Mr Z

AI Prompt for Muscle Gain: Free, by an 18-Year Coach

Francesco Zen, founder of ZTraining · Published 3 July 2026 · Updated 3 July 2026

The prompt

Copy-paste prompt, built from 18 years of coachingAct as my muscle-building coach, not a generic plan generator. Before giving me anything, ask me for: my height, current weight, a rough body-fat estimate, my training experience (new to structured training, general gym experience, or advanced/bodybuilding level), how many days a week I can realistically train, and what equipment I actually have access to. Once you have that: 1. Calculate my lean body mass: weight x (1 - body fat % / 100). 2. Set my daily protein target from lean mass, not total bodyweight, using roughly 0.7g per lb of lean mass as a baseline, scaled up for more advanced or structured training and down if I am over 50 or more casually active. 3. Set a daily fat target of roughly 40-50g a day, adjusted slightly for my sex and bodyweight. 4. Set a modest calorie surplus. Do not push it aggressively, muscle gain does not require a large excess and a bigger surplus mostly adds fat, not muscle. 5. Give me the remaining calories after protein and fat as carbohydrate. Do not cut them, they fuel the training that actually builds the muscle. 6. Only count complete proteins toward my target: meat, fish, eggs, dairy, whey, EAA. Do not credit protein from bread, rice, oats or legumes, they are carbs. 7. Build my training split around the days I actually gave you and the equipment I actually have. Do not hand me a 5- or 6-day programme if I told you I have 3. 8. Progress the plan. Do not just repeat the same weights and reps every week, tell me specifically how to add load or volume over time. 9. If I miss a session, adjust from where I actually am, do not make me restart the week or feel behind. 10. Be honest if my expectations do not match a realistic timeline, do not just tell me what I want to hear. Ask me the setup questions now, before giving me any numbers or a training split.

Why this prompt works

Most generic muscle-gain prompts hand back a flat surplus and a bodybuilder split regardless of who is asking. This one starts from lean mass and real training days instead, since a beginner at 25% body fat and an advanced lifter at 12% need meaningfully different protein and surplus sizes even at the same scale weight, and a flat formula cannot tell them apart.

The surplus is deliberately kept modest. The rate of muscle protein synthesis is the ceiling on how fast muscle is actually built, and eating far above it does not raise that ceiling, it just stores the excess as fat. The most common muscle-gain mistake is not undereating, it is bulking into a body composition that then takes months to undo.

A real-world example

Take a 35-year-old consultant: 74kg, about 18% body fat, four available training days, a bench and dumbbells at home. His lean mass sits well below his scale weight, and his protein target scales from that figure at the rate appropriate for structured gym training, not the higher rate an advanced lifter would use.

The equipment question matters as much as the numbers: a plan built around machines he does not have is a plan that ends in week one, so the split is built as four home sessions with progression written in, not a six-day gym programme he cannot attend.

Where a single prompt hits its ceiling

The target it gives you on day one stays frozen. When you have gained three kilos and your lean mass has shifted, nothing updates unless you recalculate and paste the entire prompt again. It also cannot see whether your lifts are actually progressing, the one signal that says whether any of this is working, unless you manually report every session back.

A prompt gives you a reasonable starting point within a range. What it cannot do is calibrate that range the same way every time, or notice the plan stalled in week five and change it before you have spent three months maintaining instead of building.

Common questions

Can AI actually help me build muscle?

It can build a solid starting structure if you force it to gather real numbers first: training experience, equipment, and lean mass. Without that, you get a generic bodybuilder split that ignores your actual week.

How big should a calorie surplus be for muscle gain?

Modest. A large surplus does not speed up muscle growth, it mostly adds fat, so the target should be enough to fuel training and recovery, not a big jump above maintenance.

How much protein do I need to build muscle?

Anchor it to lean body mass rather than total bodyweight, scaling up for more advanced or structured training and down if you are over 50 or newer to training.

Francesco Zen is the founder of ZTraining and ZLIFE, with 18 years of coaching experience working with executives across the UK, US, and UAE. He built Mr Z, an AI coach trained on his methodology to bring the same approach to a wider audience.