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

  • Noritoshi Fukushima1,
  • Shigeru Inoue1Email author,
  • Yuki Hikihara2,
  • Hiroyuki Kikuchi1,
  • Hiroki Sato1,
  • Catrine Tudor-Locke3 and
  • Shigeho Tanaka4
BMC Public HealthBMC series – open, inclusive and trusted201616:1104

https://doi.org/10.1186/s12889-016-3775-5

Received: 8 July 2016

Accepted: 15 October 2016

Published: 21 October 2016

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 [1012]. 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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Copyright

© The Author(s). 2016

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