Research Review: The Science of a Stretch

Stretching_(479163922)

…Questions About Stretching…

What is a stretch?     What is stretched when we stretch?     Does stretching do what we think it does?

Does stretching improve flexibility?     Does stretching improve performance?

Does stretching prevent injury?     Is there a best way to stretch?     Does stretching actually work?

Why can stretching become uncomfortable after holding a position for a long period of time?

Let’s answer these questions based on findings from various researchers who spend their time and effort studying it. For many in the health field, this is old news. But for my patients, this is an article to remind you about concepts we discussed regarding stretching and the various topics related to it.

To make it a little easier to read, this article is broken down into 6 parts because many of us are busy and do not have time to read long articles in one sitting. Each section is broken into parts to allow for breaks to digest information and return at a later time.

Here are the 6 sections (with the shortest answer possible for those may have just a minute or two to spare). Read further for more detail.

1: What is a stretch and does it work? (A stretch incorporates the elongation of every structure in the body including nerve, muscle, skin and etc. Stretching or movement exercise may or may not help with flexibility, it depends on the type and the purpose of the stretch.)

2: Does stretching improve performance? (Static stretching has been found to decrease performance. Active and dynamic stretching may be more beneficial prior to activity.)

3: How does performance decrease following static stretching? (Static stretching may trigger protective mechanisms to inhibit motor control or body activation)

4: What is the relationship of stretching and the prevention of injures? (Stretching has not been consistently proven to prevent injury. There are studies that have found that stretching may actually increase injury.)

5: What are the mechanisms of increased flexibility? (There are many hypotheses involved with stretching such as viscoelasticity / creep, plastic deformation,  changes with sarcomere length or in series, neuromuscular relaxation, sensory theory, and adaptive potential. There is research to support and disprove various concepts.)

6: So now what? Let’s Apply the Research. (I prefer to use the term mobility or movement exercise rather than stretching because there are so many different ways to promote improved flexibility and function. Since there is no holy grail or best way for everyone to move, we should try to find the best exercises to gain mobility in our own unique way.)

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Part 1: What is a stretch and does it work?

Here is a simple yet complicated question. When a body part is stretched, what structures are we actually lengthening?

We assume that we are elongating muscle while performing a stretch, but we are also elongating skin, fascia, nerves, tendons, blood vessels, and every other type of connective tissue in area involved.  This is true for stretching as well as strengthening. There is no possible way to move, stretch, or strengthen only one structure or a singular part of the body.

This means that stretching has the potential to effect our body in many ways. For example, if tension during a stretch is more on a nerve than muscle, there may be more protective mechanisms rather than increased flexibility as a result. This will be explained in more detail.

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One of the most common reasons stretching is performed is to increase flexibility. Have researchers found that stretching improves flexibility for everyone? This might seem like a silly question,  but it is an important one because there are many things we have done in the health field that have been incorrect. Read here about the history of pain science to understand what I mean.

Back to the question at hand, (I have given three answers based on research)

1. Yes – stretching improves flexibility and here are some publications:

“Active and passive stretching both appeared to increase the flexibility of tight hip flexor muscles in patients with musculoskeletal impairments.” Published by Winters MV in 2004

“These data indicate that static stretching 1 repetition for 30 seconds 3 days per week increased hamstring length in young healthy subject” Published by Davis DS in 2005

“After 4 weeks of stretching, there was a statistically significant improvement in hamstring length (p < 0.05) using active stretches as compared with passive stretches. From weeks 4 through 8, hamstring length for the active stretching groups decreased. After 8 weeks of stretching, the passive stretch group had the greatest improvement in hamstring length.” Published by Fasem JM in 2009

“Stretching produced no significant change in maximal contraction but significantly decreased stiffness and hysteresis.The present results suggest that stretching decreased the viscosity of tendon structures but increased the elasticity.” Published by Kubo K in 1985

There are hundreds of publications indicating that stretching will increase flexibility.

2. No – stretching does not improve flexibility with more research reports.

“These data also suggest that active self-stretching and PNF-R (proprioceptive neuromuscular facilitation) stretching 1 repetition for 30 seconds 3 days per week is not sufficient to significantly increase hamstring length” Published by Davis DS in 2005

“A single session of 3 straight-leg raise hamstring stretches did not change pelvis, hip, or knee running kinematics” Published by Davis Hammonds AL in 2012

“Six weeks of sustained 30-min daily stretch does not increase the extensibility of the hamstring muscle of healthy individuals.” Published by Ben M in 2010

There are also many more articles that have found that stretching does not improve flexibility. Interesting isn’t it? It will all make sense in the end. Please keep reading.

3. THE CONCLUSION FOR THE MOMENT: There are numerous research studies that show stretching improves flexibility and does not improve flexibility. So the final answer is based on a Cochrane Review that looked at over 1000 research studies. Cochrane reviews are un-biased reviews that base their conclusions on the best available research. Its conclusions should trump individual research reports. (We should still be critical of articles that are considered to be unbiased because bias and error always exists.)

