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.
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
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
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
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
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
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
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
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.
Abbreviations
CANPLAY:
Canadian physical activity levels among youth
CI:
Confidence interval
PA:
Physical activity
TMBE:
Tokyo Metropolitan board of education
Declarations
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.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. 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.
Authors’ Affiliations
(1)
Department of Preventive Medicine and Public Health, Tokyo Medical University
(2)
Faculty of Engineering, Chiba Institute of Technology
(3)
Department of Kinesiology, School of Public Health and Health Sciences, University of Massachusetts Amherst
(4)
Department of Nutritional Science, National Institute of Health and Nutrition, National Institutes of Biomedical Innovation, Health and Nutrition
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