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. 2016 Oct 21;16:1104. doi: 10.1186/s12889-016-3775-5

Pedometer-determined physical activity among youth in the Tokyo Metropolitan area: a cross-sectional study

Noritoshi Fukushima 1, Shigeru Inoue 1,✉, Yuki Hikihara 2, Hiroyuki Kikuchi 1, Hiroki Sato 1, Catrine Tudor-Locke 3, Shigeho Tanaka 4
PMCID: PMC5073463  PMID: 27769277

Abstract

Background

Providing large-scale descriptive data of objectively measured physical activity in youth is informative for practitioners, epidemiologists, and researchers. The purpose of this study was to present the pedometer-determined physical activity among Japanese youth using the Tokyo Metropolitan Survey of Physical Fitness, Physical Activity and Lifestyle 2011.

Methods

This study used a school-based survey. The Tokyo Metropolitan Board of Education originally collected pedometer-determined steps per day in the fall of 2011. Data were collected from 15,471 youth aged 6 to 18 years living in Tokyo. Participants were asked to wear pedometers for 14 consecutive days, and daily steps logged in the final 7 days were selected for this analysis.

Results

At the primary and junior high school levels, boys (12,483 and 9476, respectively) had a significantly higher mean number of steps per day than did girls (10,053 and 8408, respectively). There was no significant difference in the mean number of steps per day between the sexes at the high school level. Mean steps per day decreased consistently with age and grade level; the lowest overall steps per day was observed in the last year of junior high school, although there was a slight increase in the subsequent year, the first year of high school.

Conclusions

This study demonstrates a trend toward reduced physical activity with age in Japanese youth and a substantial difference in the number of steps per day between boys and girls in Tokyo. The age-related reduction in steps per day was greater in boys because they attained a higher peak value prior to this reduction, and sex-related differences in the step count disappeared in high school students.

Keywords: Survey, Steps, Children, Adolescents, Cross-sectional study, Descriptive epidemiology

Background

Lack of physical activity (PA) in childhood and adolescence is associated with adverse health problems such as obesity and increased cardiovascular and diabetes risk [1, 2]. Childhood PA patterns often extend into adulthood; insufficient PA during this developmental period is therefore a great public health threat [3]. To improve health outcomes, the World Health Organization recommends that children and adolescents (hereafter collectively termed “youth”) aged 5 to 17 years participate in a daily minimum of 60 min of moderate to vigorous PA [4]. Despite these recommendations, physical activity levels among youth remain low worldwide [5, 6].

Previous studies that evaluated PA levels primarily used standardized self-report questionnaires [2, 5, 6]. Although self-reporting is reasonable for large-scale epidemiological investigations, it may be less appropriate for measuring PA in children and adolescents. For example, recall bias may affect the accuracy of child data more than adult data [7]. Additionally, children may be unable to accurately summarize the sporadic and complex nature of their PA when responding to questions about habitual behavior [8, 9]. Further, cross-national comparisons of self-reported PA are affected by language and cultural differences [10–12]. Collectively, these concerns indicate a substantial need for objectively measured youth PA [13].

Pedometers and accelerometers are commonly used to objectively measure PA and are increasingly used as research tools. It has also been reported that these devices are valid and feasible in assessing PA in youth [14]. Moreover, pedometers are more cost-effective than accelerometers; the number of steps per day provides simple and practical information about PA volume for researchers, practitioners, and the lay public. There are a few examples of national surveys of young people’s objectively determined steps per day: the Canadian Physical Activity Levels among Youth (CANPLAY) survey used pedometers [15, 16], the U.S. National Health and Nutrition Examination Survey used accelerometers [17], and the European Youth Heart Study also used accelerometers [18]. Still, evidence regarding objectively measured PA among Asian youth are quite limited [5].

We aimed to examine descriptive epidemiological data for children’s and adolescents’ pedometer-determined PA levels using the Tokyo Metropolitan Survey of Physical Fitness, Physical Activity and Lifestyle 2011. Specifically, we provide descriptive epidemiological data on the number of steps per day, stratified by sex and grade level.

Methods

A schematic depicting the sampling and data assessment methodology used in this study is shown in Fig. 1.

Fig. 1.

Fig. 1

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Participant sampling flow chart and strategy for data assessment

Data source

The Tokyo Metropolitan Board of Education (TMBE) performed a cross-sectional survey to investigate PA in youth living in Tokyo by examining the number of pedometer-recorded steps per day during the 2011 fall academic term. The TMBE authority and the Tokyo Metropolitan Government approved the secondary use of these data for research purposes, and all provided data were stripped of personal identifiers.

