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Stretching Research 101 – Pros, Cons, and Myths

To stretch, or not to stretch...

Stretching…

I could talk about this for days. But instead, I decided to write a shorter article.

Here I’ll discuss the pros, cons, and myths of stretching.

Then I’ll give a brief description of how it works, so you can start to make sense of it all.

And finally, a question for you to think about whenever you are deciding how you should (or shouldn’t) include stretching in your lifestyle.

Turns out it’s not so simple.

CONTENTS:

  • Pros, Cons, and Myths
    – ‘Pros’ of stretching.
    – Myths: What it doesn’t do.
    – ‘Cons’ of stretching.
  • How Stretching Works.
    – Personal note.
  • Should you stretch?
    – How flexible do you need to be?
  • So how can you prevent injuries?
  • General Recommendations.

Stretching is any activity intended to improve your range of motion (flexibility). There are tons of types, but I won’t get into that here. When most people think of stretching, though, they think of ‘static’ stretching, where you stretch your muscle to its end point, perhaps putting a little more pressure on it, and then hold it for some amount of time.

So, why would you do this?

PROS:

– Yes, it definitely improves your flexibility 1. But remember, stretching is specific, so be sure to stretch in ways that are exactly how you want your flexibility to improve.

– Stretching seems to feel good, as long as you don’t go too crazy with it. One possible reason why it does this will be explained below (how stretching works).

– Stretching may help with sports that require above normal flexibility 2, like dancing, gymnastics, or diving.

– Stretching can slightly decrease your risk of muscle strain 3.

Myths:

Now for the bad news… ‘static’ stretching doesn’t do what we once thought it did!

– Stretching actually does not decrease your risk of overall injuries 4, 5, 6, especially overuse injuries, or anything other than a muscle strain 7. This should make sense when you think about how injuries actually happen.

– Stretching does not decrease muscle soreness 8. It might feel like it do at the time, but it don’t last. It feels good at the moment, and lasts an hour or two, but it’s not great for that next couple day exercise soreness. You’ll see why below.

– Stretching does not improve sports performance 9, 10 in sports that do not require high flexibility, like running or biking.

CONS:   Yup, cons! Stretching can actually have cons.

– Stretching more than 45 seconds has been shown to decrease muscular strength (by about 5%), power (~2%), and explosive performance (~2%) for up to an hour. The longer the stretch, the greater the weakness 11. So be sure to keep the stretching short and sweet before athletic pursuits!


Woah! So stretching isn’t all it’s cracked up to be! Why is that?

None of this means stretching “don’t work”, or that you “shouldn’t stretch”. After all, review the ‘pros’! It does have benefits. However, people need to be aware of the limitations of stretching. Only then can you implement stretching into your training regimen properly.


How Stretching Works

It seems stretching has its effect on your nervous system… but doesn’t really make your muscles longer or ‘stretchier’.

In 2010, an article in the journal physical therapy reviewed research on the basic science of stretching 12. After deconstructing many popular theories of what happens when you stretch, the authors made the following conclusions:

The idea that stretching actually increases muscle extensibility (stretchiness) is not substantiated by any good scientific research, and neither is the idea that it literally lengthens muscles.

Currently, the best theory is that stretching increases your ‘stretch tolerance’, either by decreasing the pain threshold, and/or decreasing the muscles resistance to stretching. It does the latter by temporarily altering the receptors in your muscles, tendons, and ligaments that usually react to stretching by making your muscles tighten up. There are a lot of possible mechanisms, and we don’t quite understand it all yet.

This change in the nervous system probably explains why it seems to feel good to stretch (at least during a light stretch). It decreases the feeling of tightness by increasing your tolerance.

Basically, your muscles get used to the range in which you use them. However, this effect seems to only last a couple hours… it takes weeks of consistent stretching to really increase your flexibility ‘permanently’, and if you stop stretching, it will likely go back to ‘normal’. Use it or lose it!

Personal Note:

Stretch Armstrong has no nervous system.

