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Effects of far-infrared sauna bathing on recovery from strength and endurance training sessions in men

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This study investigated effects of far-infrared sauna (FIRS) bathing on recovery from strength training and endurance training sessions, but also possible differences between FIRS and traditional (TRAD) Finnish sauna bathing. Ten healthy physically active male volunteers had on various days either a 60 min hypertrophic strength training session (STS) or a 34-40 min maximal endurance training session (ETS), which was following by 30 min bathing in special FIRS sauna at temperature of 35-50°C and humidity of 25-35%. After the sauna, subjects sat for 30 min at room temperature (21°C and 25-30% humidity). In comparison, 30 min of TRAD took place at 35-50°C and in 60-70% humidity. Performance tests included maximal isometric bench press and leg press, counter movement jump (CMJ) and maximal oxygen uptake on a treadmill. After STS, there were decreases in maximal isometric bench press (p < 0.001), maximal isometric leg press (p < 0.001), CMJ (p < 0.001) and pH (p < 0.001), but increases in heart rate (p < 0.001) and lactate concentration (p < 0.001) as expected. During recovery there were no differences in any variables between FIRS and no sauna bathing (NO SAUNA). Maximal ETS increased oxygen uptake (p < 0.001), heart rate (p < 0.001), lactate concentration (p < 0.001) and decreased pH (p < 0.001) as expected. During recovery at 30 min, CMJ was significantly (p < 0.05) higher (0.34 ± 0.09 m) after FIRS bathing than after sitting with NO SAUNA (0.32 ± 0.0 m). After sauna heart rate was higher (p < 0.05) in TRAD (92 ± 13 beats/min) than in FIRS (71 ± 7 beats/min). In conclusion, deep penetration of infrared heat (approximately 3-4 cm into fat tissue and neuromuscular system) with mild temperature (35-50°C), and light humidity (25-35%) during FIRS bathing appears favorable for the neuromuscular system to recover from maximal endurance performance. FIRS bathing is a very light loading for the body and provides a comfortable and relaxing experience.
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Meroet al. SpringerPlus (2015) 4:321
DOI 10.1186/s40064-015-1093-5
RESEARCH
Eects offar-infrared sauna bathing
onrecovery fromstrength andendurance
training sessions inmen
Antti Mero*, Jaakko Tornberg, Mari Mäntykoski and Risto Puurtinen
Abstract
Purpose: This study investigated effects of far-infrared sauna (FIRS) bathing on recovery from strength training and
endurance training sessions, but also possible differences between FIRS and traditional (TRAD) Finnish sauna bathing.
Methods: Ten healthy physically active male volunteers had on various days either a 60 min hypertrophic strength
training session (STS) or a 34–40 min maximal endurance training session (ETS), which was following by 30 min bath-
ing in special FIRS sauna at temperature of 35–50°C and humidity of 25–35%. After the sauna, subjects sat for 30 min
at room temperature (21°C and 25–30% humidity). In comparison, 30 min of TRAD took place at 35–50°C and in
60–70% humidity. Performance tests included maximal isometric bench press and leg press, counter movement jump
(CMJ) and maximal oxygen uptake on a treadmill.
Results: After STS, there were decreases in maximal isometric bench press (p < 0.001), maximal isometric leg press
(p < 0.001), CMJ (p < 0.001) and pH (p < 0.001), but increases in heart rate (p < 0.001) and lactate concentration
(p < 0.001) as expected. During recovery there were no differences in any variables between FIRS and no sauna
bathing (NO SAUNA). Maximal ETS increased oxygen uptake (p < 0.001), heart rate (p < 0.001), lactate concentration
(p < 0.001) and decreased pH (p < 0.001) as expected. During recovery at 30 min, CMJ was significantly (p < 0.05)
higher (0.34 ± 0.09 m) after FIRS bathing than after sitting with NO SAUNA (0.32 ± 0.0 m). After sauna heart rate was
higher (p < 0.05) in TRAD (92 ± 13 beats/min) than in FIRS (71 ± 7 beats/min).
Conclusion: In conclusion, deep penetration of infrared heat (approximately 3–4 cm into fat tissue and neuromuscu-
lar system) with mild temperature (35–50°C), and light humidity (25–35%) during FIRS bathing appears favorable for
the neuromuscular system to recover from maximal endurance performance. FIRS bathing is a very light loading for
the body and provides a comfortable and relaxing experience.
Keywords: Far-infrared, Sauna, Exercise, Neuromuscular, Performance
© 2015 Mero et al. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License
(http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium,
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and indicate if changes were made.
Background
Sauna bathing (Finnish sauna bathing) has been exten-
sively studied. It is a type of heat exposure, which induces
haemodynamic and endocrinological changes in some
ways similar to those evoked by physical exercise (e.g.
