Accepted: 23 September 2022

References
1. Sobolewski A, Młynarczyk M, Konarska M, Bugajska J. The influence of
air humidity on human heat stress in a hot environment. Int J Occup Saf
Ergon. 2021;27:226–36.

Sedilla and Maeda ﻿Journal of Physiological Anthropology

2.
3.

4.
5.
6.
7.

8.

9.
10.
11.
12.

13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.

(2022) 41:35

Dzyuban Y. Relationship between humidity and physiology in warmand humid conditions: a literature review. Res Collect Sch Soc Sci.
2020:3243. https://​ink.​libra​ry.​smu.​edu.​sg/​soss_​resea​rch/​3243.
Zuo C, Luo L, Liu W. Effects of increased humidity on physiologicalresponses, thermal comfort, perceived air quality, and Sick Building
Syndrome symptoms at elevated indoor temperatures for subjects in a
hot-humid climate. Indoor Air. 2021;3(31):524–40.
Kakitsuba N. Current knowledge on the effects of humidity on physiological and psychological responses. J Hum-Environ Syst. 2018;20:1–10.
Schlader ZJ, Prange HD, Mickleborough TD, Stager JM. Characteristicsof the control of human thermoregulatory behavior. Physiol Behav.
2009;98:557–62.
Schlader ZJ. The relative overlooking of human behavioral temperature
regulation: an issue worth resolving. Temperature. 2014;1:20–1.
Lei TH, Matsukawa H, Okushima D, Gerrett N, Schlader ZJ, Mündel T, et al.
Autonomic and perceptual thermoregulatory responses to voluntarily
engaging in a common thermoregulatory behaviour. Physiol Behav.
2020;215:112768.
Schlader ZJ, Coleman GL, Sackett JR, Sarker S, Chapman CL, Johnson
BD. Activation of autonomic thermoeffectors preceding the decision to behaviourally thermoregulate in resting humans. Exp Physiol.
2016;101:1218–29.
Schlader ZJ, Coleman GL, Sackett JR, Sarker S, Chapman CL, Hostler D.
Behavioral thermoregulation in older adults with cardiovascular comorbidities. Temperature. 2018;5:70–85.
Schlader ZJ, Sackett JR, Sarker S, Johnson BD. Orderly recruitment of thermoeffectors in resting humans. Am J Physiol-Regul Integr Comp Physiol.
2018;314:R171–80.
Schlader ZJ, Perry BG, Jusoh MRC, Hodges LD, Stannard SR, Mündel T.
Human temperature regulation when given the opportunity to behave.
Eur J Appl Physiol. 2013;113:1291–301.
Vargas NT, Slyer J, Chapman CL, Johnson BD, Temple JL, Mietlicki-Baase
EG, et al. The motivation to behaviorally thermoregulate during passive
heat exposure in humans is dependent on the magnitude of increases inskin temperature. Physiol Behav. 2018;194:545–51.
Schlader ZJ, Sarker S, Mundel T, Coleman GL, Chapman CL, Sackett JR,
et al. Hemodynamic responses upon the initiation of thermoregulatory
behavior in young healthy adults. Temperature. 2016;3:271–85.
Schlader ZJ, Vargas NT. Regulation of body temperature by autonomic
and behavioral thermoeffectors. Exerc Sport Sci Rev. 2019;47:116–26.
Hanna EG, Tait PW. Limitations to thermoregulation and acclimatization
challenge human adaptation to global warming. Int J Environ Res Public
Health. 2015;12:8034–74.
Nasreddine ZS, Phillips NA, Bédirian V, Charbonneau S, Whitehead V, Collin I,
et al. The Montreal Cognitive Assessment, MoCA: a brief screening tool
for mild cognitive impairment. J Am Geriatr Soc. 2005;53:695–9.
Liu W, Lian Z, Deng Q, Liu Y. Evaluation of calculation methods of mean
skin temperature for use in thermal comfort study. Build Environ.
2011;46(2):478–88.
Gagge AP, Stolwijk JAJ, Hardy JD. Comfort and thermal sensations andassociated physiological responses at various ambient temperatures.
Environ Res. 1967;1(1):1–20.
Filingeri D, Fournet D, Hodder S, Havenith G. Tactile cues significantly
modulate the perception of sweat-induced skin wetness independentlyof the level of physical skin wetness. J Neurophysiol. 2015;113:3462–73.
Fluoris AD, Cheung SS. Human conscious response to thermal input
is adjusted to changes in mean body temperature. Br J Sports Med.
2009;3(43):199–203.
Parsons K. Human thermal environments: the effects of hot, moderate,and cold environments on human health, comfort, and performance.
Florida: CRC Press, Taylor and Francis Group, LLC; 2002.
Fukazawa T, Havenith G. Differences in comfort perception in relation to local and whole body skin wettedness. Eur J Appl Physiol.
2009;106:15–24.
Flouris AD. Functional architecture of behavioural thermoregulation. Eur J
Appl Physiol. 2011;111:1–8.

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