Relationship between double leg lowering test and core strength test of the lumbar spine in normal healthy individuals

Sheshna Rameshchandra Rathod; Neeta J Vyas; Dinesh Mohanbhai Sorani

doi:10.4103/jmgims.jmgims_11_20

ORIGINAL ARTICLE

Year : 2021 | Volume : 26 | Issue : 1 | Page : 23-27

Relationship between double leg lowering test and core strength test of the lumbar spine in normal healthy individuals

Sheshna Rameshchandra Rathod¹, Neeta J Vyas², Dinesh Mohanbhai Sorani¹
¹ Department of Physiotherapy, Government Physiotherapy College, Near Government Dental College, Jamnagar, Gujarat, India
² Department of Physiotherapy, IKDRC-ITS College of Physiotherapy, Civil Hospital Campus, Ahmedabad, Gujarat, India

Date of Submission	03-Feb-2020
Date of Acceptance	04-Jan-2021
Date of Web Publication	29-Jun-2021

Correspondence Address:
Dr. Sheshna Rameshchandra Rathod
Government Physiotherapy College, Near Government Dental College, Rameshwer Nagar, Jamnagar, Gujarat
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/jmgims.jmgims_11_20

Abstract

Introduction: Core stability relies on the effectiveness of abdominal muscle function in their stabilizing role. A wide variety of tests are available to quantify the strength of trunk muscles. Aim: The objective of this study was to determine the relationship between double-leg-lowering (DLL) test and core strength test in normal healthy individuals. Materials and Methods: This study was conducted on 843 volunteers between the ages of 18 and 60 years. Assessment of core strength was done using a pressure biofeedback unit. The actual task, i.e., abdominal draw-in the test was performed with the subject lying in a prone position. Then, pressure reduction which was held up to at least 10 s was noted. The DLL test was performed with the subject lying in supine position with hands folded across the body on a plinth. The therapist passively raised both the lower limbs simultaneously to 90° hip flexion with the knees kept straight. Subjects then performed a posterior pelvic tilt and maintained this position while slowly lowering the legs to horizontal. The angle at which the back arched was noted. Grading was done in a similar manner for three times with a rest-period of 1 min in between the repeats. The best of the three repetitions was used for the analysis. Results: Spearman's correlation coefficient (ρ) between core strength test and DLL test was found to be 0.24. The median for DLL test was 4 and pressure reduction on the pressure biofeedback unit was 9 mmHg. Conclusions: We found that there is weak positive correlation between the core strength test and DLL test.

Keywords: Core stability, core strength test, double-leg-lowering test, lumbar spine

How to cite this article:
Rathod SR, Vyas NJ, Sorani DM. Relationship between double leg lowering test and core strength test of the lumbar spine in normal healthy individuals. J Mahatma Gandhi Inst Med Sci 2021;26:23-7

How to cite this URL:
Rathod SR, Vyas NJ, Sorani DM. Relationship between double leg lowering test and core strength test of the lumbar spine in normal healthy individuals. J Mahatma Gandhi Inst Med Sci [serial online] 2021 [cited 2023 Jun 4];26:23-7. Available from: https://www.jmgims.co.in/text.asp?2021/26/1/23/319832

Introduction

The conceptual model of spinal stability consists of the active subsystem, the passive subsystem and neural control.^[1] The passive subsystem includes osseo-ligamentous structures of spine; the active subsystem includes muscles that generate force to provide mechanical ability to stabilize spine; and neural control is provided by the nervous system which coordinates muscle activity in advance of predictable challenges and responds to afferent feedback to unpredictable challenges. These three subsystems are interdependent on each other and dysfunction in any one of them may lead to instability of the spine. Active muscular components of the spine are very important because without it the osseo-ligamentous spine becomes unstable even under very less force. Core stability increases by co-contractions of surrounding muscles. Leetun et al. stated that “core stability can be seen as the product of motor control and muscular capacity of the lumbo-pelvic-hip complex.”^[2] It stresses the importance of coordination along with core strength and endurance. Core strength is just one of the parts of core stability along with endurance and motor control. Core strength is the ability of a muscle to exert or withstand force. Regulation of force in surrounding muscles results in active control of spinal stability. Force-generating capacity of the trunk-stabilizing muscles is an important aspect of the assessment of patients with spine conditions.^[3],[4]

A wide variety of tests are available to evaluate and quantify strength of trunk muscles, ranging from simple manual muscle testing grades, maximum force production single-trial test, torque production tests, isokinetic strength tests, endurance tests, functional lift tasks, etc., Manual muscle testing has found to be a useful clinical tool.^[5] The double-leg-lowering (DLL) test has excellent intra-tester reliability ranging from 0.93 to 0.98.^[6],[7],[8] Core stability relies on the effectiveness of abdominal muscle function in their stabilizing role. It is found that exercises such as curls up and DLL may not provide appropriate stability to the lumbar spine.^[9] Thus, the objective of this study was to find the relationship between DLL test and core strength test in normal healthy individuals.