The authors of the Cochrane review analyzed research studies regarding stretching. If the methods of the study were good, they took it into consideration. If the methods were poor, they were not included in this review.

(To get more information about bias in research, here is an article that is easy to understand through the Liberty Voice, titled “Research Bias: What to Look for When Reading Health Articles” written by Nick Ng. Here is another article on research bias written in a medical journal titled “Identifying and Avoiding Bias in Research” written by Panucci and Wilkins.

So finally…here is what the Cochrane Review found:

“Stretching does not have clinically important effects on joint mobility in people with, or at risk of, contractures (stiffness in the body) if performed for less than seven months. The effects of stretch performed for periods longer than seven months have not been investigated.” Published by Katalinic OM in 2010.

WHAT DOES THIS MEAN???

This does not mean that you should not stretch!

Stretching can be beneficial and it can also feel good.

If it works for you and you enjoy stretching, then it is probably a good idea to keep doing it. But, it is important to understand that the mechanisms of how stretching works is not fully understood or agreed upon. So, let’s keep an open mind about this as you continue reading.

For those who have spent time stretching to help with sports or other activities and did not see results and for those who are experiencing pain and have not benefited from a stretching program, you will learn other options. That is what this website is about.

But please keep in mind that regardless of what research states, we are all individuals and we truly cannot be 100 percent accurate when we try to predict an outcome or what is best for each person. You will have to try and see how you respond as an individual.

I hope that you will learn various ways to improve your well being through novel types of stretching and mobility exercises. You may also learn how to improve mobility more efficiently and safely.

So let’s review: It appears that stretching improves flexibility in some and not in others. Clinical effects of stretching (using stretching as a treatment) to prevent joint or muscular stiffness in the short term appears to be minimal. Long term clinical effects are unclear.

Next let’s try to understand how stretching can influence performance.  You may find the best type of stretch for yourself based upon the reason why you want to stretch or improve mobility.

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Part 2: Does stretching improve performance?

It is often assumed that stretching is a good way to warm up to increase performance or activity. Researchers have found the opposite to be true for static stretching.  Dynamic stretching appears to help with performance. Here are some definitions for different types of stretching that have been studied.

Static Stretching consists of holding a stretched position for a prolonged period of time, often 20-60 seconds. Here is a video on a static hamstring stretch on YouTube: https://www.youtube.com/watch?v=z73l6oZUniQ ).

Dynamic Stretching consists of repetitive active movement into end range or close to end range without holding. Here is a YouTube video on it: https://www.youtube.com/watch?v=z7qKc5_4Tes. Notice that the instructor in the video mentioned the possibility of nerve tension while stretching the hamstrings. This concept will be discussed later. Here is another video on Dynamic Warm-ups: http://greatist.com/fitness/full-body-dynamic-warm-up

PNF-Contract Relax Stretching consists of activation of muscles for a brief period and then stretching for a brief period. It is thought that greater relaxation will occur after brief muscle contractions to enhance the body’s ability to become more flexible.  Here is a video example: https://www.youtube.com/watch?v=bg9pSuAXIYY

Ballistic Stretching involves repetitive bouncing using momentum during a stretch. It is a higher level of dynamic stretching and is not recommended by the American Academy of Orthopaedic Surgeons. Read their recommendation here in their website. Here is a video example of it: https://www.youtube.com/watch?v=eXjK49c69Qg.  There may be situations in sports and in our daily lives when ballistic stretching may be appropriate but the risk of injury may outweigh the benefits for the general population. So I will not go into detail regarding this type of stretch.

Here is what researchers have to say about stretching and performance:

“Substantial evidence is now available to state that static stretching can impair strength and power performance…” Published by Young WB & Behm DG in 2002

“After static stretching, there were significant overall 9.5% and 5.4% decrements in the torque or force of the quadriceps for maximal voluntary force. Force remained significantly decreased for 120 min (10.4%)” Published by Power K in 2004 (this study indicates that negative effects of static stretching may last for 2 hours!)

“Vertical jump height decreased after static and PNF stretching (4.0% and 5.1%, p < 0.05) and there was a smaller decrease after ballistic stretching (2.7%, p > 0.05). However, jumping performance had fully recovered 15 minutes after all stretching conditions. In conclusion, vertical jump performance is diminished for 15 minutes if performed after static or PNF stretching, whereas ballistic stretching has little effect on jumping performance. Consequently, PNF or static stretching should not be performed immediately prior to an explosive athletic movement.” Published by Bradley PS in 2007 (If you watch the Olympics, you will notice that sprinters are moving about in various positions before they race and they are not holding a stretch. Also baseball players in the on-deck circle are actively moving rather than holding a stretch.)

