Motor Variability and Equivalence

Another argument in the case against the term "muscle memory" are the concepts of motor variability and motor equivalence.  When we perform even the simplest tasks, such as reaching and pressing a button, we will never move in exactly the same pattern.  Why?  There is much variability in terms of which joints to use, how to use the joints, which muscles to use, what order to recruit the muscles in, and how much force to produce.  Although the movements will look similar, they will never be exactly the same.  The fact that we can move in a similar motion but use different patterns of joint actions and muscle activation is called motor equivalence.

If you look at some of the elite quarterbacks in the NFL, or elite pitchers in MLB, you will notice that they all have a similar throwing motion, but there are a lot of differences between them.  The pictures of Brett Favre and Peyton Manning above demonstrate this.  Also, if you watch a single quarterback make several throws over the course of a practice or game, you will notice some differences.  These differences are a good thing, because they allow us to adapt to changes in the environment.  But this variability also presents a challenge, and helps explain why elite level athletes often times fail.  If muscle memory truly existed, we would be able to repeat the same motion every single time without mistakes.  The human body would essentially function like a computer.  We know that this isn't the case.