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(15–17).
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(18–20). 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 120º shoulder abduction and 90º 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. Hands were clasped in back of the head. The subject Slowly lifting the thoracic spine so that the scapulae were off the floor with keeping abdominal muscles draw in. The subjects performed the curl-up both on the floor (stable status) and with a balance cushion (unstable status).
Pelvic bridging: The participant was lying in the supine position with arms out to the side, feet flat on the ground, knees flexed at 90° and toes facing forward. The participant lifted the pelvis to degree hip flexion get zero. The participant carried out the pelvic bridge position on the ground (stable status) and with the feet and trunk on the balance cushion (unstable status).
Prone plank: The participant assumes a prone position on the ground with elbows were below the shoulders and the brachiums were vertical to the ground, while only the toes and forearms were palpating the ground. The participant carried out the prone plank motion on the ground (stable status) and with the forearms and toes on a balance cushion (unstable status).
Side plank: The participant assumes a side plank position with elbow below the shoulder and brachiums vertical to the floor. The participant lift the pelvis off the ground such that that the body aligned in a straight line, supporting points were on elbow and feet. Subjects carried out the side plank on the ground (stable status) and with the elbow and feet on the balance cushion (unstable status).
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).
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 p-value lower than 0.05.