Posted on October 13, 2014

Story Source

By Stefanie DiCarrado DPT, PT, NASM CPT & CES

Edited by Brent Brookbush DPT, PT, MS, PES, CES, CSCS, ACSM H/FS

Original Citation: Grenier, S., McGill, S. (2007).  Quantification of lumbar stability by using 2 different abdominal activation strategies.  Archives of Physical Medicine & Rehabilitation. 88, 54-62 – ARTICLE

Forces on the lumbar spine must be mitigated by abdominal muscle support to prevent injury

Why is this relevant?:  The question of whether transverse abdominis (TVA) activation or abdominal bracing offers greater lumbar stability is a topic of much debate among human movement professionals. In this study, TVA activation is obtained via abdominal “hollowing” in which the belly button is maximally drawn to the spine.  Abdominal bracing involves an isometric co-contraction of all abdominal muscles, and is similar to how you would tighten your abs if someone were about to punch you in the gut.  This study aims to identify which technique offers the greatest lumbar stability, with and without upper extremity (UE) loading.

Study Summary

Abdominal hollowing

Review & Commentary: 

This study examines a very small sample of individuals and uses complex equations to validate findings, but provides adequate evidence to suggest that abdominal bracing provides significant stabilization to the lumbar spine with and without UE loading.

Grenier & McGill analyzed live (“in vivo”) and simulated surface EMG data and spinal kinematic (movement) data to determine muscle activity and its effect on the lumbar spine.  Surface EMG electrodes were placed on bilateral RA, internal obliques (IO),external obliques (EO), latissimus dorsi(LD), thoracic erector spinae (TES), lumbar erector spinae (LES), and LM.  The authors described the electrode placements in sufficient detail to replicate in future studies. Lumbar flexion and extension EMG data was compared to a maximal voluntary contraction (MVC) during isometric flexion/extension and reported as a percentage of the respective MVC.   A device emitting an electromagnetic field attached at the sacrum and T12 levels isolated kinematic motion in the lumbar spine (flexion, extension, lateral side-bending, and rotation).

Live data collection involved active abdominal hollowing and active abdominal bracing.  The hollowing technique required subjects to hollow their abdomen without sucking in their stomach.  It is unclear by the description how exactly to hollow one’s abdomen without sucking in the stomach, but subjects practiced until they could properly reach 20% of IO MVC (assuming synergistic contraction of the TVA) with minimal activation of EO and RA.  Bracing involved contraction of all abdominal muscles; there was no quantification of % MVC provided for bracing. Researchers monitored muscle contractions via oscillascope activity (displayed % of MVC) and ultrasound imaging (contraction = increased muscle bulk).

Subjects stood in an anatomically neutral position during testing and for 25 seconds performed 5 second intervals of the following: relaxed abdominals, hollowed stomach, relaxed abdominals, braced abdominals, and finally relaxed abdominals again.  This process was repeated three times for each of the following conditions (randomly performed): holding no weight, lifting 10kg in each hand, holding 10kg in the right hand, and holding 10kg in the left hand.

The simulations used modified EMG and kinematic data from one subject to create scenarios that the researchers could not create in the lab, namely isolated muscle contractions as their subjects were unable to perform a the isolated TVA hollowing performed during practice sessions.

• Simulations
  • Hollowing:
    • TVA/IO EMG activity adjusted to 20% MVC with RA & EO at 2% (no alterations for extensor muscles)
    • RA moment arm shortened by 5cm to mimic the decreased waist circumference that occurs during hollowing.
  • Bracing:
    • All abdominal muscle EMG activity adjusted to 20% MVC without adjusting extensor muscle.
    • Four additional scenarios in which one abdominal muscle EMG was reduced to 0% MVC and all others left at 20% MVC
    • TVA EMG adjusted to 100% while all other abdominal muscles were set to 0%

Researchers used custom stability equation with data from both the live trials and simulations.  These equations considered the summation of the passive contribution to potential energy (via intervertebral discs, ligaments, etc.) and the summation of the active contribution to potential energy (via muscles and tendons).  Authors provided several studies to validate this methodology in biomechanical and in non-biomechanical applications.  The active contribution of muscles used in the stability equations additional calculations based on a “distribution-moment muscle model” created from EMG data and muscle length from White & Panjabi (1978) (pg 57).  The model was adjusted to allow for TVAattachment and subsequent effect on the lumbar spine.