“Therefore, in healthy patients, a (Static)muscle stretch, such as used in this study, is probably of little therapeutic value.”  Published by Bohannon RW in 1985

“It was concluded that static stretching as part of a warm-up may decrease short sprint performance, whereas active dynamic stretching seems to increase 20-m sprint performance.” Published by Fletcher IM in 2004

“There was no short-term effect of stretching in the warm-up on the tennis serve performance of adult players, so adding stretching to the traditional 5-minute warm-up in tennis does not affect serve performance.” Published by Knudson DV in 2004

“…the results of this study indicate a relative performance enhancement with the dynamic warm up group (not the static stretching group), the utility of warm up routines that use static stretching as a stand-alone activity should be reassessed.” Published by McMillian DJ in 2006

“The results indicated that submaximum running and practice jumps had a positive effect whereas static stretching had a negative influence on explosive force and jumping performance. It was suggested that an alternative for static stretching should be considered in warm-ups prior to power activities” Published by Young WB  in 2003

“The results of this study suggest that performing a static stretch protocol following a dynamic warm up will inhibit sprint performance in collegiate athletes.” Published by Winchester JB in 2008

“The findings suggest that the elevation in perceived exertion following knee flexor muscle stretching may be greater in women than men, despite no significant alterations in mechanical measures of muscle fatigue.” Published by Heuser M in 2010

“The results of this inquiry strongly suggest that a total-body passive static stretching routine should be avoided before practice or competition in favor of a gradual active – dynamic movements” Published by Gergley JC in 2010

“An acute bout of stretching does not improve force or jump height, and the results for running speed are contradictory. Regular stretching improves force, jump height, and speed, although there is no evidence that it improves running economy.” Published by Shrier I. in 2004

The articles quoted above stated that static stretching limits performance and dynamic movements are better. Unfortunately, they didn’t go into detail as to why static stretching may be related to decreased performance, which leads to the next section.

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Part 3: How does performance decrease following static stretching?

Here are research reports that discussed possible reasons why performance decreases after static stretching:

“Stretching prior to stretch-shortening cycle activities like the vertical jump results in small decreases in performance in some subjects, but the non-significant biomechanical changes suggest that neuromuscular inhibition may be the mechanism rather than changes in muscle stiffness” Published by Knudson D in 2001 (In other words, decreased performance may be related to changes within the brain and the activation of protective mechanisms through the nervous system.)

“…multiple mechanisms may be involved in stretch-induced strength inhibition.” Published by Winchester JB in 2009

“A single 30-second stretch, if held at the limit of toleration, is sufficient to cause an inhibition in a person’s 1-rep-max. Additional bouts of stretching will further decrease the 1-rep max, suggesting that multiple mechanisms may be involved in stretch-induced strength inhibition.” Published by Winchester JB in 2009

These studies state that inhibition or protective mechanisms as reasons for decreased performance. What is that?

The term inhibit is defined by Webster as follows: (click here for the Webster webpage)

1. to keep (someone) from doing what he or she wants to do

2. to prevent or slow down the activity or occurrence of (something)

Muscles can become inhibited due to surgery, pain, overwork, fatigue, and stress just to name a few.  Stretching may be another factor involved with muscle inhibition due to protective responses.

So, here is a hypothesis that tries to explain how decreased performance may be due to protective mechanisms:

We often think that if something is tight, we should stretch it based on mechanical properties such has metal, wood, or plastic and force the body to bend. We also hear people referring humans as machines.

But we are much more complicated than that. What we often do not consider when we stretch our body is that nerves are also elongated. So, if we hold a stretch long enough, slow conducting nerves that communicate with the spinal cord regarding injury or potential injury may be more active to possibly promote discomfort and pain. At that point, the nervous system may be telling you to stop.

The activation of these slow conducting nerves (read more about slow conducting nerves here)  may stimulate the brain to trigger protective mechanisms to inhibit the body from over stretching and tearing.

Here are a couple of examples to understand the function of fast and slow nerve fibers and how it relates to protective mechanisms.

Have you ever touched something hot (like a hot stove) and moved your hand right away, then a second later, you experienced pain? Nerves that send messages to the brain regarding heat and light touch travel to the brain through fast conducting nerves to help the body react quickly to prevent injury. The process that involves sending messages of tissue injury to the brain consists of nerve fibers that are much slower. Therefore the painful aspect of injury can be delayed, or even absent. (You can read more about pain and injury here. Tony Ingram, a physical therapist, researcher and dancer has written a great article on his website.)

When we experience pain and discomfort the brain sends out messages to the muscles to inhibit activity. Even the potential of injury can trigger protective mechanisms.

Let’s explain it with a little more detail.

So as you hold a stretch for a prolonged period of time, those slow nerve fibers can be activated, slowly sending that message to the spinal cord, which  stops at an imaginary security guard in charge of messages that travel through an imaginary gate to the brain. The automatic processes of the nervous system controls the security guard to open the gate so that the message of injury or potential injury is sent to the brain to possibly become a painful experience. That is why holding a stretch for a brief period is not usually uncomfortable, but holding it for a prolonged period of time may send messages strong enough to overpower the guard to open the gate. Then the stretch eventually becomes uncomfortable due to injury or to protect from injury.  Often times, the sheer potential of injury (due to stretching as an example) can trigger discomfort because the possibility of injury triggers the same parts of the nervous system as if there is actual injury.

