1. Proprioceptive Neuromuscular Facilitation (PNF)
NPTI Module A

2. Proprioceptors
Proprioceptors: Specialized sensory receptors that provide the central nervous system with information needed to maintain muscle tone and perform complex coordinated movements.
Golgi Tendon Organ (GTO): Proprioceptors located near the tendon/muscle (myotendfinous) junction. When tension in the muscle increases, the GTO synapses and the muscle relaxes.
Muscle Spindle: Proprioceptors located within the muscle. When muscle is stretched the muscle spindle sends impulse to spinal cord, where it synapses with the motor neuron causing the muscle to contract.

3. Takeaway
Muscle Spindle: Located inside the muscle. When the muscle is stretched quickly, the muscle spindles send a message to the CNS to make the muscle contract to avoid injury.
EX: Knee Jerk reflex, box jumps
GTO: Located where the muscle meets the tendon. When tension increases in the GTO (slowly), the GTO causes the muscle to relax.

4. Pictures
Golgi Tendon Organ
Muscle Spindle

5. PNF Facilitates inhibition, increases ROM
Often requires a partner or trainer
More effective in increasing ROM than static stretching or dynamic stretching
Performing PNF stretching more than twice per week is not recommended

6. PNF
During a PNF stretch, three specific muscle actions are used to facilitate the passive stretch.
The isometric muscle action is referred to as “hold” and the concentric action is referred to as “contract.”
Contraction of the agonist is called “agonist contraction,” and is used during a passive stretch of the antagonist to achieve reciprocal inhibition.

7. PNF
Reciprocal Inhibition: when the agonist muscle concentrically contracts, causing the antagonist muscle to in turn relax. This relaxation of the antagonist muscle allows the agonist muscle to move the limb through the total allowed range of motion without interfering tension.
Autonomic Inhibition: When a muscle is put on stretch for a prolonged amount of time or contracts isometerically, the GTO is activated and inhibits the tension, allowing the muscle to relax and elongate. This elongation during a stretch or extreme tension helps prevent the possible tearing of a tendon or muscle. This process is known as autogenic inhibition.

8. PNF Protocol Three basic types of PNF stretching:
Hold-relax
Contract-relax
Hold-relax with agonist contraction (greatest ROM increase)
With each technique, the first phase is a passive stretch of 10 seconds. The muscle actions in the second phase give each technique it’s name.

9. PNF

10. Hold-Relax
Passive prestretch held at point of mild discomfort for 10 seconds.
Partner (trainer) applies hip flexion force and cues athlete, “Hold and don’t let me move the leg.” Athlete holds leg isometrically for six seconds.
The athlete relaxes and a passive stretch is performed and held for 30 seconds. The final stretch should be greater due to autogenic inhibition (activation of hamstrings/stretched muscle).
Source: [2]

11. Contract-Relax 10 second passive prestretch
Athlete then extends hip against resistance to a full ROM.
Athlete relaxes and a passive stretch is applied and held for 30 seconds. The increase ROM is due to autogenic inhibition (activation of hamstrings/muscle stretched).

12. Hold-Relax With Agonist Contraction
First two phases are identical to the first two phases of hold-relax. “”
Concentric action of the agonist (ex. Hip-flexors in a hamstring stretch) is used in addition to the passive stretch to increase the stretch force. The final stretch should be greater primarily due to reciprocal inhibition (activation of hip flexors) and secondarily due to autogenic inhibition (activation of hamstrings).

13. Resources
NSCA Essentials of Strength Training and Conditioning Third Edition
Physiological Principles of PNF Stretching -