To determine whether time spent outdoors was associated with increased moderate-to-vigorous physical activity (MVPA) and related health benefits in youth.

We performed a cross-sectional study of 306 youth aged 13.6 ± 1.4 years. The exposure of interest was self-reported time spent outdoors after school, stratified into three categories: none, some, and most/all of the time. The main outcome of interest was accelerometer-derived MVPA (Actical: 1500 to >6500 counts/min). Secondary outcomes included sedentary behavior, cardiorespiratory fitness, overweight status, and blood pressure.

Among the 306 youth studied, those who reported spending most/all of their after-school time outdoors (n = 120) participated in more MVPA (61.0 ± 24.3 vs 39.9 ± 19.1 min/day; adjusted P < .001), were more likely to achieve the recommended minimum 60 min/day of MVPA (aOR 2.8; 95% CI, 1.3-6.4), spent less time in sedentary activities (539 ± 97 min/day vs 610 ± 146 min/day; adjusted P < .001), and had higher cardiorespiratory fitness (49 ± 5 vs 45 ± 6 mL/kg/min; adjusted P < .001) than youth who reported no time outdoors (n = 52). No differences in overweight/obesity or blood pressure were observed across the groups.

Time spent outdoors is positively associated with MVPA and cardiorespiratory fitness in youth and negatively associated with sedentary behavior. Experimental trials are needed to determine whether strategies designed to increase time spent outdoors exert a positive influence on physical activity and fitness levels in youth.