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The aim of this study was to evaluate the relationship between basic somatic features (body mass and height) and body mass loss in physically inactive young women and men exposed to thermal stress in a dry sauna. : The research was conducted in 2015 on 685 first-year full-time students (333 women, 352 men), aged 19–20 years old. Nude body mass was measured after the students dried off before and after using the sauna. : An analysis of regression equations indicated that an increase in the body mass of women and men leads to a significant increase in sauna-induced body mass loss. On the other hand, body mass loss decreased with an increase in height in women and men, but to a smaller extent. From among the tested somatic features, body height and body mass, body mass had a decisive influence on body mass loss. Body height had a minimal and statistically non-significant impact on body mass loss. : The results of this study indicate that heavier individuals have an increased risk of dehydration and hyperthermia. Therefore, they should pay close attention to replenishing fluids lost in the sauna. The determination of body mass loss values after a visit to a dry sauna has practical significance because it supports the estimation of the fluid volume required for the maintenance of correct water balance.
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Biomedical Human Kinetics, 8, 1–9, 2016
DOI: 10.1515/bhk-2016-0001
Original Paper
Sauna-induced body mass loss in physically inactive
young women and men
Robert Podstawski1, Tomasz Boraczyński2, Michał Boraczyński2, Dariusz Choszcz3,
Stefan Mańkowski3 Piotr Markowski3
1 Department of Physical Education and Sport, University of Warmia and Mazury, Olsztyn, Poland; 2 Józef Rusiecki
Olsztyn University College, Department of Physical Education, Olsztyn, Poland; 3 Department of Heavy Duty Machines
and Research Methodology, Faculty of Technical Sciences, University of Warmia and Mazury, Olsztyn, Poland
Summary
Study aim: The aim of this study was to evaluate the relationship between basic somatic features (body mass and height) and
body mass loss in physically inactive young women and men exposed to thermal stress in a dry sauna.
Material and methods: The research was conducted in 2015 on 685 rst-year full-time students (333 women, 352 men), aged
19–20 years old. Nude body mass was measured after the students dried off before and after using the sauna.
Results: An analysis of regression equations indicated that an increase in the body mass of women and men leads to a sig-
nicant increase in sauna-induced body mass loss. On the other hand, body mass loss decreased with an increase in height in
women and men, but to a smaller extent. From among the tested somatic features, body height and body mass, body mass had
a decisive inuence on body mass loss. Body height had a minimal and statistically non-signicant impact on body mass loss.
Conclusions: The results of this study indicate that heavier individuals have an increased risk of dehydration and hyperthermia.
Therefore, they should pay close attention to replenishing uids lost in the sauna. The determination of body mass loss values
after a visit to a dry sauna has practical signicance because it supports the estimation of the uid volume required for the
maintenance of correct water balance.
Key words: Dry sauna – Thermal stress – Body mass loss – Somatic features – Physically inactive
people
Introduction
Sauna bathing, a well-known form of whole-body heat-
ing, is well-tolerated by most healthy individuals, both
young and old between childhood and old age [10, 16, 18].
Repeated sauna bathing inuences endogenous regulatory
mechanisms, mainly acute and transient cardiovascular
and hormonal changes, by maintaining a balance between
uid composition and the distribution of circulating blood
[1]. Uncontrolled sauna bathing poses various health risks,
such as severe dehydration, heat exhaustion, stroke or
burns [9, 22, 31].
In most dry sauna rooms, the temperature is main-
tained between 80 and 90°C, and sometimes even above
100°C [20, 31]. Temperatures between of 80 and 90°C at
face level are considered optimal for most people [23].
The composition of the human body changes under such
thermal conditions. Water is one of the basic components
of the human body (48 ± 6% in women; 58 ± 8% water
in men) [44]. The body of a typical man weighing 75 kg
contains approximately 45 L of water (approximately 60%
of his body mass) [37]. The water and electrolyte balance
is critical for the function of all organs and for the mainte-
nance of health in general [24, 36]. Total body water per-
centage normally remains relatively constant [36]. Every
uid compartment in the body contains electrolytes whose
concentrations and composition are critical for uid move-
ment between intracellular and extracellular compartments
and for the maintenance of membrane electrochemical po-
tentials [37]. Dehydration can be induced in a sauna (pas-
sive dehydration) [40]. Sauna-induced dehydration leads
to hyperthermia due to enhanced sweating [47]. The loss
of bodily uids corresponding to 1% body mass can reduce
endurance by 4 to 6%, strength by 4 to 7% and coordina-
tion and concentration by 8% [30]. Sweat evaporation and
Author’s address PhD Robert Podstawski, Department of Physical Education and Sport, University of Warmia and Mazury
