The term one rep max (1RM) refers to the one-time maximal amount of weight you are able to lift for a given exercise. In other words, it’s the greatest amount of weight that your muscles can bear while successfully completing one repetition of an exercise.
It is used as a benchmark to determine the appropriate amount of resistance when designing a strength training program. The American College of Sports Medicine recommends using a free weight barbell bench press when performing a 1RM test. Research has shown that it is the best weightlifting test for calculating total dynamic strength.
To find your 1RM, follow these six steps:
1. Perform 5 to 10 free weight bench press repetitions as a warm-up. Start with a weight that’s about 40-60% of your perceived maximum, meaning the amount of weight used in this step should be moderate.
2. Rest for one minute. Do some light stretching if needed.
3. Perform 3 to 5 repetitions at 60 to 80% of your perceived maximum. The amount of weight used here should be fairly more challenging than the warm-up.
4. From here, add a small amount of weight and then attempt your first one rep lift. If the lift is completed successfully, rest for 3-5 minutes before adding more weight and attempting the one rep lift again. Continue this process until a failed attempt occurs. The goal is to find your 1RM with 3 to 5 maximal efforts.
5. At the end of the process, the greatest amount of weight lifted is considered your 1RM.
6. When beginning a strength training program, use percentages of your 1RM to determine how much weight you will need to use in order to successfully achieve your goals. For example, if your 1RM is 200 pounds, 70% resistance would be 140 pounds. Which percentages you train with is highly dependent on your goals.
A few notes:
— During the bench press test, be sure to keep your back on the bench, your feet firmly planted on the floor and your hands about shoulder-width distance apart on the bar.
— Always work with a spotter.
— The spotter should hand the bar to the lifter and the lifter should being with their arms fully extended, the bar in the “up” position.
— You can use this same test for other exercises, like the leg press for example.
— 1RM tests are somewhat time consuming and if used as a benchmark for determining strength and progress with weight training programs it must be evaluated regularly. ACSM explains: “Without regular 1RM testing (e.g., each week) the percentage of 1RM actually used during training, especially at the beginning of a program, will decrease and the training intensity will be reduced."
— Keep in mind that major differences exist between free weights and machines when determining your 1RM. In general, using free weights will give you a more accurate depiction of your strength level.
— Other, less time consuming, methods of measuring your strength include calculating your repetition max—the greatest load you can lift for a specific number of repetitions for a given exercise.
Soucre: ACSM's Resources for the Personal Trainer; Third Edition