Sawada et al.
Journal of Physiological Anthropology(2024) 43:11
https://doi.org/10.1186/s40101-024-00358-3

ORIGINAL ARTICLE

Journal of
Physiological Anthropology

Open Access

Local alternating heat and cold stimulation
affects hemodynamics and oxygenationin fatigued muscle tissue and autonomic
nervous activity: a single‑arm interventional
study
Tomonori Sawada1,2, Hiroki Okawara1,2, Daisuke Nakashima1,2,3* , Kentaro Aoki2, Mira Namba2,
Shuhei Iwabuchi2, Yoshinori Katsumata4,5, Masaya Nakamura2 and Takeo Nagura1,2,3

Abstract
Background Local alternating heat and cold stimulation as an alternative to contrast bath may cause intermittent
vasoconstriction and vasodilation, inducing a vascular pumping effect and consequently promoting increased tissue
blood flow and oxygenation. This study aimed to examine the effects of local alternating heat and cold stimulation,using a wearable thermal device, on the hemodynamics of fatigued muscle tissue and autonomic nervous activity.
Methods Twenty healthy individuals experienced fatigue in the periarticular muscles of the shoulder joint due
to a typing task. Local alternating heat and cold stimulations were then applied to the upper trapezius muscle.
Muscle hardness was measured using a muscle hardness meter, and muscle tissue hemodynamics and oxygenation were evaluated using near-infrared spectroscopy before and after the stimulation. Autonomic nervous activity
was also evaluated using heart rate variability.
Results Alternating heat and cold stimulation decreased muscle hardness of the fatigued trapezius muscle
from 1.38 ± 0.15 to 1.31 ± 0.14 N (P < 0.01). The concentration of total hemoglobin in the trapezius muscle tissue increased from − 0.21 ± 1.36 to 2.29 ± 3.42 µmol/l (P < 0.01), and the tissue hemoglobin oxygen saturation
also increased from 70.1 ± 5.4 to 71.1 ± 6.0% (P < 0.05). Additionally, the heart rate variability parameter, which
is an index of sympathetic nervous activity, increased from 3.82 ± 2.96 to 6.86 ± 3.49 (P < 0.01). A correlation was foundbetween increased tissue hemoglobin oxygen saturation and increased parameters of sympathetic nervous activity(r = 0.50, P < 0.05).
Conclusions Local alternating heat and cold stimulation affected the hemodynamic response in fatigued muscle
tissue and autonomic nervous activity. This stimulation is more efficient than conventional contrast baths in termsof mobility and temperature control and has potential as a new versatile therapeutic intervention for muscle fatigue.

*Correspondence:
Daisuke Nakashima
nakashima@keio.jp
Full list of author information is available at the end of the article© The Author(s) 2024. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which
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Sawada et al. Journal of Physiological Anthropology(2024) 43:11

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Trial registration UMIN-CTR (UMIN000040087: registered on April 7, 2020, https://​upload.​umin.​ac.​jp/​cgi-​open-​bin/​
ctr_e/​ctr_​view.​cgi?​recpt​no=​R0000​45710. UMIN000040620: registered on June 1, 2020, https://​upload.​umin.​ac.​jp/​cgi-​
open-​bin/​ctr_e/​ctr_​view.​cgi?​recpt​no=​R0000​46359).
Keywords Alternating heat and cold stimulation, Trapezius muscle, Muscle hardness, Near-infrared spectroscopy,
Intramuscular hemodynamics, Heart rate variability

Background
A contrast bath is a bathing method of alternating application of hot and cold water. It is believed to induce a
vascular pumping effect by causing intermittent vasoconstriction and vasodilation, resulting in increased tissue blood flow and oxygenation, which improves healing,enhances tissue waste-product transportation to reduce
edema, improves limb function, and promotes quicker
recovery [1]. It is also expected to provide a relaxation
effect and is widely used for recovery from fatigue after
exercise, especially in athletes [2, 3]. However, contrast
bath has limitations, such as the need for a large bath, difficulty with water temperature control (as it changes witheach immersion), and hygiene issues (when multiple people use the same bath). Moreover, clear evidence is yet tobe established, given that the temperature settings, number of treatments, and durations of hot and cold water
application vary from one study to another [4–7].
Recently, a miniature apparatus with embedded Peltier elements was developed, and it allows easy program
control and protocol assembly for heat and cold stimulation using a smartphone application. This small wearable
device has the significant advantage of overcoming the
problems of conventional contrast bath therapy, which islimited by mobility, location, water temperature control,and hygiene issues, as it can provide specific, rapid, andlocalized heating and cooling stimulation at incrementsof 0.1 °C. The device also enables optimal temperature
protocol management to achieve its effect on the targeted muscle while preventing complications such as
hot/cold burns. An additional advantage is the potential
for more accurate verification of the effects of temperature change. In previous studies, we examined the effectsof local alternating heat and cold stimulation using thisdevice on a fatigued trapezius muscle and demonstrated
that the stimulation improved muscle hardness and subjective fatigue [8, 9]. Muscles generally become harderunder pathological conditions such as muscular damage,spasms, cramps, and edema [10–12]. Therefore, evaluation of muscle hardness is considered useful for assessing
muscle fatigue associated with sustained muscle contraction. On the other hand, muscle hardness is measured from the body surface according to pressure and isconstantly influenced by the skin, subcutaneous adipose
tissue, muscles located below the target muscle, andbone [11, 13], making it inadequate for the evaluationof the effect of the stimulation on the target muscle tissue itself. Near-infrared spectroscopy (NIRS) is a widelyused research instrument for measuring hemodynamics
and oxygenation in muscle tissue noninvasively, and thistechnique may be useful for assessing how local alternating heat and cold stimulation alters the hemodynamics offatigued muscle tissue due to sustained muscle contraction. Although previous studies have reported that hot
pack therapy improves total hemoglobin (corresponding to blood volume) and oxygenation levels of a target
muscle and tendon [14, 15], no study has examined therelationship between these improvements and changes inmuscle hardness. Furthermore, autonomic nervous activity may also be involved in controlling the local circulation in skeletal muscles. The sympathetic nervous system
plays a crucial role in mediating acute cardiovascularresponses to stress. During exercise, the skeletal muscle
uses a large amount of energy, which requires increased
blood volume for oxygen consumption, and it is suggested to be involved in sympathetic cholinergic vasodilation in the skeletal muscle [16, 17]. However, no study
has simultaneously evaluated the effects of contrast baththerapy and local alternating heat and cold stimulationon the local hemodynamics of skeletal muscle tissue andautonomic nervous activity and investigated the relationship between those effects.
Accordingly, this study aimed to examine the effectsof local alternating heat and cold stimulation on fatigueinduced upper trapezius muscle tissue hemodynamics
and autonomic nervous activity, in addition to previous
muscle hardness measurements. We hypothesized thatalternating heat and cold stimulation not only reduces
muscle hardness but also increases blood volume andoxygenation in the muscle tissue and sympathetic nervous activity for vasodilation in the skeletal muscle, andsome correlation would exist between these changes. To
date, the relationship between increased blood volume intargeted fatigued muscle and autonomic nervous activity
due to the use of contrast baths is not well understood.
Therefore, the findings of this study may provide support
for the physiological effects of contrast baths and suggestthat local alternating heat and cold stimulation could bea potentially beneficial approach for muscle fatigue as analternative to conventional contrast baths.

