Proprioceptive neuromuscular facilitation, or PNF, is a type of stretching that involves a muscle to repeatedly contract against resistance and then relaxed into a deeper stretch, using the nervous system to allow greater lengthening.
In practice, a practitioner or partner takes a limb into a passive stretch. Then the athlete contracts the muscle group that goes against the resistance. When that contraction stops, neural feedback from tendon and muscle sensors dampens the usual stretch reflex, so the muscle temporarily “lets go,” allowing a brief, noticeably deeper stretch that could boost range of motion.
PNF also helps manual therapists evaluate and treat varioius conditions, from flexibility and movement issues to ankle sprains and brain injuries.
PNF stretching techniques
PNF stretching may use one or more of these techniques:
- Contract-relax: Uses contraction of one muscle through its range of motion to cause relaxation in the same muscle.
- Hold-relax: Uses isometric contraction of one muscle to cause relaxation in the same muscle.
- Hold-relax with agonist contraction: Uses hold-relax first, then concentric contraction of the muscle on the opposite side to generate extra stretch.
Contract-relax
In the contract-relax technique, the target muscle is first taken into a stretch. Then you contract the muscle and push gently against resistance for a few seconds, and then relax it so it can be pushed into a deeper stretch
To perform contract-relax stretching, your partner first takes your joint involved in the stretch through its full range of motion.
When your partner moves the joint to the first point of resistance, contract for about 5 to 6 seconds before your partner cues you to relax. When you relax, your partner moves your joint to its new flexibility limit.
For example, if the hamstrings are the target muscle, your partner should flex your hip to the point of resistance. Your partner will then provide resistance in the direction of hip extension as you gently push your leg toward your partner.
When you relax, your partner moves your hip to the new resistance point and repeats this process. This continues until you are no longer seeing improvements in your available motion.
Hold-relax
In hold-relax stretching, your muscle is taken to the point of restriction and held for a short time. Then you contract the muscle that is stretched for about 5 to 6 seconds while the stretch is held. When you are cued to relax, your partner moves you into the new range of motion.
For example, to stretch your hamstrings, your partner will take your leg into hip flexion until a restriction is felt.
After about 5-6 seconds of passive stretching, you will be cued to match your partner’s resistance in the direction of hip extension.
The key to this isometric contraction is that there’s no visible movement at the joint so your partner should provide resistance enough that your muscle is working, but they shouldn’t let your leg move through any range of motion.
Hold-relax-agonist-contract
In the hold-relax-agonist-contract technique, the target muscle is first taken into a stretch and held isometrically. After it relaxes, you contract the opposite (agonist) muscle to move the joint further. This combines two neural reflexes to deepen the stretch, which are called autogenic inhibition and reciprocal inhibition (details about the terms later).
Hold-relax-agonist-contract has three distinct phases. The first two are the same as regular hold-relax stretching. The third phase uses reciprocal inhibition so rather than being cued to relax.
During the relaxation cue, your partner stretches your joint to the next resistance, and the process may be repeated.
How PNF works
Researchers Hindle et al. from Wilamette University in Salem, Oregon, described four PNF stretching mechanisms: Autogenic inhibition, reciprical inhibition, stress relaxation, and gate control theory.
Autogenic inhibition
Autogenic inhibition occurs when a muscle uses the tension that it created to relax. When you contract a muscle, the golgi tendon organ is triggered to monitor the tension so that it can protect you from injury or damage.
When the tension is too high, the Golgi tendon organ (GTO) in the target muscle’s tendon sends a warning signal to your central nervous system to relax. For instance, if you stretch your calves, you dorsiflex your foot through the available range of motion.
Once you reach the limit of motion, you push your toes toward the resistance and then relax.
After you relax, you take your ankle to the limit of motion again and repeat until you are no longer gaining flexibility.
However, Hindle et al. wrote that the role of GTOs in autogenic inhibition may be limited, as studies showed the inhibitory signal after contraction is weak or short-lived.
Reciprocal inhibition
In reciprocal inhibition, the stretched muscle reduces neural activity and relaxes as its opposing muscle group contracts. This happens through spinal reflex pathways in which sensory signals activate neurons that suppress motor activity in the target muscle.
If you stretch your calf, you move through the full available range of motion first. Once you get to the end, resistance is applied to the top of the foot and your partner cues you to pull into their hand.
When you relax, your partner stretches you to the new endpoint before you both repeat the process. Activating the muscles on the front of the ankle will create a reflexive relaxation of the calf muscles.
Stress relaxation
Stress relaxation occurs when the muscle–tendon unit is held under a constant stretch, causing resistance to gradually decrease due to the viscoelastic properties of muscle and tendon, according to Hindle et al. As resistance decreases, the tissue slowly lengthens (called creep), temporarily reducing stiffness and passive torque.
While this mechanism may contribute to short-term increases in range of motion during techniques like PNF stretching, the changes are temporary (about 80 seconds to an hour after PNF stretching) and do not clearly explain long-term improvements in flexibility, Hindle et al. reported.
