A workout engine built on rules, not random prompts.
Fit4i's core training decisions — how much weight to add, how many sets a muscle group gets this week, when to build volume up and when to deload — come from a deterministic programming engine, not a language model improvising a plan. The same inputs — recovery data, training history, equipment and goals — always produce the same programming decision. Here's exactly how it works.
Progress when you earn it
Fit4i increases weight after you complete the top of the target rep range across all working sets — not one good set, every set. Instead of adding the same fixed amount to every exercise, Fit4i calculates an increase relative to your current working weight and rounds it to equipment you can actually load.
Double progression
Session A
10 · 9 · 9 reps
Keep building reps
85 kg — unchanged
Session B
12 · 12 · 12 reps
Progression unlocked
Example equipment rounding
85 kg → 87.5 kg
A ~2.5% relative increase scales better than the same fixed jump on every exercise — and it's rounded to real, loadable equipment.
Reps in reserve (optional)
Standard increase applies
RIR input is optional — when logged, it fine-tunes the next step.
Auto-deload
Two misses in a row on the same lift — not one bad set — trigger it.
Effort changes the next step.Logging RIR (reps in reserve) is optional, but when it's available Fit4i uses it to adjust progression more precisely — a very hard set holds off on the next increase, an easy one may unlock a larger step.
When progress stalls, Fit4i doesn't keep pushing blindly. After repeated failed attempts at the same target, the working load is automatically reduced by roughly 10% to rebuild momentum from a weight you can complete — an automatic load reset, not a promise that it prevents injury.
A bench press is not only a chest set
Compound exercises also train supporting muscle groups. When you press, Fit4i knows your triceps and front delts also worked, and accounts for part of that work before adding more isolation volume — so the plan doesn't automatically pile unnecessary sets on top of a muscle that already got meaningful work.
A bench press is not only a chest set.
Chest
Bench Press · 4 sets
sets
Triceps
indirect · 0.5 / chest set
Front Delts
indirect · 0.4 / chest set
Triceps — weekly target, already adjusted
- Indirect from pressing
- 2.0
- Direct isolation assigned
- 4.0
- Effective total
These values illustrate how Fit4i accounts for indirect work inside its programming engine. The 0.5 / 0.4 credit is set per muscle-group pair — the same for every compound chest exercise.
Volume grows across the cycle — then comes back down
Fit4i starts closer to a minimum productive volume for each muscle group, gradually builds toward a higher workload across the cycle, then schedules a deload. Cycle length depends on experience level, and may be shortened further based on age and recovery.
Every muscle group has a starting point and a higher target the plan builds toward across a training cycle. Volume climbs week over week, then the final week drops to recovery levels before the next cycle begins.
Intermediate · 5-week cycle
4 building weeks + 1 deload week
These are programming targets built into the engine's rules — sometimes called MEV → MAV in strength research — not measured facts about you specifically.
Cycle length may also be shortened based on age and recovery considerations.
Recovery still has the final say
None of this runs blind to how you're doing. On a low-readiness day, Fit4i can trim a session's volume and pause the ramp until recovery improves — see how HRV and recovery adjust today's workout. Unlike many generic AI-generated plans, Fit4i applies consistent programming rules to these core training decisions, and layers recovery-aware adjustments on top.
Frequently asked questions
Is Fit4i's training engine actually AI?
The programming engine — the part that decides your progression, weekly volume and periodization — is deterministic code, not a language model. The same inputs always produce the same programming decision. Fit4i uses AI elsewhere — food-photo analysis. Core progression, weekly volume and periodization are handled by the deterministic training engine.
What is double progression?
You have a rep range for each exercise, e.g. 8–12 reps. Fit4i keeps the weight the same until you close the top of that range across every working set in a session — not just one. Once you do, the weight goes up. This rewards consistent performance instead of one lucky set.
How big is the weight increase?
It's relative, not fixed — roughly 2.5% of your current working weight, capped around 5%, then rounded to equipment you can actually load (barbell plates, dumbbell increments, machine pins). A flat +2.5 kg makes sense on a 40 kg lift and barely matters on a 150 kg one; a relative step scales with the weight itself.
What is RIR and do I have to log it?
RIR (reps in reserve) is how many more reps you felt you had left. It's optional. When you log it, Fit4i fine-tunes the next step: a very hard set (RIR 0) holds off on progression even if you hit the rep target; an easy set (RIR 4+) may unlock a larger step. Without RIR, standard double progression still runs.
What happens after a missed set?
One missed target just means the same weight next time — no penalty. Two misses in a row on the same lift trigger an automatic load reduction of about 10%, so the next session starts from a weight you can actually complete and rebuild from, instead of grinding the same weight indefinitely.
Does Fit4i know which muscles an exercise trains?
Each exercise has one primary muscle group. On top of that, compound lifts credit part of their work to the muscles they indirectly train — a press credits some volume to triceps and front delts, a row credits some to biceps and rear delts. That credit is defined per muscle-group pair, not tagged individually per exercise, and it's used to avoid stacking redundant isolation volume on muscles that already got meaningful work.
What are MEV and MAV?
They're programming volume landmarks built into Fit4i's engine — a minimum productive volume to start a training cycle from, and a higher volume the plan builds toward by the end of it — not a lab-measured physiological limit unique to you. Fit4i uses MEV- and MAV-style landmarks inside its programming logic, in the spirit of established hypertrophy programming principles.
How long is a training cycle?
It depends on experience level: 6 weeks for beginners, 5 for intermediate, 4 for advanced — each ending in a deload week at roughly half the starting volume. Cycle length may also be shortened based on age and recovery considerations.
Train with a plan that actually keeps score.
Or see the full AI workout planner this engine powers.