When I think about my clinical experience as a physical therapist, this actually makes a lot of sense.

Working in a rehabilitation hospital, I notice that people who have a complete spinal cord injury below the level of around T-10 (and often not displaying any spasticity) usually have incredible amounts of flexibility in their legs.

Of course, they can’t feel them or move them. But it is interesting to think that perhaps we all have very flexible muscles, and it’s nothing more than our nervous system that stops us from going to lengths that we are not used to.

Our nervous system says: “Woah! That’s not normal, probably not useful, and not safe!”

Confused? It’s okay, so are the researchers and scientists. All you need to worry about are the main points stated above in pros and cons.


So then, the question is:

Should you stretch?

Well, that clearly depends on your sport, your level, and your goals! For example, the goals of a weight lifter would be quite different than a dancer.

Dancers: The answer is probably yes for flexibility. But be careful. Read: Stretching for Dancers – Discussing the Research.

Strength Training: While you should probably warm-up, it seems that stretching probably isn’t a good idea (5% decrease in strength? No thanks!).

Goals should always determine your decision making.

Speaking of goals…

How flexible do you need to be?

Not everyone needs to be flexible!

If you need to open your legs wider to do some sort of movement, then perhaps you should stretch your groin regularly until you can do it. If your sport or activity requires a lot of flexibility, its probably a good idea to do some stretching before you practice or perform. It may prevent that over-stretching type muscle strain if you are in a sport where you have to kick your legs open quickly (dancing comes to mind).

However, if you don’t need to be flexible, stretching might be quite a waste of time! And even if you do need flexibility, it seems that once you have it, stretching can become a smaller part of your training program. Since it don’t seem to prevent all injuries very well, all you need is enough to maintain your flexibility.

When it comes down to it, if you don’t need to be flexible for your activity, this is probably how you should stretch:


So how can you prevent injuries?

Warm-ups that include ‘dynamic stretching’ seem to be promising.
Read: Warm-ups, and Types of Stretching part II.

Coordination: balance, stability, and agility training seems to be very important. See: Coordination Training.

Progression: don’t skip steps when trying to learn something, exercising, or rehabilitating an injury. Give your body time to adapt!

Don’t be stupid: seriously… don’t do dumb things. Most injuries are from mistakes. If your not careful, you are more likely to have an accident.


General Recommendations

If you decide stretching is something you need to do (your goals require greater than normal flexibility) then here is how you can include stretching while avoiding the ‘cons’.

1. Warm-up (raise your temperature and sweat a little) and include simple, sport-specific, ‘dynamic’ stretches. ‘Static’ stretches should be limited to 15-30 second holds, once per position. Warm-up for 10-15 minutes, or until you feel ready to rock.

2. Exercise / Compete / Perform / Practice… do your thing!

3. Lots of ‘Static’ stretching afterwards to improve flexibility, if you need to. Hold sport specific positions at the end range (avoid pain) for about a minute, repeating 2-3 times.


So, should you stretch? Well, I gave you the information. Now it’s time for you to weigh the pros and cons, and decide for yourself.

Good luck!

Share the love!

    30 Responses to Stretching Research 101 – Pros, Cons, and Myths

    1. Thomas Kurz says:

      “It seems stretching has it’s effect on your nervous system… but doesn’t really make your muscles longer or ‘stretchier’.

      “In 2010, an article in the journal physical therapy reviewed research on the basic science of stretching 12. After deconstructing many popular theories of what happens when you stretch, the authors made the following conclusions:

      “The idea that stretching actually increases muscle extensibility (stretchiness) is not substantiated by any good scientific research, and neither is the idea that it literally lengthens muscles.”

      Maybe… but the authors (Weppler and Magnusson) have not researched isometric stretching (it is not the same as PNF stretching), and how long were the studies they quoted?

    2. Thomas Kurz says:

      BTW, isometric stretching is not the same as C-R stretching either.

      • Tony Ingram says:

        Hi Thomas!

