Artigo paulo

Downloaded from bjsm.bmj.com on 9 June 2009

Changes in recruitment of transversus abdominis
correlate with disability in people with chronic low
back pain
Paulo Ferreira, Manuela Ferreira, Christopher Maher, Kathryn Refshauge, Robert
Herbert and Paul Hodges

Br. J. Sports Med. published online 26 May 2009;
doi:10.1136/bjsm.2009.061515

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BJSM Online First, published on May 26, 2009 as 10.1136/bjsm.2009.061515

Changes in recruitment of transversus abdominis correlate with disability in people
with chronic low back pain.

Paulo H Ferreira PhD1, 2, Manuela L Ferreira PhD1, Christopher G Maher PhD3, Kathryn Refshauge
PhD1, Robert D Herbert PhD3, Paul W Hodges PhD4
1
Discipline of Physiotherapy, The University of Sydney, Sydney, Australia.
2
Departamento de Fisioterapia, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil.
3
The George Institute for International Health, The University of Sydney, Sydney, Australia.
4
Centre for Clinical Research Excellence in Spinal Pain, Injury and Health, School of Health and
Rehabilitation Sciences, The University of Queensland, Brisbane, Australia.

Addresss for Correspondence:
Dr. Paulo Ferreira, Discipline of Physiotherapy, Faculty of Health Sciences,
University of Sydney, PO Box 170 Lidcombe 1825 AUSTRALIA
Tel: 61 2 93519397 Fax: 61 2 93519601
E-mail: p.ferreira@usyd.edu.au

Changes in recruitment of transversus abdominis correlate with disability in people
with chronic low back pain.

Key words: low back pain, motor control, ultrasonography.

1

Copyright Article author (or their employer) 2009. Produced by BMJ Publishing Group Ltd under licence.


ABSTRACT
Objectives: Although motor control exercises have been shown to be effective in the management of
low back pain (LBP) the mechanism of action is unclear. The current study investigated the
relationship between ability to recruit transversus abdominis and clinical outcomes of participants in a
clinical trial.
Methods: Ultrasonography was used to assess the ability to recruit transversus abdominis in a nested
design: a sample of 34 participants with chronic low back pain was recruited from participants in a
randomised controlled trial comparing efficacy of motor control exercise, general exercise and spinal
manipulative therapy. Perceived recovery, function, disability and pain were also assessed.
Results: Participants with chronic LBP receiving motor control exercise had greater improvement in
recruitment of transversus abdominis (7.8%) than participants receiving general exercise (4.9%
reduction) or spinal manipulative therapy (3.7% reduction). The effect of motor control exercise on
pain reduction was greater in participants who had a poor ability to recruit transversus abdominis at
baseline. There was a significant, moderate correlation between improved recruitment of transversus
abdominis and reduction in disability (r= -0.35; 95%CI 0.02 to 0.62).
Conclusion: These data provide some support for the hypothesised mechanism of action of motor
control exercise and suggest that the treatment may be more effective in those with a poor ability to
recruit transversus abdominis.

2


INTRODUCTION
Changes in recruitment of both the superficial and deep trunk muscles are common in people with low
back and pelvic pain. Activity of the large superficial muscles is often increased, although the nature
of the increase varies.[1] Evidence suggests increased superficial muscle activity such as increased co-
contraction of the flexor and extensor muscles[2], increased erector spinae activity during gait[3] and
during a sit-up task[4], and increased bracing of the abdominal muscles during an active straight leg
raise.[5] Conversely, activity of the deep trunk muscle, transversus abdominis is delayed[6-8] or
reduced[9,10] during movements of the limbs and trunk which challenge the stability of the spine. In
the absence of low back pain (LBP), transversus abdominis is generally activated prior to movement of
the limbs or trunk and this activity appears to be independent of the direction of limb movement.[11-
13] Healthy individuals also activate transversus abdominis in response to loading and force
application to the trunk.[14] It has been argued that this pattern of activation of transversus abdominis
is important for control of intervertebral movement[15], particularly shear forces[16], and for control of
stability of the sacroiliac joints of the pelvis.[17] In LBP, changes in control of the trunk muscles,
including transversus abdominis, are therefore thought to compromise control of the lumbar spine and
pelvis. As activity of transversus abdominis can be impaired in LBP, one of the aims of contemporary
exercise interventions (such as the motor control exercise program) for patients with LBP is to retrain
the coordination of this muscle, as a component of the intervention.[18]

