Estimated 1RM and NSI: how to track strength without maxing out

Your one-rep max, or 1RM, is the heaviest weight you could lift for a single rep on a given exercise. It is the cleanest measure of raw strength, but actually testing it is fatiguing and carries more injury risk than a normal set, so few people do it often. An estimated 1RM solves that. It predicts your single from a set you already did, turning an everyday working set into a strength number without the load and recovery cost of a true max.

The logic is intuitive: the more reps you can complete with a given weight, the heavier your true single would be. Three reps at 200 pounds points to a higher max than ten reps at 135. A prediction formula puts a number on that relationship, so a set of 185 for 5 becomes an estimated max you can track set to set. When you do lift an actual single, that gets recorded as a true 1RM and kept separate from the estimate, so you never confuse a predicted number with a weight you really moved.

Estimated 1RM has been studied for decades, and a handful of named formulas are the standard. Each is a regression equation fit to population data, taking your weight (w) and reps (r) and returning a predicted single. Wellness Project defaults to the Epley formula and lets you switch to three others in Settings:

Epley(default): w × (1 + r / 30)
Lander: w × 100 / (101.3 − 2.67 × r)
Brzycki: w × 36 / (37 − r)
O’Conner: w × (1 + r / 40)

One case skips the formulas entirely. A single rep is your one-rep max, so it is recorded exactly as lifted rather than predicted. Three of the four equations return slightly more than the weight moved at one rep, and Epley reads 3.3% high, so a real 185 pound single would otherwise post as 191. That credits load you never touched, and it makes an honest multi-rep estimate of the same number look weaker by comparison.

They all agree within a few percent at low rep counts and drift apart as reps climb. Accuracy is best at roughly five reps or fewer and gets looser past about ten, where one extra rep swings the estimate noticeably, and the hyperbolic formulas (Lander and Brzycki) overestimate badly at very high reps. That is why the app caps the reps fed into every formula at 20: once a set runs much past 20 reps, adding more reps says more about your endurance than your maximal strength, so a 25-rep set is scored the same as a 20-rep set at that weight. The honest takeaway is that no formula is universally most accurate. Pick one and stay with it, because when you are tracking change over months, a consistent method matters far more than which equation you chose.

A 1RM on its own does not tell you whether you are strong. Two hundred and twenty-five pounds on the bench means something very different for a 150 pound lifter than for a 220 pound one, and the picture shifts again with age and sex. Strength normalization fixes that by scoring your lift against a standard built for a body like yours, so the number reflects relative strength rather than just absolute load.

That is what the Normalized Strength Index (NSI) does. It takes your best estimated 1RM on a movement, divides it by an intermediate-lifter standard for your bodyweight, age, and sex, and multiplies by 100. A score of 100 means you are exactly at the intermediate benchmark for that exercise. The bands run from below 75 (below average) through novice, average, intermediate, and advanced, up to 150 or higher (elite). For bodyweight movements like pull-ups, where there may be no loaded single to estimate from, the same idea is applied to your reps against a rep standard instead.

One thing to be clear about: NSI is an athletic comparison against population strength standards, not a health assessment. A low band is a starting point on a training journey, not a verdict on your wellbeing. The standards behind it come from published strength-science references, which you can read on our health sources page.