Journal of
Physiological Anthropology

Yamazaki et al.
Journal of Physiological Anthropology(2023) 42:22
https://doi.org/10.1186/s40101-023-00339-yOpen Access

ORIGINAL ARTICLE

A two‑week exercise intervention
improves cold symptoms and sleep conditionin cold‑sensitive women
Fumio Yamazaki1* , Kana Inoue1, Nanako Ohmi1 and Chika Okimoto1

Abstract
Background We examined whether an aerobic exercise intervention in young women with cold sensitivity
symptoms improves sleep quality and decreases cold complaints. Furthermore, we examined the association
with increased foot skin temperature (Tsk) before falling asleep and decrease in sensitivity to cold in the brain.
Methods We recruited 16 female adult volunteers who had cold sensitivity and were not engaged in daily exercise
training, and they were divided into an exercise group (EXE) and a control group (CON). EXE was given a 2-week
exercise intervention that consisted mainly of walking and jogging. Before and after the intervention, temperaturesensation and body temperature parameters were measured just before bedtime; electroencephalogram measurements were taken during sleep; and subjective sleep surveys, including Oguri-Shirakawa-Azumi (OSA) sleep inventory(middle-aged and aged version) and visual analogue scale (VAS), were conducted immediately after waking up. All
experiments were performed in the winter season.
Results In EXE, overall and foot warmth and comfort increased (p < 0.05) after the 2-week exercise intervention. The
exercise intervention also decreased (p < 0.05) the scores for cold feeling in the fingertips, feet, and toes. In the OSA
sleep inventory, factor IV (refreshing) and factor V (sleep length) were increased (p < 0.05) by the exercise intervention. Subjective sleep quality evaluated by VAS increased (p < 0.05) with exercise intervention. The exercise intervention in EXE shortened middle awake time after sleep onset (p < 0.05) and prolonged deep sleep length (p < 0.05). The
exercise intervention increased (p < 0.05) alpha-wave power before sleep. In CON, all variables remained unchanged
throughout the 2-week control period.
Conclusion Short-term aerobic exercise alleviated peripheral extremity cold sensitivity symptoms and improved subjective sleep quality. Our findings suggest that these improvements were not due to increased Tsk at rest before bedtime but to decreased sensitivity to cold in the brain that was expressed as increased alpha activity.
Keywords Cold symptom, Aerobic exercise, Sleep, Thermal sensation, Skin temperature*Correspondence:
Fumio Yamazaki
fsone@n.ypu.jp
1
Department of Nursing, Faculty of Nursing and Human
Nutrition, Yamaguchi Prefectural University, 6‑2‑1 Sakurabatake,Yamaguchi 753‑0021, Japan

Background
Thermal comfort feeling exhibits inter-individual differences. A cold constitution with higher sensitivity to cold sensations is called “hi-e-sho” in Japanese.
This condition is more common in females than inmales [1–3]. Previous studies have reported that Japanese females experience severe chilliness even undertemperate thermal conditions, especially in the lower
extremities [1–5]. Cold in the lower extremities hinders© The Author(s) 2023. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which
permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to theoriginal author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images orother third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line
to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory
regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of thislicence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.