Hannuksela and Ellahham 2001; Kukkonen-Harjula and
Kauppinen 2006). In traditional saunas there are either
wood stoves or electric heaters to heat the air to approxi-
mately 70–100°C, optimally between 80 and 90°C at the
face level of the bathers (Kukkonen-Harjula and Kaup-
pinen 2006). e air typically has a relative humidity of
10–20% (Leppäluoto 1988; Kauppinen 1997). e sauna
bath consists of repeated cycles of exposure to heat. e
length of stay in the sauna depends on each bather’s own
sensations of comfort, but the duration usually ranges
from 5 to 20min. is is followed by a cooling-off period
(shower, swim, or a period at room temperature), the
length of which also depends on personal preference. A
sufficient recovery period (usually about 30min) follow-
ing a few hot/cold cycles allows for normalizing the body
temperature and cessation of sweating.
Open Access
*Correspondence: antti.a.mero@jyu.fi
Department of Biology of Physical Activity, University of Jyväskylä,
P.O. Box 35, 40351 Jyväskylä, Finland
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Meroet al. SpringerPlus (2015) 4:321
Some people find the aforementioned practice
uncomfortable. In contrast, far-infrared saunas (FIRS)
heat to 40–60°C and provide a more comfortable and
relaxing experience (Beever 2009). ese saunas utilize
120-V infrared elements, similar to the infrared warm-
ers on neonatal resuscitation beds, to radiate heat with
a wavelength of around 10µm. As infrared heat pene-
trates more deeply (approximately 3–4cm into fat tis-
sue and the neuromuscular system) than warmed air
(only a few millimeters), users develop a more vigorous
sweat at a lower temperature than they would in tradi-
tional saunas. Consequently, the cardiovascular demand
imparted by thermoregulatory homeostasis (sweating,
vasodilation, decreased afterload, increased heart rate,
and increased cardiac output) is aerobically very light
(Beever 2009).
In athletes, the traditional sauna has some positive
effects on thermoregulation, if the competition is in a
hot environment (Tyka etal. 2008). Also, during weight-
reduction, sauna bathing has been used successfully (Vii-
tasalo etal. 1987; Karila etal. 2008). In the recovery from
physical exercise, sauna bathing has been used despite
it seems that some other methods such as light aerobic
exercise, nutrition, massage, sleep, rest are more effi-
cient (e.g. Bompa and Haff 2009). e role of traditional
sauna bathing has been more recreational and relaxing
in nature. e warm temperatures and cooling-off peri-
ods may relax muscles, nerves and blood vessels. is
can produce a sensation of calm and relaxation in some
people. Conversely, the role of FIRS on recovery has
not been scientifically studied. erefore, the first aim
of the present study was to investigate effects of FIRS
bathing on recovery from strength training and endur-
ance training sessions. e rationale is primarily based
on the fact that the infrared heat penetrates very deeply
(approx. 3–4cm) into the neuromuscular system. is
may have positive effects on the neuromuscular system
during recovery. e second aim was to study possible
differences between FIRS and traditional (TRAD) Finn-
ish sauna bathing.
Methods
Subjects
e subjects were 10 healthy male volunteers, who
were accustomed to weekly sauna baths. All subjects
were physical education students and were involved
in recreational physical activity during the previous
months. Before the actual experiments, their health-
status was checked by a health questionnaire. e sub-
jects had a mean age of 25.3±8.4years, mean height of
1.78±0.07m, mean body mass of 79.6±7.5kg, mean
hemoglobin of 160 ± 10 g/l, and mean hematocrit of
0.46±0.02.
Experimental procedure
e subjects participated in six sauna bath experiments
each one separated by 1week. On the morning, at 08–09
AM, of the experimental sauna bath days (in March–
April), the subjects arrived to the lab after 10–12h fast-
ing. First a fasting blood sample was obtained (basic
health parameters not shown here) and then they had a
light breakfast. At least 1h after eating all sauna meas-
urements were performed between 09–12 AM. No food,
drink (except 5dl water in the sauna) or smoking was
allowed until the end of the experiment. No other own
sauna baths were allowed during the whole study period.
Furthermore, strenuous exercise was not allowed for
3 days and alcohol for 2days before the experimental
sessions.
In the first experiment, the subjects had 30min FIRS
bathing and then were sat for 30min at room tempera-
ture of 21°C and humidity of 25–30%. ereafter, the sub-
jects were familiarized with treadmill running, counter
movement jump (CMJ), and their one repetition maxi-
mum (1RM) in bench press and in bilateral leg press were
measured. e next four experiments (strength training
session plus FIRS 30min, strength training session plus
no sauna 30min, endurance training session plus FIRS
30min, endurance training session plus no sauna 30min;
Figure1) were performed in a randomized order. At the
end of each experiment, the subjects sat for 30 min at
room temperature. In the last experiment the subjects
had 30min traditional sauna bathing (TRAD) and then
sat for 30min at room temperature.