Participants and data collection

Primary school and junior high school are compulsory in Japan. Children are admitted to primary school at 6 years of age. They spend 6 years in primary school, followed by 3 years in junior high school. After graduation from public junior high school in 2011, 97.6 % of students in Tokyo attended high school for 3 years [19]. In Tokyo in June 2011, there were 561,329 students registered in 1308 public primary schools, 229,483 students in 626 public junior high schools, and 134,864 students in 191 public high schools. Geographically, the Tokyo metropolitan comprises 2 areas and 2 islands containing 62 municipalities: 23 Ku-Area (23 wards), Tama-Area (26 cities, 3 towns, and 1 village), and Izu and Ogasawara Islands (2 towns and 7 villages). This is a secondary analysis of a TMBE survey that did not employ random sampling. Instead each of the 62 municipalities of Tokyo were asked, at their own discretion to designate one public primary school and one public junior high school from their jurisdiction for targeted measurement. Thus, the data came from 62 primary schools and 62 junior high schools throughout Tokyo. One class per grade in each of these schools participated in this survey. The TMBE sampled high school students from the 11 school districts of the Tokyo metropolitan.

Data were collected from 10,087 students from 62 primary schools (372 classes), 5164 students from 62 junior high schools (186 classes), and 1137 students from 11 public high schools (33 classes). Participants were aged 6 to 18 years. Each school held an orientation meeting for this survey for participants and their parents or guardians in August 2011. Data were collected using pedometers and questionnaires during the fall term of 2011 (September to November).

Pedometer-determined PA

TMBE members chose the pedometer used in the survey (EX-200; Yamasa Co., Ltd., Tokyo, Japan; approximately $US 23); Yamasa is the Japanese generic name for Yamax, and this brand has been commonly used among PA researchers [20, 21]. In addition, our previous study reported acceptable comparability of the EX-200 compared with the SW-200 (Yamax Co., Ltd., Tokyo, Japan), the Kenz Lifecorder (Suzuken Corp., Nagoya, Japan), and the Active style Pro HJA-350IT (Omron Healthcare, Kyoto, Japan) among Japanese children [22]. Pedometers were placed in participants’ pockets for data collection in the present study. The EX-200 can store up to 7 days of memory data, and students recorded their step counts daily using the memory function at school under the guidance of trained teachers. Participants were asked to wear an unsealed pedometer during waking hours for 14 consecutive days; they were allowed to remove the device for water-based activities and while engaging in full-contact sports (e.g., judo). The number of steps per day during the first 7 days of monitoring was not recorded in accordance with the original TMBE survey protocol. Therefore, the data for the remaining 7 days were used in these analyses.

Data treatment and statistical analyses

Step data were treated similarly to those of the CANPLAY survey [23] to enable comparison of both sets of results. Because a single day of pedometer data can be used to accurately estimate PA levels for surveillance purposes, participants aged 6 to 18 years with at least 1 valid day of pedometer data were included in this analysis [23, 24]. Records of <1,000 or >30,000 steps per day were considered outliers and excluded from further analyses [15, 20, 23]. Valid days were thus defined as any day with recorded data between these two thresholds. Descriptive data (means, 95 % confidence intervals [CI]) for the number of steps per day were calculated based on the number of valid days for each grade level and sex (combined and separately). Ranges and percentile values were calculated for each grade level by sex. In Japan, an evidence-based recommendation for steps per day for youth aged 6 to 18 years has not yet been established. Therefore, we used criteria applied in past studies to describe the proportion of participants taking ≥10,000, ≥12,000, and 15,000 steps per day [15, 25, 26]. Specifically, these criteria were a separate body mass index-referenced criteria for boys and girls (15,000 and 12,000 steps/day, respectively) [15, 26] and a step count related to 60 min of moderate to vigorous PA for adolescent boys and girls (10,000 steps per day) [25]. Moreover, 15,000 steps per day is the target recommended by the Tokyo Metropolitan Government for boys and girls aged 6 to 18 years [27] and <7000 steps per day is a potential candidate for the lower threshold in children, which indicates a sedentary lifestyle [28]. Finally, an accumulated <5000 steps per day (originally considered to indicate a sedentary lifestyle for adults) was used as an alternative marker of a sedentary lifestyle [28]. Student’s t-test was used to test for sex differences, stratified for each grade level. Cohen’s d effect size index was used to assess the magnitude of intergroup differences and statistical significance [29]. All statistical procedures and calculations of p-values were conducted using two-tailed t-tests. Differences were considered statistically significant at p < 0.05. Statistical analyses were performed using IBM SPSS software, version 21.0 (IBM, Armonk, NY, USA).

