Albert Einstein famously quipped: “There is no hitching post in the universe.”
A hitching post, in this case, means a starting location: a point A. When an object is moving, the only way to describe how fast it’s going, and in what direction, is by comparing it to another object. In the vastness of space, there is no single consistent object—no hitching post—from which to do that. You have to pick one on a case-by-case basis, depending on what you’re trying to figure out.
When discussing human musculoskeletal anatomy and kinesiology, a similar concept is frequently—and mistakenly—applied.
The actions of your muscles are described in terms of the movement of the distal (further-from-center) insertion to the proximal (closer-to-center) origin. As a matter of fact, we derive what we call “origin” and “insertion” from this proximal/distal relationship. The bicep, for example, is considered a flexor of the elbow, moving the hand (distal) toward the shoulder (proximal). The gluteus maximus is an extensor of the hip, extending the femur (distal) relative to the pelvis (proximal).
These descriptions are all fine and well, but there are times when the proximal/distal view is not ideal in describing the movement of your joints.
Try to predict what will happen when this muscle shortens:
The red dot is one attachment point and the blue dot another. The muscle acts like a fishing line pulling them closer to each other, but which end is the fish and which is the reel? Will the blue come toward red or the red toward the blue?
The answer is: both. The muscle doesn’t know the difference between the two points of attachment; muscles only know how to do one thing and that’s shorten.
Now let’s add in a few more bones and see what happens when we fix one of our dots to something stable: a fisherman to hold our fishing pole. A more complete version the selection above looks like this:
The muscle in question is the bicep. The blue dot is where it inserts into your radius (forearm) and the red dot is its origin at the scapula (shoulder blade). The scapula is fixed to the ribcage at all of those green dots, which represent the origin of the serratus anterior. So the blue dot (our fishing line) moves toward the red dot (our fishing pole) because the red dot is being held in a fixed position by the green dots (fisherman) . . .
So what holds the green dots in place?
Replace the green dot with the red dot, replace the red with the blue and you have to once again search for the next green dot in the chain. This line of questioning can continue through every muscle, bone and joint in your body and the location of the green dot will continue moving down.
Until, that is, we get to the ground.
There may be no hitching post in space, but there is one on earth: the earth. The speed and direction of everything on the planet is described and measured in relationship to the ground, including you. Your bones operate as a complex set of levers that use the earth under your feet as a fulcrum that converts ground forces into work. The design of your skeleton—of all skeletons, really—is based on the point where feet hit the floor.
As trainers and therapists, this approach is extremely helpful. If a joint is painful or dysfunctional, there is usually some kind of loading problem: forces acting on that joint in a way that they shouldn’t. If you assume that the forces acting on all joints originate in the foot*, it’s simply a matter of tracing a line between the dysfunctional joint and the ground; somewhere along that line you’ll find a blue dot without something stable to hold on to. You’ll find a pole with no fisherman.
And this is where describing the motion of muscles from the ground up is more realistic than using proximal/distal relationships. Consider the following:
This is the gastrocnemius, or calf muscle. Gray’s Anatomy will tell you that it originates at the femur (the blue dot) and inserts into the calcaneus (red dot) and, if you ask your average trainer for an exercise that utilizes this muscle, they’ll tell you to raise your heel off the floor (pictured).
While that’s true, it’s actually a poor description of what that muscle is actually for. When your foot is plantar-flexed (pointed, as when standing on your toes) a complex set of actions is taking place in the foot that turn the arch of the foot into a rigid structure capable of channeling ground forces into forward motion. While this is happening, your knee is extending, allowing those same ground forces to be carried from the tibia (or shin) to the femur. With the foot rigid and planted firmly into the ground, it makes an ideal hitching post from which the gastrocnemius can act on the femur, decelerating the extension of the knee and readying the whole leg for the next phase of the gait cycle.
This ground-up view of the calf muscle’s function highlights a crucial element of the gait cycle; moreover, in the presence of a variety of knee dysfunctions, the only way to properly diagnose the problem is to understand gastrocnemius’ roll from this perspective.
This is just one example of how the proximal/distal perspective can be deceptive. There are a wide variety of pathologies, particularly in the foot and ankle, that are much easier to spot and correct by considering the position of the fisherman standing by the hitching post.
* Obviously, this view omits such issues as direct trauma, wherein force enters the body through other means, like whiplash from a car accident.