FIRS andTRAD sauna bath
Far-infrared sauna bathing occurred sitting in a spe-
cial FIRS sauna (Radiant FIRS SGC1210BR, Harvia Ltd,
Muurame, Finland). Its width is 1.20m, depth 1.05 m,
height 1.91m, and voltage 230-V. e type of radiator is
carbon fibre and the emitted wavelength is 4–17µm. e
temperature in FIRS sauna was set at 35–50°C (35°C at
the level of legs and 50°C at the bather’s face) and relative
humidity of 25–35%, respectively. In TRAD, the electri-
cally heated sauna temperature was similar 35–50°C, but
relative humidity was increased to 60–70% by throwing
water on the hot rocks of the sauna heater. In both sau-
nas the subjects were sitting wearing only shorts and they
had to drink 5dl water during 30min bathing.
Strength training session (STS), isometric strength tests
(ISTs), andcounter movement jump (CMJ)
A 10min warm-up consisted both 5min riding a bicy-
cle with heart rate between 120 and 140beats/min and
5min dynamic stretching exercises for whole body. After
that, the STS lasted 60 min including dynamic hyper-
trophic training in bilateral bench press and in bilateral
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Meroet al. SpringerPlus (2015) 4:321
leg press and also IST performances in bench press and
in leg press. ISTs were performed before and after the
training session, as well as following 30 min of FIRS
bath or sitting. e bilateral leg IST was performed on
an electromechanical dynamometer (David 210, David
Health Solutions Ltd., Helsinki, Finland) using three
single maximal trials with 2min recovery between each
test. Similarly the maximal bench press performance
was measured on an electromechanical dynamometer
(Bench Press, Department of Biology of Physical Activ-
ity, Jyväskylä, Finland). e arm angle was 90° in bench
press and knee angle was 110° in leg press. Maximal CMJ
was performed on a contact mat (Newtest Ltd., Oulu,
Finland) three times at each measurement point with a
recovery of 3min. e vertical rise of center of gravity
was calculated from flight time (Komi and Bosco 1978).
e best result out of three trials was selected in CMJ and
in ISTs.
e dynamic bench press and dynamic leg press train-
ing included 5×10RM with a load, which was evaluated
according to the 1RM test in pretest. If the subject could
not succeed in the last repetitions in a set the researcher
assisted slightly to enable the subject to complete all 10
reps. Recovery was 2min between sets. Each subject car-
ried out the STS at the same time in the morning in both
STS experiments and used similar absolute weights in the
dynamic training.
Endurance training session (ETS), VO2 andheart rate
A 10min warm-up consisted both 5min riding a bicycle
with heart rate between 120 and 140beats/min and 5min
dynamic stretching exercises for whole body. After that,
the ETS lasted 34–40min including 10min light aerobic
work on a bicycle and then running on a treadmill until
exhaustion (range 24–30 min). e treadmill exercise
began with an 8km/h speed and 1° angle of the treadmill.
ereafter, the speed was increased by 1km/h after every
3min. All subjects were voluntarily exhausted between
24 and 30min. During running, gaseous exchange was
measured using Sensor Medics Breath Gas Analyzer
(Vmax series 229, California, USA). e device was cali-
brated before every measurement and VO2 was deter-
mined as a mean from the final 30s of every stage. Heart
rate was measured by a Polar heart rate monitor (Polar
Electro Oy, Kempele, Finland). e same ISTs and CMJ
tests were performed before and after exercise and fol-
lowing 30min of FIRS bath or sitting.
Blood pressure
Brachial systolic and diastolic blood pressures were
measured from the arm with an electronic blood pres-
sure monitor (Omron M1, Normomedical Ltd, Helsinki,
Finland).
Blood collection andanalysis
Blood samples were drawn from the antecubital vein in
a sitting position. Analysis included hemoglobin (Hb),
serum total testosterone, cortisol, growth hormone, lac-
tate, and pH. Serum samples were kept frozen at 80°C
until analyzed. Two milliliters of blood were taken in K2
EDTA tubes (Terumo Medical Co., Leuven, Belgium) for
measurements of Hb concentration with a Sysmex KX
21N Analyzer (Sysmex Co., Kobe, Japan). For the deter-
mination of serum hormone concentrations, five millilit-
ers of blood were taken into serum separator tubes and
the concentrations were analyzed by an immunometric
chemiluminescence method with Immulite® 1000 (DPC,
Los Angeles, USA). e sensitivities of the assays were
Figure1 Experimental design. BW body weight, BP blood pressure, BS blood sample, VO2 oxygen uptake, HR heart rate, CMJ counter movement
jump, IST isometric strength test, STS strength training session, ETS endurance training session, FIRS far infrared sauna.
