OltreFit, our AI strength coach: how we made it safe

OltreFit is the strength coach we developed for iPhone and Android, available on the App Store and Google Play. An AI coach writes the training plan from the athlete’s data and updates it after every session, while 33 deterministic rules check that every proposal is feasible and safe. It is a concrete example of how we build products with artificial intelligence: the AI proposes, the code verifies.

What the coach does

• Writes and revises the plan based on the athlete’s real data and the equipment available.
• Adapts the day’s session, for example when an exercise is paused because of discomfort.
• Replies in chat, proposing changes for the user to approve.
• Carries out a weekly review of progress.
• Turns notes dictated during training into data.

How we made it safe

A coach that gets a load wrong or ignores pain can do harm. That is why the AI does not have the last word:

• 33 deterministic rules check every plan: available equipment and weights, paused exercises, sensible progressions.
• No made-up numbers: every figure the coach cites must exist in the athlete’s data.
• Warning signs: if the user describes a worrying symptom, the coach replies with a fixed message advising them to see a professional. Never medication, never diagnoses.
• The right model for each task, chosen with a preference for providers that do not retain data.

Privacy by design

• Explicit consent before the AI features are used, and daily limits per user.
• Each user can read only their own data, with access rules enforced at database level.
• Audio never leaves the phone: voice notes are transcribed on the device.
• Backend in Europe and integration with Apple Health and Health Connect.
• The app also works offline and without an account for logging workouts.

We apply the same principles to the AI agents we build for businesses: minimal permissions, deterministic checks and data under control. We discuss them in our guide to AI agents for business.