in Olsztyn, Prawocheńskiego 7, 10-720 Olsztyn, Poland podstawskirobert@gmail.com
R. Podstawski et al.
2
blood circulation in the skin are the main cooling mecha-
nisms in the body [9]. Uncontrolled sweating leads to the
loss of body mass (0.5–1.0 kg) [22]. Sauna-induced body
mass loss (BML) involves mainly the loss of body water,
but electrolytes, in particular sodium and chloride, are also
lost in various amounts depending on the sweat rate and
sweat composition [41]. Severe sweat-induced dehydra-
tion can impair exercise performance and the performance
of tasks requiring cognition and skill [25, 30]. Thus, the
critical issue in sauna bathing is to minimize dehydration
by matching uid intake with sweat loss.
In the human body, dehydration leads to a decrease in
body mass [33]. According to the literature, the loss of 1 kg
of body mass corresponds to approximately 1 L of bodily
uids lost through sweating [26, 38]. Measurements of
sauna-induced body mass loss can be used to calculate the
volume of water that should be consumed to compensate
for that loss. The physiological processes connected with
thermal stress induced by heat exposure in a sauna have
been studied and characterized by many authors, but the
precise mechanisms behind these phenomena still remain
insufciently explained [10, 22].
In view of the documented risks associated with ex-
cessive thermal stress in a sauna, BML control is a use-
ful method of preventing dehydration, hyperthermia and
the resulting health problems. Dehydration combined with
hyperthermia has more severe consequences than dehy-
dration or hyperthermia alone [3]. Signicant differences
in anthropometric measures and body composition are
noted between healthy sedentary women and men [19]. It
remains unknown whether BML can be reliably estimated
in view of considerable sex-related and individual differ-
ences in body measurements and body composition.
Therefore, the aim of this study was to evaluate the
relationship between basic somatic features (independent
variables: body mass and body height) and body mass loss
(dependent variable) in physically inactive young women
and men exposed to thermal stress in a dry sauna.
Materials and methods
Ethical approval
The research was carried out with the prior consent of
the Ethical Committee of the University of Warmia and
Mazury in Olsztyn (UWM), Poland. The study was per-
formed on student volunteers who signed an informed
consent statement.
Participants
The research was conducted in 2015 on 685 rst-year
full-time students (333 women, 352 men), aged 19–20
years old, who were enrolled at UWM. Every volunteer
visited a dry sauna during obligatory physical education
(PE) classes at the university. The analysed subjects, both
women and men, were residents of villages, towns and cit-
ies (population < 40,000) in the region of Warmia and Ma-
zury in Poland. The participants attended only mandatory
PE classes (90 minutes per week) and did not participate
in any other physical activities. The students’ physical ac-
tivity levels were evaluated using the International Physi-
cal Activity Questionnaire (IPAQ). An analysis of physi-
cal activity levels based on the IPAQ revealed that none
of the participants were sufciently active and that their
physical activity levels were below 600 MET. The exam-
ined women and men were characterized by low levels of
physical activity, and they were classied as being insuf-
ciently active. According to the IPAQ, people who are
insufciently active represent the lowest level of physi-
cal activity and do not meet the criteria for minimally ac-
tive and highly active categories [6]. The IPAQ was used
to select female and male students who would constitute
a homogenous group of respondents with regard to their
physical activity.
The participants did not visit a sauna for a least
12 months before the study. None of the examined women
were menstruating during the study. The following formu-
la was used to determine whether the number of partici-
pants constituted a representative sample in the trial (1):
µα
2 · sˆ2
n =
––
(1)
d2
where: d – maximum (acceptable) error of estimation,
sstandard deviation, µα – value from the normal distribu-
tion table N (0.1) at the acceptable condence coefcient
of 1 – α (µα = 1.96). At the assumed level of signicance
(α = 0.05), it was presumed that the error of estimation of
the average did not exceed 2% [34]. The size of a repre-
sentative sample, calculated from formula (1) at 2% error
of estimation, was 221 women and 198 men, and it was
smaller than the studied group (326 females, 348 males).
