Seasonal changes in objectively measured sedentary behavior and physical activity in Japanese primary school children
Tanaka et al. BMC Public Health
Seasonal changes in objectively measured sedentary behavior and physical activity in Japanese primary school children
Chiaki Tanaka 0
John J. Reilly 2
Maki Tanaka 1
Shigeho Tanaka 3
0 Division of Integrated Sciences, J. F. Oberlin University , 3758 Tokiwamachi, Machida, Tokyo 194-0294 , Japan
1 Department of Child Education, Kyoto Seibo College , 1 Taya-cho, Fukakusa, Fushimi-ku, Kyoto 612-0878 , Japan
2 Physical Activity for Health Group, School of Psychological Sciences and Health, University of Strathclyde , 50 George Street, Glasgow G1 1QE, Scotland , UK
3 Department of Nutritional Science, National Institute of Health and Nutrition, National Institutes of Biomedical Innovation, Health and Nutrition, 1-23-1 Toyama, Shinjuku-ku, Tokyo 162-8636 , Japan
Background: The recent prevalence of obesity in Japanese children is much higher compared to 1980. The present study compared daily sedentary behavior (SB) and physical activity (PA) between the school year and summer vacation in Japanese primary school children. Methods: Participants were 98 Japanese boys (8.9 ± 1.8 years at baseline) and 111 girls (9.1 ± 1.8 years). SB and PA were measured in May (school term) and July/August (summer vacation), 2011. SB and PA were assessed using a triaxial accelerometer (Active style Pro HJA-350IT, Omron Healthcare) for 7 consecutive days. The average number of minutes spent in SB (no more than 1.5 metabolic equivalents (METs)), light intensity activity (LPA; more than 1.5 to less than 3.0 METs) and moderate-to-vigorous physical activity (MVPA; 3.0 METs or more), and step counts were calculated for each individual. Moreover, the determinants/moderators of changes in SB and PA were examined. Results: Daily SB was significantly higher in the summer vacation than in the school year for both boys and girls (p < 0.05). Ambulatory and total LPA and MVPA, non-ambulatory LPA and step counts were lower in summer vacation in both genders (p < 0.001). Moreover, non-ambulatory MVPA was significantly lower in the summer vacation than in the school year for girls (p < 0.001). The decrease in non-ambulatory MVPA in boys and increase in SB in girls were significantly lower in those who participated in sports compared to those who did not (p < 0.040 or p < 0.033). The change in SB for boys was significantly associated with having a TV in the bedroom (p < 0.022). Conclusions: These findings show that primary school children in Japan are less active in the summer vacation, as indicated by both higher SB and lower LPA and ambulatory MVPA in both genders. Moreover, the seasonal change in non-ambulatory MVPA for Japanese children was affected by gender. This study also suggests that sports participation and bedroom TV ownership may moderate seasonal changes in PA and SB. The results emphasize the need to take summer vacation into account when planning interventions aimed at decreasing SB or increasing PA in Japanese children.
Activity pattern; Summer vacation; Accelerometry
The recent prevalence of obesity in Japanese children is
much higher compared to 1980 [
]. Previous studies
reported that overweight and obese Japanese children
experienced greater weight gain during the summer
vacations than during the school months [
maximum temperature of over 35 degrees in summer is
typical in Japan every year . Periods of high
temperatures in summer may reduce the likelihood of children
being physically active (PA) or may increase sedentary
behavior (SB). Recently, Lewis et al. (2016) reported that
daily maximum temperature was significantly associated
with moderate-to-vigorous PA (MVPA) and SB time in
primary school-aged children in Australia and Canada
]. Moreover, children’s activity levels tend to be lower
on weekdays compared to weekend days in the school
]. Identification of specific seasons that are
characterized by low PA levels and/or high periods of SB
is important for the design future public health
interventions aimed at promoting PA and reducing SB, but
summer vacation changes in PA and SB in Japanese children
are poorly understood at present.
SB is distinct from PA [
], and it is possible for an
individual to spend an excessive proportion of time in
SB, even if they meet PA guidelines [
]. A recent review
suggested that seasonal changes in SB in childhood are
not well-established [
]. We have identified only two
previous studies that examined seasonal changes in both
objectively measured PA and SB in children [
the results of these two studies were not consistent.