Yamazaki et al. Journal of Physiological Anthropology(2023) 42:22

the body’s recovery from sleep, which is associated withpoor sleep onset and a decrease in the feeling of soundsleep [6, 7]. Thus, thermal discomfort and insomnia due
to cold sensitivity in daily life reduce quality of life.
A previous study reported that when falling asleep,an increase in skin temperature (Tsk) of the peripheral
extremities and a decrease in metabolic rate decreased
core body temperature [8]. Tsk acts as an input signal
to the sleep regulation system, and increased Tsk shortens sleep onset latency [9]. In people with sensitivity tocold, increasing foot Tsk by heating the lower extremities with a far-infrared heater before bedtime improves
sleep quality and promotes recovery from fatigue [10].
Recently, Yamazaki et al. [11] reported that daily aerobic exercise over a 4-week period was effective in alleviating peripheral cold symptoms in the extremities
and suggested that the involved physiological factors
were reduced cold sensitivity in the brain and increased
cutaneous vasodilation in the feet. These studies suggest that the promotion of blood circulation throughlower extremity heating increases Tsk and has a positive effect on sleep quality by promoting sleep onset;
thus, aerobic interventions, such as walking or jogging,that promote blood circulation in lower extremity muscles may be effective in improving cold and sleep.
Previous studies examining the relationship between
sleep and chronic exercise in healthy adults suggesteda favorable effect of exercise training on sleep [12–16].
Male army soldiers who participated in an 18-weektraining program had improved sleep, particularly
increased slow-wave sleep [15]. On the other hand, inyoung women with no sleep problems, improving aerobic fitness with a 12-week endurance training program
had no effect on sleep [14].
Recently, we reported that electroencephalograms(EEG) of people with sensitivity to cold were characterized by lower alpha-wave power during eye closureat room temperature than noncold sufferers [17]. We
also reported that alpha-wave power was significantly
negatively correlated with the degree of sensitivity tocold, whereas beta-wave power at rest with eyes closed
showed a significant positive correlation [18].
This study aimed to determine the effects of a shortterm aerobic exercise intervention on sleep status andcold sensory function in young women with cold complaints. We also assessed whether the aerobic exercise
intervention improved subjective and objective sleep
quality with a decrease in cold complaints, and whether
this was associated with increased foot Tsk anddecreased cold sensation prior to sleep onset. Furthermore, we examined whether the aerobic exercise intervention increased alpha-wave power and decreased

Page 2 of 10

beta-wave power with a decrease in cold discomfort,
which would be associated with improved sleep.

Methods
Subjects

The subjects were 16 healthy females aged 20–21 who
had sensitivity to cold. The subjects had not regularly
engaged in exercise or sports activities in their daily
lives for at least the past year. The presence or absenceof exercise habits was confirmed by interviewing the
subjects. The inclusion criteria were answering five or
more of a 10-item questionnaire about body coldness
and being aware of sensitivity to cold [19]. The reliability and validity of this questionnaire in screening womenwith cold sensitivity were confirmed in a previous study[20]. According to its inclusion criteria, 35.7% of young
women were judged to have sensitivity to cold, which
was similar to previously reported rates [20]. The subjects were randomly divided into an exercise group (EXE)(n = 8) who received exercise intervention and a control
group (CON) (n = 8) who received no intervention in theorder of their application. Height (EXE, 161.1 ± 4.5; CON,156.3 ± 4.0 cm), weight (52.8 ± 6.2; 49.6 ± 3.8 kg, respectively), and body mass index (20.3 ± 1.5; 20.3 ± 1.0, respectively) were similar between the groups. There were nodifferences between the groups in sleep status in themonth before the intervention using the Japanese version of the Pittsburgh Sleep Quality Index (PSQI-J) (EXE,
5.6 ± 1.5 and CON, 4.9 ± 2.1). None of the subjects had
been diagnosed with insomnia; however, three in EXE
and three in CON had PSQI scores of 6 or higher, whichis considered a possible sleep problem. The daily sleep
habits were also confirmed by interviewing the subjects.
This study was implemented after the approval by the
Bioethics Committee of Yamaguchi Prefectural University (Approval No. 2021–26). Subjects were informed inadvance of the purpose, methods, and risks of the experiment, and written consent was obtained. The experimental results are presented as numbers and have been
managed under confidentiality.
Exercise intervention

EXE received a 2-week exercise intervention. The EXE
group exercised at least 4 days per week during the intervention period, walking at least 5000 steps per day morethan their average number of steps before the intervention. The subjects in EXE were also instructed to perform moderate exercise consisting of at least 15 min of
fast walking or jogging to warm up the body in the walking-based aerobic exercise program. The time period
and place for the exercise were decided by the subjects.
Except for the exercise, the subjects were asked to maintain the same lifestyle during the exercise intervention asYamazaki et al. Journal of Physiological Anthropology(2023) 42:22

before the intervention. In CON, the subjects maintained
the same physical activity level as before the intervention.
Experimental conditions and procedures

EEG, subjective sleep state, thermal sensation, thermal
comfort, Tsk, core body temperature, and room temperature were measured on the 2 days immediately before
and 2 days immediately after the intervention period at
the subject’s home. The variables were measured twice(2 days before and after the intervention) and averaged
over the 2 days. Thermal sensation, thermal comfort,
and temperature variables were measured daily during
the experimental period. An air conditioner was used toadjust the room temperature in the bedroom to 18 °C at
the time of measurement. Subjects were asked to go to
bed between 23:00 and 1:00, to take a bath at least 1 h
before bedtime and to soak for no more than 10 min, toeat at least 3 h before bedtime, not to drink alcohol, andto use the same clothing and bedding on the days examined before and after the intervention period. All experiments were conducted in winter (December to February)
when cold complaints are likely to occur.
Measurements
Physical activity

