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Tuesday, June 6, 2023

Decreased Recruitment of the Transverse Abdominis in Individuals with Low Back Pain

Brent Brookbush

Brent Brookbush


Research Review: Decreased recruitment of the transverse abdominis in individuals with low back pain

By Stefanie DiCarrado DPT, PT NASM CPT & CES

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

Original Citation: Hodges, P., Richardson, C. (1996). Inefficient Muscular Stabilization of the Lumbar Spine Associated With Low Back Pain: A Motor Control Evaluation of Transverse Abdominis. Spine, 21(22), 2640-2650. ARTICLE

Note the different layers of the abdominal musculature. Being the deepest layer and transversely oriented fibers provides the TVA its vertebral stabilization role.

Why is this relevant?:

Contraction of the transverse abdominis muscle (TVA) assists in lumbar stability/rigidity by limiting excessive segmental motion via increased tension in the thoracolumbar fascia, increased intra-abdominal pressure (along with the pelvic floor and diaphragm), and increased stiffness of the sacroiliac joint in conjunction with the stiff dorsal sacroiliac ligaments. This study confirms previous findings that demonstrate anticipatory firing of the TVA  in response to global movement patterns. This study also shows a lack of TVA  anticipatory firing preceding upper extremity movement in individuals with a history of low back pain. This study is highly touted for its design and use of fine-wire electromyography (EMG) to accurately describe motor recruitment in key core muscles. Based on the findings of this study (and others) it is hypothesized that this anticipatory contraction is part of a feed forward mechanism; a pre-programmed recruitment pattern to enhance postural control and stability prior to functional movement. Further, this recruitment strategy may be altered by injury, impairment, and dysfunction; resulting in latent firing, less lumbar stability and perpetuation of the cumulative injury cycle.

Special Note: There is some controversy over what this study implies (Drawing In vs Bracing, Motor Control vs. McKenzie, etc…). Regardless, of how you choose to apply the findings, this is a beautiful research study, is often cited, very well-known and it should be in your library. Even if you disagree with how it is used by the researchers themselves the findings of this study must have some impact on how each of us practice. In short, know this study!

TVA contraction offers segmental stabilization of the spine

Study Summary

Study Design Descriptive
Level of Evidence IIa: Evidence from a controlled study without randomization
Subject Demographics
  • Age: NA
  • Gender:
    • Low Back Pain (LBP) Group = 8 male; 7 female
    • Control (CON) Group = 15 age & sex matched

  • Characteristics: LBP group consisted of individuals with chronic low back pain of insidious musculoskeletal onset that required activity limitation and missed work days, and for which they had sought previous treatment.  CON group consisted of age & sex matched healthy individuals without complaint of LBP.
Outcome Measures
  • Onset of EMG activity of TVA and Lumbar Multifidi (LM) compared to global muscles: Rectus Abdominis (RA), External Obliques (EO), Internal Obliques (IO), and Anterior/Middle/Posterior Deltoid (AD, MD, PD respectively) during shoulder flexion, abduction, and extension.  Only recorded for musculature on the left side of the body.  Onset less than 50 msec after prime mover activity was considered an anticipatory response.
  • Impact of direction of upper extremity (UE) movement on muscle EMG activity
  • CON Group
    • Shoulder Flexion: TVA fired before prime mover; all other muscles fired after prime mover with no significant difference among them. EO & RA latency greater than 50 msec.
    • Shoulder Abduction: TVA & IO fired before prime mover with no significant difference between the 2. LM latency greater than 50 msec.
    • Shoulder Extension: TVA & RA fired before prime mover; IO fired shortly after prime mover.  LM latency greater than 50 msec.

  • LBP Group: no muscles fired before the prime mover with any shoulder motion.
    • Shoulder Flexion: EO activity was significantly delayed as compared to CON.  TVA activation timing was not significantly different from any other muscle.  LM onset significantly earlier than other muscles; only muscle to fire within 50 msec of prime mover activity.
    • Shoulder Abduction: LM onset earlier as compared to the CON group.  All muscles fired within 50 msec of prime mover activity.
    • Shoulder Extension: TVA onset was significantly delayed compared to IO, LM significantly delayed compared to RA and IO.  TVA &  LM latencies greater than 50 msec.

