"One-rep max" refers to the maximum amount of weight a person can lift for one repetition. Often this can be estimated surprisingly accurately from reps-to-fatigue with a smaller amount of weight. The rule of thumb that seems to work for most people is that 10 repetitions can be performed with a weight equal to approximately 75% of a maximal load, and that the number of repetitions decrease in an approximately linear fashion as the weight increases (at least in the range of 1 to 10 reps, which is what the above graph shows-- the linearity assumption tends not to be accurate for more than 10 reps).
So, the formula that works for most people is:
1 rep max = (weight lifted) * 36 / (37 - reps) weight lifted = (1 rep max) * (37 - reps) / 36 reps = 37 - ( 36 * (weight lifted) / (1 rep max) )References: Matt Brzycki, "Strength Testing - Predicting a One-Rep Max from Reps-to-Fatigue"
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Last Modified: Fri Jan 12 12:43:00 PST 2007 Don Hatch