Relationship between time spent outdoors from objective image data and overall PA time and intensity

Purpose: To investigate whether time spent outdoors measured objectively by a person wearing a camera is positively related to objectively measured physical activity (PA) time and intensity in adults.

Methods: Adults (N=62, 21-82 years old) wore an ActiGraph accelerometer and Sensecam for 1 to 8 days. Sensecam images were annotated for indoor or outdoor location. Accelerometer counts per minute (CPM) and Sensecam image data were aggregated to the minute level. Average daily total PA time was computed as minutes spent at >100 CPM and moderate to vigorous PA (MVPA) as minutes spent at >2020 CPM. A linear regression model tested the relationship between time spent outdoors and total PA time. Repeated Measures Analysis of Covariance assessed differences in percentage of MVPA obtained indoors versus outdoors. Log transformed variables were used for analyses to account for non-normal distribution.

Results: Participants spent an average of 385 (SD=138) and 75 (SD= 55) minutes indoors and outdoors per day, with a total of 104 (SD=47) and 51 (SD=34) minutes of indoor PA and outdoor PA, respectively. A one hour increase in outdoor time was associated with a 23 minute increase in PA time (p < 0.001). 68% (SD=29) of all MVPA was obtained while outdoors compared to 32% (SD=29) when indoors, which was significantly different after adjusting for wear time, age and BMI (F=16.46, p < 0.01).

Conclusions: Being outdoors may encourage physical activity and a greater amount of outdoor PA may reach moderate to vigorous intensities.