Outdoor physical activity is not associated with better mental health in a sample of predominantly Black people, but spending time in parks is.

Spending time outdoors may bolster mental health via relaxation and physical activity. Yet, most studies use self-report and involve majority White samples from higher income areas. Findings may not hold true using device-derived measurement, among minoritized participants, or in low-income neighborhoods. Our objectives were to test whether: i) time spent outdoors in physical activity is associated with mental health; ii) the effect is modified by the positive or negative outdoor conditions (amount of greenness or vacant houses/lots encountered while outdoors); iii) there is a correlation between our measures of outdoor conditions and perceived neighborhood conditions; and iv) there is a different relationship between time spent outdoors in parks (as an indicator of intentional nature exposure) and mental health. The sample of 112 participants (87% Black/African American persons) from 11 Detroit, MI neighborhoods wore a GPS and accelerometer for one week (May-Oct 2021) and completed a survey. We calculated exposure to greenness, vacant lots/houses while outdoors, and perceived neighborhood aesthetics. We fitted regression models for mental health measures separately and included time spent outdoors in PA, age, sex, and days with high precipitation. We then fitted models stratified by outdoor conditions. Last, we examined whether a similar relationship could be detected for time spent outdoors in parks. On average, ~30% of PA was conducted outdoors, and 56% of outdoor time involved PA. We observed an unexpected positive association between outdoor PA and anxiety (coef: 0.33, 95% CI: 0.14-0.51), depression (coef: 0.31, 95% CI: 0.15-0.47), and perceived stress score (coef: 0.18, 95% CI: 0.07-0.29). When stratified, we found consistent and/or larger associations for those exposed to high levels of vacant homes, high greenness (both aerial and street-level), low levels of vacant lots, and low perceived neighborhood aesthetics. Importantly and in contrast, we observed the opposite trend when examining time spent in parks (coef: -0.05, 95% CI: -0.10--0.01). These results contrast many studies showing positive relationships between time outdoors and mental health and highlight the need for research with diverse populations and better measures of outdoor conditions and intentionality of greenspace contact.