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Comparison of the effects of whole-body cooling during fatiguing
exercise in males and females
q
Rima Solianik
⇑
, Albertas Skurvydas, Kazimieras Puke
˙nas, Marius Brazaitis
Institute of Sports Science and Innovations, Lithuanian Sports University, Sporto Str. 6, LT-44221 Kaunas, Lithuania
article info
Article history:
Received 4 March 2015
Accepted 29 April 2015
Available online 8 May 2015
Keywords:
Sex
Cold stress
Central fatigue
Peripheral fatigue
Electromyography
abstract
The effects of cold stress on exercise performance and fatigue have been thoroughly investigated only in
males, and thus the general understanding of these effects relates only to males. The aim of this study
was to determine whether whole-body cooling has different effects on performance during fatiguing
exercise in males and females. Thirty-two subjects (18 males and 14 females) were exposed to acute cold
stress by intermittent immersion in 14 °C water until their rectal temperature reached 35.5 °C or for a
maximum of 170 min. Thermal responses and motor performance were monitored before and after
whole-body cooling. Whole-body cooling decreased rectal, muscle and mean skin temperatures in all
subjects (p< 0.05), and these changes did not differ between males and females. Cold stress decreased
the fatigue index (FI) of a sustained 2-min maximal voluntary contraction (MVC) only in males
(p< 0.05). There were no sex differences in central and peripheral fatigability, or muscle electromyo-
graphic activity. This observed sex difference (i.e., body cooling-induced decrease in the FI of a sustained
MVC in males but not in females) supports the view of sex effects on performance during fatiguing exer-
cise after whole-body cooling.
Ó2015 Elsevier Inc. All rights reserved.
Introduction
Cold exposure occurs in some winter sports and occupational
and leisure-time activities, and may affect physical performance
[1,5,15,16,44]. The attenuation in physical performance because
of whole-body (i.e., peripheral and central) cooling leads to
improved endurance and a lower rate of fatigability [5,19,40],
decreased strength [1,5,15,16,44] and increased muscle contrac-
tion and relaxation times [1,5,16,44]. Whole-body exposure to cold
also affects characteristics of the electrophysiological activity of
muscles; e.g., increases in the amplitude and decreases in the fre-
quency components of muscle electromyography (EMG)[36,44,50].
It has been suggested that the brain is the primary site respon-
sible for modulation of central fatigue [3,29,47]. In a recent study,
we observed that the activity of the hypothalamic–pituitary–adre
nal axis, as reflected in an increased cortisol level, increased only
in males in response to whole-body cooling [45]. There is evidence
that glucocorticoids can partly influence central dopamine release
within the brain [24,35,37,41]. Thus, in contrast to the effects of
heat [23], the increased central dopaminergic activity during cold
exposure in males may increase their central motivation to per-
form exercise and may subsequently reduce fatigue during volun-
tary exercise [6,17,23,29]. Thus, we expected that males would
have less fatigue during voluntary exercise than females because
of the greater dopaminergic activity within the brain.
Although the effects of cold stress have been thoroughly inves-
tigated in males, sex differences in these effects have yet to be
described. Existing evidence seems to support the view that there
are sex-specific physiological responses to similar whole-body
cooling. These responses include greater stress hormone responses
[45,48] and deterioration of cognitive (memory and attention) and
motor performance (short-duration maximal voluntary contrac-
tion (MVC)) in males than in females [44]. However, it is not known
whether males and females respond differently to fatiguing exer-
cise after whole-body cooling. Given that most studies on endur-
ance performance after cooling have been performed in males
and the apparent sex differences in the response to cold stress, this
study aimed to determine whether whole-body cooling has
sex-specific effects on performance during fatiguing exercise
within normothermic limits (up to 35.5°[21]).
http://dx.doi.org/10.1016/j.cryobiol.2015.04.012
0011-2240/Ó2015 Elsevier Inc. All rights reserved.
q
Statement of funding: This research received no grant from any funding agency
in the public, commercial or not-for-profit sectors.
⇑
Corresponding author. Fax: +370 37 204 515.
E-mail address: rima.solianik@lsu.lt (R. Solianik).
Cryobiology 71 (2015) 112–118
Contents lists available at ScienceDirect
Cryobiology
journal homepage: www.elsevier.com/locate/ycryo
Methods
Participants
The criteria for inclusion were: (1) age 18–25 years; (2) no
excessive sport activities, i.e., <3 times per week; (3) no involve-
ment in any temperature-manipulation program or extreme tem-
perature exposure for P3 months; (4) no medications that could
affect natural thermoregulation; and (5) no neurological pathology
or other condition that could be worsened by exposure to cold
water. In total, 32 volunteers met the inclusion criteria and agreed
to participate in this study. Participants were grouped into the
males (n= 18) or females (n= 14) group. Their physical character-
istics are presented in Table 1. Written informed consent was
obtained from all subjects after explanation of all details of the
experimental procedures and the associated discomforts and risks.
All procedures were approved by the Human Research Ethics
Committee and were conducted according to the guidelines of
the Declaration of Helsinki. Subjects were in self-reported good
health, as confirmed by medical history and physical examination.
Experimental design
Familiarization trial
To attain a stable level of performance, 1 week before the exper-
imental trials, participants attended a familiarization session dur-
ing which they were introduced to the experimental procedures.
