Difference of the thickness and activation of trunk muscles during static stoop lift at different loads between subjects with and without low back pain

Abstract

BACKGROUND:

Patients suffering from low back pain (LBP) have been reported to alter muscle contraction strategies.

OBJECTIVE:

To compare activity and thickness of the trunk muscles (external oblique (EO), internal oblique (IO), transversus abdominis (TrA), and lumbar multifidus (LM)) during static stoop lift at different lifting loads between the subjects with and without LBP.

METHODS:

Twenty eight subjects with LBP and twenty eight healthy subjects were recruited. The stoop lifting was performed in three conditions in 0%, 10%, and 20% of body weight.

RESULTS:

The activity of EO ( $F=$ 9.513) and IO ( $F=$ 7.781) was significantly increased with increasing lifting loads in subjects with LBP ( $p<$ 0.05) but not significantly in subjects without LBP. The activity of the LM ( $F=$ 124.980) was significantly increased in response to lifting loads in both groups ( $p<$ 0.05). The percent change of TrA ( $F=$ 8.797) and LM ( $F=$ 48.170) muscles thickness was significantly increased with increasing lifting loads in both groups ( $p<$ 0.05). The percent change of TrA ( $F=$ 3.780) and LM ( $F=$ 16.314) muscles thickness in subjects without LBP was greater than those in subjects with LBP at all three lifting loads ( $p<$ 0.05).

CONCLUSIONS:

The results of this study suggest that more activation of EO in subjects with LBP may contribute to increase the compressive force on the lumbar spine during stoop lift. Also, less activation of TrA and LM in subjects with LBP may contribute to decrease the lumbar stabilization during stoop lift.

Keywords

Lifting loads low back pain surface electromyography trunk muscles ultrasonography

1. Introduction

The workplace environment has achieved significant improvement through the development of the automation system and dangerous tasks are carried out by machines or robots. However, manual handling operations are still being carried out not only in industrial sites, but also in daily life. Among manual handling operations, lifting is reported as the etiology with the highest risk factor among the various causes of low back pain [1].

During lifting, compressive and shear force were imposed on the spine and muscle and ligament forces required to support the posture and facilitate movement impose excessive loads on the spine [2]. There were several injury mechanics as compressive and shear force were imposed on the spine. Richardson et al. [3] suggested that the deep muscles provided to stiffen the spinal segments for safe lifting and safe lifting would only proceed if the deep muscles were effectively and specifically rehabilitated.

Lifting capacity can be enhanced through spinal stabilization, which is achieved by cooperative co-activation of abdominal muscles and intra-abdominal pressure [4, 5]. The co-activation of abdominal muscles and intra-abdominal pressure (IAP) are important factors that contribute to trunk stabilization. By increasing intra-abdominal pressure, the compressive force of the spine is decreased [5].

The squat lifting posture has been considered a proper lifting posture for reducing the burden on low back ligaments by decreasing pressure on the 5 ${}^{\text{th}}$ lumbar segment and the 1 ${}^{\text{st}}$ sacrum [6, 7]. However, although squat lifting have been suggested a safety posture for lifting objects, many workers prefer stoop lifting as it consumes less energy [8] and is easier to keep one’s balance [9].

Various studies reported the importance of the Transversus abdominis (TrA), internal obliques (IO), and lumbar multifidus (LM) in lumbar spinal segmental stabilization [10, 11]. Clinically, abdominal muscles were reported as important determination factors in effectively carrying out daily life activities and maintaining a proper posture [12]. However, different opinions was presented in relation to the activity of abdominal muscles according to load. Tan et al. [13] reported that co-activation was not generated between these two muscle groups in submaximal efforts. Whereas, Lavender et al. [14] stated that abdominal muscles were activated during submaximal lifting. Also they focused on the global muscles and working postures in relation to lifting. Studies on the actions of the trunk stabilizer muscles during lifting motions in relation to the degrees of loads are insufficient.

In people with low back pain (LBP), there is considerable neurophysiological evidence of delayed activation of the TrA muscle [15, 16, 17]. It has been proposed that the documented motor control changes, such as dysfunction of the TrA muscle are associated with higher long-term incidence of LBP.

