An Introduction to PNF

Proprioceptive neuromuscular facilitation (PNF) is a stretching modality which intersperses static stretching with a series of muscle contractions or isometric activations. PNF uses this muscle activity to exploit certain neuromuscular traits and facilitate a greater stretch. The goal is to achieve improvements in range of movement (ROM) beyond those that can be achieved by traditional stretching.

What does it involve?

The most common PNF technique is termed ‘contract-relax’ or, more correctly, ‘hold-relax’. This is where the tight muscle is placed into a passive stretch, the tight muscle is activated isometrically, and then the muscle is stretched further. Here’s a step-by-step PNF example for attempting to increase dorsiflexion ROM:

  1. The ankle is passively and gradually moved into dorsiflexion by the coach.
  2. The coach halts the movement at the first point of resistance (not the end ROM).
  3. This position is held for prolonged period (typically between 5-30 seconds).
  4. The athlete is then instructed to resist the coach who will attempt to move the ankle further into dorsiflexion. The athlete should match the force applied by the coach and resist the movement.
  5. This isometric activation is held for predetermined duration (typically between 3-15 seconds) before the athlete then relaxes.
  6. The ankle is passively moved to the next point of resistance.
  7. This new position is again held for a prolonged period (again, typically between 5-30 seconds).
  8. Steps 4-7 may be repeated 2-3 more times or until the end ROM is achieved.

What is autogenic inhibition?

Autogenic inhibition refers to the relaxation of a muscle in response to high tension; it is a protective mechanism designed to protect the muscle from potential damage. The isometric activation of the ‘tight’ muscle during PNF is designed to induce autogenic inhibition within the muscle and therefore reduce the muscle’s resistance to stretch.

The Mechanism:

The alpha motor neurons are responsible for initiating muscle fibre contraction and therefore determining the general excitability of the muscle. The higher the excitation, the more resistant the muscle will be to stretch. When the muscle contracts tension increases within the muscle-tendon unit as whole; this is sensed by the Golgi tendon organ in the tendon. In response to this tension, the GTO activates the Ib-inhibitory interneurons. These interneurons work to inhibit the alpha motor neurons, causing fewer impulses to be generated and for the muscle to relax. Less excitation, more potential for stretch.

Is there a more effective technique?

The second technique that is often utilised is known as the ‘contract-relax-agonist-contract’ method. This technique utilises active contraction of the antagonist, or opposite, muscle to get into the stretched position. The steps are the same as the ‘contract-relax’ method with the following exceptions:

  1. The athlete actively dorsiflexes the ankle with slight passive assistance from the coach
  2. The movement is halted at the end of the athlete’s active ROM.
  3. The athlete actively dorsiflexes the ankle with some passive assistance from the coach moved to the next point of resistance.

What is reciprocal inhibition?

Reciprocal inhibition refers to relaxation of a muscle in response to the activation of its antagonist. In PNF, contraction of the opposing muscle is designed to induce reciprocal inhibition within the tight muscle and reduce the resistance to stretch.

The Mechanism:

Muscle contraction requires impulses to be sent to its specific alpha motor neurons.  When an impulse is sent, in addition to activating these alpha motor neurons, these impulses also activate Ia-inhibitory interneurons that connect to the alpha motor neurons of the antagonist muscle. As with the type IIb-inhibitory interneurons, the type Ia-inhibitory interneurons work to inhibit the alpha motor neurons, causing fewer impulses to be generated and for the muscle to relax.

Summary

PNF is a stretching modality that seeks to bring about increases in ROM by inhibiting and relaxing the tight muscle. Hopefully this article has briefly summarised PNF and its neuromechanical principles, in the second part I’ll outline how best to use PNF techniques and discuss the relevant modulating factors.

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