There are many proposed core stability exercises in a variety of positions; however, it is not clear that in which position, activation of transverse abdominis muscle is utmost. We aimed to compare the activation of transverse abdominis muscle in different core stability exercise positions through ultrasound imaging. in a 20 subjects’ study we compared the effectiveness of drawing-in and bracing maneuvers on transverse abdominis in different core stability exercise positions (supine, hook lying, supine with 90° flexed knee and hip, supine with stretched knees and 90° flexed hips, bridge, bridge with one stretched knee and Bird dog). We used activation ratio and preferential activation ratio as measurements of transverse abdominis activation. Abdominal Bracing in the bridge position showed the highest activation of transverse abdominis (
Low back pain is the most prevalent musculoskeletal problem; its lifetime and point prevalence are 58% to 84% and 4% to 33% respectively (
The rehabilitation approach toward low back pain usually includes core stability exercises to enhance the spinal stabilization (
An ultrasound (US) imaging study has been used as a technique for assessing TrA activation by measuring muscle thickness in resting and contraction states (
We conducted a comparative cross-sectional study to examine the activation of TrA in different core exercise positions.
We asked 20 healthy volunteers with the age of 18 to 50 years who were screened for medical and medication history that could adversely affect muscle health or contraindicate testing included in the study. Exclusion criteria included self-reported history of low back pain in past 6 months and any previous musculoskeletal disease. We also excluded subjects who had practiced core training within past 6 months. All subjects received written and oral information about the study procedures before participation. Also, the study protocol was approved by the Ethical Committee of university (IR.TUMS.VCR.REC.1397.698). With the purpose of preventing measurement bias, all the participants were instructed not to consume meals or liquids 3 hr prior to measurement (
One musculoskeletal ultrasonography practitioner performed the US measures. Our investigator used a portable M-Turbo US system (FUJIFILM SonoSite Inc., Bothell, WA, USA) with a 13-MHz linear transducer to visualize and obtain an US image of lateral abdominal wall muscles including TrA during different positions.
We measured changes in muscle thickness of lateral abdominal wall muscles in resting condition and during both drawing-in and bracing in the following seven positions: supine, hook lying, supine with 90° flexed knee and hip, supine with stretched knees and 90° flexed hips, bridge, bridge with one stretched knee, and Bird dog.
The transducer was being placed along the midaxillary, at the midway from the iliac crest and lower border of last rib. The transducer was adjusted to portray the best image quality, perpendicular to the skin surface. Two series of US images were obtained for each maneuver in each training position. We measured muscle thickness as the distance from the superior facial border to the inferior facial border of the muscle in millimeters after acquiring still B mode images. The investigator acquired images on the dominant side of each subject. In case of bird dog training position, the participants were instructed to use their nondominant side arm and dominant side leg. For US measurement at bridge position with the stretched knee, subjects were asked to stretch their nondominant side knee.
We used activation ratio (AR) and preferential activation ratio (PAR) of TrA as final measurements of TrA activation in drawing-in and bracing maneuvers during different training positions. In this regard, AR was defined as maneuvered TrA thickness divided by rest TrA thickness and PAR was defined as a preferential increase in TrA thickness by doing the maneuver in compare to total lateral abdominal wall change.
The reliability of AR and PAR in the estimation of TrA thickness and their relevance with clinical outcomes have been shown in the previous study (
The normality of measured variables was assessed with Shapiro–Wilk test (
In total, 25 subjects were invited but five participants were excluded before ultrasonography due to low back pain in last month (n=2), kyphosis (n=1) and practice of core training in the past 6 months (n=2). Finally, 20 participants completed the ultrasonography in all positions.
