Correlations between Repeated Use of Dry Sauna for 4 x 10 Minutes, Physiological Parameters, Anthropometric Features, and Body Composition in Young Sedentary and Overweight Men: Health Implications

Abstract

Background:
The effect of thermal stress on the physiological parameters of young overweight and sedentary men who sporadically use the sauna remains insufficiently investigated.

Aim:
The aim of the study was to determine the effect of sauna bathing on the physiological parameters of young overweight, physically inactive men and to test the correlations between physiological parameters versus anthropometric features and body composition parameters.

Materials and methods:
Forty-five overweight and sedentary men aged 20.76±2.4 y were exposed to four sauna sessions of 10 minutes each (temperature: 90-91°C; relative humidity: 14-16 %) with four 5-minute cool-down breaks. Body composition was determined before sauna, and body mass and blood pressure were measured before and after sauna. Physiological parameters were monitored during four 10-minute sauna sessions.

Results:
A significant (p<0.0001) increase in all analyzed physiological parameters was observed during four successive 10-minute sauna sessions. Heart rate, energy expenditure, blood pressure, and body mass loss were most strongly correlated with anthropometric parameters (body mass, body mass index, and body surface area) and body composition parameters (percent body fat, body fat mass, and visceral fat level). The 60-minute treatment resulted in a significant reduction in body mass (0.65 kg).

Conclusions:
Repeated use of Finnish sauna induces significant changes in the physiological parameters of young sedentary overweight men, and these changes are intensified during successive treatments. Deleterious cardiovascular adaptations were most prevalent in men characterized by the highest degree of obesity and the largest body size.

Full text

Research Article
Correlations between Repeated Use of Dry Sauna
for 4 x 10 Minutes, Physiological Parameters,
Anthropometric Features, and Body Composition in Young
Sedentary and Overweight Men: Health Implications
Robert Podstawski ,1Krzysztof BorysBawski,2
Cain C. T. Clark ,3Dariusz Choszcz ,4Kevin J. Finn,5and Piotr Gronek6
1University of Warmia and Mazury in Olsztyn, Faculty of Environmental Sciences, Chair of Tourism,
RecreationandEcology,M.Oczapowskiego5,10-719Olsztyn,Poland
2Wrocław University of Life and Environmental Sciences, Department of Anthropology, Wrocław, Poland
3Coventry University, Faculty of Health and Life Sciences, Coventry CV1 5FB, UK
4Department of Heavy Duty Machines and Research Methodology, Faculty of Technical Sciences,
University of Warmia and Mazury in Olsztyn, Oczapowskiego 11, 10-719 Olsztyn, Poland
5University of Central Missouri, Department of Nutrition and Kinesiology, USA
6University of Physical Education in Poznan, Department of Dance and Gymnastics, Poland
Correspondence should be addressed to Robert Podstawski; podstawskirobert@gmail.com
Received 17 September 2018; Accepted 25 December 2018; Published 21 January 2019
Academic Editor: Toshiyuki Sawaguchi
Copyright ©  Robert Podstawski et al. is is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
cited.
Background. e eect of thermal stress on the physiological parameters of young overweight and sedentary men who sporadically
use the sauna remains insuciently investigated. Aim.eaimofthestudywastodeterminetheeectofsaunabathingonthe
physiologicalparameters of young overweight, physically inactive men and to test the correlationsbetween physiological parameters
versus anthropometric features and body composition parameters. Materials and Methods. Forty-ve overweight and sedentary
men aged .±. y were exposed to four sauna sessions of  minutes each (temperature: -∘C; relative humidity: -
%) with four -minute cool-down breaks. Body composition was determined before sauna, and body mass and blood pressure
were measured before and aer sauna. Physiological parameters were monitored during four -minute sauna sessions. Results.
Asignicant(p<.) increase in all analyzed physiological parameters was observed during four successive -minute sauna
sessions. Heart rate, energy expenditure, blood pressure, and body mass loss were most strongly correlated with anthropometric
parameters (body mass, body mass index, and body surface area) and body composition parameters (percent body fat, body fat
mass, and visceral fat level). e -minute treatment resulted in a signicant reduction in body mass (. kg). Conclusions.
Repeated use of Finnish sauna induces signicant changes in the physiological parameters of young sedentary overweight men,
and these changesare intensied during successive treatments. Deleterious cardiovascular adaptations were most prevalent in men
characterized by the highest degree of obesity and the largest body size.
1. Introduction
Sauna has emerged as a popular form of wellness treatment
around the world in recent decades. Despite the above,
many people visit saunas out of curiosity or the desire to
follow the latest trends, and not all of them use saunas
regularly []. Finland has a population of . million, and
Hindawi
BioMed Research International
Volume 2019, Article ID 7535140, 13 pages
https://doi.org/10.1155/2019/7535140

