Alleviation of heat strain by cooling different body areas during red pepper harvest work at WBGT 33 degrees C.

Abstract

The purpose of the present study was to examine the effects of different types of personal cooling equipments (PCE) on the alleviation of heat strain during red pepper harvest simulated in a climatic chamber. The experiment consisted of eight conditions: 1) Control, 2) Neck cooling scarf A with a cooling area of 68 cm2, 3) Neck cooling scarf B (cooling area 154 cm2), 4) Brimmed hat with a frozen gel pack, 5) Cooling vest (cooling area 606 cm2), 6) Hat+Neck Scarf B, 7) Hat+Vest, and 8) Hat+Neck Scarf B+Vest. Twelve subjects worked a red pepper harvest simulated in a climatic chamber of WBGT 33 degrees C. The result showed that rectal temperature (T(re)) was effectively maintained under 38 degrees C by wearing PCE. Mean skin temperature (T(sk)) and heart rate (HR) became more stable through wearing PCE. When wearing the 'Hat+Scarf B+Vest', particularly, T(sk) and HR quickly decreased to the comfort level during the mid-rest stage. We confirmed that the vest with a cooling area of only 3.3% body surface area (BSA) was effective in alleviating heat strain in a simulated harvest work. Furthermore, the heat strain of farm workers can be considerably eliminated by the combination of the cooling vest, a scarf, and a brimmed hat, with the total cooling area of 4.2% BSA.

Full text

Page 1

Introduction
One of the heaviest farm works in Korea is known as
red pepper harvest in summer. The direct sun light,
lengthy work in a squatting position, the lack of break
time and the increase in the participation of elderly
women have been pointed out as problems in the har-
vesting of red pepper1). The fundamental method to alle-
viate worker’s heat strain is to reduce worker’s physical
thermal burden through mechanization and the improve-
ment of air-conditioning of occupational fields. However,
these ergonomic interventions are not feasible in red pep-
per fields, because workers have to pick each red pepper
by hand on fields. We have investigated the farm work
environments and worker’s workload, and presented per-
sonal cooling equipment (PCE) as an alternative for farm
workers1–3).
Over last 50 yr, there have been many studies that dealt
with PCE for alleviating heat strain. PCE can be divid-
ed into three types by coolants: air, liquid and frozen gel
(or ice or PCM). The studies have mainly focused on
soldiers performing missions in deserts, pilots sitting in a
small and hot cockpit4–7), workers in power plants or iron
mills8, 9), and workers wearing chemical protective gar-
ments for protection from harmful chemicals10, 11).
Relatively, there is few study interested in farm workers
Industrial Health 2008, 46, 620–628
Original Article
Alleviation of Heat Strain by Cooling Different
Body Areas during Red Pepper Harvest Work at
WBGT 33˚C
Jeong-Wha CHOI1, 2, Myung-Ju KIM1and Joo-Young LEE3*
1Department of Clothing & Textiles, College of Human Ecology, Seoul National University, Gwanak-Gu,
Sillim-dong, San 56–1, Seoul 151-742, Korea
2Research Institute of Human Ecology, Seoul National University, Gwanak-Gu, Sillim-dong, San 56–1, Seoul
151-742, Korea
3Department of Ergonomics, Faculty of Design, Kyushu University, 4–9–1 Shiobaru, Minami-ku, Fukuoka
815-8540, Japan
Received August 30, 2007 and accepted July 22, 2008
Abstract: The purpose of the present study was to examine the effects of different types of per-
sonal cooling equipments (PCE) on the alleviation of heat strain during red pepper harvest sim-
ulated in a climatic chamber. The experiment consisted of eight conditions: 1) Control, 2) Neck
cooling scarf A with a cooling area of 68 cm2, 3) Neck cooling scarf B (cooling area 154 cm2), 4)
Brimmed hat with a frozen gel pack, 5) Cooling vest (cooling area 606 cm2), 6) Hat+Neck Scarf
B, 7) Hat+Vest, and 8) Hat+Neck Scarf B+Vest. Twelve subjects worked a red pepper harvest
simulated in a climatic chamber of WBGT 33˚C. The result showed that rectal temperature (Tre)
was effectively maintained under 38˚C by wearing PCE. Mean skin temperature (T¯sk) and heart
rate (HR) became more stable through wearing PCE. When wearing the ‘Hat+Scarf B+Vest’,
particularly, T¯skand HR quickly decreased to the comfort level during the mid-rest stage. We
confirmed that the vest with a cooling area of only 3.3% body surface area (BSA) was effective
in alleviating heat strain in a simulated harvest work. Furthermore, the heat strain of farm
workers can be considerably eliminated by the combination of the cooling vest, a scarf, and a
brimmed hat, with the total cooling area of 4.2% BSA.
Key words: Personal cooling equipment, Heat stress, Heat strain, Farm work, Neck cooling, Thermal
comfort
*To whom correspondence should be addressed.