Results

A total of 16,388 students participated in this survey. We excluded 261 students whose sex was unspecified in the data set, 605 students without any pedometer data recorded during the final 7 days of the monitoring period, and 51 students with no pedometer data after truncation to <1000 or >30,000 steps per day as data outliers. Thus, step-defined PA was successfully measured for 15,471 students, each with at least 1 valid day of data. Overall, 3.1 % of boys and 1.6 % of girls had only 1 valid day of pedometer data; 86.2 % of boys and 90.7 % of girls had ≥4 valid days of pedometer data (Table 1).

Table 1.

Distribution of participants by valid days of pedometer wear, grade, and sex in Tokyo in 2011

Number of students per valid days of pedometer wear
Total 1 day 2 days 3 days 4 days 5 days 6 days 7 days
Grade Age n Pct n Pct n Pct n Pct n Pct n Pct n Pct n Pct
Boys
Primary school All grades 7786 100 245 3.1 344 4.4 490 6.3 830 10.7 1220 15.7 1572 20.2 3085 39.6
1 6–7 802 100 22 2.7 38 4.7 48 6.0 74 9.2 117 14.6 182 22.7 321 40.0
2 7–8 772 100 30 3.9 37 4.8 55 7.1 76 9.8 115 14.9 179 23.2 280 36.3
3 8–9 768 100 33 4.3 46 6.0 52 6.8 92 12.0 106 13.8 168 21.9 271 35.3
4 9–10 828 100 33 4.0 33 4.0 47 5.7 84 10.1 132 15.9 173 20.9 326 39.4
5 10–11 795 100 22 2.8 35 4.4 41 5.2 77 9.7 136 17.1 155 19.5 329 41.4
6 11–12 853 100 27 3.2 29 3.4 45 5.3 77 9.0 123 14.4 181 21.2 371 43.5
Junior high school 1 12–13 877 100 34 3.9 40 4.6 70 8.0 119 13.6 151 17.2 174 19.8 289 33.0
2 13–14 783 100 16 2.0 33 4.2 59 7.5 106 13.5 131 16.7 146 18.6 292 37.3
3 14–15 816 100 23 2.8 38 4.7 52 6.4 79 9.7 128 15.7 138 16.9 358 43.9
High school 1 15–16 177 100 3 1.7 9 5.1 13 7.3 15 8.5 34 19.2 16 9.0 87 49.2
2 16–17 161 100 0 0.0 4 2.5 3 1.9 21 13.0 21 13.0 30 18.5 82 50.9
3 17–18 154 100 2 1.3 2 1.3 5 3.2 10 6.5 26 16.9 30 19.5 79 51.3
Girls
Primary school All grades 7685 100 124 1.6 232 3.0 357 4.6 627 8.2 949 12.3 1575 20.5 3821 49.7
1 6–7 762 100 18 2.4 26 3.4 47 6.2 78 10.2 88 11.5 160 21.0 345 45.3
2 7–8 776 100 12 1.5 31 4.0 37 4.8 83 10.7 92 11.9 144 18.6 377 48.6
3 8–9 797 100 18 2.3 33 4.1 36 4.5 60 7.5 88 11.0 181 22.7 381 47.8
4 9–10 787 100 12 1.5 22 2.8 39 5.0 68 8.6 97 12.3 162 20.6 387 49.2
5 10–11 796 100 11 1.4 20 2.5 22 2.8 47 5.9 76 9.5 166 20.9 454 57.0
6 11–12 803 100 10 1.2 14 1.7 34 4.2 50 6.2 91 11.3 146 18.2 458 57.0
Junior high school 1 12–13 838 100 12 1.4 24 2.9 53 6.3 73 8.7 134 16.0 184 22.0 358 42.7
2 13–14 746 100 11 1.5 16 2.1 36 4.8 70 9.4 81 10.9 158 21.2 374 50.1
3 14–15 816 100 13 1.6 31 3.8 33 4.0 58 7.1 108 13.2 166 20.3 407 49.9
High school 1 15–16 197 100 5 2.5 7 3.6 8 4.1 20 10.2 33 16.8 39 19.8 85 43.1
2 16–17 213 100 1 0.5 6 2.8 5 2.3 14 6.6 38 17.8 42 19.7 107 50.2
3 17–18 154 100 1 0.6 2 1.3 7 4.5 6 3.9 23 14.9 27 17.5 88 57.1
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Table 2 shows the mean number of steps per day and 95 % CI, stratified by sex and grade level. The highest mean number of steps per day (11,659) was found among first-grade students in primary school (6–7 years old) and consistently decreased with age. The lowest mean number of steps per day (7887) was observed in students in the last year of junior high school (14–15 years old). Beyond junior high school, the mean step count modestly increased to 8485 steps per day in the first year of high school (15–16 years old), but declined as students advanced through high school (8032 steps per day at 17–18 years old). For boys, the mean number of steps per day increased from 12,575 in the first grade of primary school, peaked at 12,736 in the third grade of primary school, and subsequently ranged from 8337 to 10,218 in junior high school and from 7935 to 8583 in high school. For girls, the mean number of steps per day followed the same trend seen for both sexes combined: the highest mean number of steps per day was observed in the first grade of primary school (10,694) and consistently declined through junior high school (7437–9104), with a slight increase in the minimum value of the range in high school (8025–8398).