LM percentage thickness change has also been shown to decrease during voluntary isometric contractions, upper extremity movements in people with chronic LBP and upper extremity movements in healthy people with experimentally induced LBP as compared to healthy and symptom-free participants [18]. There is some evidence of altered abdominal muscle recruitment in people with LBP affecting specific deep stabilizing muscles such as TrA [16, 17, 19], IO [19], LM [20], diaphragm and pelvic floor muscles [21].

Delitto and Rose [22] demonstrated that the heavy load presented greater activity of erector spinae and oblique muscles than both the moderate and the light loads, and that the moderate load showed greater activity than the light loads during squat lifting. Hides et al. [23] reported that subjects with LBP showed significantly greater increases in the thickness of the IO muscle while performing a leg task, but there was no significant difference between groups for change in TrA muscle thickness.

Ultrasonography has become an increasingly popular tool to assess the contraction of the abdominal wall muscle [24, 25]. Reliability studies of ultrasonograpy measurement for muscle thickness of TrA, IO, and LM showed high levels of inter-rater and intra-rater reliability in patients with LBP [25].

Therefore, the purpose of this study was to compare the activity and the percent change of thickness of the trunk muscles during static stoop lift at different lifting loads between subjects with and without LBP.

2. Method

2.1 Subjects

In this study, twenty eight subjects with LBP and twenty eight age-, sex-, and body weight-matched healthy subjects were recruited. Subjects were included in the LBP group if they had LBP, defined as pain lasting for at least 6 months, without pain referral to the leg. Exclusion criteria for the LBP group were spinal and abdominal surgery, spinal abnormality, and spine pathology (fracture, cauda equine syndrome). For the LBP group, patients with similar levels of disability were selected by using the Oswestry Disability Questionnaire (ODI) and Visual Analogue Scale (VAS) before this study. To be eligible for the without LBP, subjects had to have no history of low back pain for the past 3 months and no neurologic and orthopedic problem. Also patients who reported above 5/10 in the VAS and above 22 score in the ODI were excluded from this study.

Before the study, the researcher explained all procedures to the subjects, and all subjects signed an informed consent.

2.2 Strain gauge

The strain gauge (Noraxon Telemyo 1.06 software, Noraxon Inc., Scottsdale, AZ, USA) was used to control the lifting load. The strain gauge was attached to the steel wire-connected steel bar (15 W 315 D $\times$ 328 H (mm)) on the back strength dynamometer. Strain gauge was connected with Noraxon software. The subjects were asked to watch a computer monitor for maintaining the predetermined lifting load. The lifting order was randomly determined to reduce variables related with the order effect.

2.3 Surface electromyography

To measure the muscle activity of EO, IO, and LM in right side at different lifting loads, a surface EMG was used (BTS Pocket EMG, Garbagnate Milanese, Milano, Italy). Surface electrodes (Ag-Ag/Cl; Biopac, diameter 2 cm, interelectrode distance 2 cm) were used for collecting EMG signals. The EMG analog signals of the 3 channels collected in each muscle were converted into digital signals. Data was processed by using the Myolab software 2.12 in PC. The sampling rate of EMG signals was set at 1,000 Hz. The frequency band-pass filter was set at 20–450 Hz and the notch filter was set at 60 Hz.

The surface electrode was attached on the lateral abdominal area, the part with the highest muscle activity. To reduce skin resistance for EMG signals, the attached area was waxed, rubbed with sandpaper to remove the dead skin cell layer, cleaned with medical alcohol cotton and actively arranged. Ground electrode was attached on the C7 spinous process. Among abdominal muscles, electrodes for EO were attached over approximately 15 cm lateral to the umbilicus, electrodes for IO were attached over halfway between the anterior superior iliac spine of the pelvis and the midline, just superior to the inguinal ligament; and electrodes for LM were attached at 2 cm lateral to L5 of the spinous process [26]. For normalization, the mean root mean square (RMS) of 3 trials of 5-second reference voluntary contraction (RVC) was calculated for trunk muscles (EO, IO, and LM). Maximum voluntary contraction has been known to be unreliable in subjects with low back pain [27]. Therefore, RVC was measured for normalization to minimize discomfort and pain in this study [28]. The subjects were positioned on the floor in a crook-lying position with hips flexed 45 ${}^{\circ}$ and knees flexed 70 ${}^{\circ}$ . For measuring the EO and IO RVC, the subjects were asked to raise both legs 1 cm off the supporting surface for 5 seconds. For measuring the LM RVC, The subjects were asked to raise both hand off the floor on table for 5 seconds [29].