Consequently, the trial can be considered homogenous
and representative of UWM students in the age group of
19–20 years old.
Instruments and procedures
The participants received comprehensive information
about the trial before the study. Body height was measured
to the nearest 0.1 mm, and body mass was measured to
the nearest 0.1 kg with calibrated WB-150 medical scales
with a stadiometer (ZPU Tryb-Wag, Poland). Body mass
(BM) and body height (BH) were the independent vari-
ables (X), and BML was the dependent variable (Y). Nude
BM was measured after the students dried off before and
after using the sauna. The subjects were placed in supine
position in a dry sauna (temperature: 90°C; relative hu-
midity: 35%) for two sessions of 10 minutes each with
a 5-minute break in between to cool the body in a paddling
Sauna-induced body mass loss in young women and men
3
pool (pool width: 100 cm; pool depth: 130 cm; water tem-
perature: +10°C). The subjects were instructed to drink at
least 1 L of water on the day before the test and 0.5 L of
water 2 hours before the test. Following that, the partici-
pants did not consume any foods or uids until after the
nal body measurements were taken.
Statistical analysis
Measurement results were processed statistically in the
Statistica PL v. 10 application with the use of descriptive
statistics and advanced models to calculate the basic indi-
cators describing the location and distribution of the ana-
lysed factors. The inuence of body mass and body height
on body mass loss in a sauna was determined by curvi-
linear regression analysis with the stepwise method. The
results of the regression analysis were presented in 2D and
3D gures [34].
Results
The basic anthropometric parameters and sauna-in-
duced body mass loss (BML) in women and men are pre-
sented in Table 1.
Body mass and body height values were evaluated
based on score tables (T scale) for the general population
of Polish women and men [7]. The tested women and men
were characterized by average body mass and body height
relative to the general population of the corresponding
age. The average scores in the evaluated population were
determined in the range of 49-53 points (women: BM = 51
points, BH = 49 points; men: BM = 53 points, BH = 52
points).
In the dry sauna, men lost more bodily uids (BML)
(p = 0.0105) than women. The differences between ex-
treme values of body mass (42.4 kg in women, 70.0 kg in
men) and body height (37.0 cm in women, 42.0 cm in men)
were very high in both women and men. The coefcient of
variation in body mass (CV = 16.35% for women, 17.98%
for men) was approximately four times higher than the
coefcient of variation in body height (CV = 4.33% for
women, 4.17% for men). Relatively low variation in body
height and considerably higher variation in body mass
signicantly contributed to disproportionately higher vari-
ation in sauna-induced body mass loss (BML) the CV
reached 46.97% in women and 46.44% in men. These
results supported the formulation of the hypothesis that
a relatively small change in the analysed variables (body
mass and body height) signicantly inuences sauna-in-
duced body mass loss in both women and men. A series
of statistical analyses were conducted to verify the above
hypothesis.
The null hypothesis (H0) claiming that the analysed
variables (BM and BH) did not inuence the average
BML values in women (BML1) and men (BML2) was re-
jected based on the results of the statistical analyses. The
hypotheses postulating the existence of regression coef-
cients for women and men were veried.
The F-value was determined at F = 364.3 for women
and F = 510.6 for men, with the probability that the cal-
culated test value for women and men will be exceeded
at p(F) < 0.001; a signicance level of α = 0.05, mul-
tiple correlation coefcient of r = 0.832 for women and
r = 0.865 for men and residual standard deviation of
0.0954 for women and 0.1166 for men were also deter-
mined. Since p(F) < α, H0 (regression coefcients equal
zero) was rejected on behalf of the alternative hypothesis
H1 (not all regression coefcients equal zero). Regression
equations describing the inuence of selected independ-
ent variables (BM and BH) on the dependent variable
(BML) were derived:
for women: BML1 = 0.1996 + 0.0159 BM1 – 0.0047 BH1 (2)
for men: BML2 = – 0.4701 + 0.0149 BM2 – 0.0009 BH2 (3)
Table 1. Basic metrics in women and men – body mass (BM), body height (BH) and sauna-induced body mass loss (BML)
No. Parameter Women Men
BM [kg] BH [cm] BML [kg] BML [%] BM [kg] BH [cm] BML [kg] BML [%]
1. Maximum 85.80 184.0 1.20 1.446 121.00 204.0 1.30 1.232
2. Minimum 43.4 0 147.0 0.10 0.221 51.00 162.0 0.10 0.192
3. Mean 59.10 164.98 0.37 0.599 75.98 180.73 0.50 0.632
4. Median 56.45 165.0 0.30 0.574 74.50 180.0 0.40 0.620
5. Standard deviation 9.663 7.148 0.171 0.190 13.662 7.528 0.231 0.195
6. Coefcient of
variation [%] 16.35 4.33 46.97 31.68 17.98 4.17 46.44 30.94
Calculated U test value – 2.5576; Probability of exceeding the calculated p(U) value = 0.0105; Signicance level – α = 0.05; p(U) < α – statistically