During familiarization trial, each subject learned to achieve and
maintain maximal-effort ankle plantar flexion for 3–4 s with a
250-ms stimulation train test at 100 Hz (TT-100 Hz) superimposed
on a MVC, and the tolerance to electrical stimulation was assessed.
Experimental trials
The experimental trials comprised of a control trial (CON) and a
passive body cooling (CL) trial. CON and CL experiments were per-
formed in random order, at least 1 week apart. The subjects
refrained from consuming any food for at least 12 h, alcohol, heavy
exercise and caffeine for at least 24 h before the experiment, and
instructed to sleep at least 8 h the night before experiment. To con-
trol for circadian fluctuations in body temperature, the experimen-
tal trials began at 7.00 am. Females were studied during the
follicular phase of the menstrual cycle. The experiments were per-
formed at 22 °C (room temperature) and 60% relative humidity.
CON experiment
On arrival at the laboratory, was performed anthropometric
measurement and the subject was asked to rest in a
semi-recumbent posture for 20 min dressed in a bathing suit.
After body temperatures stabilizations control measurements of
skin (T
SK
), muscle (T
MU
) and rectal temperatures (T
RE
) were made.
The subject was then seated in the dynamometer chair, stimulating
electrodes were placed over the posterior triceps surae muscle and
EMG electrode was placed over the soleus (SOL) muscle of the right
leg. The involuntary force-generating capacity (in Nm) of the pos-
terior calf muscle was assessed by 1-s trains of electrical stimuli at
20 (P20), TT-100 (PTT100) and 100 (P100) Hz. About 3 s was
needed to change the stimulation frequency. After 5 min-rest per-
iod a 2-min isometric MVC was then tested. The PTT100 stimulus
was superimposed on the contraction at about 3, 15, 30, 45, 60,
75, 90, 105, and 120 s. Then after 3 s was repeated pre-2 min
MVC involuntary force generating capacity assessment by 1-s
trains of electrical stimuli at P20, PTT100, P100.
CL experiment
Baseline measurements of body temperature were made as
described in the CON experiment. After the body temperature eval-
uation, the subject began the water immersion cooling protocol
which was used in previous studies [1,44,45]. During cooling, every
20 min, the subject was asked to step out of the bath and rest for
10 min in the room environment, and then to return to the water
bath for the next 20 min of immersion. Participants were
immersed semi-recumbent position up to level of manubrium at
14 °C water bath, which continued until the T
RE
decreased to
35.5 °C or until 170 min total (120 min maximum total immersion
time), at which time the immersion ended regardless of the T
RE
.
The exposure time until the T
RE
was achieved was recorded. T
RE
was recorded every 5 min throughout the cooling procedure.
Immediately after experimental cooling, the subject was towel
dried, the body temperatures were measured. After the end of
the cooling protocol, muscular function evaluation was performed
in the same order as described in the CON experiment.
Experimental measurements
Anthropometric measurements
The subject’s weight (in kg), body fat (in percent), fat free mass
(in kg) (TBF-300 body composition scale; Tanita, UK Ltd., West
Drayton, UK), and height (in cm) were estimated, and body mass
index (BMI, in kg/m
2
) was calculated during the CON experiment.
The subject’s body surface area (BSA,inm
2
) was estimated using
the following best-fit equations: BSA = 128.1 weight
0.44
height
0.60
for males and BSA = 147.4 weight
0.47
height
0.55
for
females [46]. Skinfold thickness (in mm) was measured using a
skinfold caliper (SH5020, Saehan, Masan, Korea) at 10 sites (chin,
subscapular, pectoral, suprailiac, midaxillary, abdomen, triceps,
anterior thigh, medial collateral ligament, and medial calf), and
the mean skinfold thickness was calculated [25].
Temperature recording
Body temperature values (in °C) were monitored throughout
the CON and CL experimental trials. T
RE
was monitored with a ther-
mocouple (Rectal Probe, Ellab, Hvidovre, Denmark) inserted to a
minimum of 12 cm past the anal sphincter. Data for the T
RE
base-
line and the end point of cold stress were used for CL experiment
analysis. The T
MU
and T
SK
were measured before and at the end
of the cold stress procedure. The T
MU
was measured with a needle
microprobe (MKA, Ellab, Hvidovre, Denmark) inserted at a depth of
3 cm under the skin covering the gastrocnemius lateralis muscle in
the right leg. No local anesthesia was administered before needle
insertion. After the first measurement, the insertion area was
Table 1
Physical characteristics of the participants.
Males (n= 18) Females (n= 14)
Age, year 20.7 ± 1.0 21.4 ± 2.5
Height, cm 181.7 ± 6.0 170.6 ± 6.9
*
Mass, kg 78.0 ± 8.6 63.3 ± 9.9
*
Body mass index, kg/m
2
23.6 ± 2.5 21.7 ± 3.1
Fat free mass, kg 66.1 ± 5.7 45.7 ± 3.9
*
Body fat, % 14.9 ± 3.4 27.1 ± 5.9
*
Mean subcutaneous fat, mm 11.0 ± 3.7 16.7 ± 4.9
*
Body surface area, m
2
1.97 ± 0.12 1.75 ± 0.15
*
Data are presented as mean ± standard deviation.
*
p< 0.05, compared with males.
R. Solianik et al. / Cryobiology 71 (2015) 112–118 113
marked with a sterile skin marker to ensure repeatability of needle
insertion in CON and CL experimental trials. Back, thigh, and fore-
arm skin temperatures were monitored by surface thermistors
(DM852, Ellab, Hvidovre, Denmark). The mean T
SK
was calculated
by the Burton [4] equation as: T
SK
= 0.5
Back
+ 0.36
Thigh
+ 0.14
Forearm
.