To make it even more complicated, these slow conducting nerves also have nerve endings that are triggered by positive stimulation. Let’s save this part for another day.

Do you need another example of slow and fast nerves: Skip the next three paragraphs if you do not.

Imagine yourself carrying a big box from the garage to the kitchen. As you walk through the garage, you scrape your arm along something…. ouch, it was painful for that brief moment. But you really didn’t think much of it so you put the box down and go about your business. Then someone tells you that your arm is bleeding. You look at it and them boom, there is pain.

What happened?

When you scraped your arm, the skin was cut. Fast nerve fibers sends messages regarding touch, pressure and etc to the brain. Then the brain promotes a reaction. Typically when we scratch our arm,  the brain has a memory that it is nothing serious so we go about our business. Since there was a cut, those slow nerve fibers sends the injury message to the spinal cord and it stops there at the imaginary gate. The gate can also open and close based upon other various components including expectation of pain, past experiences, stress, injury messages and etc.

In this case, past experiences tell us that minor scratches are no big deal. The gate remains closed and the injury message stays at the level of the spinal cord. When someone tells you that you are bleeding, we see the cut and then the brain becomes aware of the injury which can open the gate possibly resulting in increased pain.

Lorimer Moseley, a pain scientists talks about “Why things hurt” during a TED talk and goes over this in great detail.

That was a little sidetrack to review a little bit about the pain process.

Essentially, when we perform a static stretch, protective mechanisms can be triggered leading to deceased muscle activity due to inhibition.

Here are a couple examples of how stretching is performed in sports:

The next time you go to a baseball game, observe how the baseball players prepare their bodies to play the game

You will often see many athletes doing static stretching 2 hours prior to the game to increase flexibility. As mentioned above, protective mechanisms can last for 15 minutes to  2 hours. When a baseball player is in the on deck circle before going to bat, they are moving their bodies in an active way which may not trigger protective mechanisms.

Also, if you watch track and field events, you will notice that sprinters do not perform prolonged stretches while they wait to go into the blocks for the 100 yard dash. They typically perform dynamic movements that do not have adverse effects that static stretching has for prior to activity.

Phew…Now let’s take another break to review what has been covered

1. When we stretch many parts of the body are stretched

2. Stretching may increase flexibility in some and not in others. There many be minimal clinical effect of short term stretching. Long term effects are unclear.

3. Static stretching can decrease performance in activities that require quickness possibly due to inhibition and protective mechanisms

4. Active or Dynamic stretching does not decrease performance and can be beneficial prior to activity.

5. You can do  active / dynamic or static stretches for general flexibility. Find out what works for you.

Now, lets take a look at injury prevention.

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Part 4: What are researchers publishing regarding the relationship of stretching and the prevention of injures? 

“Despite a few outlying studies, consistently favorable estimates were obtained for all injury prevention measures except for stretching” Published by Lauersen JB in 2014 (this was published based on a systematic review of research of over 3000 research articles! They only considered high quality research for this review.)

“In stop-and-go sports like soccer, Australian Rules football, rugby or football, hamstring muscle injuries are the most common injuries. Studies with low qualitative and quantitative characteristics have been published over the last decades. It is therefore not possible to find documentation concerning the effects of static stretching on prevention of hamstring injuries.” Published by Rogan S in 2013. This is a systematic review of all research they found regarding football (American football, rugby,  and international football / soccer)

“A typical muscle stretching protocol performed during pre-exercise warm-ups does not produce clinically meaningful reductions in risk of exercise-related injury in army recruits. Fitness may be an important, modifiable risk factor.” Published by Pope RP in 2003. Based on the findings of this study involving 1538 army recruits, overall fitness may prevent injury rather than flexibility.

“The cohort (4610 participates) was followed for a mean of 4.9 years for self-reported low back pain…Those who reported stretching, as a specific flexibility activity were at a higher risk of developing low back pain compared with those who performed no flexibility exercises” Published by Sandler RD in 2014

“No evidence was found for a positive effect of stretching exercises (for tendon injuries).” Published by Peters JA in 2015

WOW! Stretching may increase flexibility but it has not been proven to prevent injury! Don’t get me wrong here. There are many studies that show that limited flexibility may be associated with injury. But just because stretching may increase flexibility, it doesn’t mean that it will translate into decreased risk of injury because flexibility is a complicated topic. The next section explains the various mechanisms of flexibility and will help you understand why stretching may improve flexibility, but may not be related to injury prevention.

The next section is also for those interested in the science and explanatory models of stretching.

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Part 5: What are the mechanisms of increased flexibility?

In 2010 Weppler et. al. published a research paper that reviewed stretching. It is one of my favorite articles on this topic. They discussed various components of stretching and provided research to support their claims. This next section is mostly based from their article.

