Dimmer. Not Flip.
This is part-two of a multipart series explaining why someone moves so differently when they catch an object they believe weighs much more than it does. For part-one, click here.
In the last post we used the analogy of tires, slides, and golf balls to discuss how bones move on each other at joints. In this blog we will discuss how muscles generate and manage the force to move one bone on the other.
To understand how muscles work, we will use the analogy of a giant tug-of-war. Each side of this giant tug-of-war is a muscle made up of not one rope, but hundreds. Each rope has a team of hyper-competitive “tuggers” assigned to it. In anatomy, these teams are called motor units and the tuggers are called muscle fibers. These muscle fibers, or hyper-competitive tuggers in our analogy, are either pulling with everything they have - or not pulling at all. Also, these motor units, or teams, are not all the same size. Some teams are large, with multiple tuggers and can generate a lot of force. However, some of teams are small, with only a few tuggers, and cannot generate much force. When our brain tells a muscle to work, it starts by recruiting a few small motor units. As more force is generated, it recruits more and larger motor units. This allows our muscles to work like a dimmer-switch; not a flip-switch.
This fine-tuning allows us to be more dexterous. The more coordinated our brain is at recruiting the right number and size of motor units, the more smoothly we can accomplish tasks. A perfect example of this is a skilled ballerina’s ability to make incredibly difficult tasks look easy; effectively causing each muscle to generate the perfect amount of force at every moment. Such coordination takes skill and practice, which is part of what we, at Dotson Physiotherapy. When injury, surgery, or deconditioning has led to poor motor coordination, we help people learn to recalibrate their internal “dimmer switch.”
However, this is only the tip of the iceberg when watching your friend catch something that weighs much less than he expects. To get the full picture look for next week’s blog, titled “Call in the Specialists.”