Identifying Optimal Moments for Delivering Digital Prompts to Reduce Prolonged Sedentary Behavior in Older Adults: An Intensive Longitudinal Study Using Sensor-Triggered Ecological Momentary Assessment.

Background: The optimal moment to deliver digital prompts for reducing sedentary behavior (SB) is when individuals are susceptible to prolonged SB (vulnerability) and open to behavior change (opportunity). This study aims to examine both vulnerability and opportunity.

Methods: A 14-day ecological momentary assessment study was conducted with 105 older adults. Participants wore a Fitbit activity tracker and an ActivPAL accelerometer and used a smartphone-based ecological momentary assessment app. Sensor-triggered questionnaires were delivered via the app after 30 minutes of SB to capture participants' activity, physical, social, and temporal contexts; feelings of pain and fatigue; and willingness to interrupt SB. Descriptive statistics identified states of vulnerability, whereas linear mixed models examined when participants are willing to interrupt prolonged SB, shedding light on states of opportunity.

Results: Ecological momentary assessment data (n = 2580) showed that older adults were most vulnerable to prolonged SB while watching TV (36.3%) and using digital devices (14.7%). Prolonged SB predominantly occurred at home (91.2%), in the evening (46.4%), when feeling fatigue (52.2%), and when experiencing mild pain (21.1%). The willingness to interrupt SB varied by activity, physical and social context, perceived pain, and level of fatigue, but not by time of day. Specifically, participants were more willing to interrupt their SB when engaging in mentally active SB and when indoors, alone, or with close relatives.

Conclusions: Contextual factors significantly influence older adults' vulnerability to prolonged SB and their willingness to interrupt it. This empirical information can guide the design of just-in-time adaptive interventions that deliver strategically timed prompts to reduce prolonged SB in older adults.