Yoga Physiology

Yoga physiology, anatomy and movement science

What does stretching do for you?

Is there any reason to stretch? And is there such a thing as too much stretching? I’ve been thinking about these questions lately, after starting to lift weights again following a hiatus of 20-some years.

My motivation when I began weight lifting in my twenties was basically cosmetic; I wanted to get bigger, which I failed at doing completely. These days I’m more concerned with my health (and with having fun).

I saw how quickly my already thin father wasted away with illness before he died last year, and I was determined to have more reserves available when I reached his age. People lose muscle as they grow older, a condition called sarcopenia, and, unfortunately, muscle mass is a predictor of longevity. We don’t store protein as we store glycogen and fat; protein gets put to use. Thus, the only significant source that the protein-hungry immune system can call upon to resupply amino acids during severe illness is working muscle. Fortunately, sarcopenia can be slowed with activity, particularly with resistance training.

Also, as thin as I am, I’m more at risk of osteoporosis than other males. I’ve been practicing yoga for long enough that it no longer presents much of a physical challenge for me, or for my bones. There is a minimal essential stress necessary to stimulate bone growth. Of course, there are asanas that remain difficult for me, but overall I doubt that my yoga practice still stresses my bones as it did when I began. Heavy deadlifts certainly do.

And an unexpected benefit of weight lifting is that it’s turned out to be fun. It’s a challenge, especially Olympic lifting, which I’ve been learning lately. I get to feel like a beginner–clumsy, weak and uncoordinated–which I don’t get in my yoga practice, as much as I may try to approach it with a beginner’s mind. So when I actually manage to hoist a heavy barbell up, it’s a thrill.

However, the primary reason I started lifting was that I felt my body had become unbalanced from asana practice. I had become hypermobile, overflexible, at the expense of strength. This was an interesting shift for me. One of the reasons I started practicing yoga seriously in the first place was to restore flexibility that I had lost with weight training back in my twenties. The situation was now reversed. I needed to tighten up to return to balance.

And now, in another interesting shift, as my muscles feel tighter, stretching feels good again. I took a yoga class the other day focusing on deep, slow stretches for the gluteal muscles and hamstrings. Mine felt like they sorely (and I mean sorely) needed the attention after a session of heavy deadlifts the day before. I had forgotten that feeling of tight hamstrings. It felt good to stretch them out, and by the end of class uttanasana wasn’t quite so much the exercise in humility it had been at the beginning of class. The stretching felt like a necessary corrective, rather than over-pulling already loose muscles.

Which brings me to the question I began with. As good as it may feel, is it in fact beneficial to stretch? Is there evidence that it actually does anything for you?

Perhaps surprisingly, in recent years exercise physiologists studying this question have largely come to the conclusion that there isn’t much evidence that it does.

It’s long been assumed that stretching could help prevent injuries among athletes. While that might be true for some specific individuals with some specific injuries, there’s little evidence that it prevents injuries overall. Athletes who don’t stretch are no more (or less) likely to be injured than athletes who do. And, although the evidence is also equivocal, some studies suggest that being hypermobile can increase your risk of injury.

Likewise, in general, stretching doesn’t seem to enhance athletic performance. In fact, stretching immediately before an athletic event probably actually decreases performance.

However, a recent study in the Journal of Strength and Conditioning Research suggests another reason stretching may be beneficial: it may help you relax.

The researchers gave 10 young men with low flexibility a short routine of three stretches, held for 30 seconds and repeated three times. The subjects’ heart rate variability was measured for 30 minutes before stretching, while stretching, and for 30 minutes afterwards.

In simple terms, heart rate variability is an indicator of the state of an individual’s autonomic nervous system. The results of the study indicated that in the period following the stretching routine the subjects had enhanced parasympathetic tone. In other words, they were less stressed and more relaxed than when the test began.

There are reasons to take these results with a grain of salt, or at least to be cautious about how generally applicable they are. For one thing, there was no control group, so we don’t know whether, if the subjects had just sat and relaxed for the same period of time, they would have seen the same results.

In addition, the men were selected for low flexibility, so we don’t know if the results would have been similar for those with more flexibility. (In fact, it’s not even clear that they were generally inflexible. They were tested with the sit-and-reach test, which is considered a standard measure of flexibility—basically, they sat in paschimottanasana, and researchers measured how far they could reach with their hands. Does this test indicate overall flexibility? It might for some individuals, but it only measures hip and spinal flexion and says nothing about other joints or other ranges of motion. However, since the stretching routine the subjects practiced was focused on the hamstrings and trunk, it was probably a valid measure for this study).

Despite the unanswered questions, this study is still intriguing. Perhaps most researchers studying stretching have been barking up the wrong tree. Maybe its benefits have less to do with effects on specific muscles, and more to do with the nervous system as a whole through inducing the relaxation response—which probably comes as no surprise to many yogis.


