• Marc A Adams, Michael Todd, Siddhartha S Angadi, Jane C Hurley, Chad Stecher, Vincent Berardi, Christine B Phillips, Mindy L McEntee, Melbourne F Hovell, and Steven P Hooker.
• College of Health Solutions, Arizona State University, Phoenix, Arizona. Electronic address: marc.adams@asu.edu.
• Am J Prev Med. 2022 Feb 1; 62 (2): e57e68e57-e68.

IntroductionPotent lifestyle interventions to increase moderate-to-vigorous physical activity are urgently needed for population-level chronic disease prevention. This trial tested the independent and joint effects of a mobile health system automating adaptive goal setting and immediate financial reinforcement for increasing daily walking among insufficiently active adults.Study DesignParticipants were randomized into a 2 (adaptive versus static goal setting) X 2 (immediate versus delayed financial incentive timing) condition factorial trial to increase walking.Settings/ParticipantsParticipants (N=512 adults) were recruited between 2016 and 2018 and were 64.5% female, aged 18-60 years, 18.8% Hispanic, 6.1% African American, and 83% White.InterventionPrinciples of reinforcement and behavioral economics directed intervention design.Main Outcome MeasuresParticipants wore accelerometers daily (133,876 day-level observations) that remotely measured moderate-to-vigorous physical activity bout minutes of ≥3 minutes/day for 1 year. Primary outcomes were between-condition differences in (1) engaging ≥1 bout of moderate-to-vigorous physical activity on each day and (2) on days with ≥1 bout, daily total moderate-to-vigorous physical activity minutes.ResultsMixed-effects hurdle models tested treatment group X phase (time) interactions using an intent-to-treat approach in 2021. Engaging in any ambulatory moderate-to-vigorous physical activity was greater for Adaptive than for Static Goal groups (OR=2.34, 95% CI=2.10, 2.60 vs OR=1.66, 95% CI=1.50, 1.84; p<0.001) and for Immediate than for Static Reinforcement groups (OR=2.16 95% CI=1.94, 2.40 vs OR=1.77, 95% CI=1.59, 1.97; p<0.01). The Immediate Reinforcement group increased by 16.54 moderate-to-vigorous physical activity minutes/day, whereas the Delayed Reinforcement group increased by 9.91 minutes/day (p<0.001). The combined Adaptive Goals + Immediate Reinforcement group increased by 16.52 moderate-to-vigorous physical activity minutes/day, significantly more than that of either Delayed Reinforcement group.ConclusionsThis study offers automated and scalable-behavior change strategies for increasing walking among adults most at-risk for chronic diseases attributed to sedentary lifestyles.Trial RegistrationThis study is registered at www.clinicaltrials.gov (ClinicalTrials.gov Identifier: NCT02717663).Copyright © 2021 American Journal of Preventive Medicine. Published by Elsevier Inc. All rights reserved.

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