(1) Participants and the survey outline
A total of 2,129 children aged between 6 and 13 from the Super Shokuiku School Project (Phase 3: January 2016) [10,20] and who belonged to one of five elementary schools in Takaoka City, Japan participated in this study. The Super Shokuiku School Project was designed to investigate food education and was supported by the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT). The overall purpose of the project was to promote healthy lifestyles in school children and improve their health. The survey was approved by the Ethics Committee of University of Toyama. Written informed consent was obtained from the participants’ parents, and participation was voluntary.
Participants were asked to complete questionnaires asking about sex, grade level, physical activity, lifestyle, overall health, enrichment of school life, social background, and parental lifestyles. The children responded with their parents if necessary. The child responded to items concerning sex, grade, physical activity, lifestyle, overall health, and enrichment of school life by themselves, while their parents responded to items concerning social background and parental lifestyles. All completed questionnaire were returned to the respective schools of each participant.
The physical activity portions of the questionnaire included the items of “frequency of physical activity”  and “preference for physical activity.”  Responses to “frequency of activity” were answered according to a 4-point scale and divided into the two following categories: “Very often (very often, often)” or “Not often (rarely, almost never).” Responses to “preference for physical activity” were also answered according to a 4-point scale, and were divided into the two following categories: “Like very much (like very much, like)” or “Dislike (don’t like so much, dislike).” Validity for both these items had already been determined by a previous study . In this context, a high frequency of physical activity was significantly associated with an increasing trend in energy expenditure originating from physical activity.
Social background and parental lifestyles
Social background was assessed based on the following items: Mother’s employment status, family structure, perceived family affluence, communication with parents, individual parental internet usage at home h/day (i.e., both the mother and father), and parental health behaviors according to Breslow (1980) (i.e., both the mother and father). The item concerning “mother’s employment status” [20,22] included three response categories (i.e., “full-time,” “part-time,” and “unemployed (housewife)”), while “family structure” [22,23] was categorized as either “three-generation family” or “nuclear family.” Further, “socioeconomic status” was determined according to perceived “family affluence” [20,22] (i.e., “affluent,” “neither,” or “not affluent”), while “communication with parents” [22,24] was categorized as either “often” or “rarely.” We also asked for the total time parents spent using the internet at home h/day. Here, responses were given according to a 6-point scale and divided into the two categories of “< 2hr (no or almost none, <1hr, and 1hr to <2hr)” and “≧ 2hr (2hr to <3h, and ≥3hr).” This was based on a 2018 report indicating that Japanese adults in their 30s spent an average of about 1.5 hours per day on the internet [10,25]. Breslow’s (1980) seven good health-related behaviors have been widely accepted for use in Westernized countries, and were thus used as parental health indicators in this study . The behaviors include (1) adequate sleep time, (2) no smoking, (3) appropriate weight control, (4) not drinking excessively, (5) regular physical activity, (6) no skipping of breakfast, and (7) not frequently snacking. We divided respondents into three groups based on their indicated number of behaviors (i.e., “low (0-3),” “middle (4-5),” and “high (6-7)”); higher numbers indicated healthier behaviors.
Child lifestyle factors
Child lifestyles were assessed based on breakfast consumption, wake-up time, bedtime, nighttime sleep duration, screen time h/day, and cram schools after school. Here, “breakfast consumption” [10,27] was classified into the two categories of “eat every day” and “skipping,” while “wake up time”  was classified into the three categories of “before 06:30,” “06:30-07:00,” and “after 07:00.” Further, “bedtime”  was classified into the three categories of “before22:00,” “22:00-23:00,” and “after23:00,” while “nighttime sleep duration”  was categorized according to the number of sleeping hours (i.e., “more than 8 hours” and “less than 8 hours”). This was based on previous research indicating that Japanese elementary school children average approximately 8.5 hours of sleep per night .
The question about “screen time h/day” for children included television and film viewing, gaming, and internet use. Here, responses were given according to a 6-point scale and divided into the two categories of “< 2h (no, almost none, <1h, and < 2h )” and “≧2h (< 3h, 3 to < 4h, and ≧4h).” In this context, the Japan Pediatric Association recommends that total screen time be limited to < 2h per day.
Overall health among child participants
A question from a validated Japanese version of the Dartmouth Primary Care Cooperative Information Project (COOP) was used to evaluate overall health among children [18,19,28]. They were specifically asked the following: “During the past 4 weeks, how would you rate your physical and mental health in general?” Subjects who rated their overall health as “excellent,” “very good,” or “good” were classified as having “good health status,” while those who answered “fair” or “poor” were classified as having “poor health status.”
Enrichment of school life
We asked two questions to subjectively assess “enrichment of school life,” including “Do you have close friends?”  and “Are you able to understand school lessons well?”  Responses were given according to 4 and 5-point scales, respectively, and then divided into the following respective categories for each question: “yes (many, a few)” or “no (not many, no friends)” and “understand well (well, relatively well)” or “ do not understand (neither, relatively poor, and poor).”
(3) Statistical analyses
Logistic regression analyses were conducted to evaluate the strengths of the associations between child physical activity and the items of social background, parental lifestyles, child lifestyles, child health, and enrichment of school life. All variables were simultaneously entered into the model during multivariate analyses. Odds ratios (ORs) and 95% confidence intervals (CIs) were also calculated. Finally, logistic regression analyses were performed to determine the strengths of the associations between “lack of physical activity” regardless of “prefer physical activity” with the items of social background, parental lifestyles, child lifestyles, overall child health, and enrichment of school life. All analyses were conducted using the statistical package for social scientists (SPSS) software version 22.0 J (SPSS, Chicago, IL, USA). Two-tailed P-values less than 0.05 were considered statistically significant for all tests.