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Magnetic resonance imaging assessment of regional abdominal muscle function in elite AFL players with and without low back pain
Manual Therapy 16 (2011) 279e284
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Manual Therapy journal homepage: www.elsevier.com/math
Original article
Magnetic resonance imaging assessment of regional abdominal muscle function in elite AFL players with and without low back pain Julie Hides a, c, *, Brita Hughes b, Warren Stanton a, c a
School of Physiotherapy, Australian Catholic University, McAuley at Banyo, Qld 4014, Australia The University of Queensland, School of Health and Rehabilitation Sciences, Division of Physiotherapy, Brisbane, Australia c Mater Back Stability Clinic, Mater Health Services, South Brisbane, Queensland 4101, Australia b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 29 April 2010 Received in revised form 12 November 2010 Accepted 19 November 2010
Changes in the motor control of trunk muscles have been identified in people with low back pain (LBP) including elite football players. Previous research has found functional differences in the anatomical regions of abdominal muscles; however, this has not been examined in football players with LBP. The aim of this study was to investigate if the ability to draw-in the abdominal wall is altered among football players with LBP, and to determine if there are functional differences between the middle and lower abdominal regions in participants with and without LBP. Forty-three elite Australian Football League players were imaged using magnetic resonance imaging (MRI) as they drew in their abdominal walls, and the trunk cross-sectional area (CSA) was measured in relaxed and contracted states. At the lower region, participants with LBP (1.1%) reduced their trunk CSA to a lesser extent than those without LBP (3.2%) (P ¼ 0.018). The results also showed that the draw-in of the abdominal wall was smaller in Region 1 (8.8%) compared to Region 2 (16.0%) and Region 3 (19.7%) (P < 0.001). This study provides evidence of regional differences in motor control and altered control of the lower region in participants with LBP. This may direct physiotherapists, especially those treating athletes, to focus on the lower abdominal region in those with LBP. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: Transversus abdominis muscle Low back pain Imaging Football
1. Introduction The incidence of low back pain (LBP) for different sports depends on the physical demands and skill sets required. Australian Rules Football (AFL) involves a combination of repetitive, highintensity activities such as kicking, sprinting and jumping which are conducive to higher injury rates compared with other sports (Seward et al., 1993; Hoskins and Pollard, 2003; Braham et al., 2004; Wilson et al., 2007). A better understanding of the function of the abdominal muscles, which have been shown to protect and support the lumbo-pelvic region (Snijders et al., 1995; Richardson et al., 2002; Hodges et al., 2003, 2005; Barker et al., 2006), may lead to a reduction in injury rates and prevalence of LBP. Although all abdominal muscles contribute to the control of the spine and pelvis, there has been a focus by researchers and clinicians alike on the function of the deepest abdominal muscle, the transversus abdominis (TrA). There is anatomical evidence that the TrA muscle can be divided into three distinct regions; the upper * Corresponding author. School of Physiotherapy, Australian Catholic University, McAuley at Banyo, Qld 4014, Australia. Tel.: þ61 7 36237530; fax: þ61 7 36237650. E-mail address: [email protected] (J. Hides). 1356-689X/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.math.2010.11.009
(superior to the 11th costal cartilage), middle (between the 11th costal cartilage and the iliac crest) and lower regions (inferior to the iliac crest and L4-5 disc) (Urquhart et al., 2005a). Intramuscular septas separating the regions of the TrA muscle have been found and these are hypothesised to prevent transmission of force allowing functionally independent regions of the muscle (Urquhart et al., 2005a). When the TrA muscle contracts bilaterally, it reduces the circumference and flattens the abdominal wall in the lower region to increase the intra-abdominal pressure and tensions the thoracolumbar and anterior fascias (Cresswell et al., 1992; Snijders et al., 1995; Hodges, 1999). While there has been considerable debate regarding the contribution of the TrA muscle to control of the lumbar spine and pelvis (McGill, 2002; Allison and Morris, 2008a; Allison et al., 2008b; Hodges, 2008), it has been argued that the TrA muscle may primarily act via modulation of intra-abdominal pressure, fascial tension and compression of the sacro-iliac joints (Cresswell et al., 1992; Snijders et al., 1995; Hodges, 1999). Clinical muscle testing of the TrA muscle has been based on its anatomical structure and horizontal fibre arrangement. Two muscle tests include observation of the abdominal wall during either a voluntary ‘drawing-in’ of the abdominal wall (Richardson and Jull, 1995), or by using automatic responses of the muscle to
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expiration (Lacôte et al., 1987). The concentric contraction of the bilateral muscle bellies of the TrA during this ‘draw-in’ manoeuvre has been viewed using ultrasound imaging and Magnetic Resonance Imaging (MRI) (Hides et al., 1998; Hides et al., 2006). Among asymptomatic subjects (Hides et al., 2006), the action of drawing-in the abdominal wall resulted in thickening of the TrA muscle and the internal oblique muscles, slide of the anterior abdominal fascia and a decrease in cross-sectional area (CSA) of the trunk (obtained by measuring around the perimeter of the whole abdominal wall). A reduction of the circumference of the abdominal wall and flattening of the anterior abdominal wall (due to the anterior abdominal wall moving in a posterior direction) is in agreement with anatomical studies (Barker et al., 2004, 2006). MRI has been used to demonstrate differences in ability to perform the drawing-in manoeuvre in subjects with a history of chronic LBP, elite AFL players and cricketers with current LBP (Richardson et al., 2004; Hides et al., 2008, 2010a). Some subjects with LBP were shown to be less able