Sawada et al. Journal of Physiological Anthropology(2024) 43:11

Methods
Study design and participantsThis was a non-randomized, single-arm interventional study registered with the UMIN Clinical Trials
Registry (registration numbers UMIN000040087 and
UMIN000040620). In Japan, shoulder stiffness is the second most common complaint (57.2 per 1000 population)
after back pain among men and is the most frequently
occurring condition (113.8 per 1000 population) among
women [18]. Moreover, since it is believed that complaints of shoulder stiffness among young adults are due
to prolonged smartphone use in recent years, this study
recruited mainly young men and women. After recruiting
participants from one clinic and one university between
March 2021 and August 2022, 20 healthy young individuals (males, 13; females, 7) without any orthopedic abnormalities of the neck or shoulders were included in thisstudy (Table 1). All the participants were informed of the
purpose of the study. Those who refused to participate
in the study or did not provide informed consent were
excluded. The participants’ average daily smartphone
use and average typing time over the past month wererecorded using a questionnaire.
Experimental protocol

All the participants were asked to visit our laboratory where the room temperature was set between 24
and 26 °C to ensure that the experiment was conductedin a similar environment as much as possible. The participants performed the typing task at a desk for 15 minusing a laptop computer to induce fatigue around theshoulder, according to previous studies [9, 19]. The participants were instructed to maintain the same posturewhile transcribing as much text as possible into the document entry software. The text used in the typing task was
an out-of-copyright Japanese novel. Intervention withalternating heat and cold stimulation was implemented
using a commercially available wearable thermal device

Page 3 of 10(WTD) (REON POCKET 2; Sony Group Corporation,
Tokyo, Japan). The WTD contains a Peltier elementthat uses voltage regulation to produce surface heatingor cooling in an area of 4.5 × 5.5 cm. It can be operatedusing a smartphone application to provide repeated cooling, heating, and pausing for a fixed number of seconds,
and the intensity can be adjusted in four levels from 1
to 4 for the heating and cooling stimulations separately,with level 1 as the weakest and level 4 as the strongest.
The intensity of the heat stimulation was set at level 3,
and that of the cold stimulation was set at level 4. The
WTD was taped over the skin of the upper trapezius
muscle on the dominant side, and the center of the device
was 2 cm lateral to the midpoint between the 7th cervicalspinous process and the tip of the acromion [9, 20, 21].
Heat stimulation was applied for 3 min, followed by cold
stimulation for 1 min, for a total of five sets. Additionally, 10 s of movement cessation was allowed between theheat and cold stimulations to reduce thermal stress on
the WTD. During the stimulation, the participants rested
in a relaxed position on a chair with a backrest. In thisstudy, the following parameters were evaluated before
and after the alternating heat and cold stimulation: trapezius muscle hardness using a muscle hardness meter,
trapezius muscle tissue hemodynamics and oxygenation
using NIRS, and autonomic nervous activity using heart
rate variability (HRV).
Measurements

Muscle hardness was quantitatively evaluated by atrained examiner using a portable muscle hardness
meter (NEUTONE TDM-Z2; TRY-ALL Corp., Chiba,
Japan). A similar device was used in previous studies [22–24]. Our previous study showed that the muscle hardness meter had excellent intratester reliability
for the trapezius muscle (ICC1,5 = 0.992–0.995) [25].
This meter displays values on a scale of 0 to 100 without units. We converted the scale values to Newton

Table 1 Participant characteristics
All (n = 20)

Males (n = 13)

Females (n = 7)

Age (years)

21.4 ± 3.2

21.6 ± 3.9

20.9 ± 1.0

Height (cm)

169.4 ± 7.4

173.8 ± 5.0

161.3 ± 3.2

Weight (kg)64.5 ± 15.3

72.1 ± 13.8

50.4 ± 3.5

Body mass index (kg/m2)

