Supporting Physical Activity Behavior Change with LLM-Based Conversational Agents

Physical activity has significant benefits to health, yet large portions of the population remain physically inactive. Mobile health applications show promising potential for low-cost, scalable physical activity promotion, but existing approaches are often insufficiently personalized to a user's context and life circumstances. In this work, we explore the potential for LLM based conversational agents to motivate physical activity behavior change. Through formative interviews with 12 health professionals and 10 non-experts, we identify design considerations and opportunities for LLM health coaching. We present GPTCoach, a chatbot that implements an evidence-based health coaching program, uses counseling strategies from motivational interviewing, and can query and visualize health data from a wearable through tool use. We evaluate GPTCoach as a technology probe in a user study with 16 participants. Through quantitive and qualitative analyses, we find promising evidence that GPTCoach can adhere to a health coaching program while adopting a facilitative, supportive, and non-judgmental tone. We find more variable support for GPTCoach's ability to proactively make use of data in ways that foster motivation and empowerment. We conclude with a discussion of our findings, implications for future research, as well as risks and limitations.