to decrease the CSA of their trunk while some subjects were not able to decrease their trunk CSA when performing the draw-in manoeuvre (Richardson et al., 2004; Hides et al., 2008, 2010a). In these cases, while attempting to draw in the abdominal wall, there was increased thickness in the oblique abdominal muscles and bulging of the abdominal wall, which resulted in an increase in the trunk CSA (Hides et al., 2010a). While these studies have provided useful information, MRI measures were conducted at only one level of the trunk located in the middle region of the abdominal wall. As it has been proposed that the TrA muscle can be divided into three functionally different regions, it may be important to conduct these same measurements at multiple levels and at different regions. The aims of this research project were to: 1) compare the ability to draw-in the abdominal wall between participants with and without LBP, 2) examine the regional differences between the lower and middle regions of the TrA muscle in performance of the abdominal draw-in manoeuvre, and 3) determine whether those with LBP are more likely to increase rather than decrease the trunk CSA when attempting to draw-in the abdomen, compared to participants without LBP. 2. Methods 2.1. Participants Forty-three professional male AFL players aged from 18 to 31 years participated in the study. The mean (SD) of participant’s age, height and weight were 22.8(3.7) years, 188.5(7.1) cm and 88.2 (6.5) kg respectively. Participants in the study provided written informed consent and the study was approved by the institutional ethics committee. 2.2. Procedures Participants underwent a clinical musculoskeletal assessment, completed a questionnaire and received an MRI assessment in a hospital setting. An experienced physiotherapist assessed all participants (patient interview and physical examination) to determine the presence of current or previous non-specific LBP. Non-specific LBP was defined as pain localised below the line of the twelfth rib and above the inferior gluteal fold. Participants with current LBP marked the location of their pain on a body chart and rated their pain intensity from 0 to 10 on a Visual Analogue Scale (VAS). Participants with current and/or a history of LBP also completed a questionnaire which included questions about previous injuries to the lumbo-pelvic region, treatment received and history of LBP. Based on the results of the assessment
participants were allocated into 1 of 4 ‘LBP groups’; no current LBP and no history of LBP (n ¼ 19), no current LBP with a history of LBP (n ¼ 8), current LBP and no history of LBP (n ¼ 4) and current LBP and a history of LBP (n ¼ 12). Due to relatively small numbers of participants in these groups they were recoded into 2 groups; No LBP ¼ No current or history of LBP (n ¼ 19) and LBP ¼ Current LBP and/or a history of LBP (n ¼ 24).
2.3. MRI assessment Participants were screened by a medical practitioner before assessment. MRI was used to acquire images of the abdomen in both relaxed and contracted states. Participants were positioned on the MRI table in a supine position with their knees resting on a small foam wedge. The participants were instructed to breathe in, then out and hold their breath at mid-expiration. A relaxed muscle image was captured to minimise image artefacts due to tissue movement during respiration. To acquire images of the contracted state, the participants were instructed to gently draw-in their lower abdomen without moving their spine or pelvis (Hides et al., 2010a). Prior to performing the muscle test, subjects were instructed to voluntarily relax the abdominal wall and this was verified by palpation and observation of the breathing pattern. Standardised instructions were given by a physical therapist who was blinded to group allocation and participant histories and presentations. The participants were allowed to practice the draw-in manoeuvre, with the instructor’s hand placed under their spine. If participants moved their spine, they were again instructed not to move their spine or pelvis and were given 1 more practice. The muscle test itself was only performed once, in line with routine testing practices and to avoid a training effect. A 1.5 Tesla Siemens Sonata MRI system (Erlangen, Germany) was used. Eighteen continuous transverse images with a slice thickness of 7 mm were taken, centred at the L4-5 disc and perpendicular to the abdominal wall (Fig. 1). A fast gradient recalled echo sequence was used with TR ¼ 4.8, TE ¼ 2.3 ms, FA ¼ 70 , FOV ¼ 40 cm and NA ¼ 2. The resulting image matrix for the images was 128 128 and interpolated to 256 256. A spine coil array was used for image acquisition and the total scanning time was 23 s. Of the 18 slices captured, the lowest 3 slices (slice 1e3) (Fig. 1) were excluded due to nonlinearity of the imaging hardware at this extreme of the imaged volume, leaving 15 slices for analysis.
2.4. Measurements Images were measured offline using Image J software (version 1.42; U.S. National Institutes of Health, Maryland, USA). Trunk CSA (excluding subcutaneous tissue) was measured in relaxed and contracted states on the 15 slices (Fig. 2). Due to the available longitudinal field of view of the MRI system, it was only possible to image a section of the abdominal wall. The middle and lower region of the TrA muscle were selected due to their proposed role in support and protection of the lumbo-pelvic region (Urquhart and Hodges, 2005b; Urquhart et al., 2005c). The intra-class correlation coefficient (ICC) was used to assess intra-rater reliability of measurement of the trunk CSA (Rankin and Stokes, 1998). Measurements of images at rest and on contraction were measured twice at slice 9 (Fig. 1) for 11 participants. An ICC (1,1) of 0.99 was achieved indicating high intra-operator reliability. A nonsignificant difference in the mean values of the 2 trials (F ¼ 0.34, P ¼ 0.58) also indicated consistency in the measurements. The operator measuring the slices was blinded to the participant’s identity, group allocation and contraction state.
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Fig. 1. MRI of the trunk showing the location of the 18 transverse slices captured and associated anatomical regions of the abdomen. Slices excluded: slices 1e3, Region 1: slices 4e8, Region 2: slices 9e13 and Region 3: slices 14e18.
