The theme song from Frozen may as well be the mantra for many yoga classes – where letting go, surrendering, and opening your (fill in the blank) are seductively crooned by the teacher at the front of the room, perhaps only a little less emphatically than Elsa’s performance. Such songs of the Sirens are layered in meaning, dispensing a wide range of advice both psychological and physical. To be told to “let it go” may be considered a form of personal coaching; an insight into how to handle the inevitable upsets in life. The same message, however, may also suggest that enhanced flexibility, greater range of motion, and those distant and aspiring asana are the tangible reward for surrendering.
It’s beautiful, it’s poetic, it’s yoga.
And I’m not arguing against it. But I am offering another perspective, another approach to flexibility. One that has emerged through a healthy interest manic obsession with the scientific literature. One that is not intended to replace the old paradigm, but rather to add to it.
I introduce to you the theory of the neural reflex mechanism. This theory establishes relaxation of the contractile components of the target muscle as the mechanism by which greater lengthening occurs [1,2]. Essentially, as your muscle resists a stretch, electromyographic (EMG) activity increases and a reflexive shortening contraction would prevent further lengthening.
In order to bypass this reflexive shortening contraction, one should attempt to decrease EMG activity (marking muscle relaxation) in order to achieve new and greater ranges of motion (ROMs). Just let it go (“it” being the target muscle). Relax into the stretch, deepen the stretch.. you get the idea.
Research shows, however, EMG activity and force production may actually increase at these new increased ROMs [3]. Stretching methods which result in the greatest improvements in ROM are actually correlated with greater EMG activity; muscle relaxation is not a requirement for increased range of motion [4,5].
In addition to relaxing into the stretch to improve flexibility, techniques that intend to alter or reduce the reflex which resist the stretch are often cued. Such techniques you may have heard of are reciprocal inhibition (RI) and autogenic inhibition (AI). The effect of these reflex activities on long term flexbility are questioned by many scientists [6-8], a topic for future blogs.
In the meantime, I challenge you to a forward bend (seated or standing) where you isometrically contract your hamstrings (target muscle) instead of contracting the quadriceps. Did you lose ROM? Probably not. Plus the isometric contraction is loading your hamstring tendons to adaptively increase their capacity to withstand a tensile load – bonus for those of who have suffered a hamstring tendon injury.
Personally, I reserve my letting go for restorative yoga. I mean fully supported, 100% supported restorative yoga, where you aren’t feeling that stretching sensation we are all addicted to. That’s really the best way surrender and quiet that EMG activity. And it has little to do with flexibility, but a lot to do with collagen organization and mechanoreceptor stimulation – topics for future blogs.
_________________________________________________
[1] Guissard, N., & Duchateau, J. (2004). Effect of static stretch training on neural and mechanical properties of the human plantar-flexor muscles. Muscle & Nerve, 29, 248–55. doi:10.1002/mus.10549
[2] Guissard, N., & Duchateau, J. (2006). Neural aspects of muscle stretching. Exercise and Sport Sciences Reviews, 34(4), 154–158.
[3] Magnusson, S. P., Simonsen, E. B., Aagaard, P., Gleim, G. W., McHugh, M. P., & Kjaer, M. (1995). Viscoelastic response to repeated static stretching in the human hamstring muscle. Scandinavian Journal of Medicine & Science in Sports, 5(6), 342–347.
[4] Moore, M. A., & Hutton, R. S. (1980). Electromyographic investigation of muscle stretching techniques. Medicine & Science in Sports & Exercise, 12(5), 322–329. doi:10.1249/00005768-198012050-00004
[5] Osternig, L. R., Robertson, R. N., Troxel, R. K., & Hansen, P. (1990). Differential responses to proprioceptive neuromuscular facilitation (PNF) stretch techniques. Medicine & Science in Sports & Exercise, 22(1), 106–111. doi:10.1249/00005768-199002000-00017
[6] Hayes, B. T., Harter, R. A., Widrick, J. J., Williams, D. P., Hoffman, M. A., & Hicks-Little, C. A. (2012). Lack of neuromuscular origins of adaptation after a long-term stretching program. Journal of Sport Rehabilitation, 21(2), 99–106.