        I’ve written on other types of stretching as well, here and here. Also, I’d like to add I agree with Paul Ingrahams sentiment toward special types of stretching as he outlines in his comprehensive article on stretching: ‘Quite a Stretch‘.

        I’m not about to go through Weppler and Magnusson’s review and pick apart each study they quote. That’s not the point. If people want to substantiate the idea that stretching actually changes muscle morphology, then researchers have to go out and do it. We can’t just take peoples word for it. Right now, the best theory that makes the most sense in the most situations is still ‘stretch tolerance’.

        If you find research that doesn’t jive with what I wrote here, by all means please post it. I’d love to read, and would be more than willing to edit my information here based on it.

        Thanks for the comment!

      • Tony Ingram says:

        Furthermore, I’d like to add that isometric, contract-relax, and PNF are all forms of active-static stretching. The only real differences are in protocol: slight variations in time, which muscles are contracted and when. Like different set-rep schemes in strength training, there may be slight differences in individual response, but they are often quite inconsequential.

        Stretching long and hard is what makes you more flexible. The one thing that everyone who achieves great flexibility has in common is hard work. They would likely achieve their goals no matter how they chose to stretch. Ask them all how and you will get different answers.

        Different protocols may be better for helping different people build their tolerance. Whether there is any difference in effectiveness is irrelevant in the discussion of how stretching actually works. There is no reason to believe any special stretching technique is the one that causes a change in morphology, while others do not.

        • Thomas Kurz says:

          Does a systematic application of isometric tensions in a strength training program change morphology of a muscle? (That’s a rhetorical question.)

          • Tony Ingram says:

            Rhetorical? Sounds like a ‘deepity’ to me.

            I’m going to take a wild guess that what you are hinting around at is this: ‘active’ stretching with isometric contractions can change muscle morphology.

            Adding contractions to stretching could indeed cause morphological changes. That’s because of the contractions, not the stretching. It’s the effect of strength training (as I have outlined in How Strength Training Works part I and part II). It still doesn’t change what the effect of bringing your muscle to it’s end range actually is. The way it improves flexibility still makes more sense as a change in ‘stretch tolerance’.

            The morphological changes that people propose stretching can cause are things like an increased number of sarcomeres in series, increased visco-elasticity, etc. None of which have been proven. An increase in cross sectional area as found in strength training is not what we are talking about here, although that might cause an increase in flexibility. Again, it would be the strengthening from contractions causing that effect, not the stretching.

            When we start complicating ‘stretching’ by adding contractions and creating different types, we still don’t change what stretching is: bringing your muscle to a ‘stretch’ (it’s end range), with the purpose of increasing the overall range of motion.

    3. Thomas Kurz says:

      “You’re references are your own books. Got any primary sources?”

      On pages 191-201 of the book. In really small type.

      “Also, you’re definition of isometric stretching cites an effect on stretch receptors that is also unsubstantiated: http://www.ncbi.nlm.nih.gov/pubmed/17052131”

      Have you read, and tried, what I suggest in the footnote to the definition on p. 16? How does that feel like? Are you sure there is no reflex involved in the postcontractive relaxation in PR?

      • Tony Ingram says:

        Hahaha

        Thomas, I’ve used many of these techniques myself as a dancer, and also in practice as a physical therapist. I know what normal (tested with a reflex hammer, pretty simple) and abnormal (spasticity in spinal cord injuries) reflexes ‘feel’ like. Don’t forget that the stretch reflex reacts to quick movements, not much in slow movements like a stretch. Furthermore it’s quite short lived.

        I’ve felt the relaxation that occurs after using active techniques. There’s no reason to believe it’s due to a change in the reflex. It could still be pain perception and tolerance. I have enough integrity not to trust my subjective experience.

        Do you want me to buy your book to find out your special secret techniques? Post the research you’re talking about please. Within your comments too, not leading back to your page in hopes of selling your books to my readers.