Interventions aimed at training the control and coordination of the trunk muscles, including transversus
abdominis, have been shown to be effective in the management of low back[19-23] and pelvic
pain.[24] However, we do not yet know whether clinical improvements are associated with changes in
the recruitment of this muscle. Because transversus abdominis is situated deep to the more superficial
abdominal muscles, intramuscular fine-wire electromyography (EMG) has been required to evaluate its
activity.[6-8, 13, 25-29] Recent data using invasive recording methods in small groups of subjects have
provided initial evidence that temporal aspects of activity of transversus abdominis can be modified
with training.[30, 31] More recently ultrasound imaging has been used to evaluate the morphology or
recruitment of deep muscles of the trunk, in an attempt to use less invasive tools.[18, 32-36] During
contraction, muscles change shape (e.g. thickness) in association with shortening of the muscle with
sliding of actin and myosin filaments (even during isometric contractions because of tendon
stretch).[36] There is a curvilinear relationship between changes in TrA thickness and
electromyographic activity, but this is almost linear when activity increases from a relaxed state up to
~20% of maximum contraction.[36]

A protocol developed to assess activity of transversus abdominis with ultrasound imaging has been
shown to be able to distinguish between people with and without LBP.[10] This protocol showed that
when subjects perform an isometric leg flexion and extension task, and the changes in thickness of
transversus abdominis are averaged across the two directions, LBP subjects have ~72% less increase in
the thickness of transversus abdominis, ~53% less in obliquus internus abdominis and ~2% less in
obliquus externus abdominis than controls. That study[10] also demonstrated moderate to substantial
correlations between ultrasound and fine wire EMG measures of muscle recruitment for transversus
abdominis and obliquus internus (Pearsons’r = 0.74 to 0.85), but not obliquus externus (Pearson’s r =
0.19).

Motor control exercise aims to train coordination of the muscles of the trunk to meet the demands for
optimal spinal function. The exercise includes training the recruitment of the deeper muscles of the
trunk such as transversus abdominis.[18] It could be hypothesised that a greater change in thickness of
the transversus abdominis muscle would be observed following this intervention than after other
3


treatments such as general exercise or spinal manipulative therapy which do not specifically train
activation of the deep muscles of the spine. To be of clinical importance, a change in ultrasound
thickness should be accompanied by improvements in clinical outcomes.

Changes in the ability to recruit transversus abdominis were measured in a sample drawn from chronic
LBP patients participating in a randomised controlled trial of motor control exercises, general
exercises, and spinal manipulative therapy.[37] The specific aims of this study were to investigate
whether:
1) The ability to recruit transversus abdominis improves following an 8-week program of motor
control exercise, general exercise, or spinal manipulative therapy;
2) Changes in recruitment of transversus abdominis are greater in patients receiving motor control
exercise than patients receiving general exercise or spinal manipulative therapy;
3) Changes in the ability to recruit transversus abdominis correlate with improvements in clinical
outcomes of perceived recovery, function, disability and pain; and
4) The effect of motor control exercise (compared to general exercise) on the clinical outcomes of
perceived recovery, function, disability, and pain depends on the subjects’ ability to recruit
transversus abdominis measured at baseline.

