Tuesday, January 8, 2019

The Lid to the Cylinder: Expanding Your View of Postural Stability

Effect of airway control by glottal structures on postural stability.
Massery M, Hagins M, Stafford R. Moerchen V. and Hodges PW.
J Appl Physiol. 2013;115:483-490.

If the title of this research article doesn’t grab your attention, how about the authors Massery? Hodges? Yes, please! After taking Mary Massery’s PT, DPT, DSc 3-day course, “IF YOU CAN’T BREATHE, YOU CAN’T FUNCTION” I was inspired to read one of her original papers.
Breathing, well it is exquisite. It is simple, yet so complex. It is life. It is the first thing we do and the last thing we do. As a former long-distance runner, I enjoyed the rhythmic pace and sound of my breath. These days, I enjoy walking as a moving meditation. Both of these activities promote a focus on the breath and with that, encourage us to be in the moment.

Through my studies of the Dynamic Neuromuscular Stabilization (DNS) approach with the Prague School of Rehabilitation, I have learned that intra-abdominal pressure (IAP) is an important contributor to our “integrated spinal stabilizing system” (ISSS).1 The coordination of the diaphragm and trunk muscles is essential for the simultaneous functions of breathing and postural support. The function of breathing takes precedence over postural support when the system is challenged or compromised,2 perhaps contributing to one of the many reasons why we lose this ability to perform both functions simultaneously. I have had great success with many patients, re-training this neuromuscular unit that can be conceptualized as a cylinder. In the abdominal cavity, this cylinder includes the diaphragm, the multifidi, and the abdominal and pelvic floor muscles all of which have been shown to have a role in creating and controlling appropriate IAP for spinal stabilization.3,4,5 In addition, the important element of the rib cage position, correcting for an inspiratory position if needed, is essential to establish better function of the diaphragm and thus the ISSS.6

When assessing a patient’s breathing pattern, I look for qualitative elements described by Kolar “the lower chest and abdomen expand evenly, the sternum moves ventrally, intercostal spaces widen, the lower thorax expands in width and A-P dimension, and accessory muscles are relaxed.”1 I have found that re-establishing this pattern along with a corrected inspiratory position of the rib cage if needed, is the key to improving the coordination of the diaphragm and thus the function of this complex neuromuscular unit of stabilization.

Previous research has shown decreased postural control of the lumbar spine and longer trunk muscle response times in patients with chronic low back pain,7 thus providing a good rationale to retrain the muscles that control IAP for improved function and postural support. In this recent work by Massery et al. 2013, the authors support the importance of IAP as well as intra-thoracic pressure (ITP) to maintain upright posture. Because the glottis contributes to the control ITP, this concept is further developed through this study and presents evidence to support the evaluation of glottal function when considering postural instability issues. 8
With that view, let’s move superiorly in the body from the abdomen to the thorax to investigate the findings of Massery et al. 2013.
A brief review of anatomy and function:
·      The glottis or glottic opening include the vocal folds and the space between the folds. The laryngeal muscles adjust the size of the opening depending on the need; abducts and opens for breathing (inhalation and exhalation) and adducts for voicing.9

Below is a summary of my understanding of the key points of this article (with the benefit of attending Mary Massery’s PT, DPT, DSc course) 8,13,14 and through the lens of an orthopedic physical therapist. To guide my thought process, I selected questions from “Critiquing Research Articles”, published by Flinders University in Adelaide, Australia.10,11,12

What is the aim of the study?
·      “This study aimed to investigate the effect of modulation of airway control on upright postural stability during postural perturbations”.8

What background information is provided that is relevant for this study?                                                                                              
·      Traditionally, we have looked at abdominal and erector spinae muscles when considering postural trunk control, it is also important to consider the contribution of IAP and ITP
·      Current research supports the following muscles in regulation of IAP/ITP: the diaphragm, intercostals, abdominals, pelvic floor muscles and glottal structures
·      The link between breathing and center of pressure (CoP) has been shown to be impaired in patients with low back pain (LBP)
·      Trunk muscles and the glottis have a primary role in regulation of ITP and therefore, should be considered when evaluating postural stability
·      This article identifies a gap in the literature regarding glottal function and its possible contribution to postural control

What methods were used?
·      Gentle trunk perturbations were applied to subjects in standing for the following seven conditions, and thoracic and CoP displacements were measured.