Page 2

in light wear, under the direct sun light with an awkward
work posture for long periods of time. For the farm work-
ers harvesting in fields in summer, points to be taken into
account for PCE are as follows: Which body region is
effective and efficient in cooling? Which coolant among
air, liquid and frozen gel is proper? Does PCE hinder
worker’s mobility? How much does it weigh? Is not it
too expensive? Is it easy to manage?
Regarding the body region cooled, the trunk has been
mainly cooled using a vest. However, even if core tem-
perature is maintained in an acceptable range by the cool-
ing vest, the head and the neck can become overheated
in some cases5). Shvartz and his colleagues have shown
that the most efficient part among the neck, the face, the
arm, the hands, the trunk, the leg, and the feet, was the
neck12). Therefore, personal devices for the neck or head
cooling as well as cooling vests can be suggested for farm
worker. Besides, farm workers in summer are exposed
to direct sun rays. The wearing of a brimmed hat is nec-
essary for workers outside in summer. It is reported that
when the temperature of the head was kept cool even if
core temperature increased by artificial manipulation,
thermal comfort did not get worse, and the sweat rate of
the face decreased5, 13).
One of the disadvantages of PCE is that the garments
are somewhat heavy. The weight of ice bags-vests is
about 2 to 7 kg14–18). Heavy clothing can cause an
increase in energy expenditure of workers. Duggan
(1988)19)has reported that when workers wore clothing
of 3 kg and 5 kg, the energy metabolism increased as
much as 5% and 9%, respectively. Therefore, PCE for
farm workers working in a squatting position for a long
time, should be as light as possible.
Regarding the type of cooling system, frozen gel packs
are known as more appropriate coolants than an air-ven-
tilated system (AVS) or a liquid cooling system (LCS)
during outside work. That is because cooling systems
using frozen gel or ice are relatively lighter than AVS and
LCS; cooling capacity of ice or frozen gel is greater than
that of cooled air or water20, 21); and the AVS or LCS
restrict body movements because of connections with
devices for supplying air or liquid. Portable AVS of LCS
are too heavy because workers would have to carry the
pump and battery on their backs. Cooling systems using
a frozen gel pack does not restrict worker’s movements22).
Lastly, the price of a cooling system using frozen gel
packs is much cheaper than a cooling system using cir-
culated air or water.
In considering the above mentioned all together, a cool-
ing vest, neck cooling scarf, head cooling or brimmed hat
with a cooling function, using frozen gel packs, can be
suggested as PCE for farm workers. Based on our pre-
vious studies about farm work in summer1), we developed
a cooling vest, a brimmed hat with a cooling function,
and cooling scarves. The present study evaluated the
effects of neck cooling scarves, a cooling vest, a brimmed
hat, and the combination of cooling garments, on physi-
ological and subjective responses during the red pepper
harvest simulated in a climatic chamber.
Methods
Subjects and personal cooling garments
Twelve young males (Mean ± SD: Age 25.4 ± 1.6 yr,
height 173.1 ± 5.0 cm, weight 69.3 ± 9.8 kg, BSA
1.86 ± 0.14 m2) participated as volunteers. None of the
subjects was an athlete. Prior to participation, written and
informed consent was obtained from all subjects, and a
medical history questionnaire was filled out. The exper-
imental protocol was approved by the ethics committee
of College of Human Ecology in Seoul National
University.
The experiment was undertaken under eight conditions:
1) Control (No cooling), 2) Neck Scarf A, 3) Neck Scarf
B, 4) Hat, 5) Vest, 6) Hat + Neck Scarf B, 7) Hat + Vest,
and 8) Hat + Neck Scarf B + Vest. Materials, design and
cooling areas (SAcooled) of these PCE were shown in
Table 1 (0.4–4.2% SAcooled). For cooling, frozen gel
packs were inserted in the cooling equipment. The packs
were filled with a water based crystals gel which is non
toxic and absorbed water. The frozen gel pack (180 g)
began to melt at the 20 min during the exposure at WBGT
33˚C, but the melting or cooling time-duration are depen-
dent to the activity of wearer. Through our preliminary
studies, the most effective brimmed hat among the three
kinds of brimmed hats we developed was selected2), and
the most effective cooling vest was also selected through
another previous study3). The reason we developed cool-
ing scarves and not a cooling hood was because of prac-
tical constraints on system design and to avoid placing a
weight burden on the head. In addition, the neck is known
as an advantageous site for heat removal because of the
proximity of large blood vessels to the skin in this area23).
As well as the effects of four kinds of PCE, the effects
of combinations of the brimmed hat with other PCE were
examined (Conditions 6–8). Subjects were dressed the
same for each trial before being fitted with PCE. They
wore shirts with long sleeves, long legged training pants,
underwear, socks, work gloves and athletic shoes. These
clothes were based on real farm workers’ work wear in
summer1).
Procedure and measurement
The experiments were conducted in a climatic cham-
ber. The environmental conditions of the climatic cham-
ber were constant at a temperature of 33 ± 0.5˚C and
ALLEVIATION OF HEAT STRAIN BY COOLING DIFFERENT BODY AREAS
621