22.3 ± 4.2

23.9 ± 4.4

19.4 ± 0.8

Right

19

13

6

Left

1

0

1

Time of smartphone use per day (h)4.9 ± 2.1

5.7 ± 2.1

3.4 ± 1.2

Time of typing per day (h)1.0 ± 1.6

1.2 ± 2.0

0.6 ± 0.3

Dominant hand (n)Sawada et al. Journal of Physiological Anthropology(2024) 43:11(N) using the following formula, based on the manufacturer’s recommendations: N = 0.023 × measured
value + 0.532. The measurement point was 2 cm lateral
to the midpoint between the 7th cervical spinous process and the tip of the acromion as well as the centerof the WTD attachment. Measurements were obtained
five times at each time point, and the mean value wasused for analysis. Muscle hardness was not only evaluated before and after the alternating heat and cold
stimulation intervention but also at baseline before thetyping task to confirm whether the task induced muscle
fatigue and increased muscle hardness, as observed in
our previous study [9].
Muscle tissue hemodynamics and oxygenation of theupper trapezius were evaluated using an NIRS system(NIRO-200NX; Hamamatsu Photonics K.K., Hamamatsu, Japan) that uses the modified Beer-Lambert(MBL) method and spatially resolved spectroscopy(SRS). A pair of photoemission and photodetection
probes were set at a constant distance of 4 cm in a
specialized rubber holder, which was fixed to the skinof the muscle belly adjacent to the alternating heatand cold stimulation area using a double-sided adhesive sheet. Changes in the concentration of oxyhemoglobin (ΔOxyHb), deoxyhemoglobin (ΔDeoxyHb), andtotal hemoglobin (ΔTotalHb) [ΔoxyHb + ΔDeoxyHb],
which is an index of the local blood volume [26, 27],
were measured using MBL methods. Additionally, tissue hemoglobin oxygen saturation (tissue oxygenationindex, TOI, expressed in percentage) was calculatedusing SRS [28–30]. The data for these parameters were
continuously obtained at 1 Hz. Among the obtained
data, the average values 2 min before and after theintervention were used for analysis.
HRV analysis was performed using dedicated analysis software (Reflex Meijin; Crosswell Corp., Yokohama,Japan). The R-R interval, which is the interval between
one QRS wave and the next, was collected at 1000 Hz
using a heart rate monitor (MWT-001; AHM Electronics Co., Ltd., Kodaira, Japan) attached to the chest. Twopower spectrum components, a high-frequency (HF)
component (0.15–0.4 Hz) and a low-frequency (LF)component (0.04–0.15 Hz), were continuously calculated using the maximum entropy method while shifting
every beat for a 30-s period of HRV [31]. HF components
can be used as a general index of parasympathetic nervous activity, and the LF/HF ratio can be used as an index
of sympathetic nervous activity [32, 33]. In addition to
HF, LF, and LF/HF, the R-R interval coefficient of variation (CVRR [%] = standard deviation/mean of the R-R
interval during the previous 30 s × 100) was also measured. Among the obtained data, the average values 2 min
before and after the intervention were used for analysis.

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Statistical analysis

Normality of the data distribution was assessed using theShapiro–Wilk test. Initially, the values of each parameter
before and after the intervention were compared using
paired t-tests. Regarding muscle hardness, the baseline
values before the typing task were further comparedwith the values before the intervention (after typing)using paired t-tests. In addition, to assess the possibilityof differences in muscle hardness values by sex, baseline
values were compared between males and females using
unpaired t-tests. The effect size for each comparison was
calculated based on Cohen’s d [34]. Moreover, to examine
the association of the intervention with changes in muscle stiffness, NIRS, and HRV parameters, correlations
between the changes in each parameter (post-intervention value minus pre-intervention value) were assessedusing Pearson’s or Spearman’s correlation coefficient,
based on the normality distribution of the parameterdata. All statistical analyses were performed using SPSS
version 25.0 (IBM Corp., Armonk, NY, USA), with statistical significance set at 0.05.

Results
Comparison of muscle hardness before and after thefatigue typing task and differences in muscle hardness
between sexes

The 15-min typing task significantly increased muscle
hardness after the task compared with that before thetask (1.34 ± 0.15 N vs. 1.38 ± 0.15 N, P < 0.05, d = 0.56). No
significant differences in muscle hardness before the typing task were found between sexes (male: 1.32 ± 0.15 N,
female: 1.40 ± 0.15 N, P = 0.30, d = 0.50).
Comparison of muscle hardness, NIRS, and HRVparameters before and after the intervention

Muscle hardness was significantly reduced after theintervention compared with that before the intervention (1.38 ± 0.15 N vs. 1.31 ± 0.14 N, P < 0.01,
d = 0.97), suggesting that the intervention caused
soft tissue softness, including muscle palpable fromthe surface of the body. Figure 1 presents the meanvalues of the muscle tissue hemodynamics and oxygenation indices using NIRS. OxyHb, ΔTotalHb, and TOI
increased after the intervention (0.06 ± 1.40 µmol/l vs.
2.92 ± 2.99 µmol/l, P < 0.01, d = 1.15; − 0.21 ± 1.36 µmol/l
vs. 2.29 ± 3.42 µmol/l, P < 0.01, d = 0.95; and 70.1 ± 5.4%
vs. 71.1 ± 6.0%, P < 0.05, d = 0.17, respectively). These
results indicate that the intervention increased blood
perfusion, including oxyhemoglobin, into the targeted
trapezius muscle tissue and facilitated oxygenation.
The mean values of the HRV-related indices are also
shown in Fig. 2. The LF, LF/HF, and CVRR increased
significantly after the intervention (538.6 ± 375.3 ­ms2

Sawada et al. Journal of Physiological Anthropology(2024) 43:11

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Fig. 1 Mean values in muscle tissue hemodynamics and oxygenation indices using NIRS at pre- and post-intervention. a Hemoglobin
concentration changes (ΔOxyHb, ΔDeoxyHb, and ΔTotalHb) by MBL. b TOI by spatially resolved spectroscopy. *P < 0.05 and **P < 0.01. Error bars
indicate standard deviation. NIRS, near-infrared spectroscopy; OxyHB; oxyhemoglobin; DeoxyHB, deoxyhemoglobin; TotalHb, total hemoglobin;
MBL, modified Beer-Lambert; TOI, tissue oxygenation index

Fig. 2 Mean values of HRV parameters at pre- and post-intervention. a HF and LF. b LF/HF and CVRR. *P < 0.01. Error bars indicate standard
deviation. HRV, heart rate variability; HF, high frequency; LF, low frequency; CVRR, coefficient of variation of R-R interval

vs. 1017.2 ± 789.4 ­ms2, P < 0.01, d = 0.59; 3.82 ± 2.96
vs. 6.86 ± 3.49, P < 0.01, d = 0.91; and 5.59 ± 1.75% vs.
6.66 ± 2.30%, P < 0.01, d = 0.49, respectively), whereas
no statistically significant difference was observed in
the HF before and after the intervention. These HRVrelated results imply that the alternating heat and cold
stimulation increased sympathetic nervous activity.
Relationship between change in muscle hardness
and changes in the other parameters by intervention

The correlation between changes in muscle hardness
and changes in NIRS or HRV parameters after intervention with alternating heat and cold stimulation wasinvestigated. No significant correlation with changes

in muscle hardness was found for the NIRS- or HRVrelated outcomes (Table 2).
Relationship between changes in NIRS and HRVparameters by intervention

The correlations between changes in NIRS and HRV
outcomes after the intervention are shown in Table 3.
Among them, the change in TOI was positively correlated with the change in the LF/HF ratio (r = 0.50,
P < 0.05) (Fig. 3).

