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Percentage-based programming sets the working weight as a share of one-rep max, and the Epley relation inverts to predict how many reps that load allows: reps = 30(1/percentage - 1). At 80% of a 140 kg max the bar carries 112 kg and should permit about seven or eight reps. Below 60% the prediction becomes unreliable because endurance rather than strength limits the set.
Working weight
weight = 1RM x percentage
Reps from percentage (Epley)
reps = 30 x (1 / percentage - 1)
This is an estimate from population-average equations, not a medical or diagnostic assessment. Individual results vary with genetics, training history and technique. Seek advice from a qualified coach or clinician before making significant changes to training.
They use different formulas - Epley, Brzycki, Lombardi - which diverge above about eight reps. All are approximations of a very individual relationship.
No. Rep capacity at a given percentage varies with the lift and the athlete; squats typically allow more reps at 80% than deadlifts.