Comparison of Biofeedback Tools to Train the Transversus Abdominis Activation in Healthy Subjects
Comparison of Biofeedback Tools to Train the Transversus Abdominis Activation in Healthy Subjects
Introduction: Non specific low back pain (NSLBP) is a low back pain (LBP) that cannot be
 attributable to a known pathology. LBP has prevalence as high as 84%, making it a heavy
 burden for health services and society worldwide. Furthermore, LBP seems to be more prevalent
 as the population gets older, and is the cause of severe functional limitations. One of the
 treatment recommended for LBP is physical therapy. It has been shown that the trunk muscles
 usually maintain trunk stability by making a sequence of postural adjustment in advance of
 distal movement to prevent any loss of balance. However, in NSLBP, this motor control
 adjusting is lacking, and, furthermore, stays so even after the resolution of acute LBP,
 which could contribute to the recurrence of LBP. Physical therapy therefore addresses NSLBP
 by rehabilitating the timing and activation of trunk muscle, among other things. The
 importance of trunk musculature has been highlighted by many studies showing the feedforward
 contraction of the trunk muscles in anticipation of extremity movement. Those trunk muscles
 comprise the transversus abdominis (TrA) and lumbar multifidus (LM). Since those muscles
 create no movement, but rather an increase in abdominal pressure, it is thus often a complex
 contraction to teach. To help with that teaching, physical therapist may use one of the two
 feedback tools that exist to teach a TrA contraction, namely the pressure biofeedback unit
 (PBU) and rehabilitative ultrasound imaging (RUSI). Unfortunately, their efficiency to help
 with the teaching of TrA contraction is yet to be shown in an elderly population, and few
 studies compared their efficiency. Furthermore, even though the teaching of the TrA
 contraction must be followed by a translation of that skill in more functional position such
 as standing, no studies looked at the effect of the feedback in supine to the skill of TrA
 contraction in standing.

 Objective: The principal aim of this study is thus to compare, throughout a healthy
 population of 60 to 80 years old, the immediate efficiency of adding PBU or RUSI to the TrA
 contraction teaching in supine. The secondary objectives are as follow: 1) to see if that
 teaching in supine can be translated by a better contraction of the TrA in standing, and if
 one of the two tools is superior in doing so and 2) to see if one tool favor a more specific
 contraction of TrA when compared to the other muscles of the lateral abdominal wall. The
 hypothesis is that the RUSI will prove superior to the PBU.

 Method: This will be a single-blinded controlled laboratory study with randomization. The
 independent variables will be the group of randomization, either PBU or RUSI. The dependent
 variable will be the TrA contraction. To answer our objectives, forty (40) healthy people
 aged between 60 and 80 will be recruited. The subjects will be healthy with no current pain
 and no history of limiting LBP in the past year. Of those, 20 will be women. The
 randomization will be made in blocks to allow a good balance of the sex throughout the
 groups. Every subject's TrA contraction (principal outcome) will be measured before and after
 the intervention (immediate effect) with the RUSI (change of thickness between resting and
 contracting state) both in supine and standing. The intervention will consist of a 5-minute
 education on the trunk muscle and their role, a brief teaching of how to contract them
 properly and the use of the feedback tool used in their group. Will follow a training program
 of 15 contractions with the feedback tool (PBU vs RUSI). Descriptive analysis will be used to
 describe the subjects. The TRA activation ratio (AR) and preferential activation ratio (PAR)
 will be compared after the intervention with Wilcoxon signed rank tests for each subject
 first. The group's mean will then be compared, first for each age group, then for each
 feedback tool as a whole with the Wilcoxon rank sum test.