Page 3

65 ± 5%RH of air humidity. To simulate sunlight on the
actual agricultural fields, artificial lamps on the ceiling of
the chamber were used. Black globe temperature was
constant at 39 ± 1˚C (WBGT 33˚C). Every experiment
started at the same time (10:00 am) to minimize the dif-
ference due to individual circadian rhythms. To minimize
the effects of acclimatization to the experiments, each
subject was exposed to the hot environment just for two
hours in a day, and the interval between successive exper-
iments was a minimum of three days. The order of wear
trials was randomized to eliminate the possible effects of
training.
Subjects were instructed not to consume alcohol or
drugs in the 48 h before testing. To avoid the specific
dynamic effects of food, subjects did not have any food
for three hours before testing but were permitted to drink
water. Experiments were conducted at the end of sum-
mer (August), when the subjects were naturally acclima-
tized to summer heat. Before entering into the climatic
chamber, subjects wore experimental garments and were
equipped with PCE. After resting for one hour in anoth-
er chamber kept at 25 ± 1˚C, subjects entered the heated
chamber.
In most previous studies concerning the efficacy of
PCE in climatic chambers, subjects rested or walked or
ran on a treadmill. However, red pepper harvest is more
dynamic than sitting on a chair, and less dynamic than
walking or running on a treadmill. Our subjects simu-
lated the red pepper harvest work based on a previous
study1). The major feature of harvesting Korean red pep-
per is to pick each red pepper by hand. To simulate the
harvesting work in the climatic chamber, we put four pot-
ted red pepper plants in a row in the chamber and hung
a total of 50 markers with the similar size as a piece of
red pepper on each plant. Subjects were instructed to
touch all markers according to the order of number from
1 to 200 and pretend it into their individual basket dur-
ing the simulated harvest work. The work lasted a total
622
J-W CHOI et al.
Industrial Health 2008, 46, 620–628
Table 1. Characteristics of personal cooling garments and experimental garments in the present study
No.Condition Garment weight (g)
Cooling area
(cm2)
Percentage of
cooling area
to BSA (%)a)
Description
1 No cooling
Frozen gel: 0
Total weight: 639
00
Cotton shirt with long sleeves, Long legged training pants,
cotton 100% underwear, cotton socks, work gloves, and
athletic shoesb)
2Neck Scarf A
Frozen gel: 60
Total weight: 74c)
68
0.37
(0.33–0.42)d)
The dimension of a frozen gel pack was 17 × 4 cm. The
pack enclosed by fabric cotton 100% was located on the
back of the neck.
3Neck Scarf B
Frozen gel: 180
Total weight: 203
154
0.83
(0.74–0.95)
The dimension of frozen gel pack was 14 × 11 cm. The
pack enclosed by fabric cotton 100% was located on the
back of the neck.
4 Hat
Frozen gel: 180
Total weight: 528
154
0.83
(0.74–0.95)
Made by reflective fabric (Nylon 100%, 78 g/m2,
180 warp/100 inch, surface reflectance 50.7%, UV-A
block 97.4%, UV-B black 99.5%, silver color), PE 100%
mesh around the head girth to ventilate. The below side
of the visor was finished with black T/C. A white and
attachable face-shade. The shade had a pocket to insert a
frozen gel pack. The frozen gel pack did not contact on
the back of the neck, but there was a little space between
the frozen gel pack and the skin of neck.
5Vest
Frozen gel:180 × 4
Total weight: 807
154 × 4=606
3.28
(2.90–3.74)
Reflective fabric same as the used at the brimmed hat
above (N.4). The two pieces of gel pack was on the chest,
and two was on the back. The body of the vest was made
by PE mesh, except pockets for inserting gel packs.
6Hat+Neck Scarf B
Frozen gel: 180
Total weight: 551
154
0.83
(0.74–0.95)
Combination of no.3 and no.4, except a gel pack from the
shade
7Hat+Vest
Frozen gel:180 × 4
Total weight:1,155
154 × 4=606
3.28
(2.90–3.74)
Combination of no.4 and no.5, except a gel pack from the
shade
8Hat+Vest+Neck Scarf B
Frozen gel:180 × 5
Total weight:1,358
154 × 5=770
4.16
(3.68–4.76)
Combination of no.3, no.4 and no.5, except a gel pack
from the shade
a)Cooling area × 100/the body surface area (BSA) of subjects; b)Work wear was based on Choi et al. (2007)1); c)Total weight includes the weight
of frozen gel; d)The range of minimum and maximum values by subject; *In condition 2 to 8, subjects wore same work wear as Condition 1.

