On movement complexity…
“One of the most commonly seen features in human movement is motor variability. Several attempts at the same task ALWAYS lead to different patterns of performance, including kinematic, kinetics, and patterns of muscle activation.” (Latash 2002)
In other words, with consecutive attempts at solving a motor task, each rep involves unique, non-repetitive neural & motor patterns. Often referred to as “repetition without repetition.”
Movement is not a well defined plan. Its more chaotic than that.
Movement is an intent (or goal), carried out by an ongoing process of adapting to variables. The number of potential variables is far greater than we can account for via movement assessment/observation.