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MUSC Health Blog

Keyword: flexibility

By Ethan Konoza, ATC
Athletic Trainer
MUSC Health Sports Medicine

Flexibility in relation to the human body can be defined as the range of motion (ROM) of a joint that is largely affected by the muscles, tendons, and bones around the joint (Borges, Medeiros, Minotto, Lima, 2017). There are several methods to increase ones flexibility and ROM. Proprioceptive neuromuscular facilitation (PNF) in particular is a stretching technique that has been shown to effectively increase ROM and flexibility (Hindle, Whitcomb, Briggs, Hong, 2012). PNF stretching can be performed to increase passive range of motion (PROM) and active range of motion (AROM). Two of the most common methods discussed in the current literature of PNF stretching include a contract relax (CR) method and a contract relax antagonist contract (CRAC) method. The CR method is performed by lengthening the muscle targeted for stretch and holding it in lengthened position while maximal isometric contracting of the same target muscle is being performed for a set amount of time. This is then followed by relaxation of the target muscle while being passively stretched. (Hindle et al., 2012; Maharjan, Mallikarjunaiah, 2015; Muscolino, 2017). The CRAC method of PNF stretching is performed similarly to CR but with an antagonist contraction instead of passive stretching following relaxation of the targeted muscle. There are four theories as to why PNF stretching is effective in increasing ROM. These include autogenic inhibition, reciprocal inhibition, stress relaxation, and the gate control theory (Hindle et al., 2012; Maharjan, Mallikarjunaiah, 2015).

Muscle spindles and Golgi tendon organs (GTO) are two types of muscle proprioceptors that are protective in nature but also play an important role in how these proposed mechanisms work to increase ROM during PNF stretching. Muscle spindles are located within the belly of a muscle and senses stretch or lengthening of a muscle (Powers & Howley, 2018; Muscolino, 2017). When a muscle becomes stretched (lengthened) to a point the muscle spindle too is stretched. The stretching of the muscle spindle causes an impulse and an afferent neuron is sent to the central nervous system (CNS) through the spinal cord. The CNS receives and interprets this information. If a muscle is lengthened too far the CNS will send an efferent neuron to cause a reflex contraction called a myotatic reflex to contract (shortening of the muscle) to prevent any more lengthening to that muscle to prevent damage or tearing. (Powers & Howley, 2018; Muscolino, 2017). The GTO is another type of muscle proprioceptor that is located near the musculotendinous junction and is attached to muscle fibers. The GTO detects changes in tension within a muscle. When a muscle contracts (shortens) increased tension is placed upon the GTO (Hindle et al., 2012; Powers & Howley, 2018; Maharjan, Mallikarjunaiah, 2015; Muscolino, 2017). The shortening of the muscle causes the GTO to become stretched and in turn creates an impulse that sends an afferent neuron to the CNS by way of the spinal cord. The CNS then interprets this information sent by the GTO detecting a pulling force on a tendon. This pulling force can damage and injure the tendon. This ultimately causes another impulse to be sent to relax the muscle so that no more tension is place upon the tendon (Powers & Howley, 2018; Muscolino, 2017) This is termed the GTO reflex or inverse myotatic reflex as it has the opposite or inverse effect of the myotatic reflex created by the muscle spindle.

It is important to note that both muscle proprioceptors discussed are protective in their design. Due to this protective element, the GTO’s inhibitory type reflex in particular can be utilized in increasing the amount of stretch that can be placed upon a muscle. Isometric contraction of the target muscle causes tension to be placed upon the muscle and its tendon, which in turn activates the GTO reflex. The GTO reflex causes relaxation of the targeted muscle due to its protective nature. This relaxation of the muscle by way of the GTO reflex prevents excessive tension or stretching on the tendon to avoid tearing or damage. This relaxation of the muscle allows for further stretch to be placed upon the targeted muscle and in turn allows for increases in ROM and ultimately flexibility seen from PNF stretching.