Discussion
To the best of our knowledge, this is the first study
to demonstrate that superficial local alternating heatand cold stimulation on fatigued muscle affects theSawada et al. Journal of Physiological Anthropology(2024) 43:11

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Table 2 Correlations between change in muscle hardness andchanges in other parameters
Muscle hardness
Spearman r

p-valueΔOxyHb

− 0.124

0.602

ΔDeoxyHb− 0.119

0.17

ΔTotalHb− 0.095

0.691

TOI

0.365

0.114

HF

− 0.391

0.088

LF

0.012

0.960

LF/HF

0.273

0.245

CVRR

0.054

0.820

Correlation analysis was performed between the changes in each participant’s
post- and pre-intervention values
OxyHB oxyhemoglobin, DeoxyHB deoxyhemoglobin, TotalHb total hemoglobin,
TOI tissue oxygenation index, HF high frequency, LF low frequency, CVRR
coefficient of variation of R-R intervalmuscle tissue and autonomic nervous activity. That is,
the findings suggest that changes in muscle hardness
may be influenced by physiological mechanisms different from muscle tissue hemodynamics and autonomic
nervous activity. Muscle hardness is defined as the resistance of the muscle tissue to perpendicular pressure [11,35]. Thermotherapy is generally expected to increase tissue temperature, local blood flow, and soft tissue extensibility, cause local vasodilation, increase metabolite
production, and reduce muscle spasms [36, 37]. For thepresent alternating stimulation, similar physiologicaleffects are expected to occur because heat is the mostprevalent stimulation. Muscle hardness measured using
a push-in muscle hardness meter is believed to specifically assess soft tissue extensibility in these physiological effects, but muscle hardness values also include theeffects of the skin, subcutaneous tissue, and deep muscle
layers [11, 13]. Previous studies have evaluated trapezius muscle stiffness in healthy young volunteers using ahemodynamics of muscle tissue and autonomic nervous activity. Our results showed that alternating heatand cold stimulation improved muscle hardness, whichis consistent with previous reports [8, 9]. However, no
relationship was found between changes in muscle hardness and changes in hemodynamics or autonomic nervous activity. The alternating heat and cold stimulation
increased ΔTotalHb with an increase in ΔOxyHb and
TOI. In addition, the results of the HRV analysis showed
an increase in LF/HF, suggesting an increase in sympathetic nervous activity. Furthermore, a significant correlation was observed between the changes in TOI andthe LF/HF ratio induced by alternating warm and cold
stimulation, suggesting that sympathetic nervous activity
is involved in muscle tissue oxygenation.
Our results indicate that the improvement in muscle
hardness by alternating heat and cold stimulation failed
to reflect changes in hemodynamics in the targeted

Fig. 3 Scatter diagram representing change in TOI and change
in LF/HF. *Value was calculated as the pre-intervention value
minus the post-intervention value. TOI, tissue oxygenation index; LF,
low frequency; HF, high frequency

Table 3 Correlations between changes in NIRS and HRV parameters
ΔOxyHbΔDeoxyHb

ΔTotalHb

TOI

Correlation
coefficientp-value

Correlation
coefficientp-value

Correlation
coefficientp-value

Correlation
coefficientp-value

HF

0.02a

0.79

0.084a0.724

0.015aLF

0.177a0.454− 0.041a0.85− 0.093a0.950− 0.308a

0.186

0.696

0.116aLF/HF

0.309b

0.185− 0.322a

0.166

0.627

0.088b0.713

0.499b

CVRR

0.252b

0.283− 0.260a

0.268

0.025

0.124b

0.603

0.375b

0.103

Correlation analysis was performed between the changes in each participant’s post-intervention and pre-intervention values
NIRS near-infrared spectroscopy, HRV heart rate variability, OxyHB oxyhemoglobin, DeoxyHB deoxyhemoglobin, TotalHb total hemoglobin, TOI tissue oxygenationindex, HF high frequency, LF low frequency, CVRR coefficient of variation of R-R intervalaSpearman’s correlation coefficientb

Pearson’s correlation coefficientSawada et al. Journal of Physiological Anthropology(2024) 43:11

muscle hardness meter and ultrasound elastography andshowed no correlation between the obtained values [23,25]. Thus, although alternating heat and cold stimulation
resulted in a decrease in muscle hardness value, thesechanges may reflect changes in the extensibility of not
only the target muscle but also the surrounding soft tissues. The improvement in peripheral blood flow expectedfrom superficial heat stimulation is generally scarce inmuscles located deeper in the skin and the subcutaneous
tissue [37]. Therefore, changes in muscle hardness value
might be more reflective of changes in the extensibility ofthe superficial soft tissue including the skin and subcutaneous tissue or blood flow within the targeted muscle
tissue. Nevertheless, muscle hardness can easily be measured in clinical practice using a muscle hardness meterbecause it is similar to palpation, and the equipment isrelatively inexpensive and portable. Therefore, further
research to scientifically identify the factors that contribute to changes in these values would be of great clinicalimportance.
In this study, intramuscular hemodynamics were evaluated using NIRS to detect physiological changes in thetarget muscle tissue due to alternating heat and cold
stimulation. The present study found that local stimulation of the upper trapezius muscle increased intramuscular oxygenated blood volume, which is consistent withfindings in a previous study that evaluated intramuscular hemodynamics during contrast baths to the lower leg
muscles using NIRS [38]. Generally, heat causes vasodilation and increases blood flow [36]. In contrast, superficial
heat agents produce more pronounced vasodilation in
the local cutaneous blood vessels but less vasodilation in
deeper vessels that run through the muscles [37]. Hence,at first glance, the WTD used in this study is presumed
to have a limited effect because the stimulation area isnarrower (4.5 × 5.5 cm) than that of conventional contrast bath therapy. However, the results showed increased
vasodilation and oxygen supply to the target muscle tissue. Desk workers engaged in intensive and prolonged
computer use are known to be at a higher risk of neckto-shoulder pain [39–41]. Furthermore, with the recent
explosion of smartphone use, musculoskeletal disordersof the neck have been increasing, especially among university students [42, 43]. Obstruction of blood flow and areduction in muscle tissue oxygenation during sustained
repetitive work have been suggested to contribute to thedevelopment of upper extremity muscle disorders [44]. In
addition, muscle blood flow is believed to have a significant impact on the development of muscle fatigue [45]because of its important role in the delivery of metabolic
waste products (e.g., inorganic phosphate, lactic acid, andH +) that contribute to muscle fatigue [46, 47]. Thus, thelocalized superficial alternating heat and cold stimulation

