What is a One Rep Max (1RM)?
A One Rep Max (1RM) is the maximum amount of weight you can lift for a single repetition of a given exercise through a full range of motion. In strength and conditioning, it is considered the gold standard for evaluating an athlete's absolute strength.
Rather than constantly "maxing out"—which carries a high risk of musculoskeletal injury and central nervous system (CNS) fatigue—strength coaches recommend lifting submaximal loads (like a 5-rep max) and plugging that data into a clinical predictive equation to estimate the true 1RM safely.
The Biomechanical Formula: The Epley Equation
Developed in 1985 by Boyd Epley, the founder of the National Strength and Conditioning Association (NSCA), the Epley Formula is the most widely validated equation for predicting 1RM. It is particularly accurate for compound movements like the squat, bench press, and deadlift.
A Practical Example
Consider Marcus, a lifter who wants to test his bench press strength. Instead of risking a failed 1-rep attempt, he loads 225 lbs on the bar and pushes it for 5 clean repetitions before hitting muscle failure.
Using the Epley formula: 225 × (1 + (0.0333 × 5)) = 262.5 lbs.
Marcus's estimated 1-Rep Max is roughly 262.5 lbs. He can use this number to program his training blocks (e.g., performing sets at 80% of his 1RM, which would be 210 lbs).