Introduction {#s0005}
============

The 2011 Great East Japan Earthquake caused serious damage. Furthermore, the prefectures of Miyagi, Fukushima, and Iwate along the Pacific coast suffered devastating damage as a result of the tsunami caused by the earthquake. In association with the disaster, the daily life of many residents of these areas has altered.

A few previous studies have reported the health status of survivors after a disaster. For example, [@bb0085] showed that the deteriorating quality of life (QOL) scores of the Chi-Chi earthquake survivors aged 16 years or older were decreased 3 years after the event. Another study ([@bb0010]) showed that QOL scores of elderly survivors 5 years post-earthquake disaster were also decreased.

Physical activity is an important factor affecting health indicators. Worldwide, public health guidelines recommend a physically active lifestyle for children and adolescents for overall health benefits ([@bb0090]). QOL is one of the health indicators, and a study ([@bb0020]) has indicated that a consistently positive association exists between physical activity level and health-related QOL among children. Furthermore, sedentary behavior, such as sitting, is associated with health consequences and outcomes independent from the health benefits of physical activity ([@bb0075], [@bb0055]).

Although physical activity is recommended for health, little is known about physical activity levels among victims of the 2011 earthquake and tsunami. In this study, we described changes in physical activity among children and adolescents living in the area affected by the 2011 earthquake and tsunami during the 3 years after the disaster.

Methods {#s0010}
=======

Participants were elementary school students in 4th, 5th, and 6th grades and junior high school students in 7th, 8th, and 9th grades. Four-time surveys of this serial prevalence study were conducted at about 6 months (I, *n* = 434), 1 year (II, *n* = 437), 2 years (III, *n* = 401), and 3 years (IV, *n* = 365) after the earthquake in Onagawa, in the Miyagi prefecture, in the Pacific coastal area of northern Japan. Ethics approval for the present study was obtained from the Tohoku Gakuin University Ethics Committee, the Human Informatics postgraduate course, and the Catholic Education Commission. All participating students and their parents/legal guardians provided written informed consent.

All students were asked to report their gender, age, grade, height, and weight. BMI was calculated using their height and weight, and students were categorized as overweight, obese, or within the normal range according to international guidelines ([@bb0025]). In addition, total minutes per day spent in sedentary behavior were assessed by a self-reported questionnaire. The students were asked to reply to the question, "During the last week, how much time did you spend sitting on a weekday and weekend? Sitting includes watching TV, playing game, having a chat, reading, and listening to music at both school and home." This question was phrased according to the international physical activity questionnaire in a previous study. In addition, physical activity questions from the WHO health behavior in schoolchildren (HBSC) survey, which has acceptable reliability and validity among children and adolescents, were also included in our questionnaire ([@bb0015]).

Accelerometer-determined steps per day were evaluated using a triaxial accelerometer device (Activity Style Pro HJA-350IT; Omron Healthcare, Kyoto, Japan) consisting of Micro Electro Mechanical Systems-based accelerometers (LIS3LV02DQ; ST-Microelectronics, Geneva, Switzerland) ([@bb0045], [@bb0050]). The accelerometers were initialized to concurrently record steps in 10-s intervals. Students were asked to wear the device for 7 or more consecutive days including at least 2 weekend days, removing them only for water activities and before going to bed at night ([@bb0060]). The students were shown how to set the accelerometer to their waists during the training session. At least 3 days with more than 10 h of daily data collection, including 2 weekdays and 1 weekend day, were required for inclusion in the analysis. Data recorded on the first and last days were removed towing to some reactivity risks and incompleteness on these days.

All analyses were conducted using SPSS version 22.0 for Windows (Predictive Analytics Software, SPSS Inc., Chicago, IL, USA). Chi-square test was used to assess differences in gender, grade, and BMI categories ([@bb0025]). The total min per day spent sitting and the number of steps per day were analyzed using the non-parametric Kruskal--Wallis test. Post hoc comparisons for dichotomous variables were based on Mann--Whitney *U* tests with a Bonferroni corrected significance level. A *p* value \< .05 was considered statistically significant.

Results {#s0015}
=======

[Table 1](#t0005){ref-type="table"} shows the characteristics and physical activity levels among elementary school students. There were significant differences (*p* \< 0.05) among children in the median time spent sitting on weekdays (Girls: *χ*^2^ = 12.3, *df* = 3.0) alone and accelerometer-determined median daily steps on both weekdays (Boys: *χ*^2^ = 12.4, *df* = 3.0; Girls: *χ*^2^ = 27.5, *df* = 3.0) and weekends (Boys: *χ*^2^ = 8.0, *df* = 3.0; Girls: *χ*^2^ = 30.0, *df* = 3.0). The median daily steps declined significantly for both genders on weekdays and for girls on weekends at period IV as compared with median daily steps at period I (*p* \< 0.05), whereas the time spent sitting decreased on weekdays. Significant difference was seen in terms of the daily steps of the boys on weekends, whereas there were no differences among periods in the post hoc test.

