1RM OConner

O'Conner: conservative 1RM estimation

The O'Conner formula estimates 1RM with a linear coefficient: 1RM = weight · (1 + 0.025·reps). Set it next to Brzycki and Epley and you'll notice it's more conservative. As you climb into higher rep ranges it leans toward underestimating the max, which is exactly why it tends to be the safer pick when you're writing prescriptions. Take a quick example. At 80 kg × 5 reps you get 1RM = 80·(1+0.125) = 90 kg. Push to 10 reps and it's 80·1.25 = 100 kg, where Brzycki returns 80·36/27 = 106.7 kg and Epley 80·1.333 = 106.7 kg. That 6-7 kg gap at 10 reps is the conservative bias at work, and it earns its keep any time undershooting beats going over.

Applications: physical therapy and beginners

It fits conservative initial prescription in strength programs nicely, and it shines in physical therapy, where rehab loads simply can't absorb an overestimate. Beginners with no movement history get a bit of extra margin, and in CrossFit it helps when you're laying out percentages for technical lifts. Coaches who deal with a mix of populations usually keep O'Conner as the default and only move to Brzycki once a lifter has reached intermediate or advanced level.

FAQ

Why use O'Conner if it underestimates? Because undershooting is the safer mistake to make. A load that's a touch lighter still does the job. One that's too heavy ends in failed reps or injury.

When to switch to Brzycki/Epley? Once the lifter has 6-12 months of steady training behind them and has cleaned up their technique on the compounds.

Does it work above 10 reps? Accuracy slips, just like it does with every other formula. Past 12 reps none of them hold up, since at that point the set has turned into a test of muscular endurance.