Who hurts
Intermediate lifters and runners who train through recurring niggles.
The problem
Every training app assumes a healthy body. One tweaked shoulder and the plan is unusable, so people either train through it badly or stop for three weeks and lose the habit.
What you build
Flag the limitation and the program rewrites: substituted movements that keep the training stimulus, adjusted volume, and a return path back to the original lift. Built on published rehab progressions, with sources shown.
Why now
Substitution logic is a constrained reasoning problem over a well-documented exercise database — a good fit, and a bad fit for a static app.
Validate it this week
Post rewrites for free in one lifting community for a month. If the same people come back with a second injury, it works.
Why you'd keep winning
A vetted substitution graph reviewed by actual physios. Slow to build, and the thing that makes it safe to recommend.
The honest risk
You are one bad substitution from hurting someone. Get clinical review, be conservative, and say plainly that it isn't medical advice.
The prompt is written to make an AI argue with you before it writes code — that first round of pushback is worth more than the scaffold.