All subjects wore a physical activity meter with a builtin three-axis accelerometer (MTN-221, ACOS Inc.,
Nagano, Japan) except for bathing time, and their physical activity was continuously recorded from 3 days before
to 14 days during the intervention period and 2 days after
the intervention period (19 days in total). The number ofsteps and amount of physical activity were analyzed using
a dedicated program. On the days when they exercised,
the content of the exercise was recorded on a recording
form.
Tsk, core body temperature, and room temperature

An infrared thermometer (NIR-10, CUSTOM Inc.,Tokyo, Japan) was used for temperature measurement.
By switching the measurement mode, this device caninstantaneously estimate core body temperature (setting mode: oral temperature) from forehead surface temperature, Tsk, and room temperature with a minimum
display temperature of 0.1 °C. The accuracy of measurements was ± 0.3 °C or less. The thermometer was left ina room at 18 °C for at least 10 min for room temperature
calibration. Throughout the experimental period, Tsk of
the left and right toes and the dorsum of the feet, room
temperature, and core body temperature were measured
before entering the bed. Foot Tsk was obtained from theaverage of the left and right Tsk of the toes and dorsumof the feet.

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Thermal sensation and thermal comfort

Thermal sensation and thermal comfort were measured
immediately before bedding throughout the experimental period using a visual analogue scale (VAS) [19]. Subjects were asked to report thermal sensation for the feet
and whole body by marking on a 15-cm line rating scale,
which was labeled “cold” 2.5 cm from the left end and“warm” 2.5 cm from the right end. We instructed the subjects to mark on the scale how strongly they experienced
the sensation of coldness or warmth. In addition, the subjects were allowed to mark the level of thermal sensation
beyond the cold or warm point, if necessary. The scales
were labeled “discomfort” and “comfort” instead of “cold”
and “warm”. Then, the length from the point of discomfort to the marked point was measured as the rating scoreof thermal sensation or thermal comfort, and presented
as a positive value.
A questionnaire survey concerning thermal sensationin 11 regions of the body (arm, abdomen, hand, fingertip, foot, toe tip, neck, shoulder, back, lower back, andbuttocks) was performed immediately before sleep, andbefore and after the intervention. Thermal sensation wasscored using the following scale: “3. feel strong coldness”,“2. feel coldness”, “1. feel coldness a little”, “0. not at all”,“ − 1. feel hotness a little”, “ − 2. feel hotness”, and “ − 3.
feel strong hotness”.
Sleep questionnaires

Subjective sleep quality was evaluated using the OguriShirakawa-Azumi (OSA) sleep inventory (middle-aged
and aged version) immediately after waking up [21]. Thisis a self-reported questionnaire composed of 16 items
each with a 4-point scale. The items are consolidated
into five subscales: factor I “sleepiness on rising”, factor II“initiation and maintenance of sleep”, factor III “frequent
dreaming”, factor IV “refreshing”, and factor V “sleep
length”. The Zi value was calculated with higher values
indicating better sleep quality. Subjects were also asked
to report subjective sleep quality for the exercise intervention using VAS. A 15-cm line rating scale, which waslabeled “did not sleep at all” 2.5 cm from the left end and“slept very well” 2.5 cm from the right end was used. In
both groups, sleep surveys using the OSA sleep questionnaire and VAS were performed twice before and after theintervention.
Sleep EEG

