Coach Claude
Building an AI Coaching Layer on Top of My Apple Watch Training Stack
I've been a runner my whole life — Kids of Steel triathlons as a kid, cross country and track through high school and university, and road races scattered throughout — but chronic injury has been the dominant story for the past few years. This year I decided to stop waiting for it to sort itself out, signed up for a half marathon in September, and did what I've been known to do lately: thought, I bet Claude can help me with this.
After digging around Reddit for ways to set up Claude as an actual run coach, I came across a GitHub repo by a developer called Arden: a FastAPI backend that syncs workouts from Apple Watch, stores them with all their data intact, and delivers structured training sessions back to the Watch. It came with an iOS app called Somatic and an MCP server that let Claude talk to the whole thing. I cloned it and started building on top.
What I added: an AI coaching layer that fires a short note to Claude Haiku after every workout sync — one thing that went well, one to work on — written straight into the workout record. Two new MCP tools: one that writes coaching notes back to workouts, one that permanently removes queue items from the server. A rebuilt dashboard with phase-coded weekly calendar and per-session coaching panel. Expanded HealthKit sync for heart rate, power, and route data. Subjective effort scores on the workout schema. And the removal of a 6-month history cap baked into the iOS app — no good reason to throw away that context.
The most valuable thing that came out of it had nothing to do with the build itself. When I first fed Claude my health data, it flagged that my heart rate was consistently high — I'd been running too hard too often, which was almost certainly driving the injury cycle. It put me onto HR-based training, and two months in my paces are improving and I haven't had a major flare-up. Everything is grounded in my actual data, which is what makes it feel different from any third-party app. September is the real test, but for the first time in a while I'm looking forward to it.
Backend, iOS app, and MCP server by Arden (aderaaij). AI coaching layer, dashboard redesign, and HealthKit sync expansions by me.
