T Nation

IPF Replaces the Wilks Formula



But yeah. It’s not all bad.


The Arnold is ditching the rising bar in favour of the powerlifting type arrangement. I shook my head…


From what Ive seen of the analysis and charting, its not that its biased towards lighter classes (in fact it isnt at all, the main criticism is that it goes too far in some cases bringing up the middleweights and definitely makes life hard for the real SHW’s) but that there is a mathematical singularity at 15 point something KG bodyweight, which is clearly outside the reference range of the data. So at 15.29 something something 6 decimals bodyweight, a 1kg lift would score hundreds of thousands of points, any lighter and your score is negative for any lift.


Even as a stats problem, there is a lot of subjectivity to be worked out.
Most adult men have the frame to be competitive at either 83 or 93. Guys with the frame to be competitive at 59 or 120+ are extreme outliers. That suggests that we should expect by random chance that most of the time a lifter in the middle weightclasses should win best lifter (because there are more of them, or at least middleweights have been selected from a larger population).

The degree to which this assertion should affect the formula is obviously subjective, but it’s important. The counterargument is that people in the outlier weightclasses might be more likely to participate in powerlifting because they can be competitive in a class where most people simply can’t.


Here is a nice chart comparing wilks and IPF across the population data.

The clear difference is that, rightly or wrongly, to maintain your IPF score, gaining bodyweight above 110kg requires you to increase your total, where Wilks basically does not. More bodyweight doesn’t hurt your Wilks above 110 as long as your total goes up even trivially.


What’s also clear is that neither formula is going to work below 50kg or above 125kg because of how thin the data points are outside of those bounds. I suspect Wilks was too pro SHW, and IPF is too anti SHW. But best fit lines across small populations are never going to be accurate.