Page 4

of 120 min (two bouts of 50-min harvest work with a 10-
min rest). Subjects drank water as much as subjects want
to drink before starting every experiment. Water intake
was prohibited during experimentation.
Rectal temperature (Tre) was measured using a portable
thermometer (LT 8A, Gram Corp., Japan) at the depth of
about 13 cm in the rectum. Skin temperatures (Tsk) were
measured for seven body parts using portable thermome-
ters (LT 8A, Gram Corp., Japan), and then mean skin
temperature (T¯sk) was calculated according the Hardy &
DuBois’ seven point equation (Eq.1):
T¯sk= 0.07 × Tforehead+ 0.35 × Ttrunk+ 0.14 × Tarm+ 0.05
× Thand+ 0.19 × Tthigh+ 0.13 × Tcalf+ 0.07 × Tfoot
-------------------------------------------------------- [Eq. 1]
Clothing microclimate temperature (Tclo) and humidity
(Hclo) were also measured on the most inner parts between
the body skin and clothes, around the chest and the back
using a portable thermo recorder (TR-72S, T&D Corp.,
Japan), with care to ensure the back Tcloand Hcloprobe
were not in contact with the frozen gel packs of the neck
cooling scarves and the cooling vest. Heart rate (HR)
was measured using a portable HR recorder (Polar, Polar
Electro 3000 INC., USA). Measurements above (Tre, Tsk,
Tclo, Hclo, and HR) were taken every minute. Total sweat
rate (TSR) was calculated through the difference between
before and after semi-nude body weight using a body
scale (Sartorius, F150S, sensitivity 1 g, Germany). Body
heat storage by Hardy and DuBois24), physiological strain
index25), and the modified Craig Index26)were calculated:
Heart storage, HS (kcal/m2)
=0.83 × (0.8∆Tre + 0.2∆T¯sk) × Weight (kg) --- [Eq. 2]
BSA (m2)
Physiological Strain Index (PSI)
=5 (Tret– Treo) +5 (HRt– HR0) -------------- [Eq. 3]
(39.5 – Treo) (180 – HR0)
Tret and HRt are simultaneous measurements taken
at any time during the exposure and Tre0 and HR0
are the initial measurements.
Craig Index (CI) =HRterminal+ ∆Tre + ∆Wt ---- [Eq. 4]
100
∆Tre = Rise in rectal temperature (˚C/h);
∆Wt = Nude weight loss (kg/h).
9-point ISO thermal sensation scale and 4-point ISO ther-
mal comfort scale were selected to evaluate subjective
perception. Subjects recorded their own thermal sensa-
tions and thermal comfort every ten minutes. The exper-
iment stopped when Treincreased up over 39˚C, or Tre
increased more than 2˚C compared to Treat the starting
point, or HR increased up over 185 bpm, or subjects want-
ed to stop.
Data analysis
Data were analyzed by using SPSS 12.0 for Windows
(SPSS, Chicago, IL). Physiological and subjective val-
ues were reported as means and SD. Differences among
eight treatments were tested using ANOVA. Duncan’s
post hoc test was applied when significant effects were
found. Statistical significance was set at p<0.05.
Results
Rectal temperature (Tre)
Treincreased under all conditions, but the increase was
effectively inhibited through wearing PCE. Overall, the
greater the cooling area was, the lower Trewas (Table 2,
p<0.05). Treincreased the mean of 0.20˚C for the con-
dition of Hat+Vest, while showed the increase of 0.62˚C
for the condition without any cooling. During the con-
dition without any cooling, Treexceeded 38˚C in eight
out of twelve subjects. However, only three subjects in
the Scarf B condition, two subjects with the Vest, and
none wearing the combination of cooling equipments
exceeded 38˚C. The time period that Trewas above 38˚C
was 31.3% of the 120 min when the Control was done,
but 0% in the conditions of Hat+Neck Scarf B, Hat+Vest,
and Hat+Vest+Neck Scarf B.
Skin temperatures (Tsk)
As expected, T¯skshowed the highest value in the con-
trol (35.2 ± 0.6˚C) and the lowest value for the condition
8 with the greatest cooling area (34.6 ± 0.8˚C, Table 2).
When the Hat+Neck Scarf B+Vest was worn, T¯skwas
maintained without gradual increases. In particular, T¯sk
quickly decreased to the comfort level during the mid-rest
stage. Forehead and the periphery temperatures did not
show any significant difference between conditions with
cooling equipment and without cooling (Table 2).
Clothing microclimate temperature and humidity (Tclo, Hclo)
Tcloon the chest was affected by wearing the Vest and
Tcloon the back by Neck Scarf B (Table 2). A mean of
Hclowas around 82–94%RH for all conditions.
Heart rate (HR) and total sweat rate (TSR)
Heart rate (HR) did not show any significant difference
by cooling when comparing the mean HR of the entire
duration. However, HR decreased quickly to the com-
fortable level during the two bouts of rest stages (Fig. 1).
PCE caused a reduction in total sweat rate and the dif-
ference between with and without cooling (p<0.05,
Table 2). Total sweat rate (TSR) in 7 cooling conditions
showed from 119–135 g · m–2· h on average, while TSR
ALLEVIATION OF HEAT STRAIN BY COOLING DIFFERENT BODY AREAS
623