Table 2.

Mean number of steps per day (with 95 % CI) among boys and girls by grade level in Tokyo in 2011

Total Boys Girls Differences of steps per day between boys and girls
Grade Age n Mean steps per day 95 % CI n Mean steps per day 95 % CI n Mean steps per day 95 % CI p value d
All grades 15471 10338 10281–10395 7786 11262 11173–11351 7685 9402 9336–9468 1860 <0.001 0.513
Primary school 1 6–7 1564 11659 11504–11813 802 12575 12369–12781 762 10694 10482–10906 1881 <0.001 0.602
2 7–8 1548 11641 11475–11806 772 12714 12491–12936 776 10573 10352–10795 2141 <0.001 0.644
3 8–9 1565 11573 11406–11740 768 12736 12512–12961 797 10452 10232–10673 2284 <0.001 0.677
4 9–10 1615 11336 11169–11503 828 12596 12381–12811 787 10010 9790–10231 2586 <0.001 0.758
5 10–11 1591 10908 10740–11077 795 12302 12085–12519 796 9517 9300–9734 2785 <0.001 0.815
6 11–12 1656 10612 10444–10781 853 12021 11807–12234 803 9117 8896–9337 2904 <0.001 0.831
Junior high school 1 12–13 1715 9674 9497–9850 877 10218 9974–10462 838 9104 8855–9353 1114 <0.001 0.299
2 13–14 1529 9273 9092–9455 783 9830 9580–10080 746 8689 8433–8946 1141 <0.001 0.316
3 14–15 1632 7887 7743–8031 816 8337 8136–8538 816 7437 7236–7638 900 <0.001 0.304
High school 1 15–16 374 8485 8147–8824 177 8583 8091–9075 197 8398 7932–8864 185 0.592
2 16–17 374 8152 7828–8477 161 8322 7827–8816 213 8025 7595–8454 297 0.373
3 17–18 308 8032 7692–8373 154 7935 7452–8417 154 8130 7647–8612 −195 0.574
(subclassification)
Primary school 1–3 6–9 4677 11624 11530–11718 2342 12674 12542–12806 2335 10571 10439–10703 2103 <0.001 0.642
4–6 9–12 4862 10950 10853–11047 2476 12303 12175–12432 2386 9545 9414–9676 2758 <0.001 0.798
1–6 6–12 9539 11280 11212–11348 4818 12483 12382–12584 4721 10053 9977–10129 2430 <0.001 0.718
Junior high school 1–3 12–15 4876 8950 8851–9049 2476 9476 9347–9604 2400 8408 8278–8539 1068 <0.001 0.302
High school 1–3 15–18 1056 8235 8042–8428 492 8294 8007–8582 564 8184 7915–8452 110 0.575
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Differences between boys and girls tested with independent t-tests and Cohen’s ds were calculated to assess the size of intergroup differences

During primary and junior high school, the step count was significantly higher among boys by 2000 and 1000 steps per day, respectively, compared with girls at the same grade level. However, during the high school years, there was no significant sex difference in numbers of daily steps (p = 0.592 for high school level 1 [15–16 years], p = 0.373 for level 2 [16–17 years], and p = 0.574 for level 3 [17–18 years]), with boys taking an absolute average of only 200 steps per day more than girls (Table 2). Table 3 shows the minimum, maximum, and percentile values for the number of steps per day in each school grade, stratified by sex.

Table 3.

