Dynamical Systems Theory; A rational approach to understanding movement systems.

“It is not the strongest of the species who survive, nor the most intelligent, but the one most adaptable to change.”

-Unknown 

This is one of my favourite quotes, even though there isn’t enough substantive evidence to give credit to anyone in particular (some suspect Darwin, go figure.) It provides pretty sound advice in terms of how things (species, systems, ideas etc.) can not only persevere and survive, but also thrive. For strength coaches who are reading this, turn off your training theory brain for a second and remember what it means to be adaptable. Adaptability is the capacity for accommodating new changes in both the internal and external environments. Plain and simple, to adapt means to be minimally effected by changes or perturbations by changing yourself or your strategies to cope. Actually, it’s possible that changes or perturbations to which you’ve been forced to adapt will make you better suited to handle different combinations of perturbations in the future.

constraints-performance

Physical performance, or resultant movement, tends to be the result of interactive perception and action as it stems from task, environment, and organismic constraints. Davids, K., Glazier, P., Araujo, D. et al. Sports Med (2003) 33: 245.

Example 1: Adaptation as a consequence of an internal/organismic perturbation

You’re in the fourth quarter of a basketball game, about to pitch your eighth inning in baseball, or on a breakaway in the final seconds of a hockey game. During all of these conditions, you are trying to perform in the presence of fatigue (internal/organismic perturbation.) Whether the game is on the line or not, you still have to produce a movement pattern which will equate to some semblance of a strong performance. In this case, the nervous system needs to find a way to send commands that will be less affected by fatigue and these commands are far more general (universally applicable patterns) than the patterns we execute when well rested. This is often accomplished by what we would typically characterize as compensatory patterns. Since a pattern is being reproduced using strategies which are different from the norm, they are generally less economical and rely on fewer, shallower attractors.

Example 2: Adaptation as a consequence of an external/environmental perturbation

Imagine you’re out for a run by the beach. You’re running along a sidewalk and as you’re doing this you take a moment to admire your surroundings. With your eyes fixed on the sunset, you fail to notice the end of the sidewalk coming up and suddenly the surface you’re running on changes from pavement to soft sand. If you manage not to fall, it’s because your nervous system reflexively reorganized the running program to accommodate for the instantaneous external (environmental) perturbation. The sand lengthens your ground contact time, it also absorbs more of and therefore decreases the ground reaction force. As a result, you have to make adjustments to your running program to accommodate this perturbation.

Example 3: Adaptation as a consequence of task perturbation

If you’ve ever tried to get back in shape, or have been subject to a collegiate strength training program, you’ve very likely been subjected to circuit training in one form or another. As you switch from exercise to exercise, you’re randomly recalling different movement patterns. Some you may have a great deal of experience with, some you may have never done before. An effective circuit has large variations in motor programs as you switch from one exercise to the next (task perturbation,) moving from a squat to a pull up for example is a good way to coerce the nervous system into more quickly and accurately recalling different movement strategies on short notice. The more consistently you can perform a quality first rep on the next exercise, the more confident you can be that learning is taking place. The key here is to remember that although the patterns are very different, the main components that will make you successful stay the same (e.g. postural control and proper breathing and bracing technique.)

These are the three primary ways in which you can create variation, or in other words perturb movement patterns that may already exist. You see, movement patterns may more effectively be described as results. They are the results of these perturbations, or constraints as they may sometimes also be called. The Organism, Task, and Environment each provide their own set of unique constraints or limits on which movement can be selected to accomplish the intent. The resulting movement chosen to accomplish that intent is also influenced by the reliability or stability of attractors within the movement database as they have been trained in the past.

dynamical-systems-title

This is the best paper I have read so far on functional variability related to constraints and perturbations.

To this point, I’ve no doubt made perturbation appear to be the bad guy in this article. In competition, maybe it is. Perturbations are literally the constraints which force us to deviate from our preferred movement patterns. In a world where we may want to believe that there is one right way to do everything, unfortunately there is not. In fact, it’s been shown in professional sport that those who have more degrees of freedom in their movement pattern selection are actually exploiting their ability to ADAPT to environmental, organismic, and task-specific constraints. Remember, it’s not the strongest or smartest, but the most adaptable that survive and thrive.

The conversation regarding movement systems as dynamical systems would be incomplete without discussing degrees of freedom and coordinative structures. Since a motor or movement task may be succinctly defined as mastering degrees of freedom and organizing control of the system, there are requisite components which offer MORE movement, working with other components which RESTRICT movement. Simply stated, degrees of freedom are “options” for movement offered by each part of the system (think of rotation in the shoulder, flexion and extension of the elbow etc.) Coordinative structures are rigidly fixed segments, or restriction of those degrees of freedom. So within the system, you have cooperative “options” and mechanical restrictions working together to produce a systemic solution to a movement problem.

If you’re looking for a more thorough definition of coordinative structures, let me ruin your day with this:

“Coordinative structures reduce the dimensionality (i.e. complexity) of the dynamical movement system by allowing humans to exploit the inherent interconnectedness of the anatomical system. An essential feature of a coordinative structure is that if one of the component parts introduces an error into the common output, the other components automatically vary their contribution to movement organisation and minimise the original error.” 

Latash ML. Scholz JP. Schoner G. Motor Control Strategies revealed in the structure of motor variability. Exerc Sport Sci Rev 2002: 30: 26-31.

So to tie these concepts together, a movement PROBLEM arises from the environmental, organismic, and task related constraints. A movement SOLUTION is the system’s response by designing a motor program which most effectively operates within those constraints. The motor program is a function of the cooperative influence between the specific athlete’s degrees of freedom and coordinative structures.

In practice, we think of efficient movers as those who have a high capacity to express mobility (deg. freedom) and stability (coord. struct.) in alternating fashion throughout the kinetic chain. When these two things are present in their respectively proper articulations, the patterns which arise are exactly what you’d like to see. So a great athlete is one who can reflexively transition between phases of movement by expressing constraint-relevant patterns through manipulating their available mobility and stability in a fluid manner.

If you’ve ever seen an exceptional athlete move in their sport, you may catch yourself intuitively recognizing that they are “just different” than the other players on the field. The fluidity of their movement patterns is largely owed to their ability to exploit degrees of freedom by adapting more quickly to the ever-changing demands of constraints.  A lesser athlete may actually restrict movement unnecessarily through overuse of coordinative structures, owing to their lack of transitional adaptability to those changing demands. This results in slower, less efficient, and more rigid movement. There is no coincidence that we think of skilled athletes as “free” or “fluid” and we think of lesser athletes as “slow” and “rigid” or “stiff.” They simply cannot reorganize their patterns fast enough to shine like their better teammates.

****I will follow up this post with a “Part 2” about Functional Variability in the future.

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