BioMed Research International
nearly  million Finns use saunas regularly, whilst other
Scandinavians also take sauna baths at least once a week for
health improvement [, ]. In addition, growing numbers
of people install saunas at home or use dierent types of
sauna (dry, steam, or infrared) in SPA centers []. Historically,
saunas were popularized by Finnish athletes during the
Olympic Games of ; consequently, sauna baths have been
introduced to training programs in many sport disciplines
[].
Athletes and individuals purport using the sauna to
cleanse the body, refresh the mind, and accelerate recovery
and relaxation []. Regular sauna use improves adaptabil-
ity to various environmental conditions, increases physical
eort, and contributes to emotional wellbeing [, ]. In
studiesconductedbyScoonetal.[]andErnstetal.
[], postexercise sauna bathing over a period of three
weeks substantially improved running performance, which
canbeattributedtoanincreaseinbloodvolume.e
Finnish sauna has been found to increase the endurance of
locomotor and cardiorespiratory systems and physiological
eciency [, ]. In scuba divers, a single sauna session
before diving has been shown to signicantly decrease
the number of circulating bubbles aer a chamber dive,
thereby minimizing the risk of decompression sickness
[].
Sauna baths are conducive to the treatment of locomo-
tive organ inammation, nonspecic ailments of the upper
respiratory system [–], and sport-induced injuries [–
]. Exercise can result in Exercise-Induced Muscle Damage
(EIMD), which produces cramps, muscle strain, impairs
muscle function, and delayed onset of muscle soreness [].
In respondents who visited a sauna before EIMD, thermal
treatment reduced sensory impairment (PF-ROM and PE-
ROM) and improved muscle functions (GS and WES) in wrist
extensor muscles []. ermal treatment and rapid cooling
aer sauna were also found to exert a complex and positive
eect on vascular and cardiac functions [, ], including
arterial stiness, BP, and some blood-based biomarkers
[].
Sauna treatment activates the endocrine system and
promotes the secretion of epinephrine [, –], ACTH,
cortisol, and prolactin as the body adapts to high temperature
[]. e endocrine system is stimulated to retain more
water in the body and maintain thermal equilibrium [].
Perspiration decreases serum sodium serum levels in the
body []. Sauna bathing decreases total cholesterol levels
and the concentrations of low-density lipids, and it increases
the content of high-density lipids []. All of these responses
might be viewed as benecial for a person with chronic
disease.
Far-infrared sauna improves the quality of life in people
suering from type  diabetes mellitus, chronic pain, chronic
fatigue syndrome, depression, and congestive heart failure
[]. Finnish sauna, a thermal treatment that heats the
entire body, has been found to produce positive clinical
eects in rheumatism patients []. In rheumatism suerers,
regular sauna use reportedly alleviates pain associated with
musculoskeletal injuries and improves joint mobility [, ].
e application of supercial heat is recommended as a short-
term palliative treatment for rheumatoid arthritis and low
back pain [].
e uses of sauna treatment to facilitate health outcomes
in persons with moderate risk of cardiovascular disease (i.e.,
sedentary behavior, overweight/obese, hypertension, and
hyperlipidemia) have not been adequately studied. Beever
[]reviewedtheliteratureusingtheterms“far-infrared”
and “sauna” which yielded only nine useful studies. Among
these studies, ve supported the use of far-infrared sauna
for reducing coronary heart disease risk factors. In addition,
a recent investigation by Laukkanen et al. [] showed a
negative association between the frequency of sauna bathing
and fatal CV events over a  year period suggesting a poten-
tial benet from sauna treatments, but these investigators
observed that further research was needed to establish a
potential mechanism.
e inuence of high temperature on physiological
parameters and body uid loss in individuals with dierent
body size (body mass and height) has been weakly researched.
Dry sauna leads to changes in physiological parameters as
well as body composition. Sauna bathing induces sweating,
which promotes passive dehydration and leads to hyper-
thermia [], mainly due to the evaporation of sweat and
enhanced blood circulation in the skin, the main cooling
mechanism in the body []. Uncontrolled sweating leads
to body mass loss (.-. kg), and uid loss can reach up
to  liters under extreme circumstances, such as sauna
competitions []. e body mass loss (BML) observed
aer sauna can be attributed mainly to the loss of body
water. e above leads to changes in electrolyte levels, in
particular sodium and chloride, subject to individual sweat
rate and sweat composition []. Dehydration induced by
severe sweating can compromise exercise performance and
cognition [–]; therefore, during sauna treatment, visitors
should minimize the risk of dehydration by matching their
uid intake with sweat loss.
A dehydration-related decrease in body mass has been
empirically shown in humans []. Approximately  L of
bodilyuidsislostthroughsweating,whichcorrespondsto
the loss of  kg of body mass [, ]. Sauna-induced body
mass loss can be measured to determine the uid intake that
is required to compensate for that decrease. e physiological
processes associated with sauna-induced thermal stress have
been widely studied, but the mechanisms responsible for
these processes have not yet been fully elucidated [, ]. e
risks associated with excessive thermal stress in a sauna have
been well documented, and dehydration, hyperthermia, and
the resulting health problems can be prevented by monitoring
BML. Dehydration combined with hyperthermia is far more
dangerous for healththan dehydration or hyperthermia alone
[].
e inuence of thermal stress during prolonged sauna
use on physiological parameters has limited research in con-
junction with the correlations between somatic features and
body composition. In addition, overweight and sedentary
individuals have a potential additive thermal stress which
might compromise the eects of sauna on health benets.
erefore, the aim of this study was to determine the eect