In order to objectively evaluate the state of nocturnal
sleep before and after intervention, EEG was recorded
from just before lights out to the time of waking using
a portable recording system (Sensor ZA-X, Proassist
Ltd., Osaka, Japan) [22]. The EEG sensor consists of aYamazaki et al. Journal of Physiological Anthropology(2023) 42:22

telemeter and receiver of a bioamplifier (sampling rate
128 Hz, frequency response 0.5 to 40 Hz). One channel
is for monitoring EEG with electrodes on the right forehead and left neck (Fp2-M1), and the second channel isfor monitoring electro-oculogram (EOG) and electromyogram with electrodes on the orbit and submental muscles. In all conditions of the experiment, sleep EEG was
performed four times, twice on 2 days before and after
the intervention.
EEG data was automatically analyzed using a sleep
analysis research program (SleepSign-Lite, KISSEICOMTEC Ltd., Nagano, Japan) and the waveforms were
evaluated with EOG by visual inspection, which has
been reported to be highly reliable [22, 23]. Sleep stages
were analyzed by dividing them into waking, rapid eye
movement (REM), light sleep (stages N1 and N2), anddeep sleep (stage N3) according to the AASM manual
for scoring rules Ver. 2.4 [24]. Each sleep stage was carefully checked and corrected by the authors after automatic analysis. The REM sleep phase was determinedfrom eye movements and beta waves. Stages N1 and N2
were grouped together as the light sleep stage: stage N1
was determined as the point at which alpha waves wereless than 50% occupied and theta waves became prominent and stage N2 was determined using spindle waves
or K-complex as indicators. Stage N3 was determined asa high amplitude delta wave occupancy of 20% or more.
In addition to the analysis of sleep stages, power spectral values of alpha waves (8–12 Hz) and beta waves (16–25 Hz) were analyzed using the sleep analysis research
program. The power spectral values were averaged during wakefulness for 2–3 min immediately before sleep
and throughout sleeping time. The values were presented
as percentages of spectral power of frequency band of
1–25 Hz. In addition, intervention-induced changes in
power spectral values were expressed as a percentagechange from the pre-intervention baseline.
Statistical analysis

Means ± SD of all measurement items were calculated.
A repeated two-way analysis of variance was performed
to test the difference between the experimental conditions in each measurement item, and Bonferroni multiple
comparison test was performed as a post hoc test when
the interaction was significant. An unpaired t test wasused to test the difference in pre-intervention means. A
level of less than 5% (p < 0.05) was considered significant.

Results
All subjects completed the experiments. The subjects’diaries on the timing of sleep, bathing, and meals during
the experiment period showed that they were almost thesame in EXE and CON.

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Physical activity

The number of steps and amount of physical activity per day before the intervention was similar between
EXE (3965 ± 1178 steps/day, 291 ± 88 kcal/day) and CON(3581 ± 1617 steps/day, 253 ± 90 kcal/day). The number ofsteps and the amount of physical activity, including fast
walking and jogging, during the intervention in EXE significantly increased (interaction effect, p < 0.05; post hoc,p < 0.05) from the pre-intervention level by 3652 ± 2080
steps/day and 155 ± 71 kcal/day, respectively. The exercise intervention-induced changes did not differ between
the first week (number of steps, + 4105 ± 2713 steps/day;amount of physical activity, + 170 ± 96 kcal/day) and thesecond week (+ 3133 ± 1574 steps/day; + 137 ± 53 kcal/day) of the exercise intervention. No significant changes(+ 269 ± 2169 steps/day, + 28 ± 105 kcal/day) wereobserved in both the number of steps and the amount ofphysical activity during the intervention period from thepre-intervention levels in CON.
Thermal sensation and thermal comfort

Figure 1 shows changes in thermal sensation and thermal comfort associated with exercise intervention. Noneof the parameters showed significant differences in preintervention values between groups. The whole-body andfeet warmth sensations and comfort feelings gradually
increased during the intervention in EXE, whereas neither of these variables changed significantly throughout
the intervention period in CON. Both the whole-bodyand feet warmth sensations and comfort feelings werehigher (interaction effect, p < 0.05; post hoc, p < 0.05) in
EXE than CON at the second week of intervention andthe post-intervention periods.
Figure 2 shows the cold sensations by body part before
and after the interventions by group. The sensations ofcoldness in the fingertips, feet, and toes decreased (interaction effect, p < 0.05; post hoc, p < 0.05) with the exercise
intervention, and EXE had lower (post hoc, p < 0.05) coldness in the feet and toes after the intervention than CON.
On the other hand, the exercise intervention did not alter
the sensations of coldness in the arms, abdomen, hands,
neck, shoulders, back, hips, and buttocks. In CON, thethermal sensations at all sites remained unchanged
throughout the time-controlled intervention period.
Foot Tsk and estimated core body temperature