4


METHODS
A sample of non-specific chronic LBP patients was taken from a randomised controlled trial[37] that
compared the efficacy of motor control exercise, general exercise, and spinal manipulative therapy. The
final 45 subjects to be enrolled in the randomised controlled trial were invited to participate in this
study, of whom 34 were eligible to participate. This sample size provided 80% power to detect a
Pearson’s correlation coefficient between TrA recruitment and clinical outcome measures of at least 0.4
(fair)[38] with 95% confidence intervals of 0.2 to 0.6. The study was approved by the Ethics
committees of the University of Sydney and the South Western and Western Sydney Area Health
Services. Recruitment of transversus abdominis was measured using a published ultrasonography
protocol.[10] The ultrasound measurement was made before participants were randomised to a motor
control exercise group, a general exercise group, or a spinal manipulative therapy group and again after
the application of 12 sessions of treatment over an 8-week period. The clinical outcomes of perceived
recovery, function, disability, and pain were also collected at the time of the ultrasound
measurement.[37]

Subjects
Patients aged between 18 and 80 years with chronic low back pain (symptoms for at least 3 months)
with or without pain referral to the leg, but without neurological deficit were recruited for the study. To
be included in the trial, patients needed to have persistent pain or disability for at least 3 months, and
they had to score at least 3 points on the Roland Morris Disability Questionnaire and at least 2 units on
the 0-10 pain scale at the screening consultation. Exclusion criteria were: spinal surgery in the past 12
months; pregnancy at the first assessment; suspected or diagnosed serious spine pathology
(inflammatory spondyloarthropathy, fracture, malignancy, cauda equina syndrome, or infection); nerve
root compromise; contra-indications to exercise; or poor English comprehension.

Intervention
Based on the randomisation procedure, participants received motor control exercise, general exercise,
or spinal manipulative therapy. Participants allocated to the motor control exercise group were
prescribed exercises aimed at improving control of lumbopelvic movement and stability. Exercises
included training function of specific deep muscles of the low back region, coordination of deep trunk
muscles with diaphragmatic respiration pattern, control of a neutral lumbar posture, and reduction of
any excessive superficial trunk muscle activation.[39] Participants allocated to the general exercise
group received the program described by Klaber Moffet[40], which is based on a biopsychosocial
model and aims to overcome a fear of movement and to improve physical function in both the short-
and long-term. For subjects allocated to the spinal manipulative therapy group, joint mobilisation
techniques, but not thrust manipulation techniques, were applied to the participant’s spine or pelvis
using grades and techniques that were at the discretion of the treating physiotherapist.[41]

Clinical outcomes
Clinical outcomes were measured at baseline and after eight weeks of treatment. Global impression of
recovery was measured on an 11-point scale.[42] Disability was measured using the 24-item version of
the Roland Morris Disability Questionnaire.[43] Average pain intensity over the last week was
measured on a numerical rating scale [42] Function was measured with a modified Patient-Specific
Functional Scale.[42]

5


Ultrasonography
Ultrasound images were made with a 5.5 cm, 5 MHz linear array ultrasound transducer1*. The
transducer was placed transversely across the right abdominal wall along a line mid-way between the
inferior angle of the rib cage and the iliac crest. The medial edge of the transducer was positioned so
that the medial edge of transversus abdominis was aligned in the right-hand one-third of the ultrasound
image when the subject was relaxed. The location of the transducer was recorded for standardisation of
placement across measurement sessions. All ultrasound measures were made blinded to the subject’s
treatment group.

Procedure
A previously published ultrasonography protocol was used to measure change in thickness of TrA as an
indirect measure of recruitment during a task that involved generation of flexion and extension torque
at the knee.[10] Unlike other measurements of voluntary TrA recruitment such as the abdominal
drawing-in manoeuvre, this protocol involved measurement of automatic activation of trunk muscles
during the leg task with no conscious attention to the abdominal muscles. Participants were positioned
in supine on a bed with arms crossed over the chest, the hips flexed to 50 degrees and knees flexed to
90 degrees. Knee flexion and extension force was monitored with a spring scale attached to a belt
strapped around the ankles. Patients were instructed to remain relaxed prior to testing and then to
perform isometric knee flexion or extension contractions to target forces of 7.5% of body weight. The
order of testing movement direction was randomised and patients were provided with verbal feedback
about force by the examiner reading the spring scale. Two repetitions of each task were performed and
static transversus abdominis ultrasound images were made both at rest and once the target isometric
knee flexion or extension force had been reached. Reliability analysis for this ultrasonography protocol
has been shown to be excellent with an Intraclass Correlation [3,1] Coefficient of 0.85 and a minimal
detectable change score of 1.16%.[44]

