Bill Hartman 35:24–37:57
If we had a fulcrum, there would be a lot of pressure and heat that would be released every time we moved and we would destroy our joints in no time. And so we don't want fulcrums in our joints. In fact, if you do have a fulcrum in your joint, you're probably talking to the orthopedic surgeon right now. So now what we have to understand is that we have to have mechanisms that keep these bones from touching. So let's break these down. Now let's start with structure. So your 99% water, 1% stuff, your 1% stuff is almost all the same and it's all viscoelastic tissue. And so I have representation of viscoelastic tissues in my silly putty. And so this is viscoelastic, so it's going to behave very similarly. And so this tissue will behave differently depending on the forces that are applied. So if I stretch this gently, I get this nice elongation of my silly putty, but if I pull it really hard and fast, it snaps off clean. So what that means is the tissue behavior changes based on the forces that are applied. And so when I apply a high rate of force, I get very, very stiff viscoelastic tissue. So this is the overcoming action that I always talk about when we're talking about concentric overcoming or eccentric overcoming behaviors. So I have an increased stiffness of tissue. So if I had an orientation of fibers as such, that if I loaded them at a higher rate, I can make them really, really stiff. And so we actually have that. So when we look at the fascia that surrounds everything. So we talk about the periosteum. We talk about the fascia that surrounds all of the ligament structure and all the structures around the knee. So the knee is very busy when you look at it from a connective tissue standpoint. And so what happens is when we load that joint, those viscoelastic tissues behave very, very similar to my silly putty. They get very, very stiff, and they create this rigidity around the knee, and that actually pushes the bones apart. So now we have a mechanical protective mechanism that helps us keep those bones apart. So that's very, very useful. It's a little counterintuitive too by the way when you think about it. It's like you think of these are like tension elements and stretchy stuff. They become very, very stiff. So keep that in mind.
joint mechanicsviscoelastic tissuebone separationbiomechanicsconnective tissue