How Does PNF Stretching Work?

    There are various different types of stretching: ballistic, dynamic, static, PNF, ... etc. If you've read my previous post about how to improve your flexibility quickly and safely, then you would have seen how the various stretches compare to each other. It may be no surprise to you that, because of its effectiveness, one of my favorite types of stretching is PNF stretching.

    Proprioceptive Neuromuscular Facilitation (PNF) stretching is a type of stretching that involves contracting a target (TM) muscle and then bringing that muscle into a passive stretch. PNF differs from dynamic stretching, and ballistic stretching, but still uses static stretching as one of its components. My article on improving flexibility is a good one to read to get familiarized with the different types of stretching so as to get the most out of this article.

    Based on its description, most people can get a rough idea of how to do a PNF stretch. However, there are many variables and different styles of PNFS. In order to understand how to do this type of muscle energy technique most effectively, it would be best to understand how and why PNFs work. That is exactly what we'll be exploring in greater detail in this post.

Anatomy of PNF Stretching

Photo by camilo jimenez on Unsplash

If you examine the name, Proprioceptive Neuromuscular Facilitation, it implies that this technique facilitates the conditioning of the muscle and nerve interactions via the proprioceptors. Proprioceptors, according to Merriam-Webster, are sensory receptors that sense and respond to changes in the body, such as the positioning of arms, legs, and general posture.

There are many kinds of proprioceptors in the body, including the following:

• Muscle Spindles
• Golgi Tendon Organs
• Joint receptors
• Vestibular system
• Skin

For the purposes of this article, we will mostly be focusing on Golgi tendon organs, muscle spindles, and skin.

    One could say that proprioceptors help us to avoid harm. The way they do this is by inhibiting muscle movement when nociceptors detect potentially noxious stimuli. Nociceptors, as you might have guessed, are sensory receptors that send a signal to the central nervous system in response to being stimulated by noxious stimuli.

    Noxious stimuli are things such as heat, mechanical stimuli, and chemical changes that could pose a threat to the health of the body. Often, these noxious stimuli cause pain. In regard to stretching, mechanical stimuli are the most relevant stimuli. This is because mechanical stimuli include stretching, strain, pressure, and the sensations of force being applied to the muscles.

Mechanics of PNF Stretching

Photo by Kenny Eliason on Unsplash

To understand how PNF stretching actually works, we'll have to get a little deeper into the anatomy of proprioceptive neuromuscular facilitation. Let's examine the mechanics of what is going on that causes the release after a successful PNF stretch. As is written above, nociception causes the proprioceptors to act defensively and prevent further movement through the range of motion (ROM).

    To understand how the muscle succeeds in greatly increasing its ROM, one article suggests that it is necessary to take into account the gate control theory. According to the scholarly article written by Hindle KB et al., the gate control theory describes the concept that when 2 different receptors are signaling simultaneously, only one type of signal can be perceived at a time. Hindle et al. use the example of pressure sensations compared to pain sensations. According to this article, the sensation of pressure is facilitated by larger nerve fibers that are myelinated. In contrast, pain receptors are fed by smaller fibers, some that aren't even myelinated. 

    Myelin is an insulator that essentially works for nerve signals in a similar way to how electrical insulation works for copper wiring; myelin helps maintain signal strength and clarity over a longer distance than if it were unmyelinated. What this translates to is that myelinated fibers are sending a more clear and stronger signal, especially if those fibers happen to be larger than competing fibers. In the case of pressure vs. pain, this means that pain cannot be perceived because pressure signals would override pain signals if they were sent at the same time.

    The reason why any of that is relevant in regard to PNF stretching is that nociceptors are triggered during a stretch. This causes proprioceptors such as muscle spindles and Golgi tendon organs (GTO) to inhibit the muscle from lengthening. When PNF stretching is performed, a load is put on the muscle which causes a sensation that, via gate control theory, prevents the successful transmission of pain nociceptor signals and therefore prevents proprioceptors from inhibiting ROM. This can lead to profound improvements in ROM in a short amount of time.

    As a massage therapist, I use PNF stretching on nearly a daily basis. Hindle's article reads that the effects of PNFs can last 90 minutes or longer. I have personally seen countless cases in which my clients could barely move one of their legs prior to their massage, and after doing PNFs for the correct muscle groups, those clients were able to walk normally even 2 weeks after their massage. In my opinion, and I believe the article by Hindle et al. agrees, the durations for which one may experience improvement after PNF stretching depends on the stresses those muscles are going through after the stretching session.

