Objective: Lack of regular physical activity (LPA) and the number of days/week with physical activity >60 minutes/day (Ndw) may be associated with school-health-relational difficulties (SHRDs) during the life-course. This study assessed their associations and the confounding role of socioeconomic features (nationality, family structure, parents' education/occupation/income) among younger adolescents. Methods: This cross-sectional population-based study included 1,559 middle-school adolescents from north-eastern France (10-18 years, 98% under 16 years, 778 boys and 781 girls). They completed over one-hour teaching period a questionnaire collecting last-12-month LPA and last-7-day Ndw (dependent variables), and risk factors including socioeconomic features, SHRDs (previous grade repetitions, last-12-month poor general health status/physical health/psychological health/social-relationships, depressive symptoms (and age at onset and duration from onset); cumulated number noted SHRDcn). Data were analyzed using logistic/linear regression models. Results: LPA was common (32.5%) and associated with all SHRDs (sex-age-adjusted odds ratio saOR reaching 1.99, p < .001) and depressive-symptoms duration (saOR 1.63 (p < .05) and 2.11 (p < .001) for 1-2 and ≥3 years, respectively, vs. no depressive symptoms). A dose-effect association was found between SHRDcn and LPA (24.0, 33.7, 45.6, and 53.5%; saOR 1.59, 2.58, and 3.43; for SHRDcn 1-2, 3-4, and ≥5 respectively, vs. SHRDcn = 0, p < .001). Ndw was similarly associated with all SHRDs and SHRDcn (sex-age-adjusted regression coefficient reaching -1.10 day/week, p < .001). These results were robust when controlling for socioeconomic features (18%<contribution<51%). Conclusions: Physical activity is associated with SHRDs, and socioeconomic features have an elevated confounding role. Healthcare providers can detect/reduce SHRDs and consequently improve physical activity among adolescents and prevent physical inactivity in adulthood.
• Lack of physical activity (LPA) is strongly associated with school-health-relational difficulties (SHRDs) affecting most adolescents.• There are dose-effect associations between cumulative number of SHRDs and both LPA and number of days/week with physical activity >60 min/day (Ndw).• These links are robust when controlling for socioeconomic features which have a strong confounding role.• The risk of LPA and reduced Ndw increase with the duration of depressive symptoms from their onset.• Prevention to detect/reduce SHRDs may improve physical activity, especially for most at-risk adolescents.