signicant differences
R. Podstawski et al.
4
These correlations are presented graphically in Fig-
ures 1a and 1b.
An analysis of equations (2) and (3) and their graphical
interpretations (Fig. 1a and 1b) indicates that an increase in
the body mass of female and male subjects leads to a sig-
nicant increase in sauna-induced body mass loss (BML).
BML1 decreased with an increase in female height (BH1).
This trend was also noted in men, but to a smaller extent.
Equations (2) and (3) can be used to stimulate BML under
conditions described in this experiment (two 10-minute
visits to a sauna at a temperature of 90°C and relative hu-
midity of 35%). The results of BML simulations based on
body mass and body height data are presented in Tables 2
and 3.
The results of the simulation presented in Table 2 indi-
cate that in both women and men, an increase in body mass
(on the assumption that body height remains constant) leads
to an increase in BML values in both absolute (kg) and rela-
tive (%) terms. With an increase in BML [%], the difference
in the value of this indicator levelled out between female
Gender BM [kg] BML [kg] BML [%]
Women
49 0.2032 0.415
54 0.2827 0.524
59 0.3622 0.614
64 0.4417 0.690
69 0.5212 0.755
Men
65 0.3355 0.516
71 0.4249 0.598
76 0.4994 0.657
81 0.5739 0.709
86 0.6484 0.754
Table 2. Sauna-induced body mass loss (BML) subject
to body mass (BM) in women (BH = 165 cm) and men
(BH = 181 cm). The simulation was based on equations (2)
and (3)
Gender BH [cm] BML [kg] BML [%]
Women
155 0.4092 0.264
160 0.3857 0.241
165 0.3622 0.220
170 0.3387 0.199
175 0.3152 0.180
Men
171 0.5084 0.297
176 0.5039 0.286
181 0.4994 0.276
186 0.4949 0.266
191 0.4904 0.257
Table 3. Sauna-induced body mass loss (BML) subject
to body height (BH) in women (BM = 59 kg) and men
(BM = 76 kg). The simulation was based on equations (2)
and (3)
> 1.2
40
40
45
50
55
60
65
70
75
80
85
90
50
60
70
80
90
100
110
120
130
Body mass [kg]
Body mass [kg]
Body height [cm]
Body height [cm]
BML [kg]
< 1.2
< 1
< 0.8
< 0.6
< 0.4
< 0.2
< 0
160
145
150
155
160
170
180
190
185
175
165
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
BML [kg]
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
165
170
175
180
185
190
195
200
205
210
> 0.8
a) b)
< 0.8
< 0.6
< 0.4
< 0.2
< 0
Fig. 1. Sauna-induced body mass loss (BML) subject to body mass (BM) and body height (BH) in women (a) and men (b)
Sauna-induced body mass loss in young women and men
5
and male respondents. Practically no differences in relative
BML [%] were observed between groups characterized by
the highest body mass. In the group of the heaviest women,
BML [kg] was more than 150% higher than in the group
of the lightest women. The difference in BML between the
lightest and the heaviest men was clearly smaller (below
100%). A comparison of the lightest men and women re-
vealed a difference in BML of more than 50%, whereas the
difference between the heaviest groups of respondents was
estimated at only 20%.
The results of the simulation presented in Table 3 in-
dicate that unlike in the above comparison, an increase in
body height (on the assumption that body mass remains
constant) was accompanied by a minimal decrease in
BML [kg] in women, but no changes in BML in men. The
above results suggest that BML is largely determined by
body mass.
The stepwise method was used to simplify polynomial
terms (equations 2 and 3). BML equations were derived
based on body mass values in women and men. The result-
ing correlations were presented graphically in Figures 2a
and 2b.