Normative steps per day by grade level and sex in Tokyo in 2011

Percentiles
Grade Age Minimum 1 3 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 97 99 Maximum
Boys
Primary school 1 6–7 1523 2767 6569 7563 8743 9310 9996 10423 10742 11259 11663 12010 12397 12905 13292 13776 14146 14794 15268 16021 16813 18004 18886 22157 24315
2 7–8 1005 4789 6582 7264 8509 9210 9822 10314 10822 11205 11732 12268 12660 13108 13572 14002 14336 14860 15408 16305 17101 18630 19725 22100 26775
3 8–9 1032 4639 6148 7183 8377 9467 9939 10345 10880 11293 11763 12128 12563 13059 13483 13983 14496 14962 15522 16264 17187 18627 19893 21601 29999
4 9–10 1591 4343 6105 6971 7937 8929 9710 10260 10680 11027 11579 12087 12536 13027 13491 13927 14506 14952 15606 16284 17344 18436 19545 21291 27000
5 10–11 1987 4340 6136 7091 8019 8774 9345 9760 10236 10613 11229 11556 11992 12460 12864 13391 13885 14478 15087 16174 17083 18567 19522 21678 29994
6 11–12 1846 3967 5609 6321 7298 8309 8910 9546 9991 10508 10908 11389 11726 12168 12794 13248 13825 14355 14977 15675 16684 18540 19457 21787 30000
Junior high school 1 12–13 1035 2535 4290 4785 5892 6454 7104 7591 7929 8294 8731 9122 9516 9982 10605 11198 11811 12441 13186 14250 15430 17732 18775 21286 29265
2 13–14 1034 2544 3822 4252 5304 6169 6644 7120 7524 8013 8362 8735 9224 9645 10242 10755 11472 12173 12832 13727 15003 17200 18263 21536 27659
3 14–15 1000 2096 3324 3882 4800 5283 5789 6069 6539 6870 7135 7477 7802 8160 8642 8994 9428 9973 10441 11249 12381 14799 16217 19984 26603
High school 1 15–16 2171 3235 3922 4214 4719 5298 5592 6212 6560 6951 7268 7488 7951 8187 8578 9009 9516 10012 10641 11556 13316 16905 18602 21309 24046
2 16–17 1410 2108 3016 3288 4185 4606 5246 5714 6079 6695 6988 7408 7760 8158 8560 8764 8984 9662 10952 12146 14043 16059 17676 20211 20311
3 17–18 1007 1146 2922 3317 3914 4372 5033 5343 6118 6393 6733 7081 7439 7758 8519 9114 9354 10007 10375 11354 12366 14254 15746 18292 19257
Girls
Primary school 1 6–7 1269 3846 6201 6807 7668 8172 8621 8939 9262 9647 10072 10424 10715 10972 11263 11585 11886 12293 12746 13251 13837 14779 15708 17307 21908
2 7–8 1511 3987 5933 6563 7352 7806 8346 8737 9128 9415 9767 10114 10441 10766 11148 11492 11824 12318 12712 13295 13966 15249 16348 17919 20879
3 8–9 1315 4018 5698 6197 7224 7818 8269 8668 9028 9327 9645 9935 10219 10639 11025 11299 11625 12095 12557 13323 14019 14954 15796 17877 24133
4 9–10 1549 4121 5544 6131 6789 7297 7877 8190 8551 8960 9315 9716 9952 10176 10450 10772 11101 11469 11943 12482 13186 14596 15476 17789 22450
5 10–11 2697 4024 5110 5637 6461 7020 7508 7878 8163 8492 8732 9099 9372 9698 10019 10317 10669 10977 11415 11887 12777 13745 14944 15826 22195
6 11–12 1953 3953 5171 5590 6400 6791 7067 7487 7753 8033 8252 8622 8884 9234 9532 9832 10103 10427 10902 11399 12153 13626 14504 16596 20504
Junior high school 1 12–13 1833 2880 3777 4445 5231 5758 6296 6649 7001 7386 7766 8265 8648 8969 9410 9879 10426 11077 11856 12760 14001 15518 16216 18181 23343
2 13–14 1451 3176 4042 4466 5298 5786 6231 6572 6909 7211 7521 7873 8212 8542 8820 9273 9732 10151 10791 11519 12893 15101 16404 18749 24388
3 14–15 1346 2705 3640 4213 4711 5129 5447 5757 6134 6374 6669 6862 7144 7386 7699 8089 8408 8707 9140 9806 10474 11687 12625 14656 20730
High school 1 15–16 1086 2037 3362 3797 4722 5103 5828 6369 7027 7277 7530 7798 8141 8403 8955 9329 9689 9971 10623 11447 12799 14323 14889 16004 17258
2 16–17 3126 3227 3814 4396 5091 5191 5628 6108 6454 6903 7142 7388 7656 8010 8351 8663 9024 9320 9919 10570 11422 12787 14899 16251 20525
3 17–18 3000 3115 3646 4518 4966 5565 6135 6292 6684 6942 7158 7462 7592 7864 8320 8697 9305 9694 9989 10531 11570 14000 14864 16570 17308
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Table 4 compares the results of this study, which used Yamasa EX-200 pedometers, and those of the CANPLAY survey, which used Yamax Digiwalker SW-200 pedometers [16]. The mean number of daily steps taken by boys in primary school was similar for the two surveys. However, at the higher-grade levels, pedometer-determined PA levels were lower for boys living in Tokyo than for their Canadian counterparts by approximately 1000 to 2000 steps per day. Similarly, the number of steps taken per day by girls living in Tokyo was lower by approximately 1000 steps per day than that of Canadian girls across all grades.

