PNF Basic Principle: Traction & Approximation
When rehabilitating a patient who has had a neurological incident, like a stroke or a brain injury, many times they have difficulty voluntarily moving the way they want, let alone moving the way we want them to move.
Knowing when and how to appropriately apply the traction and approximation principle helps us tap into subcortical motor strategies to guide voluntary movement control in both clinical and training scenarios.
Traction is defined as the elongation of a segment or structure. Traction is typically used to increase a muscular response and promote movement, and typically used with pulling and anti-gravity movement.
An easy example is when we think of the upper extremity and 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”).
The traction that is provided by the external load is thought to pre-activate phasic type II receptors and thus eliciting an involuntary contraction of the cuff and the synergistic muscle groups as well to prevent the joint from being subluxed or dislocated. Obviously the application of traction is a little more complicated in a neurological setting, but understanding the foundational scientific premise allows us to be creative as we try to blend voluntary and involuntary movement control strategies.
Approximation is defined as the compression of a segment/joint surfaces and is also typically used to promote reflex stability. This is commonly used with pushing and weight bearing activities. It is thought that providing a joint with compression stimulates static type I receptors, and thus facilitating postural extensors and stabilizers.
A simple application of this principle is shown in image 1. Manual compression is being applied toward the elbow on the ground to give the client more awareness for proper position in a side sit on elbow position - a variation of the Turkish get up exercise. Be mindful of the other principles such as verbal cueing when coaching this and ask the client “can you get long through your arms?” or whatever they respond to.
Just like anything else, there are exceptions to this principle, where traction can be used for stability and approximation used to promote movement. When practicing PNF we are constantly blending and seamlessly applying all the principles and philosophies because they live through interdependence, despite the fact that they have to be taught independently.