How do your joints collaborate to produce movement? Any movement? When I reach down, unscrew the lid off my water bottle, bring the water bottle to my lips and drink, there are an infinite number of ways I could do this (the degrees of freedom problem, for those of you who like to throw around the motor control terms). And yet my joints organize in a very specific way, without any thought from me. Why?
This concept has fascinated me for years. I have read motor control textbooks, seeking to understand different theories. Dynamical systems theory, for instance, says it is the interaction between the person, the environment, and the task that determines how we move and how we learn new movements. This is fine, where does that information about the person come from? Is it from sensorimotor maps, informing how the sensory input from the world is related to motor output? And if that is the case, how does that influence the motor output? Why do I tip my hand and my head at the same time when I drink from my water bottle? Why don’t I tip one first? Or why don’t I only tip one? (Clearly, I have too much time on my hands, since I can amuse myself with this line of thinking for days.)
At some point in the not-too past, I began writing a book with movement savant Adarian Barr who views movement through the lens of a lever. The way he sees it is the input (environment, task, current position), determines the output (movement needed to complete the task). The output is produced by a series of levers.
So what is a lever? Confession: the only reason I passed college physics is because Sy, the cute head coach for the men’s golf team, took pity on me and invited me over to eat pizza while he enthusiastically explained kinetic energy to me. By the time I got to upper division courses, I carefully skirted biomechanics as much as I could, taking the one required course, filling the rest of my time with exercise physiology, psychology, and neurology, physiology, and behavior.
This means I had to look up what a lever actually was before I could write about it. And I had to watch endless videos explaining the concept before I actually started to get it.
But I digress. A lever is a simple machine that moves load. It does this through a lever arm (which can be thought of as a long beam) and a fulcrum point. Effort is applied somewhere along the lever arm to create rotation around the fulcrum. The result? Movement.
So in the human body, a lever arm is a bone. The pivot point (fulcrum) is a joint. Effort comes from the muscles. And the load that is being moved can either be the body or something external.
Consider these examples.
I nod my head up and down. What is the fulcrum? What is the lever arm? What is the effort? What is the load?
The fulcrum is the joint where the head meets the cervical spine (atlanto-occipital joint). This joint is why the head can move up and down.
The lever arm is the head.
The effort is moving the head against gravity. This is performed by the neck muscles that nod the head up and down.
The load is also the head. The head is heavy! Changing its relationship to gravity requires effort.
I stand up from a chair. What is the fulcrum? What is the lever arm? What is the effort? What is the load?
The answer depends on how I do it. Let’s pretend I am using my gastrocnemius and hamstrings for the effort. The fulcrum, in this scenario, would be the hip and ankles. (Rotation occurs at the hip joint so my torso can change position in space and at the ankle so my shin can change location in space.)
The lever arms are the torso and the shin. The torso is changing position relative to the lower legs. The shin is changing position relative to the thigh and foot.
The effort comes from the muscles that move the torso up over the pelvis, the muscles that move the thigh under the pelvis, and the muscles that move the knee over the foot.
The load is the torso.
I throw a ball forward with my left arm. What is the fulcrum? What is the lever arm? What is the effort? What is the load?
Again, it depends on how I do it, but let’s pretend it’s a basic toss, where I step my right foot forward as I throw the ball. The fulcrums are the wrist and the shoulder.
The lever arm is the arm (how convenient is that) and the hand.
The effort comes from the muscles around the shoulder blade and the fingers.
These examples are simplistic, and you could do on a much more in depth deep dive for all three of those examples by playing with where the effort is coming from, how different joints are positioned, and altering the position of load. All of these things change how levers are used.
Understanding levers gives you options—options for moving differently, options for completing a task more skillfully, and options to develop more effective exercises and programming. Taking the time to more fully understand how you are the lever will make improve your coordination and improve your coaching and teaching. This is why Adarian and I are teaching a 90 minute webinar on the topic (replay will be available if you can’t attend live). Join us.