Table 4.

Comparison of mean number of steps per day among boys and girls between Canada (in 2005–2011) and Tokyo in 2011

Boys Girls
Canadaa Tokyo Canadaa Tokyo
Pedometer Yamax SW-200 Yamasa Ex-200 Yamax SW-200 Yamasa Ex-200
Age Steps per day Steps per day Steps per day Steps per day
6 12,435 12,575 11,627 10,694
7 12,700 12,714 11,507 10,573
8 12,989 12,736 11,435 10,452
9 13,097 12,596 11,490 10,010
10 13,030 12,302 11,638 9517
11 12,694 12,021 11,367 9117
12 12,211 10,218 10,510 9104
13 11,816 9830 10,122 8689
14 11,114 8337 9988 7437
15 10,650 8583 9476 8398
16 10,344 8322 9252 8025
17 10,493 7935 9343 8130
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aThe Canadian Physical Activity Levels Among Youth (CANPLAY) survey [16]. Yamax SW-200 pedometers were used in the CANPLAY survey, and Yamasa EX-200 pedometers in the Tokyo survey. The SW-200 was worn on a belt, the EX-200 was placed in a pocket

The proportion of students taking ≥10,000, ≥12,000, and ≥15,000 steps per day was 60.5, 41.2, and 17.4 %, respectively, for boys and 39.1, 17.6, and 3.9 %, respectively, for girls (Fig. 2). Boys showed a distinct decrease in the number of steps per day between the sixth primary school grade and the first junior high school grade. Girls showed a gradual decline in the number of steps per day from the start to the finish of primary school, with a slight increase during the first year of junior high school.

Fig. 2.

Fig. 2

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Proportion of students taking ≥10,000, ≥12,000, or ≥15,000 steps per day by sex and school grade

The proportion of students taking <7000 and <5000 steps per day was 14.1 and 4.7 %, respectively, for boys and 20.7 and 5.0 %, respectively, for girls (Fig. 3). The proportion of boys taking <7000 and <5000 steps per day rapidly increased between the sixth grade of primary school and the first grade of junior high school, and continued to increase toward high school. The proportion of girls taking <7000 steps per day gradually increased from the first grade level to the last year of junior high school. There was a moderate relative decrease in the proportion of girls taking <7000 steps per day in the first year of high school, but a subsequent steady increase in later years.

Fig. 3.

Fig. 3

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Proportion of students taking <7,000 or <5,000 steps per day by sex and school grade

Discussion

Using a representative sample of the Tokyo metropolitan area, this is one of the largest surveys worldwide to investigate pedometer-determined PA levels in children and adolescents. The results indicate that in primary school (age 6–12 years), junior high (age 12–15 years), and high school (age 15–18 years), boys took an average of 12,483, 9476, and 8294 steps per day, respectively, while girls took an average of 10,053, 8408, and 8184 steps per day, respectively. The mean number of daily steps was significantly higher for boys than for girls through 6 to 15 years, with an overall decreasing age-related trend for both sexes. Boys tend to be more active than girls at most ages, although this difference disappears in high school, and a reduction in PA levels from childhood to adolescence has been previously reported [17, 18, 25]. Until now, there has been limited objective data for large-scale evaluations of PA levels in Japanese children and adolescents [5]. The step patterns of our Tokyo students are similar to those reported in a review of pedometer data from 43 studies of young people in 13 countries [30].

Although high school is not compulsory in Japan, more than 95 % of students in Tokyo attend high school after passing their entrance examination [19]. Generally, Japanese students in the third year of junior high school spend substantial time studying for this examination. Therefore, students in their final junior high school year may focus more on studying than on PA, which may explain why this group has the lowest overall mean step count and the highest proportion of youth accumulating fewer steps per day relative to the two indices of a sedentary lifestyle.

