Knees, Feet, and Ground — the Critical Interface

The knees are some of the most critical, and also most vulnerable, joints in the human body. Protecting the knees in routine training is a primary requirement for long-term participation in martial arts. Equally important, the things a student should do to protect his or her knees can be a gateway to learning how to optimize the power and effectiveness of a wide variety of techniques, regardless of the art being practiced. Let’s start with the key principle: Keep the foot and the knee in alignment.

I had 20+ years of training and a sandan in karate, with a little judo and European fencing while in college, before I had the opportunity to begin training in kenjutsu. One of the first things I was taught was how to walk properly. My sensei illustrated how most people tend to walk, with feet splayed outwards and essentially falling forward with each step. Because the knee points forward while the foot is angled to the outside, every step places strain on the knee. Maybe just a little, but enough that the strain can produce damage over time. 

Read more at https://www.ittendojo.org/articles/knees-and-feet