[7] Hindle, K. B., Whitcomb, T. J., Briggs, W. O., & Hong, J. (2012). Proprioceptive Neuromuscular Facilitation (PNF): Its Mechanisms and Effects on Range of Motion and Muscular Function. Journal of Human Kinetics, 31, 105–113. doi:10.2478/v10078-012-0011-y
[8] Sharman, M. J., Cresswell, A. G., & Riek, S. (2006). Proprioceptive Neuromuscular Facilitation Stretching Mechanisms and Clinical Implications. Sports Medicine, 36(11), 929–939.
Extend Your Learning: Online Education With Jules
Yoga Biomechanics Livestream
My flagship 3-day livestream course is for teachers who have an insatiable curiosity about human movement and kinesiology, are eager to know what the research says about yoga, and are open to accepting that alignment rules aren’t always accurate. Includes 30 days of access to the livestream replay and slides. 18 CEUs. Learn more >
Hi Jules,
Yes, yes, yes!! In my search for sound information, Paul Grilley, You, Katie Bowman, Judith Hanson Lasator PH.D, PT, Yoga teacher, Dough Keller, over many, many years. I have finally HEALED my tissues!! Yah!! After years of Vinyasa yoga, with little awarness of guarding/bracing/engaging to protect, my ligaments felt shot. But I renewed the ligament with SUPPORTED Yin Yoga, not going out of bounds of reasonable natural ROM and added structure to the Hatha Yoga using science. 15 years later, (in my 50’s) I am stronger, pain free and have steady energy!!! You my friend are right on and thankfully SOME of the yoga practitioners are getting it!! Thank you for your contribution to BALANCE, (which is what HA-THA) stand for afterall!
Yay for new posts in the new year!
A couple of questioning, curious thoughts:
I wonder whether you’re conflating the psychological experience of “letting go” with the supposed neuromuscular phenomenon of decreased EMG activity. When I am thinking “let it go,” I might even imagine this is what is happening in my muscles, though the research you cite indicates this (like Frozen) is a fairy tale. BUT, what if the psychological experience “let it go” is actually facilitating the ability to tolerate the increased EMG activity associated with increased ROM. Relaxation of mind may not create relaxation of muscle, but it may be vital to the stretch tolerance that so much research points to now. This is way out of journal territory, of course, but I would love to see a study exploring what kinds of mental processes promote or inhibit changes in ROM. In the meantime, for years I have told myself and my students, “You’re not training your muscles to let go. Your training your mind to let this position be okay.”
Also, this paragraph may be a little misleading:
In addition to relaxing into the stretch to improve flexibility, techniques that intend to alter or reduce the reflex which resist the stretch are often cued. Such techniques you may have heard of are reciprocal inhibition (RI) and autogenic inhibition (AI). The effect of these reflex activities on long term flexbility are questioned by many scientists [6-8], a topic for future blogs.
To my understanding, RI and AI are not techniques–they are basic neuromuscular mechanisms. The technique in studies 7-8 was PNF, and while they both question whether RI and AI are indeed the mechanisms at work in PNF, they both also seemed to conclude that PNF itself was a very effective technique for increasing both short and long term ROM, within certain parameters. In 6 the technique was static stretching, and the conclusion seemed the same. In essence, they all seemed to say, “This works, it just doesn’t work for the reasons you think it does.” Am I misreading?
Thank you again, Jules. I just did a forward bend contracting my hamstrings as you suggested. (I am generally pretty flexible in forward bends, so often do them without much engagement–and I have hurt myself as a result.) Anyway, I did the forward bend you challenged us to, and it was lovely–deeper and more comfortable in both the hams and the lower back. Aha!
Yes. RI and AI are not techniques. Yet they are often referred to as such. They are reflexes and are very real. But I don’t believe that attempting to utilize them as methods to increase flexibility (which I have heard people do) will have any substantial effect on ROM. PNF is great…but there are other mechanisms at work which we are attempting to explain.