The Complete Guide for Applying Traction and Approximation for Motor Control into Your Clinical Practice.
Knowing why and how to clinically apply traction & approximation during motor control training is a powerful tool in both the orthopedic and neurological settings. The goal of this article is to provide you with enough of the why and how to apply these neuro-based principles into practice right away. When rehabilitating a patient who has had a neurological incident, like a stroke, many times it’s difficult for them to voluntarily move the way they want, let alone moving the way we want as clinicians. If traction and approximation can be pivotal for guiding reflex motor control to assist voluntary movement in these neurological cases, they can also be catalysts a technique tweak in the orthopedic clinic.
What does the Reflex Model of Motor Control have to do with Traction & Approximation?
Knowing why we should consider using traction and approximation principle starts with understanding the underlying premise behind the reflex model of motor popularized by Dr. Charles Sherrington. Dr. Sherrington was a neurophysiologist in the late 1800s who decerebrated cats (removing the cerebral cortex by cutting through the midbrain & brainstem) and applied various forms of afferent stimulus through stretch or some sort of noxious input to the periphery of the body such as a pin prick.
He then observed the efferent (motor) response. He found that no matter the afferent input stimulus, quick stretch or pin prick, there would always be a stereotypical muscle response, despite the removal of the cerebral cortex. “For Sherrington, reflexes were the building blocks of complex motor behavior. He believed that complex behavior could be explained through the combined action of individual reflexes that were chained together.” (Sherrington, 1947) (Shumway-Cook, Woolacott 2012) This is essentially a spinal reflex loop which is very similar to the physiology of the stretch reflex. A caveat here is that, according to Mark L. Latash, “Charles Sherrington viewed muscle reflexes not as hardwired stereotypical responses to stimuli but rather as tunable mechanisms that formed the basis of motor behavior (See Action potential threshold section below). Control of movements, according to Sherrington, was performed by changing parameters of reflexes, in particular of the tonic stretch reflex, an idea very close in spirit to the EP-hypothesis” (See article by Latash: Evolution of Motor Control: From Reflexes and Motor Programs to the Equilibrium-Point Hypothesis)
For every model of motor control there are inherent limitations because not one model can capture all the variables of a complex dynamic system as is the human body. The obvious limitation in this model is that movement can’t be exclusively explained by reflexes, given our conscious mind. In other words, if the cerebral cortex is left attached to the rest of the CNS, then we have to acknowledge that both reflex and voluntary movements play a role in adaptable movement behavior.
Traction, Approximation, and The Action Potential Threshold
With that said, the use of traction and approximation seems to provide us direct access into facilitating reflex motor control at the level of joint mechanoreceptors (Phasic type II and Static type I receptors). One of the basic neurophysiological concepts that is vital to understand from Sherrington’s work is the All-or-None principle as it relates to the action potential threshold of the joint mechanoreceptors (any peripheral receptor). This principle is depicted in the image below and states that when a peripheral receptor is sufficiently stimulated (mechanical disruption is enough to elicit voltage threshold) an electrical signal (action potential) is propagated back to the spinal cord which then elicits a reflex motor response(spinal reflex). When applying traction or approximation, our goal is to provoke intra- or extra- articular mechanoreceptors to optimize sensory afferents during motor control training. Referencing the image below, the “stimulus” can either be traction or approximation, which is used to promote a reflex muscular response with the intent to promote either stabilization or movement. I’d like to re-emphasis the point made by Latash earlier with respect to Sherrington’s perspective on reflexes: “Control of movements, according to Sherrington, was performed by changing parameters of reflexes, in particular of the tonic stretch reflex.” Although we are discussing joint mechanoreceptors and not the stretch reflex, the action potential threshold is what would be considered a “changing parameter of reflexes” because it is now well accepted that the CNS, via descending pathways and other mechanisms, can modulate the sensitivity of peripheral neurons. Thus the action potential threshold of the mechanoreceptors can change moment to moment based on the CNS’s experience with the given input. In other words the force application, speed, and frequency of the application of traction or approximation may need to change to maintain the “novelty” of the input during treatment in order to elicit the desired motor response (in the event that the CNS habituates to the input). The constant changing of the manual application of traction and approximation highlights that this is just as much and art as it is a science.
Traction is defined as the elongation of a segment or structure. This is commonly associated with pulling or anti-gravity movements. Traction seems to pre-activate Phasic Type II receptors which facilitates synergistic trunk musculature to prep for anti-gravity function.
Approximation is defined as the compression of a segment/joint surfaces. This is commonly associated with pushing and weight bearing activities. Approximation seems to pre-activate Static Type I receptors which seems to facilitate postural stabilization and co-contraction of agonist/antagonists.
Think of traction and approximation as two completely opposite ways of imposing a mechanical force.
How do I apply Traction & Approximation into my clinical practice?
An easy example of traction is the function of the “rotator cuff” when we are carrying something heavy. The traction or distraction that occurs through the glenohumeral joint stimulates a reflex contraction of the “rotator cuff” (in this case the “anti-distraction cuff”). In the event that a client with shoulder pain is advised not to carry something heavy, traction can be applied more delicately as shown in the side sit on elbow image below. Let’s say the goal is to optimize scapular-thoracic (ST) and glenohumeral (GH) stabilization in the affected shoulder (non-weight bearing shoulder in the image). The clinician or coach can apply intermittent axial traction through the top arm with a verbal cue to the client “don’t let me lift your elbow off the floor.” The intermittent traction forces provokes reflex co-contraction through ST & GH segments as the client learns to “lock it in.” Keep in mind the principle of Therapist Position while applying either traction or approximation.
Image 5
Using the same image of side sit on elbow, we can discuss an application of approximation. Manual compression is being applied toward the elbow on the ground to give the client more awareness for proper position in the a side sit on elbow position - a variation of the Turkish Get Up exercise.
The motor learning research that has been put out by Gabriel Wolf suggests external focused cues prevail with retention tests for motor performance versus internal focused cues (Literature and practical application discussed in Nick Winelman’s book “The Language of Coaching). Be creative with verbal cueing and attempt to use sensory rich external focus cues instead of internal anatomy-focused cues when coaching.
Instead of the internal cue of “get long through your arms” or “pull your shoulder blade down and back” we may choose to say “drive your elbow through earth” or “your elbow is a sword drive it through the earth.”
In terms of pairing external cues with the use of approximation and timing, from experience, it’s easier to use a verbal cue that requires the client to resist the force being imposed on them. So we would say “don’t let me push the sword any further into the earth” as we are applying approximation through the top arm directing our force toward the bottom elbow. In this way, we pair voluntary motor responses (verbal cues) and involuntary motor responses (spinal reflex loop via approximation) to get the client to stabilize the shoulder girdle.
Note that there is no “right” or “wrong” way to apply traction & approximation. When there is a specific intention (i.e “Hold don’t let me move you”), the rule of thumb is to do what works. Keep in mind that optimal motor learning takes place with variable repetition as emphasized by the dynamic systems model of motor control. For an in-depth break down of the dynamic systems model read this article: Dynamic Systems Theory of Motor Development: The Complete Guide for Sports Rehab Professionals.
