Comparison of the effect of exercise on stable surface versus unstable surface on cross section area of lumbar multifidus muscle and thickness of abdominal muscle in patients with chronic low back pain CURRENT STATUS:

Objective The aims of this study were, comparison the effects of core stability exercises performed on a stable or unstable surface on the thickness of abdominal and lumbar multifidus muscle in patients with nonspecific chronic low back pain. Method Thirty-four patients were randomly assigned to an unstable or stable surface group (n = 17 each). Both groups did five core stability exercises for 6 weeks (three times per week). the thickness of the core muscle was evaluated pre and post-treatment. Results After 6 weeks of training, in both groups, all variables improve. internal oblique muscle thickness and transversus abdominis thickness in the unstable surface group improved significantly more than those in the stable surface group (p <0.05). Conclusion Our findings indicate exercise on an unstable surface more effective in improving the core muscle thickness relative to stable surface in patients with non-specific chronic low back pain. However, extra studies are required to support our findings.

10% of cases have specific cause. possible sources of pain in "non-specific CLBP" are some degenerative conditions, metabolic bone disease, psychogenic pain, inflammatory conditions, infectious causes, trauma, referred pain and congenital disorders (8,9).
According to European Guidelines the first stage treatment for Management of Non-Specific CLBP is exercise therapy (3). The core has been define as a muscular girdle to stabilize the trunk and spine, with and without limb movement. the aim of core Stability exercise is training and coordination of abdominal and lumbopelvic region (3,10). In healthy subjects in order to stabilize the lumbar spine, the transversus abdominis and multifidi are the first muscles to be contracted before shoulder and leg movement (4,10). But in patients with LBP contraction of these muscles was significantly delayed (11).
Ultrasound imaging is an objective and non-invasive method for measuring muscle morphology, cross-sectional areas (CSA) and muscle thicknesses (4,12). In addition, ultrasound has been used for evaluation of muscle atrophy and hypertrophy as well as for assessment of the effectiveness of the rehabilitation programs(4).
I.R. Scott et al. reported significant increases in CSA of LM when sitting on an unstable surface compared to a stable surface in both healthy subjects and patients with CLBP (5). It has been assumed that performing training on unstable conditions provides higher stress to the entire musculature (13).
Previous studies noted that an unstable surface stimulated the sensory and motor system further than a stable surface (14).
The objective of this research was to compare trunk muscle thickness under stable and unstable conditions in patients with chronic non-specific LBP. Based on previous study, our supposed was that when performing training on an unstable surface trunk muscle thickness more increase.

Study Design
This study was single-blind randomized clinical trial and conducted between July 2019 and December 2019. This study was approved by the Ethics Committees of Shiraz University of Medical Science in date 2019-02-27 and registered in the Iranian Registry of Clinical Trials (IRCT) as IRCT20190527043730N1. all participants were conscious of their treatment but were blinded to the sort of treatment in the other group.
Subjects: The sample size was determined via the difference between two independent means (two groups: t test-means) formula. Thirty-four Patients with non-specific CLBP were recruited to the Faculty of Rehabilitation Sciences of Shiraz University of Medical Sciences through printed advertisements on notice boards at various clinics. these patients randomly allocated into two experimental groups equally: group A carried out core stability training on a stable surface and group B carried out them on an unstable surface. The participants were randomized via permuted block randomization method with 2 block size.
The inclusion criteria consisted of: Patients with diagnosed mechanical low back pain, both males and females, age of 18-40 years, LBP with an onset duration > 3 months, pain intensity of 3-8 in the VAS Patients with minimum to moderate disability on ODI (15). The exclusion criteria consisted of: patients with pregnancy, spinal fractures, herniated discs, acute back pain, systemic disc herniation, severe osteoarthritis, spondylolisthesis and spondylolysis, lower limb length discrepancy, previous surgery on vertebral column, malignancy, scoliosis (15)(16)(17).

Outcome measurements
Before and after the treatment, data on the thickness of the transverse abdominis (TrA), internal oblique (IO), external oblique(EO) and lumbar multifidus(LM), as well as cross-section area (CSA) of LM were collected using ultrasound Imaging.

Thickness of the lateral abdominal muscles
Bilateral thickness of the EO, IO and TrA muscles were measured using a HS-2600 diagnostic ultrasound imaging unit (Honda Electronics Inc., Honda, Japan) that was set in B-mode and used a head transducer with 7.5 MHz, 60-mm, board band linear array (18). All thickness were measured at the relaxation and during the abdominal drawing-in maneuver (ADIM). The lateral abdominal muscles measurement was performed with the Participant in the supine crook-lying position and the transducer placed transversely at the center point of the anterior axillary line (the midpoint amid the iliac crest and the last rib). In the supine crook-lying position, a Pressure Biofeedback Unit (PBU, Chattanooga Group, Hixson, TN, USA) was located below the participant's lumbar spine and the bulb was filled with the air up to a pressure of 40 mmHg (18)(19)(20). Then, the abdominal muscle activation measurements were recorded while the participants performed the ADIM. In this maneuver participants gently pull their lower abdominal muscles in toward their spine While pressure applied to the PBU was increased 0, 2 or 4 mmHg. contraction held for 7 s. all image was stored at the end of expiration.