2.5. Data coding The 15 slices of the abdominal wall available for analysis were classified into 3 equal sized groups of regions with 5 slices in each, in accordance with anatomical boundaries of the TrA muscle. Fig. 1 shows that Region 1 represented the lower region, Region 2 was located in the lower half of the middle region and Region 3 represented the upper half of the middle region of the TrA muscle. Slice 9 was taken at the L4-5 disc in all participants which is the anatomical boundary between the lower and middle regions (Urquhart et al., 2005a). Analysis of the data also took into account the multi-directional nature of participant’s ability to draw-in the abdominal wall. That is, an increase in the trunk CSA (abdominal bulging) (Hides et al., 2010a) was not the same as being able to draw-in the abdominal wall. Therefore participants were also classified into two groups with respect to their abdominal draw-in ability; ‘able’ and ‘unable’. Participants were included in the ‘able’ group if the draw-in resulted in a decrease in the trunk CSA for three or more out of the five slices for each region. Participants were allocated to the ‘unable’ group if the abdominal contraction resulted in an increase in the CSA at three or more of the five slices. 2.6. Statistical analysis
Fig. 2. MRI slices showing CSA of the abdominal muscles when (A) relaxed and (B) contracted after performing the abdominal draw-in manoeuvre. The draw-in manoeuvre has resulted in a decrease in the CSA of the trunk on contraction.
Statistical analyses were performed using SPSS (version 15, SPSS Inc., Chicago, USA) with statistical significance set at P < 0.05. The data for one participant was excluded due to inadequate coverage of the measuring device leaving data for 42 participants in the analysis. A preliminary analysis of variance (ANOVA) was conducted to examine the demographic characteristics of the LBP groups. Outcome measures in the analysis were age, height and weight and the between subjects factor was the ‘LBP groups’.
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J. Hides et al. / Manual Therapy 16 (2011) 279e284 Abdominal Draw-in Manoeuvre
Abdominal draw-in size (cm )
30 25 20 15 10 5 0 LBP
No LBP
LBP
No LBP
LBP
No LBP
Region 1
Region 2
Region 3
Lower
Middle
Middle
Fig. 3. Mean contraction size of the abdominal draw-in manoeuvre in cm2 (relaxed minus contracted trunk CSA) of the 3 abdominal regions. The error bars represent standard deviation. Note the significant difference in abdominal contraction size of Region 1 (lower region) between the LBP and no LBP group.
Repeated measures analysis of covariance (ANCOVA) was used to analyse the trunk CSA in response to the drawing-in manoeuvre. In order to make the outcome measure uni-dimensional, representing drawing-in of the abdominal wall, the initial analysis focussed on participants who could effectively perform the manoeuvre. The outcome measure for the analysis was trunk CSA in relaxed and contracted conditions averaged across the five slices in each region. The between subjects factor in the analysis was ‘LBP groups’ (LBP and no LBP). The repeated measures factor was ‘abdominal contraction’ (relaxed and contracted). Age, height and weight were included as covariates in the analysis. A Type I sum of squares model was selected as previous studies have shown that higher order interactions between muscle size and mass is problematic for a Type III model (Hides et al., 2007). Due to variation across abdominal regions in the number who could perform the draw-in manoeuvre, separate analyses were performed for each of the three regions. An additional analysis was conducted to compare the size of the abdominal draw-in manoeuvre across the three abdominal regions. Using the same analysis design described above, a subset analysis was performed on participants who could perform the draw-in manoeuvre at all three regions (n ¼ 24). A-priori contrasts were also performed to determine regional differences. A binomial logistic regression was conducted to compare the proportions of participants who were ‘able’ (n ¼ 25) or ‘unable’ (n ¼ 17) to perform the abdominal draw-in manoeuvre. The between subjects factor was ‘LBP groups’ and the covariates in the analysis were age, height and weight. This analysis was conducted on the data for Region 1 as there was a sufficient number of participants ‘unable’ to perform the abdominal draw-in manoeuvre for this region.
3. Results The mean (SD) for the VAS scores of participants who had current LBP was 3.5(2.4). There was no significant difference between the LBP groups in age, height and weight (all p > 0.05). More participants
were able to perform the abdominal draw-in manoeuvre at Region 3 (88.1%), followed by Region 2 (80.9%) with the lowest number of participants able to perform the draw-in at Region 1 (64.3%). The following mean differences in trunk CSA between the relaxed and contracted states were found: Region 3: no LBP ¼ 20.9 cm2 and LBP ¼ 18.7 cm2; Region 2, no LBP ¼ 21.9 cm2, LBP ¼ 13.1 cm2; Region 1: no LBP ¼ 12.89 cm2 and LBP ¼ 4.66 cm2 (Fig. 3). The results of the ANCOVA showed a statistically significant difference between the LBP groups in the ability to perform the abdominal draw-in manoeuvre in Region 1 (F ¼ 6.64, P ¼ 0.018). Calculation of the percentage change from relaxed to contracted condition, based on the means in Table 1, indicated that participants in the LBP group (1.1%) were less able to draw-in the abdominal wall at the lower region than participants in the no LBP group (3.2%). However the analysis did not show a significant difference between LBP groups for Region 2 (F ¼ 1.97, P ¼ 0.171) and Region 3 (F ¼ 0.20, P ¼ 0.661) (Table 1). The results of the subset analysis conducted on participants who were able to draw-in the abdominal wall indicated a significant interaction between “abdominal contraction” and “region” (F ¼ 29.33, P < 0.001). A-priori contrasts showed that the abdominal draw-in was significantly different between Regions 1 and 2 (F ¼ 29.18, P < 0.00) and approached statistical significance between Region 2 and 3 (F ¼ 4.07, 0.057). The percentage change from relaxed to contracted condition (averaged across LBP groups) indicated that the size of the contraction in Region 1 (8.8%) was smaller than Region 2 (16.0%) and Region 3 (19.7%). At Region 1 there was a sufficient portion of participants who were unable to perform the contraction and increased their trunk CSA when attempting to draw in the abdominal wall to warrant analysis (Fig. 4). There was no significant difference between the number of participants who were unable to perform the abdominal draw-in manoeuvre between the LBP groups at the lower