[Table 2](#t0010){ref-type="table"} shows the characteristics and physical activity levels among junior high school students. There were significant differences (*p* \< 0.05) among adolescents in the time spent sitting on weekdays (Boys: *χ*^2^ = 16.8, *df* = 3.0; Girls: *χ*^2^ = 11.8, *df* = 3.0) and in accelerometer-determined median daily steps on both weekdays (Girls: *χ*^2^ = 17.9, *df* = 3.0) and weekends (Boys: *χ*^2^ = 15.6, *df* = 3.0). The median daily steps declined significantly among girls on weekdays and among boys on weekends at period IV as compared with the median daily steps at period I (*p* \< 0.05), whereas for girls, the time spent sitting on weekdays decreased.

Discussion {#s0020}
==========

The present study showed that accelerometer-determined steps per day among children living in an area affected by earthquake and tsunami on both weekday and weekend decreased significantly, whereas the sedentary time among girls on weekdays only decreased over the 3 years of the study. Similarly, the daily steps of adolescents were decreased, whereas the sedentary behavior of both genders on weekdays was decreased over the 3 years. This decrease of the daily steps may result from the environment around the neighborhoods in which the participants reside. [@bb0035] reported positive associations between neighborhood environment and physical activity among youths. The neighborhood environment in the coastal area catastrophically damaged by the tsunami continues to undergo repair, which could make the neighborhood less favorable for physical activities. In addition, some students may have poor neighborhood environments due to living in temporary dwellings. The schools survived the tsunami because the buildings were located on a hill. Therefore, it seemed that it was important for children and adolescent girls to ensure performing physical activity at an appropriate time in school owing to a significant decrease in their daily steps on weekdays.

To meet current physical activity guidelines ([@bb0040], [@bb0090]) for children and adolescents to accumulate a minimum of 60 min of moderate-to-vigorous physical activity, [@bb0080] recommended 13,000; 11,000; and 10,000 steps per day for boys (aged 6--11 years), girls (aged 6--11 years), and adolescents of both genders (aged 12--19 years), respectively. Another study ([@bb0005]) recommended 11,500 accelerometer-determined daily steps for youths and both genders. At 3 years after the earthquake, the median steps of the children and adolescents in this study were lower than these guidelines.

There are few studies about the daily steps of Japanese children and adolescents during the pre-disaster period. For example, one cross-sectional study ([@bb0065]) reported an accelerometer-determined mean daily steps of Japanese children aged 9--10 years (*n* = 288) on both weekday (Boys: 18,333 ± 3869 steps; Girls: 13,957 ± 2970 steps) and weekend (Boys: 11,932 ± 4827; Girls: 9767 ± 4542). Another study ([@bb0070]) reported the mean daily steps of Japanese adolescents aged 12--15 years (*n* = 314) on both weekday (Boys: 13,772 ± 4764; Girls: 11,209 ± 2636) and weekend (Boys: 8311 ± 4743; Girls: 7159 ± 3338). In comparison with those in the previous studies, the mean daily steps in children and adolescents living in an area affected by the disaster are considered to be lower. Particularly, the mean daily steps of children of both genders on weekdays at periods IV in the present study were approximately 6500 steps lower than those of the previous study.

In this study, the data was collected from a serial prevalence study. The cause and effect relationship of changes in physical activity is not clear. Future research should elucidate longitudinal demographic and sociocultural factors that contribute to changes in physical activity and sedentary behavior among children and adolescents living in the damaged coastal area. Furthermore, time spent sitting was determined based on the responses to an item in the self-administered questionnaire. Certainly, it may be somewhat difficult for children and adolescents to recall their sedentary time. However, even in a situation of a limited methodology, such as that of an earthquake disaster, we need to evaluate physical activity for health promotion. It seemed to be important to report sedentary time using a self-administered questionnaire for comparison with data for a current or future disaster.

Conflict of interest statement {#s0025}
==============================

The authors declare that there are no conflicts of interest.

The work of this study was supported by JSPS KAKENHI Grant Number 26750323 and 24680065.

###### 

Characteristics, physical activity, and sedentary behavior among elementary school students.

