Berger looked at lifting logs from many exercises. He tried different formulas until he found one that worked well for each exercise type.
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The Berger 1RM formula was developed by Robert Berger and takes yet another approach compared to the previously mentioned methods.
Berger's formula is:
1RM = Weight / (1 - (Reps/Constant)) Where: Weight = Load lifted (lbs or kg) Reps = Number of reps completed Constant = A value that varies based on the exercise For example, for the bench press the constant is 40, so the formula becomes: 1RM = Weight / (1 - (Reps/40))
To derive this formula, Berger analyzed training log data from hundreds of lifters across many different exercise variations. He looked at their actual max weights lifted for 1 rep, and the weights/reps they could do at other submaximal intensities.
Through analyzing the relationship between max weight, reps, and exercise type, Berger determined that the constant in his formula varies based on the exercise leverages and muscle groups involved.
Some example constants he provided: Bench Press: 40 Squat: 48 Deadlift: 45
Berger chose these constant values for each exercise as they minimized the error between predicted and actual 1RMs in his dataset when plugged into the formula.
So in essence, Berger derived an exercise-specific family of 1RM prediction equations based on empirically fitting a larger constant into his 1RM = Weight / (1 - Reps/Constant) model for each movement pattern.
This exercise-specific approach is what differentiates Berger's method from the more generalized coefficient-based formulas of Brzycki, Adams and Baechle. Berger accounted for biomechanical differences between exercises.