Feasibility Test of Personalized (N-of-1) Trials for Increasing Middle-Aged and Older Adults' Physical Activity.

Purpose: To test the effectiveness and feasibility of a remotely delivered intervention to increase physical activity (walking) in middle-aged and older adults.

Design: This study used a personalized (N-of-1) trial design.

Setting: This study took place at a major healthcare system from November 2021 to February 2022.

Subjects: Sixty adults (45-75 years, 92% female, 80% white) were recruited.

Intervention: A 10-week study comprising a 2-week baseline, followed by four 2-week periods where four behavior change techniques (BCTs) - self-monitoring, goal setting, action planning, and feedback - were delivered one at a time in random order.

Measures: Activity was measured by a Fitbit, and intervention components delivered by email/text. Average daily steps were compared between baseline and intervention. Participants completed satisfaction items derived from the System Usability Scale and reported attitudes and opinions about personalized trials.

Results: Participants rated personalized trial components as feasible and acceptable. Changes in steps between baseline and intervention were not significant, but a large heterogeneity of treatment effects existed, suggesting some participants significantly increased walking while others significantly decreased.

Conclusions: Our intervention was well-accepted but use of BCTs delivered individually did not result in a significant increase in steps. Feasibility and heterogeneity of treatment effects support adopting a personalized trial approach to optimize intervention results.