Further, were calculated percentage body temperature values
changes.
Cold strain index calculation
The cold strain index (CSI) is capable of indicating cold stress. It
wascalculatedasfollows[27]:CSI = 6.67(T
REt
–T
RE0
)(35 – T
RE0
)
–1
+
3.33(T
SKt
–T
SK0
)(14 – T
SK0
)
–1
, where T
RE0
and T
SK0
are baseline,
whereas T
Ret
and T
SKt
are final rectal and skin measurements,
respectively; 14 water temperature; 35 T
RE
threshold. T
RE
and
T
SK
were assigned a weighting using the constants 6.67 and 3.33,
respectively. This index rated cold strain on a universal scale of
0–10 as 1–2 (no/little strain), 3–4 (low strain), 5–6 (moderate
strain), 7–8 (high strain) and 9–10 (very high strain).
Force-generating capacity measurement
The voluntary and involuntary torque of ankle plantar flexion
muscles was measured using an isokinetic dynamometer (System
4; Biodex Medical Systems, Shirley, NY, USA) calibrated according
to the manufacturer’s service manual with a correction for gravity
performed using the Biodex Advantage program (version 4.X).
Subjects were seated in the dynamometer chair with the trunk
inclined at 45°with respect to the vertical, and with hip, knee
and ankle joint angulations of, respectively, 90°, 100°(full knee
extension = 180°) and 90°. For 2-min MVC endurance assessment
measurement, the subject was instructed to achieve and maintain
maximal effort of ankle plantar flexion for 120 s. Each trace was
inspected visually to ensure that there were no artefactual spikes
at the start of the signal curve. The arms were crossed on the chest
with the hands grasping the trunk-supporting belt during all tests
on the dynamometer. To help ensure a maximal effort, standard
vocal encouragement was provided during each voluntary ankle
plantar flexion trial by the same experienced investigator.
The subject positioning during electrical stimulator assessment
were essentially the same as those described above. Muscle stim-
ulation was applied using flexible surface electrodes (MARP
Electronic, Krakow, Poland), covered with a thin layer of electrode
gel (ECG–EEG Gel; Medigel, Modi’in, Israel), with one electrode
(8 12 cm) placed transversely across the width of the proximal
portion of the posterior calf just below the popliteal fossa, and
the other electrode (8 8 cm) covered the distal portion of the
muscle just below the muscle fibres of the gastrocnemius. A con-
stant current electrical stimulator (MG 440; Medicor, Budapest,
Hungary) was used to deliver 0.5-ms square-wave pulses at
150 V. Peak torques (in Nm; measured from the baseline to the
peak torque) induced by a 1-s electrical stimulation at P20 (repre-
senting the steep section of the force–frequency relationship
curve) and at P100 (which is close to maximal force) were mea-
sured with a 3-s rest interval between electrical stimulations.
Further fatigability index (FI, in percent) for voluntary and involun-
tary torques were calculated (FI = ((value before or 3 s of 2 min
MVC–value after or 120 s of 2-min MVC)/value before or 3 s of
2-min MVC)100 for involuntary and voluntary torques, respec-
tively). The peak amplitude, contraction time (CT; in ms; the time
interval from the beginning of a twitch to the peak torque) and
half-relaxation time (HRT; in ms; the time from the peak to
half-maximum torque) were measured in resting PTT100 contrac-
tions, and percentage CT +HRT change after 2-min MVC was calcu-
lated. Moreover, at approximately 3, 15, 30, 45, 60, 75, 90, 105 and
120 s of 2-min MVC,aPTT100 stimuli was superimposed on the
voluntary contraction. These PTT100 contractions were used to
assess the central activation ratio (CAR) of the posterior surae mus-
cle. The CAR was calculated using the following equation:
CAR =MVC/(MVC +PTT100), where a CAR of 1 indicates complete
activation, whereas a CAR of less than 1 indicates central activation
failure or inhibition. Furthermore, was calculated percentage CAR
decrement level at the end of 2-min MVC.
Muscles activity-generating capacity
The subject positioning was essentially the same as those
described above (see ‘‘Force-generating capacity measurement’’).
After careful preparation of the skin (shaving, abrading, and clean-
ing with alcohol wipes) to obtain low impedance, bipolar Ag–AgCl
surface bar electrode (10 mm diameter, 20 mm centre-to-centre
distance) (DataLog type no. P3X8 USB, Biometrics Ltd, Gwent,
UK) were used for EMG recording. For the SOL, the electrode was
placed at 2/3 of the line between the medial condylis of the femur
to the medial malleolus. The actual electrode position was marked
with a waterproof pen, therefore, the same recording site was used
in the CON and CL experiments. The ground electrode was posi-
tioned on the tarsus of the same leg. EMG signals were recorded
by amplifiers (gain 1000), sampled at 5 kHz, bandpass filtered
(passband 20–460 Hz), notch-filtered at 50 Hz using a
Butterworth filter, and demeaned. The EMG signal was telemetered
to a receiver that contained a differential amplifier with an input
impedance of 10 M
X
, the input noise level was less than 5
l
V,
and the common mode rejection ratio was higher than 96 dB.