                                       I               II              III           IV                                                    
  ------------------------------------ --------------- --------------- ------------- --------------- ------------------------------------- ------------------
  Girl, *n* (%)                        108 (54)        108 (54)        82 (55)       57 (52)         n.s.                                  
  Grade, *n* (%)                                                                                                                           
   4th                                 65 (33)         65 (33)         45 (31)       38 (33)         n.s.                                  
   5th                                 66 (33)         66 (33)         55 (37)       33 (29)                                               
   6th                                 69 (35)         69 (35)         47 (32)       43 (38)                                               
  Body mass index, *n* (%)                                                                                                                 
   Normal                              106 (83)        127 (84)        87 (81)       78 (81)         n.s.                                  
   Overweight and obesity              21 (17)         25 (16)         21 (19)       18 (19)                                               
                                                                                                                                           
  Physical activity of HBSC, *n* (%)                                                                                                       
  Boys                                                                                                                                     
   Active                              62 (79)         59 (74)         50 (76)       37 (70)         n.s.                                  
   Inactive                            16 (21)         21 (26)         16 (24)       16 (30)                                               
  Girls                                                                                                                                    
   Active                              49 (59)         42 (41)         34 (41)       28 (49)         n.s.                                  
   Inactive                            34 (41)         61 (59)         48 (59)       29 (51)                                               
                                                                                                                                           
  Time spend on sitting, min/day                                                                                                           
  Boys                                                                                                                                     
   Weekday                                                                                                                                 
   25 percent tile                     321             189             223           206             n.s.                                  
   50 percent tile                     485             510             399           323                                                   
   75 percent tile                     611             707             617           580                                                   
   Mean ± SD                           485 ± 227       483 ± 277       431 ± 254     418 ± 265                                             
   Weekend                                                                                                                                 
   25 percent tile                     305             238             248           347             n.s.                                  
   50 percent tile                     477             510             500           480                                                   
   75 percent tile                     643             719             694           632                                                   
   Mean ± SD                           480 ± 231       484 ± 271       484 ± 262     515 ± 221                                             
  Girls                                                                                                                                    
   Weekday                                                                                                                                 
   25 percent tile                     366             336             227           179             [⁎⁎](#tf0010){ref-type="table-fn"}    I \> IV
   50 percent tile                     550             566             407           360                                                   
   75 percent tile                     728             675             633           615                                                   
   Mean ± SD                           533 ± 248       517 ± 242       435 ± 255     416 ± 278                                             
   Weekend                                                                                                                                 
   25 percent tile                     304             289             285           324             n.s.                                  
   50 percent tile                     527             542             573           488                                                   
   75 percent tile                     698             726             726           645                                                   
   Mean ± SD                           532 ± 252       538 ± 247       539 ± 258     504 ± 242                                             
                                                                                                                                           
  Steps per day                                                                                                                            
  Boys                                                                                                                                     
   Weekday                                                                                                                                 
   25 percent tile                     11,209          9200            9627          8870            [⁎⁎](#tf0010){ref-type="table-fn"}    I \> II, IV
   50 percent tile                     12,920          11,171          11,773        10,854                                                
   75 percent tile                     15,297          14,773          16,971        14,775                                                
   Mean ± SD                           13,582 ± 3733   12,138 ± 4447   1305 ± 4701   11,765 ± 4302                                         
   Weekend                                                                                                                                 
   25 percent tile                     5925            4205            3751          5066            [⁎](#tf0005){ref-type="table-fn"}     n.s.
   50 percent tile                     9698            6467            6510          7691                                                  
   75 percent tile                     12,912          10,628          12,890        11,270                                                
   Mean ± SD                           10,128 ± 5278   8240 ± 5288     9292 ± 7965   8501 ± 5060                                           
  Girls                                                                                                                                    
   Weekday                                                                                                                                 
   25 percent tile                     7562            6780            7227          5947            [⁎⁎⁎](#tf0015){ref-type="table-fn"}   I, III \> II, IV
   50 percent tile                     8529            7836            8955          7475                                                  
   75 percent tile                     9846            8925            11,066        8567                                                  
   Mean ± SD                           8765 ± 1976     7913 ± 1767     9302 ± 2985   7609 ± 2382                                           
   Weekend                                                                                                                                 
   25 percent tile                     4950            3049            3692          2769            [⁎⁎⁎](#tf0015){ref-type="table-fn"}   I \> II, III, IV
   50 percent tile                     7714            4748            5679          4903                                                  
   75 percent tile                     10,555          7240            8215          6751                                                  
   Mean ± SD                           8082 ± 4123     5349 ± 3053     6084 ± 3360   5372 ± 3752                                           

n.s.: not significant.

*P* \< 0.05.

*P* \< 0.01.

*P* \< 0.001.

###### 

Characteristics, physical activity, and sedentary behavior among junior high school students.