        I’m sure under your coaching I can get the splits (whether that’s an important thing to strive for or not) but here I’m talking about physiology. I don’t need to try or feel anything. The reason we do science is to not be encumbered by our subjective experience, anecdotes, and beliefs (as a licensed professional, I have an obligation not to). I’m looking for proof here. In the absence of actually carrying out the experiments mentioned here ourselves, the best we can do is provide references to the study’s already completed.

        If we’re going to continue this exchange please post up-to-date primary peer reviewed references.

        • Thomas Kurz says:

          “Don’t forget that the stretch reflex reacts to quick movements, not much in slow movements like a stretch. Furthermore it’s quite short lived.”

          Which is why in isometric stretching the ROM increases are best done within one second of the relaxation that follows the nearly maximal tension.

          “Do you want me to buy your book to find out your special secret techniques? Post the research you’re talking about please.”

          I don’t care to sell my book to you or your readers. I was just too lazy to re-type my own writing. What I wanted to do was to point out that the authors of the study you quote have omitted a long-known stretching-strengthening (or is it strengthening-stretching?) technique–the isometric stretching. I wondered what you’d say if I point this out. Now I know.

          “I’m sure under your coaching I can get the splits …”

          Sounds like you think that the footnote on p. 16 talks about a stretch. It does not. Here it is (I have found my original file for the chapter and the page):
          These relaxations following strong tensions feel just like Dr. Jacobson’s Progressive Relaxation.

          And about the splits: I know a few things about phys-ed and sports training. Of those things the easiest to sell were (and still are) methods of obtaining those silly splits. I do not advocate stretching, I just sell the know-how (you want hula hoops, here are your hula hoops…).

          • Tony Ingram says:

            “What I wanted to do was to point out that the authors of the study you quote have omitted a long-known stretching-strengthening (or is it strengthening-stretching?) technique–the isometric stretching. I wondered what you’d say if I point this out. Now I know.”

            Well let me clarify my thoughts on that specifically.

            I don’t quite understand why the authors would have specifically included isometric stretching. After all, it was a review article on anatomical and physiological changes induced by stretching, not an experiment. Either way, I don’t think it would make much of a difference. As I explained in a previous comment, there’s no reason to think isometric stretching could cause a change in muscle morphology leading to increased flexibility. However, it may lead to changes indicative of any type of strengthening. Still, the increase in flexibility would likely be due to an increase in ‘stretch tolerance’. It wouldn’t surprise me if the pre-stretch contraction increased tolerance.

            Overall: I think bringing up a specific type of stretching is pedantic.

            The point of my original article (which I feel this whole conversation has now detracted from) was that stretching in general isn’t as helpful as we once thought it was, and doesn’t work in the ways we used to think. It still is helpful for flexibility, which is important for particular athletes, like dancers, as I have discussed here: Stretching for Dancers – Discussing the Research.

            Before this entire conversation, I had already written a two-part series about stretching types: The Problem with ‘Types’ of Stretching – Part I, and Part II, partly because I wanted to avoid this conversation. I truly feel that being ostentatious with details (which are often inconsequential – read my posts) is often a form of posturing to create an image of expertise. This is not my goal on this site; my goal is to simplify things (because things usually are simpler than people make them out to be).

            Anyway, now that I have explained how I feel about what you’ve brought up, I assume we’re finished with this enlightening discussion.

            I hope this conversation ends up adding to peoples knowledge on the topic, rather than confusing them.

    4. Paul says:

      You said that strength decreases by 5 percent for the next hour. So after that hour everything is back to normal?

      • Tony Ingram says:

        Hi Paul,
        I think that’s what was observed – a temporary decrease in strength. Which probably isn’t a big deal (your strength as measured by 1RM would surely be decreased after any other modality of exercise, so this shouldn’t be a surprise). But it certainly provides rationale for not static stretching before a strength training session!
        Thanks for the great questions!
        Tony

    5. Any examples of animals increasing their flexibility through training or are they born about as flexible as they need to be? Your bunny stretching video is similar to the way tigers, dogs etc… stretch any other examples of animals stretching to adapt to their surroundings? Lastly, why do kids lose flexibility as they get older?

