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On the role of transversus abdominis in trunk motor control
Örebro University, School of Health and Medical Sciences.ORCID iD: 0000-0003-3474-3200
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

All trunk muscles are important contributors to spine stability. However, the deepest abdominal muscle, transversus abdominis (TrA), with its characteristically horizontal fibre orientation seems to serve a unique function in trunk motor control. The main mechanical role of TrA is believed to be to contribute to vertebral alignment during imposed moments on the trunk, executed mainly via either regulating the pressure level within the abdominal cavity and/or transmit forces to the spine via the thoracolumbar fascia. However, the complete function of TrA and what factors affect its activation are still not fully understood. The purpose of the present thesis was to investigate the role of TrA in trunk motor control, specifically in relation to the presence or absence of postural demand on the trunk.

The timing and magnitude of TrA activation were investigated, in relation to other trunk muscles, with intramuscular fine-wire electrodes in different loading situations and body positions with varying postural demand.

In a side-lying position, with no postural demand of keeping the trunk upright, the activation of TrA was delayed relative the superficial abdominal muscles compared to previous experiments performed in a standing position. The timing and magnitude of activation of TrA did not depend upon the direction of perturbation. In the standing position, different static arm positions revealed that the activation of TrA co-varied with variations in the degree of postural demand on the trunk and also the imposed moments, regardless of moment direction. Finally, a study on rapid arm flexion movements confirmed that TrA is part of the pre-programmed anticipatory response in advance of known perturbations. The activation magnitude of TrA was the same regardless if the arm movement induced flexion or extension  moments on the trunk.

In conclusion, the activation of TrA is associated with the upright postural demand on the trunk and with balancing imposed moments acting on the spine, regardless their direction. The findings are in support of the beliefs that TrA act as a general, direction non specific, stabilizer of the lumbar spine.

Place, publisher, year, edition, pages
Örebro: Örebro universitet , 2011. , 67 p.
Series
Örebro Studies in Medicine, ISSN 1652-4063 ; 54
Keyword [en]
transversus abdominis, trunk muscles, EMG, intramuscular, IAP, motor control, postural control, spine stability, postural demand
National Category
Medical and Health Sciences
Research subject
Medicine
Identifiers
URN: urn:nbn:se:oru:diva-15047ISBN: 978-91-7668-796-3OAI: oai:DiVA.org:oru-15047DiVA: diva2:405950
Public defence
2011-05-20, Wilandersalen, Universitetssjukhuset, Örebro, 09:00 (Swedish)
Opponent
Supervisors
Available from: 2011-03-24 Created: 2011-03-24 Last updated: 2016-12-02Bibliographically approved
List of papers
1. Trunk muscle coordination in reaction to load-release in a position without vertical postural demand
Open this publication in new window or tab >>Trunk muscle coordination in reaction to load-release in a position without vertical postural demand
2008 (English)In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 185, no 3, 383-390 p.Article in journal (Refereed) Published
Abstract [en]

The aim of this study was to investigate the coordination between the innermost muscle layer of the ventro-lateral abdominal wall, the transversus abdominis (TrA), and other trunk muscles, in reaction to a load-release without the postural demand of keeping the trunk upright. Eleven healthy male volunteers participated. Intramuscular fine-wire electromyography (EMG) was obtained bilaterally from the TrA, rectus abdominis (RA), obliquus externus (OE) and erector spinae (ES) muscles. The subjects lay on their right side on a horizontal swivel-table with immobilized pelvis and lower limbs and with the trunk strapped to a movable platform allowing for trunk flexion and extension. Subjects maintained trunk flexion or extension at different force levels against a static resistance, which was suddenly released. They were instructed to resume the start position as fast as possible. EMG signals were analysed with respect to amplitude and timing of muscle activation. Following released static flexion, TrA increased its activity in synergy with ES. Also in released static extension, TrA increased its activity, but now in synergy with RA and OE. The direction-independent activation of TrA indicates a role of this muscle in controlling inter-segmental movements of the lumbar spine. This function was not accompanied by an early activation of TrA as has been shown previously for trunk perturbations in standing, i.e. a situation with an additional demand of maintaining the trunk posture upright against gravity.

