Adaptive Goals and Reinforcement Timing to Increase Physical Activity in Adults: A Factorial Randomized Trial

Abstract

Introduction: Potent 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 design: Participants 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/participants: Participants (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.

Intervention: Principles of reinforcement and behavioral economics directed intervention design.

Main outcome measures: Participants 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.

Results: Mixed-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.

Conclusions: This study offers automated and scalable-behavior change strategies for increasing walking among adults most at-risk for chronic diseases attributed to sedentary lifestyles.

Trial registration: This 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.

Figures

Figure 1.

CONSORT diagram of participant flow. DQ, disqualified.

Figure 1.

CONSORT diagram of participant flow. DQ, disqualified.

Figure 2.

Effects of goal setting (left panels) and reinforcement timing (right panels) on changes to engaging in any MVPA minutes/day (top panels) and on mean MVPA bout minutes/day (bottom panels).a,b,c aData represent 10-day baseline and 365-day intervention phases. bVertical dashed lines denote transition between baseline and intervention phases. cBaseline phase (Days Post Randomization <0) and intervention phase (Days Post Randomization ≥0). MVPA, moderate-to-vigorous physical activity; Rf, reinforcement.

Figure 3.

Differences between intervention groups in likelihood of any MVPA (top panel) and mean MVPA bout minutes/day (bottom panel).a,b,c aData represent 10-day baseline and 365-day intervention phases. bVertical dashed line denotes transition between baseline and intervention phases. cBaseline phase (Days Post Randomization <0) and intervention phase (Days Post Randomization ≥0). MVPA, moderate-to-vigorous physical activity; Rf, reinforcement.