BioMed Research International 
of thermal stress on physiological parameters and their
correlations with somatic features and body composition
parameters in young, overweight, and sedentary males.
2. Materials and Methods
2.1. Ethical Approval. e study was conducted upon the
prior consent of the Ethics Committee of the University
of Warmia and Mazury in Olsztyn (UWM), Poland. e
study was performed on student volunteers who signed an
informed consent statement.
2.2. Participants Selection. e study was conducted in 
on  full-time volunteer male students aged - years
(.±.). e pool of potential participants were informed
about the purpose of the study during obligatory physical
education (PE) classes at the University of Warmia and
Mazury in Olsztyn. e students who agreed to participate in
the study ( men) were notied by e-mail and text message
whether they met the inclusion criteria and were provided
with the date of nal recruitment. Forty-ve students meeting
the below inclusion criteria were recruited for the study. e
participants attended only mandatory PE classes ( minutes
per week); they did not undertake extracurricular physical
activity and had rarely visited a sauna before the study. e
participants conrmed that they did not take any medications
or nutritional supplements, were in good health, and had no
history of blood diseases or diseases aecting biochemical
and biomechanical factors. None of the evaluated participants
had respiratory or circulatory ailments. Physical activity (PA)
levels (quantitative analysis) were evaluated with the use of
the Polish short version of the standardized and validated
International Physical Activity Questionnaire (IPAQ) [].
e IPAQ was used only to select a homogenous sample of
male students, and the results were presented only in terms
of Metabolic Equivalent of Task (MET) units indicative of the
participants’ PA levels. e participants declared the average
weekly number of minutes dedicated to PA (minimum of 
minutes) before the study. e energy expenditure associated
with weekly PA levels was expressed in terms of MET units
[]. e MET is the ratio of the work metabolic rate to
the resting metabolic rate, and  MET denotes the amount
of oxygen consumed in  minute, which is estimated at .
mL/kg/min. Based on the declared frequency, intensity, and
duration of PA, the respondents were classied into groups
characterized by low L < METs-min/week), moderate
(M <, METs-min/week), and high (H ≥, METs-
min/week) levels of activity. Only male students characterized
by low levels of PA (energy expenditure of up to  METs per
week) and a sedentary lifestyle were chosen for the study.
2.3. Instruments and Procedures. e participants received
comprehensive information about sauna rules during PE
classes preceding the study. ey were asked to drink at least
 L of water on the day of the test and . L of water  hours
before the session. e participants did not consume any
foods or other uids until aer the nal body measurements.
All participants visited a dry sauna during weekly PE
classes on the same day, in the same location and over
the same period of time, to minimize the eect of diurnal
variation on the results []. Every participant attended
four sauna sessions (temperature: ∘C; relative humidity:
- %) of  minutes each and remained in a sitting
position during each session. Aer every  minute session,
students recovered in a room with a temperature of ∘C.
Every recovery session lasted  minutes, during which the
participants took a shower set to a temperature of -∘C.
e volunteers could also cool down in a paddling pool
(pool width:  cm; pool depth:  cm; water temperature:
+∘C).
Body height was measured to the nearest . mm with a
stadiometer, and nude body mass was measured to the nearest
. kg with a calibrated WB- medical scale (ZPU Tryb
Wag, Poland) prior to the rst sauna session. Nude body mass
was also measured aer the last -minute cooling break (aer
 minutes of the experiment) to calculate body mass loss
(BML). Somatic features, including body mass, body mass
index (BMI), body surface area (BSA), and the waist-hip ratio
(WHR), and body composition parameters, including body
mass, total body water (TBW), protein and mineral content,
body fat mass (BFM), fat-free mass (FFM), skeletal muscle
mass (SMM), percent body fat (PBF), InBody score, target
weight, visceral fat level (VFL), basal metabolic rate (BMR),
and degree of obesity, were determined by bioelectrical
impedance [] with the InBody  body composition
analyzer before the rst sauna session. During exposure to
high temperature in the sauna, physiological parameters,
including heart rate (HRmin,avg,max ), recovery time, peak
training eect (PTE), energy expenditure, estimated oxy-
gen uptake (VO2avg,max ), estimated excess postexercise oxy-
gen consumption (EPOCavg,peak ), estimated respiratory rate
(avg,max ), and physical eort (easy, moderate, dicult, very
dicult, maximal), were measured indirectly with Suunto
Ambit Peak Sapphire heart rate monitors which are widely
used in studies of the type []. HR monitors were placed
on the le or right wrist (for le-handed and right-handed
participants), and the sensors were attached to the chest.
Every pulsometer was calibrated to male sex, year of birth,
body mass, and PA level. Blood pressure (BP) was determined
with an automatic digital blood pressure monitor (Omron
M Comfort, Japan) before the rst session and immediately
aer each session with the participant remaining in a sitting
position.
2.4. Statistical Analysis. e measured data were processed
statistically in the Statistica PL v.  application with the
use of descriptive statistics. e values of the asymmetry
coecient (AC) were calculated to analyze the normality
of distribution. e arithmetic means of the parameters
measured aer each of the four sauna sessions were compared
by one-way (univariate) analysis of variance (ANOVA).
e Least Signicant Dierence (LSD) post hoc test was
performed when the F value was statistically signicant. e
above test is particularly recommended for planned repetitive
experiments or longitudinal data with equal group size. e
direction and strength of the relationships between interval
features were determined by calculating Pearson’s correlation
coecient (r).

