I’ve built an AI running coach (yes, yet another one out there). It’s not for everyone though. I’ve built exactly the coach that I wanted myself.
I started running more seriously about 4 years ago and have since then become kind of a nerd. I read a lot of science books about running and constantly try to optimize my training. For reference, I run around 50-60 km per week and am currently targeting a sub-17 5K.
Anyway, I started using LLMs as a way to get feedback and inspiration in my planning, and thought it worked pretty well. We all know that LLMs aren’t perfect, but after keeping my chat session going and tuning it, it got better and better. However, that was up until a certain point when it started forgetting and guessing important information. Also, I had to manually give it a lot of information and (of course) it was just reactive.
So, I wanted an AI coach that:
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Knew my schedule and preferences
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Automatically had all the relevant data
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Remembered what really mattered
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Proactively reached out
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Focused on ongoing dialog (not static plans or data questions)
So that’s what I built. I also wanted as good quality as possible, without completely losing sight of the cost. Therefore the more complex parts are using Claude Opus (currently 4.8), while the more simple tasks are using Claude Sonnet (currently 5).
I have just launched on both App Store and Google Play, and of course, it connects directly to your intervals.icu account.
If this sounds interesting, please check it out on www.fartlek.io. All feedback is welcome and appreciated! To make sure my costs aren’t running away I have limited the number of concurrent free trials. If you don’t get a spot, you could just try again later.