region (Chi square ¼ 0.003, P ¼ 0.958, Odds Ratio ¼ 1.04). Of the participants who were unable to perform the abdominal draw-in manoeuvre at Region 1, 43% were in the LBP group and 36% were in the no LBP group. This indicated that inability to perform the abdominal draw-in manoeuvre (abdominal bulging) was not a function of LBP. 4. Discussion The results of the current study showed that elite footballers with LBP did not perform the muscle test for the TrA muscle (drawing in the abdominal wall) as well as footballers without LBP despite their continued full participation in vigorous training and high fitness levels. Although still able to function at a high level and fulfil performance criteria demanded by their sport, the elite footballers with current LBP possessed a reduced ability to draw-in the abdominal wall in the lower region of the abdomen compared with asymptomatic footballers. The finding of a reduced ability to draw in the abdominal wall in subjects with LBP is consistent with previous studies which have also provided evidence of altered function of the TrA muscle in
Table 1 Marginal means of CSA of the abdominal draw-in manoeuvre in relaxed and contracted states in participants who were able to draw-in the abdominal wall.a,b Region 1 n ¼ 25
Relaxed Contracted a b
Region 2 n ¼ 34
Region 3 n ¼ 37
LBP (SD)
No LBP (SD)
LBP (SD)
No LBP (SD)
LBP (SD)
No LBP (SD)
430.0 (27.0) 425.3 (26.4)
405.9 (27.1) 393.0 (26.5)
397.2 (21.7) 384.1 (22.1)
406.2 (21.7) 387.3 (22.2)
442.5 (27.0) 423.9 (31.0)
461.3 (27.1) 440.5 (31.1)
CSA measurements in cm2. P (Region 1) ¼ 0.018; P (Region 2) ¼ 0.171; P (Region 3) ¼ 0.661.
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recruit their superficial muscles in line with the demands of their sport, which involves repetitive trunk and hip flexion when kicking (Baczkowski et al., 2006). Some important clinical implications can be drawn from the results of the current investigation. LBP is known to be a problem among elite AFL players. The abdominal muscles have been identified as one group of muscles which play a role in protecting and supporting the lumbo-pelvic region (Snijders et al., 1995; Richardson et al., 2002; Hodges et al., 2003, 2005; Barker et al., 2006) and re-education of the abdominal drawing-in manoeuvre has been associated with decreased levels of LBP in elite athletes (Hides et al., 2010b). It would seem from the current study that the presence of LBP may have a regional effect on the ability to draw-in the abdominal wall. Although more studies are required, this finding may indicate that clinicians should perform regional assessments and possibly region specific re-education of abdominal wall function in these elite athletes. In addition, the current study showed that some footballers without LBP could not draw in the abdominal wall in the lower region. Further studies could investigate whether identification of those athletes who cannot perform the abdominal drawing-in manoeuvre may be of use in athlete screening programs and in developing interventions to lower injury rates. This study has some limitations. It was conducted on a specific group of participants, elite male AFL players of similar ages. Caution should be exercised when generalising to other LBP and sporting populations. As the results of this study represent a new finding, future studies are needed to investigate the presence of regional differences of abdominal wall function in other sporting and clinical groups. Fig. 4. MRI slices showing CSA of the abdominal muscles when (A) relaxed and (B) contracted after performing the abdominal draw-in manoeuvre with the CSA of the trunk muscles (excluding subcutaneous tissue) outlined. The draw-in manoeuvre has resulted in an increase in the CSA of the trunk. Note the increase in the thickness of all of the muscles of the antero-lateral abdominal wall and the rectus abdominis associated with this attempt to draw in the abdominal wall.
participants with LBP (Hides et al., 2008, 2009, 2010a). However, these previous studies used measurements from only a single slice (at the level of the L3-4 disc) in the middle region of the TrA muscle. This procedure did not allow examination of functional differences across the regions, and the results for a single slice may not represent functioning of the whole middle region. The current study involved an average of five slices for each region of the abdominal wall. The results for L3-4 are consistent across studies, indicating that subjects with LBP were less able to decrease their trunk CSA. However, the methodology used in the current study differs from previous studies making direct comparisons difficult. When averaged over five levels, the result for the middle region across groups was not significant in the current study, suggesting the effect of LBP may possibly have a localised effect on the TrA muscle. In this sample of elite AFL players there was a relatively high prevalence of LBP as indicated by the number of participants with current and/or a history of LBP (55.8%) and there were a large number of participants who were unable to perform the abdominal draw-in manoeuvre at the lower region (40.5%). Some participants could not decrease their trunk CSA, but instead increased it when attempting to draw-in the abdomen (Fig. 4). This has been previously reported in people with LBP and has been explained by an increased contraction of the superficial abdominal muscles (Richardson et al., 2004; Hides et al., 2009, 2010a). However in the current study, this pattern was seen in participants with and without LBP. This may reflect a tendency for AFL players to over
5. Conclusion This study has found that people with current and/or a history of LBP are less able to perform the abdominal draw-in manoeuvre at the lower abdominal region when compared with people who have never experienced LBP. In addition this research has provided added support for the presence of functional differences in the anatomical regions of the TrA muscle. Future research investigating motor control of the abdominal muscles in the presence of LBP should ensure all abdominal regions are considered to account for the regional differences in TrA muscle function. While further research should be conducted examining regional differences in motor control of the TrA muscle in the general LBP population there is preliminary evidence to suggest that the lower region of the TrA muscle should be the focus of specific retraining interventions.
Acknowledgments The authors would like to thank Associate Professor Stephen Wilson, Margot Wilkes, Dilani Mendis, Mark Strudwick, the UQ Centre for Advanced Imaging, the Brisbane Lions AFL club and the participants.