Page 5

for the absence of cooling equipment had a mean of
145 ± 43 g · m–2· h.
624
J-W CHOI et al.
Industrial Health 2008, 46, 620–628
Table 2. Physiological responses during 120 min exposure in climatic chamber
No coolingNeck Scarf A Neck Scarf BHat Vest
Hat+Neck
Scarf B
Hat+Vest
Hat+Vest+Neck
Scarf B
Tre(˚C)
∆Tre(˚C)1)
MaximumTre(˚C)2)
Persons showing
Tre≥38˚C3)
37.9 (0.2)b
0.62 (0.22)c
38.2 (0.3)d
37.8 (0.2)b
0.48 (0.16)bc
38.0 (0.2)cd
37.8 (0.2)b
0.45 (0.13)bc
37.9 (0.2)bc
37.5 (0.2)a
0.34 (0.20)ab
37.7 (0.2)a
37.6 (0.3)a
0.20 (0.33)ab
37.7 (0.3)a
37.6 (0.2)a
0.40 (0.28)ab
37.7 (0.2)ab
37.6 (0.2)a
0.20 (0.25)a
37.7 (0.3)a
37.5 (0.3)a
0.31 (0.19)abc
37.7 (0.3)a
8 7312000
Time showing Trere≥38˚C
(% of 120 min)4)
31.317.6 11.32.34.4000
T¯sk(˚C)5)
∆T¯sk6)
35.2 (0.6)b
34.9 (0.5)ab
34.9 (0.4)ab
34.8 (0.5)ab
34.5 (0.6)a
34.9 (0.5)ab
34.7 (0.7)ab
34.6 (0.8)a
0.87 (0.55)b
0.70 (0.47)ab
0.69 (0.35)b
0.82 (0.60)b
0.76 (0.46)b
0.46 (0.22)b
0.73 (0.33)b
0.16 (0.14)a
T forehead(˚C)7)
T abdomen(˚C)7)
T arm(˚C)7)
T hand(˚C)7)
T thigh(˚C)7)
T calf(˚C)7)
T foot(˚C)7)
35.9 (0.5)
34.7 (1.1)b
35.6 (0.7)
35.6 (0.6)
35.3 (0.7)c
34.8 (1.0)
35.7 (0.7)
34.5 (0.8)ab
35.5 (0.5)
35.5 (0.4)
34.8 (0.9)abc
34.6 (0.9)
35.9 (0.6)
34.5 (0.7)ab
35.2 (0.8)
35.2 (0.8)
34.5 (0.6)ab
35.0 (0.5)
35.7 (0.5)
34.1 (0.8)ab
35.3 (0.7)
35.3 (0.5)
34.9 (0.5)bc
34.9 (0.8)
35.7 (0.6)
33.7 (0.9)a
35.1 (0.8)
35.2 (0.7)
34.3 (0.8)a
34.6 (1.1)
36.0 (0.4)
34.5 (1.1)ab
35.2 (0.4)
35.5 (0.7)
34.5 (0.6)ab
35.0 (0.4)
35.7 (0.5)
34.2 (1.6)ab
35.1 (0.7)
35.6 (0.5)
34.3 (0.6)ab
34.7 (0.5)
35.9 (0.5)
33.9 (1.7)a
35.2 (0.8)
35.3 (0.8)
34.3 (0.8)a
35.0 (0.7)
36.1 (0.6) 36.0 (0.6)36.1 (0.6)35.9 (0.5)35.9 (0.5)35.8 (0.9) 35.8 (0.7)35.7 (0.8)
Tclo-chest (˚C)8)
Tclo-back (˚C)8)
Hclo-chest (%RH)9)
Hclo-back (%RH)9)
