How the plan is built

How does it decide which days train what?

By how often you train. One to three days a week means full body every session, because anything narrower would leave muscles untrained for too long. Four days becomes upper and lower. Five adds push, pull and legs on top of upper/lower. Six is push, pull and legs run twice. If your goal is fat loss or general fitness, some of those lifting days become conditioning days instead.

How much work do you get per muscle?

Enough to grow, not so much that you cannot recover. Every muscle has a weekly range of working sets that research associates with progress — a minimum effective volume and a maximum recoverable volume. Your plan steers each muscle into that band based on your goal and experience, and never exceeds the top of it.

Work where a muscle is only a secondary mover counts partially, never as a full set. Rows train your biceps, but not the way curls do. Timed conditioning does not count toward muscle-building volume at all.

Why does the program get easier some weeks?

Because you adapt while you recover, not while you train. Programs run in blocks that go intro, build, peak, then deload — a recovery week at a fraction of your normal set volume. Beginners get them less often, because they accumulate less fatigue. Short programs may not need one at all.

You can see exactly which weeks are deloads in the preview, before you start. Nothing is hidden until you get there.

Why does it tell you reps in reserve instead of a weight?

Because the right weight changes daily and the right effort does not. A strength block is prescribed like this: three sets of eight to twelve at RIR 1 — meaning stop each set with about one rep left in you. On a strong day that is a heavier bar. On a bad day it is a lighter one. Both are the correct session.

How close to failure you get depends on your goal. Building muscle takes the hardest sets. General fitness stays a step back from that. Fat loss keeps the most in reserve, because lifting in a calorie deficit exists to keep the muscle you have, not to grind you down. Within a block the target tightens across sets and across weeks, so effort climbs even when the weight has not.

How does it know what weight you can lift?

It doesn't, so it asks. The first working set of a movement you have no history for comes with a loose target: pick something moderately challenging and aim for three or four reps in reserve. You log what you used. From then on it remembers, and you never set that number again.

How does next week change based on this week?

It compares what you logged against what was prescribed and sorts the result into four outcomes: you beat the target with reps to spare, you hit it, you landed inside the range, or you missed the bottom of it. Combine that with how hard the session felt and the load for the coming weeks moves up, holds, or comes down.

Conditioning is judged the same way, from your average heart rate against the block's target zone — or from your effort rating if you trained without a strap. A block with neither is never judged. Silence is not a measurement.

How does it work around an injury?

By removing exercises, not by warning you about them. Name one of nine areas — ankle, elbow, foot, hip, knee, lower back, neck, shoulder or wrist — and every movement flagged as contraindicated for it drops out of the pool your plan is built from. Impact level and spine load get weighted down too. Your experience level sets a ceiling on difficulty, never a floor.

Fitness Flow is not medical advice. If something hurts, see a physiotherapist or a doctor — then tell the app what to avoid.

Is it AI?

No, and that is the point. The programming knowledge lives in small tables a human coach can read: which split fits which frequency, what the volume bands are, how rep ranges map to goals, what a deload does to tonnage. Same answers in, same plan out. When a plan is wrong, someone can point at the row that made it wrong and fix it.