In theory, BML for women and men can be estimated
based on body mass values with the use of the equations
below:
for women: BML1 = – 0.4878 + 0.0144 BM1 (4)
for men: BML2 = – 0.6128 + 0.0146 BM2 (5)
The percentage of the explained variation is 66.15%
for women (equation 4) and 74.69% for men (equation 5).
Multiple correlation coefcients for equations (4) and (5)
are very high at 0.813 for women and 0.864 for men. Re-
sidual standard deviation reached 0.1001 for women and
0.1165 for men. High correlation coefcients and relatively
low residual standard deviations indicate that the derived
models (equations) t empirical data well. Equations (4)
and (5) can be used to predict BML values in women and
men with high accuracy.
The results of BML simulations based on body mass
values in women and men are presented in Table 4.
The results of the simulation presented in Table 4 in-
dicate that BML increases with a rise in body mass val-
ues in both women and men. An increase in body mass
by one kilogram increased BML values by 0.0144 kg in
women and 0.0146 kg in men on average. The differ-
ence in BML values between women and men decreased
with an increase in body mass. Men were characterized
by higher BML than women in each body mass category,
but in similar weight groups, men tended to lose less body
mass than women.
a) b)
40 45 50 55 60 65 70 75 80 85 90
Body mass [kg]
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
BML [kg]
BML [kg]
40 50 60 70 80 90 100 110 120 130
Body mass [kg]
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Fig. 2. Sauna-induced body mass loss (BML) subject to body mass (BM) in women (a) and men (b). The results are presented
in the condence interval of 0.95 (dotted lines)
Table 4. Sauna-induced body mass loss (BML). The
simulation was based on equations (4) and (5)
Gender BM [kg] BML [kg] BML [%]
Women
49 0.2178 0.444
54 0.2898 0.537
59 0.3618 0.613
64 0.4338 0.678
69 0.5058 0.733
Men
65 0.3362 0.517
71 0.4238 0.597
76 0.4968 0.654
81 0.5698 0.703
86 0.6428 0.747
R. Podstawski et al.
6
Body height did not exert a signicant inuence on
BML in women or men. The derived equations explained
3.5% of variation in women and 25% of variation in
men. The results are presented graphically in Figures 3a
and 3b.
The results of statistical analyses suggest that from
among the tested variables, body mass is the key determinant
of BML in both women and men. Body height had a mini-
mal and statistically non-signicant inuence on BML. The
error generated by equations with one variable (BM, equa-
tions 4 and 5) and two variables (BM and BH, equations 2
and 3) ranged from 0.1% to 0.6% BML. It is recommended
that equations with one variable (BM, equations 4 and 5)
are used because they are easier to interpret than equations
with two independent variables (BM and BH, equations 2
and 3) and t empirical data similarly well.
Discussion
The main objective of this study was to evaluate the
relationship between basic somatic features (body mass
and body height) and body mass loss (BML) in physically
inactive young women and men exposed to thermal stress
in a dry sauna. As was previously mentioned, sweating
and water evaporation from the skin are the most effective
mechanisms of heat elimination in humans. Sauna bathing
has been shown to affect the uid, electrolyte and acid-
base balance resulting from sweating and thirst [33]. Dur-
ing sauna bathing, sweating begins quickly and reaches
peak levels after approximately 15 minutes, with an aver-
age total secretion of 0.5 kg [15]. The magnitude of core
temperature elevation ranges from 0.1 to 0.25oC for every
percent of BML [28, 39].
According to Sawka and Montain [37], in situations
of prolonged high sweat loss, body water loss (BWL) in
adults can reach 2–8%. Body water loss of 2% can re-
duce work capacity by 20%. Marked dehydration (5%
BWL) reduces threshold and slope responses for sweating
[29, 39]. Dehydration in excess of 5% BWL can have seri-
ous health implications, and BWL higher than 8–10% has
lethal consequences [35].
One of the rst studies concerning the effects of sweat-
ing on uid balance was carried out by Kozłowski and
Saltin [21]. In their study, sweating-induced dehydration
was analysed in six healthy males who were exposed to
a temperature of 80°C during a 2.5-hour visit to a sauna.
The average decrease in body mass was 3.1 kg (4.1%).
In several studies, the average body water loss dur-
ing a standard sauna visit was estimated at 400–600 g
[12, 14]. Similar BWL values were observed by Pilch et
al. [33]. The authors investigated changes in BML and
various physiological and biochemical indicators in 10
healthy female subjects (aged 19–21 years old) who vis-
ited a Finnish sauna every other day for a total of seven
visits (temperature: 80.1°C; relative humidity: 26.6%; du-
ration: 30 minutes). On average, the subjects’ body mass
decreased by 550 g after the rst visit (0.94% decrease
in initial body mass) and by 560 g after the seventh, nal
visit (0.96% decrease in initial body mass).