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Meroet al. SpringerPlus (2015) 4:321
0.5nmol/l for testosterone, 5.5 nmol/l for cortisol, and
2.6µg/l for growth hormone. e intra-assay coefficient
of variation (CV) was 5.7% for testosterone, 4.6% for cor-
tisol, and 4.2% for growth hormone. Blood samples for
lactate were obtained from the fingertip and collected
into capillary tubes (20µl), which were placed in a 1ml
hemolyzing solution and analysed automatically after
the completion of testing according to the manufactur-
er’s instructions (EKF diagnostic, C-line system, Biosen,
Germany). pH was analyzed with IL GEM Premier 3000
Blood Gas System (Instrumentation Laboratory, Lexing-
ton, MA, USA). e intra-assay CV was 0.1% for pH.
Statistics
Before applying statistical methods, the data was checked
for normality by Shapiro–Wilk’s test and the homogene-
ity of variances by Levene’s test. en statistical analy-
ses were performed with PAWS Statistics version 20.0
for Windows (SPSS, Inc, Chicago, IL, USA). Differences
between conditions were determined through one-way
ANOVA. Bonferroni correction was used as a post hoc
test. Data are presented as mean±SD. e statistical dif-
ference was considered to be significant at the p<0.05
level.
Results
FIRS andTRAD
Table 1 presents the results for FIRS and TRAD.
After sauna, heart rate was higher (p <0.05) in TRAD
(92±13 beats/min) than in FIRS (71 ±7 beats/min).
Serum cortisol decreased in both FIRS and in TRAD
being at the lowest (p < 0.05) at the end of recovery.
Serum growth hormone increased in both FIRS and
in TRAD and was highest (p <0.05) after sauna and at
30min of recovery.
STS, FIRS andrecovery sitting
e average training session work load of the sub-
jects was in bench press 2,505 ± 346 kg and in leg
press 7,583±998 kg. Maximal isometric bench press,
Table 1 Measured variables in30min FIRS bathing andin 30min traditional (TRAD) sauna bathing (mean±SD)
a Subjects drank 0.5dl water in sauna which is included in body mass.
b Signicantly (p<0.05) dierent from before value.
c Signicantly (p<0.05) dierent from FIRS after sauna value.
Variable Before sauna 15min insauna After sauna Recovery 30min
Body mass (kg)a
FIRS 79.7 ± 7.1 79.4 ± 7.5
TRAD 80.6 ± 8.6 80.1 ± 8.6
Hemoglobin (g/l)
FIRS 159 ± 10 157 ± 10 157 ± 9 156 ± 9
TRAD 158 ± 8 160 ± 8 160 ± 9 159 ± 8
Heart rate (beats/min)
FIRS 70 ± 9 72 ± 9 71 ± 7 64 ± 7
TRAD 71 ± 8 81 ± 10 92 ± 13c68 ± 9
Blood pressure (mm Hg)
FIRS systolic 138 ± 13 127 ± 14 129 ± 11 129 ± 12
FIRS diastolic 83 ± 15 73 ± 13 77 ± 11 78 ± 10
TRAD systolic 133 ± 13 129 ± 14 133 ± 11 127 ± 12
TRAD diastolic 76 ± 15 74 ± 13 75 ± 11 82 ± 10
pH
FIRS 7.40 ± 0.03 7.42 ± 0.02 7.42 ± 0.02 7.40 ± 0.02
TRAD 7.41 ± 0.02 7.43 ± 0.02 7.43 ± 0.03 7.42 ± 0.02
Testosterone (nmol/l)
FIRS 18.8 ± 4.7 18.3 ± 5.3 17.9 ± 5.1 18.9 ± 6.3
TRAD 20.0 ± 5.3 18.7 ± 3.5 21.0 ± 5.6 19.8 ± 5.5
Cortisol (nmol/l)
FIRS 399 ± 88 367 ± 122 354 ± 133 329 ± 109b
TRAD 546 ± 122 467 ± 143b409 ± 117b380 ± 127b
Growth hormone (µg/l)
FIRS 0.7 ± 1.3 5.2 ± 12.6 5.4 ± 5.1b11.2 ± 8.0b
TRAD 0.6 ± 0.6 6.9 ± 8.7 19.4 ± 26.1b11.9 ± 20.0b
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maximal isometric leg press and CMJ decreased signifi-
cantly (p<0.001) after STS, but there were no differences
between FIRS and NO SAUNA (Table2). Also, in the
other variables there were expected but similar changes
after STS in the groups.
ETS, FIRS andrecovery sitting
Table 3 presents the results for ETS and FIRS 30 min
bathing or for ETS and sitting in a normal room (NO
SAUNA) 30 min and, in both cases, during recovery
sitting another 30 min. Maximal ETS increased heart
rate (p <0.001), lactate concentration (p <0.001) and
decreased pH (p < 0.001) as expected in both groups.
Table 2 Measured variables in STS and FIRS bathing
30min or inSTS andsitting ina normal room (NO SAUNA)
30min andin bothcases during recovery sitting another
30min (mean±SD)
a Signicantly (p<0.001) dierent from before value.
b Signicantly (p<0.05) dierent from before value.
c Subjects drank 0.5dl water in sauna which is included in body mass.