  • LM fired after the prime mover (deltoid) in both groups.
ConclusionsRegardless of arm movement direction, individuals without a history of low back pain initiate movement with an anticipatory contraction of the TVA.  A history of low back pain resulted in latent firing of the TVA during upper extremity movement patterns as well as movement specific timing reactions.  In contrast, LM seemed to have direction specificity and lack of preemptive firing under both conditions.
Conclusions of the ResearchersIn asymptomatic individuals the TVA fires before upper extremity movement, regardless of direction.  The increased latency in TVA firing, as well as a trend toward direction specific activity in those with low back pain, may demonstrates an overall error in recruitment strategy and motor control. The lack of stability before movement may put other trunk musculature  at a mechanical disadvantage, or may place greater (potentially harmful) forces on passive structures. At the time of this publication, researchers were unclear of the significance of the earlier activation of LM with shoulder abduction in the LBP group.

Notice the depth of the TVA

Review & Commentary:

Although an older study with a small sample size, the information gathered within this study provides strong evidence to support TVA activation prior to limb movement in "healthy" individuals, and a latency in those with low back pain. Researchers designed a strong methodology using fine-wire EMG, with the intent of isolating abdominal muscle activation patterns and limiting erroneous data collected from overlapping musculature. Previous studies used weight acceptance as the independent variable but in this study researchers used quick limb movement to further investigate the role of the CNS in recruiting optimal recruitment patterns. Further, this study used both unilateral and bilateral UE movement and monitored activity of larger movers of the lumbar spine to determine if anticipatory flexion, extension, and/or rotational forces of the spine were also involved in anticipating and stabilizing for the moments created by upper extremity motion. This methodology design allowed for greater observation of optimal and non-optimal motor control than previous studies involving weight acceptance.

Subject screening was quite strict. LBP participants were screened for non musculoskeletal causes which could influence data collected. Inclusion criteria included: insidious low back pain for at least 18 months of a severity requiring the subject to modify activity to include at least 3 days of missed work; having a minimum of 1 sporadic episode of varying intensity per year. Additionally, subjects must have sought previous medical treatment and/or rehabilitation for their low back pain. Subjects were excluded from the study if they demonstrated an observable spinal deformity, neurological symptoms, had a history of lumbar surgery, joint disease, or had trained the muscles in questions within 3 months prior to testing.

Researchers wisely chose two forms of EMG data collection: surface electrodes for superficial muscles (RA , deltoid, LM ) and needle electrodes for deeper muscles (TVA EO IO ). Both forms have advantages and disadvantages that are discussed later within this article. The fine wire needle electrodes were inserted using real time ultrasound imaging to ensure consistent placement within the proper muscle. The authors documented and described the needle insertion technique with sufficient detail to reproduce the study using a larger sample or more specific population. Researchers took care to monitor background noise of nearby muscles that could interfere with the readings. Background noise was low in both the CON and LBP groups which indicates the findings were not influenced by pre-existing muscle activity or erroneous data due to a low signal to noise ratio.

The authors standardized the procedure to minimize performance errors by ensuring equal weight distribution through both feet using auditory corrective cues. Subjects were instructed to relax if EMG activity rose above resting level during quiet standing. Subjects performed 10 repetitions of shoulder flexion (to 60 degrees), shoulder abduction (to 60 degrees), and shoulder extension (to 40 degrees) with a 5 minute rest between each directional session. Testing focused on speed of movement, not range, with cues provided visually and at varying times so that subject were unable to anticipate when arm movement was expected. The order in which the directional sessions were performed was also randomized.

Researchers randomly selected 5 subjects from the LBP and CON groups to test and verify limb velocity performed separately from EMG studies, which, as the researchers point out could create erroneous activity levels as limb velocity is measured by having the subjects pull a cable. However, the same 10 reps were performed as in the EMG data collection to maintain consistency. The researchers concluded that differences in limb movement velocity did not impact the results of this study as velocities were consistent across both groups.