 Impact: Age and LBP both influence the motor control and feedforward contraction of the trunk
 muscles. Since NSLBP is highly prevalent throughout the ages and cost a lot for the society,
 the identification of the best tool to help in teaching the TrA contraction is crucial. This
 project will provide the first steps to justify a bigger controlled study on NSLBP. Moreover,
 this project will familiarize the Canadian physical therapist society to the use of RUSI, a
 tool still seldom used in the clinic in Canada but highly promising.
1. Introduction Low back pain is defined as a pain in the lower back bad enough to limit
 your usual activities or change your daily routine for more than 1 day, that may or may
 not go down one or both legs and lasting at least a day. The pain must be comprised on
 the back, within the limits of the lower rib and the lower gluteal fold. Low back pain
 (LBP) can further be compartmentalized in "specific LBP", by definition a LBP that be
 attributable to a known cause, or in "non-specific LBP" (NSLBP), defined as a LBP that
 cannot be associated to a known cause. LBP is one of the leading causes of functional
 limitations and sick leave, carrying a heavy financial cost for both individuals and
 society. According the 2010 Global burden Disease study, LBP is classified the 6th in
 the overall burden when compared to 290 other pathologies. Global prevalence of LBP is
 between 11% and 84%, and would reach its peak value à 80 years old. Therefore, the
 impact of LBP would be more important in societies where the life expectancy is higher,
 such as Canada and the United States. Moreover, aging would be accompanied by an
 increase in the frequency of severe back pain, as well as an increase in the prevalence
 of pain and other symptoms and conditions associated with low back pain, occasioning
 higher social and functional limitations. It also is one of the main causes of physical
 therapy consultation, which uses therapeutic exercises, such as core muscle training to
 address it. Yet, it is unknown as today which method is to be privileged to teach how to
 contract those muscles in the elderly.

 2. Literature review One of the favoured approaches in physical therapy to address LBP is
 the training of the core muscles, specifically the transversus abdominis (TrA). In a
 healthy subject, trunk muscles will maintain trunk stability by making a sequence of
 postural adjustment in advance of distal movement to prevent any loss of balance. This
 fine tuning adjusting happening before any kinesthetic or sensorial feedback may happen,
 it is considered as planned by the central nervous system (CNS). Yet, it has been shown
 that those postural adjustments are lacking in the patients with LBP, and would persist
 even after the resolution of the LBP episode, which might contribute to the recurrence
 of LBP. Furthermore, aging is also accompanied by a diminution of motor control of the
 trunk, constituting a part of the LBP in the elderly. Fortunately, these postural
 adjustments of the TrA have been shown to be trainable again.

 Teaching to contract the TrA often gets to be quite a challenge, since its contraction
 creates no visible movement. It requires an understanding and/or a good feeling of the
 desired contraction from the patient. To help in the teaching of the TrA, physical therapists
 (PT) may use one of the few feedback tools that have been shown to be efficient in that
 regard. Biofeedback is a technique where the biological information otherwise unknown to the
 patient is transmitted in real time to him. That information goes over what is usually
 accessible for those patients. In physical therapy, biofeedback comes from the biomechanical
 measure of physiological measure of the human body. Adding biofeedback to a usual physical
 therapy intervention enables the patient to control physical adjustments that were thought to
 be controlled by the CNS, such as the postural adjustments. It also allows for a better
 tuning in the tasks and engages the patient in a more proactive therapy. In the literature,
 two non-invasive biofeedback tools used in clinics are documented for their efficiency to
 assist in the teaching of the TrA contraction and for their validity to measure its
 activation, the rehabilitative ultrasound imaging (RUSI) and the pressure biofeedback unit
 (PBU).

 The use of RUSI by physiotherapists is growing. RUSI is a non-invasive technique to provide
 immediate visual feedback on changes in the thickness of the abdominal wall muscles,
 reflecting the contraction of these muscles, more specifically the TrA. This is done by
 transmitting, on a screen, an ultrasound image produced by a probe placed on the abdomen of
 the participant. The probe emits ultrasound waves which passes through the tissues and then
 return to the probe in the form of echoes. RUSI would detect recruitment of TrA at a
 contraction as low as 12% of the maximum voluntary contraction (MVC), and recruitment of the
 internal oblique (OI) when contracted to 22% a MVC. This visual feedback, coupled with the
 usual explanations for TrA recruitment, reduces the number of trials required for an
 effective recruitment of TrA in patients with and without low back pain immediately after
 training and in the short-term follow-up.

