System identification of Just Walk: A behavioral mHealth intervention for promoting physical activity

Tutorial for Using Control Systems Engineering to Optimize Adaptive Mobile Health Interventions

“…Furthermore, when and where individuals fit steps in also changes (eg, weekend warriors vs evening gym rats) over time and also can vary between individuals. Our prior work [ 22 , 89 ] shows that individual variables (eg, stress and busyness) and contextual factors (eg, weekend or weekday) have different relationships to steps for different people. These idiosyncratic determinants change over time.…”

“…Semiphysical modeling, on the other hand, includes theorized model structures, predicted dynamics, and other factors that are either known or theorized to be true in terms of the interrelationship between variables. One could think of semiphysical modeling as a dynamical version of structural equation modeling [ 22 , 89 ]. In brief, theorized model structures, such as Figure 2 , along with predicted dynamics (eg, feedback loops are the ways in which the relationships occur dynamically) are articulated within a mathematical model [ 97 , 124 ].…”

“…With these tasks defined in abstract, we turn to the Just Walk example. In our previous work [ 21 , 22 , 89 ], we conducted human-centered design work to develop an app for adults who are midlife and older, overweight, and sedentary. We then conducted a 12-week system identification open loop experiment, which is described below.…”

“…This was because, although we did conduct secondary data analyses to vet our dynamical model [ 100 ], the secondary data analyses did not enable us to do rigorous estimation and validation of our dynamical model. On the basis of this, and our desire to develop an eventual model-based controller, we conducted an open loop system identification experiment [ 89 , 121 , 125 ].…”

“…For example, we have been developing an adaptive PA intervention, Just Walk, which includes goal setting, positive reinforcement, and self-monitoring components [ 20 - 22 ]. The end goal for this intervention is to help individuals meet and maintain PA guidelines of 10,000 steps per day by developing an intervention that is responsive to the idiosyncratic and dynamic nature of steps (see Case Study Overview section for more details).…”