Before recording the EMG, we set the channel sensitivity at 3 V
and excitation output at 4600 mV as recommended by the manu-
facturer. EMG files were stored simultaneously on the biometrics
memory card and PC hardware, and dedicated software
(Biometrics DataLOG, Gwent, UK) was used for data processing
and analysis. The EMG signals such as the root mean square
(RMS, in mV) and mean frequency (MnF, in Hz) were extracted
from a 1000-ms epoch coinciding with 1-s force interval just
before each PTT100 superimposed on a MVC.
Statistical analysis
To compare differences between males and females, ttests for
independent samples were used for data with a normal distribu-
tion (height, weight, BMI, fat free mass, body fatness, skinfold
thickness and BSA). The Mann–Whitney Utest was used for age,
which was not normally distributed. Repeated-measures analysis
of variance (ANOVA) was used to analyse the changes in tempera-
ture and muscle function variables including the percentage
change in the CAR and CT + HRT, and FI for voluntary and involun-
tary torques. The means were compared between males and
females using a univariate ANOVA. Two-way repeated-measures
ANOVA with two within-subject factors was used to analyse the
effects of temperature (CON vs COLD) and time during the 2-min
MVC (at 3, 15, 30, 45, 60, 75, 90, 105 and 120 s) on all variables with
sex as a between-group factor. The data are reported as
mean ± standard deviation. The level of significance was set at
p< 0.05. If a significant effect was found, the statistical power
(SP, in percent) was estimated. All statistical analysis was per-
formed using SPSS v.21.0 (IBM Corp., Armonk, NY, USA).
Results
Physical characteristics
The baseline characteristics of the subjects are described in
Table 1. Sex differences were found in all subject characteristics
114 R. Solianik et al. / Cryobiology 71 (2015) 112–118
except for age and BMI. Height, weight, fat free mass, and BSA were
higher in males (p< 0.05), whereas the body fatness, and mean
skinfold thickness were lower in males (p< 0.05).
Effect of cold stress on thermal responses
Table 2 summarizes the body temperatures and CSI for the
males and females in the CON and CL experiments. Body tempera-
ture did not differ between the CON and baseline CL measure-
ments. In the CL experiment, passive cooling time did not differ
between males and females (136.6 ± 45.7 min for males and
142.7 ± 40.7 min for females). T
RE
,T
MU
and T
SK
decreased
(p< 0.05, SP > 99%) after cold exposure in males and females, but
body temperature variables and the CSI did not differ between
males and females.
Effect of cold stress on muscle properties during voluntary muscle
contraction
Fig. 1 presents the MVC and CAR values during the 2-min MVC in
males and females before and after body cooling. No significant
interaction was observed between condition and sex for the
2-min MVC and CAR. Temperature had no effect on the 2-min
MVC, whereas CAR was significantly greater after cold exposure
in males and females (p< 0.05, SP > 99%) (Fig. 1B). Body cooling sig-
nificantly decreased the FI of MVC in males (p< 0.05, SP > 60%)
(Fig. 1A) but did not affect the percentage change in CAR in males
or in females. As shown in Fig. 1, the MVC and CAR decreased sig-
nificantly during the exercise time (2-min MVC)(p< 0.05, SP > 99%)
in the CON and CL trials. Not surprisingly, the 2-min MVC torque
values were greater in males than in females (p< 0.05, SP > 65%)
(Fig. 1A), but the 2-min CAR values did not differ between males
and females. The FI of MVC was significantly lower in females than
in males in the CON trial (p< 0.05, SP > 90%) (Fig. 1A) but did not
differ in the CL trial.
Effect of cold stress on electrically evoked muscle properties
Table 3 presents the FI of electrically evoked skeletal muscle
torques in males and females. Body cooling significantly decreased
the FI of P20 (p< 0.05, SP > 99%) but had no effect on the FI of P100
in males and females. There were no significant differences in the
FI of P20 and P100 before and after cooling between males and
females.
As shown in Fig. 2, the percentage 2-min sustained isometric
exercise induced an increase in muscle CT +HRT was significantly
higher in the CON trial compared with the CL trial (p< 0.05,
SP > 99% for males and SP > 60% for females). There were no signif-
icant differences in the percentage change in CT +HRT of PTT100
before and after cooling between males and females.
Effect of cold stress on skeletal muscle EMG
Fig. 3 presents the skeletal muscle EMG amplitudes and fre-
quencies in males and females before and after body cooling. No
significant interaction was observed between condition and sex
for the SOL RMS and MnF. Body cooling significantly increased
the 2-min SOL RMS (p< 0.05, SP > 99%) (Fig. 3A) and decreased
the SOL MnF (p< 0.05, SP > 99%) (Fig. 3B). As shown in Fig. 3, the
SOL RMS and MnF decreased significantly (p< 0.05, SP > 99%) over
the exercise time in both the CON and CL trials in males and
females. The SOL RMS was greater in males subjects than in females
(p< 0.05, SP > 99%), whereas the SOL MnF values did not differ
between males and females.
Discussion
The main aim of this study was to determine whether
whole-body cooling induces any sex-specific differences in the per-
formance of fatiguing exercise, specifically the sustained isometric
2-min MVC. Although we observed a decrease in cold-induced vol-
untary fatigability (i.e., the FI of MVC) only in males, there were no
differences between males and females in body temperature, cen-
tral and peripheral fatigability, and electrophysiological changes of
the soleus muscle. To our knowledge, this is the first study to
examine sex-specific differences in ankle plantar flexion perfor-
mance after moderate whole-body immersion-induced cold strain.
