Elsevier

Manual Therapy

Volume 19, Issue 6, December 2014, Pages 534-540
Manual Therapy

Original article
Individuals with chronic low back pain do not modulate the level of transversus abdominis muscle contraction across different postures

https://doi.org/10.1016/j.math.2014.05.010Get rights and content

Abstract

The aim of this study was to evaluate the thickness of the transversus abdominis (TrA) muscle in three basic postures in subjects with and without chronic low back pain. Subjects were classified into a chronic low back pain group (n = 27) and a healthy control group (n = 23). The thickness of the TrA muscle was measured at rest and during the abdominal drawing-in manoeuvre (ADIM) in supine, sitting and standing postures using B-mode ultrasound imaging. Contraction ratio (TrA thickness during the ADIM/TrA thickness at rest) was calculated for each posture. At rest, the TrA thickness in the sitting and standing postures was significantly greater than in the supine posture (p < 0.017) in the control group, but similar in all three postures in the low back pain group. TrA thickness was similar in the low back pain and control group in all three postures. During the ADIM, TrA thickness was significantly greater in the control group than in the chronic low back pain group in all three postures. The contraction ratio was also significantly higher in the control group than in the chronic low back pain group in all three postures. These results indicate that the automatic postural contraction of the TrA observed in the control subjects in the sitting and standing postures was not demonstrated in subjects with chronic low back pain. The present study revealed the one aspect of different response of the TrA muscle to changing posture between two groups.

Introduction

Chronic low back pain (LBP) is defined as pain and/or disability that persists for more than 3 months without a clear neurological finding (van Tulder et al., 2002). Approximately 60–80% of the population in many countries is afflicted with LBP at least once in their lifetime (Manchikanti, 2000, Ihlebaek et al., 2006).

Previously, many prospective studies have revealed that there were multiple factors underlying the development of LBP. These various risk factors can be classified into three main categories: biomechanical (Marras et al., 2000), psychological (Bigos et al., 1992) and personal (Biering-Sorensen, 1984). Cholewicki et al. (2005) concluded that the delayed muscle reflex response significantly increases the odds of sustaining a low back injury (LBI), and these delayed latencies appear to be a preexisting risk factor, and are not the effect of a LBI. Although there are numerous factors that affect the development of LBP, the dysfunction of the abdominal and back muscles that control the spine is one of them (Panjabi, 1992, Richardson and Jull, 1995, O'Sullivan et al., 1997, Hides et al., 2001). There is considerable evidence that these deep trunk muscles play an important role in trunk stability. For example, transversus abdominis (TrA) muscle activation preceded rapid movement of the upper and lower limbs, and the TrA was activated independently from the other trunk muscles to increase the stability of the spine in preparation for sudden postural disturbances (Hodges and Richardson, 1997, Hodges and Richardson, 1998, Hodges and Richardson, 1999). In addition, bilateral activation of the TrA can increase the tension of the thoracolumbar fascia (Barker et al., 2006), increase intra-abdominal pressure (Hodges et al., 2003a, Hodges et al., 2001, Hodges et al., 2005), and compress the sacroiliac joint (Richardson et al., 2002).

Several studies have reported that changes in the activity of deep trunk muscles that control the intersegmental stability of the spine, such as the lumbar multifidus and TrA, are associated with LBP (Hodges and Richardson, 1996, Ferreira et al., 2004, Hides et al., 2008). Hodges and Richardson (1998) reported that the onset of the TrA activity was later in subjects with LBP than in the control subjects without LBP, and Kiesel et al. (2008) reported that experimentally induced pain decreased the activity of the TrA muscle. This indicates that there is a pain-related change in the activation of the TrA muscle. Additionally, Critchley and Coutts (2002) demonstrated that thickness of the TrA muscle during the abdominal drawing-in manoeuvre (ADIM) was significantly lower in subjects with chronic LBP than in the control subjects without LBP. The ADIM involves a voluntary contraction of the TrA muscle, and has been widely used to assess the TrA muscle function in clinical practice and as a component of LBP treatment (Richardson et al., 1999).

The TrA muscle also contracts automatically during movements of the limbs that involve a change in posture, such as an active straight leg raise. These contractions of the TrA muscle do not have a conscious element, and this automatic activation of deep trunk muscles is a mechanism to protect the lumbar spine (Hodges and Moseley, 2003b). For example, activity of the internal oblique (IO) and lumbar multifidus muscles was lower in poor postures, such as a slump sitting and sway standing, compared to erect sitting and standing (Snijders et al., 1995, O'Sullivan et al., 2002, O'Sullivan et al., 2007). The increase in the thickness of deep abdominal muscles, namely the TrA and IO, during the active straight leg raise test was small in the subjects with unilateral lumbopelvic pain (Teyhen et al., 2009), which may suggest that the protective mechanism is not functioning normally in individuals with pain. However, Rasouli et al. (2011) reported that no significant difference was found between healthy individuals and LBP patients in the ultrasound measurement of the TrA thickness in subjects in the relaxed sitting position on a chair with both feet on the ground. They explained that these findings indicate that the difference in the percentage of the thickness change in the TrA muscle between subjects with and without LBP increased as the stability of the sitting position decreased. Although it is not known whether there is actually a difference in the stability level, their study was the first investigation to collectively assess variation in thickness of the deep abdominal muscles (which can be associated with variation in muscle activity) in sitting positions with different stability levels in patients with chronic LBP and to compared them to those without LBP using ultrasound measurement. Although there have been several investigations of the change in thickness of the TrA muscle during the ADIM in subjects with LBP, there have been few investigations of the activation of the TrA muscle during automatic postural contractions.

