How the GPT is instructed and framed

Lucas Werthein, the COO and co-founder of Cactus, shares how he built a personalized AI wellness coach using ChatGPT to optimize his athletic performance while managing past injuries. After multiple surgeries on his knees, shoulder, and foot, Lucas created a system that synthesizes data from medical imaging, blood tests, wearable devices, and nutrition plans to provide personalized recommendations. His AI coach helps him balance competitive tennis, weightlifting, and running a company while maintaining his goal of “feeling 25 in a 40-year-old body.” Lucas demonstrates how this approach transforms siloed health information into actionable insights that protect joints, optimize recovery, and extend peak performance.

What you’ll learn:

1. How to configure a ChatGPT with multiple data types, including MRIs, x-rays, blood tests, and wearable metrics, to create a comprehensive health profile
2. A framework for setting clear performance boundaries that prioritize joint protection, energy optimization, and injury prevention
3. Techniques for using AI to balance nutrition around special events like social dinners while maintaining performance goals
4. How to use images and videos to get AI feedback on physical symptoms and injury recovery timelines
5. A method for validating and contextualizing medical advice by having AI synthesize information from multiple health-care providers
6. Why creating clear rules and anti-prompts helps AI deliver practical, evidence-based recommendations instead of trendy supplements or extreme protocols

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Copy Lucas’s Health Coach Prompt: https://www.lennysnewsletter.com/p/how-to-create-your-own-ai-performance-coach

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Brought to you by:

WorkOS—Make your app enterprise-ready today

Google Gemini—Your everyday AI assistant

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Where to find Lucas Werthein:

Website: https://cactus.is/

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Where to find Claire Vo:

ChatPRD: https://www.chatprd.ai/

Website: https://clairevo.com/

LinkedIn: https://www.linkedin.com/in/clairevo/

X: https://x.com/clairevo

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In this episode, we cover:

(00:00) Introduction to Lucas’s athletic background and injury history

(04:55) The challenge of synthesizing siloed health data

(06:11) Building a GPT to optimize performance and recovery

(09:57) Demonstrating the data types integrated into the AI coach

(13:54) Configuring the GPT with clear performance goals and boundaries

(16:31) Setting realistic expectations for the AI coach

(17:50) Creating nutrition, training, and recovery frameworks

(21:47) Establishing hard boundaries and anti-prompts

(24:25) Example: Managing nutrition around special events

(27:30) Accessibility and affordability of on-demand coaching

(28:24) Practical examples and real-life scenarios

(29:31) Using AI for injury management and recovery planning

(34:19) Validating expert opinions and translating medical advice

(37:25) Vision for the future of AI in personal health coaching

(43:27) Other AI workflows: synthetic clients and AI co-founders

(48:48) Final thoughts on AI reliability and evolution

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Tool referenced:

• ChatGPT: https://chat.openai.com/

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Other references:

• InBody scan: https://inbodyusa.com/

• Whoop: https://www.whoop.com/

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Production and marketing by https://penname.co/. For inquiries about sponsoring the podcast, email jordan@penname.co.