Before the intervention period, no significant differences were found between groups in foot Tsk (EXE,
24.5 ± 3.0 °C; CON, 25.4 ± 3.2 °C) and estimated core bodytemperature (EXE, 36.6 ± 0.2 °C; CON, 36.3 ± 0.3 °C). No
significant changes in foot Tsk and estimated core bodytemperature were observed throughout the intervention
period in either group. Room temperature at time of bodyYamazaki et al. Journal of Physiological Anthropology(2023) 42:22

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Fig. 1 Changes in thermal sensation and thermal comfort in the whole-body and feet with 2-week exercise or time-controlled interventions.
*p < 0.05 vs. before, †p < 0.05 vs. control

Fig. 2 Changes in cold feeling in each region with 2-week exercise or time-controlled interventions. *p < 0.05 vs. before, †p < 0.05 vs. control grouptemperature measurement was maintained at a constantlevel throughout the experimental period. No significant
differences were found between groups in room temperature (EXE, 18.9 ± 1.5 °C; CON, 18.3 ± 3.0 °C).

Sleep questionnaires and sleep EEG

The evaluation results of sleep conditions using the
OSA Sleep Inventory are shown in Table 1. There
were no significant differences between groups in theYamazaki et al. Journal of Physiological Anthropology(2023) 42:22

Table 1 Evaluation of subjective sleep quality using the Oguri–
Shirakawa–Azumi sleep inventory, middle-aged and aged
version, before and after interventions in the exercise and control
groupsExerciseControl

BeforeAfter

BeforeAfter

Factor I (sleepinesson rising)

51.5 ± 6.6

55.8 ± 5.0

45.7 ± 5.7

44.3 ± 6.1

Factor II (initiationand maintenanceof sleep)42.9 ± 13.4 51.7 ± 12.1 41.0 ± 8.7

44.1 ± 11.2

Factor III (frequent
dreaming)

49.4 ± 14.4 54.7 ± 5.4

Factor IV (refreshing)

43.6 ± 14.4 56.2 ± 7.8* 46.9 ± 9.5

46.1 ± 8.5

Factor V (sleep length)44.0 ± 6.6

47.0 ± 9.1*

43.4 ± 12.4 43.9 ± 14.5

58.8 ± 9.6* 51.7 ± 8.6

p < 0.05 vs. before

Fig. 3 Changes in subjective evaluations of quality of sleep
with 2-week exercise or time-controlled intervention. *p < 0.05 vs.
before intervention

pre-intervention values for any of the five factors. In
EXE, the intervention increased (interaction effect,p < 0.05; post hoc, p < 0.05) factor IV (refreshing) andfactor V (sleep length); however, no significant changes
were observed in either factor in CON.
Figure 3 shows sleep quality evaluated using VAS
before and after the interventions. There was no significant difference between groups in pre-intervention
sleep quality. The intervention increased (interaction
effect, p < 0.01; post hoc, p < 0.0001) sleep quality in
EXE (+ 4.3 ± 2.9), whereas no significant difference wasobserved in CON before and after the intervention
period (− 0.2 ± 1.3). Post-intervention sleep quality
tended to be higher in EXE than in CON (post hoc,
p = 0.05).

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There was no difference between the groups in the
pre-intervention values for any of the sleep variables byanalyzing EEG (Table 2). Analysis of sleep EEG revealed
that the exercise intervention shortened (interaction
effect, p < 0.05; post hoc, p < 0.05) wake after sleep onset
time and prolonged (interaction effect, p < 0.05; post hoc,p < 0.05) deep sleep time. No other sleep variables weresignificantly different before and after the intervention
and between groups. In addition, bedtime was not different before (EXE, 0:15 ± 0:31; CON, 0:03 ± 0:49) and after(EXE, 0:27 ± 0:35; CON, 23:45 ± 0:49) the intervention inboth groups.
The exercise intervention increased (interaction effect,p < 0.05; post hoc, p < 0.05) alpha-wave power during presleep arousal by 71.1 ± 48.4% from pre-intervention values but did not change the average value (− 2.0 ± 25.6%)
during sleep (Table 3). There was no significant difference
in alpha-wave power before and after the time-controlledintervention period in the CON group. Neither betawave power on awakening before falling asleep nor the
average values during sleep were altered by the exercise
intervention.