Here are the various hypothesis involved with stretching:

1. Viscoelasticity or a biomechanical term called creep.

MerrianWebster defines creep as “to change shape permanently from prolonged stress or exposure to high temperatures”.

Elasticity of our body can change. If you were to pull the skin of a younger person, it returns back to its original state quickly. But for an older person, the  skin returns back to its original state much slower. The skin can become permanently stretched due to various reasons and can have varying degrees of elasticity. It is thought that muscles can change its elasticity when stretched.

What about the “viscus” portion of viscoelasticity?

Our body consists of approximately 60% water, which means that stretching muscle also involves viscosity, the thickness of fluids within and surrounding muscle. If fluid is too thick there is increased friction and decreased movement. If viscosity is too low, there will also be increased friction of muscle, tendon and etc during movement. The optimal degree of viscosity will enhance movement.

Many studies have concluded that stretching can effect creep / viscoelasticity to promote increased flexibility. Published by Kubo 1985, Webright WG in 1997, Zito M in 1997, Taylor DC in 1999, Winters MV 2004.

Many studies have also shown that the viscoelastic properties of stretching are nonexistent or short term from 20 seconds up to 1 hour. Published by Magnusson SP in 1996, Magnusson SP in 2000, McNair PJ in 2001, Duong B in 2001, Ryan ED in 2008, Tian M 2011)

Here we go again,  studies show change and some do not. This is the common theme of every hypothesis or theory involving stretching. So there may not be a universally valid theory or reason why movement or stretching enhances flexibility.

Why is that?

Structures have elastic and plastic properties. When an object is initially stretched, it goes through an elastic phase of stretch. When the tension is removed, the elastic properties allow the object to return to its original state. When an object is stretched past its elastic properties, then plastic deformation occurs.

Wikipedia has an article on the stress strain curve that explains elastic and plastic deformation here.

If you were to pull a rubber band or spring with a certain degree of tension, it will increase its length. When the tension is removed, it returns back to its original state. Our skin, tendons, ligaments, bones, and etc also have the same type of elastic property. When we stretch, there is a short term increase in flexibility but after a while, the body part returns back to its original state. This can be why some research studies find no changes following changes,  some state that there is change,  and some report  that increased flexibility can be short term.

2. Plastic or permanent deformation of muscle tissue.

Weppler describes plastic / permanent deformation as follows: “The classical model of plastic deformation would require a stretch intensity sufficient to pull connective tissue within the muscle past the elastic limit and into the plastic region of the torque/angle curve so that once the stretching force is removed, the muscle would not return to its original length but would remain permanently in a lengthened state.”

The same thing occurs with elastic bands on clothing, which can stretch and return to its functional tightness to keep our pants up. But once it is over-stretched past its functioning tension, the elasticity is permanently changed.

Researchers have suggested that plastic deformation can be a reason for increased flexibility. (Published by Sapega AA in 1981, Hortobágyi T in 1985, Wessling KC in 1987, Zito M in 1997, Chan SP in 2001, Feland JB in 2001, Draper DO in 2004)

Researchers have also stated that plastic deformation is not the reason why muscles increase flexibility. (Published by Wepler CH 2010, Cipriani DJ in 2012)

Let’s say that plastic deformation did occur to improve flexibility, there might be a problem with overly stretching muscle because it may trigger more protective mechanisms, decrease the ability to produce force, and possibly lead to injury. (Published by Avela J in 1985, Fowles JR in 2000)

3. Increased sarcomeres in series or increased sarcomere length.

A sarcomere consists of contractile tissue found in muscle filaments which form myofibrils that make muscle fibers. Sarcomeres run the length of muscle tissue and are arranged in series. You can learn what a sarcomere is by checking out this site.

It has been suggested that stretching programs of 3 to 8 weeks can increase the length of sarcomeres and that it can be associated with increased flexibility in animal studies. Published by Williams PE in 1978, Wessling KC in 1987, Webright WG in 1997, Gajdosik RL in 2001, Chan SP in 2001, Gajdosik RL in 2005

This may be the most valid mechanical theory involved with stretching, but this investigation has not been performed on humans.

Muscle fibers can change from fast twitch to slow twitch based of activity so it may be possible for stretching to change muscle physiology. Weppler states that technology may eventually allow us to assess this without injuring muscle tissue of humans tested.

4. Neuromuscular relaxation.

It is proposed that stretching may decrease involuntary muscle contraction associated with stretch reflexes to improve flexibility.  A stretch reflex is the natural muscle contraction that occurs during a stretch. It is often performed during during physician, physical therapy, or chiropractic evaluations. A reflex hammer can test the stretch reflex of various tendons in the body.

