Stage-environment fit in high-pressure contexts: differential buffering effects of family support types on adolescent physical activity and sedentary time

Background: The transition from middle to high school is characterized by surging academic stress, a precipitous decline in moderate-to-vigorous physical activity (MVPA), and alarming increases in sedentary time (ST). While family support is known to buffer stress, the specific types of support required may shift dramatically across developmental stages. Guided by Stage-Environment Fit Theory and the Stress-Buffering Hypothesis, this study investigated whether the buffering effects of family tangible support versus emotional support on device-measured MVPA and ST differ between middle and high school students. Methods: A stratified sample of 523 adolescents (298 middle school, 225 high school) from diverse regions in China was recruited. MVPA and ST were objectively measured using ActiGraph GT3X+ accelerometers over seven consecutive days. Self-reported questionnaires assessed chronic academic stress and family support types. Multi-Group Structural Equation Modeling (MG-SEM) was employed to test the moderated effects. Results: < 0.01). Conclusion: The efficacy of family interventions is heavily contingent upon developmental timing. Combatting the dual burden of physical inactivity and sedentary behavior in high-pressure educational systems requires a transition from tangible parental involvement in early adolescence to autonomy-respecting emotional support in late adolescence.