Previous research suggest that sedentary behavior is emerging as a risk behavior for chronic disease and mortality (Katzmarzyk et al., 2009; Thorp et al., 2012). But it is unknown what factors influence sedentary behavior in Japanese adolescents. Therefore, the aim of this study was to clarify the associated factors of sitting time in Japanese adolescents.

Participants were 140 (mean age: 13.0±0.9, female: 49.3%, mean body mass index [BMI]: 19.7±3.0) 1st to 3rd grade (7th to 9th grade in USA) students of public junior high schools near Saga area in Japan. All students completed the questionnaires. Sitting time and moderate-to-vigorous physical activity (MVPA) was measured by the International Physical Activity Questionnaire. Physical fitness scores and academic performances (school grade) were received from school records. The physical fitness tests that were authorized by Japanese Ministry of Education, Culture, Sports, Science and Technology were used. The sum total of the 8 subjects grades (Japanese, social studies, math, science, English, music, arts, physical education) were used as academic performance scores.

Mean weekday and weekend sitting time were 442.8±217.5min and 485.8±255.3min, respectively. Using multiple regression analysis that controlled for several covariates (age, gender, BMI, physical fitness score, MVPA), weekday sitting time was significantly associated with gender (beta=0.244) and academic performance (beta=0.286), and weekend sitting time was significantly associated with gender (beta=0.217) only.

These results suggest that less weekday sitting time was associated with being male, greater physical fitness and worse academic performances among Japanese junior high school students.