In a study by Coles et al. [5], 10 male subjects attended
six 15-minute sessions in a dry sauna (at a temperature of
48.9°C) with 5-minute breaks between sessions. The study
involved two different procedures (euhydration trial vs.
dehydration trial). No uids were ingested at any time dur-
ing the dehydration procedure. The euhydration procedure
was identical to the dehydration procedure, with the ex-
ception that during each 5-minute break, the subjects were
instructed to drink a volume of water equivalent to the
body mass lost during the previous 15-minute sauna ses-
sion. The subjects’ BML was 0.33 ± 0.19 kg (euhydration
trial) and 1.99 ± 0.35 kg (dehydration trial). Euhydration
145 150 155 160 165 170 175 180 185 190
Body height [cm]
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
a) b)
BML [kg]
160 165 170 175 180 185 190 195 200 205 210
Body height [cm]
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
BML [kg]
Fig. 3. Sauna-induced body mass loss (BML) subject to body height (BH) in women (a) and men (b). The results are presented
in the condence interval of 0.95 (dotted lines)
Sauna-induced body mass loss in young women and men
7
resulted in 0.4% BML and dehydration resulted in 2.3%
BML. Westerterp-Plantenga et al. [46] reported signicant
differences (p < 0.001) in the BML values (–1.82 kg; in
the range of –1.53 to –2.04 kg; 3.0 ± 0.5%) of 30 non-
obese (BMI = 22.8 ± 1.6) and obese (BMI = 28.5 ± 1.9)
subjects who attended three 20-minute sauna sessions at
a temperature of 80°C. In a study by Thomas et al. [43],
the mean BML (normalized to body mass %) of 12 healthy
adults after a 30-minute sauna visit was 0.91 ± 0.34%
(range 0.33–1.4%).
In our study, where a similar procedure was applied,
male subjects lost 0.50 kg (0.63%), whereas female sub-
jects lost 0.37 kg (0.60%) on average. In light of the cited
results, the BML values reported in our study do not seem
to pose a considerable health risk. Due to the considerable
differences in body measurements and body composition
between females and males, the results of our study were
analysed to determine whether sex signicantly inuences
BML values.
Numerous studies analysing differences between the
sexes demonstrated a much higher increase in whole-body
sweat rate in men than in women as the result of adapta-
tion to humid heat [2, 4, 8, 45]. Avellini et al. [2] observed
a signicantly higher increase in the whole-body sweat
rate in men than in women (35% vs. 15%) after 10 days
of adaptation to humid heat. Mehnert et al. [27] reported
highly signicant sex-related differences in sweat rates.
The differences remained statistically signicant even
when women and men were matched for body surface
area or surface-to-mass ratio. Similar differences were ob-
served in resting and exercising subjects in other studies
[11, 13].
In our study, the average body mass loss was 130 g
(26%) higher in men than in women. A statistically sig-
nicant difference (p = 0.0105) in BML [%] was observed
between the sexes (0.60% and 0.63%, respectively). The
average BML [kg] in our research was similar to that re-
ported in men in other studies [23, 33, 42], but lower than
that noted by Pilch et al. [32]. The fact that women lost
less body mass [kg] could be attributed to the fact that fe-
males are generally characterized by lower levels of total
body water (48 ± 6%) [44] and a higher content of adipose
tissue, which reduces sweating, evaporation and BML
[kg] [12, 14]. Women also require a greater increase in
body temperature before they begin to sweat. They do not
sweat as much as men, and they maintain a steady body
temperature less effectively than men [17]. The above
observations were conrmed in our study, in which men
lost more body mass than women. The presented simula-
tions revealed that men with a body mass similar to that
of women were characterized by lower BML in kg and
%. The above can probably be attributed to differences
in body surface between the sexes, which inuences heat
loss through radiation [26]. Men whose body mass is
similar to that of women are characterized by less body
fat and greater body surface. Therefore, our results could
also suggest that body fat is a signicant determinant of
BML. Women with more body fat than men probably lose
more body mass to maintain thermal homeostasis (rela-
tively constant body temperature). Further work is needed
to determine the correlations between body measurements
and body composition vs. BML.
