Background

One article which proved useful (linked below) details some common knee injuries and the causes as to each. Keeping the causes of pain and injury of the knee helped to design a better knee pad by knowing what to protect and how.
https://www.medicalnewstoday.com/articles/319324.php

Another article which proved useful (linked below) uses the data of thousands of men and geometrical analysis in order to design a knee-pad for the US Army. It further details important notes regarding how to shape the knee pad in regard to how it contours, the size variability for differently sized knees, and material usage.

https://www.sciencedirect.com/science/article/pii/S235197891500791X