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using a WTD in this study overcomes the limitations ofconventional alternating baths and may be an effective
intervention or prevention strategy for desk workers
and university students with symptoms in the neck andshoulder regions.
The results of this study demonstrated that local alternating heat and cold stimulation also affects HRV parameters, which is an index of sympathetic nervous activity.
To date, no study has examined the effects of local alternating heat and cold stimulation or conventional contrast
baths on autonomic nervous activity. Massage therapies
for relaxation have been reported to produce beneficial
physiological effects such as a decrease in heart rate andblood pressure [48, 49]. Decreased heart rate is believed
to be caused by either increased parasympathetic nervous activity or decreased sympathetic nervous activity[50]. Several previous studies have shown that massage
increases the HF component, which is an index of parasympathetic nervous activity [51], and decreases the LF/
HF ratio, which is an index of sympathetic nervous activity [52, 53]. However, in this study, alternating heat andcold increased LF, LF/HF, and CVRR, suggesting that
sympathetic nervous activity increased. More interestingly, the correlation analysis between changes in HRV
and NIRS parameters revealed a significant positive correlation between LF/HF and TOI. Generally, the activation of the sympathetic nervous activity causes bloodvessels to constrict and the heart rate to increase. Consequently, blood pressure and the amount of perfusionin peripheral tissues increase. Previous studies have suggested that sympathetic cholinergic vasodilation in skeletal muscles is involved in increased oxygen demand inmuscle tissues due to increased exercise load [16, 17]. In
addition, heat stress is also believed to induce important
physiological responses similar to those induced by exercise [54]. These include increase in skin and muscle blood
flow, heart rate, and sympathetic nervous activity [55, 56].
Sympathetic nervous activity increases by approximately
90% in the muscle vasculature and 300–600% in the skinvasculature during passive heat stress [56–58]. Further,detailed investigation is needed to determine whether the
sympathetic vasodilation effects in skeletal muscle can be
induced by local alternating warm and cold stimulation
as well as during intense exercise or whole-body heating.
Nevertheless, the new finding of the correlation between
increased sympathetic nervous activity and increased
oxygenation in the muscle tissue by alternating heat andcold stimulation is an interesting result that could partly
explain the stimulation effects.
The limitations of this study warrant further discussion.
First, because this study included only healthy young
male and female individuals (age range, 19–35 years), theresults cannot be generalized to older adults or patients

Sawada et al. Journal of Physiological Anthropology(2024) 43:11

with neck and shoulder pain. Second, this was a singlearm interventional study and did not perform comparisons with the no-stimulation condition or detailed
examination of whether the effects of alternating heatand cold stimulation on muscle tissue hemodynamics
and HRV differ between fatigued and non-fatigued conditions. To address these two limitations, future researchshould be conducted to examine whether similar effects
can be obtained by expanding the intervention to include
older adults and patients with neck and shoulder pain
and investigate the effects of the alternating stimulation,
eliminating temporal effects, by conducting an additionalno stimulation condition. Third, the factor responsible for the changes in muscle hardness measured by themuscle hardness meter remains unclear. Future research
could explain the changes in muscle hardness by assessing not only the targeted muscle tissue but also superficial skin blood flow or subcutaneous tissue stiffness.
Finally, changes in autonomic nervous activity observedwith local alternating heat and cold stimulation cannot
be applied to the effects of conventional contrast baththerapy. A previous study examining the effects of warm
hand bathing on autonomic nervous activity reported
an increase in heart rate and a decrease in HF, resulting
in increased sympathetic activity [59]. In contrast, otherstudies have demonstrated that warm footbaths decrease
the LF/HF ratio and suppress sympathetic activity [60,61]. Therefore, the effects on autonomic nervous activity
may vary depending on the site and extent of stimulation.

Conclusions
Similar to that in a contrast bath, the local alternatingheat and cold stimulation used in this study improved
hemodynamics and oxygenation indices in the target
muscle tissue. The results of the HRV analysis indicatedthat sympathetic nervous activity increased by stimulation. Furthermore, an association was found between
an increase in oxygenation indices in the muscle tissue
and changes in sympathetic nervous activity parameters. These findings enhance our understanding of thephysiological effects of contrast baths on muscle tissue
hemodynamics. This stimulation is more efficient thanconventional contrast baths in terms of mobility andtemperature control and has potential as a new versatile
therapeutic intervention for muscle fatigue.
Abbreviations
CVRR	Coefficient of variation of R-R interval
HF	High frequency
HRV	Heart rate variability
LF	Low frequency
MBL	Modified Beer-Lambert
NIRS	Near-infrared spectroscopy
SRS	Spatially resolved spectroscopy
TOI	Tissue oxygenation index

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Acknowledgements
We thank Kenji Itoh and Yoichi Ito (Sony Corporation) for their technicalassistance in this study.
Authors’ contributions
TS, HO, and DN conceived and designed the study. TS, HO, KA, MN, and SI conducted the experiments and analyzed the data. TS drafted the manuscript andprepared the tables and figures. All authors edited and revised the manuscript.
YK provided the experimental environment and assisted with data analysis.
MN supervised the study. DN and TN administered the project and acquired
funding. All the authors have read and agreed to the published version of thismanuscript.
Funding
This research was supported by the Sony Corporation, KGRI/IoT Healthcare
Research Consortium (grant number 02–066-0008) and JSPS KAKENHI (grant
number JP22K17616).
Availability of data and materials
The datasets used and/or analyzed in the current study are available from thecorresponding author upon reasonable request.