There are studies that suggest that changes in stretch reflexes promote increased flexibility..  (Published by Tanigawa MC in  1972, Hortobágyi T in 1985, Smith CA in 1994, Spernoga SG in 2001, Chan 2001, de Weijer VC in 2003)

But many studies refute this claim. (Moore Ma in 1980, Liebesman J in 1994, Magnusson SP in 1998, Sharman MJ in 2006)

5. Sensory theory

Numerous studies have found positive change to no change in mechanical properties related to stretching and flexibility. These mechanical components of stretching are hypothesized to occur, they just haven’t been consistently proven to be a concrete theory explaining why flexibility can increase.

This means we should be careful when explaining how stretching can improve flexibility because we really don’t know why. But let’s not throw away these ideas since research and learning will always be on-going. Just know that they are there. Also innovative or different concepts will arise that may help improve our understanding of stretching and flexibility and here is an example a concept from 2010:

Weppler and colleagues reviewed many research articles covering stretching and concluded that the most consistent set of changes associated with flexibility in many studies involve the following:

improved range of motion without changes in mechanical properties

increased  torque or pressure of the stretch tolerated during a stretching program

changes in sensation involving pain onset, maximum stretch, or maximum pain tolerance with improved range of motion

Here is a quote from their study: “A growing body of research refutes mechanical theories (traditional theories involved with stretching muscles), suggesting instead that in subjects who are asymptomatic, increases in muscle extensibility observed immediately after a single stretching session and after short term (3- to 8-week) stretching regimens are predominantly due to modification in subjects’ sensation.” Published by Weppler CH in 2010.

They have found that the “modification of sensation” was the most consistent factor related to increased flexibility.

What does this mean? … How can we use this article to our benefit?

Weppler’s comment that increased flexibility is “predominantly due to modification in subjects’ sensation” may mean that we should focus on how the body feels while we stretch. Focus on the sensation of the stretch and allow the brain and the nervous system to process the stretch or movement exercise in a nonthreatening way. This might be an important factor with improving flexibility to decrease inhibition and protective mechanisms.

Regardless of whether we agree or disagree with their findings, we should take advantage of sensation as a component of our flexibility exercises. Also, I highly recommend clinicians to read Weppler’s article especially since it is free / open access.

6. Adaptive Potential

Adaptive Potential involves the body’s ability to interact with its environment in an efficient manner. It is defined as “the ability of the system to tolerate a repetitive movement, a forceful blow or a prolonged position” (Published by Dorko BL 1988)

I really like this term because it makes sense to me.

Dorko explains the difference between flexibility vs. adaptive potential and I have added my personal notes below:

Flexibility Adaptive Potential What does this mean? (personal notes)
Demonstrated by measurable joint range. Demonstrated by a painless response to repetitive movement, a forceful blow or a prolonged position.  If flexibility is gained, it may not be of use unless we are able to tolerate repetition, pressure and be able to maintain the gained range of movement.
Implies easy, painless active or passive excursion of tissue in many planes. Implies the ability to account for, tolerate and disperse long or short-term force. It is great to be able to move in many ways in a pain free manner, but we should also be able to tolerate force or tension for short and long durations.
Primarily dependent on connective tissue length and secondarily on CNS activity. Primarily dependent on CNS “plasticity” and secondarily on connective tissue length.  Muscle flexibility is more related to the mechanical properties that may occur such as changes in viscoelasticity, plasticity, changes in the cellular level (sarcomeres- actin, myosin), and neuroreflexes. Movement limited by adaptive potential is more related to various mechanisms involved in the nervous system such as sensation, fear, avoidance of movement, increased protective responses, impaired neuromuscular control and inhibition of movement due to pain, injury, or potential injury.
Can be seen and measured with relative ease Difficult to measure; typically inferred by history. Flexibility is easily measure by testing the degree of movement. There is limited ability to test the aforementioned components of adaptive potential
Tends to change slowly in either direction May rapidly alter in response to a series of processes Significant change in muscle flexibility takes time. There is potential for rapid changes in mobility if limited movement is related to decreased adaptive potential. (Changes in sensation may change quickly) There are also components of adaptive potential that will take time to change. (For example, fear of movement after injury may improve quickly or linger for a prolonged period of time. )

What this might mean is that flexibility gained from stretching is not functional unless our body can control it and adapt to the new range of motion. Otherwise there may be an increased risk of  injury because there is more movement that the body is not able to safely control.

The concept of adaptive potential is not new, but it is rarely mentioned. More research on this topic is needed.

Part 6: So now what? Let’s Apply the Research

How do we utilize concepts such as sensation and adaptive potential to improve flexibility, decrease pain, and possibly prevent injury? (Please keep in mind that there are situations when an injury simple cannot be prevented.)

1. Stretch as you normally have done even if it is contract-relax, static or dynamic especially if it feels good, because you may be modifying your sensation of the stretch in a positive way.   Try to not be too aggressive to minimize the potential of triggering protective mechanisms.

2. Pay attention to your body to promote improved sensation and adaptive potential via motor control exercises. (this can include body awareness, movement awareness, mindfulness with movement, and eccentric control just to name a few)

Be mindful of the exercise you are performing. Pay attention to your body while you are moving. Feel your body move into good quality movement. Feel where your body is more limber and more limited while doing active range of motion exercises or active stretching.

