How PT Lab's AI actually works

It's not ChatGPT

PT Lab uses Google Gemini under the hood, but the AI isn't a free-form chat. It's wrapped in a very specific system prompt that constrains it to exercise programming and nothing else. You can't ask it to write a blog post or tell a joke — or rather, you can, but it'll refuse and give you a workout instead.

This is intentional. A chatbot gives you text. PT Lab gives you a structured workout with exercises, sets, reps, and weights that you can log sets against and that feeds back into future routines.

What the AI sees

When you generate a routine, the AI gets:

• Your profile (age, sex, experience level, goal, restrictions, equipment, problem areas)
• Your lifting stats (key weights you've entered)
• Your last 5 routines and what you logged in them (sets, reps, weights, completion)
• Your last 10 check-ins (soreness, mood, sleep)
• Your favorite exercises
• Any goals you've set
• The specific focus, notes, and constraints you entered for this routine

What it never sees: your name, email, or any personally identifying information. The AI works with anonymized training context only.

How it decides what to recommend

It follows hardcoded programming rules: proper exercise ordering (warm-up → compound → secondary → accessory → isolation → cool-down), appropriate rep schemes for each role (3-6 for main strength, 6-10 for hypertrophy, 12-15 for accessories, 15-20 for pump work), warm-up sets on heavy compounds, and safety rules around restrictions and sensitive areas.

It also considers your soreness and sleep. High soreness for 3 days? It programs lighter. Crushing sleep and feeling great? It pushes harder.

What it can't do

• Watch your form. It has no eyes.
• Give medical advice or prescribe treatments. It's not a doctor.
• Tell you exactly when to deload — it can suggest one based on patterns, but you have to listen to your body.
• Replace a human coach for form correction, accountability, or psychological support.