In contrast to our expectations, we did not observe any differ-
ence in central fatigue level (i.e., CAR) between males and females
after whole-body cooling. Changed dopaminergic activity may
affect central motivation to perform sustained isometric exercise
and should alter centrally mediated components of fatigue
[6,12,17,23]. In accordance with previous studies [2,5],we
observed an increase in CAR after cold exposure, which may have
occurred partly via increased neural drive at the supraspinal level
[12,13]. As reported in previous investigations central fatigue
increased during sustained exercise, as shown by the decrease in
CAR [39,43]. Reductions in motor cortex excitability and central
drive are observed during sustained exercise [39]. By contrast,
whole-body cooling increases neural drive at the spinal and
supraspinal levels in both males and females [1,44]. Therefore, cold
exposure may cause a similar increase in CAR in males and females.
We found no significant differences in the peripheral fatigue
level, as measured by the electrically induced properties of skeletal
muscles, between males and females. This is consistent with the
similar decreases in body temperature in males and females. As
previously observed, characteristics of evoked contractions of
skeletal muscle are unaffected until cooling is quite severe
(T
MU
<27°C) [9]. Although our subjects’ T
MU
reached 30.6 °C, we
found that whole-body cooling induced a significant decrease in
the FI of P20 and percentage CT +HRT in both males and females.
Results showed that cooling increased the low-frequency fatigue
resistance, as measured by the FI of P20. Westerblad et al. [49]
reported that a decrease in the release of calcium from the
Table 2
Cold strain index and body temperatures in the control experiment and in the before and after cooling experiments.
Males Females
CON Before CL After CL Change, % CON Before CL After CL Change, %
T
RE
,°C 37.0 ± 0.3 37.0 ± 0.2 36.0 ± 0.5
§
2.7 ± 1.4 36.9 ± 0.3 36.9 ± 0.1 36.0 ± 0.6
§
2.5 ± 1.5
T
SK
,°C 32.1 ± 1.0 32.4 ± 1.0 18.8 ± 1.2
§
41.7 ± 4.1 31.8 ± 1.1 32.2 ± 0.5 20.0 ± 2.9
§
37.8 ± 9.0
T
MU
,°C 36.3 ± 0.3 36.3 ± 0.4 30.6 ± 2.5
§
15.6 ± 6.9 36.0 ± 0.6 36.0 ± 0.6 30.6 ± 2.3
§
15.0 ± 6.4
CSI 5.8 ± 1.6 5.4 ± 2.0
Data are presented as mean ± standard deviation. CON, control; CL, cooling; T
RE
, rectal temperature; T
SK
, skin temperature, T
MU
, muscle temperature; CSI, cold strain index.
§
p< 0.05, significant difference from the values before cooling.
R. Solianik et al. / Cryobiology 71 (2015) 112–118 115
sarcoplasmic reticulum is one of the mechanisms responsible for
the decrease in low-frequency fatigability. It has also been sug-
gested that calcium release from the sarcoplasmic reticulum decli-
nes more in fatigued muscles in normothermic conditions
(T
MU
=37°C) than in hypothermic conditions (T
MU
=22°C and
25 °C) [8,49]. The slowed CT +HRT in cooled muscles reflects the
temperature dependency of one of the underlying processes such
as a decreased rate of calcium release and/or slowing of the net
cross-bridge attachment rate, calcium removal from the myo-
plasm, calcium dissociation from troponin, and cross-bridge
detachment rate [8].
In contrast to our expectations, we did not observe any
sex-specific differences in MVC during fatiguing exercise after
whole-body cooling. In agreement with our previous study [2] cold
exposure had no effect on MVC. We suggest that the higher CAR
might have blunted the possible cold-induced decrease in MVC.
As shown in previous studies [5,8,10] cold seems to have advan-
tage on fatigability rate. Interestingly, the FI of MVC decreased after
cold exposure only in males. There was no difference in the per-
centage change in CAR between males and females, which could
suggest if there is any sex-specific differences at the spinal and
supraspinal levels [39]. Another explanation involves the increases
in peripheral stress hormone levels. Males have a greater glycolytic
capacity and a greater reliance on glycolytic pathways than
females [18,42]. During cold stress, epinephrine and cortisol mobi-
lize glucose, thereby increasing its availability for muscle metabo-
lism [32], which may decrease the fatigability rate [18].Ina
previous study, Solianik et al. [45] observed cold-induced increases
in cortisol and epinephrine levels in males but not in females.
These changes may have increased the amount of fuel available
in muscle and corresponded in a lower FI of MVC during fatiguing
exercise in males.
We found no sex differences in electrophysiological signals (i.e.,
RMS and MnF) of the soleus muscle after whole-body cooling. The
RMS values of the surface EMG are commonly used to assess the
muscle activation level imposed by the central nervous system
[20], which decreases after sustained isometric MVC [26]. After
cold exposure, the EMG activity can be increased by increased
reflex excitability [31]. In our previous study [44], we found a sim-
ilar whole-body cooling-induced increase in spinal and supraspinal
0
50
100
150
200
250
MVC (Nm)
CON-trial CL-trial
Males Females
*
¥ ¥ ¥
¥
¥ ¥
¥ ¥
¥
¥
¥ ¥ ¥ ¥ ¥ ¥
¥
¥
¥
¥ ¥ ¥
¥
¥
¥
¥
¥
¥
¥
¥ ¥ ¥
A
0.5
0.65
0.8
0.95
1.1
1.25
3 15 30 45 60 75 90 105120 3 15 30 45 60 75 90 105120
CAR
¥
¥
¥
¥
¥
¥ ¥
¥ ¥
¥ ¥ ¥ ¥ ¥ ¥ ¥
¥
Time (s) Time (s)
B
30
40
50
60
70
§
Fatigue index of MVC (%)
*
*
0
10
20
30
40
50
60
Males Females
Change of CAR (%)
§¥
§¥
§¥
§¥
¥
§¥
§¥
§¥
§¥
§¥
§¥
§¥
§¥
§¥
¥
§
Fig. 1. Effects of control (CON) and cooling (CL) trials on maximal voluntary contraction (MVC) and central activation ratio (CAR). Values are shown as mean ± standard
deviation.
