Online Program

Joint Modeling the Frequency and Duration of Physical Activity Using Data from a Lifestyle Intervention Trial

*Juned Siddique, Northwestern University 
Donald Hedeker, University of Chicago 
Bonnie Spring, Northwestern University 

Keywords: joint model, shared parameter, physical activity, accelerometry

U.S. physical activity guidelines for adults require at least 150 minutes of moderate-intensity physical activity per week, which is to be performed in bouts of at least 10 minutes. Thus, two key components for measuring physical activity are the frequency of exercise bouts and the duration of bouts. In interventions to increase physical activity levels, participants can achieve federal guidelines three ways: 1) keep bout durations constant, but increase the number of bouts per week; 2) keep frequency of bouts constant, but increase bout duration; 3) increase both the number of bouts and their duration. Current approaches to modeling physical activity ignore the frequency of exercise bouts and focus on accumulated minutes of physical activity bouts. We propose a statistical model that jointly models both the frequency of exercise bouts and the duration of bouts. Our model allows us to investigate the mechanism by which participants increase their physical activity levels, potentially providing insights on intervention effectiveness.