Engagement With Remote Delivery Channels in a Physical Activity Intervention for Senior Women in the US.

Purpose: Identify the effects of engagement with different intervention delivery channels on physical activity (PA), and the participant subgroups engaging with the different channels, among Women's Health Initiative Strong and Healthy () PA trial participants.

Design: Secondary analysis of data from , a pragmatic trial that used passive randomized consent.

Setting: United States (remote intervention in all 50 states).

Sample: 18,080 U.S. women, aged 68-99 years, assigned to the PA intervention arm.

Measures: 6 dichotomous variables operationalized engagement: Engagement with Targeted Inserts, Email (opened), Email (clicked links), Website (logging in), Website (tracking), Interactive Voice Response (IVR). PA was measured using the CHAMPS PA questionnaire.

Analysis: Linear regressions evaluated effects of engagement on PA. Conditional Inference Trees identified subgroups of participants engaging with different channels based on demographic and psychosocial variables.

Results: Engagement with each channel, except IVR, was associated with significantly more hours/week of PA (square root coefficients .29 - .13, values <.001). Consistently across channels, features that identified subgroups of participants with higher engagement included younger age, and higher levels of PA and physical function. Subgroups with the highest engagement differed from those with the lowest in most participant characteristics.

Conclusions: For equitable population-level impact via large-scale remotely-delivered PA programs, it may be necessary to identify strategies to engage and target harder to reach subgroups more precisely.

Clinical Trial Registration: The trial is registered at ClinicalTrials.gov (No. NCT02425345).