ALGORITHM · §1.0

No black box.

Every prescription Calyber gives you is built from the weight, reps, and reps-in-reserve you logged, and every number traces back to those inputs. Here is exactly how the engine works, in plain terms. Open any section for the formula.

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The 70-second explainer walks the chain: a logged set (the weight, the reps, and the reps in reserve) feeds the strength estimate, the fatigue index, and the autoregulation rules, which together produce your next session. Every recommendation is traceable to your own data, never a black box.

§1 · The strength estimate

After a few sets on a lift, Calyber estimates how strong you are on it right now: not from a generic chart, but from the exact weight, reps, and reps-in-reserve you logged. Every prescription that follows is built on that estimate, and it updates set by set.

▸Formula & worked example

Calyber estimates your one-rep max with an Epley-form equation:

e1RM = W × (1 + R / 36)

W is the load you lifted; R is reps performed plus your reps-in-reserve. A second constant (40) is applied when you enter a heavier weight than your working baseline, so a strength jump isn't over-credited.

Worked example: 145 lb for 10 reps at RIR 2 → 145 × (1 + 12/36) = 193 lb estimated 1RM.

Full breakdown, variants & calculator →

§2 · The fatigue index

Each muscle carries a single fatigue reading, drawn from how you performed and how worked it was. When fatigue starts to limit performance, the plan eases volume before it quietly costs you a productive week.

▸Inputs, formula & thresholds

The Muscle Group Fatigue Index (MGFI) is two normalized sub-scores, each on a 0.00-1.00 scale:

readiness    = performance × 0.60 + soreness × 0.40
accumulation = sets × 0.50 + soreness × 0.30 + workload × 0.20

Readiness asks whether the muscle can perform today; accumulation asks how much it has absorbed across the block. Crossing a threshold reduces the next set count or schedules a recovery session.

Inputs table, worked example & thresholds →

§3 · The autoregulation rules

After every session, three checks run in order: should the load change, should the volume change, and does a muscle need recovery. Each is a fixed rule with a measurable threshold: never a feeling, never a guess.

▸The three checks
  • ΔLoadadjusts the weight from your e1RM trend and measured RIR bias.
  • ΔVolumemoves the set count within your MEV-MRV range for each muscle.
  • Recoverywhen the fatigue index crosses its threshold, prescribes a deload or recovery session at a reduced load.

Every output is deterministic: the same inputs always produce the same prescription.

The full five-stage calibration loop →

§4 · Traceability

Every prescription shows the inputs that produced it: a visible Basis line in the app. Nothing is inferred behind the scenes; you can check the math on any number the engine gives you.

▸What that guarantees
  • —Every formula uses only data from your own sessions, with no population averages standing in for you.
  • —Every output lists the inputs that produced it.
  • —No step uses statistical inference; every decision is a fixed threshold or a formula.

Check the math on your own training.

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