BioMed Research International
3. Results
e results are presented in ve tables. e participants’
anthropometric features and physiological parameters are
presented in Table .
e surveyed male students lost a signicant (p<.,
t=., df=) amount of bodily uids (.±. kg) aer
the -minute experiment ( sauna sessions of  minutes
each with four -minute breaks between sessions). e
participants’ average body mass (. kg) was excessive
relative to height (. cm), and the subjects were classied
as overweight based on their BMI (. kg/m2) according
to WHO standards. e lowest BMI values (. kg.m2)
were within the norm, whereas the highest BMI values (.
kg.m2) were indicative of class III obesity. e waist-hip
ratio (.) approximated the upper limit of the healthy
range (WHR>.) and was not indicative of android obesity
(WHR ≥), with relatively high values of VFL (. kg) and
high degree of obesity (.). According to the percent
body fat scale developed by ompson [] and the noted
BFM values (. kg), the evaluated students (PBF=.%)
belonged to a “potential risk” group (.-.%). High BFM
values were accompanied by relatively high values of SMM
and FMM (. and . kg, respectively), whereas the
average values of systolic (SBP) and diastolic blood pressure
(DBP) were within the norm (. mmHg and .
mmHg, respectively).
e values of HRmin,mean,max increased signicantly
(p<.) during successive -minute sauna sessions with -
minute breaks between sessions. e average HR was deter-
mined at  bpm during the rst sauna session and at .
bpm (dicult eort) during the fourth session. Maximum
HR values (HRmax) reached up to  bpm (maximal eort)
during the fourth session. e recommended recovery time
(calculated automatically by HR monitors) was . h aer
the rst sauna session, and it diered signicantly (p<.)
aer the fourth session at . h. e participants burned
., ., ., and . kcal during every successive
-minute session in the sauna. Between the rst and the
fourth session, the values of VO2mean and VO2max increased
signicantly from . (1st)to.L/min/kg(4th)and
from . (1st) to . L/min/kg (4th ), respectively. A
signicant (p<.) increase was also noted in EPOCmean
and EPOCpeak values (.-. L/min and .-. L/min,
respectively). e average respiratory rate was . breaths
per minute during the rst -minute session, and it increased
signicantly (p<.) to . breaths per minute during the
fourth session. e values of SBP and DBP also increased
signicantly (p<.) from . (1st) to . mmHg
(4th), and from . (1st) to . mmHg (4th), respectively.
e highest number of HR readouts were within the easy
eort range (< bpm: . s) during the rst sauna session,
within the moderate eort range (- bpm: . and
. s, respectively) during the second and third session,
and within the dicult eort range (- bpm: . s)
during the fourth session. Between the second and fourth
sauna session, HR values increased signicantly (p<.)
within the very dicult eort range (- bpm; from .
s to . s), and HR values indicative of maximal eort (≥
bpm) were not observed (Table ).
Body height was not signicantly correlated with any of
the analyzed body composition parameters, excluding DBP
during the rst sauna session (r=.). All HR values were
signicantlycorrelatedwithbodymass,BMI,BSA,andWHR
during the third and/or fourth session. Energy expendi-
ture was signicantly correlated with all body composition
parameters between the second and the fourth session. e
values of VO2avg were bound by a signicant positive correla-
tion with BMI and WHR during the fourth session, whereas
a signicant negative correlation was noted between VO2max
and body mass, BSA, and WHR during the second session.
e values of EPOCavg,peak and respiratory ratesavg,max were
signicantlycorrelatedwithbodymass,BMI,BSA,andWHR
during the fourth session, and signicant correlations were
observed only incidentally in the remaining cases. Blood
pressure (SBP and DBP) was most signicantly correlated
with body mass, BMI, BSA and WHR during all sauna ses-
sions. e increasing values of correlation coecients during
every successive sauna session point to increasingly stronger
correlations between the analyzed anthropometric features
and indicators (mainly body mass, BMI, BSA, and WHR)
and physiological parameters (HRmin,mean,max,energyexpen-
diture, VO2avg,max,EPOC
avg,peak, respiratory rateavg,max,and
BPSBP,DBP) during prolonged sauna use (Table ).
All analyzed values of HRmin,mean,max were signicantly
correlated with body composition parameters (TBW, pro-
teins, minerals, BFM, FFM, SMM, and PBF) and PBSBP,DBP
values before sauna and during the third and fourth sauna
session. Energy expenditure was signicantly correlated with
the above parameters already during the second session. Sig-
nicant correlations between VO2avg,max,EPOC
avg,peak,and
respiratory rateavg,max were rarely observed, and they were
noted mainly during the four session. e values of BPSBP,DBP
were most signicantly correlated (between the rst and
the fourth session) with SBP and DBP before sauna. e
increasing values of correlation coecients during successive
sauna sessions point to stronger correlations between body
composition parameters (TBW, proteins, minerals, BFM,
FFM, and SMM) and energy expenditure, and, to a smaller
extent, between body composition parameters and HR,
EPOCavg,peak, and respiratory rateavg,max during prolonged
sauna use. No such trends were observed in the correlations
between SBP and DBP values during each session and before
sauna, and the values of rwere highly varied (Table ).
e values of HRmin,mean,max,EPOC
avg,peak,andrespi-
ratory rateavg,max were signicantly correlated with body
composition parameters (PBF, BFM, FFM, VFL, obesity
degree) mostly during the fourth session and, less frequently,
during the third session; and they were correlated with
BML during the rst and second session. Energy expen-
diture was signicantly correlated with BML during every
session, and with the remaining parameters during the
second or the third session. e values of rdecreased for
the correlation with BML and increased for the correlations
with the remaining parameters. e values of BP SBP,DBP
were most signicantly correlated with PBF, BFM, WFL
and obesity degree (increasing trend). Body mass loss was

