Bib had a theory that those who injured themselves easier would gain faster. However, there is almost no way of proving that without collecting a ton of data. Even with that info, I don’t think it could prove anything without eliminating variables.
There is a big debate over the years here, if ligament stretching does anything for gains. I think this primarily started within the hanging community or at least with people that are against hanging. However, again this is a big debate and nothing is proven.
All we have are theories and nothing has been proven as far as I know. The only thing that I am positive of is that gains are possible. It also seems that people gain using different methods and training regimens. I do wonder if there is a most effective way, or does it depend on the individual. Can we lump people into groups that gain best with certain methods.
To me the biggest problem is there are so many variables and people don’t do the best job of tracking things. Plus so many things are subjective. Then you throw in poor measuring techniques, erection quality, liars and commercial interests.
I am curious how you are going to test the other ligaments in your body. If you did find a way of testing the other ligaments in the body then you need to compare that with other people that PE. Then you need good starting measurements and making sure that multiple people are doing almost identical routines. Then you need to categorize many different variables that also might affect gains. You need to do your best to either eliminate those variables or group people by all the different variables so you are comparing only the ligament differences. Then you need to draw a comparison with however you are defining ligament differences to gains that have been made. Then cross your fingers that people measured accurately, actually followed the routine, and that there are no liars in your study. Plus hopefully nobody identifies another variable that you didn’t take into account that throws all your theories into question.
Then after all that, you have identified that someone is a fast or slow gainer. Which they could probably figure out just by doing PE.