Discussion
This is the first study to investigate the effects of an
aerobic exercise intervention on sleep state and thermosensory function in people with sensitivity to cold.
Short-term aerobic exercise, such as walking and jogging,alleviated coldness of the extremities in the normal temperature environment, which was considered to be due tothe decrease in cold sensation. The aerobic exercise intervention improved subjective sleep quality, which wasthought to be associated with shorter wakefulness andlonger deep sleep.
Thermal sensation and comfort feeling

Previous studies reported reduced effects of coldness in
extremities in young women by 4-week aerobic exercise
intervention [11] and by 3-month mixed aerobic andresistance training [25]. In the present study, thermal sensation and comfort of the whole body and feet increased
gradually during the exercise intervention, and both values significantly increased 2 weeks after the intervention
compared to the pre-intervention values. As there was no
significant increase in comfort feelings during the firstweek of the exercise intervention, our findings suggestthat 1 week is too short a time period to reduce thermal
discomfort in people with sensitivity to cold under theexperimental condition.
In prior studies, the relationship between sensitivity
to cold and exercise habits was examined by comparing
coldness between those with and without exercise habits.
An internet survey of 6729 patients reported that thoseYamazaki et al. Journal of Physiological Anthropology(2023) 42:22

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Table 2 Analysis of sleep variables using EEG and EOG recording systems before and after interventions in the exercise and control
groupsExerciseControl

BeforeAfter

BeforeAfterTime in bed, min402.4 ± 50.6

431.6 ± 83.5

399.1 ± 77.1

424.8 ± 56.9

Total sleep time, min384.5 ± 53.0

421.5 ± 82.3

388.9 ± 78.4

413.3 ± 56.5

Wake after sleep onset, min10.3 ± 9.7

2.4 ± 3.3 *5.9 ± 5.7

3.6 ± 3.6

Sleep latency, min

6.1 ± 6.4

6.9 ± 5.6

5.2 ± 1.8

6.0 ± 3.8

Wake total time, min12.6 ± 10.7

10.1 ± 5.7

15.8 ± 12.6

14.9 ± 10.3

REM total time, min

66.8 ± 14.1

78.4 ± 8.9

64.0 ± 17.0

80.5 ± 21.2

NREM total time, min

317.2 ± 41.8

343.0 ± 78.7

324.9 ± 69.7

332.9 ± 47.9

Light total time (stages N1 + N2), min263.2 ± 33.1

258.8 ± 62.9

273.0 ± 64.9

276.6 ± 42.4

Deeply total time (stage N3), min54.1 ± 16.9

84.3 ± 22.2 *#51.8 ± 29.2

56.3 ± 36.5

Sleep efficiency, %95.4 ± 3.9

97.6 ± 1.3

96.4 ± 2.9

97.3 ± 1.1

EEG electroencephalography, EOG electro-oculography, REM rapid eye movement, NREM non-REM*

p < 0.05 vs. before#

p < 0.05 vs. control

Table 3 Changes in spectral power of alpha- and beta-bands
before and after interventions in the exercise and control groups
Exercise
BeforeControl
After

BeforeAfterAlpha-wave power
before sleep, %7.9 ± 6.3 12.5 ± 10.3 * 7.3 ± 4.5 7.0 ± 3.9

Beta-wave power
before sleep, %2.5 ± 2.0 3.8 ± 3.0

1.6 ± 0.9 1.9 ± 1.2

Alpha-wave power during sleep, %4.4 ± 0.9 4.3 ± 1.4

4.3 ± 2.5 4.4 ± 2.2

Beta-wave power during sleep, %1.5 ± 1.0 1.4 ± 1.0

1.2 ± 0.7 1.2 ± 0.9*

p < 0.05 vs. before

who were less physically active were more likely to beaware of cold [26]. In a study of 212 female college students, Tsuyushige et al. [27] reported that cold symptoms
were milder in those who performed physical exercise ona daily basis than in those with no exercise habits. Theseprior studies were cross-sectional studies that comparedthose with and without exercise habits. The present study
was a randomized controlled trial intervention study thatfound that a 2-week short-term exercise intervention was
effective in reducing coldness in women with sensitivity
to cold.
When changes in coldness were examined by bodypart (Fig. 2), coldness in the fingertips, feet, and toes
decreased with the exercise intervention, and the EXE
group had significantly lower coldness in their feet andtoes after the intervention than the CON group. We
found that aerobic exercise was effective in relieving