Variable Before STS After STS Recovery
30min Recovery
60min
Isometric bench press (kg)
FIRS 96.6 ± 14.6 78.9 ± 12.4a83.7 ± 13.2a
NO SAUNA 97.2 ± 15.9 80.3 ± 12.7a84.6 ± 13.1a
Isometric leg press (kg)
FIRS 428 ± 79 374 ± 70a383 ± 78a
NO SAUNA 424 ± 70 362 ± 69a372 ± 83a
Heart rate (beats/min)
FIRS 68 ± 10 129 ± 16a87 ± 10 77 ± 10
NO SAUNA 67 ± 8 125 ± 8a76 ± 8 67 ± 8
Blood pressure (mm Hg)
FIRS systolic 130 ± 13 158 ± 15a129 ± 13 128 ± 12
FIRS diastolic 74 ± 9 75 ± 18 76 ± 6 78 ± 12
NO SAUNA
systolic 132 ± 15 163 ± 13a129 ± 10 129 ± 12
NO SAUNA
diastolic 74 ± 9 75 ± 18 76 ± 6 78 ± 12
pH
FIRS 7.41 ± 0.02 7.32 ± 0.06a7.42 ± 0.02 7.41 ± 0.02
NO SAUNA 7.41 ± 0.02 7.34 ± 0.02a7.40 ± 0.03 7.41 ± 0.02
Lactate (mmol/l)
FIRS 1.8 ± 0.9 13.2 ± 1.7a4.4 ± 1.6 2.4 ± 0.9
NO SAUNA 2.6 ± 1.7 12.1 ± 1.9a3.8 ± 0.8 2.5 ± 0.7
Testosterone (nmol/l)
FIRS 18.1 ± 5.2 22.7 ± 6.5b20.3 ± 5.4 20.1 ± 5.9
NO SAUNA 18.5 ± 7.5 22.3 ± 6.4b20.5 ± 7.5 19.8 ± 7.4
Cortisol (nmol/l)
FIRS 471 ± 162 449 ± 159 435 ± 213 368 ± 242b
NO SAUNA 467 ± 197 441 ± 216 401 ± 219 320 ± 189b
Growth hormone (µg/l)
FIRS 0.2 ± .0.2 43.3 ± 36.6a16.6 ± 12.2b6.5 ± 7.0
NO SAUNA 1.3 ± 3.5 40.5 ± 41.9a13.5 ± 17.3b6.6 ± 8.8
Body mass (kg)
FIRS 81.1 ± 6.3 80.8 ± 6.2 80.7 ± 6.2c80.6 ± 6.2c
NO SAUNA 80.9 ± 6.6 80.6 ± 6.6 80.5 ± 6.6 80.5 ± 6.6
CMJ (m)
FIRS 0.37 ± 0.05 0.33 ± 0.05a0.34 ± 0.05a
NO SAUNA 0.37 ± 0.06 0.33 ± 0.07a0.33 ± 0.08a
Table 3 Measured variables in ETS and FIRS bathing
30min or inETS andsitting ina normal room (NO SAUNA)
30min andin bothcases during recovery sitting another
30min (mean±SD)
a Signicantly (p<0.001) dierent from before value.
b Signicantly (p<0.05) dierent from before value.
c Subjects drank 0.5dl water in sauna which is included in body mass.
d Signicantly (p<0.05) dierent from NO SAUNA value.
