Ah, mobility. The most neglected part of any workout routine. The most forgotten part of any training program. The most underappreciated variable to achieving strength, improving movement, decreasing pain, and reducing the risk of injury.  There’s more to an intelligent mobility program than just hanging out in positions that stretch muscles for one minute at a time.

There is also Dynamic Stretching and Proprioceptive Neuromuscular Facilitation (PNF). Both of these stretching modalities have different purposes. You’ve probably heard people talk about how dynamic stretching is better than static stretching. The truth is, they’re wrong. Like I said, they serve different purposes.

Flexibility is not just how long your muscles are. It also includes your tendons, ligaments, fascial sheaths, joint structures, and skin. That is why a complete approach to mobility, or the ability for joints to have free motion, should include different training modalities such as foam rolling, static stretching, dynamic stretching, and PNF.

Also, you’re going to hear me interchange flexibility and mobility. That is because I believe they are one in the same. Flexibility is the range of motion of a joint. The pure definition of mobility is the “ability to be moved freely and easily.” Although people separate the two, those two definitions seem so similar to me that they are synonymous when it comes to the human body.

Proprioceptors

The biggest difference when it comes to static stretching, dynamic stretching, and PNF, apart from the way they are accomplished, is the interaction they have on these things we call proprioceptors.

Proprioceptors are these little sensory receptors in the human body that respond to movement and position. Close your eyes, and then point your finger in any direction. Then, while keeping your eyes closed, try to touch your other finger to the very tip of the outstretched finger. You’ll find that, even while not being able to see the outstretched finger, that your other hand could get pretty close to such a small point on your body. The reason for this accuracy in body awareness is due to proprioceptors.

These proprioceptors also detect stretch in muscles. There are two in particular: muscle spindles and golgi-tendon organs (GTOs).

Muscle spindles monitor changes in muscle length. These proprioceptors are found in the belly of muscles. During rapid stretching movements, these little guys send signals to the central nervous system to activate the muscle. The goal here is to prevent the muscle from getting rapidly overstretched, which may cause damage. This activation due to stretching is caused by the stretch reflex.

Golgi-tendon organs, or GTOs, are located close to where the muscle meets the tendon, or the musculotendinous junction. These guys are sensitive to increases in muscular tension. As a muscle lengthens, GTOs will become activated and relax the muscle (that sounds like a contradiction, but it’s not). This happens one of two ways.

There is autogenic inhibition, which is when GTOs are activated as a result of a contraction in the muscle, followed by a passive stretch.

Then, there is reciprocal inhibition, which is when GTOs are activated as a result of a contraction of the antagonist (opposing) muscle group, that causes a relaxation in the muscle being stretched. For example, if you were to lie down on the ground and raise your leg, you actively contracting your hip flexors will relax your hamstring due to reciprocal inhibition.

So, why do these proprioceptors matter when it comes to dynamic stretching and PNF? Guess what, I have an answer.

Dynamic Stretching

Dynamic stretching is a great warmup tool to restore tissue flexibility before a workout. These drills are often called “mobility drills.” However, like I stated, I believe these terms are interchangeable. At any rate, dynamic stretching has an important place in your mobility routine.

Dynamic stretching uses sports-specific movements to prepare the body for activity. Typically, they are a movement or a combination of movements that are actively shifted into and out of. This type of stretching does not consist of holding positions for long periods of time, like static stretching or PNF.

Dynamic stretching is the only form of stretching that should occur before a workout. There are good reasons for this. Firstly, we want to restore our natural tissue length before training. Muscles have what we call elasticity, or the ability for the tissue to return to original resting length after a passive stretch. Dynamic stretching is geared towards this property. The passive stretching that occurs in dynamic stretch returns our tissues to original resting length; however, we do not want to improve tissue length. That’s where static stretching and PNF come in.

Before a workout, we want to consider the movements that occur in our training and mimic those movements in our dynamic stretching. For example, if I’m doing Barbell Front Rack Squats that day, then something like this World’s Greatest Mobility may be a good mobilization.

In this drill, my first movement is a shin pull where I’m pulling my leg into flexion and external rotation, just like the bottom of a squat. Then I step back into an elbow-instep reverse lunge where I’m trying to get into deep hip flexion. Again, I’m trying to replicate the bottom of my squat in this scenario.

How does dynamic stretching relate to the proprioceptors we mentioned earlier? Dynamic stretching is supposed to happen before a workout. The reason this is is because dynamic stretching activated muscle spindles due to the brief stretch. The goal here is to move a muscle briefly to end range and then move out of this stretch. This will help utilize the stretch reflex mentioned earlier, activate our muscle spindles which are important proprioceptors for strength and speed training, activate our muscles themselves, and utilize our muscle tissue elasticity to bring them back to resting length. All important stuff!