The differences in PA levels between children in Tokyo and those in Canada can be interpreted in four ways. First, Canadian and Japanese children may actually have different PA levels. Second, this difference may result from variations in the survey-specific pedometers used and their positioning. The EX-200 (used in this survey) is an in-pocket pedometer and the SW-200 (used in the CANPLAY survey) is worn on a belt. The EX-200 is a triaxial accelerometer with a filter function that monitors continuous walking activity to recognize actual steps; it is programmed to count steps when an individual takes ≥10 steps without pausing for <2 s (e.g., if a subject moves <10 steps and pauses for ≥2 s, the previous steps will not be counted). Silcott et al. [31] reported that pedometers with a filter function might underestimate step counts compared with pedometers without a filter function. Although there is no data directly comparing steps measured by the EX200 and the SW-200, Tanaka et al. reported that the EX-200 underestimated step counts by 7.9 % compared with the Kenz Lifecorder among children aged 6 to 12 years [22] (additionally, Schneider et al. reported no significant difference in step count values between the Kenz Lifecorder and the SW-200 [21]). These findings suggest that the EX-200 step counts may be lower than those obtained by the SW-200. Thus, differences among devices should be considered. Third, the sampling method in this TMBE-administered survey was different from the CANPLAY which employed random sampling and collected data through the mail. In contrast, the Tokyo survey asked each municipality to choose one primary and one junior high school from its district. All geographical areas throughout Tokyo were covered by this method. However, it is uncertain whether this sampling method lead to underestimation or overestimation of the step counts. Finally, children’s activity levels may be affected by seasonal variation [32]. Craig et al. [15] reported that Canadian children’s PA is lower in the fall and winter than in the spring and summer. Because this survey was conducted in the fall in Tokyo, further study is needed to determine the effect of seasonal changes on PA levels in Japanese children and adolescents.

Vincent et al. [33] assessed pedometer-determined daily step counts in a convenience sample of children aged 6 to 12 years in the U.S. (n = 711), Sweden (n = 680), and Australia (n = 563). Although there are potential issues with the sample size, sampling bias, and the different pedometers used in the present survey, the Tokyo survey reported approximately 3000 and 1000 fewer steps for boys per day than Swedish and Australian boys, respectively, but a similar level of activity to American boys. We observed a similar pattern for girls, who took approximately 2000 and 1000 fewer steps per day than Swedish and Australian girls, respectively, but accumulated a similar mean number of steps per day as American girls.

There are no clear guideline recommendations for number of steps per day for children and adolescents. However, we interpreted the present data in the context of previously published step-defined criteria. Certainly, it is optimal to use criteria that have been established based on health-related values. However, practical effectiveness should also be taken into consideration when setting any single criterion. For example, if almost all (or very few) people meet a specified value, then its practical effectiveness for educational and public health purposes is questionable. The present results include implications regarding the practical effectiveness of various criteria. We found that the proportion of boys and girls meeting specific criteria (i.e., 10,000, 12,000, and 15,000 steps per day) decreased with age. Additionally, distinct sex-specific patterns were observed. The Tokyo Metropolitan Government has recommended ≥15,000 steps per day for children and adolescents, regardless of age or sex [27]. However, our findings reveal that many children and adolescents (except primary school boys) do not meet this target. Therefore, a criterion of ≥15,000 steps per day seems very high and thus not practically effective, especially for girls. Two courses of action might improve the situation. First, appropriate age- and sex-specific targets may be set. Second, a graduated scale of values might describe PA distribution better than a single target value and may encourage less active children to improve their PA level. Although it seems too low as an optimal value for health, a criterion of ≥10,000 steps per day showed dynamic patterns across age and sex in this survey. This suggests that ≥10,000 steps per day is a practically effective criterion for evaluating lifestyle changes/differences across age and sex for education and public health purposes. For children, <7000 steps per day has been suggested as an appropriate sedentary lifestyle index [15, 28]. In this survey, the proportion of students meeting this criterion increased with age as anticipated. However, its practical effectiveness was limited for primary school boys, who accumulated a higher average number of steps per day than this value, suggesting the need for age- and sex-specific values on a graduated scale for youth.