BioMed Research International 
T : Descriptive statistics of the studied anthropometric features and physiological parameters (N=) before sauna.
Features Mean SD min-max AC
Body mass [kg] before sauna . . .-. .
Body mass [kg] aer sauna . . .-. .
Body mass loss [kg] ∗). . .-. -.
Body height [cm] . . .-. -.
BMI (Body Mass Index) [kg/m2]. . .-. .
BSA (Body Surface Area) [m2]. . .-. .
WHR (Waist-Hip Ratio) . . .-. .
TBW (Total Body Water) [L] . . .-. -.
Proteins [kg] . . .-. -.
Minerals [kg] . . .-. -.
SMM (Skeletal Muscle Mass) [kg] . . .-. -.
SBP (Systolic Blood Pressure) [mmHg] . . - -.
DBP (Diastolic Blood Pressure) [mmHg] . . - -.
PBF (Percent Body Fat) [%] . . .-. .
BFM (Body Fat Mass) [kg] . . .-. .
FFM (Fat Free Mass) [kg] . . .-. -.
VFL (Visceral Fat Level) [kg] . . .-. .
Obesity Degree . . - .
InBody score . . - -.
Targe t w e i g h t . . - .
BMR (metabolism) [kcal] . . - -.
MET (Metabolic Equivalent of Task) [mL/kg/min] . . - -.
Key: AC: asymmetry coecient, ∗t=.,df =, and p<..
signicantly correlated only with SBL (decreasing trend). e
increasing values of correlation coecients during successive
sauna sessions point to stronger correlations between the
analyzed body composition parameters (excluding BML)
versus energy expenditure, BPSBP,DBP,and,toalesserextent,
between body composition parameters versus HRmin,mean,max ,
EPOCavg,peak, and respiratory rateavg,max during prolonged
sauna use (Table ).
4. Discussion
e current study produced a number of interesting obser-
vations. e energy expenditure of the evaluated males
during four -minute sauna sessions was most frequently
correlated with body mass, somatic indicators (BMI, BSA,
and WHR), body composition parameters (TBW, proteins,
minerals, BFM, FFM, SMM, BFM, VFL, and obesity degree),
and BPSBP,DBP before sauna use. ese ndings suggest
that the energy expenditure of young men during sauna
bathing is inuenced by various factors, in particular body
mass (<r<), BMI (<r<) and BSA (<r<
). is study demonstrated that individuals with higher
body mass, body area, body fat mass and muscle mass
expend relatively more calories during sauna bathing. e
presented results also conrmed previous ndings that
energy expenditure is inuenced by the duration of sauna
bathing. During the rst  minutes, the evaluated males
expended around  calories on average, but their energy
expenditure increased signicantly (p<.) to more than
 calories during the last -minute session. In partic-
ipants with the highest values of anthropometric features
and body composition parameters, maximal energy expen-
diture reached  calories during  minutes of sauna
use.
Increased energy expenditure was accompanied by grow-
ing values of HRavg during successive sauna sessions (from
 bpm during the rst session to more than  bpm
during the fourth session). ese results indicate that average
physical eort during the fourth sauna session was within
the dicult range (- bpm). e highest HR values
within the very dicult range (- bpm) were also noted
during the fourth session, reaching up to  bpm in extreme
cases. e above results were also observed in men with
the highest values of somatic indicators. In young people
who regularly use the sauna, HR increases to approximately
- bpm and may exceed - bpm with a rise in
ambient temperature [, , , –]. e increase in
HR can be even higher in participants who do not use
the sauna regularly, which can be attributed to the lack
of physiological adaptation to high temperature []. e
rise in HR is also inuenced by other factors, such as the
length of stay in the sauna, age, sex, and physical endurance
[].Inthisstudy,maleparticipantsrarelyusedthesauna
and were characterized by low PA and overweight; and in
extreme cases, the noted HRmax values approximated the
lower boundary of the maximal eort range (≤ bpm).
In terms of health outcomes, the increase in HR to around
 bpm is regarded as a benecial adaptive response, whereas

BioMed Research International
T : Comparison of the arithmetic means of physiological parameters (N = ) aer every sauna session [dierences in arithmetic means
are highly statistically signicant ∗)-post hoc LSD test].
Parameter
Sauna session Difference
1234
Mean SD min-max Mean SD min-max Mean SD min-max Mean SD min-max Fp
HRmin [bpm] . . - . . - . . - . . - . <.
HRakg[bpm] . . - . . - . . - . . - . <.
HRmax [bpm] . . - . . - . . - . . - . <.
Recovery time [h] . . - . . - . . - . . - . <.
PTE-Peak Training Effect . . .-. . . .-. . . .-. . . .-. . <.
Energy expenditure [kcal] . . - . . - . . - . . - . <.
VO2akg[mL/kg/min] . . - . . - . . - . . - . <.
VO2max [mL/kg/min] . . - . . - . . - . . - . <.
EPOCakg[mL/kg] . . - . . - . . - . . - . <.
EPOCmax [mL/kg] . . - . . - . . - . . - . <.
Respiratory rateakg
[brpm] . . - . . - . . - . . - . <.
Respiratory ratemax
[brpm] . . - . . - . . - . . - . <.
Systolic blood
pressure-SBP [mmHg] . . - . . - . . - . . - . <.
Diastolic blood
pressure-DBP [mmHg] . . - . . - . . - . . - . <.
Physical effort
Easy <107 [bpm] . . - . . - . . - . . - . <.
Moderate 107-124 [bpm] . . - . . - . . - . . - . <.
Difficult 125-141 [bpm] . . - . . - . . - . . - . <.
Ver y D i ffi c u l t 142-159
[bpm] . . - . . - . . - . . - . <.
Maximal ≥160 [bpm] All values are zero
∗indicates that the dierence between the rst and the second sauna session was not signicant only for DBP (close to signicance, p= .).
an increase in excess of  bpm can have adverse conse-
quences because it is associated with higher cardiac eort and
diastole shortening []. e mechanism underlying the rise
in HR probably relies on an increase in blood temperature
and reex stimulation of energetic cardiac beta-receptors
[]. High humidity in the sauna room also inuences HR,
but humidity was relatively low (-%) in this study. Heart
rate decreases slowly during prolonged and gradual body
cooling, such as a cold shower. Baseline HR is restored
approximately - hours aer sauna if the body is cooled at
room temperature [] In the present study, all participants
took a cold shower during -minute breaks, and only  men
stepped into a cold paddling pool (-∘C) for less than 
seconds. e evaluated students spent the remainder of the
break in a sitting position in a room with a temperature of
∘C.Despitetheabove,theparticipants’HRvaluesdidnot
return to baseline values, but continued to increase during
successive sauna sessions. e above could suggest that -
minute breaks were not long enough for participants whose
HR and BP values exceeded the recommended norm during
successive sauna sessions.
Sauna bathing at a temperature of ∘Ccaninduce
massive bodily eort which not always delivers positive
health eects, both physiological and psychological. Similar
observations were made in our previous study [] which
demonstrated that sauna bathing had a highly relaxing and
calming eect on most students; notwithstanding, in Pod-
stawski et al. [], .% men and .% women experienced
discomfort due to excessive temperature, claustrophobia,
excessive number of sauna users and the presence of the
opposite sex. e eect of sexual dimorphism seems to be
more linked with the participants’ sociocultural status, which
was conrmed in our successive study []. e average values
of HRmin during the rst sauna session were relatively high
(. bpm), which could be indicative of psychological
discomfort.
Similar values of HR (. bpm) before sauna use were
also observed in men who did not train professionally and
visited a sauna sporadically. ese results were signicantly
higher than in men with average and high training levels
(. bpm and  bpm, respectively) who were regular sauna
users. During a -minute stay in the sauna ( sessions of