From a practical point of view, it is important to deter-
mine which of the two basic somatic features, body height
or body mass, has a greater inuence on BML. Our nd-
ings have revealed that the correlation between body mass
and BML is directly proportional and statistically signi-
cant. The relationship between body height and BML is
inversely proportional and statistically non-signicant,
which implies that BML decreases with an increase in BH
(when body mass is stable).
The regression equations derived in our study can be
used to determine the inuence of the analysed somatic
features on BML values in young women and men ex-
posed to thermal stress in a dry sauna. The derived equa-
tions support highly accurate estimations of body mass
loss in a sauna. From among the two independent vari-
ables (somatic features) analysed in this study, body mass
had a decisive impact on BML values in both women and
men. On average, a body mass increase of 1 kg leads to
a BML of 0.0144 kg in women and 0.0146 kg in men. Av-
erage BML values in men were approximately 30% higher
than in women. In groups of female and male respondents
characterized by a similar body mass, BML values were
approximately 16–23% higher in women than in men. The
noted difference was reduced with an increase in body
mass.
Conclusions
The results of our study indicate that physiological
responses to thermal stress in a dry sauna differed sub-
ject to gender, body mass and body height. From among
the tested somatic features, body mass had a decisive in-
uence on BML. Men whose body mass was similar to
that of women were characterized by lower BML, which
indicates that the physiological effort required to main-
tain constant body temperature is lower in men. The ob-
served differences could be attributed to lower body fat
and greater body surface area in men than in women. In
both men and women, an increase in body mass was ac-
companied by a rapid increase in BML values [%], which
suggests that body fat signicantly inuences BML. Body
height had a minimal and statistically non-signicant im-
pact on BML. Our ndings suggest that BML can be es-
timated based on subjects’ initial body mass. A directly
proportional correlation between body mass and BML
R. Podstawski et al.
8
indicates that regardless of gender, heavier participants, in
particular those with higher body fat, are at a greater risk
of dehydration and hyperthermia; therefore, they should
pay close attention to replenishing uids lost in a sauna or
shorten their visits to saunas. The determination of BML
values after a visit to a dry sauna has practical signicance
because it supports the estimation of the uid volume re-
quired for the maintenance of correct water balance. Ther-
moregulation involves complex mechanisms; therefore,
future research should involve a higher number of varia-
bles describing somatic features, height/weight indicators
and body composition.
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Received 17.10.2015
Accepted 01.02.2016
© University of Physical Education, Warsaw, Poland
Acknowledgments
The authors would like to thank the University of Warmia
and Mazury in Olsztyn, Poland for nancial support.
... The studies that have observed the effects of sauna baths on body composition have been carried out on sedentary and overweight people [13,14,27]. In addition, the temperature used in the studies mentioned above was lower than in the present study and involved fewer sessions. ...
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The effect of acute, thermal-induced, dehydration on V · O 2 recovery time and heart rate response following short-duration submaximal arm ergometry, done in a temperature-controlled, thermoneutral environment was investigated. Ten males performed three, 1 min, submaximal bouts of arm ergometry, at an intensity equal to 1.5 W kg 1 of body mass, in both hypohydrated and euhydrated conditions. Dehydration was induced via intermittent dry sauna exposure and water restriction, followed by a 1 h, thermoneutral, pre-exercise, recov-ery period. Euhydration was characterized by the sauna exposure with water replacement equivalent to loss of body mass. The randomized, cross-over design was analyzed using analysis of variance with repeated meas-ures on all factors. Volunteers lost a significant (p 0.05) amount and percentage of body mass (1.9 0.35 kg; 2.3 0.36%), and when hypohydrated showed a significant increase in urine specific gravity (1.015 0.007). The mean time for recovering to baseline V · O 2 in the euhydrated condition (363.72 41.17 s) was not signifi-cantly different (p 0.05) from the hypohydrated condition (339.43 28.51 s), and the mean heart rate at recovery baseline for the euhydrated condition (60.37 3.62 beats min 1) was not significantly different from the hypohydrated condition (61.72 2.97 beats min 1). Thus hypohydration of 2.3% of body mass had no significant effect on V · O 2 recovery time and heart rate response following intermittent exercise. While there are many reasons to hydrate well during exercise, the results from this investigation suggest that moderate levels of dehydration may not increase the time required to recover between repeated bouts of short-duration submaximal exercise done in temperate environments.
