Changes in physical activity patterns of students from primary to secondary school: a 5-year longitudinal study

Study design and participants

This longitudinal study was conducted at a private elementary school and a secondary school in adjacent facilities in Tokyo, Japan. Data was collected annually (either February or March) from 2015 to 2020. The two study groups were as follows: 1) the group initially interviewed in 2015 and followed each year between February and March for 5 years longitudinally (n=32) and 2) the group initially interviewed in 2016 and for 5 years was followed up longitudinally between February and March each year (n = 31). This study began in 2015 by collecting baseline data from children in fourth grade (9-10 years) (Group 1, n= 32) and 2016 (Group 2, n= 31). The children attended the same class, which was randomly selected by the school administration. We surveyed these children annually for five consecutive years until they reached eighth grade (secondary school; ages 13–14). A total of 63 healthy children (56% girls) provided baseline data in 2015 and 2016 and were followed up over the five-year study period.

Before the start of the study and at each follow-up and data collection point, parents received full information from their children’s teachers about the purpose and methods of the study. Written parental consent was returned to the teachers after the participants’ parents had an opportunity to verify their child’s participation. All procedures involving human participants were performed in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its subsequent amendments or comparable ethical standards. The study protocol was approved by the Ethics Committee of the Graduate School of Human Informatics Study, Tohoku Gakuin University (reference number 2017R001). Only children with written parental consent were included in the study.

measurements

demography and anthropometry

The age, class, sex, body weight, and height of each participating child were determined using a self-completed questionnaire. Weight status, defined as percentage overweight (POW), was assessed using Japanese cutoff values ​​based on the national reference data for Japanese children33. In short, POW is commonly used to assess child obesity in medical institutions and schools in Japan, and is calculated as the ratio of weight to standard weight based on gender, age, and height. The POW criteria for obesity and underweight are ≥ 20% and ≤ − 20%, respectively, with the normal range being -20% to 20%. These obesity and underweight criteria have been shown to correspond to age-adjusted BMI percentiles of >86-89% and <2-6%, respectively33.

PA measurements

Participants’ usual PA was assessed using a three-axis accelerometer (HJA-750C Active Style Pro, Omron Healthcare, Kyoto, Japan) measuring 40 × 52 × 12 mm and weighing 23 g including batteries. This three-axis accelerometer collects information about the time spent on ambulatory and non-ambulatory activities of varying intensities. The accuracy of this device has been reported in previous studies34.35. Based on standard adult predictive equations and the results of a previous study in children36, the following conversion equations were used. Ambulatory activities were calculated as 0.6237 × MET score + 0.2411 and non-ambulatory activities were calculated as 0.6145 × MET score + 0.5573. Time spent on activities requiring ≥3 METs, 1.6-2.9 METs, and ≤1.5 METs were considered MVPA, LPA, and SB, respectively. We used the macro program (version 190829) developed and distributed by the Japan Physical Activity Research Platform ( to process the accelerometer data.

The accelerometry methods, including epoch length, non-wearing time, and valid wearing minutes and days, were defined based on previous studies32.37. Participants were asked to wear the accelerometer on the waist for ≥ 7 consecutive days throughout waking hours, except when showering, bathing, or swimming. The accelerometers were set to record data at 10 s sample intervals (epochs) throughout the wear period. Any time period with > 10 min of consecutive zero counts was defined as wear-free time within a day. Valid accelerometric data was analyzed at each data collection point, including > 600 min/day for at least four days, including a day off from school.

Statistical Analysis

We used LMM with REML methods to examine whether daily MVPA, LPA, and SB times changed during the five-year transition from elementary to secondary school. Based on previous findings, the model included school grade (time-coded: 0, 1, 2, 3, and 4) and grade2 (time-coded: 0, 1, 4, 9, and 16) in each wave of yearly time, sex, POW, and daily accelerometer wear time as independent covariates in the fixed part of the model19.

We considered two LMM models, LMM I and II, each performed with and without adjustments for the fixed effects of gender and the interaction between gender and grade. These models allowed for a random effect within the group where the initial assessment time was different. We also fitted the models with the random effect of each participant’s time-coded school grade. A quadratic trend was used to estimate the periods over which MVPA, LPA, and SB had changed. All valid data at each point in time were included in the analysis, as LMMs are robust to missing data and can estimate longitudinal trends with incomplete datasets38. LMMs were used because they are robust to missing data and can estimate longitudinal trends with incomplete datasets. This method allowed us to include all valid data collected at any point in time in the analyses. A total of 52, 54, 52, 53, and 53 participants were analyzed in ratings 1, 2, 3, 4, and 5, respectively, in this five-year longitudinal study (Table 2).

All statistical analyzes were performed with Stata for Windows version 15.1 (Stata, College Station, TX, USA). All significance tests were two-tailed and the results were considered statistically significant P< 0.05.

Ethical Approval

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and the 1964 Declaration of Helsinki and its subsequent amendments or comparable ethical standards. The study design was approved by the Ethics Committee of the Graduate School of Human Informatics Study, Tohoku Gakuin University (reference number 2017R001).

letter of acceptance

Informed consent was obtained from the parents of all individual participants enrolled in the study.

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