Declarations
Ethics approval and consent participate
The experimental design was approved by the P-One Clinic Ethical Committee
and Institutional Review Board of Keio University School of Medicine (approval
number: 20190326). The study was conducted in accordance with the principles of the Declaration of Helsinki. All participants provided informed consent
prior to the experiment.
Consent for publication
Not applicable.
Competing interests
Daisuke Nakashima is the president of Grace Imaging Inc. and holds sharesin the company. The other authors declare that they have no competinginterests.
Author details
1
Diagnosis and Treatment Division, Nagura Orthopedic Clinic, Chuo, Tokyo,
Japan. 2 Department of Orthopaedic Surgery, Keio University School of Medicine, Shinjuku, Tokyo, Japan. 3 Department of Clinical Biomechanics, Keio
University School of Medicine, Shinjuku, Tokyo, Japan. 4 Institute for Integrated
Sports Medicine, Keio University School of Medicine, Shinjuku, Tokyo, Japan.
5
Department of Cardiology, Keio University School of Medicine, Shinjuku,
Tokyo, Japan.
Received: 9 November 2023 Accepted: 20 March 2024

References
1. Cochrane DJ. Alternating hot and cold water immersion for athlete
recovery: a review. Phys Ther Sport. 2004;5:26–32. https://​doi.​org/​10.​1016/j.​ptsp.​2003.​10.​002.
2. Versey NG, Halson SL, Dawson BT. Water immersion recovery forathletes: effect on exercise performance and practical recommendations. Sports Med. 2013;43:1101–30. https://​doi.​org/​10.​1007/​
s40279-​013-​0063-8.
3. Higgins TR, Greene DA, Baker MK. Effects of cold water immersion andcontrast water therapy for recovery from team sport: a systematic review
and meta-analysis. J Strength Cond Res. 2017;31:1443–60. https://​doi.​org/​
10.​1519/​JSC.​00000​00000​001559.
4. Walsh MT. Chapter 6. Hydrotherapy: the use of water as a therapeutic
agent. In: Thermal agents in rehabilitation. 3rd ed. Philadelphia: F. A. Davis
Company; 1996.

Sawada et al. Journal of Physiological Anthropology

5.
6.
7.
8.

9.

10.
11.
12.

13.
14.
15.

16.

17.

18.
19.

20.

21.

22.
23.

(2024) 43:11

Hing WA, White SG, Bouaaphone A, Lee P. Contrast therapy–a systematic
review. Phys Ther Sport. 2008;9:148–61. https://​doi.​org/​10.​1016/j.​ptsp.​
2008.​06.​001.
Breger Stanton DE, Lazaro R, Macdermid JC. A systematic review of theeffectiveness of contrast baths. J Hand Ther. 2009;22:57–69. https://​doi.​
org/​10.​1016/j.​jht.​2008.​08.​001. quiz 70.
Bieuzen F, Bleakley CM, Costello JT. Contrast water therapy and exercise
induced muscle damage: a systematic review and meta-analysis. PLoS
ONE. 2013;8:e62356. https://​doi.​org/​10.​1371/​journ​al.​pone.​00623​56.
Sawada T, Okawara H, Nakashima D, Iwabuchi S, Matsumoto M,
Nakamura M, et al. Effects of alternating heat and cold stimulation
using a wearable thermo-device on subjective and objective shoulder stiffness. J Physiol Anthropol. 2022;41:1. https://​doi.​org/​10.​1186/​
s40101-​021-​00275-9.
Sawada T, Okawara H, Nakashima D, Iwabuchi S, Matsumoto M, Nakamura M, et al. Effects of alternating heat and cold stimulation at different
cooling rates using a wearable thermo device on shoulder muscle stiffness: a cross-over study. BMC Musculoskelet Disord. 2022;23:669. https://​doi.​org/​10.​1186/​s12891-​022-​05623-z.
Fischer AA. Tissue compliance meter for objective, quantitative documentation of soft tissue consistency and pathology. Arch Phys Med
Rehabil. 1987;68:122–5.
Murayama M, Nosaka K, Yoneda T, Minamitani K. Changes in hardnessof the human elbow flexor muscles after eccentric exercise. Eur J Appl
Physiol. 2000;82:361–7. https://​doi.​org/​10.​1007/​s0042​10000​242.
Yanagisawa O, Niitsu M, Kurihara T, Fukubayashi T. Evaluation of humanmuscle hardness after dynamic exercise with ultrasound real-time tissue
elastography: a feasibility study. Clin Radiol. 2011;66:815–9. https://​doi.​
org/​10.​1016/j.​crad.​2011.​03.​012.
Horikawa M, Ebihara S, Sakai F, Akiyama M. Non-invasive measurement method for hardness in muscular tissues. Med Biol Eng Comput.
1993;31:623–7. https://​doi.​org/​10.​1007/​BF024​41811.
Okada K, Yamaguchi T, Minowa K, Inoue N. The influence of hot
pack therapy on the blood flow in masseter muscles. J Oral Rehabil.
2005;32:480–6. https://​doi.​org/​10.​1111/j.​1365-​2842.​2005.​01448.x.
Kubo K, Yajima H, Takayama M, Ikebukuro T, Mizoguchi H, Takakura N.
Effects of acupuncture and heating on blood volume and oxygen saturation of human Achilles tendon in vivo. Eur J Appl Physiol. 2010;109:545–
50. https://​doi.​org/​10.​1007/​s00421-​010-​1368-z.
Ishii K, Matsukawa K, Liang N, Endo K, Idesako M, Hamada H, et al. Evidence for centrally induced cholinergic vasodilatation in skeletal muscle
during voluntary one-legged cycling and motor imagery in humans.
Physiol Rep. 2013;1:e00092. https://​doi.​org/​10.​1002/​phy2.​92.
Matsukawa K, Ishii K, Liang N, Endo K. Have we missed that neuralvasodilator mechanisms may contribute to exercise hyperemia at onsetof voluntary exercise? Front Physiol. 2013;4:23. https://​doi.​org/​10.​3389/​
fphys.​2013.​00023.
Ministry of Health. LaW: comprehensive survey of living conditions 2019;2019. https://​www.​mhlw.​go.​jp/​toukei/​saikin/​hw/k-​tyosa/k-​tyosa​19/​index.​
html. Accessed 13 Oct 2020
Horikawa M. Effect of visual display terminal height on the trapezius
muscle hardness: quantitative evaluation by a newly developed muscle
hardness meter. Appl Ergon. 2001;32:473–8. https://​doi.​org/​10.​1016/​
s0003-​6870(01)​00026-6.
Ishikawa H, Muraki T, Sekiguchi Y, Ishijima T, Morise S, Yamamoto N, et al.
Noninvasive assessment of the activity of the shoulder girdle muscles
using ultrasound real-time tissue elastography. J Electromyogr Kinesiol.
2015;25:723–30. https://​doi.​org/​10.​1016/j.​jelek​in.​2015.​07.​010.
Ishikawa H, Muraki T, Morise S, Sekiguchi Y, Yamamoto N, Itoi E, et al.
Changes in stiffness of the dorsal scapular muscles before and after computer work: a comparison between individuals with and without neckand shoulder complaints. Eur J Appl Physiol. 2017;117:179–87. https://​doi.​
org/​10.​1007/​s00421-​016-​3510-z.
Ariji Y, Gotoh A, Hiraiwa Y, Kise Y, Nakayama M, Nishiyama W, et al. Sonographic elastography for evaluation of masseter muscle hardness. Oral
Radiol. 2013;29:64–9. https://​doi.​org/​10.​1007/​s11282-​012-​0111-3.
Akagi R, Kusama S. Comparison between neck and shoulder stiffness
determined by shear wave ultrasound elastography and a muscle hardness meter. Ultrasound Med Biol. 2015;41:2266–71. https://​doi.​org/​10.​1016/j.​ultra​smedb​io.​2015.​04.​001.