cold symptoms in the peripheral extremities, but not in
the trunk. These findings support a previous study thatreported that walking exercise decreased cold sensitivity in the brain and increased the cutaneous vasodilator
response in the feet [11]. As the peripheral extremities
are more susceptible to cold prior to intervention, theeffect of exercise on alleviating cold symptoms may be
more readily apparent than the trunk.
We hypothesized that an increased core temperature
and an enhanced blood flow in the skin during exercise
would alleviate cold symptoms. In a previous study ofcold-sensitive women, we reported that (1) the discomfort feeling during hand cooling was decreased by
the increase in core body temperature associated with15 min of leg exercise, and (2) the pattern of changes
in cold sensation after exercise varied due to differences in Tsk increase in different body regions [28].
Thus, a single bout of exercise produced a transient
decrease in thermal discomfort, both systemically due
to an increase in core body temperature and regionally
due to different increases in Tsk by part; however, once
body temperature was restored to pre-exercise levels,
the warm and cold sensations also returned to normal. The 2-week exercise intervention did not change
the estimated core body temperature and foot Tsk during rest at normal resting temperatures. These findings
were consistent with a previous study in which bodytemperature was measured by thermistor thermometer
before and after a 4-week aerobic exercise intervention [11]. Thus, there were significant changes in thermal sensation and discomfort that were considered tobe due to decreased sensitivity to cold and discomfort
under normal temperature conditions.

Yamazaki et al. Journal of Physiological Anthropology(2023) 42:22

Changes in sleep status

In the OSA Sleep Inventory used in this study, factor IV(refreshing) and factor V (sleep length) increased with
exercise intervention. The exercise intervention also
increased sleep quality in subjective sleep assessment
using VAS. The effectiveness of physical activity as oneof the preventive measures for insomnia and sleep disorders has been reported in previous studies [29, 30].
Inoue et al. [31] conducted a 2-year longitudinal study of3679 community-dwelling elderly people to examine theassociation between exercise habits and sleep, and foundthat those who exercised at least 5 days per week wereless likely to experience mid-wake, one of the symptoms
of insomnia, than those who did not exercise, indicatingthat habitual exercise may help control insomnia symptoms. Kubitz et al. [32] reported in a meta-analysis thatboth transient and habitual exercise increased deep sleep
and total sleep time in healthy subjects with less midwaking incidents. The present study found that the exercise intervention in EXE resulted in shorter mid-awake
times and longer deep sleep times without changing total
sleep time (Table 2). Thus, participants with cold sensitivity in EXE were able to continue to sleep deeply atnight to recover from the mild fatigue caused by physical activity, which led to a sense of recovery from fatigue
and longer subjective sleep duration, which in turn led tohigher subjective sleep quality.
Since there was no difference in pre-bedtime foot Tsk
before and after the intervention in either group, theimprovement in sleep quality due to the exercise intervention was not related to the increase in foot temperature. On the other hand, we found a decreased sensitivity
to cold in the peripheral extremities before falling asleep
without a change in body temperature. Thus, the decreasein thermal discomfort associated with decreased cold
sensitivity may have contributed to the improvement insleep quality due to the exercise intervention.
Alpha activity in EEG is increased during relaxing andeye-closed resting, and is decreased as a result of aging
and pathological states [33–35]. In healthy young adults,
the degree of cold sensitivity is significantly negatively
correlated with values of alpha-wave power during eyeclosed resting under normal temperature conditions,whereas it is significantly positively correlated with values of beta-wave power [18]. In subjects with sensitivity
to cold, a previous study reported that the spectral powerof alpha-waves (ranging from 8 to 10 Hz) was lower
than normal control subjects during normothermia andwhole-body cooling in the daytime [36]. In that study,
since whole-body cooling and rewarming did not acutely
change alpha-wave power in both subject groups, it may
take a certain period of time for suppression of thermal
discomfort associated with decreased cold sensation