How to Do PNF Stretching

With all the technical details written so far in this blog post, it should make sense how PNF stretching techniques can cause big improvements in flexibility in a seemingly magical way. You will run into articles that claim that there are 3 ways to do PNFs. There are also articles that state that there are 5 ways. No matter the enumeration, these techniques basically all boil down to the same few concepts.

The five ways that I've seen to do PNFs are the following:

1. Hold-relax
2. Contract-relax
3. Hold-relax-contract
4. Contract-relax-antagonist-contract
5. Hold-relax-swing

    Regardless of the PNF technique used, I believe that partner stretching is the most efficient way to do it. In my opinion, some PNF stretches aren't practical to be done singlehandedly. This is because a person can easily inadvertently contract the muscle during the relaxing and stretching phase, which could take away much of the physiologic benefit that PNFs have to offer. With that being explained, let's take a look at these stretching techniques in some detail. 

Hold-relax

Video by AIF Education

    To do a hold-relax PNF, it is very simple: just take the target muscle (TM) to a comfortable stretch of at least 10 seconds, isometrically contract the TM for at least 6 seconds, and relax into a deeper stretch. If you've never done PNFs before, you might be surprised at how much further your limb can move as you do this technique.

    Let's break this down so you can see how the mechanics of this concept work. In the initial passive stretch, there is a nociception caused by the extent of the stretch. 

    The nociceptors sense the tension of the stretch, signal pain, and say, "Nope! We're not moving that limb any further!"

     Next, the client performs an isometric contraction for at least 6 seconds, this causes the Golgi tendon organ (GTO) and muscle spindles to sense a different and more powerful nociceptor signal. In essence, the nociceptors are becoming overstimulated and used to the pressure being applied. 

    This immersion of nociception causes the nociceptors to calm down and allow a further range of motion without inhibition. In other words, the nociceptors refrain from sending signals to trigger the proprioceptors. Therefore, the proprioceptors have no reason to inhibit the range of motion. This results in a person being able to move their limb to its full, natural ROM and then improve the muscle length from there.

    I hope this breakdown of how the physiology of hold-relax PNFs works helps to explain why PNFs in general bypass physiologic limitations that otherwise could not be circumvented.

Contract-relax

Video by AIF Education

    Contract-relax PNF is done very similarly to hold-relax. The difference is that instead of doing an isometric contraction, the client does a concentric contraction. This means that the muscle contracts through its full range of motion. To do contract-relax PNFs, take the TM to a comfortable stretch, hold that stretch for at least 10 seconds, contract the TM through its full ROM, relax the TM, and then bring the relaxed TM to its new and improved ROM. 

    Sometimes there won't be much of an improvement. This is because these sudden gains in ROM depend on how much proprioceptors are inhibiting the muscle's movement. If the proprioceptors are not interfering with ROM (which they usually are to some degree), then a PNF release may seem to be ineffective at improving ROM.

Hold-Relax-Antagonist-Contract

Hold-relax-antagonist-contract PNF stretching is a type of PNF that is less commonly found in articles talking about PNF techniques. This seems to be very similar to contract-relax-antagonist-contract (CRAC). Actually, reading some articles about hold-relax-antagonist-contract can be confusing because their explanations can be vague. After reading an article that included "hold-relax-contract," as one of its listed PNF techniques, I had to dig pretty deep to come to the conclusion that the author was probably writing about hold-relax-antagonist-contract.

So, if you see hold-relax-contract, I think they're talking about contracting the antagonist muscle, rather than contracting the target muscle into the trainer's pressure.

To do a hold-relax-antagonist-contract PNF perform the following steps:

1. Passively stretch the TM for approximately 10 seconds or more.
2. Isometrically contract the TM for at least 6 seconds.
3. Relax the TM and concentrically contract the antagonist muscle so that you are contracting into the stretch, complementing the pressure of the trainer.

Contract-Relax-Antagonist-Contract

Video by Functional Training Institute

Contract-relax-antagonist-contract is generally done in the following steps:

1. Passively stretch the target muscle for about 10 seconds.
2. Concentrically contract the TM for about 6 seconds or more.
3. Relax.
4. Concentrically contract the antagonist muscles for about 6 seconds or more.
5. Relax.
6. Stretch the TM again for 10 seconds.

The last step is done because when the antagonist muscles contract a phenomenon known as reciprocal inhibition takes place. This means the reciprocal muscles are inhibited; they cannot interfere. The reciprocal muscle to the antagonist muscle is the agonist muscle, which is the target muscle that was being passively stretched in step 1. Therefore, the target muscle is being physiologically released by the contraction of the antagonist muscles.