⁄
p< 0.05, compared with males;
§
p< 0.05, compared with CON-trial;
¥
p< 0.05, compared with the beginning (3 s) of 2 min MVC.
Table 3
Fatigability indexes of electrically induced skeletal muscle properties before and after body cooling.
Males Females
Before After Change Before After Change
P20, % 25.3 ± 5.4 19.5 ± 10.1
§
40.6 ± 29.8 28.8 ± 8.7 21.0 ± 7.2
§
33.7 ± 19.3
P100, % 21.6 ± 7.5 26.4 ± 11.2 29.7 ± 74.1 21.8 ± 8.9 19.9 ± 7.3 5.7 ± 50.6
Data are presented as mean ± standard deviation. P20 and P100, 20 Hz and 100 Hz electrical stimulus, respectively.
§
p< 0.05, compared with before cooling.
0
10
20
30
40
50
60
70
80
90
CON-trial CL-trial Change
CT+HRT (%)
Males Females
§
§
Fig. 2. Sustained isometric exercise induced alteration of muscle contraction and
half relaxation times (CT +HRT) in the control (CON) and cooling (CL) trials. Values
are shown as mean ± standard deviation.
§
p< 0.05, compared with CON-trial.
116 R. Solianik et al. / Cryobiology 71 (2015) 112–118
excitability in males and females, which might have led to a similar
increment in the EMG amplitude in both males and females.
Previous studies have shown that cold decreases nerve [28,38]
and motor unit (MU) action potential [14,33,34] conduction veloc-
ities and that these decreases increase the temporal summation of
action potentials of MUs resulting in an increased EMG amplitude
[14,30,34].
The frequency content of EMG provides information about the
firing frequency of MUs during exercise [7], which decreases after
sustained isometric MVC [11,39]. It has been hypothesized that the
decline in MU firing rate maintains force by protecting against con-
duction failure and by optimizing the input to MUs as their con-
tractile properties change [11]. The mechanism responsible for
the decrease in MU firing frequency after fatiguing exercise local-
izes to the spinal and supraspinal levels [39]. As shown in our
recent studies [1,44], whole-body cooling increases the latency
time at the supraspinal and spinal levels. The decrease in
cold-induced muscle EMG MnF is linked to a simultaneous decrease
in the conduction velocities of MU action potentials [14,22,33,34],
action potentials across sarcolemma [14,33,34] and nerve [28,38].
A previous study showed that whole-body cooling increased the
latency time at the supraspinal, spinal and sarcolemma levels to
a similar extent in both sexes [44], which is consistent with the
similar cold-induced decrement in the EMG MnF in males and
females.
Conclusions
Whole-body cooling-induced stress had a similar effect on cen-
tral and peripheral fatigability, and on the responses of electro-
physiological signals in males and females. Although cold stress
decreased the rate of fatigue during sustained MVC only in males,
the mechanism remains obscure and further research is needed.
This is the first study to find evidence supporting the idea of
sex-specific effects on performance during fatiguing exercise after
whole-body cooling.
References
[1] M. Brazaitis, N. Eimantas, L. Daniuseviciute, D. Mickeviciene, R. Steponaviciute,
A. Skurvydas, Two strategies for response to 14 °C cold-water immersion: is
there a difference in the response of motor, cognitive, immune and stress
markers?, PLoS One 9 (2014) e109020
[2] M. Brazaitis, A. Skurvydas, K. Puke
˙nas, L. Daniusevici
ute
˙, D. Mickeviciene
˙,R.
Solianik, The effect of temperature on amount and structure of motor
variability during 2-minute maximum voluntary contraction, Muscle Nerve
46 (2012) 799–809.
[3] K. Bruck, H. Olschewski, Body temperature related factors diminishing the
drive to exercise, Can. J. Physiol. Pharmacol. 65 (1987) 1274–1280.
[4] A.C. Burton, Human calorimetry: the average temperature of the tissues of the
body, J. Nutr. 9 (1935) 261–280.
[5] F. Cahill, J.M. Kalmar, T. Pretorius, P.F. Gardiner, G.G. Giesbrecht, Whole-body
hypothermia has central and peripheral influences on elbow flexor
performance, Exp. Physiol. 96 (2011) 528–538.
[6] J.M. Davis, S.P. Bailey, Possible mechanisms of central nervous system fatigue
during exercise, Med. Sci. Sports Exerc. 29 (1997) 45–57.
[7] C.J. De Luca, The use of surface electromyography in biomechanics, J. App.
Biomech. 13 (1997) 135–163.
