I coded an AI endurance coach in 30 minutes

I coded an AI endurance coach in 30 minutes.

Not a chatbot that says "You got this!"

I used Claude Code.

Here's what I built:

First, I wrote an athlete profile. My PBs, my injury history, my limiters. One paragraph of honest context.

Then I crafted a system prompt based around the Norwegian Method.

That's 80% easy, 20% at threshold. No middle ground.

The key was building logic gates into the prompt:

Gate 1: IF hip tightness > 7 THEN lock out running. Only prescribe mobility.

Gate 2: IF heart rate drifts into the grey zone between easy and hard THEN flag it immediately.

No cheerleading. No "listen to your body." Hard rules.

I fed it 365 days of workout data.

It immediately flagged that 22% of my long runs were in the grey zone.

My ideal target was under 5%.

It spotted that my pace falls apart at minute 85. Right when I bonk.

It swapped my Tuesday tempo for a hip reset session and prescribed a 60g/hr carb strategy for long efforts.

The whole thing runs from my terminal. One command. No app. No subscription.

Most people prompt AI like a generalist: "Write me a training plan."

I prompted it like a specialist: "You are a clinical physiologist. You cannot out-train a mechanical restriction. If the hip locks, everything stops."

Same model. Completely different output.

The difference between an AI tool and an AI toy is specificity. Tell it what breaks you, not just what you want to achieve.

P.S. I teach this exact approach to AI prompting inside Prompt Writing Studio. System prompts, logic gates, and how to turn a chatbot into a specialist tool.