Page 9 of 10

24. Aikawa R, Kishino T, Shibasaki S, Harashima K, Nakajima S, Ohnishi H, et al.
Relationship between trapezius muscle hardness and transverse cervicalartery flow in association with neck and upper-back stiffness. Clin Physiol
Funct Imaging. 2020;40:385–9. https://​doi.​org/​10.​1111/​cpf.​12658.
25. Sawada T, Okawara H, Nakashima D, Iwabuchi S, Matsumoto M, Nakamura M, et al. Reliability of trapezius muscle hardness measurement: acomparison between portable muscle hardness meter and ultrasoundstrain elastography. Sensors (Basel). 2020;20:7200. https://​doi.​org/​10.​3390/​s2024​7200.
26. Boushel R, Langberg H, Olesen J, Gonzales-Alonzo J, Bülow J, Kjaer M.
Monitoring tissue oxygen availability with near infrared spectroscopy(NIRS) in health and disease. Scand J Med Sci Sports. 2001;11:213–22.
https://​doi.​org/​10.​1034/j.​1600-​0838.​2001.​110404.x.
27. Quaresima V, Lepanto R, Ferrari M. The use of near infrared spectroscopyin sports medicine. J Sports Med Phys Fitness. 2003;43:1–13.
28. Bringard A, Denis R, Belluye N, Perrey S. Effects of compression tights
on calf muscle oxygenation and venous pooling during quiet resting in supine and standing positions. J Sports Med Phys Fitness.
2006;46:548–54.
29. Kurihara K, Kikukawa A, Kobayashi A, Nakadate T. Frontal cortical
oxygenation changes during gravity-induced loss of consciousness inhumans: a near-infrared spatially resolved spectroscopic study. J Appl
Physiol. 1985;2007(103):1326–31. https://​doi.​org/​10.​1152/​jappl​physi​ol.​
01191.​2006.
30. Grassi B, Quaresima V. Near-infrared spectroscopy and skeletal muscle
oxidative function in vivo in health and disease: a review from an exercise
physiology perspective. J Biomed Opt. 2016;21: 091313. https://​doi.​org/​
10.​1117/1.​JBO.​21.9.​091313.
31. Shiraishi Y, Katsumata Y, Sadahiro T, Azuma K, Akita K, Isobe S, et al. Real‐
time analysis of the heart rate variability during incremental exercise
for the detection of the ventilatory threshold. J Am Heart Assoc. 2018;7.
https://​doi.​org/​10.​1161/​JAHA.​117.​006612
32. Pagani M, Lombardi F, Guzzetti S, Rimoldi O, Furlan R, Pizzinelli P, et al.
Power spectral analysis of heart rate and arterial pressure variabilities asa marker of sympatho-vagal interaction in man and conscious dog. Circ
Res. 1986;59:178–93. https://​doi.​org/​10.​1161/​01.​res.​59.2.​178.
33. Heart rate variability: standards of measurement, physiological interpretation and clinical use. Task force of the European Society of Cardiology and
the North American society of pacing and electrophysiology. Circulation.
1996;93:1043–65. https://​doi.​org/​10.​1161/​01.​CIR.​93.5.​1043.
34. Cohen J. Statistical power analysis for the behavioral science. New York:
Academic Press; 1977.
35. Murayama M, Watanabe K, Kato R, Uchiyama T, Yoneda T. Associationof muscle hardness with muscle tension dynamics: a physiologicalproperty. Eur J Appl Physiol. 2012;112:105–12. https://​doi.​org/​10.​1007/​
s00421-​011-​1959-3.
36. Rennie GA, Michlovitz SL. Chapter 5. Biophysical principles of heating andsuperficial heating agents. In: Thermal agents in rehabilitation. 3rd ed.
Philadelphia: F. A. Davis Company; 1996.
37. Cameron MH. Chapter 8. Superficial cold and heat. In: Physical agents inrehabilitation: from research to practice. 4th ed. St Louis: Elsevier/Saunders; 2013.
38. Shadgan B, Pakravan AH, Hoens A, Reid WD. Contrast baths, intramuscular hemodynamics, and oxygenation as monitored by near-infrared
spectroscopy. J Athl Train. 2018;53:782–7. https://​doi.​org/​10.​4085/​
1062-​6050-​127-​17.
39. Juul-Kristensen B, Kadefors R, Hansen K, Byström P, Sandsjö L, Sjøgaard
G. Clinical signs and physical function in neck and upper extremities
among elderly female computer users: the NEW study. Eur J Appl Physiol.
2006;96:136–45. https://​doi.​org/​10.​1007/​s00421-​004-​1220-4.
40. Andersen LL, Hansen K, Mortensen OS, Zebis MK. Prevalence and anatomical location of muscle tenderness in adults with nonspecific neck/shoulder pain. BMC Musculoskelet Disord. 2011;12:169. https://​doi.​org/​
10.​1186/​1471-​2474-​12-​169.
41. Brandt M, Sundstrup E, Jakobsen MD, Jay K, Colado JC, Wang Y, et al. Association between neck/shoulder pain and trapezius muscle tenderness in
office workers. Pain Res Treat. 2014;2014:352735. https://​doi.​org/​10.​1155/​
2014/​352735.
42. Namwongsa S, Puntumetakul R, Neubert MS, Boucaut R. Factors associated with neck disorders among university student smartphone users.
Work. 2018;61:367–78. https://​doi.​org/​10.​3233/​WOR-​182819.