2.4 Ultrasonography

SonoAce X4 ultrasonography (SonoAce X4, Medison, Seoul, Korea) was used to measure the muscle thickness of IO, TrA, and LM muscles according to different lifting loads. The thickness of the IO, and TrA muscles were measured using a 5–7 Mhz linearly arranged probe. The thickness of the LM muscle was measured using a 5–7 MHz curved probe.

Ultrasound images of abdominal muscles (IO and TrA) were taken at a depth of 5 cm and 6 cm from the skin [30]. LM muscles were set at 7 cm [31]. To measure the thickness of trunk muscles, the transparent vertical line (center line) placed at the center of the monitor was used to standardize the muscle thickness measurement line [32]. After saving data in computer, caliper was used for measurement. The thickness of each muscle was normalized with mean values of muscle thickness measured in resting position. To measure the thickness of IO and TrA, the probe was placed at the lateral margin 25 mm anterior to the half point between the upper iliac crest and the subcostal angle on the center line of the right axilla and adjusted so that the lateral abdominal muscles were clear in a direction parallel to the muscle fibers of the TrA [33]. All ultrasonography images were collected when an exhalation was completed in order to minimize the mobilization of the TrA. The thickness was measured after drawing a vertical line on the 5 cm position on the horizontal plane on the most medial side of the TrA [34]. To measure the muscle thickness of the LM muscle, the subjects laid down prone position and L4-5 spinous processes were palpated and marked, the transducer was placed upright on the centerline of the lumbar spine, and the facet joint was made to appear on the center of the monitor by moving the probe placed longitudinally until the spinal facet joint was clearly seen [35]. The mean of TrA, IO, and LM thickness was calculated for the percent change of muscle thickness [18, 30].

Table 1
Descriptive characteristics for subjects without and with LBP (N $=$ 56)

Variable	Without LBP		LBP ${}^{\text{e}}$		$t$	$p$
Age (yrs)	22.67	$\pm$ 1.38 ${}^{\text{d}}$	23.75	$\pm$ 3.51	$-$ 1.50	0.14
Height (cm)	169.03	$\pm$ 8.70	165.83	$\pm$ 5.97	1.60	0.11
Mass (kg)	59.02	$\pm$ 10.08	58.68	$\pm$ 8.58	0.13	0.89
BMI ${}^{\text{a}}$ (kg/m ${}^{2}$ )	20.50	$\pm$ 1.94	21.24	$\pm$ 2 .19	$-$ 1.13	0.18
ODI ${}^{\text{b}}$			20.85	$\pm$ 1.69
Current symptoms onset (months)			17.28	$\pm$ 9.30
VAS ${}^{\text{c}}$			3.89	$\pm$ 0.73

${}^{\text{a}}$ BMI: Body mass index. ${}^{\text{b}}$ ODI: Oswestry Disability Index. ${}^{\text{c}}$ VAS: Visual analogue scale. ${}^{\text{d}}$ Mean $\pm$ standard deviation. ${}^{\text{e}}$ LBP: Low back pain.

2.5 Procedure

Stoop lifting posture was defined as the lifting position with trunk flexed 30 degrees with knee extension. Subjects participated in a 5-minute warm-up exercise before and after the lifting activity. Subjects were provided with a sufficient explanation on the posture and experimental procedure. Each subject practiced the lifting technique for familiarization with the testing procedure until performing correct lifting technique. Lifting loads were determined according to subject’s body weight. 10% and 20% of their individual body weights were calculated.

The test was performed three conditions in 0%, 10%, and 20% of body weight. 0% of body weight means lifting posture without lifting load. Subjects were asked to hold the lifting loads of 10% and 20% of their body weight in random order and hold the posture for 5 seconds. Each trial was classified as invalid if subjects were performed excessive lumbar rotation by visual judgment during stoop lifting. If an invalid trial occurred, the data were discarded, and the subject repeated the trial. To minimize muscle fatigue, subjects were given 2 minutes of resting time interval lifting loads.