Fortunately, dynamic stretching will not activate those golgi-tendon organs if done properly. This is important for exercise performance. I will discuss why down below.

Proprioceptive Neuromuscular Facilitation

“When we compare PNF and Static Stretching, the clear winner in the debate of which provides the best stretch effect for improving tissue length is PNF.”

PNF was initially developed as a rehabilitation system to help individuals with hypertonicity (hyperactive and shortened muscles). The idea is that these types of stretches would help relax the muscular tissue using the known neurology of how muscles work. And, it worked. The efficacy of PNF then transferred to athletes to improve flexibility. As far as improving flexibility is concerned, PNF is probably the king out of the three modalities that we see in the gym and I’ll tell you why that is.

First, let me describe PNF stretching. PNF stretching usually occurs between an athlete and their partner/trainer. It involves active and passive movements to activate certain physiological properties of the muscle that is being stretched. The partner provides the stretch or resistance, while the athlete works against it or relaxes into it. I placed videos down below to show you how this system works.

We discussed golgi-tendon organs and how they work. These GTOs, when activated, relax the muscle further to improve passive ranges of motion. When we are about to exercise, we want activated muscles. Active muscles will improve function and decrease the risk of injury. However, when we are done, we want to relax our muscles and take advantage of their plasticity, or their ability to increase length after a passive stretch. Activating GTOs will help do that.

The main development of PNF came from the principles of reciprocal and autogenic inhibition that were discussed earlier. These two physiological principles allow tissues to improve ranges of motion more effectively than just passively stretching. That is why there are three types of PNF stretching methods: hold-relax, contract-relax, and hold-relax with agonist contraction.

There are three phases for each of these different techniques. The first part of each of them is a 10 second passive stretch. The next two phases are named by the techniques. For example, the hold-relax method’s second phase is an isometric contraction against the partner’s resistance. Then, the athlete will relax again as the partner finds a new endrange for the tissue after the isometric contraction.

Hold-Relax

The first step, just like the others, begins with the 10 second passive stretch. Then, like in this video, the athlete pushes against their partner isometrically for 6 seconds. Afterward, the athlete relaxes and allows the partner to push them further into the passive stretch. Because of autogenic inhibition, the athlete should be able to achieve a newfound range of motion. This passive stretch is held for 30 seconds or longer.

The example in this video is of a PNF mobility on the hamstrings. However, PNF can be done on almost all major muscle groups.

Contract-Relax

The contract relax method again has that initial 10 second passive prestretch. Then, the athlete contracts through the full ROM of the muscle being stretched against the resistance of the partner. Here, you can see the athlete fully contract his hamstring against the resistance of the trainer. Afterwards, the “relax” phase is utilized and held for 30 seconds. Again, we are utilizing that autogenic inhibition concept and the athlete should be able to achieve a greater stretch after the activation.

Hold-relax with Agonist Contraction

This last method is supposed to combine the first method with a little added bonus to get the maximum benefit. Just like the hold-relax method, after the initial passive stretch, the athlete will isometrically push against the resistance for 6 seconds and then allow their trainer to push them into a stretch for 30 seconds. However, while doing so, the athlete will actively contract the agonist muscle to elicit the reciprocal inhibition response to further activate their GTOs. In our supine hamstring PNF example, as seen in the videos, that will mean contracting their hip flexors while the trainer pushes them into hip flexion to provide the maximum stretch effect to their hip extensors (mainly, in this case, the hamstrings).

Although the hip flexors are antagonists to the hamstrings, which is why they should be contracted to promote reciprocal inhibition, they are agonists in hip flexion, which is the direction of the stretch. That is why this method says “agonist” contraction and not “antagonist” contraction.

Now, with this last method, we are taking advantage of autogenic and reciprocal inhibition to enhance the stretch effect.

PNF vs. Static Stretching

When we compare PNF and Static Stretching, the clear winner in the debate of which provides the best stretch effect for improving tissue length is PNF. However, that does not come without it’s caveats.

PNF is restrictive because a lot of it requires a partner. This is ineffective in situations where the athlete is training on their own. There are methods out there to do self PNF. I plan on utilizing those methods and writing a blog in the near future reviewing their effect.

Static stretching is great when it comes to using simple, easy to understand movements, that will provide a lengthening effect. At the moment, I primarily use static stretching with my athletes because it is something I can teach them and they can do on their own, independent of me being there or my coaching.

Also, both PNF and static stretching should be done at the end of a training session because of the relaxation effect it has on muscles.

So, when it comes to stretching, do it dynamically before and statically after training. Also, if you have a buddy, use PNF for the maximum effect. If you’re still holding stretches for thirty seconds during your warmup after reading this blog post, I give up on you.

‍

References

Haff, G., & Triplett, N. T. (2016). Essentials of strength training and conditioning. Champaign, IL, IL: Human Kinetics.

‍