Seasonality in PA and SB can be affected by many factors,
including climate, the school education system, and the
evaluation methodology of PA and SB. Moreover, it
remains unclear to what extent objectively measured
habitual PA and SB changes longitudinally between the
school year and summer vacation, and whether any
changes are modified by gender in children. Our
previous study  showed that Japanese preschool children
spend more non-ambulatory activity than ambulatory
activity during moderate intensity activity. The present
study sought to examine longitudinal changes in habitual
PA and SB measured objectively, in the school year and
summer vacation in primary school aged Japanese
children. Moreover, the determinants/moderators of
objectively measured changes in SB and PA were examined
(the influence of gender, sports participation, home
environment and psychological aspects were considered).
Our convenience sample included 209 Japanese primary
children from 4 public primary schools in urban areas in
Tokyo and Kyoto. Participants were invited to
participate by leaflets, such as a newsletter, at their school.
Informed consent was obtained from all participants and
their parents, and the Ethical Committee of J. F. Oberlin
University approved the study protocol (No. 10007).
Baseline data of anthropometric measurements, SB and
PA were collected in May 2011 during the school year.
The average temperatures in the school period and
summer vacation were 19.3 (standard deviation (SD) 2.4)
degrees and 27.3 (SD 2.5) degrees, the maximum
temperatures were 24.5 (SD 3.8) degrees and 31.6 (SD
3.3) degrees, and the average humidities were 59.9 (SD
12.0) % and 68.7 (SD 6.3) %. All temperature and
humidity data in summer vacation were higher than those
of the school term in spring [
Objective measurement of sedentary behavior and physical activity
SB and PA in free-living conditions were evaluated with
a triaxial accelerometer (Active style Pro HJA-350IT,
Omron Healthcare, Kyoto), 74 × 46 × 34 mm and 60 g
including batteries. Participants wore the accelerometer
on the left side of the waist for both the school year and
the summer vacation measurements. The device is
described in detail elsewhere [
]. In brief, the synthetic
acceleration of three axes using signals before and after
high-pass filtering was calculated, and we obtained the
ratio of the unfiltered to filtered synthetic acceleration.
The average of the absolute value of the filtered
acceleration from 10 s epochs was used to estimate PA
intensity. Our previous study reported the algorithm for the
classification of non-ambulatory activities such as
playing games, throwing a ball, cleaning and clearing away
and ambulatory activities such as walking and running
by the unfiltered/filtered acceleration ratio [
Discrimination with the ratio provided the highest rate of
correct discrimination, 99.8 % when the value of the ratio
was 1.12. The percentage of correct discrimination with
the ratio used by the Active style Pro (1.16) was
comparable (98.7 %). Moreover, strong linear relationships were
found for both non-ambulatory (metabolic equivalents
(METs) = 0.0136 synthetic acceleration +1.220, R2 = 0.772)
and ambulatory (METs = 0.0056 synthetic acceleration
+0.944, R2 = 0.880) activities, except for climbing up and
down. In fact, our previous study showed that
nonambulatory time as measured by triaxial accelerometry
was much longer than ambulatory time during
mediumintensity PA in free-living Japanese preschool children
]. Our previous studies of adults showed that the
relative contributions of non-ambulatory MVPA time and
ambulatory MVPA time as measured by the Active style
Pro depended on sex, age and occupation [
counts were also measured, because they are used widely
in many studies and investigations to objectively evaluate
PA. When the Active style Pro is used for the evaluation
of SB and PA in primary school children, the values of
METs are overestimated , because the predictive
equations were established for adults. Therefore, we used the
following conversion equations for primary school
children obtained from the results of Hikihara et al. [
The ambulatory activities : 0:6237 the value of MET by
the Active style Pro
The non‐ambulatory activities
the value of MET by the Active style Pro
The duration of ambulatory or non-ambulatory
activity in each intensity were calculated. Moreover, total PA
in each intensity was obtained as a sum of ambulatory
time and non-ambulatory time.
SB and PA were monitored continuously for 7 days or
more. In the summer vacation, some participants
couldn’t return the device on the same day. Therefore,
participants were requested to remove the device after
7 days or more from the beginning of the measurement.