Materials and Methods

Ethical approval for the study was taken from the Institutional Ethics Committee. We enrolled 1010 volunteers between 18 and 60 years of age of both genders from the city of Jamnagar, Gujarat, India in this study. Of these, we excluded 167 subjects who had the following ailments: low back pain (subjects who had missed work due to back pain in the preceding 2 years), subjects who had undergone lumbar spine surgery, pregnant women, subjects with severe kyphosis or scoliosis, spinal stenosis, neurological disease, cancer, trauma to the lumbar spine, nerve root entrapment, or musculoskeletal disorders. After exclusion, this study was conducted on 843 volunteers. Double blinding was done as the therapist and the subjects were not aware about the grades on DLL and core strength tests.

Procedure

Stratified random sampling was used. Subjects were invited to participate in the study through word-of-mouth publicity. Every alternate subject who was willing to participate was enrolled. Each volunteer was given a subject information sheet and written consent was taken from the subjects in a language that was understood by them. Demographic data such as age, gender, weight, and height of each volunteer was compiled. Weight was measured using a weighing scale (Omron, Model no. HN-286). Height was measured with a stadiometer (Krups).

Assessment of core strength

Assessment of core strength was made by assessing the strength of transversus abdominis with a pressure biofeedback unit (Stabilizer^TM, Chattanooga, California, USA).^{[10],[11],[12]} Before using it, inter-rater and intra-rater reliability of pressure biofeedback unit was measured, and it was found to be good to excellent with intra-class correlation coefficient 0.89 and 0.87 for inter-rater reliability and intra-rater reliability, respectively.^[13] To avoid bias, the same machine was used throughout the study. The calibration of the machine was done by loading it with 4.5 kg weight for 24 h. A difference of 0.5 mmHg was considered acceptable before using the machine.^[14]

Familiarization was done with description of the task and demonstration of test performance. Description of the task was done by asking the volunteers to assume the transversus abdominis to be the natural “corset” surrounding abdomen that supports the spine, without producing movement similar to the external corset. Volunteers were made to distinguish between trunk movement and drawing-in by demonstration of the task. Practice trials were done in four-point kneeling position, as due to gravitational stretch on the muscles, it increases the awareness of the abdominal wall and promotes complete relaxation of the abdominal wall. In the four-point-kneeling position, the position adapted by subject was such that hips are positioned directly over the knees, and shoulder over the hands with elbows extended. In this position the subject was instructed to take normal breaths in and out, and then, without breathing in, draw the abdomen in toward the spine. Once the contraction was achieved normal breathing was commenced.^[15] Adequate practice trials were given till the subjects mastered the technique. During practice trials, visual and verbal cueing and palpation of the muscle medial to the anterior superior iliac spine were done to facilitate subject to master the technique. Then, proper rest-periods were given before commencement of the actual task to avoid the effect of fatigue. The actual task, i.e., the abdominal draw-in test, was performed with the subject lying in a prone position on a hard surface with arms by the side. A pressure biofeedback unit was placed under the abdomen with the navel in the center and the distal edge of the pad in line with the right and left anterior superior iliac spines [Figure 1]. The pressure biofeedback unit was then inflated to 70 mmHg and was allowed to stabilize, allowing for the detection of fluctuations in pressure due to normal breathing, which was approximately 2 mmHg for each inhalation and exhalation. Subjects were instructed to perform abdominal drawing-in. The instructions were given to breathe in and out and then, without breathing-in, to slowly draw in the abdomen so that it lifted up off the pad, keeping the spinal position steady. Deep inspiration was avoided. During this test, the investigator closely monitored the pressure gauge of the pressure biofeedback unit and the subject to detect whether any compensatory mechanisms were employed. This included movements of the pelvis and spine, breath holding, rib elevation, and bulging of the abdomen.^{[10],[11],[12],[15]} Then pressure reduction which was held at least up to 10 s was noted. A stop watch was used to note the time. A sudden rise in pressure indicated fatigue. The same procedure was repeated for three times and the best of the three repetitions was used for the analysis. The rest time between the measurements was 1 min.