 The PBU is a simple and inexpensive device that measures the change in pressure in a
 three-compartment bag filled with air placed under the patient's lumbar spine whilst lying on
 his back (supine position). The movement of the lumbar spine on the three-compartment bag
 produced by a false contraction of the TrA changes the intensity of the pressure and this
 change can be seen on an adjustable gauge, and therefore avoided. However, Lima et al. (2012)
 have shown a low association between the pressure measured with the PBU and the surface
 electromyography (EMG) (r = 0.2, p <0.2), with a sensitivity and a specificity of 60%. A
 systematic review by the same author concludes that inter- and intra-evaluative reliability
 ranges from medium to good (intra-class correlation (ICC) of 0.42 to 0.82 and 0.5 to 0.81,
 respectively) and a construct validity ranging from medium to excellent (ICC from 0.48 to
 0.90). Nevertheless, it is a widely used apparatus for learning TRA in physiotherapy because
 of its low cost and ease of use.

 Only three studies compared the efficacy of RUSI and PBU on the recruitment of TrA in both
 young and asymptomatic individuals and low back pain. Bajaj et al. (2010) report that low
 back pain patients trained with RUSI acquire more rapidly the ability to recruit TrA
 (significant reduction in the number of trials required to activate the TrA and the number of
 days needed to consolidate learning) than those performed with the PBU. Lee et al. (2016)
 randomized a sample of young and asymptomatic individuals into three groups according to the
 type of feedback used during training: tactile, RUSI or PBU. The primary measurement was the
 thickness of the TrA measured with an ultrasound. An increase in TrA thickness (reflecting a
 better TrA activation) was observed in all three groups. When compared to the tactile
 feedback group, the RUSI group had significantly higher TrA thickness. Finally, Wooldridge et
 al. (2014) compared the immediate effect of training with different types of feedback (PBU,
 RUSI and PBU + RUSI) in a population similar to that of Lee et al. (mean age = 22.2 years).
 The authors report no significant difference in the activation of TrA, measured with
 different parameters extracted from ultrasound images, pre and post-training and between
 groups.

 In summary, although two studies show that the recruitment of the TRA would be more effective
 following training with the RUSI, the heterogeneity of interventions and outcome measures
 means that the current level of evidence does not allow a decision on its superiority in
 young people. Moreover, the results of these studies cannot be generalized to an elderly
 population. Aging can disrupt the anticipated postural adjustments, and an effective modality
 of training in young people may not be conclusive for the elderly. Finally, no study has
 verified whether the training of recruitment of the TrA, which is generally carried out in
 supine position, allows the transfer of the learnt skills to other more functional positions,
 such as the standing position, for either of the tools.

 Aim The main goal of this study is to compare the immediate (pre-post laboratory) effect of a
 TRA recruitment training with RUSI to that of training with the PBU on the thickness of the
 TrA, an indirect measure of recruitment measured in the supine position (SP) in a healthy
 elderly population. Secondary objectives are (1) to determine whether one of the feedback
 tools is more effective in facilitating preferential recruitment of TrA versus oblique
 muscles and (2) to determine whether one of the feedback tools is more effective in
 transferring the recruiting capacity of the TrA from the SP to the standing position. The
 main assumption is that in SP, the thickness of the TrA will be greater following the
 teaching with RUSI compared to teaching with the PBU. The secondary hypotheses are 1) the
 RUSI will allow a preferential recruitment of the TrA; and 2) the thickness of the TrA in the
 standing position will be greater following the teaching with the RUSI.

 Methods Ideally, the effectiveness of an intervention is assessed by a randomized controlled
 trial (RCT). However, the prerequisite for an RCT are as follows: 1) plausibility of
 previously demonstrated effect; 2) demonstration that the research procedures are well
 established in real situations and 3) the possibility of recruiting a large number of
 participants. The plausibility of effects is still verified in a new population with valid
 and reliable instruments. The investigators propose an experimental "before-after" laboratory
 study to document the immediate effects. The independent variable will be the type of
 feedback used (RUSI vs PBU) during a TrA recruitment training session, and the dependent
 variable will be TrA thickness, an indirect measure of TrA recruitment.

