Abdominal muscle activation increases lumbar spinal stability: Analysis of contributions of different muscle groups

Department of Orthopaedics and Rehabilitation, University of Vermont, Burlington, USA.
Clinical biomechanics (Bristol, Avon) (Impact Factor: 1.97). 05/2011; 26(8):797-803. DOI: 10.1016/j.clinbiomech.2011.04.006
Source: PubMed


Antagonistic activation of abdominal muscles and increased intra-abdominal pressure are associated with both spinal unloading and spinal stabilization. Rehabilitation regimens have been proposed to improve spinal stability via selective recruitment of certain trunk muscle groups. This biomechanical analytical study addressed whether lumbar spinal stability is increased by such selective activation.
The biomechanical model included anatomically realistic three-layers of curved abdominal musculature, rectus abdominis and 77 symmetrical pairs of dorsal muscles. The muscle activations were calculated with the model loaded with either flexion, extension, lateral bending or axial rotation moments up to 60 Nm, along with intra-abdominal pressure up to 5 or 10 kPa (37.5 or 75 mm Hg) and partial bodyweight. After solving for muscle forces, a buckling analysis quantified spinal stability. Subsequently, different patterns of muscle activation were studied by forcing activation of selected abdominal muscles to at least 10% or 20% of maximum.
Spinal stability increased by an average factor of 1.8 with doubling of intra-abdominal pressure. Forcing at least 10% activation of obliques or transversus abdominis muscles increased stability slightly for efforts other than flexion, but forcing at least 20% activation generally did not produce further increase in stability. Forced activation of rectus abdominis did not increase stability.
Based on analytical predictions, the degree of stability was not substantially influenced by selective forcing of muscle activation. This casts doubt on the supposed mechanism of action of specific abdominal muscle exercise regimens that have been proposed for low back pain rehabilitation.