[8] C.J. de Ruiter, D.A. Jones, A.J. Sargeant, A. de Haan, Temperature effect
on the rates of isometric force development and relaxation in the fresh
and fatigued human adductor pollicis muscle, Exp. Physiol. 84 (1999)
1137–1150.
[9] E. Drinkwater, Effects of peripheral cooling on characteristics of local muscle,
Med. Sport Sci. 53 (2008) 74–88.
[10] E.J. Drinkwater, D.G. Behm, Effects of 22 degrees C muscle temperature on
voluntary and evoked muscle properties during and after high-intensity
exercise, Appl. Physiol. Nutr. Metab. 32 (2007) 1043–1051.
[11] A.J. Fuglevand, D.A. Keen, Re-evaluation of muscle wisdom in the human
adductor pollicis using physiological rates of stimulation, J. Physiol. 549 (2003)
865–875.
[12] S.C. Gandevia, Neural control in human muscle fatigue: changes in muscle
afferents, motoneurones and motor cortical drive [corrected], Acta Physiol.
Scand. 162 (1998) 275–283.
[13] S.C. Gandevia, Spinal and supraspinal factors in human muscle fatigue, Physiol.
Rev. 81 (2001) 1725–1789.
[14] L.M. Garcia, A.B. Soares, C. Simieli, A.V. Boratino, R.R. Guirro, On the effect of
thermal agents in the response of the brachial biceps at different contraction
levels, J. Electromyogr. Kinesiol. 24 (2014) 881–887.
[15] G.G. Giesbrecht, G.K. Bristow, Decrement in manual arm performance
during whole body cooling, Aviat. Space Environ. Med. 63 (1992) 1077–
1081.
[16] G.G. Giesbrecht, M.P. Wu, M.D. White, C.E. Johnston, G.K. Bristow, Isolated
effects of peripheral arm and central body cooling on arm performance, Aviat.
Space Environ. Med. 66 (1995) 968–975.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
SOL RMS (mV)
CON-trial CL-trial
Males Females
*
¥
¥
¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥
¥
¥
¥
¥ ¥
A
0
40
80
120
160
200
3 15 30 45 60 75 90 105 3 15 30 45 60 75 90 105 120
SOL MnF (Hz)
¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥
¥ ¥
B
Time (s)
Time (s)
120
§
¥
§¥
§¥
§¥
§¥
§
¥
§
¥
§¥
§¥
§¥
§¥
§¥
§¥
§¥
§¥
§
¥
§¥
§¥
§¥
§¥
§¥
§¥
§¥
§
¥
§
¥
§
¥
§
§
§
§
¥
§¥
§¥
§¥
§¥
§¥
§
Fig. 3. Effects of control (CON) and cooling (CL) experiments on the soleus muscle (SOL) mean frequency (MnF) and root mean square (RMS). Values are shown as
mean ± standard deviation.
⁄
p< 0.05, compared with males;
§
p< 0.05, compared with CON-trial;
¥
p< 0.05, compared with the beginning (3 s) of 2 min MVC.
R. Solianik et al. / Cryobiology 71 (2015) 112–118 117
[17] M.P. Hadjicharalambous, L.P. Kilduff, Y.P. Pitsiladis, Brain serotonergic and
dopaminergic modulators, perceptual responses and endurance exercise
performance following caffeine co-ingested with a high fat meal in trained
humans, J. Int. Soc. Sports Nutr. 7 (2010) 22.
[18] A.L. Hicks, J. Kent-Braun, D.S. Ditor, Sex differences in human skeletal muscle
fatigue, Exerc. Sport Sci. Rev. 29 (2001) 109–112.
[19] P.R. Jones, C. Barton, D. Morrissey, N. Maffulli, S. Hemmings, Pre-cooling for
endurance exercise performance in the heat: a systematic review, BMC Med.
10 (2012) 166.
[20] L.A. Kallenberg, H.J. Hermens, Behaviour of motor unit action potential rate,
estimated from surface EMG, as a measure of muscle activation level, J.
Neuroeng. Rehabil. 3 (2006) 15.
[21] S. Kushimoto, S. Yamanouchi, T. Endo, T. Sato, R. Nomura, M. Fujita, D. Kudo, T.
Omura, N. Miyagawa, T. Sato, Body temperature abnormalities in non-
neurological critically ill patients: a review of the literature, J. Intensive Care
2 (2014) 14.
[22] L. Lindstrom, R. Magnusson, I. Petersén, Muscular fatigue and action potential
conduction velocity changes studied with frequency analysis of EMG signals,
Electromyography 10 (1970) 341–356.
[23] D. Low, D.A. Purvis, T. Reilly, N.T. Cable, The prolactin responses to active and
passive heating in man, Exp. Physiol. 90 (2005) 909–917.
[24] M. Marinelli, P.V. Piazza, Interaction between glucocorticoid hormones, stress
and psychostimulant drugs, Eur. J. Neurosci. 16 (2002) 387–394.
[25] W.D. McArdle, M.M. Toner, J.R. Magel, R.J. Spina, K.B. Pandolf, Thermal
responses of men and women during cold-water immersion: influence of
exercise intensity, Eur. J. Appl. Physiol. Occup. Physiol. 65 (1992) 265–
270.
[26] D.A. Milder, E.J. Sutherland, S.C. Gandevia, P.A. McNulty, Sustained maximal
voluntary contraction produces independent changes in human motor axons
and the muscle they innervate, PLoS One 9 (2014) e91754.