 Participants:

 The investigators will recruit 40 people aged between 60 and 80 according to a
 non-probabilistic sampling method from the Nabù recruitment bank of the Center for Aging
 Research (CdRV) and a non-probabilistic sampling method by convenience. These participants
 will be randomized to two intervention groups: RUSI or PBU. The randomization will be
 stratified by gender (in equal proportion) using sealed envelopes and of a random number
 table. Participants must be between the ages of 60 and 80 years of age and be in good health
 (no chronic conditions restricting activities or requiring punctual care) without back pain
 for more than 12 months and be free from pain since less 1 week. They should be unable to
 contract the TrA specifically (i.e. without contraction of the oblique internal (OI) or
 oblique external (OE) muscles in response to a simple instruction). Those able to contract
 their TrA specifically will be excluded, and statistics will be kept to describe that sample.
 The participants will have to live in the community or in semi-autonomous residence, and will
 be excluded participants with a history of spinal, abdominal or lower extremity surgery,
 neurological or respiratory problem, structural scoliosis, body mass index greater than 30,
 pacemaker, lower Mini Mental State Examination (MMSE) to 24 or previous TrA training
 experience. The recruitment procedures will go on until the full sample size is reached with
 admissible participants.

 Sample size :

 The sample size (n=40) was calculated to respect an effect size of 0.7 with an alpha error of
 5%.

 Procedure for data collection:

 Those interested in participating will contact the Project Coordinator to verify their
 eligibility and schedule a meeting. Upon arrival at the Research Center of the Centre
 hospitalier universitaire de Sherbrooke (CRCHUS), a member of the research team will welcome
 them and verify their ability to recruit the TrA to confirm their eligibility to participate.
 They will be asked to contract the TrA following a standardized verbal instruction and the
 presence or absence of contraction (i.e. movement of muscle fibers) will be checked with
 ultrasound. Individuals who will be excluded because of their ability to contract the TRA
 will receive, from a physiotherapist, the advice that is provided in current practice to
 improve their performance in contracting the TRA. The consent form will be presented and
 explained to those who will meet this last inclusion criterion. Once their free and informed
 consent is obtained, participants will be randomized to the two intervention groups. They
 will provide their age and they will be measured and weighed. This data will be used to
 describe the sample. They will also be asked to complete a questionnaire to diagnose the
 presence of urinary incontinence (QUID), which will be used as a covariance in the analyzes.

 Interventions (independent variables):

 RUSI Group: Participants will be taught about the anatomy of abdominal wall muscles and the
 general functioning of RUSI. Then, they will be invited to take the SP position, knees
 flexed. The feedback will consist of an ultrasound image transmitted to brightness (B)-mode.
 In order to obtain an image of the TrA, the probe will be placed halfway between the 12th rib
 and the iliac crest. The probe will be moved laterally to have the rim of the thoraco-lumbar
 fascia at the right edge of the screen, so that the 3 muscles of the abdominal wall are
 clearly seen, i.e. the oblique external (OE), oblique (OI) and TrA, according to the method
 described by Teyhen et al. ( 2005). Participants will receive the necessary education to
 understand the image and the desired recruitment according to a standardized protocol. They
 will then be asked to perform 15 contractions held 10 seconds of the TrA with a visible
 thickening of the TrA on the RUSI monitor exceeding the measurement at rest (visible on the
 monitor). One-minute rest will be allowed between each contraction to avoid fatigue.
 Participants will have to watch the RUSI monitor during the 15 tests. These parameters were
 determined from previous studies.

 PBU Group: Participants will receive the same instruction on the anatomy of abdominal wall
 muscles and general information about the PBU device. They will be invited to take the same
 position as for the RUSI group (SP, knees flexed). The feedback will be to visualize the
 intensity of pressure on the dial of a STABILIZER PBU. The PBU will be placed under the
 lumbar spine of the participants and inflated to 40 mmHg, as recommended by the manufacturer.
 Participants will receive the education necessary to understand the tool and the desired
 recruitment according to a standardized protocol. They will then be asked to perform 15
 contractions of the TrA with a duration of 10 seconds while maintaining the constant pressure
 at 40 mmHg ± 2 mmHg. A minute of rest will be allocated between each contraction.
 Participants will have to watch the PBU dial during the 15 tests.

 For both groups, interventions will be given by the same physiotherapist (PT treating)
 experienced with the use of both tools, and the duration of the lessons (anatomy and general
 information) will be the same.