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Available from: Sharon Henry, Oct 28, 2015
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    • "Sounding somewhat like a paradox, the question is vital: why should core stability be improved in chronic LBP sufferers if there is no strong evidence of tissue damage or structural body changes due to instability? And even if each case of chronic LBP was characterized by instability, the isolated training of only deep muscles should seem to be insufficient (Stokes et al., 2011; Gnat et al., 2013). Addressing this issue, a Canada-based research group has adopted a contrasting approach, which highlights the prominent role of more superficial muscles i.e. obliqus internus and externus abdominis and quadratus lumborum (McGill, 2002; Grenier and McGill, 2007; Brown and McGill, 2009) in the lumbar spine stability processes. "
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    ABSTRACT: Background: Chronic low back pain (LBP) is the most common cause of disability, hence multiple attempts have been undertaken to develop therapeutic strategies aimed at addressing the issue. The most commonly used strategies include motor control exercises of deep core muscles that stabilize the lower back. However, on the practical side, they require application of special devices, such as ultrasonography or electromyography as well as instructions and support provided by trained personnel. Despite the lack of high-quality empirical evidence, these exercises are extensively used in clinical practice. Narrative Review: The vast body of literature collected suggests that the cause of chronic LBP should be sought in the structural and functional alterations within different levels of the central nervous system. These alterations and maladaptations apply to both the molecular and tissue levels. Nevertheless, successful treatment of these changes is currently possible due to an affordable, cognitive therapeutic approach. It encompasses a number of strategies that aim to restore the normal function of the nervous system using brain plasticity processes. These include graded motor imagery, mirror therapy, graded exposure, pain education, sensory training and pain coping strategies. Conclusions: Lack of clear advantage in the application of the core stability exercises over other, potentially cheaper alternatives, implies a shift-paradigm from the existing bio-medical model of chronic LBP treatment towards modern cognitive approaches. As results of numerous studies confirm the validity of the approach aimed at restoring the structure and function of the central nervous system in contrast to the still common concept of treatment of the peripheral tissues of the body, more rigorous systematic reviews and meta-analysis are required. Evidence from this kind of evaluation may contribute to the shift in current beliefs regarding the treatment of chronic LBP.
    Full-text · Article · Jun 2015
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    • "For the lateral abdominal muscles, no significant difference was found in muscle thickness ratio depending on the selected angles (30 o , 60 o , 90 o ) during the two exercises . We considered that lateral abdominal muscles might mainly act on the maintenance of trunk stability instead of the exercise motion itself, leading to the results differing from those of the RA muscle[6,12,16]. In addition, we thought that there might be differences in muscle activities depending on the angles when doing the exercises, including trunk rotation or lateral bending motions; it is considered that additional studies are needed to be conducted in the future. "
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    ABSTRACT: Objective: To investigate the changes of activation of the abdominal muscles depending on exercise angles and whether the activation of rectus abdominis differs according to the location, during curl up and leg raise exercises, by measuring the thickness ratio of abdominal muscles using ultrasonography. Methods: We examined 30 normal adults without musculoskeletal problems. Muscle thickness was measured in the upper rectus abdominis (URA), lower rectus abdominis (LRA), obliquus externus (EO), obliquus internus (IO), and transversus abdominis (TrA), at pre-determined angles (30°, 60°, 90°) and additionally at the resting angle (0°). Muscle thickness ratio was calculated by dividing the resting (0°) thickness for each angle, and was used as reflection of muscle activity. Results: The muscle thickness ratio was significantly different depending on the angles in URA and LRA. For curl up-URA p=0 (30°<60°), p=0 (60°>90°), p=0.44 (30°<90°) and LRA p=0.01 (30°<60°), p=0 (60°>90°), p=0.44 (30°>90°), respectively, by one-way ANOVA test-and for leg raise-URA p=0 (30°<60°), p=0 (60°<90°), p=0 (30°<90°) and LRA p=0.01 (30°<60°), p=0 (60°<90°), p=0 (30°<90°), respectively, by one-way ANOVA test-exercises, but not in the lateral abdominal muscles (EO, IO, and TrA). Also, there was no significant difference in the muscle thickness ratio of URA and LRA during both exercises. In the aspect of muscle activity, there was significant difference in the activation of RA muscle by selected angles, but not according to location during both exercises. Conclusion: According to this study, exercise angle is thought to be an important contributing factor for strengthening of RA muscle; however, both the exercises are thought to have no property of strengthening RA muscle selectively based on the location.
    Full-text · Article · Jan 2015 · Annals of Rehabilitation Medicine
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    • "It is believed that trunk muscle weakness is an important risk factor for this disorder [5]. Additionally, the abnormal patterns of muscle activity could affect the biomechanics of spinal movements and result in mechanically induced pain [6–8]. "
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    ABSTRACT: Objective: To evaluate trunk muscle strength and EMG activation during isokinetic axial rotation at different angular velocities. Method: Twenty-four healthy young men performed isokinetic axial rotation in right and left directions at 30, 60, and 120 degrees per second angular velocity. Simultaneously, surface EMG was recorded on external oblique (EO), internal oblique (IO), and latissimus dorsi (LD) bilaterally. Results: In each direction, with the increase of angular velocity, peak torque decreased, whereas peak power increased. During isokinetic axial rotation, contralateral EO as well as ipsilateral IO and LD acted as primary agonists, whereas, ipsilateral EO as well as contralateral IO and LD acted as primary antagonistic muscles. For each primary agonist, the root mean square values decreased with the increase of angular velocity. Antagonist coactiviation was observed at each velocity; however, it appears to be higher with the increase of angular velocity. Conclusion: Our results suggest that velocity of rotation has great impact on the axial rotation torque and EMG activity. An inverse relationship of angular velocity was suggested with the axial rotation torque as well as root mean square value of individual trunk muscle. In addition, higher velocity is associated with higher coactivation of antagonist, leading to a decrease in torque with the increase of velocity.
    Full-text · Article · Apr 2014
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