I gave a talk at a local Running Room last week, where I opened by asking if anyone has tight hamstrings. Guess how many raised their hands. If your guess is about 90%, you’re right. I then asked half the attendees to lie on their backs while the other half observed. I instructed those on the floor to place their arms on the floor at their sides with palms facing up, and straighten their legs with toes pointed toward the ceiling. I then asked them to keep both knees straight and lift one leg up as high as they could.
That is repeated movements and prolonged postures that cause movement disorders by causing what she refers to as directional susceptibility to movement (DSM) and relative flexibility. This is an extension of basic physics: movement will follow the path of least resistance. In an ideal body, that path will move in a manner that maintains optimal positioning of joints and involvement of appropriate muscles so that it does not cause wear. In a body that has been changed through repeated movement or prolonged postures, the path of least resistance can lead to suboptimal movement.