Each subject underwent a postural evaluation due to the effect this may have on muscle activation and joint motion. Researchers measured lumbar lordosis in standing using gravity goniometers and calculated the curve using geometric equations. No significant differences were found between the two groups. The authors did not discuss specific findings nor how they related to the muscle activity detected.

The authors detailed potential limitations of this study including the lack of analysis of segmental spinal motion due to the limitation of equipment in 1996, the use of uniplaner movement patterns, the potential of cross talk with EMG studies, and the inability to locate motor points for the TVA EO IO RA . As most motion occurs in multiple planes the findings in this study may have low transference to functional tasks, however, as the study did test motion in several planes it may be possible to extrapolate the potential patterns that would result from multiplaner motion. Cross talk is a possible occurrence in all EMG studeis, but this study demonstrated consistently significant onset timings for the TVA EO IO , RA  across all subjects. Researchers found it difficult to determine the motorpoint of the TVA EO , and IO  which may have limited the ability to detect the immediate onset of muscle activation; however, needle placement was standardized implying their would have been no change in the outcome of the comparative analysis.

Further research on core muscle recruitment and the TVA  may provide a means of modeling changes in motor planning with injury, intervention to prevent injury, and potentially influence strategies for rehabilitation from injury. A follow-up study may compare the effect of various exercises designed to target the TVA  and their effect on motor unit recruitment in individuals with low back pain.

Additionally, low back pain may be caused by a variety of pathoanatomical issues such as disc protrusion, dural adhesion, facet dysfunction and instability. Each condition may create variance in motor recruitment and is worthy of further investigation.

Why is this study important?

The importance of this study lies is its ability to demonstrate the increased latency of TVA  firing in those with low back pain. Clinically, it is a common notion that postural muscles, such as the TVA , should preemptively fire to stabilize the core in anticipation of forces imparted on the kinetic chain. This study is evidence that this notion is, in fact, correct, and takes another step to identify specific muscles and examining the timing of the TVA , LM , and global trunk musculature (RA IO EO ) in relation to activity of the prime mover of shoulder motion, the deltoid, in those with low back pain.

Further, the integration of global core muscles to resist moments created by UE motion was implied as activation of the RA EO , and IO with shoulder extension would imply a neutralization of the extension moment occurring with limb movement, and early activity in the EO IO , RA , and LM with shoulder abduction helps control the resultant lateral flexion moment. These activation patterns may indicate pre-planned reactions to the perturbation introduced to the kinetic chain. The pre-activation of the TVA  regardless of the direction of limb movement is discussed by the researcher, including the hypothesis that although the TVA  is unable to resist a specific motion it is capable of increasing lumbar rigidity, enhancing stability. Individuals with LBP potentially experience edema near the spine, pain, strained ligaments, capsular compression, muscle fatigue, and non-observable postural deviations that may affect the onset timing of the muscles in question due to the "lowered excitability of the motorneuron pool" (2647).

It is notable that the LM  did not fire preemptively in either group. One possible explanation is that the lumbar LM  function only to correct lateral flexion of the spine, implying that motion of the spine must occur first. The LM did fire earlier in those with low back pain during shoulder abduction.

How does this affect practice?

This study implies that intervention for low back pain should incorporate a motor control approach, and potentially activation of the TVA . Further, conditioning of the global core musculature to resist motion may be an essential progression of a routine aimed at recovery from low back pain. For any human movement professional, the evidence presented here offers guidance in exercise selection not only for treatment of low back pain but in prevention of dysfunction through improved timing, mechanics, and internal stabilization.

How does it relate to Brookbush Institute Content?

Verbal and manual cues to "Draw-in" during all activities, and isolated activation of the TVA when an individual exhibits signs of dysfunction, are consistently used in the Brookbush Institute during rehabilitation, fitness and performance enhancement programs. The spinal stabilization provided by the TVA  is recognized throughout the predictive models of Lumbo Pelvic Hip Dysfunction , Sacroliac Joint Dysfunction , and Upper Body Dysfunction . The following videos emphasize proper technique to activate not only the TVA , but integrate TVA activation with gluteus maximus activation.

TVA Isolated Activation

TVA and Gluteus Maximus Activation and Progressions

© 2014 Brent Brookbush

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