National Category
Medical and Health Sciences
Research subject
Medicine
Identifiers
urn:nbn:se:oru:diva-15119 (URN)10.1007/s00221-007-1159-x (DOI)17957362 (PubMedID)
Available from: 2011-03-28 Created: 2011-03-28 Last updated: 2016-12-02Bibliographically approved
2. Trunk muscle reactions to sudden unexpected and expected perturbations in the absence of upright postural demand
Open this publication in new window or tab >>Trunk muscle reactions to sudden unexpected and expected perturbations in the absence of upright postural demand
2009 (English)In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 196, no 3, 385-392 p.Article in journal (Refereed) Published
Abstract [en]

The aim was to increase the understanding of the multifunctional role of the trunk muscles in spine control, particularly transversus abdominis (TrA). In 11 healthy males, intramuscular fine-wire electromyography (EMG) was obtained bilaterally from TrA, obliquus externus (OE), rectus abdominis (RA) and erector spinae (ES). The subjects lay on their right side on a horizontal swivel-table with immobilized pelvis and lower limbs and the trunk strapped to a movable platform. Unexpected or expected release of loads attached to the table by steel cables produced a perturbation inducing either trunk flexion or extension. The timing and the amplitude of activation of TrA were independent of direction of induced trunk movement. Furthermore, timing of TrA activation was simultaneous to or later than that of the more superficial abdominal muscles. Expectation of the perturbation caused a general shortening of onset latencies. The results indicate a direction independent function of TrA in lumbar spine control. Balancing the trunk vertically appears to add specific demands, since the recruitment of TrA in relation to the other abdominal muscles differed from earlier experiments in standing.

Place, publisher, year, edition, pages
Berlin: Springer, 2009
National Category
Medical and Health Sciences
Research subject
Medicine
Identifiers
urn:nbn:se:oru:diva-15118 (URN)10.1007/s00221-009-1860-z (DOI)19488742 (PubMedID)
Available from: 2011-03-28 Created: 2011-03-28 Last updated: 2016-12-02Bibliographically approved
3. Activation of transversus abdominis varies with postural demand in standing
Open this publication in new window or tab >>Activation of transversus abdominis varies with postural demand in standing
2011 (English)In: Gait & Posture, ISSN 0966-6362, E-ISSN 1879-2219, Vol. 33, no 3, 473-477 p.Article in journal (Refereed) Published
Abstract [en]

Transversus abdominis (TrA) is a multifunctional muscle, being involved in pressure regulation within the abdominal cavity and thereby in direction independent stabilization of the spine and resistance to imposed trunk flexion moments. Indirect evidence suggests a role of TrA also in postural control of the erect human trunk. The main purpose here was to investigate if the magnitude of TrA activation is related to postural demand. Eleven healthy males performed seven different symmetrical static bilateral arm positions holding 3kg in each hand. The arm positions were selected to systematically vary the height of the centre of mass (COM) keeping imposed moments constant and vice versa. EMG was recorded bilaterally with fine-wire intramuscular electrodes from TrA and obliquus internus (OI) and with surface electrodes from rectus abdominis (RA) and erector spinae (ES). Intra-abdominal pressure (IAP) was measured via a pressure transducer in the gastric ventricle. TrA was the only muscle that displayed activation co-varying with the vertical position of the COM. Further, TrA activation increased, together with IAP and ES activation, with imposed flexion moment, i.e. with arms extended horizontally forward. In contrast to OI, RA and ES, TrA activation was independent of the direction of the imposed moment (arms held inclined forward or backward). In conclusion, TrA activation level is uniquely associated with increased postural demand caused by elevated COM. Also, TrA appears to assist in counteracting trunk flexion via increased IAP, and contribute to general spine stabilization when the trunk is exposed to moderate flexion and extension moments.

Place, publisher, year, edition, pages
Amsterdam: Elsevier, 2011
National Category
Medical and Health Sciences
Research subject
Medicine
Identifiers
urn:nbn:se:oru:diva-15117 (URN)10.1016/j.gaitpost.2010.12.028 (DOI)21269831 (PubMedID)
Available from: 2011-03-28 Created: 2011-03-28 Last updated: 2016-12-02Bibliographically approved
4. Trunk muscle activation at the initiation and breaking of bilateral arm flexion movements of different amplitudes
Open this publication in new window or tab >>Trunk muscle activation at the initiation and breaking of bilateral arm flexion movements of different amplitudes
2011 (English)Manuscript (preprint) (Other academic)
National Category
Medical and Health Sciences
Research subject
Medicine
Identifiers
urn:nbn:se:oru:diva-15125 (URN)
Available from: 2011-03-28 Created: 2011-03-28 Last updated: 2016-12-02Bibliographically approved

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