A Personalized Exercise Assistant using Reinforcement Learning (PEARL): Results from a four-arm Randomized-controlled Trial

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Main Authors: Lee, Amy Armento, Hegde, Narayan, Deliu, Nina, Rosenzweig, Emily, Suggala, Arun, Lakshminarasimhan, Sriram, He, Qian, Hernandez, John, Seneviratne, Martin, Singh, Rahul, Kalkar, Pradnesh, Shanmugam, Karthikeyan, Raghuveer, Aravindan, Singh, Abhimanyu, Nguyen, My, Taylor, James, Alla, Jatin, Villar, Sofia S., Emir-Farinas, Hulya
Format: Preprint
Published: 2025
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author Lee, Amy Armento
Hegde, Narayan
Deliu, Nina
Rosenzweig, Emily
Suggala, Arun
Lakshminarasimhan, Sriram
He, Qian
Hernandez, John
Seneviratne, Martin
Singh, Rahul
Kalkar, Pradnesh
Shanmugam, Karthikeyan
Raghuveer, Aravindan
Singh, Abhimanyu
Nguyen, My
Taylor, James
Alla, Jatin
Villar, Sofia S.
Emir-Farinas, Hulya
author_facet Lee, Amy Armento
Hegde, Narayan
Deliu, Nina
Rosenzweig, Emily
Suggala, Arun
Lakshminarasimhan, Sriram
He, Qian
Hernandez, John
Seneviratne, Martin
Singh, Rahul
Kalkar, Pradnesh
Shanmugam, Karthikeyan
Raghuveer, Aravindan
Singh, Abhimanyu
Nguyen, My
Taylor, James
Alla, Jatin
Villar, Sofia S.
Emir-Farinas, Hulya
contents Consistent physical inactivity poses a major global health challenge. Mobile health (mHealth) interventions, particularly Just-in-Time Adaptive Interventions (JITAIs), offer a promising avenue for scalable, personalized physical activity (PA) promotion. However, developing and evaluating such interventions at scale, while integrating robust behavioral science, presents methodological hurdles. The PEARL study was the first large-scale, four-arm randomized controlled trial to assess a reinforcement learning (RL) algorithm, informed by health behavior change theory, to personalize the content and timing of PA nudges via a Fitbit app. We enrolled and randomized 13,463 Fitbit users into four study arms: control, random, fixed, and RL. The control arm received no nudges. The other three arms received nudges from a bank of 155 nudges based on behavioral science principles. The random arm received nudges selected at random. The fixed arm received nudges based on a pre-set logic from survey responses about PA barriers. The RL group received nudges selected by an adaptive RL algorithm. We included 7,711 participants in primary analyses (mean age 42.1, 86.3% female, baseline steps 5,618.2). We observed an increase in PA for the RL group compared to all other groups from baseline to 1 and 2 months. The RL group had significantly increased average daily step count at 1 month compared to all other groups: control (+296 steps, p=0.0002), random (+218 steps, p=0.005), and fixed (+238 steps, p=0.002). At 2 months, the RL group sustained a significant increase compared to the control group (+210 steps, p=0.0122). Generalized estimating equation models also revealed a sustained increase in daily steps in the RL group vs. control (+208 steps, p=0.002). These findings demonstrate the potential of a scalable, behaviorally-informed RL approach to personalize digital health interventions for PA.
format Preprint
id arxiv_https___arxiv_org_abs_2508_10060
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle A Personalized Exercise Assistant using Reinforcement Learning (PEARL): Results from a four-arm Randomized-controlled Trial
Lee, Amy Armento
Hegde, Narayan
Deliu, Nina
Rosenzweig, Emily
Suggala, Arun
Lakshminarasimhan, Sriram
He, Qian
Hernandez, John
Seneviratne, Martin
Singh, Rahul
Kalkar, Pradnesh
Shanmugam, Karthikeyan
Raghuveer, Aravindan
Singh, Abhimanyu
Nguyen, My
Taylor, James
Alla, Jatin
Villar, Sofia S.
Emir-Farinas, Hulya
Machine Learning
Consistent physical inactivity poses a major global health challenge. Mobile health (mHealth) interventions, particularly Just-in-Time Adaptive Interventions (JITAIs), offer a promising avenue for scalable, personalized physical activity (PA) promotion. However, developing and evaluating such interventions at scale, while integrating robust behavioral science, presents methodological hurdles. The PEARL study was the first large-scale, four-arm randomized controlled trial to assess a reinforcement learning (RL) algorithm, informed by health behavior change theory, to personalize the content and timing of PA nudges via a Fitbit app. We enrolled and randomized 13,463 Fitbit users into four study arms: control, random, fixed, and RL. The control arm received no nudges. The other three arms received nudges from a bank of 155 nudges based on behavioral science principles. The random arm received nudges selected at random. The fixed arm received nudges based on a pre-set logic from survey responses about PA barriers. The RL group received nudges selected by an adaptive RL algorithm. We included 7,711 participants in primary analyses (mean age 42.1, 86.3% female, baseline steps 5,618.2). We observed an increase in PA for the RL group compared to all other groups from baseline to 1 and 2 months. The RL group had significantly increased average daily step count at 1 month compared to all other groups: control (+296 steps, p=0.0002), random (+218 steps, p=0.005), and fixed (+238 steps, p=0.002). At 2 months, the RL group sustained a significant increase compared to the control group (+210 steps, p=0.0122). Generalized estimating equation models also revealed a sustained increase in daily steps in the RL group vs. control (+208 steps, p=0.002). These findings demonstrate the potential of a scalable, behaviorally-informed RL approach to personalize digital health interventions for PA.
title A Personalized Exercise Assistant using Reinforcement Learning (PEARL): Results from a four-arm Randomized-controlled Trial
topic Machine Learning
url https://arxiv.org/abs/2508.10060