While by design the GTO acts as a protective measure by sending an inhibitory reflex to the target muscle, we are essentially using this reflex as means of enhancing the effectiveness of the stretch. That is getting the muscle to relax so that we can further stretch the muscle. By adding tension to the GTO by asking our athletes to isometrically contract during PNF stretching we are triggering their bodies into sending this inverse myotatic reflex to inhibit any further contraction of that targeted muscle. This inhibitory reflex is what allows us to stretch the targeted muscle further. Stretching the soft tissue is just one area of the mobility and ROM puzzle. Optimizing mobility leads to proper execution of functional movements, which in turn reduces the likelihood of injury and ultimately improves performance.


Borges, M. O., Medeiros, D. M., Minotto, B. B., Lima, C. S. (2017). Comparison between static stretching and proprioceptive neuromuscular facilitation on hamstring flexibility: systematic review and meta-analysis. European Journal of Physiotherapy, 20. 12-19.

Hindle, K., Whitcomb, T., Briggs, W., & Hong, J. (2012). Proprioceptive Neuromuscular Facilitation (PNF): Its Mechanisms and Effects on Range of Motion and Muscular Function. Journal of Human Kinetics, 31: 105-113.

Maharjan, J., Mallikarjunaiah, H. S. (2015). Proprioceptive neuromuscular facilitation stretching versus static stretching on sprinting performance among collegiate sprinters. International Journal of Physiotherapy, 2, 619-626.

Muscolino, J. E. (2017). Kinesiology: The Skeletal System and Muscle Function. MO, St. Louis. Elsevier

Powers, S. K., & Howley, E. T. (2018). Exercise physiology: Theory and application to fitness and performance. New York, NY: McGraw-Hill Education.

Guest Post by:

Richard Mahieu
Athletic Trainer
MUSC Health Sports Medicine


Do you ever feel like you do not have enough time for exercise every day? You are not alone. There have been many times in my relatively short life that the world has knocked my activity schedule off  its rails. To combat this I have begun to add small changes to my daily work and personal life to increase my daily activity aside from a workout. I would like to share some of the activities that I have altered, added or plan to add in the hopes that they will help some of our readers to increase their daily activity level and improve their quality of life. Some of these may sound silly, but I do believe that every little bit helps. As always, start with small and safe changes first and speak to your physician if you have any reservations or issues.

Get dressed standing up. Putting socks and pants on standing up every day may improve your overall balance and strengthen the smaller stabilizer muscles in your hips, legs and feet. The same goes for your shoes. Tying your shoes while standing forces you to work on the flexibility of your lower back, hamstrings and calves. To ease into this habit, begin with your back and/or your posterior against a wall so that you have something to grab onto if you lose your balance.

Adjust how you walk. Walking faster can elevate your heart rate enough to give you a small amount of cardiovascular workout without getting you sweaty in the office or in the grocery store. If you are outside in the South Carolina summer, then you are likely sweaty already so no additional harm done! You can also stay on your toes to give your calves and foot and ankle stabilizers an additional workout.

Stand as often as you can. Instead of sitting at your computer, try standing at it. There are products on the market now that allow you to raise your computer to high enough level to stand at. This allows you to hit two birds with one stone by exercising your back and leg muscles while you are at work doing the daily grind. You can also do the same thing while eating. These are also great ways to avoid a sore rear from hard and uncomfortable chairs. If you have the luxury of being able to get up and walk around at work, take advantage of it as much as possible!

Take the stairs. Take the stairs instead of the elevator or escalator if you have that option. Walking up stairs often is another great way to get small amounts of cardiovascular activity into your daily life without taking up too much of your time. If you have to reach the 10th story, start off small by getting onto the elevator on the second or third floor. If you can already manage all of the floors you need to climb to get to your destination, then maybe you can begin to skip steps on your ascent.

A few other activities that you can sneak into everyday life are to park farther away from the store or work entrance or try to carry more bags of groceries into your house or to your car at once. Be careful not to overdo it though! Start small and good luck!


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