Data extraction
Transversus abdominis thickness was measured using ultrasonography with custom-designed software.
A grid was placed over the image and measures of muscle thickness of transversus abdominis were
made at three sites: the middle of the image and 1 cm (calibrated to the image scale) on either side of
the midline. The average of the three measures from each image was recorded for analysis and the
thickness for each direction of movement was expressed as a proportion of the thickness at rest and
averaged over the 2 repetitions of the task. Change in thickness of transversus abdominis was obtained
by averaging the values for both directions of movement.

Statistical analysis
Means and standard deviations were employed to describe demographic data, recruitment of
transversus abdominis recorded as a change in thickness measured with ultrasonography, and clinical
outcomes (perceived recovery, function, disability and pain).

Changes in recruitment of transversus abdominis and clinical outcomes within groups were analysed
with paired t-tests. Differences between treatment groups in the ability to recruit transversus abdominis
were analyzed using a one-way ANOVA and Tukey post hoc tests on the change scores. Pearson’s r
was used to analyse the relationship between changes in transversus abdominis recruitment and
changes in clinical outcomes. Linear regression was used to analyze whether the effect of motor control
exercise (contrasted to general exercise) on final clinical outcomes was influenced by subject’s ability

1
Logic 100 Pro General Electric
6


to recruit transversus abdominis at baseline after adjusting for baseline clinical outcomes. A
significance level of 5% was chosen a priori.

RESULTS
Forty-five participants in the randomized control trial within which the present study was nested, were
invited to participate. Of these, 4 refused to participate, 3 did not tolerate the test procedure because of
pain in the knee or hip joints, and in 4 it was not possible to obtain a clear image of transversus
abdominis due to excessive adipose tissue. A total of 34 participants were therefore recruited into this
study. The final sample included 11 participants in the motor control exercise group, 10 patients in the
general exercise group, and 13 patients in the spinal manipulative therapy group (Figure 1).

<<figure 1 approximately here>>

Baseline demographic data, recruitment of transversus abdominis, and clinical outcomes are presented
in Table 1. Patients attended a mean (SD) of 8.7 (2.6) motor control exercise sessions, 11.2 (1.5)
general exercise sessions, and 9.2 (2.4) spinal manipulative therapy sessions. All 34 patients were
reassessed after treatment. There were no significant between-group differences in the baseline clinical
outcomes or TrA recruitment (one-way ANOVA, p 0.05 for all comparisons). Between-group
≥
comparisons were conducted on change scores or ANCOVA-adjusted scores using the baseline as a
covariate so that any discrepancies in baseline scores would not cause bias.

7

Table 1 – Baseline characteristics of the study participants.

MCE (n=11) GE (n=10) SMT (n=13)
Age (years) 47.5 (17.3) 54.9 (11.3) 45.4 (17.7)
Weight (kg) 78.7 (13.0) 70.1 (12.0) 72.6 (10.2)
Height (cm) 171.0 (10.8) 160.7 (6.6) 165.0 (8.5)
Female n (%) 6 (55) 7 (70) 10 (77)

Pain duration (weeks) 104 (93) 183 (134) 114 (86)

Work status (number (%)
Full time 1 (10) 0 (0) 3 (23)
Part time 2 (20) 0 (0) 3 (23)
Not working 7 (70) 11 (100) 7 (54)
Transversus abdominis recruitment 4.6 (7.7) 13.7 (14.9) 8.5 (11.3)

Perceived recovery at baseline (-5 to 5) -2.91 (1.64) -3.70 (1.06) -2.38 (2.32)
PSFS at baseline (1-30) 11.09 (3.21) 9.70 (4.14) 11.62 (4.66)
RM at baseline (0-24) 14.00 (4.94) 12.70 (6.00) 9.77 (5.93)
Pain at baseline (0-10) 6.36 (2.20) 7.50 (1.35) 5.38 (2.22)

Values shown are means and standard deviations (except for work status).
Transversus abdominis recruitment measured as change in muscle thickness as % of resting thickness; PSFS patient specific functional scale;
RM Roland Morris disability questionnaire; MCE motor control exercise; GE general exercises; SMT spinal manipulative therapy.

