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Strength & Load

Estimated 1-Rep Max (e1RM)

Also known as: Predicted 1RM, NPI (Normalized Performance Index)

A mathematical estimate of the heaviest weight you could lift for a single repetition, derived from a submaximal set. It lets us track strength progress without you ever needing to actually max out.

Formula

e1RM = weight x (1 + (reps + RIR) / 30) [Epley formula with RPE adjustment, where RIR = 10 - RPE]

Example

Squat: 100 kg x 5 reps at RPE 8 (RIR = 2). e1RM = 100 x (1 + (5 + 2) / 30) = 100 x 1.233 = 123.3 kg.

How Afitpilot Uses This

We auto-select an "anchor exercise" each session (scored by tonnage share, recurrence, and data quality) and plot its e1RM over time. A linear regression on the last 4-7 data points gives you a trend line — rising, stable, or declining — with a confidence rating (High / Medium / Low).

e1RM benchmarks & accuracy

Who / ContextValueNote
Intermediate powerlifter (85 kg)Squat 140-180 kg / Bench 100-130 kg / DL 170-220 kgElite lifters 50-80% higher
Regular gym goerBench 60 kg x 8 @ RPE 7 = e1RM ~76 kgTrack your max without ever maxing out
Active aging (65 yr)Leg press 80 kg x 10 @ RPE 8 = e1RM ~107 kgSafer than actual 1RM testing
Formula accuracy3-10 reps: within ~5% of true 1RM15+ reps: can overestimate 10-15%

Known Limitations

  • •The Epley formula was derived from studies primarily on compound barbell lifts. Its accuracy degrades for isolation exercises, very low rep ranges (1-2), very high rep ranges (15+), and machine-based movements.
  • •RPE is self-reported. If your RPE perception is consistently over- or under-estimated, e1RM drifts proportionally. We mitigate this by requiring minimum 2 sets for anchor selection.
  • •The formula assumes linear force-velocity characteristics, which breaks down at extremes. A set of 20 at RPE 8 is not the same physiological stimulus as a set of 3 at RPE 8, even if the formula says so.

What We're Improving

  • Planned

    Multi-Formula e1RM with Confidence Intervals

    Run Epley, Brzycki, and Lombardi formulas in parallel and report the median with a confidence band, rather than relying on a single formula.

  • Future

    Prilepin's Table as LLM Strength-Prescription Guardrail

    Validate LLM-generated strength sessions against Prilepin's reps-per-set / total-reps ranges for the implied %1RM (derived from targetRpe → RIR → e1RM). Two surfaces: a plan-generation guardrail that flags or corrects out-of-range prescriptions, and a post-session signal that compares actual sets × reps × estimated %1RM against the optimal range. Deferred until we have 20+ real LLM-generated weeks audited; a ~8% high-intensity overshoot rate on a small fixture set was borderline-but-too-small to act on.

Science Context

The Epley formula (1985) is one of several 1RM estimation models. Alternatives like Brzycki and Lombardi produce slightly different estimates. We chose Epley for its simplicity and reasonable accuracy in the 3-12 rep range, which covers most training prescriptions. Adding the RIR adjustment (from RPE) improves accuracy for submaximal sets where reps-in-reserve are known.