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Article
The aim of this study was to evaluate the validity of the recently proposed predicted heat strain (PHS) model with respect to gender, particularly in relation to the estimation of admissible exposure durations for work in hot environments. Two experiments addressing the effects of the climatic conditions inside vehicles during summer with altogether 96 females and 114 males were analysed. Each subject was exposed for 2 h to a typical summer climate. Highly significant gender-related differences were found for the observed sweat rates. When adjusting the sweat rate to anthropometric measures the differences remained statistically significant, even if females and males were matched for body surface area or surface-to-mass ratio. There is much evidence in the literature that gender-related differences in sweat loss diminish once they are adjusted to anthropometric variables or to physical fitness. However, thermal indices like the PHS model rely on absolute values of the physiological response to heat stress. Therefore, a systematic overestimation of the sweat loss for women could imply an underestimation of body heat storage and core temperature accordingly. A possible approach to revised limit values in the PHS model could be to reduce the values of the maximum sweat rate for women.Relevance to industryWork in hot environments is still present at many industrial workplaces, particulary in underdeveloped countries. International standards provide exposure limits for the prevention of heat disorders. The results of this study indicate that these limits should be revised with respect to gender-related differences in sweat loss.
Article
This investigation determined the effect of different rates of dehydration, induced by ingesting different volumes of fluid during prolonged exercise, on hyperthermia, heart rate (HR), and stroke volume (SV). On four different occasions, eight endurance-trained cyclists [age 23 +/- 3 (SD) yr, body wt 71.9 +/- 11.6 kg, maximal O2 consumption 4.72 +/- 0.33 l/min] cycled at a power output equal to 62-67% maximal O2 consumption for 2 h in a warm environment (33 degrees C dry bulb, 50% relative humidity, wind speed 2.5 m/s). During exercise, they randomly received no fluid (NF) or ingested a small (SF), moderate (MF), or large (LF) volume of fluid that replaced 20 +/- 1, 48 +/- 1, and 81 +/- 2%, respectively, of the fluid lost in sweat during exercise. The protocol resulted in graded magnitudes of dehydration as body weight declined 4.2 +/- 0.1, 3.4 +/- 0.1, 2.3 +/- 0.1, and 1.1 +/- 0.1%, respectively, during NF, SF, MF, and LF. After 2 h of exercise, esophageal temperature (Tes), HR, and SV were significantly different among the four trials (P < 0.05), with the exception of NF and SF. The magnitude of dehydration accrued after 2 h of exercise in the four trials was linearly related with the increase in Tes (r = 0.98, P < 0.02), the increase in HR (r = 0.99, P < 0.01), and the decline in SV (r = 0.99, P < 0.01). LF attenuated hyperthermia, apparently because of higher skin blood flow, inasmuch as forearm blood flow was 20-22% higher than during SF and NF at 105 min (P < 0.05). There were no differences in sweat rate among the four trials. In each subject, the increase in Tes from 20 to 120 min of exercise was highly correlated to the increase in serum osmolality (r = 0.81-0.98, P < 0.02-0.19) and the increase in serum sodium concentration (r = 0.87-0.99, P < 0.01-0.13) from 5 to 120 min of exercise. In summary, the magnitude of increase in core temperature and HR and the decline in SV are graded in proportion to the amount of dehydration accrued during exercise.
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This study examined the effects of age and physical activity on body composition and fat distribution by comparing differences between young and older endurance trained men and women with differences between young and older sedentary people. Although indices of total body adiposity (fat mass, percent body fat) were higher in the older than in the young people in both the trained and the sedentary groups, the magnitude of the difference was markedly less in the trained group (P less than 0.01). The average differences in fat mass between young and old sedentary men and women were 10.1 kg and 12.2 kg, respectively, but only 4.3 kg and 5.5 kg in trained men and women. Skinfold thicknesses were approximately 24% and approximately 47% larger at all sites (triceps, thigh, subscapula, pectoralis, umbilicus, suprailiac) in the older than in the young trained men and women, respectively. Similar differences were found between young and older sedentary people except at central, upper body sites, where the relative differences in skinfold thicknesses between young and older sedentary people were 2- to 6-fold greater than in trained people. Thus, people who exercise regularly appear to accumulate less adipose tissue in upper, central body regions as they get older, potentially reducing the risk for the metabolic disorders associated with upper body obesity.