Measurement of deep abdominal muscle activity has typically been performed using fine-wire electromyography (EMG) or magnetic resonance imaging (MRI) (Hodges and Richardson, 1996, Hodges and Richardson, 1997, Hodges and Gandevia, 2000, Saunders et al., 2004, Hides et al., 2006). However, these techniques are invasive and costly to use in laboratory or clinical practice. Ultrasound imaging is an alternative method that is now widely used for the measurement of trunk muscle activity. Ultrasound imaging is noninvasive, simple to use, and can record a change in the shape of even deep trunk muscles. In addition, ultrasound imaging can be used to provide clinical biofeedback of abdominal muscle activation for subjects with chronic LBP (Goldby et al., 2006). Estimates of muscle activity obtained using ultrasound imaging correlated well with results obtained by fine-wire EMG for contractions of the TrA less than 12% of maximal voluntary contraction and contractions of the IO less than 22% of maximal voluntary contraction (Hodges et al., 2003c). McMeeken et al. (2004) found good to high correlation between the needle EMG recordings of the TrA and ultrasound changes in thickness of the muscle at all activity level, and correlated well with an MRI measurement, with intraclass correlation coefficients (ICCs) from 0.78 to 0.95 (Hides et al., 2006). Ferreira et al. (2011) concluded that ultrasound measures of deep trunk function during isometric low load tasks is a valid discriminative tool in LBP but highly dependent on operator's level of training. With changes in posture, changes in muscle thickness may be associated with changes in muscle activation, but may also reflect other variables such as intra-abdominal pressure, contraction of adjacent muscles and transducer orientation during relative movement of muscle fibres. Observed changes in muscle thickness may relate to activation levels, but intramuscular EMG would be needed to be certain whether the changes in muscle morphology do reflect activity levels.

Although changes in the thickness of the TrA and other deep abdominal muscles have been documented during tasks that involve voluntary contractions, changes in the thickness of the TrA during automatic postural contractions remain unclear. Therefore, the purpose of this study was to quantify the TrA thickness in voluntary and automatic postural contractions in subjects with and without LBP.

Section snippets

Subjects

Twenty seven subjects with chronic LBP (LBP group) and 23 subjects without chronic LBP (control group) were recruited to participate in this study. The mean ± SD age, height, and weight of subjects in the LBP group was 20.8 ± 1.1 years, 163.8 ± 9.2 cm, 57.0 ± 7.5 kg respectively, and of subjects in the control group was 20.6 ± 1.1 years, 162.5 ± 6.5 cm, 56.4 ± 6.3 kg, respectively. Subjects were excluded from the control group if they had a history of LBP, any neurologic disorder, or pain of

Results

The demographics of the LBP and control groups are summarised in Table 1. There was no statistically significant difference in age, height or weight between the two groups, but there was significant difference in ODI score (p < 0.05). The ICC3,2 was greater than 0.95 (excellent) for repeat ultrasound measurements of the TrA muscle during all tested positions. This indicates that there was a high intra-rater reliability for the measurements (Table 2). Likewise, the SEMs and MDC showed the

Discussion

The present study showed that the measurement of the TrA thickness using ultrasound imaging had high intra-rater reliability regardless of the posture. Previous studies that have investigated intra-rater reliability have reported an ICC of 0.98–0.99 for a supine posture (Rankin et al., 2006), 0.97–0.99 for a sitting posture (Ainscough-Potts et al., 2006), 0.88 for a standing posture (Bunce et al., 2002), and 0.88 during walking (Bunce et al., 2002). In this study, the ICC ranged from 0.94 to

Conclusion

The present study used ultrasound imaging to investigate the TrA thickness during voluntary and automatic postural muscle contractions in subjects with and without LBP. The results revealed that the TrA thickness increased when posture was changed from supine crook-lying to sitting or standing in the control subjects without LBP, but that this response was not present in the subjects with LBP. Additionally, during voluntary contractions in the ADIM, the TrA thickness was lower in the LBP group

Acknowledgements

The authors special thank all study subjects, and the physiotherapist, Yukina Sado for her assistance with this present study.

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