The Weight Lifting and Body building calculator compute metrics for weight lifting including several different functions for one-rep maximums. One-Rep Maximum calculator approximates the maximum weight a person can lift based on a set number of repetitions of a lesser weight. The calculator has several formulas for calculating the max weight. See the descriptions of the different formulas below.
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Wikipedia writes the following in their definition of One-Repetition Maximum:
"One-repetition maximum (one rep maximum or 1RM) in weight training is the maximum amount of force that can be generated in one maximal contraction. One repetition maximum can be used for determining an individual's maximum strength and is the method for determining the winner in events such as powerlifting and weightlifting competitions. One repetition maximum can also be used as an upper limit, in order to determine the desired 'load' for an exercise (as a percentage of the 1RM)."
The following formulas can help you to calculate your one-repetition maximum:
Epley Formula
The Epley Formula, 1RM = w(1 + r/30), was presented by Boyd Epley in 1985 and is one of the simplest one-repetition maximum formulas available. This formula is similar to the Brzycki Formula, and for reps over 10, the Epley and Brzycki Formulas should yield the same answers. However, for reps below 10, the Epley Formula will provide a slightly higher maximum. Neither equation is 100% correct, but each one offers a baseline for weight lifting.
Source Lifting Revolution : http://www.liftingrevolution.com/strength-training-for-women-how-to-find-your-1-rep-max/
Wathen Formula
The Wathen formula (1RM= 100w/ 48.8+53.8-0.075r) was computed by D. Wathen in 1994. This formula, just like the other six one rep max formulas, is used to calculate the amount of weight needed for weight lifting or body building. It has been confirmed to be accurate by Knutzen (1999) at predicting the amount of weight needed to an accuracy of 0.5 kg.
Reference:
Cybulski, G., et al. Determination and Prediction of One Repetition Maximum (1RM): Safety Considerations. Journal of Human Kinetics. 2008. 19, 109-120.
Mayhew et al. Formula
The Mayhew et al. Formula can be found on Wikipedia. The Mayhew et al. formula is: (100*w/52.2 + 41.9*e^(-0.055*r)). It is used for accuracy in predicting the one-repetition maximum for dead lift, squat, and bench press. The details for the use of this formula, and the research behind it is found in the Wikipedia reference page.
Wikipedia cites the use of the source:
LeSuer, Dale A.; McCormick, James H.; Mayhew, Jerry L.; Wasserstein, Ronald L.; Arnold, Michael D. (November 1997). "The Accuracy of Prediction Equations for Estimating 1-RM Performance in the Bench Press, Squat, and Deadlift". Journal of Strength and Conditioning Research 11 (4): 211–213. doi:10.1519/00124278-199711000-00001.
The link to the Wikipedia page is: https://en.wikipedia.org/wiki/One-repetition_maximum