33.3 (0.7)b
35.1 (0.7)b
86.9 (8.6)abc
32.8 (0.6)b
34.6 (0.7)b
86.9 (10.8)abc
32.7 (1.0)b
30.3 (4.0)a
84.2 (11.0)ab
32.9 (0.6)b
34.3 (0.6)b
86.6 (9.8)abc
28.8 (3.5)a
33.9 (0.9)b
92.6 (8.6)c
32.8 (1.0)b
30.5 (2.8)a
81.8 (12.1)a
29.3 (3.2)a
33.8 (0.7)b
91.4 (9.4)bc
28.8 (3.3)a
28.8 (4.3)a
90.0 (10.0)abc
93.6 (8.8) 92.0 (6.8) 94.1 (6.6) 89.5 (10.5)87.6 (12.0)91.4 (8.1) 91.9 (12.0)93.2 (9.0)
HR (bpm) 94 (10)91 (11)93 (10)90 (11)89 (12)91 (13)91 (11) 91 (10)
HR at 110 min (bpm)10)
102 (11)b
98 (10)b
99 (8)b
99 (11)b
96 (10)ab
91 (15)ab
92 (12)ab
87 (10)a
TSR (g · m–2· hr)11)
145 (43)b
119 (116)a
132 (55)a
133 (60)a
116 (86)a
130 (42)a
123 (46)a
135 (68)a
Data are expressed as mean (SD); Superscripts (a–d) show subsets grouped by ANOVA and Duncan’s Post Hoc test. i.e., Trefor three conditions (No cool-
ingb, Neck scarf Aband Neck scarf Bb) was significantly higher than Treof the rest of conditions (Hata, ..., Hat+Vest+Neck Scarf Ba); 1) The increase of
Treto the highest value starting at the initial point; 2) The highest value of Treduring the 120 min exposure; 3) Person numbers among total 12 subjects
showed cases that rectal temperature increased more than 38˚C during the 120 min exposure; 4) The percentage of time showing that Trewas greater than
38˚C during the 120 min exposure; 5) Mean skin temperature; 6) The increase of mean Tskto the highest value starting at the initial point; 7) Local skin
temperature; 8) Clothing microclimate temperature; 9) Clothing microclimate humidity; 10) Heart rate at the last point during the second work stage (at
110 min); 11) Total sweat rate.
Fig. 1. Heart rate (HR) in the climatic chamber during the red pepper harvest simulated in the climatic chamber for 120 min
(Graphs shows mean values for 12 subjects).