BackgroundPhysical activity levels in childhood have decreased, making the promotion of children’s physical activity an important issue. The present study examined gender and grade differences in objectively measured sedentary behavior, physical activity, and physical activity guideline attainment among Japanese children and adolescents.MethodsIn total, 329 boys and 362 girls age 3–15 years completed the survey. School grade, gender, height, and weight were collected by questionnaires and physical activity objectively measured using an accelerometer (Lifecorder Suzuken Co.). Physical activity level (in MET) was classified as sedentary (<1.5), light (≥1.5 to <3), moderate (≥3 to <6), or vigorous (≥6). Continuous zero accelerometer counts for ≥20 min were censored and a valid accelerometry study required at least 3 days (2 weekdays and 1 weekend day) with > 600 min/day total wear time. Two-way analysis of covariance and logistic regression analyses, adjusted for weight status and accelerometer wear time, were used to examine gender and grade differences in physical activity variables and the likelihood of physical activity guideline attainment by gender and grade level.ResultsParticipants were sedentary 441.4 (SD, 140.1) min/day or 53.7 % of the average daily accelerometer wear time of 811.2 (118.7) min, engaged in light physical activity 307.1 (70.0) min or 38.4 % of wear time, moderate physical activity 34.6 (14.8) min (4.3 %), vigorous physical activity 28.3 (19.1) min (3.6 %), and took 12462.6 (4452.5) steps/day. Boys were more physically active and took more steps/day than girls. Students in higher grades were less active than those in lower grades. Boys were significantly more likely to meet physical activity guidelines than girls (OR: 2.07, 95 % CI: 1.45–2.96). Preschoolers (6.66, 4.01–11.06), lower-grade elementary school students (17.11, 8.80–33.27), and higher-grade elementary school students (7.49, 4.71–11.92) were more likely to meet guidelines than junior high school students.ConclusionsBoys and lower-grade students engaged in more physical activity and were more likely to attain guidelines than girls and higher-grade students. These findings highlight the need for effective and sustainable strategies to promote physical activity in Japanese school children.

To increase physical activity levels among Japanese adolescents, implementation of after-school programs or environmental modifications developed within the school setting could be effective strategies.

Purpose: Background: Physical activity is a complex behavior which involves the interaction of multilevel factors at the individual, social and environmental level. However, previous studies have largely focused on psychological and/or social environmental factors and the direct impact of such factors on physical activity. There are few studies having examined how multilevel factors may interact to influence activity level. Therefore, the purpose of the present study was to examine both direct and indirect effects of multilevel factors on school-based physical activity in Japanese adolescent boys. Methods: In this cross-sectional survey of the Japanese adolescent lifestyles, 379 junior high school boys were invited to complete self-report measures of age, grade, weight, height, self-efficacy, social support (family, friends and teachers), school physical environment (equipment, facilities and safety) and average minutes per week of physical activity during lunch time and after-school hours occurring at school. Structural equation modeling analyses controlling for age were utilized to examine the effects of body mass index (BMI), self-efficacy, social support and school physical environmental variables on lunchtime and after-school physical activity. Results: During lunch time, self-efficacy exhibited direct positive effects on physical activity. BMI, facilities, and safety were indirectly associated with lunchtime physical activity through self-efficacy. However, there were no significant relationships of equipment and social support with lunchtime physical activity. During after-school hours, family support and facilities directly affected physical activity. Self-efficacy was indirectly related with physical activity through family support. BMI, equipment, and safety indirectly affected physical activity through self-efficacy and/or family support. Conclusion: Effects of multilevel factor on physical activity among adolescent boys differed according to context, which implies that interventions to promote physical activity should be context-specific. Findings encourage the development of future effective interventions to promote physical activity through self-efficacy during lunch time as well as family support during after-school hours.

Background: Identifying correlates of physical activity that can be targeted as potential mediators is important for developing interventions to promote physical activity in adolescent girls. However, the mediated effects of multilevel correlates of physical activity remain poorly understood. Therefore, the present study aimed to examine direct and mediated effects of personal, social and perceived school physical environmental factors on school-based physical activity of Japanese adolescent girls. Methods: In this cross-sectional survey of the Japanese adolescent lifestyles, 344 junior high school girls were invited to complete self-report measures of age, grade, weight, height, self-efficacy, social support (family, friends and teachers), perceived school physical environment (equipment, facilities and safety) and physical activity at school (min per week during lunch time and after-school hours). Structural equation modeling analysis controlling for age was performed to examine the effects of body mass index (BMI), self-efficacy, social support and school physical environmental variables on lunchtime and after-hours physical activity. Results: The final structural model demonstrated an acceptable fit for each context-specific physical activity. During lunch recess, perceived equipment and friend support exhibited direct effects on physical activity; perceived facilities, safety, and selfefficacy were indirectly associated with physical activity through friend support. During afterschool hours, both family and friend support directly affected physical activity at school; perceived safety, facilities and self-efficacy exhibited indirect effects on physical activity through family or friend support. However, there were no significant associations between equipment and after-school-hours physical activity. Regardless of contexts, BMI had neither direct nor indirect effects on physical activity. Conclusion: Social support from family and friends was identified as factors mediating the effects of perceived environment and self-efficacy on school-based physical activity among Japanese adolescent girls. This finding encourages the future development of effective interventions to promote physical activity through family and friend support in the future.

Although cross-sectional studies regarding the relationship between physical fitness and academic achievement among Japanese children have been previously reported, no longitudinal study has yet been reported for Japanese children. The purpose of this study was to examine the cross-sectional and longitudinal relationships between physical fitness and academic achievement among Japanese adolescents. This cohort study included 1,189 seventh-and ninth-grade students from two schools. The follow-up period was 2 years. A physical fitness test involving eight test items (hand grip, sit-ups, sit and reach, side-to-side jump, 20-m shuttle run, 50-m dash, standing broad jump and handball throwing) was conducted to evaluate the fitness of the participants. Academic achievement in Japanese, mathematics and a foreign language (English) was assessed at baseline and follow-up using cumulative guidance records. Participants were classified into low-low, high-low, low-high, and high-high groups based on physical fitness test results at baseline and follow-up. Compared with the groups showing low fitness levels, those showing high fitness levels for all items of the physical fitness test expect handball throwing had increased odds of showing high academic achievement levels in all three subjects at baseline and/or follow-up compared with the low-fitness groups. Sit-ups and 20-m shuttle run in the high-high and lowhigh groups were related to higher academic achievement levels at follow-up compared with those in the low-low group for both boys and girls. Therefore, this study suggests that various physical fitness outcomes are positively associated with high academic achievement levels for Japanese children.