Gate control theory
Hindle et al. wrote that in the gate control theory, when two pressure and pain stimuli are sent to the spinal cord and the brain simultaneously. Pressure “wins” because it travels faster via the larger, myelinated nerve fibers that conduct signals more quickly than the smaller unmyelinated fibers carrying pain signals (nociception). This “closes the gate” on pain in the spinal cord’s dorsal horn, reducing how much pain is perceived.
During PNF stretching, they wrote when the muscle is stretched beyond its active range of motion, the applied force is perceived as a noxious stimuli and is seen as potentially damaging, “which invites the GTOs to activate in an effort to inhibit the force and prevent injury. As this process is repeated with a consistent protocol, the nociception…decreases as it becomes more accustomed to increased muscle and tendon length, as well as increased force.”
PNF stretching safety
It’s important for both the “stretcher” and the “stretchee” to understand that maximum force and contraction are not necessary to create a response in your body. You can use PNF safely and effectively with low level contractions. You should feel the target muscle turn on, but you don’t need to be anywhere near maximal force generation.
When your limb is stretched, it should be taken to the point where restriction is felt. There’s no benefit to aggressively applying more pressure to the stretched muscle in this position.
When your partner cues you to contract, think about matching their resistance, not overpowering them. This will ensure that neither of you is injured. The strength mismatch between your hamstrings and your partner’s shoulders can be rather large so take this into consideration before you push or pull.
PNF stretching can be applied to your upper or lower body and is universally applicable to all muscle groups. In its purest form, these stretches involve specific hand placements and movement in patterns that mimic daily activities.
These patterns are often referred to as D1 and D2 and refer to highly specific movement directions to ensure all of the muscles of a joint are involved in the motion. In its more well-known form, the science of PNF is applied to traditional stretching positions. This means you can take any stretch position you can think of and turn it into a PNF stretch. Oftentimes, PNF is thought of as “partner stretching” but it can be done with a wall or other immovable object if a partner isn’t available.
PNF stretching vs. static stretching
A 2017 systematic review found that neither PNF or static stretching is superior when it comes to increasing hip flexion however this may be misleading. Five studies met the inclusion criteria, but only one of them measured hamstring length using a clinically-accepted technique.
The study that measured hamstring length via hip range of motion during a straight leg raise is the only study to find PNF was a superior approach.
The other four studies used inclinometry and goniometry to measure knee extension angle and found no difference in range motion after the application of stretching regardless of technique.
In reality, there are a ton of variables involved in stretching which makes it difficult to compare one technique to another.
The age, gender, fitness level, type of stretch, duration of hold, and measurement tool (e.g. stand and reach, sit and reach, straight leg raise, knee extension angle) all play a role in determining the stretch’s effectiveness.
A 2019 systematic review found that PNF stretching improved immediate and short-term flexibility. The data suggest that clinicians should expect large gains in hamstring flexibility specifically when using PNF stretching techniques.
These improvements may be a function of increases in stretch tolerance as much as mechanical and neural factors. Improvement in range of motion after repeated procedures may be a by-product of increased stretch tolerance.
Although the evidence found PNF and static stretching creates similar results, PNF was slightly superior right after stretching. For long-term changes, the type of stretching doesn’t seem to make much difference.
PNF stretching may not be ideal if you like a solo workout; static or dynamic stretching may be easier to apply in this situation. But if you have a workout partner, PNF may be just what you both need.
PNF stretching origins
PNF was developed by Dr. Herman Kabat in the 1940s and was later formalized in U.S. physical therapy education and physical therapists Margaret (Maggie) Knott and Dorothy Voss in the 1950s.
Kabat partnered with Sister Elizabeth Kenny, who was successfully treating patients with polio using manual resistance and neurophysiology principles.
Their group effort in rehab led to the practice of PNF to improve muscle function in activities of daily living. At its core, PNF is just as useful today as it was when Kabat and Knott developed it.
Penny Goldberg, DPT, ATC
Penny Goldberg, DPT, ATC earned her doctorate in Physical Therapy from the University of Saint Augustine and completed a credentialed sports residency at the University of Florida. She is a Board Certified Clinical Specialist in Sports Physical Therapy.
Penny holds a B.S. in Kinesiology and a M.A. in Physical Education from San Diego State University. She has served as an Athletic Trainer at USD, CSUN, and Butler University.
She has presented on Kinesiophobia and differential diagnosis in complicated cases. Penny has published on returning to sports after ACL reconstruction and fear of movement and re-injury.
Outside of the clinic, Penny enjoys traveling, good cooking with great wine, concerts, working out and playing with her dogs.
Nick Ng, BA
Nick Ng is the editor of Massage & Fitness Jounal and the managing editor for My Neighborhood News Network.
An alumni from San Diego State University with a bachelor’s degree in graphic communications, Nick had completed his massage therapy training at International Professional School of Bodywork in San Diego in 2014. In 2021, he earned an associate’s degree in journalism at Palomar College.
When he gets a chance, he enjoys weightlifting at the gym, salsa dancing, and exploring new areas in the Puget Sound area in Washington state.