Variable Before ETS After ETS Recovery
30min Recovery
60min
VO2 (ml/kg/min)
FIRS 5.7 ± 0.9 62.7 ± 4.2a5.3 ± 0.8 4.9 ± 0.6
NO SAUNA 5.7 ± 0.7 62.9 ± 3.5a5.4 ± 0.9 5.0 ± 0.6
Heart rate (beats/min)
FIRS 75 ± 9 201 ± 11a99 ± 9 80 ± 11
NO SAUNA 75 ± 10 200 ± 10a93 ± 11 79 ± 14
Blood pressure (mm Hg)
FIRS systolic 139 ± 12 168 ± 20b114 ± 11 121 ± 8
FIRS diastolic 80 ± 10 80 ± 12 73 ± 10 72 ± 6
NO SAUNA
systolic 138 ± 12 182 ± 17b125 ± 12 126 ± 8
NO SAUNA
diastolic 78 ± 10 86 ± 17 74 ± 10 75 ± 6
pH
FIRS 7.40 ± 0.0 7.30 ± 0.04a7.40 ± 0.02 7.40 ± 0.02
NO SAUNA 7.41 ± 0.02 7.29 ± 0.04a7.40 ± 0.03 7.41 ± 0.02
Lactate (mmol/l)
FIRS 2.0 ± 1.0 12.0 ± 2.7a4.4 ± 2.3 2.1 ± 0.4
NO SAUNA 1.8 ± 0.6 12.9 ± 4.1a4.4 ± 2.1 2.3 ± 0.8
Testosterone (nmol/l)
FIRS 18.8 ± 3.9 23.6 ± 5.1 20.6 ± 5.1 20.4 ± 5.5
NO SAUNA 18.5 ± 4.4 23.5 ± 6.4 19.5 ± 6.7 18.0 ± 4.7
Cortisol (nmol/l)
FIRS 531 ± 151 640 ± 132 601 ± 121 491 ± 132
NO SAUNA 519 ± 117 639 ± 112 616 ± 196 609 ± 211
Growth hormone (µg/l)
FIRS 2.2 ± .0.9 65.5 ± 41.6a26.6 ± 11.2b7.5 ± 8.0
NO SAUNA 1.5 ± 3.8 57.5 ± 39.9a23.5 ± 16.3b7.6 ± 8.8
Body mass (kg)
FIRS 79.8 ± 7.6 79.4 ± 7.4 78.9 ± 7.4c78.9 ± 7.4c
NO SAUNA 79.6 ± 7.6 79.1 ± 7.5 78.9 ± 7.5 78.9 ± 7.4
CMJ (m)
FIRS 0.37 ± 0.08 0.32 ± 0.10 0.34 ± 0.09d
NO SAUNA 0.37 ± 0.08 0.32 ± 0.09 0.32 ± 0.08
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CMJ after FIRS bathing was significantly (p < 0.05)
higher (0.34± 0.09m) than after sitting with no sauna
(0.32±0.0m).
Discussion
Main ndings
e main results showed that maximal isometric bench
press, maximal isometric leg press and CMJ decreased
strongly after STS as expected, but during recovery
there were no differences in any variables between FIRS
and NO SAUNA bathing. Maximal ETS increased heart
rate, blood lactate concentration and decreased pH as
expected. During recovery from ETS at 30min CMJ was
significantly higher after FIRS bathing than after sitting
with NO SAUNA bathing. Without training sessions,
heart rate was higher after TRAD sauna than after FIRS
bathing.
FIRS, STS andETS
Maximal isometric strength both in legs and arms and
CMJ decreased strongly after the hypertrophic type STS
as expected and were not recovered after 30min either
in FIRS or in NO SAUNA condition. Also, as expected,
there were large increases in heart rate, blood pressure,
acidity, lactate, testosterone and growth hormone con-
centrations immediately after STS. All these variables
were recovered at 30min after STS except growth hor-
mone, which recovered after 1h. It was surprising to see
a non-significant decrease in the cortisol concentration
immediately after STS and at 30 min during recovery.
One hour after STS the decrease was already strong. As
discussed earlier, the circadian rhythm tends to strongly
decrease cortisol in the morning, whereas a resistance
training stimulus tends to increase an acute cortisol con-
centration (e.g. Kraemer and Ratamess 2005). Obviously,
the overall stress of STS was not sufficient to increase
the concentration in the morning. Overall, during recov-
ery after STS there were no differences in any variables
between FIRS and NO SAUNA bathing. e only trend
difference (p=0.11) between FIRS and NO SAUNA con-
ditions was observed in CMJ, where performance was
slightly better at 30min recovery in FIRS bathing.
Oxygen uptake increased, probably to its maximum,
at the end of the 34–40min ETS. is is supported by
the high heart rate values. Also, blood pressure, acidity,
and lactate increased strongly at the end of ETS. All those
variables recovered during 30min and there were no dif-
ferences between FIRS and NO SAUNA bathing. ere
were increases in the concentrations of all three hor-
mones, but only statistically significant in growth hor-
mone. GH concentration recovered slowly and returned
to baseline 1h after ETS. e profile of cortisol was dif-
ferent from STS, because it increased at the end of ETS,
although the increase was not significant. Consequently,
it seems that ETS was metabolically slightly more stress-
ful than STS, especially when heart rate was 200beats/
min. Recovery of the legs from ETS was better with FIRS
bathing, because CMJ was clearly better compared to NO
SAUNA condition after 30min. e reason for greater
recovery in jumping ability may be infrared heat during
30min penetrating deeply (approx. 3–4cm) into fat tis-
sue and the neuromuscular system (Beever 2009) com-
pared to the air at room temperature 21°C and humidity
25–30% in NO SAUNA condition. Consequently, the
heated force production and relaxation of the leg muscles
were better. is result is partly confirmed with the result
in the STS condition, although it was only a trend.