Figure 1: Abdominal drawing-in manoeuvre

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Double-leg-lowering test

Volunteers lay down supine with hands folded across the body on a plinth having a firm surface. The therapist passively raised both the lower limbs simultaneously to 90° hip flexion with the knees kept straight [Figure 2]. A pressure biofeedback unit was kept under the lower back. Subjects then performed a posterior pelvic tilt and baseline pressure was set at 40 mmHg.^[16],[17] They maintained this position while slowly lowering the legs to horizontal. A decrease in pressure might suggest inability to maintain posterior pelvic tilt. Strength was graded on the ability to keep the lower back flat on the surface; the angle at which the back arched was noted and correlated with the grading system.^[18]

Figure 2: Double-leg-lowering test

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The following grading system was used:

Unable to maintain the posterior pelvic tilt
Able to maintain posterior pelvic tilt between 76° and 90°
Able to maintain posterior pelvic tilt between 46° and 75°
Able to maintain posterior pelvic tilt between 16° and 45°
Able to maintain posterior pelvic tilt between 0° and 15°.

Grading was done in a similar manner three times with a rest-period of one min between the repeats. The best of three repetitions was used for the analysis.

Statistical analysis

Data analysis was performed using the SPSS reference (IBM Corp. Released 2011. IBM SPSS Statistics for Windows, Version 20.0. Armonk, NY: IBM Corp.). Normality tests were done using Shapiro–Wilk test and the data were found to be skewed. Correlation analysis was performed using Spearman's correlation. The level of significance was kept at P < 0.05.

Results

The study included 66% of male and 34% of female volunteers [Table 1]. Females were found to have lower core strength compared to males [Figure 3]. Muscle grades for DLL are almost the same in both males and females [Figure 4].

Figure 3: Females demonstrates lower core strength compared to males

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Figure 4: Males and females demonstrates similar muscle grades on Double leg lowering test

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Table 1: Characteristics of volunteers

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As shown in [Table 2], the Spearman correlation coefficient (ρ) between DLL and core strength tests was 0.24 (P < 0.01). As shown in [Figure 5], there is a weak positive relationship between DLL and core strength tests.

Figure 5: Weak positive correlation is shown between double leg lowering test and core strength test

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Table 2: Correlation between double-leg-lowering test and core strength test

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Discussion

Our results showed weak positive correlation between DLL and core strength tests (ρ = 0.24) suggesting that DLL test may represent the strength of transversus abdominis. Individuals performing with the higher score on DLL test may have higher pressure reduction on the pressure biofeedback unit. Muscle work during DLL test is found to be eccentrically controlled by rectus abdominis and external obliques as they work to maintain the pelvis in a posteriorly tilted position. Thus the usefulness of DLL test in measuring core strength can be questioned.^{[6],[18],[19]}

Abdominal drawing-in manoeuvre involves contraction of transversus abdominis, whereas DLL involves combined work of rectus abdominis, transversus abdominis, and lower fibers of obliques. We studied both the techniques and found was weak positive correlation between the two, suggesting that better measure of core strength is through abdominal drawing-in maneuver rather than DLL test.

Our findings are supported by those of Haladay et al. who found moderate relationship between DLL and lower abdominal muscle activity (ρ = 0.26). They assessed internal oblique and transversus abdominis muscles together through surface electromyography in 10 healthy participants.^[20] In addition, they also found that better performance of DLL is present in young subjects compared to older subjects. This supports the notion that as age increases performance on DLL decreases.^[6] Majority of subjects are able to perform grade 4 of DLL.

There are certain limitations of our study. History of low back pain was asked subjectively in the form of yes or no. This could have affected our results as low back pain can hamper the function of transversus abdominis. Second, marking on the pressure biofeedback unit is in even numbers, and odd numbers are not mentioned on it. Hence, the assessor may be biased to note down only even numbers. The pressure biofeedback unit is found to a less valid tool for accurate results, but it may be clinically helpful. Next, the prone position may be uncomfortable to obese individuals. Lastly we did not assess the endurance of core muscles.

We believe that further studies using more sophisticated instruments to assess strength of core muscles can provide further insight into this issue. More strata for sampling technique can be used based on body-mass index, waist-hip ratio, and physical activity. The relationship between limits of stability and core muscles can also be determined.

Conclusion

Our study shows that DLL test shows weak positive correlation with tests which measure the core strength of the spine. It aids in measurement of the strength of transversus abdominis.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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