Roybal Via Habit Formation

This pilot study will develop and evaluate ViaHabit, a personalized, cue-based walking intervention designed to promote physical activity habit formation among sedentary midlife adults. The study is based on the premise that routine transitions, defined as periods when one daily activity has ended and another has not yet begun, may represent receptive opportunities for initiating new health behaviors. The long-term goal is to increase physical activity during midlife, a critical period for reducing risk factors associated with cognitive decline and dementia.

The study will enroll approximately 10 adults aged 45 to 65 years who are physically inactive and experience competing work, caregiving, parenting, or other role demands. Participants must own or be willing to use an iPhone-compatible device and be able to walk without assistance.

The study uses a 12-week, single-arm, within-subject design consisting of two phases. During Phase 1 (2-week observation period), participants will use an Apple Watch, smartphone applications, and digital calendar tools to collect multimodal data on daily behavior, including physical activity, location patterns, calendar events, and contextual information. These data will be used to develop individualized computational models of participants' daily routines and identify recurring routine transitions that may serve as effective cues for physical activity initiation.

Following model development, participants will enter Phase 2 (4-week intervention period). In a virtual coaching session, participants will identify up to two routine transitions that can function as cues for walking and will create personalized "if-then" action plans linking those cues to a 15-minute brisk walk. Automated smartwatch notifications will be delivered when the selected routine transitions occur to increase cue salience and support initiation of physical activity. Walking behavior will be continuously monitored through wearable devices.

The primary objectives are to evaluate the feasibility of identifying individualized routine transitions from passive sensing data and the feasibility and acceptability of delivering a personalized, cue-based walking intervention anchored to those transitions. Secondary and exploratory outcomes include adherence to study procedures, walking behavior, cue-triggered behavioral enactment, habit strength, physical activity levels, and cognitive function. Habit strength will be assessed using measures of behavioral automaticity, while cognitive function will be evaluated through mobile cognitive assessments administered during the intervention period.

The findings will inform the development of scalable, data-driven interventions that leverage naturally occurring daily routines to support physical activity habit formation and healthy aging.

• ViaHabit (Behavioral): ViaHabit is a personalized, cue-based walking intervention designed to promote physical activity habit formation in sedentary midlife adults. Following a 2-week observation period, individualized routine models are developed using data collected from wearable devices, smartphones, and digital calendars. Participants then complete a coaching session to identify up to two routine transitions that can serve as cues for physical activity and develop personalized if-then action plans linking each cue to a 15-minute brisk walk. During the 4-week intervention period, automated smartwatch notifications are delivered at the selected routine-transition cues to increase cue salience and support initiation of walking behavior. The intervention aims to strengthen cue-behavior associations through repeated pairing of routine completion cues with walking, thereby increasing behavioral automaticity and physical activity participation.

Primary outcomes

• Feasibliity of the ViaHabit Intervention - Recruitment [Week 8 (end of intervention)]: Feasibility will be assessed by participant recruitment rates.
• Feasibliity of the ViaHabit Intervention - Retention [Week 8 (end of intervention)]: Feasibility will be assessed by participant retention rates.
• Feasibliity of the ViaHabit Intervention - Data Collection [Week 8 (end of intervention)]: Feasibility will be assessed by participant completion of Phase 1 data collection.

Secondary outcomes

• Habit Strength for Walking [Baseline and weekly during the 4 week intervention period through Week 8]: Habit strength will be assessed using the 4-item Self-Reported Behavioral Automaticity Index (SRBAI), adapted to each participant's selected routine-transition cue. Higher scores indicate greater automaticity of walking behavior in response to the cue.

Sex: All, ages: 45 Years to 65 Years

Inclusion Criteria:

* Age 45 to 65 years.
* Reports no leisure-time physical activity during the past month and engages in <400 MET-minutes/week of physical activity as assessed by the IPAQ-Short Form.
* Has competing role demands, defined as ≥10 hours/week of paid work, caregiving, parenting, or volunteer activities.
* Owns an iPhone (iOS smartphone) with reliable internet access and is willing to use study-related mobile applications and wearable devices.
* Able to walk without assistance.
* Uses, or is willing to use, a digital calendar application and share de-identified event timing data with the study team.
* Able to understand study procedures and provide informed consent.

Exclusion Criteria:

* Plans to relocate or engage in extended travel during the next 3 months.
* Pregnant or planning to become pregnant during the study period.
* Currently participating in another physical activity or behavioral intervention study.
* Has a medical condition that may limit safe participation in walking, impair the ability to provide informed consent, or interfere with study adherence.