Thickness of the lumbar multifidus
Longitudinal view of bilateral LM muscle at the L4-5 level was obtained at rest and during a contralateral arm lift with the participant positioned prone. In order to reduce the lumbar curve used a cushion below the abdomen and the hip. The transducer was located longitudinally along the L4 spinous process, shifted laterally, and then slightly was angled in a medial direction. This point was directly over the L4/L5 facet joint. The space between this landmark and the plane between the muscle and subcutaneous tissue was used to the thickness measurement of LM.

Cross-section area of the lumbar multifidus
To determine the CSA of LM, in first the transducer was placed longitudinally on the L4 spinous process, then was rotated 90 degrees to put transversely in the midline. The echogenic vertebral laminae were used as a landmark to recognized the inferior border of the LM muscle. The multifidus muscle is bordered medially by the acoustic shadow from the tip of the spinous process of the vertebral, and the superior border was determined by the thoracolumbar fascia. The lateral border was provided by the fascia separating multifidus muscle from the longissimus. The contralateral upper extremity lifting task was performed with 120 º shoulder abduction and 90 º elbow flexion.
participant lifted a light hand weight off the table nearly 5 cm and held it for 8 s.

Intervention and procedure
In this study, subjects who satisfied the selection criteria were randomly divided into the stable surface group (group A) and unstable surface group (group B).
During the study period, all subjects completed general physical therapy, consisting of a 20-minute hot pack treatment, 20-minute Conventional TENS, characterized by continuous stimulation at high frequencies (80-100 Hz), with wave durations of 50-100 ms and low intensities, and 5-minute ultrasonic treatment (0.8-1 MHz) (21). After patients had undergone general physical therapy, they had performed the lumbar stabilization exercise program. The lumbar stabilization exercise program was consist of elbow-toe, back bridge, side bridge, hand-knee, and curl-up motions.
Both the groups were asked to carry out 5 types of core stability exercises thrice a week for 6 weeks (total of 18 sessions) (22). The intensity of the exercise program was advanced every 2 weeks.
Curl-up: The participant was on the supine position with knees bent and feet flat on the ground. Bird-Dog: The participants were placed in a quadruped position and were requested them to raise the upper limb directly, whilst concurrently raising the opposite lower limb as well as keep it direct. In this position, participants held their pelvis in a neutral position and also were breathing as normal.
Participants performed the bird-dog on the floor (stable status) and with a balance cushion (unstable status). (16,17,23).

Data analysis
For the data analysis, SPSS version 23 software was used. The normality of all variables was performed by Shapiro-Wilk test. The demographic characteristics (age, height, weight, pain intensity and oswestry disability index) were not significant differences between the two groups (P > 0.05) (Table1). The independent t-test and Mann-Whitney U test were used to compare the size of the muscles, before and after the trunk stabilization exercises, between the two experimental groups for parametric and nonparametric data, respectively. The paired t-test and Wilcoxon test were used to analyze the muscle size in each group, before and after the trunk stabilization exercises for parametric and nonparametric data, respectively. The statistical significance level was accepted A pvalue lower than 0.05. Comparison of changes between the two groups revealed that the resting thickness of the left internal oblique, resting thickness of the left TrA, resting and contraction thickness of the left multifidus muscle, resting and contraction thickness of the right internal oblique, resting and contraction thickness of the right TrA and cross-sectional area of left multifidus muscle during rest and contraction in group B greater than those in the group A (p < 0.05). Other variables showed no significant difference between the two groups (p > 0.05).

Discussion
This study examined whether core stability exercises performed on an unstable surface were more effective at improving abdominal muscle thickness and thickness and cross-section area of lumbar multifidus muscle rather than stable surface during 18 session treatment. surface increased proprioception in trunk muscles (12). As a result, many investigators claim training under unstable conditions improve joint position sense, balance, posture and proprioception that focus on muscle recruitment, and also provides a greater stress on the core musculature (29,30).

Conclusion
This study provides evidence of increased thickness of internal oblique, TrA, and lumbar multifidus muscles when training on an unstable surface compared to a firm surface in individuals with CLBP.
These findings supported the use of an unstable surface in rehabilitation to improved trunk muscle size. This study was approved by the Ethics Committees of Shiraz University of Medical Science in date 2019-02-27. participants were provided exact information about the study process and safety and they were allowed to exclude from the study without revealing any reason at any time. All patients signed informed consent.

Consent for publication
Not applicable.

Availability of data and material
The raw data sets used and/or analyzed in this study are available from the corresponding author on reasonable request.

Competing interests
The authors declare that they have no conflicts of interest.

Funding
This study did not receive any external funding.

Authors' contributions
ME participated in the data collection, data analysis and writing of the manuscript; FGN participated in the data collection, data analysis and writing of the manuscript; FE participated in the data analysis and interpretation of data; ST participated in the design, data analysis and revisions of the manuscript. CONSORT flowchart