Grenier & McGill mentioned that abdominal hollowing may move the attachment of the RA closer to the spine; therefore, reducing its moment arm, potential energy, and with that, its ability to stabilize.  However, this seems to be an error in logic.  The moment arm of the rectus abdominis will always average to be from pubis to ribs 5 through 7, regardless of how the rectus abdominis may curve the force created is attempting to approximate these two points.  More important would be the relative length tension of the rectus abdominis.  In this case, cuing hollowing and/or abdominal distension may reduce force by changing the length of the rectus abdominis (RA).  It would seem to the author, that TVA inhibition along with deconditioning of all core musculature would result in a lengthened RA, more often than a shortened  RA (think pot belly’s vs washboard abs, or the relative number of posterior pelvic tilts when compared to anterior pelvic tilts).  If this is the case,TVA activation may actually improve the force production of the RA by reducing distension, shortening this muscle to its optimal length. At, this point it should also be noted that the TVA activation used in this study does not match the technique described by Richarson et. al, – drawing in the lower abdominal region, with a co-contraction of the multifidus, and maintaining the ability to breath (1).

The authors of this study acknowledge its limitations, specifically the use of surface electrodes recording IO data with assumed synergy of the TVA, testing an anticipated loading response rather than sudden loading response, and a limited population sample.  Grenier & McGill cited several sources where the TVA and the IO fire simultaneously and explained the simulations assume full TVA activation and in doing so, decrease the need for liveTVA data collection.  However, the research study would have benefited from the use of needle EMG to measure activity of the TVA directly.

Grenier & McGill acknowledged that their study examined muscle activity with a pre-planned loading strategy; therefore, the muscle reactivity may not match that of an unexpected load. They continue to state that unexpected loads may result in the TVA firing initially to provide stability prior to the onset of the global core musculature.  They also propose any delay in firing may be “mechanically insignificant” although other studies indicate otherwise (TVA Study, Latency Study) (pg 60).

The limited sample size indicates a larger study is needed to confirm results.  Further, various populations must be studied in vivo to fully understand the affects of hollowing vs bracing on lumbar stability.

The intricate equations create a complicated study that is difficult to interpret unless the reader is very familiar with physics.  This makes it all too easy for some individuals to assume the equations are accurate and appropriate, rather than critically evaluating the data.  This does not take from the brilliance of the model used, but critical evaluation of this study is a challenge due to the method used to measure data.  Although McGill has developed a systematic, mathematical approach for determining spinal stability, one must question if these equations are too standardized and assume too much about muscle alignment, compression and its contribution to stability, and how EMG % of MVC translates to force placed on the lumbar spine. The authors specifically mentioned the importance of the reader to recognize the mechanical nature of the data and that it cannot be used exclusively to dictate a rehabilitation program.

Due to the similar nature of this article with the previously posted “Drawing-in” Offers Greater SIJ Stability Than Bracing.  It is worth noting why these studies CANNOT BE COMPARED.

• The current study examined lumbar stability where as Richardson et. al. (2002) examined SIJ stability. Simply put, these articles measure different things.
• The current study used complex, custom calculations to determine kinematic perturbation; Richardson et. al. measured direct rigidity through transmission of vibration from the pelvis to sacrum.  In essence, the studies did not use the same measurement tool to validate findings.
• The hollowing technique described in this study does not match the description of the “drawing in” technique used by Richardson, Hodges and Hide (1).
• It is mentioned several times throughout this study that hollowing is a means of increasing TVA activation only, butRichardson et. al. allude to an intrinsic system of muscles including the LM, pelvic floor, diaphragm and potentiallyIO; therefore, this study may need to include these muscles in data collection for hollowing, their contribution to force on the lumbar spine, as well as their contribution to increasing intra-abdominal pressure to the data gathered on the TVA alone.
• Last, Richardson et. al. mentioned in their study that even after a 2 minute rest muscle activity remained higher for the second test.  Grenier & McGill tested bracing second in this study – this may skew their data to the benefit of bracing.  Interestingly, the data in Table 1, page 60 of this article lists the stability index values for each condition – the stability index for hollowing without holding any weight was much lower than that of bracing without holding weight (474.6+85.4 vs 511.3+39.5 respectively). However, as weight was added, the stability index increased during hollowing and surpassed that of bracing without weight.  When weight is added to the R UE, the stability index is similar for hollowing and bracing ( 533.4+57.7 vs 546.1+59.7 respectively). This may indicate hollowing, or TVA activation, may provide adequate stability with minimal loading whereas the increased stability provided by bracing may not be necessary unless the load is significant.

