One-Rep Max (1RM)

A 1RM can be measured (you attempt singles until you find your true maximum) or estimated from submaximal sets using a prediction formula. The Epley formula is the most commonly cited: 1RM ≈ weight × (1 + reps/30). The Brzycki formula (weight × 36 / (37 − reps)) tends to be slightly more accurate at lower rep ranges. Both formulas lose accuracy as rep counts rise above 10 — a 15-rep max tells you relatively little about your true 1RM.

Most programs do not require testing a true 1RM. 5/3/1 Beyond uses a training max — 90% of your estimated 1RM — to set percentages conservatively. This is deliberate: the training max should feel manageable, not maximal. The AMRAP top set is where the actual strength is expressed and measured.

In LiftProof, 1RM estimation happens automatically. When you log an AMRAP set, LiftProof calculates an estimated 1RM using the Epley formula and uses it to recommend your next training max. You can override the estimate if you have tested a true 1RM recently.

Testing a true 1RM is worth doing periodically to recalibrate the estimate. Single-rep attempts carry injury risk if they happen without preparation — several warm-up sets, incrementing by 5–10% per attempt, and stopping when velocity drops significantly. Testing a 1RM cold after months of submaximal training is not how maximal strength is accurately measured.

• Source 01

  Epley 1985 — Poundage Chart↗(opens in a new tab)

  Original Epley formula, published in Boyd Epley's NSCA strength manual appendix.

• Source 02

  Brzycki 1993 — Strength Testing — Predicting a One-Rep Max from Reps-to-Fatigue↗(opens in a new tab)

  Commonly used 1RM prediction formula based on reps to fatigue.

• Source 03

  Helms et al. 2017 — Application of the Repetitions-in-Reserve Based Rating of Perceived Exertion Scale for Resistance Training↗(opens in a new tab)

  Context for how 1RM estimation and RPE interact in auto-regulated training.