Understanding the question
A repetition-based equation can estimate a one-repetition maximum from the load lifted and repetitions completed, but it does not measure an actual maximum. Predictions depend on the exercise, the equation, the individual and whether the set approached the endpoint assumed by the equation. Estimates from high-repetition sets tend to involve more extrapolation and can be influenced by endurance and discomfort. These calculations are useful for monitoring a consistent exercise under comparable conditions, especially when frequent maximal testing is unnecessary. They should be labeled estimated and should not be treated as a promise that the predicted weight can be lifted safely today.
What a useful investigation needs to consider
Different formulas can produce different answers from the same set. Choosing whichever gives the highest value creates an artificial improvement rather than better evidence of strength.
A set stopped with several repetitions remaining does not provide the same input as a repetition-maximum set. Adding an uncertain RIR estimate can help contextualize it but also adds prediction error.
Changing technique, equipment or range of motion breaks comparability. A precise-looking estimated maximum cannot repair inconsistent source data or establish that muscle size has increased.
Read the detailed explanation
The companion article explores estimated one-repetition maximums in more depth, with topic-specific explanations and source material.
Estimated one-repetition maximumsSources and further reading
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