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LLM-driven text-based coaching prompts grounded in the Transtheoretical Model of Change increase daily step count compared to generic prompts in adults at risk for cardiovascular disease.

The My Heart Counts study is a prospective observational cohort with an embedded randomized crossover trial (N=15,000) evaluating personalized LLM-generated coaching prompts versus generic prompts. The primary endpoint is change in daily step count, analyzed using mixed-effects models.

Last updated: Jul 7, 2026•1 RCTs•📖 Read as article →

Evidence Score

Evidence Score42/100
Human RCT★★☆☆☆
Meta-analysis☆☆☆☆☆
Mechanism★★★★★
Safety★★★★☆
Confidencelow

Study Evidence

Study 1. Design and rationale of the my heart counts cardiovascular health study: a large-scale, fully digital biobank, and randomized trial of large language model-driven coaching of physical activity.

observational

Schmiedmayer P, Johnson A, Schuetz N, Kollmer L, Goldschmidt P, Delgado-SanMartin J, Zhang KW, Mantena SD, Tolas A, Montalvo S, Ramirez-Posada M, O'Sullivan JW, Oppezzo M, King AC, Rodriguez F, Ashley E, Lawrie A, Kim DS · American journal of preventive cardiology (2026)

Participants: N/A
Duration: Not specified (crossover design with intervention weeks)
Intervention: LLM-driven text-based coaching prompts grounded in the Transtheoretical Model of Change vs. generic text-based prompts
Outcome: Change in daily step count (primary), mean active minutes, calorie burn, submaximal and maximal cardiorespiratory fitness, sleep quality, resting heart rate, heart rate variability
Effect Size: N/A
Population: Adults (N=15,000) across the United States and United Kingdom, recruited via smartphone application

Result:

PubMed: 42395096DOI: 10.1016/j.ajpc.2026.101565

Mechanism Graph

LLM generates personalized coaching prompts based on Transtheoretical Model of Change
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Prompts are delivered via smartphone application
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Participants receive prompts during intervention weeks in crossover design
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Result: Change in daily step count compared to generic prompts

Limitations

  • ⚠Results are not yet available as recruitment commenced in March 2026 and is ongoing
  • ⚠Platform exclusivity (iOS only initially, Android planned for 2027) may limit generalizability
  • ⚠Reliance on smartphone-based passive data collection may introduce selection bias toward tech-savvy individuals

Frequently Asked Questions

What is the primary outcome of the My Heart Counts trial?▼

The primary outcome is the change in daily step count between LLM-driven and generic text-based intervention arms.

How many participants are enrolled in this study?▼

The target enrollment is 15,000 adults across the United States and United Kingdom.

What is the intervention being tested?▼

The intervention is personalized text-based coaching prompts generated by a large language model (LLM) grounded in the Transtheoretical Model of Change, compared to generic prompts.

When did recruitment for this study begin?▼

Recruitment commenced in March 2026 and is ongoing.

Products

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References

  1. 1.Schmiedmayer P, Johnson A, Schuetz N, Kollmer L, Goldschmidt P, Delgado-SanMartin J, Zhang KW, Mantena SD, Tolas A, Montalvo S, Ramirez-Posada M, O'Sullivan JW, Oppezzo M, King AC, Rodriguez F, Ashley E, Lawrie A, Kim DS. "Design and rationale of the my heart counts cardiovascular health study: a large-scale, fully digital biobank, and randomized trial of large language model-driven coaching of physical activity.." American journal of preventive cardiology, 2026. PMID: 42395096 DOI: 10.1016/j.ajpc.2026.101565
Disclaimer: This content is for educational purposes only and is not medical advice. Evidence scores reflect the quality and quantity of available research, not clinical recommendations. Always consult a healthcare professional before starting any supplement or intervention.