My Heart Counts Cardiovascular Health Study: Next Gen (MHC)

My Heart Counts Cardiovascular Health Study

The My Heart Counts Cardiovascular Health Study will utilize mobile health capabilities of smartphones to assess daily activity measures and compare these to measures of cardiovascular health risk factors and fitness. The study aims to collect cardiovascular health data on a diverse population by making the application available on both iOS and Android platforms. Using smartphone sensors and connected devices, the study will collect physical activity metrics, heart rate data, and responses to health questionnaires. The study includes a randomized crossover trial component examining the effectiveness of personalized activity coaching prompts generated by a language model compared to generic prompts.

Study Overview

• Status: Not yet recruiting
• Conditions: Physical Activity; Cardiovascular Health
• Intervention / Treatment: Behavioral: Personalized LLM Coaching; Behavioral: Generic Activity Prompts

Detailed Description

My Heart Counts is a smartphone-based mobile cardiovascular health research study designed to collect data on physical activity and heart health across a broad population. This new version expands on the original study (IRB-31409) with several key improvements: inclusion of Android users alongside iOS, creation of a Spanish-language version, and, for future versions of the app, development of a platform architecture that can host multiple sub-studies.

The study will utilize smartphone sensors and connected devices to measure physical activity patterns, fitness levels through standardized tests (6-minute walk test, 12-minute run/walk test), and cardiovascular risk factors reported through health questionnaires. All data collection occurs remotely through participants' smartphones without requiring clinical visits.

A key component of the study is a 14-day randomized crossover trial evaluating the effectiveness of different physical activity coaching approaches.

Participants will experience both personalized coaching messages generated by a large language model and standard activity prompts, each for 7 days, in a randomly assigned order. The primary outcome will be the change in physical activity levels between intervention periods.

The study will serve as a digital biobank, with data made available to qualified researchers after appropriate de-identification. This platform approach will enable efficient recruitment for future cardiovascular health sub-studies without requiring development of new applications.

• Study Type: Interventional
• Enrollment (Estimated): 15000
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Anders Johnson; Phone Number: 8016984141; Email: acjohn@stanford.edu
• Study Contact Backup: Name: Daniel Seung Kim,, MD, PhD, MPH; Phone Number: (206) 465-5858; Email: myheartcounts@stanford.edu

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• 18 years of age or older
• Resident of the United States
• Able to read, understand and consent to study

Exclusion Criteria:

• Not owning a compatible iOS or Android smartphone

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Prevention
• Allocation: Randomized
• Interventional Model: Crossover Assignment
• Masking: None (Open Label)

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Active Comparator: Personalized LLM Coaching	Behavioral: Personalized LLM Coaching; Participants receive daily text messages containing exercise coaching prompts generated by a large language model (LLM) that are personalized to the user's demographic information for a period of 7 days.
Placebo Comparator: Generic Activity Prompts	Behavioral: Generic Activity Prompts; Participants receive generic daily activity prompts for a period of 7 days (e.g., "Push yourself! Reach 10,000 steps today.")

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in Physical Activity levels	Change in daily physical activity levels as measured by step count smartphone sensors and connected health devices.	Time Frame: 14 days (7 days in each intervention period)

Collaborators and Investigators

• Sponsor: Stanford University
• Collaborators: Imperial College London; University of Washington

Study record dates

Study Major Dates

• Study Start (Estimated): April 30, 2026
• Primary Completion (Estimated): December 31, 2035
• Study Completion (Estimated): December 31, 2035

Study Registration Dates

• First Submitted: June 13, 2025
• First Submitted That Met QC Criteria: February 19, 2026
• First Posted (Actual): February 23, 2026

Study Record Updates

• Last Update Posted (Actual): February 23, 2026
• Last Update Submitted That Met QC Criteria: February 19, 2026
• Last Verified: February 1, 2026

More Information

Terms related to this study

• Keywords: physical activity; mobile health; cardiovascular risk; digital health; fitness; behavioral interventions; heart health
• Additional Relevant MeSH Terms: Behavior; Motor Activity
• Other Study ID Numbers: 78735

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No
• product manufactured in and exported from the U.S.: No