A person's one rep maximum (1RM) is the heaviest weight that can be lifted with good form.  It is the standard by which absolute strength is measured, typically in exercises such as the bench press, squat, deadlift, etc. One rep maxima 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 rep maxima can also be used as an upper limit, as in the cases of determining the desired load for an exercise (percentage of 1RM).
Various protocols call for lifting some percentage of 1RM. However, many consider the risk of injury when attempting a 1RM to be equal to or higher than when performing multiple rep sets. In response to this, there have been various proposals for ways to calculate an approximation of the 1RM. FFitness's view is that yes, if a person does not regularly train with heavy loads, true 1RM testing is dangerous, however, given our propensity for incorporating static strength training into our DCs, veteran FFitness participants can reasonably be expected to safely do true 1RM testing.
In some instances, it is more feasible to calculate an individual's 1RM, rather than perform a true test (see below for instructions on administering). Examples where you'd want to calculate 1RM are when you need to determine percentage of 1RM and you haven't tested 1RM for some time, when an individual has not engaged in strength training long enough to safely participate in a true 1RM test, or any other time you wish.
The Epley Formula
The Epley Formula, presented by Boyd Epley in 1985, is perhaps the easiest formula to remember, and is pretty accurate for calculating 1RM. The formula is as follows:
Weight × ( 1 + ( 0.033 × Number of repetitions ) )
Testing True 1RM
After a warm up, a weight that is achievable is selected. Then after a rest of several minutes, the weight is increased and the lift is again executed. The athletes chooses subsequent weights and repeats the process until only one full and correct lift of that weight is executed. That is the true 1RM.
- Estimating 1RM and Training Loads - a 1RM estimation chart
- 1RM estimation calculator - excel spreadsheet
- ↑ Donche, Dan (2008). FF Trainer Certification Guide. USA: Fatal Fitness.