Table 1. Definitions and instructions for breathing/voicing conditions
J Appl Physiol. 2013;115:485.

Breathing Conditions
Airway flow at time of perturbation
Glottis position during perturbation
Instructions to patient
1.   Max. inhalation + breath-hold
“Take the biggest breath you can then hold your breath until the weight drops.”
2.   Ah/voicing
Partially open
“In a normal, full speaking voice, say “ah” for as long as you can until the weight drops.”
3.   Natural breathing
“Breathe normally. Do not take deep breaths. Do not take shallow breaths. Don’t hold your breath. Just breathe normally until the weight drops.”
4.   Counting out loud
Partially open
“Count out loud to seven in a normal, full speaking voice until the weight drops. Do not talk softly. Do not shout. Just use your normal full voice.”
5.   Normal exhalation + breath-hold
“Take an easy breath in. Exhale normally. Then hold your breath until the weight drops.”
6.   Normal exhalation + airway open (no breath-hold)
“Take an easy breath in. Exhale normally. Pause. Keep your airway open until the weight drops by thinking that you could exhale for a few seconds more if you needed to.”
7.   Sigh H sound
“Take a deeper breath than normal then say “ha” like a sigh. Do not push the air out. Let the air fall out like a normal sigh until the weight drops.”

What were the main findings?
·      Thorax
o   Displacement was greatest when the glottis was completely open (sigh) and thus more stable when the glottis was completely closed
·      CoP
o   Displacement was greatest (with backward perturbation) when the glottis was completely open or closed and thus more stable when the glottis was at mid-range (voicing)

What is the significance of this research?
In response to minimal trunk perturbations, thoracic and CoP strategies differed. It is well known that breath holding, theoretically creating a stiff trunk is used as a strategy for heavy lifting. However, either extreme of glottal conditions (maximum opening/closing) appears to decrease the more subtle and dynamic postural control related to CoP.
·      Therefore,
o   Maximum closure as with a breath holding strategy may be beneficial for short term tasks requiring heavy lifting (maximally stabilizing the thorax).
o   Mid-range control as with talking may be more beneficial for tasks requiring dynamic postural control (minimizing CoP displacements).

What conclusions were reached?
·      Modulation of the airway by the glottis affects balance and so may be an important concept to incorporate when working with patients with balance and/or breathing impairments.

My thoughts on integrating this information into my practice
How do I view trunk and postural stability now? In addition to muscles that regulate IAP, it now includes the upper trunk, ITP and the lid to the cylinder – the glottis. I feel that my cylinder is now complete! In my practice, I have collaborated often with several women’s health physical therapists and now, I think I need to spend some time with our speech therapy colleagues!

·      A few more thoughts:
o   I now have more strategies for my patients with balance impairments and will consider counting or voicing to promote control of the CoP as they work on postural stability.
o   I will be more aware of the connection between LBP, poor spinal stabilization, and possible balance impairments.
o   When I work with patients to improve spinal stabilization, often times they cannot coordinate both breathing and abdominal bracing at the same time. This requires more skill and coordination. A strategy to help improve this coordination by monitoring a continuous breath, is to have patients count out loud. I am now aware that with this counting strategy, the glottis is activated in mid-ranges contributing to the control of ITP/IAP and ultimately to their postural stability when I progress the challenge to more dynamic and functional positions.
o   Re-training a patient’s spinal stabilization abilities can improve pain and many functions. In addition to the patient interview and direct assessment of breathing and stabilization strategies, additional cues that guide me to address this impairment are: an inspiratory rib cage position, patients who run out of breath while talking, complaints of incontinence, abdominal and trunk skin creases, asymmetrical trunk muscle bulk, trembling muscles with supine to sit, over developed superficial muscles and now complaints of balance are all possible indicators that the spinal stabilizing system may be impaired. 

