I actually just wanted to learn the AI agent Claude Code*. Now I have an AI Cycling Coach that reads my training data, understands Joe Friel’s training methodology, and tells me whether to train hard or recover today. The best part? It knows my back problems, my ultra-race goals, and responds like a real coach, every day, as often as I want.
* Claude Code is an AI Agent for developers that doesn’t just make code suggestions but works directly in the terminal. Claude Code writes code and understands the context of your entire project while doing so.
The Problem
I’m training for 300 km – 600 km Brevets starting April 2026 and a 1200 km insanity ride in 2027. Six training days per week, multi-discipline (cycling, strength, core, yoga), a past spinal surgery, and the eternal question: Am I training right?
I track everything with intervals.icu, a database and analysis platform. TSS, CTL, ATL, TSB: the numbers are there. But numbers alone don’t coach. They don’t tell me whether my intensity or core training is sufficient. Whether I’m in the right phase. Whether I should actually rest instead.
At the same time, there was this curiosity: Claude Code was everywhere in the tech feed. What can this tool really do? So I thought: What if I just build myself a coach?
Claude Code: From Visual Studio to Coach
Claude Code is a command-line tool (or works in an IDE like Visual Studio) that lets you use Claude directly for coding tasks. Write code, debug, create files, and understand the context of the entire project.
My plan was simple:
- the coach must know my data (training, wellness) → integration with intervals.icu API
- the coach must understand how training works → Joe Friel’s training methodology as foundation
- the coach must know me personally → profiles with goals, medical history, preferences
- And I want to talk to it → chat interface powered by Claude Sonnet 4.5
Here’s where it gets interesting: I’m not a full-time developer. I can read code, but setting up complex architectures takes time. Claude Code changed the game.
What I Built with Claude Code
The Dashboard: I wanted WHOOP-style status circles for recovery, sleep, HRV, strain. Plus a TSB chart over 42 days with color zones (green = optimal, red = danger zone). Claude Code built the complete responsive layout: desktop, mobile, canvas charts, hover tooltips, and even voice input!
The Coaching Prompt: The heart of it all. A system prompt that explains to Claude how to act as a coach. With my complete profile (goals, medical history, current form, Joe Friel’s methodology, zones). Claude Code helped structure this so the coach truly responds like a real coach: with context and concrete action recommendations.
Multi-Athlete Support: In case someone else wants to use the app too, Claude Code built a complete routing system with JSON configs. Select athlete, go.
The AI Coaching App in Detail
Dashboard: My Training World at a Glance
The dashboard shows me in seconds where I stand:
- Status Circles: Recovery, Sleep, HRV, Strain (TSS) – like WHOOP, but for cycling
- TSB chart over 42 days with CTL/ATL lines
- Zone-colored TSB: Green (optimal), Yellow (fresh), Red (danger zone)
- Mobile-optimized: Voice input, compact view
AI Coaching Chat: My Personal Coach
This is where it gets wild. I can ask my coach:
- “What does my training look like this week?”
- “I feel flat today, but my TSB is at -15. What do you recommend?”
- “My core training: Is that enough for ultra-distances?”
The coach knows:
- My goals (300 km Brevet in April, 1200 km in 2027)
- My history (spinal surgery → core strength is critical)
- My current form (TSB -18, CTL 85, ATL 98)
- Joe Friel’s methodology (periodization, TSB targets, 70-80% Zone 2)
Example Dialogue:
Me: "What does my week look like? I'm planning 4 rides + 2 core sessions."
Coach: "Your TSB is at -18, right in the optimal training range.
CTL is rising nicely. Good!
For this week:
→ 3 longer Zone 2 rides (not 4) – you're building base right now
→ 1 tempo session (Sweet Spot), but short (60min max)
→ 2 core sessions are perfect – essential given your history
→ 1 complete rest day (active recovery or yoga)
Watch out for: HRV. If it keeps dropping, cancel the tempo session and
replace with Zone 1. Your body tells you what works."What Works Now and What ChatGPT Can’t Do
Claude Code is a game-changer for side projects
It would have taken me weeks to build something like this before. With Claude Code? A weekend. Not because Claude does everything perfectly, but because it handles the repetitive, annoying parts. I could focus on the concept, UX, and coaching logic.
AI coaching works when the context is right
The difference between “ChatGPT, how do I train for ultra-races?” and this coach? Context. ChatGPT doesn’t know me. My coach knows my current form, my goals, my limitations, my history. That’s the difference between generic tips and real coaching.
Costs remain manageable
Through prompt caching (system prompt is cached for 24h), the app costs €5-15 per month. Cheaper than any coaching app. And more personal. The app runs completely locally on my computer and is available via HTTPS throughout the home network: no cloud, no subscriptions.
Conclusion: Curiosity Pays Off
I wanted to understand Claude Code. Now I have a personal training coach that knows me better than any app.
The lesson? Build what you need yourself. Not what you want to sell. Not what’s trendy. But what solves your own problem. For me, that was a coach who knows Joe Friel, understands my back problems, and tells me whether to push hard or recover today.
For you, it might be something else. But if you want to build something like this – Claude Code makes it possible. In a weekend. Out of curiosity. If you have questions about the app, Claude Code, or AI coaching, just write me!