FIRS andTRAD sauna bathing
In TRAD saunas there are either wood stoves or
220-V heaters (used in the present study) to heat air to
70–100°C, which then heats the bather mainly via con-
vection. e air has a relative humidity of 10–20% (Lep-
päluoto 1988; Kauppinen 1997). It is typical of a Finnish
sauna to have dry air and a high temperature (Karjanoja
et al. 1997). However, many bathers in Finland throw
water on the hot rocks of the sauna heater. Consequently,
humidity increases strongly even up to 80%. FIRSs heat
air to 50–60°C providing a more comfortable and relax-
ing experience (Beever 2009). As infrared heat penetrates
more deeply into fat and the neuromuscular system than
warmed air, bathers develop a more vigorous sweat at
a lower temperature than they would in TRAD saunas
(Beever 2009). In the present study, we wanted to com-
pare FIRS bathing to TRAD sauna bathing in a control
condition using the same temperature of 35–50°C, but
in TRAD sauna the relative humidity was increased
to 60–70% (compared to 25–35% in FIRS) by throw-
ing water on the hot rocks of the sauna heater. is was
done, because most of the Finnish athletes and recrea-
tional people use this type of TRAD sauna bathing dur-
ing recovery from intensive exercise.
Heart rate was 92beats/min immediately after TRAD
sauna bathing, which was higher than after FIRS sauna
bathing (71beats/min). e mean value of all three meas-
urement points during recovery was 16% higher after
TRAD sauna bathing. e main reason for the results
is the large difference in relative humidity. ere were
no differences in other measured variables between the
two experiments. e concentration of testosterone was
unchanged after both saunas, which confirms earlier
studies (Leppäluoto etal. 1986; Kukkonen-Harjula etal.
1989). It is interesting to observe decreases in cortisol
concentrations during recovery from these two light
“aerobic” sauna conditions, which may partly be due to
the early morning time between 09–12 AM. It is known
Page 7 of 7
Meroet al. SpringerPlus (2015) 4:321
that normally, the highest cortisol secretion occurs in
the second half of the night with peak cortisol produc-
tion occurring in the early morning. Following this, cor-
tisol concentration declines throughout the day with the
lowest concentrations late in the evening (e.g. Tsigos and
Chrousos 2002). Results in earlier studies investigat-
ing sauna bathing and cortisol are somewhat conflict-
ing (Hannuksela and Ellahham 2001). Growth hormone
concentration increased significantly also in both sauna
conditions, which confirms earlier studies (Kukkonen-
Harjula etal. 1989; Hannuksela and Ellahham 2001; Pich
etal. 2003). Finally, the results with FIRS bathing show
that it is a very light loading for the body and provides a
comfortable and relaxing experience.
Conclusion
In conclusion, deep penetration of infrared heat (approxi-
mately 3–4cm into fat tissue and neuromuscular system)
under mild temperature (35–50°C), and light humidity
(25–35%) conditions during FIRS bathing are favorable
for the neuromuscular system to recover from maximal
endurance performance. In practice, FIRS bathing may
be used among other recovery methods in athletes and
also in other physically active people. FIRS bathing is a
very light loading for the body compared to TRAD and
provides a comfortable and relaxing experience.
Abbreviations
FIRS: far-infrared sauna; STS: strength training session; ETS: endurance training
session; TRAD: traditional; CMJ: counter movement jump; BW: body weight;
BP: blood pressure; BS: blood sample; VO2: oxygen uptake; HR: heart rate; IST:
isometric strength test.
Authors’ contribution
AAM (corresponding author) was responsible for the study design, the
execution of the measurements, the statistical analysis and the draft of the
manuscript. JT and MM participated in the study design, execution of the
measurements, the statistical analysis and the draft of the manuscript. RP
participated in the study design, analysis of blood variables and in the drafting
of the manuscript. All authors read and approved the final manuscript.
Acknowledgements
This project was partly funded by Harvia Ltd, Muurame, Finland and the
Department of Biology of Physical Activity, University of Jyväskylä, Finland. The
authors would like to thank the subjects and research assistants.
Compliance with ethical guidelines
Competing interests
The authors declare that they have no competing interests.
Consent for publication
They signed informed consent and the study was approved by the local
University Ethical Committee.
Received: 9 January 2015 Accepted: 9 June 2015
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... In the present study, the deterioration of CMJ performance during recovery was attenuated by IRS compared to PAS. IRS during recovery has previously been found to improve CMJ performance after a single endurance training session, but not after a strength training session [3]. In that study, however, participants were not athletes and performed a hypertrophic strength training session [3]. ...
... IRS during recovery has previously been found to improve CMJ performance after a single endurance training session, but not after a strength training session [3]. In that study, however, participants were not athletes and performed a hypertrophic strength training session [3]. ...
... Because relatively little research has been conducted on IRS and recovery of physical performance, it may also be important to compare our findings with studies that have examined recovery after traditional sauna bathing. Traditional saunas heat the air to approximately 70-100°C, which then heats the occupant primarily by convection [2,3]. In other words, heat is transferred by the movement of the heated air to the occupant. ...
... The existing sauna literature has reported physiological responses from passive exposure to FIRS (Mero et al., 2015;Burgess et al., 2020;Kominami et al., 2020), as well as dry (Gayda et al., 2012;Zalewski et al., ...