Sawada et al. Journal of Physiological Anthropology(2024) 43:11

43. Chan LLY, Wong AYL, Wang MH, Cheung K, Samartzis D. The prevalence ofneck pain and associated risk factors among undergraduate students: alarge-scale cross-sectional study. Int J Ind Ergon. 2020;76:102934. https://​doi.​org/​10.​1016/j.​ergon.​2020.​102934.
44. Visser B, van Dieën JH. Pathophysiology of upper extremity muscle disorders. J Electromyogr Kinesiol. 2006;16:1–16. https://​doi.​org/​10.​1016/j.​jelek​
in.​2005.​06.​005.
45. Abbiss CR, Laursen PB. Models to explain fatigue during prolonged
endurance cycling. Sports Med. 2005;35:865–98. https://​doi.​org/​10.​2165/​
00007​256-​20053​5100-​00004.
46. Westerblad H, Allen DG, Lännergren J. Muscle fatigue: lactic acid or
inorganic phosphate the major cause? News Physiol Sci. 2002;17:17–21.
https://​doi.​org/​10.​1152/​physi​ology​online.​2002.​17.1.​17.
47. Allen DG, Lamb GD, Westerblad H. Skeletal muscle fatigue: cellularmechanisms. Physiol Rev. 2008;88:287–332. https://​doi.​org/​10.​1152/​physr​
ev.​00015.​2007.
48. Weerapong P, Hume PA, Kolt GS. The mechanisms of massage and effects
on performance, muscle recovery and injury prevention. Sports Med.
2005;35:235–56. https://​doi.​org/​10.​2165/​00007​256-​20053​5030-​00004.
49. Field T. Massage therapy research review. Complement Ther Clin Pract.
2014;20:224–9. https://​doi.​org/​10.​1016/j.​ctcp.​2014.​07.​002.
50. Delaney JP, Leong KS, Watkins A, Brodie D. The short-term effects ofmyofascial trigger point massage therapy on cardiac autonomic tone inhealthy subjects. J Adv Nurs. 2002;37:364–71. https://​doi.​org/​10.​1046/j.​
1365-​2648.​2002.​02103.x.
51. Fazeli MS, Pourrahmat MM, Liu M, Guan L, Collet JP. The effect of headmassage on the regulation of the cardiac autonomic nervous system: apilot randomized crossover trial. J Altern Complement Med. 2016;22:75–
80. https://​doi.​org/​10.​1089/​acm.​2015.​0141.
52. Lindgren L, Rundgren S, Winsö O, Lehtipalo S, Wiklund U, Karlsson M, et al.
Physiological responses to touch massage in healthy volunteers. Auton
Neurosci. 2010;158:105–10. https://​doi.​org/​10.​1016/j.​autneu.​2010.​06.​011.
53. Kim DW, Lee DW, Schreiber J, Im CH, Kim H. Integrative evaluation of
automated massage combined with thermotherapy: physical, physiological, and psychological viewpoints. BioMed Res Int. 2016;2016:2826905.
https://​doi.​org/​10.​1155/​2016/​28269​05.
54. Thomas KN, van Rij AM, Lucas SJ, Gray AR, Cotter JD. Substantive hemodynamic and thermal strain upon completing lower-limb hot-water
immersion; comparisons with treadmill running. Temperature (Austin).
2016;3:286–97. https://​doi.​org/​10.​1080/​23328​940.​2016.​11562​15.
55. Vuori I. Sauna bather’s circulation. Ann Clin Res. 1988;20:249–56.
56. Crandall CG, González-Alonso J. Cardiovascular function in the heatstressed human. Acta Physiol (Oxf ). 2010;199:407–23. https://​doi.​org/​10.​1111/j.​1748-​1716.​2010.​02119.x.
57. Niimi Y, Matsukawa T, Sugiyama Y, Shamsuzzaman AS, Ito H, Sobue
G, et al. Effect of heat stress on muscle sympathetic nerve activity inhumans. J Auton Nerv Syst. 1997;63:61–7. https://​doi.​org/​10.​1016/​s0165-​
1838(96)​00134-8.
58. Keller DM, Cui J, Davis SL, Low DA, Crandall CG. Heat stress enhancesarterial baroreflex control of muscle sympathetic nerve activity via
increased sensitivity of burst gating, not burst area, in humans. J Physiol.
2006;573:445–51. https://​doi.​org/​10.​1113/​jphys​iol.​2006.​108662.
59. Kudo Y, Sasaki M, Kikuchi Y, Sugiyama R, Hasebe M, Ishii N. Effects ofa warm hand bath on the blood flow in the shoulder, skin and deep
body temperature, autonomic nervous activity, and subjective comfort
in healthy women: an experimental cross-over trial. Jpn J Nurs Sci.
2019;16:88–100. https://​doi.​org/​10.​1111/​jjns.​12216.
60. Yamamoto K, Aso Y, Nagata S, Kasugai K, Maeda S. Autonomic, neuroimmunological and psychological responses to wrapped warm
footbaths–a pilot study. Complement Ther Clin Pract. 2008;14:195–203.
https://​doi.​org/​10.​1016/j.​ctcp.​2008.​04.​001.
61. Yamamoto K, Nagata S. Physiological and psychological evaluation of thewrapped warm footbath as a complementary nursing therapy to induce
relaxation in hospitalized patients with incurable cancer: a pilot study.
Cancer Nurs. 2011;34:185–92. https://​doi.​org/​10.​1097/​NCC.​0b013​e3181​
fe4d2d.

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