The protective effect of physical activity on mental health of middle school students at different stages during the COVID-19 outbreak.

This study aims to further understand the changes in physical activity level(PAL) and mental health among adolescents before and after the outbreak of COVID-19 and explore the protective role of physical activity (PA) on the mental health of adolescents during major disasters. A convenient sampling method was used to conduct a cross-sectional survey. The cross-sectional data from 2838 Chinese middle school students (mean age = 14.