5 responses to “What does stretching do for you?

  1. Narisara May 3, 2011 at 9:16 am

    Hello Joe,

    Thanks for the blog post and for telling this story. It is very inspirational to see how these motion tools can come back around to serve a different purpose.

    I was wondering what you think about Yin Yoga.
    As you may know, it is stretching right out of the gate, with little to no warm up and requires heightened sensitivity to one’s body and a non-ambitious state of mind. Thanks for any thoughts on this practice, or combining it with other yoga / non-yogic practices.

    • Joe Miller May 3, 2011 at 8:58 pm

      Hi Narisara
      Personally, I’ve liked practicing yin yoga, although I haven’t done it a lot. There’s a feeling of quiet introspection and settling that happens for me. Physiologically, the connective tissue elements of muscle are able to lengthen most effectively with low force and long duration holds, but also when the temperature of the tissue is elevated. That suggests that practicing some sort of dynamic warm up before a yin session to increase the temperature of the muscles might be more effective. However, my personal feeling is that I come to a yin style practice not with the intention of creating longer connective tissues, but to become quiet, and, as you said, to cultivate a non-ambitious state of mind.

  2. Kyle May 5, 2011 at 12:37 pm

    Thank you for such a thought provoking piece. I especially connected to it because for a while now I’ve been less interested in “stretching” in my practice (which really only brought me injury in the past) and much more interested in exploring the effects of the asanas on my being as a whole and how they can support me in my life. And this for me often involves facilitating a quieting effect. The questions your article brings up fascinate me: What would the mechanism be that could potentially connect the action of stretching with activation of the parasympathetic nervous system? Why do sometimes I feel like I need the sensation of stretch and sometimes I don’t need that sensation to cultivate that quality of quiet? How does this relate to a person’s overall level of flexibility?
    Regarding the benefits of stretching, one thing that I didn’t see you address which I think is relevant is the amount of people whose quality of life deteriorates through lack of flexibility as they age. I worked with a student recently who because of a lack of range of motion had difficult putting on and taking off his shirt. Or grandparents who have trouble getting down to the floor to play with their grandchildren. Of course there is also the argument that the flexibility element is the least important and through neuromuscular re-patterning the range will increase without having to worry about stretching (the expertise of the somatics field: Alexander, Feldenkrais, Body-Mind Centering, etc.).
    One question I’m curious about. I’ve heard many times that generally speaking connective tissue is flexible but not elastic, in that it does not go back to its resting length when its shape is changed, and therefore the intention of stretching connective tissue is a mistake. While this has made a lot of sense to me in my body and in healing old injuries (while ironically improving my flexibility), it also strikes me as overly simplistic. For one, connective tissue is not all the same. And above you mentioned how to stretch the connective tissue elements of muscles (implying that that is not an undesirable thing to do across the board). Curious if you had anything you wanted to add to the “stretch the connective tissue” debate.
    Thanks again for the thought provoking piece.

    • Joe Miller May 7, 2011 at 10:05 pm

      Kyle, you raise some interesting questions. First, the question of mechanism: how could stretching increase parasympathetic tone? Of course, we don’t really know from this study whether that happened; maybe the benefit came from just sitting quietly. But, there are neuromuscular afferents that innervate the reticular formation, which in turn projects to the hypothalamus, the main regulatory center of the autonomic nervous system. So it’s plausible that reductions in peripheral muscle tone while stretching, as muscle spindles adapt or from stimulation of Golgi tendon organs, could lead to more parasympathetic dominance.
      I agree that maintaining mobility is important. For me, there is a difference between mobility and flexibility. I conceive of mobility as the capacity to move purposefully through a range of motion, which implies the ability to control that motion, while flexibility is more about simple passive range of motion and tissue extensibility. While flexibility can play a role in mobility, I think it’s a small part. The motor learning aspect is much more important. That’s why disciplines like Feldenkrais which focus on regaining awareness and learning are helpful in maintaining mobility.
      As for the question about connective tissues, that’s a big one. Connective tissues differ in fiber type and the composition of ground substance. They have different degrees of elasticity and susceptibility to plastic deformation, different abilities to heal, and different functions. Ligaments, for instance, need to be a certain length to maintain joint stability, so stretching them isn’t likely to be helpful. On the other hand, connective tissues elements within the belly of a muscle can probably stretch safely. Even so, stretching muscles without regard to function just for the sake of greater flexibility doesn’t make much sense. At some point, I’ll write a series about what happens as muscles stretch, but for now, I’ll leave it at that.

  3. Kyle May 15, 2011 at 2:46 pm

    I love the distinction between mobility and flexibility. Very useful.
    I eagerly look forward to your series on the physiology of muscle stretching and will try to wait patiently for it.

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