Perhaps, it might be wise to put away the headphones and music once in a while so that you (specifically, your central nervous system) can listen and feel your body while exercising rather than the beat of your favorite song.

One type of exercise that focuses on body awareness involves movement based on Moshe Feldenkrais. Click here to learn more about him.

Here are some articles and videos about Feldenkrais to get a better understanding:

“Muscle length can be increased through a process of active movement (awareness through movement) that does not involve stretching.” Published by Stephens J in 2006

“Feldenkrais (awareness with movement) method is an effective intervention for chronic neck/scapular pain in patients with visual impairment.” Published by Lundqvist LO in 2014

“This study has demonstrated that the three outcome measurement tools selected in this study all showed statistically significant improvements in daily function, pain and health-related quality of life after a series of Feldenkrais sessions. The length of time clients had been experiencing their symptoms prior to commencing Feldenkrais sessions (a median time of 12 months) suggests that the changes were not simply due to spontaneous recovery.” Published by Connors KA in 2010

Feel free to click on the Youtube videos below to see his work in action. You will be sent to Youtube.com.

https://www.youtube.com/watch?v=TYFyKm-bbOs

https://www.youtube.com/watch?v=y6NnVWeJ-nY

https://www.youtube.com/watch?v=0cfYsRm4xTw

http://www.feldenkraisseattle.net/articles/ (currently under construction)

Movements based on eccentric control:

Eccentric movement is a form of motor control. Slowly controlling your body during resistive movements, active movement, and dynamic stretching may promote more mindfulness allowing you to pay attention to the sensation of movement. Also focusing on eccentric exercise many help you control your body in various positions allowing the body to adapt to various types of stress on the body

For example, we often see people lift a very heavy weight and then drop it to the floor at the gym. They are not using eccentric control. When we slowly try to lower something to the floor, our muscles and brain must work harder to control the body. This may promote improved outcomes.

Here are some quotes on eccentric control:

“The results support the hypothesis that eccentric training is an effective method of increasing lower limb flexibility” Published by O’Sullivan K in 2012

“An eccentric hamstring exercise program was associated with lower rates of new and recurrent hamstring injuries in Danish male soccer players.” Published by Nichols AW in 2013

“An eccentric strengthening exercise program for the hamstring muscles that can be performed during training can help prevent hamstring injuries in soccer players.” Published by Schache A. in 2012

Here are videos that talk about eccentric control:

https://www.youtube.com/watch?v=A9dF7YLVccY

https://www.youtube.com/results?search_query=eccentric+exercise&page=3

https://www.youtube.com/watch?v=35X454_43KA

Here are other studies that report that neuro-muscular motor control or body awareness is important for movement:

“Understanding the neuromuscular influences on muscle flexibility will assist in the development of new rehabilitative and injury preventative techniques. The present pilot study implicates neural contributions to muscle flexibility.” Published by Krabak BJ in 2001

“These results indicate that changes in passive range of motion or core endurance do not automatically transfer to changes in functional movement patterns. This implies that training and rehabilitation programs may benefit from an additional focus on ‘grooving’ new motor patterns if new found movement range is to be used.” Published by Moreside JM in 2013. This study indicates that even if flexibility was gained, we need to learn motor control to improve function.”

“Additional biomechanical and neuromuscular differences were also identified as potential risk factors (for injury).” Published by Landry SC in 2014

3. Use various “neuromobilization” techniques. As with everything in this website, this method of gaining flexibility especially requires monitoring by a health care professional because it is very easy to overdo it and promote nerve irritation. For my patients, please give me a phone call if you need to review this.

Neuromobilization focuses on the anatomy of our nerves. Every movement of our body elongates nerves in various ways. For example bringing the arm up and out to the side will elongate the median nerve. Then turning the palm upward elongates it even more. Extending the fingers back will put even more tension on it.  It sounds simple, but there are multiple variations in the anatomy of how our nerves travel within our body so one movement will be best for someone but not ideal for someone else.

In 2008, a systematic review of neurodynamic / neuromobilization was published and they did not find that it was significant. Since then research on neuromobilization has increased and here are some findings:

“…passive extensibility of neural tissues can limit hamstring flexibility” Published by McHugh MP in 2012

“Findings suggest that a neurodynamic sliding technique can increase hamstring flexibility in healthy, male soccer players” Published by Castellote-Caballero Y in 2013

“…neurodynamic sliding technique will increase hamstring flexibility to a greater degree than static hamstring stretching in healthy subjects..” Published by Castellote-Caballero Y in 2014

“The findings demonstrate that different types of nerve gliding exercises have largely different mechanical effects on the peripheral nervous system. The findings of this study and a discussion of possible beneficial effects of nerve gliding exercises on neuropathological processes may assist the clinician in selecting more appropriate nerve gliding exercises in the conservative and post-operative management of common neuropathies.” Published by Coppieters MW in 2008

Here are a couple of videos on the median nerve. As a reminder, please consult with a health care profession especially when beginning these exercises. Nerves are very sensitive and you do not want to irritate them.

https://www.youtube.com/watch?v=ANY7yPRn-qk

https://www.youtube.com/watch?v=b4HsNPc-xdg

For health care professionals, there is a medical journal article explaining neuromobilization here.