... Future work should examine the duration of time necessary for complete ANS recovery from FIRS exposure following a maximal task, as well as a live-fire event, and this length of time should be taken into consideration when developing post-fire call protocols. 2014), Finnish (Sohar et al., 1976;Mero et al., 2015;Laukkanen et al., 2018), or unspecified (Bruce-Low et al., 2006Leicht et al., 2018) saunas. However, no studies have assessed the acute impact of FIRS on the ANS following a bout of maximal exercise in PPE, including an SCBA, to simulate FF work demands. ...
... An Extech IR200 Non-Contact Infrared Thermometer (Test Equipment Depot, Melrose, MA, USA) measured temperature (x̄ = 50.64 ± 2.20°C) at approximately shoulder height for each participant, which is consistent with the environmental conditions of prior FIRS research (Mero et al., 2015;Burgess et al., 2020). Humidity was measured using a standard hygrometer and recorded when each participant entered the chamber (x̄ = 45.63 ± 7.54%). ...
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... Sauna use has been extensively studied, and there is scientific evidence to indicate that thermal stress induces similar hemodynamic and endocrinal changes to those evoked by physical exercise [1,5,6]. There are many indications for sauna therapy, and studies investigating the benefits of and contraindications to sauna bathing have been conducted in Finland since the late 1970s [7,8]. ...
... A review of the literature revealed that despite a relatively large number of papers describing the effects of thermal stress on the human body, the vast majority of studies have investigated sauna sessions lasting 30 min or less when the temperature exceeded 80 • C [6,18,[25][26][27][28]. There is a general scarcity of published data concerning the effects of repeated sauna use on the physiological profiles of healthy and physically active men who regularly use the sauna. ...
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... Shifts in core body temperature can impact microbiome function because of the sensitivity of the gut epithelium to temperature, and this may lead to dysbiosis in some athletes [10]. A variety of sauna bathing therapies are being applied in sport for exercise recovery, treatment of inflammation, improvement in cardiovascular stability, fluid balance, and thermal tolerance [11,12]. The impact of post-exercise sauna on the gut microbiome remains unknown. ...
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The effects of three weight reduction methods on maximal strength, rate of force development, vertical jumping height, and mechanical power were studied in track and field athletes and volleyball players. The three methods were sauna, diet with diuretic, and diuretic alone. The reductions in weight achieved were 3.4%, 5.8%, and 3.8% of body weight after sauna, diet + diuretic, and diuretic, respectively (P less than 0.001). Maximal isometric leg strength and the rate of isometric force development were decreased after the sauna and diet + diuretic treatments. Dehydration caused by the diuretic method alone did not impair neuromuscular performances. As had been expected from theoretical calculations, the rise of the body center of gravity in vertical jumping was slightly improved with all three treatments, the improvement being the greatest following the diuretic treatment (7.1%, P less than 0.001). However, when the work performed was extended for 15 s, an improved power output could be observed only with the diet + diuretic treatment (P less than 0.01). No explanation for the results observed could be made in terms of physiologic parameters.
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Ten healthy male volunteers were exposed to the dry heat of a Finnish sauna (+80 degrees C) for 1 h twice a day for a period of 7 days. After each exposure rectal temperature rose by 0.8-1.1 degrees C and body weight dropped by 0.7-0.9 kg. The systolic blood pressure recorded 3-5 min after the sauna did not change during the experiments but the diastolic blood pressure decreased by 7-37 mmHg (P less than 0.05). The pulse rate rose from 75-80 to 106-116 beats min-1 (P less than 0.05) after the sauna. The increased responses of pulse and temperature adapted to heat exposures so that they were significantly lower after the 3rd day (rectal temperature) or after 6th day (pulse). Metabolic rate increased by 25-33% (P less than 0.01) after the first day. Serum total proteins, Hb and Htc were significantly increased on the 1st and 3rd days but not later, although the dehydration in response to sauna was unchanged as judged from the weight losses. Serum K, Na and Fe were significantly decreased on the 3rd and 7th day indicating that special attention should be given to the electrolyte balance in long-lasting intense heat exposure. No ECG changes were found in recordings taken on the 7th day.
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In summary, sauna baths are well tolerated and pose no risk to healthy people from infancy to old age, including healthy women in their uncomplicated pregnancy. The normal sauna bath, with moderate cool-off phases, increases the cardiac work load about as much as a brisk walk. It has been well established that the sauna bath, no matter what the cool-off type, does not pose any circulatory risk to healthy people. Cardiovascular patients with essential hypertension, coronary heart disease or past myocardial infarction, who are stable and relatively asymptomatic in their everyday life may also take sauna baths without undue risk. As a rule of thumb, if a person can walk into a sauna, he or she can walk out of it. Misuse and abuse of the sauna are another matter.