Dynamic Systems Theory

Task Constraints

Dynamic systems theory (DST) theorizes that new movements can arise suddenly and abruptly over time. DST also states that novel movements are governed by constraints (Clark, 1995). Like a funnel guiding water, constraints “steer” the development and refinement of motor patterns as well as skill acquisition over time. Constraints can be broken down to three main categories: task, environmental, and organismic (McKeon, 2006).

A task can be defined as an activity requiring voluntary head and limb movement to achieve a specific goal, or purpose (Magill, 2011). An exercise-based example of a task could be a deadlift. The task of a deadlift is to lift an object off of the floor, finishing in an upright posture. A task constraint, then, would be any modification of the task that helps steer the development/quality of the movement behind it. The deadlift demands a highly coordinated effort by the sensorimotor system to manage many joints, muscles and movements. A common term to describe the array of elements (i.e., from a neuromuscular/joint/muscle perspective) involved in a movement, and how they are managed efficiently, is known as the degrees of freedom (DOF) (Magill, 2011). Thus, DOF increases proportionally to increasing movement complexity.

The DOF within a deadlift can be managed by task constraints in many ways. Two common movement errors during a deadlift include knees tracking in front of the toes, as well as flexion of the lumbar spine and cervical extension of the neck. I control the DOF by having a client stand directly in front of a bench (knees close to the bench). As the client hip hinges, the only natural recourse (because knees cannot move forward) is to drive the clients hips posteriorly (with some knee flexion), thereby inducing a hip hinge. If the client is having trouble maintaining a neutral spine during the hinge, a secondary task constraint, in the form of a dowel or broom handle, is placed along the entire spine. The client is instructed to keep the head and hips tight to the dowel. When the client loses contact, he/she knows to re-adjust thereby inducing a neutral spine during the hinge. Please see my YouTube link below showing task constraints and progressions of the deadlift:

https://www.youtube.com/watch?v=FCXap4KGI_o&list=PLD5Xk-dZZYNpCkTMo7ZC8kLnkp4Gi_5Wb

Environmental Constraints

An environmental constraint can be defined as elements of the environment, which are external to the person and the task, that helps develop movement (McKeon, 2006). In continuing with the theme of the deadlift, an environmental constraint could be the firmness of the floor, which the client is lifting from. The floor could be sand, foam, a Bosu etc… Considering the complexity of the deadlift, and the DOF it requires from a novice individual, initially controlling the deadlifting surface is paramount as a means of minimizing overall complexity of the movement. Thus, a firm floor allows the client to focus on the task, and task constraints, while minimizing the DOF and improving the predictability of the environmental constraint (i.e., firm floor) (McKeon, 2006).

Organismic Constraint

The third constraint found within the dynamic systems theory is the organismic constraint, which can be defined as structural or functional impairments (i.e., from trauma or genetics) that limit the acquisition of movement skills (McKeon, 2006).

A prevalent example of an organismic constraint found within my clientele would be lower crossed syndrome (LCS). One of several characteristics of LCS includes restriction of the rectus femoris/psoas of the anterior side and overactive/facilitated thoraco-lumbar extensors of the posterior side (Sahrmann, 2002). Such restrictions can hinder the range of motion necessary to complete a deadlifting pattern. Moreover, forcing a client into a deadlift, with the aforementioned anterior hip restrictions, could cause lumbar flexion during the eccentric and concentric phases of the movement. Such postures have been correlated to low back pain and disc degeneration (McGill, 2007). Thus, avoidance of vulnerable spinal positions during the deadlift is paramount.

As a means of mitigating some or all of the organismic restrictions (i.e., tight/overactive hip flexors), self-myofascial release (SMR) and stretches are implemented to lengthen the aforementioned regions. Such methods help increase the range of motion (ROM), thereby circumventing the posterior pelvic tilt that can occur during the deadlift pattern. Please see below for visual illustrations of stretches and SMR to loosen the anterior hip regions prior to deadlifting:

Injuries and the Constraints They Affect

Injuries directly affect the organism. Since an injury occurs within a region of the body, the body itself becomes limited or restricted to some degree. Considering an organismic constraint is defined as structural or functional impairments that limit the acquisition of movement skills, injuries have the capacity to alter movement strategies, thusly inducing/exacerbating organismic constraints (McKeon, 2006).

McKeon (2006) argued that part of an organism’s ability to survive is predicated on having movement options. Multiple movement strategies allow room for the organism to achieve the same task, providing a means of survival and homeostasis. An example to illustrate the aforementioned concept could be a hunter stranded in the woods with a broken hand (i.e., organismic constraint). Although his dominant right hand is broken, he must still eat until he is rescued. The ability to aim and shoot his rifle (i.e., the task) cannot be achieved by pulling the trigger with his right hand. However, he can use his left hand (i.e., alternate movement strategy) as the trigger finger. Although the hunter may not be as coordinated with his left hand relative to his right, the task still has the capacity to be achieved successfully.

References

Clark, J. E. (1995). On becoming skillful: Patterns and constraints. Research Quarterly
for Exercise and Sport, 66(3), 173-183.

Magill, R. A. (2011). Motor learning and control: Concepts and applications (9th ed.). New York: McGraw-Hill.6, P.O., (2009). Cultivating functional variability: The dynamical-systems approach to rehabilitation. Athletic Therapy Today, 14(4), 1-3.

McGill, S. (2007). Low back disorders: Evidence-based prevention and rehabilitation(2^nded.). Windsor, ON: Human Kinetics.

McKeon, P. O. (2006). Cultivating functional variability: The dynamical-systems approach to rehabilitation. Athletic Therapy Today, 14(4), 1-3.

Sahrmann, S. (2002). Diagnosis and treatment of movement impairment syndromes (1st ed.). St. Louis, MO: Mosby Inc.

-Michael McIsaac