To measure the muscle activity of EO, IO, and LM in right side according to three different lifting loads, EMG signals were measured for 5 seconds according to the lifting loads. This study used the average value of EMG signals of 3 seconds, excluding the first and last second. Measurement was performed three times and 3 minute resting periods were allowed between each trial.

To measure muscle thickness of IO, TrA, and LM during lifting at different loads, the subjects were asked to hold the stoop lifting posture. The one investigator checked the lifting loads on the monitor connected to the strain gauge. Muscle thickness was measured at the last point of the exhalation during maintaining lifting posture for 5 seconds. The different loads were given in random orders. Mean value of three trials was used for data analysis. To minimize muscle fatigue, 1 minute resting period was given between trials.

An intra-rater reliability pilot study in subjects with 10 and without 10 LBP for the measurement of thickness of IO, TrA, and LM muscle was high intraclass correlation coefficient (ICC ${}_{3,1}$ ): range (0.78–0.99).

2.6 Statistical analysis

Independent-samples $t$ -tests were used to test difference in demographics between subjects with and without LBP group. A 2 $\times$ 3 mixed model analysis of variance (ANOVA) with between-subjects factor and within-subjects factor was used to determine the main effects and interaction effects between the muscle activity and muscle thickness for IO, TrA, and LM at different lifting loads. Post hoc multiple comparisons test was performed if a significant difference was identified. The significance level was set at $\alpha=$ 0.05. All statistical analyses were conducted using PASW 18.0 (SPSS Inc, Chicago, IL, USA).

3. Results

3.1 Descriptive characteristics

The descriptive characteristics of the 56 subjects included in the study are shown in Table 1. There were no significant differences in age, height, weight, or body mass index (BMI) between the subjects with and without LBP ( $p>$ 0.05). The mean ODI score was 20.85 $\pm$ 1.69 and mean VAS was 3.89 $\pm$ 0.73 in LBP group (Table 1).

Table 2
The muscle activity (% RVC) of EO, IO, and LM depending on different loads in the subjects without and with LBP

	0%		10%		20%		$p_{\textit{loads}}$	$p_{\textit{group}}$
EO ${}^{\text{a}}$
Without LBP ( $n=$ 28)	48.05	$\pm$ 3.26 ${}^{\text{e}}$	51.25	$\pm$ 3.84	62.47	$\pm$ 6.57	$<$ 0.001	0.002
LBP ( $n=$ 28)	56.95	$\pm$ 5.64	79.68	$\pm$ 6.88	88.10	$\pm$ 6.95
IO ${}^{\text{b}}$
Without LBP	51.58	$\pm$ 4.91	56.11	$\pm$ 4.39	58.85	$\pm$ 3.79	0.001	0.356
LBP	48.74	$\pm$ 3.98	63.29	$\pm$ 7.32	72.97	$\pm$ 7.24
LM ${}^{\text{c}}$
Without LBP	27.03	$\pm$ 14.66	99.70	$\pm$ 8.39	141.53	$\pm$ 10.90	$<$ 0.001	0.034
LBP	21.94	$\pm$ 1.28	91.25	$\pm$ 6.12	107.98	$\pm$ 7.06

Values are mean $\pm$ standard error, RVC: Reference voluntary contraction, EO: External oblique, IO: Internal oblique, LM: Lumbar multifidus, LBP: Low back pain.

Table 3

The mean ( $\pm$ standard error) of the IO, TrA, and LM muscle thickness at different lifting loads in the subjects without and with LBP

	0%	10%	20%	$p_{\textit{loads}}$	$p_{\textit{group}}$
IO
Without LBP ( $n=$ 28)	0.78 $\pm$ 0.03	0.77 $\pm$ 0.02	0.79 $\pm$ 0.03	0.101	0.454
LBP ( $n=$ 28)	0.73 $\pm$ 0.02	0.79 $\pm$ 0.02	0.80 $\pm$ 0.32
TrA
Without LBP	0.36 $\pm$ 0.00	0.37 $\pm$ 0.01	0.41 $\pm$ 0.01	0.001	0.036
LBP	0.29 $\pm$ 0.00	0.29 $\pm$ 0.00	0.30 $\pm$ 0.00
LM
Without LBP	2.54 $\pm$ 0.05	2.77 $\pm$ 0.08	3.03 $\pm$ 0.08	0.001	0.001
LBP	2.53 $\pm$ 0.03	2.64 $\pm$ 0.04	2.72 $\pm$ 0.06

IO: Internal oblique, TrA: Transversus abdominis, LM: Lumbar multifidus, LBP: Low back pain.