BioMed Research International 
T : Correlations between anthropometric features and physiological parameters aer successive sauna sessions (values in bold are
statistically signicant).
Trai t s Sauna
session
HR Energy expend.
[kcal]
VO2EPOC Respiratory
rate
Blood
pressure
min avg max max –
min avg max avg peak avg max SBP DBP
Body height
[cm]
 -. -. -. -. -. -. -. -. -. -. -. -. -0.31
 . -. -. -. . -. -. -. -. . . -. -.
 . . . -. . . . -. -. -. -. -. -.
 -. -. -. . -. -. -. -. -. -. -. -. -.
Body mass [kg]
 -. -. -. . -. -. . -. -. -. -. 0.53 0.32
 . . -. -. 0.39 -. -0.35 -. -. . -. 0.52 0.36
.0.34 . -. 0.66 . -. . . . . 0.61 0.49
0.36 0.44 0.31 -. 0.70 . . 038 0.44 0.33 0.40 0.63 0.49
BMI (Body
Mass Index)
[kg/m2]
 -. -. -. . . . . -. -. -. -. 0.71 0.50
 . . -. -. 0.37 -. -. . -. . -. 0.69 0.53
.0.33 . -. 0.66 . -. . . . . 0.75 0.66
0.45 0.56 0.47 -. 0.81 0.31 . 0.51 0.59 0.45 0.51 0.77 0.68
BSA (Body
Surface Area)
[m2]
 -. -. -. -. -. -. . -. -. -. -. 0.46 .
 . . -. -. 0.37 -. -0.35 -. -. . . 0.45 .
.0.34 0.30 -. 0.64 . -. . . . . 0.54 0.41
0.32 0.37 . -. 0.63 . . 0.30 0.36 . 0.33 0.55 0.39
WHR
(Waist-Hip
Ratio)
 -. -. -. . -. -. . -. -. -. -. 0.70 0.51
 . . -. -. 0.35 -. -0.31 . -. . -. 0.71 0.59
 . . . . 0.47 -. -. -. . . . 0.72 0.61
0.31 0.48 0.42 -. 0.54 0.33 . 0.47 0.55 0.31 0.40 0.79 0.68
 minutes each with -minute breaks; temperature: ∘C;
humidity: -%), the HR values of sedentary men increased
most signicantly (. bpm) relative to the participants
with average and high training levels ( and . bpm,
respectively) []. In a study by Pilch et al. [], the HR
values of  professional swimmers and  untrained students
(aged - years), participating in three -minute sauna
sessionswith-minutebreaks(temperature:.
∘C, humid-
ity: .%), increased from  and  bpm to  and 
bpm, respectively, aer the third session. In a follow-up study
conducted on  males (aged - years), who attended three
-minute sauna sessions with -minute breaks (temperature:
∘C, humidity: -%), Pilch et al. [] observed that HR
values increased signicantly from . bpm before sauna
to  bpm immediately aer sauna. A study of  healthy
men (mean age of  years, in the range of  to  years)
exposed to a temperature of -∘Cforminutesinasauna
revealed an increase in HR values from . to . bpm [].
e HR values of scuba divers did not change signicantly
aer a -minute session in a dry sauna (∘C) []. e HR
values of professional runners were determined at around 
bpm aer  to  minutes of sauna bathing (temperature:
.±.∘C, humidity: up to %) [].
Blood pressure (SBP and DBP) increased signicantly
aer successive sauna sessions, and the average BP during
the fourth session (/ mmHg) was indicative of stage 
hypertension [], which could point to preexisting health
conditions that were manifested under exposure to thermal
stress. A study of men with various training levels (high,
average and men who did not train professionally) revealed
an increase in SBP values (from . to , from . to
., from . to . mmHg) and a decrease in DBP
values during sauna (from . to ., from . to .,
from . to . mmHg, respectively) []. ree -minute
sessions separated by -minute breaks (temperature: .,
humidity: up to .%) increased SBP values from . to
. mmHg and decreased DPB values from . to .
mmHg in  healthy males aged - years []. Aer
 minutes of bathing in a dry sauna (∘C), SBP values
decreased signicantly (± mmHg, p=.), whereas
DBP values remained unchanged []. In men aged -
years exposed to a temperature of -∘Cforminutesin
a sauna, SBP values increased from  to  mmHg []. In
the present study, the highest BP of / mmHg was noted
in participants with the highest values of somatic indicators
and body composition parameters (overweight or obesity).
evaluesofSBPandDBParegenerallyhigherinoverweight
or obese men and women than in normal weight individuals
[]. ese values are oen indicative of hypertension and
indeed other comorbidities []. For this reason, it is advo-
cated that individuals with diagnosed hypertension should
use the sauna at lower temperatures (-∘C), which are
characteristic of steam sauna, but are not accompanied by
high humidity (%) [, ]. Humidity is low in the Finnish

