Associations of Physical Activity, Sedentary Behavior, and Body Mass Index with Abnormal Posture among Primary School Students: A Cross-sectional Study

Abstract

This cross-sectional study examined the relationships among physical activity (PA), sedentary behavior (SB), body mass index (BMI), and postural abnormalities in 305 sixth-grade students from urban and rural schools in Shenyang, China. Standardized assessments and mediation analyses were employed. The findings revealed alarming public health concerns, with 84.26% of students showing suspected scoliosis, 51.8% being overweight or obese, and 88.5% engaging in more than two hours of sedentary behavior per day. PA was negatively correlated with both BMI (r = −0.462, p < 0.01) and postural abnormalities (r = −0.513, p < 0.01), whereas SB showed positive correlations with BMI (r = 0.375, p < 0.01) and postural abnormalities (r = 0.586, p < 0.01). Mediation analysis indicated that PA and SB partially mediated the association between BMI and postural abnormalities. The total effect of BMI (0.059) was partitioned into a direct effect (0.026, 44.07%) and indirect effects through PA (0.015, 25.42%), SB (0.013, 22.03%), and the sequential pathway PA→SB (0.005, 8.48%). These findings suggest that BMI affects postural health not only through direct mechanical loading but also indirectly by reducing PA and increasing SB. The study highlights the urgent need for integrated school-based interventions that promote active lifestyles, reduce sedentary time, and manage body weight to prevent postural abnormalities in children.