3.2 Muscle activity of EO, IO, and LM muscles at different lifting loads

A significant main effect was found for lifting loads ( $p<$ 0.001) and the group ( $p=$ 0.002) for EO muscle, and a significant interaction ( $p=$ 0.087) was not revealed. For IO muscle, the main effect was found for lifting loads ( $p=$ 0.001). There were no significant main effects for the group ( $p=$ 0.356) and the interaction ( $p=$ 0.116) between lifting loads and group. There was significant main effect for lifting loads ( $p<$ 0.001) and the group ( $p=$ 0.034), and a significant interaction ( $p<$ 0.001) for LM muscle. The result of interaction was reveals that the activity of LM muscle in subjects without LBP was greater than those in subjects with LBP at the lifting loads of the 20% of body weight. The result of interaction (lifting loads $\times$ group) was reveals that the activity of LM muscle in subjects without LBP was greater than those in subjects with LBP at the lifting loads of the 20% of body weight.

In the without LBP group, the activity of EO and IO muscles was no significant difference among three different loads. The muscle activity of LM was significantly increased in 10% compared to in 0%, increased in 20% compared to 10%, and 20% compared to in 0% of the subject’s body weight. In the LBP group, the activity of EO, IO, and LM muscles was significantly increased 10% compared to in 0%, increased in 20% compared to 10%, and 20% compared to in 0% of the subject’s body weight (Table 2).

3.3 The percent change of muscle thickness of trunk muscles at different lifting loads

For IO muscle, the main effect for lifting loads ( $p=$ 0.101), group ( $p=$ 0.454), and the interaction ( $p=$ 0.916) was no significantly different. A significant main effect for lifting loads (TrA: $p=$ 0.001; LM: $p=$ 0.001), group (TrA: $p=$ 0.0.36; LM: $p=$ 0.001), and interaction (TrA: $p=$ 0.024; LM: $p=$ 0.001) was revealed for TrA and LM muscles. The result of interaction was reveals that the percent change of TrA and LM muscle thickness in subjects without LBP was greater than those in subjects with LBP at the lifting loads of the 20% of body weight.

In the without LBP group, the percent change of IO muscle thickness was no significantly different among lifting loads. The percent change of muscle thickness of TrA was significantly increased in 20% compared to in 0%, increased in 20% compared to 10% of the subject’s body weight. The percent change of muscle thickness of LM was significantly increased in 10% compared to in 0%, increased in 20% compared to 10%, and 20% compared to in 0% of the subject’s body weight. In the with LBP group, the percent change of muscle thickness of IO was no significantly different among lifting loads. The percent change of muscle thickness of TrA was significantly increased in 10% compared to in 0% of the subject’s body weight. The percent change of muscle thickness of LM was significantly increased in 10% compared to in 0%, increased in 20% compared to 0% of the subject’s body weight (Table 3).

4. Discussion

The purpose of this study was to compare the activity and the percent change of thickness of EO, IO, TrA, and LM muscles between the subjects with and without LBP during lifting at different loads in stoop posture.

This is the first study to investigate the percent change of thickness and activity of trunk muscles during stoop lift at different loads. In the present study, there was significantly increased in activity of EO and IO muscles depending on increasing lifting loads in subjects with LBP, whereas, the activity of EO and IO muscles was no significantly increased according to lifting loads in without LBP group. The percent change of the thickness of IO muscle was no significantly different according to lifting loads in both groups. Sitilertpisan et al. [36] stated that the lateral abdominal muscle group (EO, IO, and TrA muscles) shared a role in controlling the lumbar spine during weight-lifting. The EO and IO muscles may control the rotary torque and balance the external loads on the lumbar segment [37, 3, 38]. In present study, the activity of EO and IO muscles in subjects without LBP group was no significant difference at three different loads (48%–62% range of RVC). However, the activity of EO and IO muscles in subject with LBP was significant difference at three different loads (56–88 range of RVC). These results suggest that the activation of EO and IO muscles may contribute to maintain the lumbar spine stability in subject with LBP, which did support our research hypothesis.

