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PNF Stretching


By looking through the internet one is lead to believe that pnf stretching is all there is to PNF. Proprioceptive neuromuscular facilitation (PNF) is an effective way of using reflexes to assist muscular relaxation.  Stretching using these principles is only one part of a system used by physical therapists to help muscular strengthening, stability, neuromuscular control, as well as mobility and coordination. This has been shown to be superior to static stretching in some literature.

Where did PNF come from?
What is a PNF pattern?
Contract-Relax
Hold-Relax
Contract-Relax-Antagonist-Contract
Neuromuscular Mechanisms
pnf stretching exercises

Where did PNF come from?

Proprioceptive neuromuscular facilitation (PNF) was first developed by Margaret Knott PT, and Herman Kabat MD in the 1940's to treat neurological dysfunctions. This was an attempt to gain better control in a population of neurologically impaired instead of just offering the standard treatment at the time which was range of motion exercises and gait training. Treatment involved reeducation of developmental movements and postures. This approach helped patients become more efficient in their movements and activities of daily living.

Muscle recruitment is enhanced through the use of the appropriate reflex and proprioceptive stimuli. The efficient recruitment of motor patterns involves the use of  the following PNF techniques:
  • resistance - resistance applied to a muscle contraction will facilitate a smooth motor response through optimal muscle contraction and relearning. The type and degree of resistance varies to achieve the appropriate motor response.
  • irradiation - irradiation is the overflow of neuronal excitation from stronger motor units to weaker ones, or units that may be inhibited by injury. This is done by applying graded resistance to larger muscle groups to enhance contraction in the weaker groups.
  • traction - the application of traction perpendicular to the arc of motion is used to facilitate an enhanced motor response .
  • manual pressure - neuromuscular responses are influenced by contact with the skin and deeper pressure receptors.
  • stretch reflex  - The stretch reflex is a stimulus that increases the state of responsiveness of a motor unit to cortical stimulation. This reflex is stimulated by the quick elongation of muscle. The stretch stimulates extrafusal and intrafusal muscle spindles to create a contraction. The muscle spindle and its reflex constitute  a feedback device that operates to maintain muscle length. The reflex produces a brief isolated contraction; however, with resistance  can facilitate a muscular response. 
  • and approximation - A compressive force to approximate joint surfaces can facilitate a motor response and promote stability.
A lot of the concepts developed by Knott and Kabat  have been tested scientifically and are used throughout rehabilitation settings across the world.(1)


What is a PNF pattern?

PNF patterns of movements were developed because all normal coordinated human movements occur in spiral or diagonal motions. Muscular contractions are strongest and most coordinated during these diagonal patterns of movement. These diagonal patterns involve rotation of the extremities and require core stability. Muscular contraction is also enhanced through irradiation and there is optimal facilitation of the stretch reflex in a synergistic muscle group during movements within these patterns of movement.(2)

PNF Methods Applied to Stretching to Aid in the Lengthening and Relaxation of Muscles

Contract-Relax

This is also known as "active assisted" stretching in some of the literature.

The golgi tendon organs lie in the tendon of a muscle that mediate the stimulation of inhibitory interneurons in the spinal cord that cause relaxation of that muscle's motor neuron. They also make excitatory connections with the motor neurons that supply the antagonists of that muscle. Since the golgi tendon organs are in series with the muscle fibers they are stimulated by both passive stretch and active contraction of the muscle.  The golgi tendon organ therefore acts as a transducer in a feedback circuit that helps to regulate muscle force through inhibition and relaxation of the muscle.

The contract-relax technique uses the development of tension in a muscle by isotonic contraction to facilitate the relaxation  and therefore stretch a muscle. By facilitating the relaxation of muscles we can improve circulation and improve extensibility of myofascial tissues. To accomplish this the muscle is placed in a maximally stretched position  and resistance is applied to a muscle contraction  of the muscle that is being stretched (direct contraction)  or that muscles antagonist (reciprocal relaxation).  Movement occurs during this contraction. Following this contraction the limb is relaxed and upon relaxation is actively or passively stretched further.
  • Direct Contraction - For example, when stretching the hamstring, the hip is placed in 90 degrees with the patient lying on his back. The knee is flexed against moving resistance isotonically and then relaxed. The hip held at 90 degrees, the knee is moved into its fully extended position so as to apply a stretch to the hamstring.
  • Reciprocal Relaxation - For example, when stretching the hamstring, the hip is placed in 90 degrees with the patient lying on his back. The knee is then extended against resistance, contracting the quadricep. The activity in the quadricep causes reciprocal inhibition of the hamstrings allowing for a greater stretch.

Hold-Relax

The hold-relax PNF stretching technique is used to facilitate the relaxation of muscles to gain range of motion. This method uses an isometric contraction rather than an isotonic one. To achieve this the limb is place in painfree range and an isometric contraction is sustained. The limb is then moved into the new range. The hold-relax method of PNF stretching  is facilitated by the golgi tendon organ to allow a reflexive relaxation of the muscle. It can be done individually or with assistance from a trainer or physical therapist. The danger of the hold relax PNF stretching technique is that with this inhibition of muscle activity, it may predispose an athlete to injury if done prior to an athletic event.


Contract-Relax-Antagonist-Contract

The first part of this stretch is similar to the hold-relax whereby the muscle being stretched is isometrically contracted for 3 to 6 seconds, then the antagonist muscle will immediately contract for 3 to 6 seconds. The joint is then pushed into its new range.



Neuromuscular Mechanisms

PNF Stretching: The Role of the Stretch Reflex
The muscle spindle is a long thin nerve receptor found within the muscle. Information from this receptor transmits information to the spinal cord regarding muscle length and the speed of lengthening. When a muscle is stretched quickly this muscle spindle fires and causes a reflexive contraction within that muscle that is undergoing the stretch. The greater the speed of stretch, the stronger the reflex contraction in the muscle being stretched.
PNF Stretching: Reciprocal Inhibition
inhibition of the antagonist muscle group is mediated by the muscle spindle. If the agonist muscle contracts, then the spindle fires, sending messages to the spinal cord causing the antagonist muscle to relax.
PNF Stretching: Autogenic Inhibition
The golgi tendon organ is a nerve receptor found in tendons. This receptor fires when tension increases within the tendon. This tension can be due to stretch or contracting muscle. When the golgi tendon organ fires a signal is sent to the spinal cord causing the agonist muscle to relax.

During pnf stretching, these three mechanisms all work together to allow normal smooth movements and can be manipulated through PNF techniques to increase our ability to stretch.
1. Carter, A., Kinzey, S., Chitwood, L., & Cole, J. (2000). Proprioceptive neuromuscular facilitation decreases muscle activity during the stretch reflex in selected posterior thigh muscles. Journal of Sports Rehabilitation, 9(4), 269-278.
2. Knott, M., & Voss, D. (1968). Proprioceptive Neuromuscular Facilitation (2nd ed.). Harper & Row: Philadelphia.