Every prescription Calyber gives you traces back to the weight, reps, effort, and recovery you logged, shown in plain terms with the formula one click away.
Free to start, no card required.
The 70-second explainer follows one logged set through strength estimation, the fatigue check, and the fixed autoregulation rules to produce your next prescription.
You do not need to understand every formula to use it.
You can see why load or volume changed.
You can inspect the inputs, thresholds, and rules.
How it works
One logged set flows through four steps to your next prescription. Each step is a fixed rule, so the plan reacts only to your training, not a guess or a generic template, and the same training always produces the same plan.
§1 · Strength estimate
Calyber estimates your current strength from the set you actually performed: load, reps, and reps in reserve. That estimate becomes the anchor for your next target, and it updates set by set.
e1RM = W x (1 + R / 36)
You lifted 145 for 10 reps with 2 left in reserve, so Calyber treats it as a 12-rep performance and estimates a 193 lb single.
Terms:
Calyber uses a modified Epley-form estimate. R is reps plus reps in reserve. The constant is 36 for a same-weight round trip, and 40 when you enter a weight above your working baseline, so a strength jump is not over-credited.
§2 · 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.
MGFI is the per-muscle fatigue reading Calyber tracks, combining current readiness with accumulated workload.
Crossing a threshold reduces the next set count or schedules a recovery session.
Terms:
readiness = performance x 0.60 + soreness x 0.40 accumulation = sets x 0.50 + soreness x 0.30 + workload x 0.20
§3 · Autoregulation
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.
Adjusts the weight from your e1RM trend and measured RIR bias.
Moves the set count within your MEV to MRV range for each muscle.
Prescribes a deload or recovery session when the fatigue index crosses its threshold.
Every output is deterministic: the same logged data and training state produce the same prescription.
| Signal | What Calyber sees | What Calyber does |
|---|---|---|
| Strength up | e1RM rising, RIR on target | Increase load |
| Strength flat | e1RM flat, effort already high | Hold load |
| Fatigue high | MGFI crosses threshold | Reduce volume or recovery session |
| Volume low | Sets below the productive range | Add sets |
| Volume high | Sets near the recovery ceiling | Hold or reduce sets |
§4 · Traceability
Every prescription shows the inputs that produced it: a visible Basis line in the app. Nothing is hidden behind the scenes. Every output shows the inputs and rules that produced it, so you can check the math on any number the engine gives you.
No black-box model. Calyber uses visible inputs, stored training state, and fixed rules, so the same logged data and training state produce the same prescription.
§5 · Boundaries
Questions
It is calculated from your own logged training, not copied from a population template.
Yes. Every prescription includes a Basis line with the inputs and the rule that produced it.
No. It does not assess technique, injury risk, or context outside your logged training data.
No. It adjusts load, volume, or recovery based on your measured performance and fatigue.
No. It uses fixed rules, visible inputs, and stored training state. The same logged data and training state produce the same prescription.
References
Epley, B. (1985). Poundage Chart. Boyd Epley Workout. Lincoln, NE: Body Enterprises.
Zourdos, M.C., Klemp, A., Dolan, C., et al. (2016). Novel resistance training-specific rating of perceived exertion scale measuring repetitions in reserve. J Strength Cond Res, 30(1), 267-275. doi:10.1519/JSC.0000000000001049
Schoenfeld, B.J., Ogborn, D., Krieger, J.W. (2017). Dose-response relationship between weekly resistance training volume and increases in muscle mass: a systematic review and meta-analysis. J Sports Sci, 35(11), 1073-1082. doi:10.1080/02640414.2016.1210197
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