8


The clinical and ultrasound measures are shown in Table 2. All 3 groups improved in the clinical
outcomes of perceived recovery, function, disability and pain at the 8-week follow-up. Transversus
abdominis recruitment improved by 7.8% in the motor control exercise group and deteriorated by 4.9%
in the general exercise and 3.7% in the spinal manipulative therapy groups. Paired t-tests revealed that
none of these changes were statistically significant. However the change in recruitment observed with
motor control exercise approached significance (t10 = 2.02; p = 0.07).

9

Table 2 - Baseline, final, and improvement scores for transversus abdominis recruitment and clinical outcomes, for all groups.

MCE (n=11) GE (n=10) SMT (n=13)

Transversus abdominis Baseline 4.6 (7.7) 13.7 (14.9) 8.5 (11.3)
recruitment (% change from Final 12.4 (11.6) 8.8 (12.1) 4.9 (9.1)
resting thickness)
Improvement 7.8 (12.8) -4.9 (10.7) -3.7 (10.9)
Baseline -2.91 (1.64) -3.70 (1.06) -2.38 (2.32)

Perceived recovery (-5 to 5)
Final 2.09 (2.88) 1.50 (3.24) 3.08 (1.66)
Improvement 5.00 (3.10)* 5.20 (2.94)* 5.46 (2.85)*
Baseline 11.09 (3.21) 9.70 (4.14) 11.62 (4.66)
PSFS (1-30) Final 18.91 (6.55) 14.50 (6.29) 20.92 (5.66)
Improvement 7.82 (7.33)* 4.80 (3.79)* 9.31 (6.55)*
Baseline 14.00 (4.94) 12.70 (6.00) 9.77 (5.93)
RM (0-24) Final 7.36 (6.59) 9.00 (6.04) 4.15 (2.76)
Improvement 6.64 (5.68)* 3.7 (5.06)* 5.62 (5.09)*
Baseline 6.36 (2.20) 7.50 (1.35) 5.38 (2.22)
Pain (0-10)
Final 4.00 (2.37) 4.70 (1.77) 2.92 (1.71)
Improvement 2.36 (3.20)* 2.80 (2.70)* 2.46 (2.33)*

Values are means and standard deviations. Change scores calculated so positive scores are improvements. *denotes significant at p<0.05. Transversus
abdominis recruitment measured as change in muscle thickness as % of resting thickness; PSFS patient specific functional scale; RM Roland Morris
disability questionnaire; MCE motor control exercise; GE General Exercises; SMT spinal manipulative therapy.

10


There were significant differences between groups with respect to the improvement in transversus
abdominis recruitment (F2,31 = 4.09; p = 0.026). Motor control exercise produced 12.7% greater
improvement in transversus abdominis recruitment than general exercise (p = 0.043) and 11.4%
greater improvement than spinal manipulative therapy (p = 0.053). No difference in improvement
was found between the spinal manipulative therapy and general exercise groups (p = 0.963).

When data from the 3 groups were pooled (Fig 2), there was a correlation between improvements in
recruitment of transversus abdominis and improvements in the clinical outcomes of perceived
recovery (r= 0.27; 95%CI -0.08 to 0.55); Roland Morris disability scores (r= -0.35; 95%CI 0.02 to
0.62); patient-specific functional scores (r = 0.19; 95%CI -0.16 to 0.50) and pain (r = -0.28; 95%CI
0.07 to -0.56). Only the correlation with the Roland Morris disability score was statistically
significant.