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Original article
Magnetic resonance imaging assessment of regional abdominal muscle function in elite AFL players with and without low back pain Julie Hides a, c, *, Brita Hughes b, Warren Stanton a, c a
School of Physiotherapy, Australian Catholic University, McAuley at Banyo, Qld 4014, Australia The University of Queensland, School of Health and Rehabilitation Sciences, Division of Physiotherapy, Brisbane, Australia c Mater Back Stability Clinic, Mater Health Services, South Brisbane, Queensland 4101, Australia b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 29 April 2010 Received in revised form 12 November 2010 Accepted 19 November 2010
Changes in the motor control of trunk muscles have been identified in people with low back pain (LBP) including elite football players. Previous research has found functional differences in the anatomical regions of abdominal muscles; however, this has not been examined in football players with LBP. The aim of this study was to investigate if the ability to draw-in the abdominal wall is altered among football players with LBP, and to determine if there are functional differences between the middle and lower abdominal regions in participants with and without LBP. Forty-three elite Australian Football League players were imaged using magnetic resonance imaging (MRI) as they drew in their abdominal walls, and the trunk cross-sectional area (CSA) was measured in relaxed and contracted states. At the lower region, participants with LBP (1.1%) reduced their trunk CSA to a lesser extent than those without LBP (3.2%) (P ¼ 0.018). The results also showed that the draw-in of the abdominal wall was smaller in Region 1 (8.8%) compared to Region 2 (16.0%) and Region 3 (19.7%) (P < 0.001). This study provides evidence of regional differences in motor control and altered control of the lower region in participants with LBP. This may direct physiotherapists, especially those treating athletes, to focus on the lower abdominal region in those with LBP. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: Transversus abdominis muscle Low back pain Imaging Football
1. Introduction The incidence of low back pain (LBP) for different sports depends on the physical demands and skill sets required. Australian Rules Football (AFL) involves a combination of repetitive, highintensity activities such as kicking, sprinting and jumping which are conducive to higher injury rates compared with other sports (Seward et al., 1993; Hoskins and Pollard, 2003; Braham et al., 2004; Wilson et al., 2007). A better understanding of the function of the abdominal muscles, which have been shown to protect and support the lumbo-pelvic region (Snijders et al., 1995; Richardson et al., 2002; Hodges et al., 2003, 2005; Barker et al., 2006), may lead to a reduction in injury rates and prevalence of LBP. Although all abdominal muscles contribute to the control of the spine and pelvis, there has been a focus by researchers and clinicians alike on the function of the deepest abdominal muscle, the transversus abdominis (TrA). There is anatomical evidence that the TrA muscle can be divided into three distinct regions; the upper * Corresponding author. School of Physiotherapy, Australian Catholic University, McAuley at Banyo, Qld 4014, Australia. Tel.: þ61 7 36237530; fax: þ61 7 36237650. E-mail address: [email protected] (J. Hides). 1356-689X/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.math.2010.11.009
(superior to the 11th costal cartilage), middle (between the 11th costal cartilage and the iliac crest) and lower regions (inferior to the iliac crest and L4-5 disc) (Urquhart et al., 2005a). Intramuscular septas separating the regions of the TrA muscle have been found and these are hypothesised to prevent transmission of force allowing functionally independent regions of the muscle (Urquhart et al., 2005a). When the TrA muscle contracts bilaterally, it reduces the circumference and flattens the abdominal wall in the lower region to increase the intra-abdominal pressure and tensions the thoracolumbar and anterior fascias (Cresswell et al., 1992; Snijders et al., 1995; Hodges, 1999). While there has been considerable debate regarding the contribution of the TrA muscle to control of the lumbar spine and pelvis (McGill, 2002; Allison and Morris, 2008a; Allison et al., 2008b; Hodges, 2008), it has been argued that the TrA muscle may primarily act via modulation of intra-abdominal pressure, fascial tension and compression of the sacro-iliac joints (Cresswell et al., 1992; Snijders et al., 1995; Hodges, 1999). Clinical muscle testing of the TrA muscle has been based on its anatomical structure and horizontal fibre arrangement. Two muscle tests include observation of the abdominal wall during either a voluntary ‘drawing-in’ of the abdominal wall (Richardson and Jull, 1995), or by using automatic responses of the muscle to
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expiration (Lacôte et al., 1987). The concentric contraction of the bilateral muscle bellies of the TrA during this ‘draw-in’ manoeuvre has been viewed using ultrasound imaging and Magnetic Resonance Imaging (MRI) (Hides et al., 1998; Hides et al., 2006). Among asymptomatic subjects (Hides et al., 2006), the action of drawing-in the abdominal wall resulted in thickening of the TrA muscle and the internal oblique muscles, slide of the anterior abdominal fascia and a decrease in cross-sectional area (CSA) of the trunk (obtained by measuring around the perimeter of the whole abdominal wall). A reduction of the circumference of the abdominal wall and flattening of the anterior abdominal wall (due to the anterior abdominal wall moving in a posterior direction) is in agreement with anatomical studies (Barker et al., 2004, 2006). MRI has been used to demonstrate differences in ability to perform the drawing-in manoeuvre in subjects with a history of chronic LBP, elite AFL players and cricketers with current LBP (Richardson et al., 2004; Hides et al., 2008, 2010a). Some subjects with LBP were shown to be less able to decrease the CSA of their trunk while some subjects were not able to decrease their trunk CSA when performing the draw-in manoeuvre (Richardson et al., 2004; Hides et al., 2008, 2010a). In these cases, while attempting to draw in the abdominal wall, there was increased thickness in the oblique abdominal muscles and bulging of the abdominal wall, which resulted in an increase in the trunk CSA (Hides et al., 2010a). While these studies have provided useful information, MRI measures were conducted at only one level of the trunk located in the middle region of the abdominal wall. As it has been proposed that the TrA muscle can be divided into three functionally different regions, it may be important to conduct these same measurements at multiple levels and at different regions. The aims of this research project were to: 1) compare the ability to draw-in the abdominal wall between participants with and without LBP, 2) examine the regional differences between the lower and middle regions of the TrA muscle in performance of the abdominal draw-in manoeuvre, and 3) determine whether those with LBP are more likely to increase rather than decrease the trunk CSA when attempting to draw-in the abdomen, compared to participants without LBP. 2. Methods 2.1. Participants Forty-three professional male AFL players aged from 18 to 31 years participated in the study. The mean (SD) of participant’s age, height and weight were 22.8(3.7) years, 188.5(7.1) cm and 88.2 (6.5) kg respectively. Participants in the study provided written informed consent and the study was approved by the institutional ethics committee. 2.2. Procedures Participants underwent a clinical musculoskeletal assessment, completed a questionnaire and received an MRI assessment in a hospital setting. An experienced physiotherapist assessed all participants (patient interview and physical examination) to determine the presence of current or previous non-specific LBP. Non-specific LBP was defined as pain localised below the line of the twelfth rib and above the inferior gluteal fold. Participants with current LBP marked the location of their pain on a body chart and rated their pain intensity from 0 to 10 on a Visual Analogue Scale (VAS). Participants with current and/or a history of LBP also completed a questionnaire which included questions about previous injuries to the lumbo-pelvic region, treatment received and history of LBP. Based on the results of the assessment
participants were allocated into 1 of 4 ‘LBP groups’; no current LBP and no history of LBP (n ¼ 19), no current LBP with a history of LBP (n ¼ 8), current LBP and no history of LBP (n ¼ 4) and current LBP and a history of LBP (n ¼ 12). Due to relatively small numbers of participants in these groups they were recoded into 2 groups; No LBP ¼ No current or history of LBP (n ¼ 19) and LBP ¼ Current LBP and/or a history of LBP (n ¼ 24).
2.3. MRI assessment Participants were screened by a medical practitioner before assessment. MRI was used to acquire images of the abdomen in both relaxed and contracted states. Participants were positioned on the MRI table in a supine position with their knees resting on a small foam wedge. The participants were instructed to breathe in, then out and hold their breath at mid-expiration. A relaxed muscle image was captured to minimise image artefacts due to tissue movement during respiration. To acquire images of the contracted state, the participants were instructed to gently draw-in their lower abdomen without moving their spine or pelvis (Hides et al., 2010a). Prior to performing the muscle test, subjects were instructed to voluntarily relax the abdominal wall and this was verified by palpation and observation of the breathing pattern. Standardised instructions were given by a physical therapist who was blinded to group allocation and participant histories and presentations. The participants were allowed to practice the draw-in manoeuvre, with the instructor’s hand placed under their spine. If participants moved their spine, they were again instructed not to move their spine or pelvis and were given 1 more practice. The muscle test itself was only performed once, in line with routine testing practices and to avoid a training effect. A 1.5 Tesla Siemens Sonata MRI system (Erlangen, Germany) was used. Eighteen continuous transverse images with a slice thickness of 7 mm were taken, centred at the L4-5 disc and perpendicular to the abdominal wall (Fig. 1). A fast gradient recalled echo sequence was used with TR ¼ 4.8, TE ¼ 2.3 ms, FA ¼ 70 , FOV ¼ 40 cm and NA ¼ 2. The resulting image matrix for the images was 128 128 and interpolated to 256 256. A spine coil array was used for image acquisition and the total scanning time was 23 s. Of the 18 slices captured, the lowest 3 slices (slice 1e3) (Fig. 1) were excluded due to nonlinearity of the imaging hardware at this extreme of the imaged volume, leaving 15 slices for analysis.
2.4. Measurements Images were measured offline using Image J software (version 1.42; U.S. National Institutes of Health, Maryland, USA). Trunk CSA (excluding subcutaneous tissue) was measured in relaxed and contracted states on the 15 slices (Fig. 2). Due to the available longitudinal field of view of the MRI system, it was only possible to image a section of the abdominal wall. The middle and lower region of the TrA muscle were selected due to their proposed role in support and protection of the lumbo-pelvic region (Urquhart and Hodges, 2005b; Urquhart et al., 2005c). The intra-class correlation coefficient (ICC) was used to assess intra-rater reliability of measurement of the trunk CSA (Rankin and Stokes, 1998). Measurements of images at rest and on contraction were measured twice at slice 9 (Fig. 1) for 11 participants. An ICC (1,1) of 0.99 was achieved indicating high intra-operator reliability. A nonsignificant difference in the mean values of the 2 trials (F ¼ 0.34, P ¼ 0.58) also indicated consistency in the measurements. The operator measuring the slices was blinded to the participant’s identity, group allocation and contraction state.
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Fig. 1. MRI of the trunk showing the location of the 18 transverse slices captured and associated anatomical regions of the abdomen. Slices excluded: slices 1e3, Region 1: slices 4e8, Region 2: slices 9e13 and Region 3: slices 14e18.
