One Rep Max

Definition: One Rep Max, or 1RM is a measure of how much you can lift for one repetition of an exercise. When you determine your 1RM, you can use a percentage of this to figure out how much weight to use for different exercises. Since it's hard to lift enough weight to only do 1 rep without hurting yourself (if you're a beginner), it's best to guess how much weight you need and adjust it throughout the workout.