Landers fine-tuned Brzycki's formula using data from lifters of all strength levels, not just the super strong ones.
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The Landers 1RM formula was developed by Jared Landers and is an adaptation of the Brzycki formula discussed earlier.
The Landers formula is: 1RM = Weight / (1.0644 - (0.0644 x Reps))
Where: Weight = Load lifted (lbs or kg) Reps = Number of reps completed
The key difference from Brzycki's original 1.0278 - (0.0278 x Reps) formula is that Landers adjusted the coefficients to 1.0644 and 0.0644 respectively.
Landers derived these new coefficient values by analyzing strength training data from hundreds of lifters across a wide range of strength levels - from novice to elite.
Through regression analysis on this large dataset, Landers found that the 1.0644 and 0.0644 coefficients provided a better overall fit and minimized prediction errors when compared to actual measured 1RMs.
Essentially, Landers fine-tuned the coefficients from Brzycki's formula to account for a broader population sample beyond just the elite powerlifters that Brzycki's original formula was based on. This adjustment makes the Landers formula potentially more accurate for a wider range of lifter abilities and training experiences compared to just using Brzycki's coefficients derived from elite lifters.
While a relatively small tweak mathematically, the Landers 1RM formula demonstrates how these prediction equations can be refined and updated as they are validated on new and larger datasets from diverse populations.
It aims to make the 1RM estimate more generalizable across different strength levels.