Participants were requested to wear the device at all
times, except under special circumstances, such as
dressing, bathing and swimming. Non-wear time was
defined as periods with over 1 h of consecutive zero
counts. In fact, many participants wore the
accelerometer during sleep. Because sleep and sedentary time
cannot be discriminated, we analyzed data collected
between 7:00 and 21:00 to exclude sleep time. We
included days with more than 10 h (600 min) of wearing
time per day. The accelerometry data reduction criteria
used in the present study were similar to those in other
]. Penpraze et al. [
] indicated that the
reliability of PA monitoring was nearly the same from 3 to
10 days in young children. Cliff et al. [
] suggested at
least 3 days of monitoring in young children was
required for reliable measures. Participants with data from
at least 2 weekdays and at least 1 weekend day in the
school years and at least 3 days in the summer vacation
were included in the analysis. Participants attended
classes at their school on weekdays in the school year and
lived freely on weekend. On the other hand, they went
to their school on neither weekdays nor weekend days
in the summer vacation. Thus, during the summer
vacation, the minimal number of days was set at 3 days
without differentiation between weekend and weekdays.
Potential determinants/moderators of changes in sedentary time and physical activity
The present study considered potential moderators of
seasonal changes using a socio-ecological model as
]. Some items like demographic and
biological, psychological and behavioral domains have
been considered in public health surveillance with
physical fitness in children and youth in Japan, in surveys
carried out by the Ministry of Education, Culture,
Sports, Science and Technology, by the Japan Sports
Agency, by a national survey of Japanese Society of
School Health, and finally by a survey carried out by
Sasagawa sports foundation [
1, 26, 27
]. We included as
potential moderators those variables which were
considered important in Japan and which can be measured
using standard questionnaires used widely in Japanese
public health surveillance.
The variables studied for each domain were:
a. a demographic and biological domain: gender; age.
b. a psychological domain: body image, perception of
sports, health and activity.
c. a behavioral domain: attendance at sports clubs.
d. a physical environmental domain: television set in
The data were collected from participants who
answered with their parents. Only the psychological
domain was collected by personal interview for children or
questionnaire for their parents, respectively.
We measured participants’ body height and body weight
to the nearest 0.1 cm and 0.1 kg, respectively. Height
and body weight was measured without shoes, but with
clothing. Net body weight was calculated as the
weight of clothing subtracted from the measured body
weight. We measured the anthropometric
measurements once at each season according to the method
described by School Health Survey of the Ministry of
Education, Culture, Sports, Science and Technology
]. We calculated body mass index (BMI) as weight
in kilograms divided by height in meters squared.
Weight status was classified as normal weight,
overweight/obese, or thin using Japanese cut-offs for
weight status that were established based on national
reference data for Japanese children [
weight was calculated as follows:
Relative weight = [measured body weight (kg) –
standard weight for gender, age, and height (kg)]/ standard
weight for gender, age, and height (kg) × 100 (%)
※ standard weight for gender, age, and height (kg) = a
× measured height (cm) – b
a and b are gender- and age-specific.
The cut-offs of weight status are as follows: Overweight/
Obesity combined: ≥ + 120 %, Normal weight: −120 +
120 % and Thinness: ≤ − 120 %.
The time spent at SB and each PA intensity per day
was calculated by METs: average number of weekday
and weekend minutes spent in SB (METs ≤ 1.5), LPA
(1.5 < METs < 3.0), MVPA (3.0 ≤ METs), moderate PA
(MPA) (3.0 ≤ METs <5.9) were calculated for each
individual, and then average weekly values were
calculated. For the data in the school year, average values
were calculated by weighting for 5 weekdays and 2
weekend days (Weighted data = (average for
weekdays × 5) + (average for weekend days × 2) / 7). The
PA assessed by the accelerometer is presented as: (1)
ambulatory activity or non-ambulatory activity in each
intensity category (LPA, MVPA and MPA); and (2)
number of steps registered per day. Values of SB and
PA were adjusted by baseline and follow-up wear
The initial sample comprised 356 participants. Due to
missing data (no consent to take part/unable to trace for
follow-up measures [n = 46], no accelerometer data at
baseline or follow-up [n = 94], no height/weight data at
follow-up [n = 7]), our longitudinal sample comprised
data from 209 children. A few questions weren’t
answered completely by children or parents. Therefore,
there were missing data in the analysis of the
determinants/moderators of objectively measured changes in SB
and PA. Numbers of each analysis were described in
each Table. There was no significant difference between
the relative weight at baseline of the participants and
children who dropped out (boys: p = 0.101, girls: p =
0.391). The follow-up data were collected at the end of
July or middle of August during the summer vacation
(mean interval, 64 (SD 10) days).
A paired sample t-test was used to compare
baseline and follow-up measurements, for each gender.
