RESUMEN
Physical activity is universally acknowledged for its benefits to mental health; however, the specific intensities and timings that best benefit adolescents' mental health, crucial due to their significant influence on daily schedules, have not been thoroughly investigated. This study addresses the substantive research gap by exploring the varied effects of physical activity intensity (light versus moderate to vigorous) and timing (weekdays versus weekends and holidays) on adolescent mental health. Utilizing a large-scale longitudinal dataset (NT1 = 84,054; NT2 = 44,623) from 158 schools, this research describes the current state of adolescent physical activity and investigates the effects of physical activity on mental health outcomes, including positive (i.e., life satisfaction, positive mental health) and negative indicators (depression, anxiety), over a 6-month period. Participants were adolescents aged 9-19 years (mean age = 12.73 ± 2.43 years, 48.9% female), with the analysis adjusted for potential confounding factors. Results showed that as adolescents grow older, their engagement in moderate-to-vigorous physical activity during both weekdays and weekends/holidays tends to decrease, while light physical activity during weekdays increases. Multilevel regression analysis indicated that moderate-to-vigorous physical activity during weekends/holidays at Time 1 positively correlated with better mental health outcomes at Time 2 (six months later), featuring enhanced positive indicators and reduced negative ones. Moderate-to-vigorous physical activity on weekdays at Time 1 was positively linked to mental health at Time 2. Light physical activity during weekends/holidays at Time 1 positively predicted life satisfaction and positive mental health at Time 2. In contrast, light physical activity on weekdays at Time 1 negatively correlated with life satisfaction at Time 2. The study underscores the importance of promoting moderate-to-vigorous physical activity, particularly on weekends and holidays, to improve mental health outcomes among adolescents.