2.5. Data coding The 15 slices of the abdominal wall available for analysis were classified into 3 equal sized groups of regions with 5 slices in each, in accordance with anatomical boundaries of the TrA muscle. Fig. 1 shows that Region 1 represented the lower region, Region 2 was located in the lower half of the middle region and Region 3 represented the upper half of the middle region of the TrA muscle. Slice 9 was taken at the L4-5 disc in all participants which is the anatomical boundary between the lower and middle regions (Urquhart et al., 2005a). Analysis of the data also took into account the multi-directional nature of participant’s ability to draw-in the abdominal wall. That is, an increase in the trunk CSA (abdominal bulging) (Hides et al., 2010a) was not the same as being able to draw-in the abdominal wall. Therefore participants were also classified into two groups with respect to their abdominal draw-in ability; ‘able’ and ‘unable’. Participants were included in the ‘able’ group if the draw-in resulted in a decrease in the trunk CSA for three or more out of the five slices for each region. Participants were allocated to the ‘unable’ group if the abdominal contraction resulted in an increase in the CSA at three or more of the five slices. 2.6. Statistical analysis
Fig. 2. MRI slices showing CSA of the abdominal muscles when (A) relaxed and (B) contracted after performing the abdominal draw-in manoeuvre. The draw-in manoeuvre has resulted in a decrease in the CSA of the trunk on contraction.
Statistical analyses were performed using SPSS (version 15, SPSS Inc., Chicago, USA) with statistical significance set at P < 0.05. The data for one participant was excluded due to inadequate coverage of the measuring device leaving data for 42 participants in the analysis. A preliminary analysis of variance (ANOVA) was conducted to examine the demographic characteristics of the LBP groups. Outcome measures in the analysis were age, height and weight and the between subjects factor was the ‘LBP groups’.
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J. Hides et al. / Manual Therapy 16 (2011) 279e284 Abdominal Draw-in Manoeuvre
Abdominal draw-in size (cm )
30 25 20 15 10 5 0 LBP
No LBP
LBP
No LBP
LBP
No LBP
Region 1
Region 2
Region 3
Lower
Middle
Middle
Fig. 3. Mean contraction size of the abdominal draw-in manoeuvre in cm2 (relaxed minus contracted trunk CSA) of the 3 abdominal regions. The error bars represent standard deviation. Note the significant difference in abdominal contraction size of Region 1 (lower region) between the LBP and no LBP group.
Repeated measures analysis of covariance (ANCOVA) was used to analyse the trunk CSA in response to the drawing-in manoeuvre. In order to make the outcome measure uni-dimensional, representing drawing-in of the abdominal wall, the initial analysis focussed on participants who could effectively perform the manoeuvre. The outcome measure for the analysis was trunk CSA in relaxed and contracted conditions averaged across the five slices in each region. The between subjects factor in the analysis was ‘LBP groups’ (LBP and no LBP). The repeated measures factor was ‘abdominal contraction’ (relaxed and contracted). Age, height and weight were included as covariates in the analysis. A Type I sum of squares model was selected as previous studies have shown that higher order interactions between muscle size and mass is problematic for a Type III model (Hides et al., 2007). Due to variation across abdominal regions in the number who could perform the draw-in manoeuvre, separate analyses were performed for each of the three regions. An additional analysis was conducted to compare the size of the abdominal draw-in manoeuvre across the three abdominal regions. Using the same analysis design described above, a subset analysis was performed on participants who could perform the draw-in manoeuvre at all three regions (n ¼ 24). A-priori contrasts were also performed to determine regional differences. A binomial logistic regression was conducted to compare the proportions of participants who were ‘able’ (n ¼ 25) or ‘unable’ (n ¼ 17) to perform the abdominal draw-in manoeuvre. The between subjects factor was ‘LBP groups’ and the covariates in the analysis were age, height and weight. This analysis was conducted on the data for Region 1 as there was a sufficient number of participants ‘unable’ to perform the abdominal draw-in manoeuvre for this region.
3. Results The mean (SD) for the VAS scores of participants who had current LBP was 3.5(2.4). There was no significant difference between the LBP groups in age, height and weight (all p > 0.05). More participants
were able to perform the abdominal draw-in manoeuvre at Region 3 (88.1%), followed by Region 2 (80.9%) with the lowest number of participants able to perform the draw-in at Region 1 (64.3%). The following mean differences in trunk CSA between the relaxed and contracted states were found: Region 3: no LBP ¼ 20.9 cm2 and LBP ¼ 18.7 cm2; Region 2, no LBP ¼ 21.9 cm2, LBP ¼ 13.1 cm2; Region 1: no LBP ¼ 12.89 cm2 and LBP ¼ 4.66 cm2 (Fig. 3). The results of the ANCOVA showed a statistically significant difference between the LBP groups in the ability to perform the abdominal draw-in manoeuvre in Region 1 (F ¼ 6.64, P ¼ 0.018). Calculation of the percentage change from relaxed to contracted condition, based on the means in Table 1, indicated that participants in the LBP group (1.1%) were less able to draw-in the abdominal wall at the lower region than participants in the no LBP group (3.2%). However the analysis did not show a significant difference between LBP groups for Region 2 (F ¼ 1.97, P ¼ 0.171) and Region 3 (F ¼ 0.20, P ¼ 0.661) (Table 1). The results of the subset analysis conducted on participants who were able to draw-in the abdominal wall indicated a significant interaction between “abdominal contraction” and “region” (F ¼ 29.33, P < 0.001). A-priori contrasts showed that the abdominal draw-in was significantly different between Regions 1 and 2 (F ¼ 29.18, P < 0.00) and approached statistical significance between Region 2 and 3 (F ¼ 4.07, 0.057). The percentage change from relaxed to contracted condition (averaged across LBP groups) indicated that the size of the contraction in Region 1 (8.8%) was smaller than Region 2 (16.0%) and Region 3 (19.7%). At Region 1 there was a sufficient portion of participants who were unable to perform the contraction and increased their trunk CSA when attempting to draw in the abdominal wall to warrant analysis (Fig. 4). There was no significant difference between the number of participants who were unable to perform the abdominal draw-in manoeuvre between the LBP groups at the lower region (Chi square ¼ 0.003, P ¼ 0.958, Odds Ratio ¼ 1.04). Of the participants who were unable to perform the abdominal draw-in manoeuvre at Region 1, 43% were in the LBP group and 36% were in the no LBP group. This indicated that inability to perform the abdominal draw-in manoeuvre (abdominal bulging) was not a function of LBP. 4. Discussion The results of the current study showed that elite footballers with LBP did not perform the muscle test for the TrA muscle (drawing in the abdominal wall) as well as footballers without LBP despite their continued full participation in vigorous training and high fitness levels. Although still able to function at a high level and fulfil performance criteria demanded by their sport, the elite footballers with current LBP possessed a reduced ability to draw-in the abdominal wall in the lower region of the abdomen compared with asymptomatic footballers. The finding of a reduced ability to draw in the abdominal wall in subjects with LBP is consistent with previous studies which have also provided evidence of altered function of the TrA muscle in
Table 1 Marginal means of CSA of the abdominal draw-in manoeuvre in relaxed and contracted states in participants who were able to draw-in the abdominal wall.a,b Region 1 n ¼ 25
Relaxed Contracted a b
Region 2 n ¼ 34
Region 3 n ¼ 37
LBP (SD)
No LBP (SD)
LBP (SD)
No LBP (SD)
LBP (SD)
No LBP (SD)
430.0 (27.0) 425.3 (26.4)
405.9 (27.1) 393.0 (26.5)
397.2 (21.7) 384.1 (22.1)
406.2 (21.7) 387.3 (22.2)
442.5 (27.0) 423.9 (31.0)
461.3 (27.1) 440.5 (31.1)
CSA measurements in cm2. P (Region 1) ¼ 0.018; P (Region 2) ¼ 0.171; P (Region 3) ¼ 0.661.
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recruit their superficial muscles in line with the demands of their sport, which involves repetitive trunk and hip flexion when kicking (Baczkowski et al., 2006). Some important clinical implications can be drawn from the results of the current investigation. LBP is known to be a problem among elite AFL players. The abdominal muscles have been identified as one group of muscles which play a role in protecting and supporting the lumbo-pelvic region (Snijders et al., 1995; Richardson et al., 2002; Hodges et al., 2003, 2005; Barker et al., 2006) and re-education of the abdominal drawing-in manoeuvre has been associated with decreased levels of LBP in elite athletes (Hides et al., 2010b). It would seem from the current study that the presence of LBP may have a regional effect on the ability to draw-in the abdominal wall. Although more studies are required, this finding may indicate that clinicians should perform regional assessments and possibly region specific re-education of abdominal wall function in these elite athletes. In addition, the current study showed that some footballers without LBP could not draw in the abdominal wall in the lower region. Further studies could investigate whether identification of those athletes who cannot perform the abdominal drawing-in manoeuvre may be of use in athlete screening programs and in developing interventions to lower injury rates. This study has some limitations. It was conducted on a specific group of participants, elite male AFL players of similar ages. Caution should be exercised when generalising to other LBP and sporting populations. As the results of this study represent a new finding, future studies are needed to investigate the presence of regional differences of abdominal wall function in other sporting and clinical groups. Fig. 4. MRI slices showing CSA of the abdominal muscles when (A) relaxed and (B) contracted after performing the abdominal draw-in manoeuvre with the CSA of the trunk muscles (excluding subcutaneous tissue) outlined. The draw-in manoeuvre has resulted in an increase in the CSA of the trunk. Note the increase in the thickness of all of the muscles of the antero-lateral abdominal wall and the rectus abdominis associated with this attempt to draw in the abdominal wall.
participants with LBP (Hides et al., 2008, 2009, 2010a). However, these previous studies used measurements from only a single slice (at the level of the L3-4 disc) in the middle region of the TrA muscle. This procedure did not allow examination of functional differences across the regions, and the results for a single slice may not represent functioning of the whole middle region. The current study involved an average of five slices for each region of the abdominal wall. The results for L3-4 are consistent across studies, indicating that subjects with LBP were less able to decrease their trunk CSA. However, the methodology used in the current study differs from previous studies making direct comparisons difficult. When averaged over five levels, the result for the middle region across groups was not significant in the current study, suggesting the effect of LBP may possibly have a localised effect on the TrA muscle. In this sample of elite AFL players there was a relatively high prevalence of LBP as indicated by the number of participants with current and/or a history of LBP (55.8%) and there were a large number of participants who were unable to perform the abdominal draw-in manoeuvre at the lower region (40.5%). Some participants could not decrease their trunk CSA, but instead increased it when attempting to draw-in the abdomen (Fig. 4). This has been previously reported in people with LBP and has been explained by an increased contraction of the superficial abdominal muscles (Richardson et al., 2004; Hides et al., 2009, 2010a). However in the current study, this pattern was seen in participants with and without LBP. This may reflect a tendency for AFL players to over
5. Conclusion This study has found that people with current and/or a history of LBP are less able to perform the abdominal draw-in manoeuvre at the lower abdominal region when compared with people who have never experienced LBP. In addition this research has provided added support for the presence of functional differences in the anatomical regions of the TrA muscle. Future research investigating motor control of the abdominal muscles in the presence of LBP should ensure all abdominal regions are considered to account for the regional differences in TrA muscle function. While further research should be conducted examining regional differences in motor control of the TrA muscle in the general LBP population there is preliminary evidence to suggest that the lower region of the TrA muscle should be the focus of specific retraining interventions.
Acknowledgments The authors would like to thank Associate Professor Stephen Wilson, Margot Wilkes, Dilani Mendis, Mark Strudwick, the UQ Centre for Advanced Imaging, the Brisbane Lions AFL club and the participants.
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