The associations between change in SB or PA and
determinants variables at baseline were analyzed by
analysis of covariance (ANCOVA) adjusted for
school, follow-up period, age, SB or PA at baseline.
Moreover, when each first analysis was signifıcant, in
the fınal stage of the analysis, SB or PA variables
were also adjusted in the same model. When the
number of each answer was below 10 participants,
the category was added to the next other category.
Results are shown as means ± SD. Statistical analysis
was performed with IBM SPSS statistics 20.0 for
Windows (IBM Co., Tokyo, Japan). P < 0.05 was
Characteristics of study participants
The characteristics of study participants are presented
in Table 1. Average age for boys and girls was 8.9
(SD 1.8) years old and 9.1 (SD 1.8) years old at
baseline, respectively. Five percent of boys and 6
percent of girls were overweight/obese. The duration of
accelerometry was much greater than the minimum
criteria specified (at least 3 days and 10 h), with an
average of 7.4 days and 13.3 h for boys, and 8.1 days
and 12.8 h for girls at baseline and 7.2 days and
13.4 h for boys, and 8.8 days and 12.8 h for girls at
follow-up, respectively. The percentage of the sample
which had 2 weekdays and 1 weekend day data was
95 % for boys and 93 % for girls at follow-up,
respectively. The results of psychological, behavioral
and physical environmental domains are shown in
Time spent at different activity intensity levels for
ambulatory and non-ambulatory activity and total
time, and step counts are shown in Table 2. Daily SB
significantly increased from baseline to follow-up for
boys (from a mean of 341 to 354 min) and girls (from a
mean of 357 to 371 min). Ambulatory and total time
in LPA, MVPA and MPA, non-ambulatory in LPA and
step counts for boys significantly decreased from
baseline to follow-up (e.g., from 76 to 65 min for total
MVPA). Ambulatory, non-ambulatory and total time
in LPA, MVPA and MPA, and step counts for girls
significantly decreased from baseline to follow-up (e.g.,
from 61 minutes to 51 min for total MVPA).
Determinants/moderators of changes in sedentary behavior and physical activity
The decrease in non-ambulatory MVPA was significantly
lower for boys who participated in sports, both for the
school periods and summer vacation, than those who
did not (Table 3). The increase in SB, and decrease in
ambulatory LPA and step counts were significantly
lower for girls who participated in sports than those
who did not (Table 3). The change in SB for boys
was significantly associated with bedroom television
(TV) ownership (Table 4), with significantly more
adverse change in SB in those who had a TV in the
The perception of sports and body image by boys,
health perception by boys’ parents, activity and sports
perceptions by girls, and the sports perceptions and
body image by girls’ parents were associated with change
in SB and PAs, respectively (see attached Additional files
1 and 2: Table S1a, Table S1b). The decrease in PA was
significantly lower in boys with positive perceptions of
sports than those who had negative perceptions. The
decrease in PA was significantly lower in boys with
negative perceptions of their child’s health than those who
had positive perceptions by their parents. The decrease
in PA in non-ambulatory activity was significantly
higher in boys with overweight or obese perception
than those who wanted to maintain the present body.
The decrease in MPA was significantly lower in girls
or their parents with positive perceptions of sports
than those who had negative perceptions. The
decrease in MPA in ambulatory activity was significantly
lower in girls with overweight or obese perception
than those who wanted to maintain the present body
by their parents.
This study examined the longitudinal changes of
objectively evaluated SB and PA, between the school
year and summer vacation in Japanese primary school
children. To our knowledge, no previous study has
addressed changes in objectively-evaluated sedentary
time and physically activity with discrimination
between ambulatory and non-ambulatory PA in
elementary school children at the school year and summer
vacation. As we hypothesized, SB increased and PA
decreased significantly in the summer vacation in
both genders. Adverse changes in the summer
vacation were moderated by membership of sports clubs,
not having a TV in the bedroom, positive perceptions
of sports for boys or positive perceptions of sports
and activity for girls and their parents and negative
perception of boy’s health for their parents. In detail,
there were significant decreases in ambulatory and
total LPA, MVPA, MPA and step counts in the
summer vacation in both genders, while non-ambulatory
Abbreviations: LPA light physical activity, MVPA moderte-to-vigorous physical activity, MPA moderate physical activity, SD standard deviation, CI confidence interval
MVPA and MPA were significantly lower in the
summer vacation just in girls.