<<figure 2 approximately here>>

The effect of motor control exercise (versus general exercise) was greater in subjects who had a
poorer ability to recruit transversus abdominis at baseline, however the estimates of this interaction
effect are imprecise and only statistically significant for the pain outcome. The interaction effect for
pain was: 18.1 (1.2 to 34.9) p= 0.037. The interpretation of this finding is that a subject who had a
baseline transversus abdominis activation score of 0.00 would have 3.6 units less pain at the
conclusion of treatment than a subject whose baseline transversus abdominis activation score was
0.20 ie (0.00-0.20)x18.1 = -3.6. The interaction effects for the other outcomes were Roland Morris
disability (effect = 16.1; -34.0 to 66.2; p = 0.506); patient-specific function (effect = -13.7; -67.2 to
39.9; p = 0.597); and for perceived recovery (effect = -19.9; -45.3 to 5.5; p = 0.116).

11


DISCUSSION
This study shows that, in chronic LBP, the improvement in recruitment of the trunk muscle
transversus abdominis, measured by changes in thickness with ultrasonography, was greater in
those who performed motor control exercise than in those who undertook a program of general
exercise or spinal manipulative therapy. The motor control exercise group showed an absolute
increase in recruitment of transversus abdominis of 7.8% compared with a slight decrease in
recruitment of transversus abdominis in the general exercise group (-4.9%) and in the spinal
manipulative therapy group (-3.7%). All these values exceeded the previously reported minimal
detectable change score of 1.16% for the ultrasonographic measurement of transversus abdominis.
This magnitude of change demonstrates that changes in recruitment with the implementation of
treatments are above the potential error associated with the measurement.

Our results suggest that relieving pain with spinal manipulative therapy or encouraging general
activity with a general exercise program is not sufficient to maximally improve the ability to recruit
transversus abdominis. We found that application of a motor control exercise program was the most
effective method for improving recruitment of transversus abdominis in people with chronic LBP.
Improvements in transversus abdominis recruitment associated with motor control training have
also been identified in the short term (4 weeks) in LBP patients[45] as well as in asymptomatic
subjects.[46] Other studies of fine-wire EMG recordings of transversus abdominis activity have
reported changes in timing of muscle activation after motor control training, both immediately[31]
and at 6 months.[30] Similar results have been noted for other deep muscles of the spine in another
trial evaluating physical treatment of acute LBP.[47] Hides et al[47] found in patients with acute
LBP, that motor control exercise, but not usual medical care, reduced multifidus asymmetry
between the symptomatic and asymptomatic sides. Similar to the present study, the participants in
Hides and colleagues’ study in both groups exhibited similarly large improvements in pain and
disability at the end of four weeks of treatment, however the group that did not receive multifidus
exercise did not restore the symmetry of multifidus. Although the short term outcomes were similar
for pain and disability differences were apparent in the long term, the group who had restored
symmetry of multifidus experienced a significantly reduced rate of recurrence of episodes.[47]

When data from the three treatment groups in our trial were pooled there was a moderate correlation
between change in recruitment of transversus abdominis and perceived recovery. This correlation
was positive, which means that an increase in recruitment of transversus abdominis correlated
moderately well with improvements in perceived recovery. There was also a moderate, negative
correlation between increase in recruitment of transversus abdominis and disability measured with
the Roland Morris questionnaire, which means that an increase in the recruitment of transversus
abdominis was associated with reductions in disability. Although neither pain nor function was
statistically significantly correlated with transversus abdominis recruitment, the effects were in the
anticipated direction.