BioMed Research International
T : Correlations between body composition parameters and blood pressure before sauna and physiological parameters aer successive
sauna sessions (values in bold are statistically signicant).
Parameters Order of
entry
HR Energy expend.
[kcal]
VO2EPOC Respiratory
rate
Blood
pressure
min avg max max –
min avg max avg peak avg max SBP DBP
TBW (Total
Body Water)
[L]
 . . . -. . . . . . . . . .
 . . -. -. 0.29 -. -. -. -. . . . .
.0.37 0.33 -. 0.53 . . . 0.29 . . . .
0.29 . . -. 0.53 . -. . . . . . .
Proteins [kg]
 . . . -. . . . . . . . . .
 . . -. -. 0.30 -. -. -. -. . . . .
.0.37 0.33 . 0.54 . . . 0.30 . . 0.29 .
0.29 . . -. 0.55 . -. . . . . . .
Minerals [kg]
 . . -. -. . . . -. . . . . -.
 . . -. -. 0.30 -. -. -. . . . . .
.0.38 . -. 0.52 . -. . . . . . .
0.31 . . -0.31 0.49 -. -. . . . . . .
SMM (Skeletal
Muscle Mass)
[kg]
 . . . -. . . . . . . . . .
 . . -. -. 0.29 -. -. -. -. . . . .
.0.37 0.33 . 0.53 . . . 0.29 . . . .
0.29 . . -. 0.55 . -. . . . . . .
SBP (Systolic
Blood Pressure)
before sauna
[mmHg]
 -. -. -. -. . . . . . -. -. 0.91 0.63
 . . -. -. 0.36 -. -. . -. . -. 0.90 0.66
 . . . . 0.61 . . . . . . 0.91 0.73
0.48 0.46 0.43 -0.29 0.65 . . 0.48 0.50 0.29 0.36 0.91 0.73
DBP (Diastolic
Blood Pressure)
before sauna
[mmHg]
 -. . . . . . . . . . . 0.84 0.82
 . . -. -. 0.32 -. -. . -. . -. 0.80 0.85
 . . . . 0.48 . . . . . . 0.77 0.81
0.36 0.42 0.36 -. 0.58 . . 0.47 0.50 0.34 0.42 0.84 0.79
sauna (-%), which stimulates hemodynamic changes,
including a decrease in BP and vascular resistance []. Air
humidity is increased by pouring water onto heated stones,
which induces a minor and transient (- mmHg) increase
inSBP[].ImamuraandKiharademonstratedaminor,but
statistically signicant decrease in the BP values of patients
who regularly visited an infrared sauna over a period of
two weeks [, ]. In people who assume a seated position
in the sauna, BP may not be maintained within a constant
range because peripheral vasodilation in the lower limbs
and the absence of muscle pump activity under exposure to
high temperature can decrease reex vasoconstriction and
venous return [, ]. Coronary vasospasm can further
disrupt the equilibrium between oxygen demand and oxygen
supply to the myocardium [], and it increases the risk
of arrhythmia, myocardial ischemia and infarction [, ].
In this study, male students maintained a standardized
sitting position in the sauna, which could increase their SPB
and DBP, especially that the participants were overweight,
had a sedentary lifestyle and rarely visited the sauna. e
above risks are particularly high in people suering from
coronary atherosclerosis, which is why cooling by whole body
immersion is not, de facto, recommended for every sauna
user [, ]. Sauna bathing rarely confers undesirable eects
on participants with a healthy cardiovascular system [, ].
Cooling by immersion in cold water is not recommended
for patients with cardiovascular problems, however, gradual
cooling, including in a shower, is advised [].
e eects of sauna bathing on BP reported in the liter-
ature vary considerably, depending on the applied method
of measurement, type of sauna, duration of exposure which
elicits the evaporation eect, and user adaptation to high tem-
perature. Considerable variations were reported in studies
where BP was measured with a sphygmomanometer, ranging
from a minor increase [, ] or the absence of any changes
[, –] to a decrease in SBP [, –] and DBP values
[–, , , , , , ].
e body mass loss associated with sauna bathing is also a
very important indicator. Sweat volume during sauna bathing
is estimated at . to . kg/h, and sweating is generally
intensied with a rise in temperature and humidity, although
individual responses may vary []. During  minutes of
sauna bathing, the BML of the evaluated males was estimated
at . kg, and it accounted for .% of their body mass.

BioMed Research International 
T : Correlations between body composition parameters relating to adipose tissue and physiological paramete rs aer successive sauna
sessions (values in bold are statistically signicant).
Parameters Sauna
session
HR Energy expend.
[kcal]
VO2EPOC Respiratory
rate
Blood
pressure
min avg max max –
min avg max avg peak avg max SBP DBP
PBF (Percent
Body Fat) [%]
 -. -. -. . -. -. -. -. -. -. -. 0.66 0.51
 . . -. -. . -. -0.29 . -. . -. 0.69 0.55
 . . . . 0.44 -. . . . . . 0.69 0.60
.0.36 0.37 -. 0.52 . . 0.34 0.42 . 0.30 0.77 0.66
BFM (Body Fat
Mass) [kg]
 -. -. -. . -. -. -. -. -. -. -. 0.61 0.44
 . . -. -. 0.32 -. -0.32 -. -. . -. 0.64 0.51
 . . . -. 0.53 -. -. . . . . 0.67 0.58
.0.42 0.38 -. 0.59 . . 0.38 0.46 0.30 0.38 0.74 0.64
FFM (Fat Free
Mass) [kg]
 . . . -. . . . . . . . . .
 . . -. -. . -. -. -. -. . . . .
.0.37 0.33 -. 0.53 . . . 0.29 . . . .
0.29 . . -. 0.54 . -. . . . . . .
VFL (Visceral
Fat Level) [kg]
 -. -. -. . -. -. -. -. -. -. -. 0.62 0.45
 . . -. -. 0.34 -. -0.34 -. -. . -. 0.64 0.51
 . . . -. 0.53 -. -. . . . . 0.67 0.58
0.31 0.44 0.37 -. 0.59 . . 0.41 0.48 0.31 0.39 0.74 0.64
Obesity Degree
 -. -. -. -. . . . -. -. -. -. 0.71 0.48
 . . -. -. 0.35 -. -. . -. . -. 0.69 0.52
.0.33 . -. 0.68 . -. . . . . 0.75 0.65
0.46 0.56 0.48 -. 0.82 0.31 . 0.52 0.59 0.46 0.50 0.77 0.68
BML (Body
Mass Loss) [kg]
0.40 0.41 . -. 0.59 0.32 -. . 0.29 . -. 0.36 .
.0.42 . -. 0.55 . . 0.34 . 0.33 . 0.35 .
 . . . . 0.43 . . . . . 0.29 0.35 .
 . . . -. 0.29 . -. . . . . 0.33 .
e values of BML were also signicantly correlated with
anthropogenic indicators, body composition parameters and
physiological parameters. e results of our study indicate
that persons with a high BMI are more prone to dehydration,
which is why individuals should replenish lost uids during
sauna bathing. Analogous results were noted in our previ-
ous study [] which demonstrated signicant correlations
between BMI and BML and highlighted that the loss ofbodily
uids in a dry sauna can be accurately predicted based on
BMI values. Body mass loss, expressed as a percentage of total
body mass increased disproportionately with an increase in
the subjects’ BMI. Body mass loss was lowest in underweight
students, and it was higher in participants with normal body
weight. BML values were very high in overweight and obese
males and females and were approximately twofold higher
than in underweight women, with similar correlations were
noted in men []. In our previous study [], BML values
measured aer sauna bathing were signicantly higher in
female and male subjects with higher body mass, but they
tended to be lower in taller participants (less so in men). With
every kilogram increase in body mass, the corresponding
BML values increased by . kg in women and .
kginmenonaverage.Inthepresentstudy,BMLwasnot
correlated with height, probably because this parameter was
not correlated with physiological indicators such as HR,
energy expenditure, VO2avg,max,EPOC
avg,peak,respiratory
rateavg,max, and SBP (Table ). Sweating begins shortly upon
entering the sauna and peaks aer approximately  minutes.
e average total sweat secretion has been estimated at .
kg []. Body core temperature increases by . to .∘C
per every percent of BML [, ]. Kozłowski and Saltin []
conducted one of the rst studies into the eect of sweating on
the uid balance, analyzing sweating-induced dehydration in
 healthy males who were exposed to a temperature of ∘C
in a sauna for . hours, which is nearly four times longer
than in our study. In Kozłowski and Saltin [], the average
BML during the .-hour sauna session was determined at
. kg (.%). In other studies, the average sauna-induced
BML was estimated at – g [, ]. In a study of
swimmers and untrained subjects who attended three sauna
sessions of  minutes each (temperature: .∘C, humidity:
up to .%), BML was determined at . and . kg,
respectively. e results of the present study were similar
to those reported by Pilch et al. [] who analyzed changes