A previous review [
] described the influence of
season on accelerometer-determined measures of SB and
PA in children. Significant seasonal variation in PA was
reported in all UK studies, being highest in summer and
lowest in winter. In non-UK studies (other European
countries, USA and New Zealand) significant seasonal
variation in PA was not found, and findings were
inconclusive for SB [
]. Recently, Lewis et al. reported that
daily maximum temperature was significantly associated
with MVPA and SB time in Australia and Canada.
MVPA and SB time appear to be optimal when the
maximum temperature ranges between 20 and 25 °C in both
]. In the present study, the maximum
temperatures were 24.5 (SD 3.8) degree in the school year
and 31.6 (SD 3.3) degree in summer vacation. Moreover,
the average humidities in the summer vacation (68.7
(SD 6.3) %) were also higher than in the school year
(59.9 (SD 12.0) %) [
]. Thus, weather characteristics
might affect seasonal change of PA and SB in Japan, as
in Australia and Canada. Moreover, another review [
identified only two previous studies that examined
change in total energy expenditure or objectively
measured SB and PA between the school year and summer
vacation in children. Zinkel et al. [
] demonstrated a
seasonal pattern in total energy expenditure by doubly
labeled water method in a cross-sectional study of
6-to13 year old children in the greater Washington DC area,
total energy expenditure was higher during the school
year. However, after statistically controlling for fat free
mass, total energy expenditure was no longer
significantly seasonal. McCue et al. [
] reported that SB
increased and LPA and MPA declined (but not MVPA or
vigorous PA) by accelerometry in longitudinal designed
study for 9-to-11 year old Minnesota children. The
present study findings are similar to the results of
McCue et al.’s study on the change in SB, LPA and
MPA. However, MVPA changes in the present study
were not similar: one of the reasons might be the
difference in weather. Hot and humid weather during the
summer vacation both in Tokyo and Kyoto may have
kept participants from going outside, resulting in
decreased PA and increased SB. In addition,
accelerometry used in the present study and that in the
previous studies were quite different. The Active style Pro
can accurately discriminate ambulatory and
nonambulatory PA, while ActiGraph with the cut point
method tends to underestimate non-ambulatory PA
]. Another possible reason for differences between
studies is that McCue et al. [
] studied a small
sample (19 boys and 11 girls).
There appears to be even less comparable literature
on the determinants or moderators of seasonal
changes in PA and SB in children. Rowlands et al.
] considered the influence of gender on seasonal
variation in PA in a longitudinal study of 64 nine to
11 year old UK children measured in summer and
winter. Seasonal differences in activity level were
largest for weekday activity in boys and only present for
Abbreviations: LPA light physical activity, MVPA moderate-to-vigorous physical activity, MPA moderate physical activity, SE standard error, Δ change, Δvariables were
calculated as follow-up values minus baseline values
a except for physical education in the school period, adjusted for school, follow-up periods, age and sedentary behavior or physical activity at baseline
b adjusted for sedentary behavior or moderate-to-vigorous physical activity at baseline
weekend activity in girls, where activity levels were
higher in the summer than the winter. On the other
hand, the impact of season on ambulatory and total
LPA, MVPA and MPA, non-ambulatory LPA, SB and
step counts were comparable between genders in the
present study. Only girls spent less time in
nonambulatory MVPA and MPA in summer vacation
than the school year. The reason for the reduction in
non-ambulatory PA during the summer vacation in
the present study is not clear. However, for Japanese
adult women, habitual time spent in non-ambulatory
MVPA is longer than that of men [
]. Evidence from
our study supports the suggestion that not only
ambulatory activity but also non-ambulatory activity is
an important factor in evaluating PA in girls. These
data may be particularly important for providing
insight into improving gender-related disparities in PA
The present study suggested a possible gender
difference in the determinants/moderators of seasonal changes
in PA and SB. For boys, participation in sports, not having
a television set in the boy’s bedroom, positive perceptions
of sports by themselves and the negative perceptions of
child’s health by their parents might be better targets for
intervention for boy’s SB and non-ambulatory and
ambulatory PAs. In the case of girls, participation in sports, the
positive perceptions of or highly perceived competence in
sports or activity by themselves or their parents and the
negative perceptions of child’s body by their parents might
be important for girls’ SB and PA changes in the summer
vacation. Recent reviews reported that sport participants
have more PA than those who do not participate and
higher engagement with sport and PA can lead to
improvements in self-esteem, at least in the short term [
]. Moreover, another review showed that having a
television set in the bedroom was positively associated with TV
viewing time .