      • Tony Ingram says:

        I can’t think of any examples of animals doing any sort of flexibility training other than little stretches like the bunny video. Kids lose their flexibility for a few reasons: as they grow, their epiphysial plates fuse, which is a good thing. In general people lose flexibility mostly due to dis-use, and as we age, connective tissue usually becomes ‘stiffer’ – which has something to do with increased disulfide bonds or something, can’t remember the exact biochemistry. Personally, I’d say disuse is one of the biggest factors, and aging gets way too much blame. Just look at kids play – they use their full range of motion all the time. Then watch a typical adults day to day life. The most flexibility they need is bending to tie their shoes.

    6. Oooh ooh, last question. If stretching is controlled neurologically. How flexible are you when you are unconscious or passed out? Shouldnt you be able to hit your physical max without the limitation of your nervous system interfering?

      • Tony Ingram says:

        Thats an interesting question. I’m sure a person would wake up if you stretched them. But when “knocked out”, you have to support a persons head when you pick them up because their righting reactions aren’t working. Furthermore, I’ve heard that when surgeons have someone under anaethesia, they have to be careful not to dislocate their joints when moving them because their muscles aren’t active at all. Very interesting stuff!

        Hope that answers your questions! Thanks for asking, and reading!

      • Eric says:

        Yes it is an interesting question! Havnt took the time to search the litterature but i dont think we have absolutly no muscle tone when unconscious. I lost counscious many times myself when i was young and i only had urination once. and i know for sure that a freshly dead animal is wayyyy more atonic than a sleeping animal, even if there is probably some electric activity for some time after the death. That said yes i guess an uncounscious or dead animal is way more flexible. And btw, what we see as an articular limitation to a movement is sometime really much more restricted by the muscles. For exemple, when i first saw a ruptured Achilles tendon, i almost freaked out (i didn’t knew yet the tendon was ruptured) when i looked at the dorsiflexion: the dorsal aspect of the foot touched the leg… :)

        • Tony Ingram says:

          “the dorsal aspect of the foot touched the leg…”

          Woah are you serious!? That’s crazy! I would have probably freaked out too.

          Interesting and great points Eric, really appreciate the insights. I may edit the article slightly, as I think I worded those things a little too black-and-white, and it’s far more complicated (as you pointed out). Perhaps my surgery anecdote isn’t quite accurate. But I still notice the flexibility of SCI patients.

          • Eric says:

            oh yes i am serious. my brain told me: ok calm down (I remember my pulse surging)… now you have to look at the tibia while dorsiflexing the foot just to make sure there isn’t any fracture (i know not very probable since the patient was walking on its foot without any crutches, but i needed to make sure). the tibia wasn’T bending. so i said to myself: ok no more possibilities… ruptured achilles tendon. the thompson test was positive of course. I finally said to the patient: go back to see A doctor (not YOUR doctor – he was refered by a physician as suffering an ankle strain) … I am still impressed by the range of motion available at this joint…

    7. Donald Lee says:

      “Currently, the best theory is that stretching increases your ‘stretch tolerance’, either by decreasing the pain threshold, and/or decreasing the muscles resistance to stretching. It does the latter by temporarily altering the receptors in your muscles, tendons, and ligaments that usually react to stretching by making your muscles tighten up. There are a lot of possible mechanisms, and we don’t quite understand it all yet.”

      Tony,

      I’m interested in the latter part about “decreasing the muscle’s resistance to stretching.” I skimmed through Weppler and Magnusson’s review article, and it says the following regarding neuromuscular relaxation:

      “Some authors,34,53 furthermore, have suggested that neuromuscular reflexes adapt to repeated stretch over time, which enhances the stretched muscles’ ability to relax and results in increased muscle extensibility.

      Experimental evidence does not support any of these assertions.13,14,54,55 Stretch reflexes have been shown to activate during very rapid and short stretches of muscles that are in a mid-range position, producing a muscle contraction of short duration.54 However, most studies of subjects who were asymptomatic and whose muscles were subjected to a long, slow, passive stretch into end-range positions did not demonstrate significant activation of stretched muscles.14,54,56,57

      The increase in end-range joint angles, therefore, could not be attributed to neuromuscular relaxation.”