In the present study, the use of unsealed pedometers meant that participants were aware of their step counts, potentially leading to reactivity bias. Because TMBE did not record the steps per day for the first 7 days, our ability to test for reactivity was hampered. However, Craig et al. [23] showed no evidence of reactivity in a population sample of 5- to 19-year-olds wearing unsealed pedometers for 7 days. Other studies have reported no evidence of reactivity bias and have generally concluded that this is not a problem when evaluating children [13]. Additionally, Clemes and Deans [34] reported that the reactivity effect diminishes after the first week of monitoring, returning to normal levels in the second week. Therefore, the data obtained in the second week of our 2-week surveillance were probably not systematically affected by reactivity bias.

Study strengths and limitations

This study has several strengths. Because the participants were sampled throughout Tokyo, their mean number of steps per day is representative of PA levels in Tokyo youth. Using the same adjusted treatment methods for pedometer data as used in the CANPLAY study enabled between-study comparisons. Finally, in this study, more than 86 and 90 % of boys and girls, respectively, wore their pedometers for a minimum of 4 days; it has been reported that 4 or more valid days of data in youth enhances data reliability [35].

Study limitations must be acknowledged. First, this was that was a secondary analysis of a survey conducted by an education authority and we had no input regarding the original study design. Despite this, the survey represents an important source of objectively monitored data on children. Although this is the largest study of in-pocket pedometer-determined PA in youth (and is thus a useful reference data source for others using this type of device), these pedometers do tend to underestimate absolute step-defined PA levels. Regardless, it is reasonable to assume that the observed data trends are valid. Second, the lack of private school students in the sample may influence the results. In 2011, the proportion of students in the Tokyo metropolitan area attending private primary, junior high, and high schools was 4.5, 25.5, and 55.9 %, respectively [36]. The difference in tuition costs for private schools may indicate differences in familial socioeconomic status. If socioeconomic status affects youth PA levels, the present data may not accurately reflect PA in the larger Tokyo youth population. Third, the TMBE survey complied with the organization’s safety policy, thus allowing students to remove their pedometers during vigorous full-contact activity (unfortunately, this was not tracked); this may have underestimated the overall number of steps per day. Finally, the issue of wearing compliance should be considered. Students recorded their step counts at school under the guidance of trained teachers. However, no other methods were employed to confirm whether they actually wore the pedometers as directed.

Conclusion

This study demonstrates that children’s pedometer-determined PA generally decreases with age and that there is a substantial difference in the number of steps taken per day between boys and girls in Tokyo. The PA decrease was greater in boys because they achieved initial higher peak values; once the students reached high school, the sex difference in the number of steps per day disappeared. These findings contribute to our current understanding of the PA levels of youth living in Tokyo and will be useful for surveillance, screening, and comparison purposes, as well as planning strategies.

Acknowledgements

We thank all the study participants and data collectors for their willingness to participate in this survey. We also thank all members of the Tokyo Metropolitan Board of Education and the Tokyo Metropolitan Government who helped make this study possible.

Availability of data and materials

The data described herein come from a secondary use of dataset collected by the Tokyo Metropolitan Board of Education with their permission. The data is not permitted to be opened for public use.

Authors’ contributions

SI conceived the study. NF carried out the analysis, and drafted the manuscript. SI, CTL, and ST interpreted results and critically edited the manuscript. HS and HK provided statistical expertise, and contributed to discussion. YH advised on and reviewed data analysis, and contributed to discussion. All authors read and approved the final manuscript.

Competing interests

The author declares that they have no competing interests.

Consent for publication

Not applicable.

Ethics approval and consent to participate

Ethical approval was obtained from the Tokyo Medical University Ethics Committee (No. 2762). Data were collected as administrative data by the Tokyo Metropolitan Board of Education and the Tokyo Metropolitan Government. The Tokyo Metropolitan Board of Education and the Tokyo Metropolitan Government approved the secondary use of these data for research purposes.

Abbreviations

CANPLAY

Canadian physical activity levels among youth

CI

Confidence interval

PA

Physical activity

TMBE

Tokyo Metropolitan board of education

Contributor Information

Noritoshi Fukushima, Email: fukufuku@tokyo-med.ac.jp.

Shigeru Inoue, Phone: +81-3-3351-6141, Email: inoue@tokyo-med.ac.jp.

Yuki Hikihara, Email: hikihara.yuki@it-chiba.ac.jp.

Hiroyuki Kikuchi, Email: kikuchih@tokyo-med.ac.jp.

Hiroki Sato, Email: hrksato-tky@umin.ac.jp.

Catrine Tudor-Locke, Email: ctudorlocke@umass.edu.

Shigeho Tanaka, Email: tanakas@nih.go.jp.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Data Availability Statement

The data described herein come from a secondary use of dataset collected by the Tokyo Metropolitan Board of Education with their permission. The data is not permitted to be opened for public use.

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