One of the most important functions of abdominal muscles is to increase trunk stability (
Patients with low back pain usually show a smaller increase in transverse abdominis thickness during their tasks. Similar results in EMG suggests impaired motor control of transverse abdominis among low back pain patients (
The AR formula, calculated by dividing thickness in the contracted state by thickness at rest, is a measure of activation for TrA (
AD targets TrA and therefore spinal stability. However, there is some evidence suggesting that bracing exercises can improve both TrA activity and spinal stability to a better degree (
Our study has several limitations. In this study, we did not calculate the reliability of US but it has been extensively tested and shown to be a reliable tool in measuring TrA thickness (
There are many proposed core stability exercises in a variety of positions; however, it is not clear that in which position, activation of transverse abdominis muscle is utmost. We compared the effectiveness of drawing-in and bracing maneuvers in different core stability exercise positions (supine, hook lying, supine with 90° flexed knee and hip, supine with stretched knees and 90° flexed hips, bridge, bridge with one stretched knee, and Bird dog) through US imaging. We used transverse abdominis AR as a measure of activation and PAR as a measure of the subject’s ability to isolate the muscle. Our study showed significantly higher activation of transverse abdominis in bridge position and during AB.
We should thank Mr. Rousta and Mr. Arabi for their kind helps.
No potential conflict of interest relevant to this article was reported.
Training position: (A) supine, (B) Hook lying, (C) 90° flexed knee and hips, (D) stretched knees and 90° flexed hips, (E) bridge, (F) bridge with one stretched knee, and (G) bird dog. These figures are presented with the consent of the subject.
Recruitment of transverse abdominis in each training position. (A) Activation ratio, (B) preferential activation ratio.
Descriptive characteristics of study subjects
Characteristic | Value |
---|---|
Age (yr) | 29.50±3.34 |
Female gender | 18 (90) |
Height (cm) | 165.75±4.95 |
Mass (kg) | 58.45±9.52 |
Body mass index (kg/m2) | 21.20±2.66 |
Values are presented as mean±standard deviation or number (%).
The thickness of TrA during rest, abdominal drawing-in, and abdominal bracing in different training positions
Position | Rest | Maneuver | |
---|---|---|---|
Supine | 0.30±0.07 | AD: 0.44±0.11 | <0.01 |
AB: 0.52±0.11 | |||
| |||
Hook lying | 0.31±0.05 | AD: 0.43±0.12 | 0.07 |
AB: 0.48±0.08 | |||
| |||
90° flexed knee and hip | 0.31±0.09 | AD: 0.42±0.13 | <0.01 |
AB: 0.54±0.13 | |||
| |||
Stretched knees and 90° flexed hips | 0.33±0.06 | AD: 0.48±0.15 | 0.28 |
AB: 0.51±0.13 | |||
| |||
Bridge | 0.40±0.20 | AD: 0.54±0.17 | <0.01 |
AB: 0.60±0.16 | |||
| |||
Bridge with one stretched knee | 0.36±0.18 | AD: 0.50±0.18 | 0.38 |
AB: 0.52±0.17 | |||
| |||
Bird Dog | 0.40±0.14 | AD: 0.43±0.12 | <0.01 |
AB: 0.53±0.16 |
Values are presented as mean±standard deviation (cm) or number (%).
TrA, transverse abdominis; AD, abdominal drawing-in; AB, abdominal bracing.
Activation measures of TrA in different core training positions
Maneuver | Measure | Positions | |||||||
---|---|---|---|---|---|---|---|---|---|
| |||||||||
Supine | Hook lying | 90° flexed knee and hip | Stretched knees and 90° flexed hips | Bridge | Bridge with one stretched knee | Bird dog | |||
AD | AR | 1.52±0.46 | 1.47±0.45 | 1.45±0.51 | 1.65±0.56 | 1.85±0.60 | 1.70±0.51 | 1.54±0.59 | 0.02 |
PAR | 0.27±0.38 | 0.26±0.35 | 0.07±0.42 | 0.15±0.37 | 0.43±0.46 | 0.37±0.50 | 0.29±0.49 | <0.01 | |
| |||||||||
AB | AR | 1.76±0.29 | 1.68±0.43 | 1.86±0.56 | 1.78±0.53 | 2.06±0.56 | 1.74±0.49 | 1.90±0.76 | 0.10 |
PAR | 0.36±0.23 | 0.37±0.35 | 0.25±0.43 | 0.17±0.43 | 0.49±0.49 | 0.36±0.53 | 0.45±0.54 | 0.02 |
Values are presented as mean±standard deviation.
TrA, transverse abdominis; AD, abdominal drawing-in; AB, abdominal bracing; AR, activation ratio; PAR, preferential activation ratio.