A comparison of ultrasound and electromyography measures of force and activation to examine the mechanics of abdominal wall contraction
Introduction
In recent years, ultrasound imaging has become an increasingly popular tool to assess the contraction of the abdominal wall muscles (e.g., Ferreira et al., 2004, Hodges et al., 2003, Misuri et al., 1997, Rankin et al., 2006, Whittaker, 2008). Muscle thickness obtained from ultrasound is often interpreted as an indicator of muscle force generation. In addition, with appropriate considerations, electromyogram (EMG) amplitude can be linked to muscle force. The relationship between ultrasound measured muscle thickness and EMG-based muscle activation has not be definitively tested, but has yielded interesting findings within a limited scope of abdominal contraction types. For example, Hodges et al. (2003) documented very little change in muscle thickness beyond activations greater than 20% MVC, and both John and Beith (2007) and Coghlan et al. (2008) demonstrated decreases in external oblique (EO) thickness during activation. These discrepancies motivated this comparative study of ultrasound and EMG measures of abdominal wall muscle activation.
Proper activation and contraction of the abdominal wall is considered important for several reasons. First, abdominal muscles generate forces to produce moments in flexion, lateral bend and axial twist (Gatton et al., 2001, Marras and Mirka, 1990, McGill, 1991, McGill, 1996, Pope et al., 1986, Thelen et al., 1994). Second, properly coordinated abdominal muscle contraction is necessary to maintain a stable spinal column (Brown and Potvin, 2005, Brown et al., 2006, Cholewicki and McGill, 1996, Gardner-Morse and Stokes, 1998). Finally, reports have highlighted the functional role of the abdominal muscles in pressurizing the abdominal cavity, which also can have a stiffening effect on the lumbar spine (Cholewicki et al., 1999, Cholewicki et al., 2002, Cresswell and Thorstensson, 1989, Essendrop and Schibye, 2004). For these reasons, it is essential that assessments of abdominal muscle function and contraction be carefully considered, whether via ultrasound or EMG.
The morphology of the abdominal wall muscles creates a composite laminate-like structure. The external oblique (EO), internal oblique (IO), and transverse abdominis (TrA) are broad sheet-like muscles that overlay one another, have muscle fibres that are obliquely oriented with respect to each adjacent layer, and are tightly bound together through networks of connective tissue. These connective tissues play a mechanical role, enabling force and stiffness to be transmitted between the muscular layers (Brown and McGill, 2009), and likely influencing the resulting contraction dynamics and muscular deformations. Various approaches and magnitudes of torso contraction will differentially recruit muscles around the trunk (McGill et al., 2003), thereby affecting the force and stiffness generated in muscle synergists and antagonists, in fascial connections, and in the pressurized abdomen. Muscle thickness not only relies on a muscle’s own force generation, but also on the forces generated in neighbouring muscles, particularly when its fibre orientation is oblique to its neighbour, due to the transmittal of force via intervening connective tissues (Huijing and Baan, 2003). All of these factors play a role in determining how the abdominal muscles will shorten and thicken upon contraction, thus creating a complex network from which to assess muscle function.
In addition, as abdominal muscles shorten, the site being measured on the muscle will move to a new location within the image (or, depending upon the amount of shortening, potentially outside of the image). A majority of the research that has been conducted has employed a standardized static location within the image to measure changes in muscle thickness with contraction, thus not accounting for potential shortening of the muscle. This may lead to error in the estimation of thickness changes as the observed muscle section shortens.
Considering the aforementioned affects that abdominal muscle morphology and measurement location may have on ultrasound measures of abdominal muscle thickening, this study was designed to evaluate the concordance of conclusions about contraction dynamics obtained from both ultrasound and EMG measures.
Section snippets
Participants
Five healthy males (average/standard deviation: age = 25.2/3.8 years; height = 1.80/0.04 m; mass = 76.4/5.3 kg) volunteered from the University population. All were free from any history of chronic or acute episodes of back pain and abdominal dysfunction. Informed consent, approved by the University Office of Research Ethics, was obtained from each participant.
Data collection
Surface electrodes were placed along the line of fibres of seven muscles on the right side of the body: rectus abdominis (RA); external oblique
Comparison of ultrasound and EMG measures
The IO (Fig. 4) muscle did not demonstrate any clear relationship between ultrasound thickness change measures and EMG activation measures for the abdominal bracing and hollowing contractions, and showed even further discrepancies during the ramped moment contractions (across all contractions, r = 0.14; 95% confidence intervals: −0.09 to 0.35). Similarly, the EO muscle lacked a definitive relationship between the measures of ultrasound thickness change and EMG activation (across all contractions,
Discussion
It appears that there are very complex dynamics between abdominal wall muscles during different strategies of contraction. This is most likely due to the wall forming a mechanical composite with the fibres of one layer adhered to an adjoining layer through an intervening sheet of connective tissue. This is akin to a “plywood-like” architecture. Due to the mechanical linkage between the muscular layers, contraction in one layer may directly affect the shortening and thickening of an adjacent
Conclusions
A very complex relationship exists between muscle activation and change in muscle thickness, as the relative activation of muscles surrounding the entire torso will in part dictate the extent to which the abdominal wall muscles can shorten and thicken during different types and levels of contraction. The composite laminate nature of the abdominal wall muscles acts such that contraction in one layer will cause forces to be transmitted through the intervening connective tissue attachments to
Conflict of interest
None declared.