[27] D.S. Moran, J.W. Castellani, C. O’Brien, A.J. Young, K.B. Pandolf, Evaluating
physiological strain during cold exposure using a new cold strain index, Am. J.
Physiol. 277 (1999) R556–R564.
[28] R. Mucke, D. Heuer, Behaviour of EMG parameters and conduction velocity in
contractions with different muscle temperatures, Biomed. Biochim. Acta 48
(1989) S459–S464.
[29] B. Nielsen, T. Hyldig, F. Bidstrup, J. González-Alonso, G.R. Christoffersen, Brain
activity and fatigue during prolonged exercise in the heat, Pflugers Arch. 442
(2001) 41–48.
[30] J. Oksa, H. Rintamäki, S. Rissanen, S. Rytky, U. Tolonen, P.V. Komi, Stretch- and
H-reflexes of the lower leg during whole body cooling and local warming,
Aviat. Space Environ. Med. 71 (2000) 156–161.
[31] J. Oksa, Neuromuscular performance limitations in cold, Int. J. Circumpolar
Health 61 (2002) 154–162.
[32] T. Pääkkönen, J. Leppäluoto, Cold exposure and hormonal secretion: a review,
Int. J. Circumpolar Health 61 (2002) 265–276.
[33] J. Petrofsky, M. Laymon, Muscle temperature and EMG amplitude and
frequency during isometric exercise, Aviat. Space Environ. Med. 76 (2005)
1024–1030.
[34] J. Petrofsky, M. Laymon, The relationship between muscle temperature, MUAP
conduction velocity and the amplitude and frequency components of the
surface EMG during isometric contractions, Basic Appl. Myol. 15 (2005) 61–74.
[35] P.V. Piazza, F. Rougé-Pont, V. Deroche, S. Maccari, H. Simon, M. Le Moal,
Glucocorticoids have state-dependent stimulant effects on the mesencephalic
dopaminergic transmission, Proc. Natl. Acad. Sci. U.S.A. 93 (1996) 8716–8720.
[36] H. Piedrahita, J. Oksa, C. Malm, E. Sormunen, H. Rintamäki, Effects of cooling
and clothing on vertical trajectories of upper arm and muscle functions during
repetitive light work, Eur. J. Appl. Physiol. 104 (2008) 183–191.
[37] J.C. Pruessner, F. Champagne, M.J. Meaney, A. Dagher, Dopamine release in
response to a psychological stress in humans and its relationship to early life
maternal care: a positron emission tomography study using [11C]raclopride, J.
Neurosci. 24 (2004) 2825–2831.
[38] S. Racinais, J. Oksa, Temperature and neuromuscular function, Scand. J. Med.
Sci. Sports 20 (2010) 1–18.
[39] F. Ranieri, V. Di Lazzaro, The role of motor neuron drive in muscle fatigue,
Neuromuscul. Disord. 22 (2012) S157–S161.
[40] M. Ross, C. Abbiss, P. Laursen, D. Martin, L. Burke, Precooling methods and their
effects on athletic performance: a systematic review and practical
applications, Sports Med. 43 (2013) 207–225.
[41] F. Rougé-Pont, V. Deroche, M. Le Moal, P.V. Piazza, Individual differences in
stress-induced dopamine release in the nucleus accumbens are influenced by
corticosterone, Eur. J. Neurosci. 10 (1998) 3903–3907.
[42] D.W. Russ, J.A. Kent-Braun, Sex differences in human skeletal muscle fatigue
are eliminated under ischemic conditions, J. Appl. Physiol. 94 (2003) 2414–
2422.
[43] A. Skurvydas, M. Brazaitis, J. Andrejeva, D. Mickeviciene, V. Streckis, The effect
of multiple sclerosis and gender on central and peripheral fatigue during 2-
min MVC, Clin. Neurophysiol. 122 (2011) 767–776.
[44] R. Solianik, A. Skurvydas, D. Mickevic
ˇiene
˙, M. Brazaitis, Intermittent whole-
body cold immersion induces similar thermal stress but different motor and
cognitive responses between males and females, Cryobiology 69 (2014) 323–
332.
[45] R. Solianik, A. Skurvydas, A. Vitkauskiene
˙, M. Brazaitis, Gender-specific cold
responses induce a similar body-cooling rate but different neuroendocrine and
immune responses, Cryobiology 69 (2014) 26–33.
[46] P. Tikuisis, P. Meunier, C.E. Jubenville, Human body surface area: measurement
and prediction using three dimensional body scans, Eur. J. Appl. Physiol. 85
(2001) 264–271.
[47] G. Todd, J.E. Butler, J.L. Taylor, S.C. Gandevia, Hyperthermia: a failure of the
motor cortex and the muscle, J. Physiol. 563 (2005) 621–631.
[48] J.A. Wagner, S.M. Horvath, K. Kitagawa, N.W. Bolduan, Comparisons of blood
and urinary responses to cold exposures in young and older men and women,
J. Gerontol. 42 (1987) 173–179.
[49] H. Westerblad, S. Duty, D.G. Allen, Intracellular calcium concentration during
low-frequency fatigue in isolated single fibres of mouse skeletal muscle, J.
Appl. Physiol. 75 (1993) 382–388.
[50] J. Winkel, K. Jørgensen, Significance of skin temperature changes in surface
electromyography, Eur. J. Appl. Physiol. Occup. Physiol. 63 (1991) 345–348.
118 R. Solianik et al. / Cryobiology 71 (2015) 112–118