                                       I             II            III           IV                                                  
  ------------------------------------ ------------- ------------- ------------- ------------- ------------------------------------- ------------------
  Girl, *n* (%)                        104 (48)      104 (48)      88 (49)       84 (57)       n.s.                                  
  Grade, *n* (%)                                                                                                                     
   7th                                 70 (33)       70 (33)       65 (37)       42 (28)       n.s.                                  
   8th                                 79 (37)       79 (37)       44 (25)       58 (38)                                             
   9th                                 66 (31)       66 (31)       66 (38)       51 (34)                                             
  Body mass index, *n* (%)                                                                                                           
   Normal                              157 (86)      129 (87)      129 (84)      115 (88)      n.s.                                  
   Overweight and obesity              26 (14)       20 (13)       24 (16)       15 (12)                                             
                                                                                                                                     
  *Physical activity of HBSC, n (%)*                                                                                                 
  Boys                                                                                                                               
   Active                              80 (78)       64 (82)       66 (73)       49 (77)       n.s.                                  
   Inactive                            23 (22)       14 (18)       24 (27)       15 (23)                                             
  Girls                                                                                                                              
   Active                              55 (57)       39 (46)       49 (56)       42 (50)       n.s.                                  
   Inactive                            41 (43)       46 (54)       39 (44)       42 (50)                                             
                                                                                                                                     
  *Time spend on sitting, min/day*                                                                                                   
  Boys                                                                                                                               
   Weekday                                                                                                                           
   25 percent tile                     258           182           160           194           [⁎⁎](#tf0020){ref-type="table-fn"}    I \> II, III, IV
   50 percent tile                     607           324           297           300                                                 
   75 percent tile                     787           615           602           639                                                 
   Mean ± SD                           547 ± 285     413 ± 272     390 ± 265     405 ± 265                                           
   Weekend                                                                                                                           
   25 percent tile                     345           390           266           333           n.s.                                  
   50 percent tile                     542           573           536           552                                                 
   75 percent tile                     733           750           704           800                                                 
   Mean ± SD                           546 ± 253     561 ± 251     497 ± 255     561 ± 270                                           
  Girls                                                                                                                              
   Weekday                                                                                                                           
   25 percent tile                     338           265           240           240           [⁎⁎](#tf0020){ref-type="table-fn"}    I \> IV
   50 percent tile                     665           510           575           398                                                 
   75 percent tile                     838           724           823           625                                                 
   Mean ± SD                           596 ± 281     496 ± 270     533 ± 304     449 ± 260                                           
   Weekend                                                                                                                           
   25 percent tile                     460           426           313           345           n.s.                                  
   50 percent tile                     665           605           611           560                                                 
   75 percent tile                     845           778           837           743                                                 
   Mean ± SD                           633 ± 238     610 ± 240     575 ± 278     553 ± 243                                           
                                                                                                                                     
  *Steps per day*                                                                                                                    
  Boys                                                                                                                               
   Weekday                                                                                                                           
   25 percent tile                     6338          5494          6449          6014          n.s.                                  
   50 percent tile                     9586          9214          8067          9339                                                
   75 percent tile                     11,444        11,278        11,077        12,532                                              
   Mean ± SD                           9310 ± 3452   8947 ± 3765   8479 ± 3248   9507 ± 4430                                         
   Weekend                                                                                                                           
   25 percent tile                     3876          3287          3175          1718          [⁎⁎⁎](#tf0025){ref-type="table-fn"}   I \> IV
   50 percent tile                     6850          5085          5757          3337                                                
   75 percent tile                     13,418        7457          8416          7066                                                
   Mean ± SD                           8816 ± 6288   5843 ± 3741   6521 ± 4218   4947 ± 4646                                         
  Girls                                                                                                                              
   Weekday                                                                                                                           
   25 percent tile                     6521          5668          5962          5044          [⁎⁎⁎](#tf0025){ref-type="table-fn"}   I \> IV
   50 percent tile                     8275          7369          7315          6960                                                
   75 percent tile                     10,651        9589          8805          8731                                                
   Mean ± SD                           8815 ± 3370   7560 ± 2658   7343 ± 2396   6673 ± 2712                                         
   Weekend                                                                                                                           
   25 percent tile                     3251          3161          2949          1784          n.s.                                  
   50 percent tile                     4917          4805          4352          3253                                                
   75 percent tile                     7248          7804          6960          7185                                                
   Mean ± SD                           5784 ± 3609   5458 ± 3242   5414 ± 3801   4817 ± 4133                                         

n.s.: not significant.

*P* \< 0.01.

*P* \< 0.001.