Page 8 of 10

in the brain to occur, characterized by increased alphaactivity during eye-closed resting. The present study
showed for the first time that the alleviation of pre-sleep
coldness by aerobic exercise practice for 2 weeks in young
women with sensitivity to cold occurred with an increase
in alpha-wave power, but not with a suppression of betawave power. Interventions using yoga exercise [37] andbody-mind training [38] also increase physical and mental relaxation, as indicated by decreased serum cortisoland state anxiety and increased alpha waves. These findings suggest that there is a relationship between lower
alpha-wave power before sleep onset and cold discomfort. Thus, the thermally induced relaxing effects of light
exercise in the daytime may decrease chills and insomnia
in the nighttime.
Some considerations are required to interpret theresults in this study. First, in the present study, we used
an infrared thermometer for temperature measurement.
In previous studies, an infrared forehead skin thermometer for core temperature measurements did not provide
reliable values of body temperature during periods ofincreasing body temperature [39] and after cold provocation [40]. Thus, previous studies suggest that thermometry using an infrared thermometer should be used underthermally steady state [39, 41], such as resting state in aconstant room temperature; thus, we used these conditions in the present study. One-week endurance training
for 2 h per day in a hot environment reduces core bodytemperature by 0.1–0.5 °C [42], whereas a previous study
reported that 4-week aerobic exercise training at lightintensity in a normal temperature environment did notalter core body temperature during rest before sleep [11].
These findings suggest that the alleviation in cold sensedue to aerobic exercise intervention in the cold-sensitive
subjects observed in the present study was not due toan increase in resting body temperature, but rather to adecrease in cold sensitivity at normothermia.
Second, the lifestyle behaviors of subjects were notas strictly controlled as a laboratory sleep experiment.
In the present study, we dictated subjects to a bedtime
range, timing and method of bathing, and eating as well
as monitoring their physical activities. Since the experimental conditions, excluding physical activity, in EXE
were similar to the subjects in CON, the response differences between groups in thermal sensation and sleep
before and after the intervention period were considered
to be due to the effect of exercise itself.
Finally, it was not possible to quantify how much discomfort associated with cold feet before falling asleep
was involved in the improvement of sleep quality by
aerobic exercise. Thus, it will be necessary to compare the effects of aerobic exercise on sleep and cold
sensation before falling asleep, and alpha-wave powerYamazaki et al. Journal of Physiological Anthropology(2023) 42:22

in people who do not have sensitivity to cold. Further
experiments are needed to investigate whether there isa cutoff value for the percentage of alpha-wave power
between cold-sensitive and normal young women.
In conclusion, in cold-sensitive young women, a2-week aerobic exercise intervention centered on walking and jogging alleviated coldness in the peripheral
extremities and improved subjective sleep quality withshorter mid-awake time and longer deep sleep time.
These improvements were not due to increased Tsk
before sleeping but to decreased discomfort to cold,
which was presented as increased alpha-wave power.
Abbreviations
Tsk	Skin temperature
EEG	Electroencephalogram
EOG	Electro-oculogram
EXE	Exercise groupCON	Control group
OSA	Oguri-Shirakawa-Azumi
VAS	Visual analogue scale
PSQI-J	Japanese version of the Pittsburgh Sleep Quality Index
REM	Rapid eye movement
NREM	Non-rapid eye movement
Acknowledgements
The authors are grateful to the subjects for their cooperation in this study. The
authors thank Medical English Service (www.​med-​engli​sh.​com) for English
language editing.
Authors’ contributions
FY developed the study concept and was involved in the design of the study.
KI, NO, and CO acquired and analyzed the data. All authors contributed to theinterpretation of data. FY prepared and contributed to drafting the manuscript. All authors read and approved the final manuscript.
Funding
This study was supported by JSPS KAKENHI Grant Number JP22K11682 andYamaguchi Prefectural University Joint Research Promotion Program.
Availability of data and materials
The datasets generated during the current study are not publicly available but
are available from the corresponding author on reasonable request.

Declarations
Ethics approval and consent to participate
This study was conducted in accordance with the principles outlined in the
Declaration of Helsinki and was approved by the Yamaguchi Prefectural University Bioethics Committee (approval number: 2021 − 26). Informed consent
to participate in the study and for the publication of this report was obtained
from all participants. The authors confirm that there is no identifying information concerning the participants in the manuscript and that the information
has been fully anonymized. Furthermore, the authors affirm that all mandatory
health and safety procedures were followed in the course of conducting any
experimental work reported in this paper.
Consent for publication
Not applicable.
Competing interests
The authors declare that they have no competing interests.

Page 9 of 10

Received: 28 April 2023 Accepted: 19 September 2023

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