There were several limitations to the current study.
The accelerometer used in the present study has been
validated and has been widely used to evaluate PA in
Japan, but may not accurately assess all types of PA,
such as swimming, cycling and bathing. Nixon et al.
] reported that objectively measured seasonal
differences in sleep duration in 7 year old children with
actigraphy found substantially less sleep in the
summer than during the school year. Sleep duration
varies considerably among individuals. The duration is
affected by day of the week, season, and having
younger siblings. The present study might be missing
shifts in wake-sleep times that may be seasonal and
the differences in wake and sleep time between
different children. Future studies should consider sleep
times where possible, though this is presents practical
problems for researchers. For example, Dayyat et al.
] reported that the description of a child’s sleep by
the parent does not result in a correct estimate of
sleep onset or duration. Therefore, the present study
stipulated a set sleep time for all participants. The
vast majority of children in the present study were
not obese. As a consequence, it may not be
appropriate to extend our results to more obese populations.
The potential moderators of seasonal changes were
limited to those readily available, and other potential
moderators (e.g. socio-economic status) might have
been important but were not measured and not
readily available. Finally, while the present study identified
seasonal changes, the precise reasons why these
changes occurred (weather, differences in behavior
between school days and school holidays) could not be
confirmed. Nonetheless, the present study had a
number of strengths. The longitudinal design and
objective measures of PA and SB were strengths. The study
had a larger sample size than most previous
longitudinal studies of seasonality in children. Finally, the
relatively short period between baseline and follow up
measures in the present study would have minimized
potential age/maturation-related differences in the
behaviors measured, so that any changes could be
interpreted as seasonal rather than maturational. Future
studies should prospectively examine the change in
patterns of SB to obtain more evidence on this
These present study suggests that Japanese primary
school children of both genders have higher SB and
lower LPA and ambulatory MVPA during the summer
vacation. The results emphasize the need to take
Abbreviations: LPA light physical activity, MVPA moderate-to-vigorous physical activity, MPA moderate physical activity, SE standard error, Δ change, Δvariables were
calculated as follow-up values minus baseline values, adjusted for school, follow-up periods, age and sedentary behavior or moderate-to-vigorous physical activity
summer vacation into account when developing PA or
SB interventions for primary school children in Japan.
This study also suggests some factors that may moderate
seasonal changes in PA and SB in Japanese children:
sports participation may mitigate the adverse changes
for boys and girls; television in the bedroom may
exacerbate the seasonal change.
Additional file 1: Table S1a. Associations between change of physical
activity and children’s perception or their parents’ perception of sports,
body image or health in boys (PDF 124 kb)
Additional file 2: Table S1b. Associations between change of
sedentary behavior or physical activity and children’s perception or their
parents’ perception of sports or body image in girls (PDF 103 kb)
LPA: Light intensity activity; METs: Metabolic equivalents; MPA: Moderate
physical activity; MVPA: Moderate-to-vigorous physical activity; PA: Physical
activity; SB: Sedentary behavior; TV: Television
The authors would like to thank the participants for their cooperation in this
study. We also wish to thank Ms. Hiroko Kogure and the staffs of the
National Institute of Health and Nutrition, National Institutes of Biomedical
Innovation, Health and Nutrition and Mr. Joe Yoshimi from Graduate School
of Comprehensive Human Sciences, University of Tsukuba for their help with
This work was supported by a Grant-in-Aid for Scientific Research (A)
24240092 (to C. Tanaka and S. Tanaka), a grant from the Mizuno Sports
Promotion Foundation in 2010 (to IP. C. Tanaka).
Availability of data and materials
The data for this study are not publicly available but may be shared upon
request. For further information on the data and materials used in this study,
please contact the corresponding author.
CT and ST designed research. CT and MT coordinated data collection. CT, ST
and MT analyzed data. CT, JJR and ST discussed the analysis and interpreted
the results. CT wrote the paper and had primary responsibility of the final
content. All authors reviewed the manuscript critically and approved the
Dr. Shigeho Tanaka received consigned research funds from Omron
Healthcare Co., Ltd. The remaining authors declare no competing interests.
Consent for publication
Ethics approval and consent to participate
The Ethical Committee of J. F. Oberlin University approved the study
protocol (No. 10007) and informed consent was obtained from all
participants and their parents.
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