    To provide an example of a target muscle and its antagonist, the quadriceps could be a target muscle, and their antagonist would be the hamstrings.

    Notice that I explain what is usually done to perform these techniques. That is because there are many different ways to do these PNFs. Near the end of this post, I will share with you my own special recipe for how I do PNFs with the highest success rate that I realized as a result of experimenting with every PNF technique I've ever read about.

    Before we get into that, let's take a look at a riskier PNF that I never attempt.

Hold-Relax-Swing

Hold-relax-swing is another odd PNF that I have rarely ever heard of. I'm not even sure that it's truly a PNF or someone's own creation that they decided to throw into their list of PNF techniques. According to the authors at ro.co, hold-relax-swing adds an element of ballistic or dynamic stretching into a hold-relax PNF. The TM is contracted, then relaxed, then swung into a stretch. 

    Clearly, this technique carries with it all the risks of standard ballistic stretching or dynamic stretching and is possibly even more risky, due to the PNF release done prior to the swing. It is recommended that if anyone attempts this type of technique that they should be masters of muscle control who can confidently and safely go into a stretch in this way.

    If you've read my previous article on stretching to improve ROM, then you know that ballistic stretching is dangerous compared to static or PNF stretching and that studies have shown that ballistic stretching tends to yield inferior gains in ROM, anyway.

My Own Special Recipe for PNF Stretching

Image by Mohamed Hassan from Pixabay

As you know, I really believe the best way to do PNFs is with a partner. By "partner" I don't strictly mean that it's a fellow athlete trading off partner-assisted stretches with you prior to an athletic activity. Probably the best "partner stretching" you can have is that which is done by a trained professional. 

    As a massage therapist and Rossiter coach, most of my clients have seen me specifically for my PNF stretching techniques. Other healthcare workers who can perform these physiologically beneficial stretches are physical therapists, kinesiologists, chiropractors, and there are many more. One of the biggest advantages of hiring a trained professional is that a trained professional has lots of experience doing PNFs every day of the week. They also have formal education on how to do these techniques and learn them in greater detail via continuing education.

    All that considered, it's unfortunately true that simply having a massage license does not make one educated in massage. It's literally scary how many massage therapists lack some very fundamental knowledge of that which they are certified. Several of my clients have told me that they have been getting massages almost every week for decades and they've never had anyone try to lengthen muscles to correct their posture or do PNFs to get rid of their physiologic tension and shortness in their muscles.

    The reason why I mention this is because this technique I'm about to describe isn't something that anyone should just simply attempt just because they've seen the steps described on how to do it. To do this PNF sequence safely and effectively not only requires the steps on how to do it, but it also requires education on all the anatomy, physiology, and mechanics of how the body works so that one does not get injured inadvertently. I have met a few clients that told me they were very cautious about having stretches done because some massage therapists who didn't know what they were doing caused them an injury.

    So, once you have found a professional that can be trusted to do PNFs safely for you, you may find that their own way of doing it is a bit different than the standard ways that I have described in this blog post. Based on my experimentation and experiences, this is the way that I do PNFs to provide the highest rate of success for my clients:

1. Passively stretch the target muscle (TM) for 25 to 30 seconds.
1. This stretch is very gentle.
2. Have the client contract the TM through a full range of motion with no more than 20% effort. This contraction is held for about 15 seconds.
1. You may have seen in the scholarly articles that I've linked in this blog that some experts were advocating 100% effort in the contraction. This is not necessary and is potentially injurious.
2. You will find various durations when researching PNFs. The longest duration for the contraction that I've seen is 15 seconds and that duration has provided for the highest success rate that I've seen in regard to PNFs increasing ROM.
3. Typically PNFs are done with either an isometric contraction or a concentric contraction. My technique combines both.
3. The client relaxes entirely the limb to be stretched. Think "ragdoll."
4. While the limb is fully relaxed, the target muscle is brought to another comfortable stretch. Typically at this point, the limb is able to move much further than on the first attempt.
5. If this method seems ineffective, I follow up with a reciprocal inhibition stretch, which tends to succeed if the contract-and-relax approach does not.

Note: You may notice that I hold the stretches longer. This is because in my profession, I am not trying to just release tension prior to a sport event, but I am also working toward allowing the muscles to lengthen to provide long-term relief from the tensions my clients have. In doing it this way, I am also targeting specific muscles to improve posture my legitimately encouraging the muscles to grow longer.

As alway, remember that no post ever in my blog is meant to be construed as medical advice. This blog is just for information and entertainment. I hope you found this information useful and interesting. Please leave a comment on my blog to share your own experiences with PNFs and massage as a client.

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