The conflicting information provided in this study and “Drawing-in” Offers Greater SIJ Stability Than Bracing indicates further research is needed on the role ofTVA activation (drawing in) and the affect of bracing and “drawing in” on lumbosacral stability.

Why is this study important?

This study is important because it offers a second cue for increasing lumbar stability (“bracing” versus “drawing in”), as stability unto itself, is thought to reduce the risk of low-back injury and may be important for reducing acute and chronic low back pain in a clinical setting. This study also examines the effect loading has on the lumbar spine in regard to trunk muscle activity. This study may be evidence that bracing is appropriate for higher intensity activity, as bracing increases activity and force production of trunk musculature.

How does it affect practice?

With weighted upper extremity movements, abdominal bracing may provide greater lumbar stability than drawing in alone, and should be considered when designing an exercise routine or rehabilitation program.  However, a single approach used dogmatically for all individuals is not a practical approach to exercise selection.  Grenier & McGill said it best, “In reality, a single focus on either strategy may not be optimal (or even possible) for functional tasks that show a great diversity in load and velocity.”

How does it relate to Brookbush Institute Content?

The Brookbush Institute’s main focus is to provide practical, evidence-based education in the field of human movement science (HMS).   Research assists in our search for congruence, that is, the integration of theory, research, observation, practice and outcomes in pursuit of continued advancements in HMS – but research can lead to further questions, and even debate.  The Brookbush Institute is dedicated to the integration of knowledge, not the use of one set of studies to invalidate the life’s work of another individual.  We are vehemently opposed to using research in this manner. We have far more to learn from inclusion than exclusion.  You may find this article interesting –  Just Because You’re Right, Doesn’t Make Me Wrong.

This study offers conflicting evidence that abdominal bracing provides greater lumbar stability than abdominal hollowing. Conflicting research should indicate to the reader that one study is not enough to answer this clinical question, and certainly not enough to “prove” the validity of a concept, theory or model.  A single research study can only shows a correlation between a “yes” or “no” and a single direct question (hypothesis).  A question that is often limited to one method, one population, one design, and one measurement tool.  To fully understand the effect of abdominal bracing vs TVA activation, or to provide enough support for an even larger model of motor control, lumbar stability, and/or low back pain, would require dozens, if not 100’s of  studies.

Although content and instruction by the Brookbush Institute tends to focus onTVA activation, and the “drawing in” maneuver the predictive models of postural dysfunction (UBD, LLD,LPHCD & SIJD), there is no mention of  “drawing in” and “bracing” as two opposing techniques. The Brookbush Institute classifies these activities as a progression of increasing stabilization and muscle recruitment that may serve to increase stability/rigidity of the lumbar spine.  We hope this is at least somewhat evident in the exercises used for TVA Activation, Core Strength and Subsystem Integration in both the Brookbush Institute’s “Integrated Warm-Up” and “Rehabilitation Templates”  (You can view these templates at the bottom of this article – Introduction to Postural Dysfunction)

From the article “Transverse Abdominis“:

• “In summary, neuromuscular reeducation of the intrinsic stabilization subsystem should be addressed first, followed by reeducation and conditioning of the global musculature (core subsystems), and finally integration into functional tasks.  All steps are necessary for a complete recovery from low back pain and/or the attainment of optimal performance.   “Drawing in” should be sufficient for stabilization of the lumbar spine and pelvis during most daily activity – that is activity without an added external load or significant increase in velocity.  “Bracing” is necessary during an individuals higher intensity activity – this could range from reaching over-head in an older individual, to loaded activities like carrying groceries in the middle aged and healthy, to weight lifting and sport in the athletic population.  Cue the “drawing-in” maneuver during all activities, and “bracing” when appropriate.  Even the Valsalva maneuver may be considered an appropriate progression beyond “drawing in” and “bracing” for the upper limits of individuals functional capacity (i.e 1 Rep Max).”

1. Richardson, C., Snijders, C., Hides, J., Damen, L., Pas, M., Storm, J. (2002) The Relation Between the Transversus Abdominis Muscles, Sacroiliac Joint Mechanics, and Low Back Pain. Spine. 27 (4), 399-405

2. White AA, Panjabi M. (1978) Clinical biomechanics of the spine. Toronto: Lippincott.

© 2014 Brent Brookbush