Gym 74
How the 1RM is estimated
Your one-rep max is the heaviest weight you can lift once. You don't have to go to your limit to find it: a normal set gives a reasonable estimate. Here is exactly which formula Gym 74 uses, and why.
What this article is about
Your one-rep max (1RM) is the heaviest weight you can lift once. This article shows how Gym 74 estimates it from an ordinary set, so you can compare your strength without lifting a true max every time.
After reading you will know
- The Epley formula, with a worked example
- Why your number is comparable with what you see in other apps
- When the estimate cannot be trusted
The formula
1RM = weight × (1 + reps ÷ 30)
Gym 74 uses Epley's formula. Lift 90 kg for 5 reps and it works out to 105 kg. Every rep beyond the first counts for roughly 3.3% extra.
At one rep the formula gives 3.3% more than you lifted, which makes no sense: a single-rep set is your maximum. In that case Gym 74 returns the weight you actually lifted.
An example
| Set | Calculation | Estimate |
|---|---|---|
| 100 kg × 1 | measured, not estimated | 100.0 kg |
| 90 kg × 5 | 90 × (1 + 5 ÷ 30) | 105.0 kg |
| 80 kg × 8 | 80 × (1 + 8 ÷ 30) | 101.3 kg |
| 60 kg × 12 | 60 × (1 + 12 ÷ 30) | 84.0 kg |
Look at the first two rows: 90 kg for 5 reps estimates higher than a single heavy rep at 100 kg. That is why the app looks at the set with the highest estimate rather than the heaviest set.
Why this formula
There are at least seven common formulas and within the rep range people actually train in they agree closely. Epley is the one used in gyms and in many training apps, so your number is comparable to what you see elsewhere.
To be straight about where it comes from: Epley is not from peer-reviewed research. It was a poundage chart from the University of Nebraska strength programme, meant to show athletes their progress without making them test a true max every time. The evidence came later, when LeSuer and colleagues compared seven formulas against real maxima.
That study found high correlations for every formula, but also that all of them consistently underestimated the deadlift. So treat the number as a direction, not a verdict.
What the estimate is not
- Not a measurement. It is a calculation from one set, not a weight you lifted.
- Not reliable for long sets. The formula was built on sets of roughly 2 to 10 reps. Above 12 Gym 74 marks the estimate as unreliable and always prefers a set within that range.
- Only meaningful if you took the set close to failure. Stop with four reps left and the number says little.
- Not advice to go and lift that 1RM. Testing a true max takes a build-up and preferably someone watching.
Sources
The formula shown above is the formula in the code. These are the sources it comes from and was tested against:
- Epley, B. (1985). Poundage Chart. Boyd Epley Workout. Lincoln, NE: Body Enterprises. The original source of the formula. A training chart, not a scientific publication.
- LeSuer, D. A., McCormick, J. H., Mayhew, J. L., Wasserstein, R. L., & Arnold, M. D. (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. journals.lww.com Compared seven prediction equations against real maxima on bench press, squat and deadlift in 67 participants.
- Brzycki, M. (1993). Strength testing — predicting a one-rep max from reps-to-fatigue. Journal of Physical Education, Recreation & Dance, 64(1), 88–90. tandfonline.com The most common alternative. Gym 74 does not use it, but it belongs here to understand where estimates can differ.