Acknowledgment
The authors thank the Natural Sciences and Engineering Research Council (NSERC), Canada, for financial support.
References (35)
- et al.
How the inherent stiffness of the in-vivo human trunk varies with changing magnitudes of muscular activation
Clin. Biomech.
(2008) - et al.
Constraining spine stability levels in an optimization model leads to the prediction of trunk muscle cocontraction and improved spine compression force estimates
J. Biomech.
(2005) - et al.
Mechanical stability of the in vivo lumbar spine: implications for injury and chronic low back pain
Clin. Biomech.
(1996) - et al.
Intra-abdominal pressure mechanism for stabilizing the lumbar spine
J. Biomech.
(1999) - et al.
Modelling the line of action for the oblique abdominal muscles using an elliptical torso model
J. Biomech.
(2001) - et al.
Can activity within the external abdominal oblique be measured using real-time ultrasound imaging?
Clin. Biomech.
(2007) - et al.
Sagittal plane moment arms of the female lumbar region rectus abdominis in an upright neutral torso posture
Clin. Biomech.
(2005) A revised anatomical model of the abdominal musculature for torso flexion efforts
J. Biomech.
(1996)- et al.
Correcting trunk muscle geometry obtained from MRI and CT scans of supine postures for use in standing postures
J. Biomech.
(1996) - et al.
Appropriately placed surface EMG electrodes reflect deep muscle activity (psoas, quadratus lumborum, abdominal wall) in the lumbar spine
J. Biomech.
(1996)
Coordination of muscle activity to assure stability of the lumbar spine
J. Electromyogr. Kinesiol.
The relationship between EMG and change in thickness of transversus abdominis
Clin. Biomech.
Quantitative interpretation of lumbar muscle myoelectric signals during rapid cyclic attempted trunk flexions and extensions
J. Biomech.
Regional morphology of the transversus abdominis and obliquus internus and externus abdominis muscles
Clin. Biomech.
Effects of different levels of torso coactivation on trunk muscular and kinematic responses to posteriorly applied sudden loads
Clin. Biomech.
Ultrasound imaging of the lateral abdominal wall muscles in individuals with lumbopelvic pain and signs of concurrent hypocapnia
Manual Ther.
Effects of tensioning the lumbar fasciae on segmental stiffness during flexion and extension
Spine
Cited by (80)
Dynamic-MRI quantification of abdominal wall motion and deformation during breathing and muscular contraction
2022, Computer Methods and Programs in BiomedicineCitation Excerpt :Mechanical properties of abdominal wall muscles have also been investigated in vivo during activation[12] revealing that local stiffness of the abdomen was related to muscle activity. Specific muscle activation patterns have been identified[13–15] using electromyography (EMG). A major recruitment of the lateral abdominal muscles (LM) i.e. transversus abdominis (TA), internal obliquus (IO) and external obliquus (EO) compared to rectus abdominis (RA) during coughing, voluntary abdominal contraction (Valsalva maneuver) and forced exhalation has been reported[13–15].
Structural remodelling of the lumbar multifidus, thoracolumbar fascia and lateral abdominal wall perimuscular connective tissues: A cross-sectional and comparative ultrasound study
2020, Journal of Bodywork and Movement TherapiesUse of Shear Wave Elastography to Quantify Abdominal Wall Muscular Properties in Patients With Incisional Hernia
2020, Ultrasound in Medicine and BiologyNumerical modelling of abdominal wall mechanics: The role of muscular contraction and intra-abdominal pressure
2020, Journal of the Mechanical Behavior of Biomedical MaterialsApplication of Ultrasonography in the Assessment of Abdominal and Lumbar Trunk Muscle Activity in Participants With and Without Low Back Pain: A Systematic Review
2019, Journal of Manipulative and Physiological TherapeuticsCitation Excerpt :McMeeken et al and Djordjevic et al used abdominal hollowing in supine position,22,31 whereas Hodges et al assessed abdominal muscle activity during isometric activity of all abdominal muscles (abdominal bracing) during sitting position.17 As a result of simultaneous high activation of all the abdominal muscles, several factors would restrain muscle expansion, such as increased compression forces of the adjacent muscles, stiffening of the connective tissue,24 and increased intra-abdominal pressure.23 In addition, the sitting position that was used in the study by Hodges et al17 would likely lead to the shift of abdominal contents that prevents maximum shortening of abdominal muscle (increasing muscle thickness).15
- 1
Present address: Department of Orthopaedic Surgery, University of California San Diego, San Diego, CA, USA.