      From my cursory reading, it appears that the authors are contradicting that second part of your statement.

      I was thinking about the implications, with respects to strength training, of the review article’s conclusions on neuromuscular relaxation as a result of stretching. It appears to me that the following statement indicates that the stretch reflex…of say the Squat…would not be affected by obtaining much more hip flexibility than is required: “Stretch reflexes have been shown to activate during very rapid and short stretches of muscles that are in a mid-range position, producing a muscle contraction of short duration.”

      I had previously assumed that it was well-known that too much flexibility would negatively affect the stretch reflex due to musculotendinous stiffness (intrinsic stiffness and reflex stiffness). I searched around a bit and was able to come across the possible mechanisms for stretch reflex modulation in “Voluntary modulation of human stretch reflexes”, Ludvig et al, 2007. I was unable to come across anything concrete regarding altered stretch reflex sensitivity, whether due to stretching or something like plyometrics.

      Am I understanding this issue incorrectly?

      • Tony Ingram says:

        Hi Donald,

        When I wrote “decreasing the muscle’s resistance to stretching” I meant it in a very broad context: possibly through central or corticospinal influence – as opposed to the stretch reflex which is (as I understand) a spinal reflex. This is speculative, of course, as I doubt “stretch tolerance” isn’t simply due to decreasing pain thresholds or increasing pain tolerance (I wonder if pain even has anything to do with it?). I’m not sure. But I think I can say with some certainty that improvements in flexibility from stretching have more to do with the nervous system than once thought.

        “… the stretch reflex…of say the Squat…would not be affected by obtaining much more hip flexibility than is required…” – I’d agree with you there – I think your reasoning is sound.

        I’m not sure what you mean by “musculotendinous stiffness (intrinsic stiffness and reflex stiffness)”. I haven’t read much about stretching science lately, so I am not really sure what is meant by “stiffness” (resistance to stretch, I think?). I’ll also have to give that Ludvig paper a read, looks interesting!

        In the general sense, I think you are understanding the issue just fine. Obviously the topic of stretching is surprisingly deep – which is funny considering it has such little effect, negative or positive, on most measures of human function other than range of motion. I certainly don’t claim to know it all, and intend to keep reading about it once I finish a few other projects I am currently working on.

        Good question / comment! This comment section is becoming quite rich in extra information for those who decide to actually read through it. Thanks for the contribution!

        Tony

    8. Tony,

      Great piece with some valuable takeaways! One of my mentors, Malachy McHugh, and Peter Magnusson have done some awesome work on this topic. We also recently (2010) published a study (http://www.ncbi.nlm.nih.gov/pubmed/20738821) in the scandinavian journal entitled “The role of neural tension in hamstring flexibility,” that you would enjoy. We also have part 2 which is in review and undergoing the second round of edits which means that it should be a go. Basically the outcome was that static stretching of the hamstrings resulted in a stretch induced strength loss with no rightward shift in the length tension curve. Look forward to your next post and keep up the good work. If you havent checked out the Ekstrom et al article re: muscle strains in soccer players it is worthwhile as the methodology was pretty tight. Anyways, it’s always great to hear from someone who speaks in denominators rather than numerators. Cheers and Happy New Year!

      • Tony Ingram says:

        Hey Chris,
        Once again thanks for the comment and the valuable additions. I think I may edit this article to add a little detail about mechanisms, and highlight some uncertainty regarding the research – stretching is surprisingly complex and I feel this article comes off as claiming that range improvements are just increases in stretch tolerance.
        Your research is interesting as usual – the hamstrings are so often studied in stretching research, despite the many factors that influence their flexibility. Neural tension is very interesting, and I may write a post on it using your study as a reference! What Ekstrom article are you talking about? I can’t find it! I’ll look harder later.
        Thanks again!
        Tony

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