An important finding of the study was the interaction between subject’s ability to recruit transversus
abdominis at baseline and the effect of motor control exercise (versus general exercise) on pain
outcomes. The effect we found was in the direction suggested by clinical theories. In the main
trial[37] we demonstrated that motor control exercise produced better short-term outcomes than
general exercise and so on average motor control exercise is superior. However the interaction
effect means that motor control exercise worked best for participants who had a poor ability to
recruit transversus abdominis and conversely for participants who have a good ability to activate
this muscle general exercise may be a better treatment option. We are aware that it is possible to
generate spurious findings when looking for treatment interaction effects in clinical trials.[48,49] To
reduce the risk of this we specified our analysis a priori and confined our analysis to one predictor
that was biologically plausible. We used the preferred approach of a statistical test of an interaction
and confined the analysis to primary outcomes.
12


Although we have demonstrated that the baseline ability to recruit TrA modifies the treatment effect
of motor control exercise (versus general exercise) it would be premature to attempt to apply this
research finding to the routine clinical management of LBP. We first need to replicate the result in a
larger, independent sample so that we can generate a more precise estimate of the magnitude of
effect modification and also generate cut-off scores for the ability to recruit TrA. Such data could be
used to develop a clinical prediction rule. Lastly the rule would have to be validated in a clinical
trial and then demonstrate the impact of implementation of the rule on the outcomes of care in
subsequent research.[50] We expect this process to take some years.

Conclusion
It has been uncertain whether motor control exercises lead to changes in activation of transversus
abdominis and whether these changes are associated with clinical improvements. Our findings show
that, after adjusting for baseline values, a greater change in the automatic activation of transversus
abdominis, measured by ultrasonography, occurs after a motor control exercise program than after
other interventions, and this change in muscle activity is associated with improvements in disability.
The study also demonstrated that the pain-relieving effect of motor control exercise is greater in
subjects who have a poor ability to recruit this muscle at baseline.

13


WHAT IS ALREADY KNOWN ON THIS TOPIC
• Recruitment of transversus abdominis is impaired in patients with LBP.
• Motor control exercises aimed at training the control and coordination of the trunk muscles,
including transversus abdominis, are effective in the management of LBP.

WHAT THIS STUDY ADDS
• Changes in the recruitment of transversus abdominis appear to be specific to the
implementation of motor control exercises and are moderately associated with improvements in
disability.
• The treatment effects of motor control exercise are greater in those with a poorer ability to
recruit transversus abdominis.

Acknowledgements: the trial was funded by the Motor Accident Authority of NSW; Chris
Maher, Rob Herbert and Paul Hodges are supported by the National Health and Medical Research
Council of Australia.

Competing interests: none

Figure legends
Figure 1 - Flowchart of progress of patients. TrA, transversus abdominis.
Figure 2 - Overall correlation between changes in recruitment of transversus abdominis measured
with ultrasonography and changes in clinical outcomes. Lines represent the r2 line of best fit; PSFS
Patient Specific Functional Scale; RM Roland Morris; TrA, transversus abdominis.

14


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"The Corresponding Author has the right to grant on behalf of all authors and does grant on
behalf of all authors, an exclusive licence (or non-exclusive for government employees) on a
worldwide basis to the BMJ Publishing Group Ltd and its Licensees to permit this article to
be published in British Journal of Sports Medicine editions and any other BMJPGL products
to exploit all subsidiary rights, as set out in our licence
http://bjsm.bmjjournals.com/ifora/licence.pdf "

18

Last 45 patients randomised to controlled
trial invited to participate in the study

4 patients refused to participate
3 patients did not tolerate test procedure
4 patients did not show a clear image of
transversus abdominis on screen

34 patients admitted to study

Randomisation

Baseline measures
• TrA recruitment Motor control General Spinal
• Perceived recovery exercise group exercise group Manipulative
• Function (n=11) (n=10) group
• Disability (n=13)
• Pain
Treatment (8 weeks)

Follow-up measures
• TrA recruitment Motor control General Spinal
• Perceived recovery exercise group exercise group Manipulative
• Function (n=11) (n=10) group
• Disability (n=13)
• Pain

6
A B
25

4
20
Perceived recovery

PSFS change
2
15
R=0.2
0
R=0.3
R=0.4
10
-2

5
-4

-6 0
-0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4

TrA recruitment change TrA recruitment change

C
C D
8
4
4 R=-0.4
2
0
R=-0.3

Pain change
RM change

-4 0
RM change

-8
-2
-12
-4
-16
-20 -6
-0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4
TrA recruitment change
TrA recruitment change

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