 BioMed Research International
in BML and physiological and biochemical parameters in
 healthy males attending three -minute sauna sessions
(temperature: ∘C, humidity: -%) with -minute breaks.
e participants assumed a sitting position in the sauna and
lost . kg of bodily uids. Coles et al. [] studied 
male subjects who remained in a dry sauna for six -minute
sessions (temperature .∘C) with -minute breaks between
sessions. e experiment involved a euhydration trial and a
dehydration trial. e participants did not ingest any uids
during the dehydration trial. e experimental procedure was
identical in both trials, the only dierence being that during
the euhydration trial, the participants were asked to drink
water in a volume corresponding to the amount of body mass
lost in the previous sauna session. e subjects lost . kg
of body mass (.%) in the euhydration trial and . kg
(.%) in the dehydration trial. In a study of  nonobese
and obese individuals exposed to a temperature of ∘Cfor
three -minute sauna sessions, BML values (-. kg; in the
range of -. to -. kg; . ±.%) diered signicantly
(p <.) between nonobese (. ±.) and obese (. ±
.) subjects []. omas et al. [] determined the average
BML (normalized to body mass %) of  healthy adults at
. ±.% (in the range of .–.%) aer a -minute
sessioninthesauna.ebodymassofscubadiversdecreased
signicantly (-± g; p<.) aer  minutes in a dry
sauna (∘C) [].
5. Limitations
e use of Suunto Ambit Peak Sapphire heart rate monitors
for measuring the participants’ physiological parameters was
a potential limitation of this study. However, the evaluated
males were exposed to extreme temperature (∘C), and
dierent measuring equipment could not have been used as
eectively in a study conducted on a large and homogenous
sample ( males) with similar environmental conditions
(day, hour, duration, temperature, and humidity). Future
studies may therefore wish to examine the reliability and
validity of various HR monitors in extreme conditions.
6. Conclusions
Young, overweight, and sedentary men (aged - years)
who rarely use the sauna lose around . kg of bodily uids
on average during four -minute sauna sessions (temper-
ature: ∘C, humidity: %) with four -minute breaks in
between sessions (total of  minutes). e noted values of
physiological parameters (energy expenditure, HRmin,av g,max,
BPSBP,DBP,VO
2avg and max ,EPOC
avg and peak,andrespiratory
rateavg and max) increased signicantly aer every -minute
session and even exceed the recommended norms (HR and
BP during the third and fourth session). In some cases,
elevated BP values could be indicative of preexisting health
conditions that were manifested upon relatively long (
minutes) exposure to thermal stress. Sauna sessions last-
ing  minutes could be excessive and dangerous to the
health of men who are considerably overweight. e above
parameters and BML were highly correlated not only with
anthropometric indicators (in particular body mass, BMI,
BSA, and WHR), but also with body composition parameters,
in particular those indicative of high body fat content (BFM,
PBF, and VFM) and high degree of obesity. Physiological
parameters are less correlated with TBW, minerals, proteins,
SMM, and initial values of SBP and DBP. ese correlations
signicantly contribute to the loss of bodily uids. e
resultsofthisstudycomplementpreviousresearchndings
and expand our knowledge about factors which signicantly
aect physiological parameters during sauna bathing. As
such, these ndings should be acutely considered by indi-
viduals, practitioners, and clinicians in the adoption of sauna
exposure.
Data Availability
e Excel data used to support the ndings of this study
are restricted by the Ethics Committee of the University
of Warmia and Mazury in Olsztyn (UWM), Poland, in
order to protect participants’ privacy. Data are available from
Robert Podstawski, e-mail: podstawskirobert@gmail.com,
for researchers who meet the criteria for access to condential
data.
Conflicts of Interest
All authors declare that there are no conicts of interest
regarding the paper and its publication.
Acknowledgments
e funding for this research received from the University of
Warmia and Mazury in Olsztyn does not lead to any conicts
of interest.
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