I want to thank Mary Massery, PT, DPT, DSc and her team for their exploration of the mechanics of breathing and postural stability, for contributing to my practice, and for linking multiple systems in the body enabling us to look at our patients as a whole.  

That’s all for now, in the meantime I’m keeping my glottis tuned for the next Mary Massery course and research article!

Tracey Wagner PT, DPT, OCS, FAAOMPT
Movement Links Instructor
Assistant Professor, Samuel Merritt University

Tracey Wagner is an Assistant Professor and Samuel Merritt University teaching musculoskeletal courses and is working on developing a part time clinical practice and her line of scholarship in the area of movement science. She is a DNS Certified Practitioner, as well as a Movement Links Certified Clinician and Instructor. She moved to the beautiful Bay Area after a 17-year career working for Kaiser Permanente Woodland Hills, serving there as a clinical specialist, mentor, and educator.   Tracey has been published in the Journal of Orthopaedic and Sports Physical Therapy (JOSPT) for a case report on muscle imbalances of a professional triathlete and received the California Physical Therapy Association’s 2010 Clinician Research Publication Award.



1.    Kolar P et al. Clinical Rehabilitation. 1st ed. Prague, Czech Republic: Alena Kobesvoa, Rehabilitation Prague School;2013:56-58, 275-279.
2.    Hodges PW, Heijnen I, Gandevia SC. Postural activity of the diaphragm is reduced in humans when respiratory demand increases. J Physiol. 2001;537:999-1008.
3.    Hodges PW, Eriksson AE, Shirley D, Gandevia SC. Intra-abdominal pressure increases stiffness of the lumbar spine. J Biomech. 2005;38(9):1873-1880.
4.    Hodges PW, Sapsford R, Pengel LHM. Postural and respiratory functions of the pelvic floor muscles. Neurourol Urodyn. 2007;26:362-371.
5.    Finta R, Nagy E, Bender T. The effect of diaphragm training on lumbar stabilizer muscles: a new concept for improving segmental stability I the case of low back pain. J Pain Res. 2018;(11):3031-3045.
6.    Kolar P, Sulc J, Kyncl M, et al. Postural Function of the Diaphragm in Persons With and Without Chronic Low Back Pain. J Orthop Sport Phys Ther. 2012;42(4):352-362.
7.    Radebold, Andrea, MD; Cholewicki, Jacek, PhD; Polzhofer, Gert K., BA; Greene, Hunter S., MD. Impaired postural control of the lumbar spine is associated with delayed muscle response rimes in patients with chronic idiopathic low back pain. Spine. 2001;26(7):724-730.
8.    Massery M, Hagins M, Stafford R. Moerchen V. and Hodges PW. Effect of airway control by glottal structures on postural stability. J Appl Physiol. 2013;115:483-490.
10. Student Learning Center, Flinders University, Adelaide, Australia. http://www.flinders.edu.au/slc_files/Documents/Blue%20Guides/Critiquing%20Research%20Articles.pdf
11. Ryan, F, Coughlan, M & Cronin, P 2007, ‘Step-by-step guide to critiquing research. Part 2: qualitative research’, British Journal of Nursing,, vol. 16, no. 12, pp. 738-743.
12. Stockhausen L & Conrick, M 2002, ‘Making sense of research: a guide for critiquing a paper’, Contemporary Nurse, vol. 14, no. 1, pp. 38-45.
13. Massery, M. Class notes for continuing education course: “If you can’t breathe, you can’t function”. Samuel Merritt University. August 3-5th, 2018
14. Mary Massery PT, DPT, DSc. http://www.masserypt.com

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