 Dependent variable and measuring tools:

 The dependent variable is the change in thickness of the TrA muscle between the rest state
 and the recruitment state measured from an ultrasound image (LOGIQ E, GE Healthcare, 13 Mega
 Hertz (MHz) linear probe, at B-mode). Before and after the intervention, three images will be
 taken in the SP, knee-flexed (main objective) position at rest and during a TrA recruitment
 maneuver carried out according to the following instruction: "inhale then exhale, then bring
 your navel back to your vertebral column ". Three other images will be recorded in standing
 position (secondary objective 1), both at rest and when recruiting the TrA according to the
 same instruction. During these measurements, the ultrasound device will be arranged so that
 the participants cannot see the screen. The image capture will be taken with the probe in
 transverse plan and positioned midway between the 12th rib and the iliac crest. It will be
 moved laterally to have the rim of the thoraco-lumbar fascia at the right edge of the screen,
 allowing a clear image of the 3 muscles of the abdominal wall (i.e. OE, OI and the TrA). The
 angle on the skin will be adjusted to have the best image quality by keeping the same
 position perpendicular to the skin. The use of anatomical markers rather than superficial
 markers on the skin will improve reliability and reproduce clinical reality. Resting and
 activation measures will be taken at the end of the expiration to standardize the effect of
 breathing. This method has been demonstrated to be valid and reliable for indirectly
 measuring the activation of abdominal wall muscles in asymptomatic individuals. This measure
 has also been validated in an elderly population . In addition to the change in thickness of
 the TrA (main variable), other parameters will be used for secondary analysis purposes, such
 as the activation ratio (AR) and preferential activation ratio (PAR). Image recording and the
 intervention will be performed by a physiotherapist (PT measurement) with this expertise. She
 will be blinded the participant's group.

 Analysis :

 Descriptive analysis will be used to describe the sample. The investigators will compare the
 change in thickness of the pre and post-intervention TrA using Wilcoxon's signed row tests
 for dependent groups. Then, the averages for each group will be compared (RUSI vs PBU, young
 and elderly) using tests of the sum of the Wilcoxon ranks for independent groups. Analyzes of
 covariances (ANCOVA) will be used to study the effect of the presence of urinary incontinence
 (categorical variables) on changes in TrA thickness. In the event of missing or invalid data,
 a sensibility analysis will be made post hoc. The analysis will be made using the Statistical
 package for the social sciences (SPSS v.25).

 5. Potential Bias Participants and the attending physiotherapist will not be blinded for the
 intervention, but the physiotherapist responsible for the analysis and image capture will be
 unaware of the groups of randomization. The fact that the main variable measurement tool (TrA
 thickness) is also used as a feedback tool for one of the groups could induce an intervention
 bias. Note, however, that for the measurement of the main variable, no participant will see
 the monitor; they will therefore have no visual feedback. However, contact of the probe on
 the abdomen during ultrasound measurement will provide a tactile stimulation similar to that
 which the RUSI group was exposed during surgery. It is possible that these favours the
 realization of the task by the participants of this group during the measurement of the main
 variable. However, the investigators believe that this effect will have a trivial impact. The
 limitations of the other measurement tools would further compromise the validity or
 feasibility of our study (eg noise in the surface EMG or implanted EMG which is an invasive
 procedure).

 6. Clinical Benefits Age and NSLBP have been shown to affect motor control of trunk
 stabilizing muscles. Knowledge is limited and non-consensual for the young population and
 absent for the elderly. It is therefore the first study to focus specifically on the training
 of the TrA in a population of elderly people. This research project will allow us to realize
 the first steps (plausibility of the effect of RUSI and PBU in healthy elderly people, tuning
 of the procedures, testing of the recruitment and data collection procedures) to justify a
 larger RCT comparing the two feedback tools to promote recruitment of the TrA, reduce pain
 and improve function in a population suffering from NSLBP. Due to the high prevalence of
 NSLBP in the general population and particularly in the elderly, it is important to identify
 the most effective tool to optimize rehabilitation (better efficiency and less time).
Inclusion Criteria:

 -  Good health

 -  without back pain for more than 12 month

 -  free from pain for 1 week

 -  live in community,

 Exclusion Criteria:

 -  No chronic health condition restricting activities or requiring punctual care

 -  a capacity to specifically contract the TrA

 -  surgery to the thorax, abdomen or spine in the last 3 years

 -  pacemaker

 -  BMI>30

 -  previous training of TrA

 -  structural scoliosis

 -  lower than 24 on the MMSE