4. Use a method called graded motor imagery

You can read about it here and at the official graded motor imagery website.

Most of the studies on graded motor imagery involve movement regarding chronic pain and the ability to function. I found one study specifically on flexibility:

“Psychological and physiological effects of motor imagery could explain the increase in range of motion, suggesting that imagery enhances joint flexibility during both active and passive stretching” Published by Guillot A in 2010.

In short, what this means is that visualizing the body move can promote flexibility. Visualizing an activity can stimulate parts of the brain that are active as if you are actually doing it and this may enhance neuromuscular control and promote decreased protective mechanisms. Check out the graded motor imagery website to learn more about this concept. I highly recommend it.

5. Promote various and novel movement patterns to stimulate the brain in a positive way.  This means that moving in a variety of ways will stimulate the brain to promote more adaptability to various movements. Do not do the same thing over and over. This may promote brain boredom. For example, you can focus on neuromobilization for a couple of weeks, then focus on movement awareness for a couple of weeks and then active dynamic movements for a couple of weeks. You can add and change things daily, but give your brain and body a chance to feel improvement.

Here are articles that discuss variability or novel movements:

“Only those subjects for whom pain induced a reduction in variability of the postural strategy failed to return to a normal strategy when pain stopped.” Published by Moseley GL in 2006. This study reported that a decrease in movement variability is a result of pain.

“From our perspective, the goal of neurologic physical therapy should be to foster the development of optimal amount of movement variability by incorporating a rich repertoire of movement strategies. The development of such a repertoire can be enhanced by incorporating a multitude of experiences within the therapeutic milieu. Promoting complex variation in human movement allows either motor development or the recovery of function after injury not to be hard coded, but determined instead by the active engagement of the individual within their environment.” Published by Stergiou N in 2006

“…vibration training, alone or combined with stretching, is a viable alternative to a standard stretching routine when attempting to increase shoulder flexibility. Adding vibration training to a flexibility regimen may improve the likelihood of regularly performing flexibility sessions because of increased variety.” Published by Ferguson SL in 2013

Here are some videos on novel movements and movement variability by a Cory Blickenstaff, physical therapy at Forward Motion PT:

https://www.youtube.com/watch?v=IXj64-Sv16E

https://www.youtube.com/watch?v=hm0MY9jt9rk

6. Go out and try something new!

Try Yoga, Pilates, gyrotonics, line dancing, and etc. Each method of movement has similar principles. Overall, there might not be a right or wrong way to move or exercise, but there might be an ideal one for you.

The Take Home Message:

  1. Research studies have found that there are many concepts involved with stretching that are not consistently supported.
  2. Various types of movement exercises can promote improved mobility.
  3. It is important to understand the purpose of stretching and to utilize the best type of movement exercise based upon your reasoning. For example, it may be better to perform active movements for sprinters and basketball players instead of static stretching up to 2 hours before activity.
  4. It is important to pay attention when we perform mobility exercises through body awareness or mindfulness instead of mindless stretching and movements.
  5. Improving motor control can be achieved through actual brain exercises (graded motor imagery)
  6. Even if flexibility is gained it does not mean that there will be improved gains or prevention of injury. The body must have adaptive potential to utilize the newly gain flexibility.
  7. There might not be a best way to improve flexibility for everyone. But each individual might find what is best for them. Try various types of movement methods such as Pilates, Yoga, Feldenkrias, Animal Flow, and etc. in order to find a method that you respond to in a positive way.
  8. Instead of using the term stretching, I prefer to use general terms such as “movement exercise” or “mobility exercise” because stretching  is a specific term with a lot of conflicting research. Besides, stretching is only one  type of movement exercise out of the many that we can do to improve how move.
  9. Utilize concepts of sensation and adaptive potential while performing movement / stretching exercises.

I hope I have given you the tools to help improve the way you move. I want to wish you the best of luck as you promote improved movement ability and control.

Further Reading:

During my quest to understand stretching, I have read many articles that contradict each other. Feel free to read the articles that I have referenced.

Also many health care providers have answered these same questions that I have presented and have interesting as well as different viewpoints regarding stretching and movement. Feel free to check them out.

http://saveyourself.ca/articles/stretching.php

http://www.theptdc.com/2014/06/should-my-training-clients-stretch/

http://breakingmuscle.com/mobility-recovery/stretching-doesnt-work-the-way-you-think-it-does

http://www.somastruct.com/problems-sensory-theory-of-stretching/

http://www.exercisefraud.com/streching.html

References:

Artwork: from Wikimedia commons at http://commons.wikimedia.org/wiki/File:Stretching_%28479163922%29.jpg

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