Hides et al. [24] examined the thickness of the TrA and IO muscles via ultrasonography during rest and with a load of 25% of body weight during a simulated unilateral weight bearing task against a footplate in supine with healthy subjects. And they reported that thickness of the TrA and IO muscles significantly increased under load of 25% of body weight compared during rest, and the thickness of the TrA muscle increased more than the IO muscle. Granata and Orishimo [39] conducted a biomechanical model study related to lifting weights (4.5 and 9.0 kg) and heights (0, 20, 40, 60, and 80 cm) in static lifting postures with 20 normal adults. And they reported that as the weight and heights increased, the activity of the abdominal and back muscles increased. They stated that abdominal muscles acted to maintain the stability of the trunk through co-contraction with the erector spinal muscle, and that if the erector spinal muscle would contract alone during lifting motions, the spine would become unstable. In this our study, the activity of EO and IO muscles and the percent change of muscle thickness of IO muscle in subject without LBP was not significantly different depending on lifting loads, but the activity of EO and IO muscles and the percent change of muscle thickness of IO muscle in subject with LBP was significantly increased depending on lifting loads. We prostrate that the strategy of control for stability the lumbar spine during lifting loads in static stoop posture differ from the subjects with LBP and without LBP. The overactivity of superficial muscles leads to increase the compressive force on lumbar spine and disk. Further studies are needed to determine whether long-term trunk deep muscle strengthening exercise can decrease the activity of superficial muscles during static lifting.

Biomechanical studies showed that the LM has a high capacity to stabilize the spine when spinal stability is challenged [40, 41], and control the spinal segments neutral zone [42]. Ferreira et al. [34] used both ultrasound imaging and fine-wire EMG to compare the recruitment of the abdominal muscles in response to an isometric low load task when isometrically flexed and extended the knee against the force transducer. Results showed that subjects with LBP had significantly less increases in thickness (or less contraction) of the TrA muscle as seen on ultrasound imaging in response to the task. Also there was no difference between groups for EMG activity for OI or OE. Healthy individuals also activate the TrA muscle in response to loading and force application to the trunk [43]. It has been argued that this pattern of activation of the TrA muscle is important for the control of intervertebral movement, particularly shear forces [44] and for the control of stability of the sacroiliac joints of the pelvis [45]. In LBP, changes in control of the trunk muscles, including the TrA muscle, are therefore thought to compromise control of the lumbar spine and pelvis. Results of our study showed that there was a significant difference between groups for activity of the EO muscle, whereas there was no significant difference between groups for the thickness and activity of IO muscle. This result suggests that the LBP group would use co-contraction of EO muscles to stability the lumbar spine rather than IO muscle. However, the increased co-contraction of global muscle such as EO will increase the compression forces acting on the spine. The percent change of the thickness of TrA and LM muscles were significantly increased in response to lifting loads in both groups ( $p<$ 0.05). The subjects with LBP had a significantly smaller increase in the activity of LM muscle and the thickness of TrA and LM muscles with response to lifting loads compared without LBP. We postulate that less activation of TrA and LM muscles may be contributed to the muscle atrophy and muscle weakness.

This study has some limitations. First, the subjects with LBP are young, mild disability (ODI $=$ 20.85 $\pm$ 1.69, and low pain scale (VAS $=$ 3.89 $\pm$ 0.73) so that the participants cannot hold the lifting loads without pain. Therefore, the results of this study cannot be generalized to all LBP patients. Second, deep muscles such as TrA, LM, diaphragm, and pelvic floor contribute to lumbar stabilization; however, the muscle activity of diaphragm and pelvic floor muscles was not measured in this study. Further study is needed to compare the activity and the percent change of diaphragm and pelvic floor muscle according to lifting loads. Third, thickness of IO, TrA, and LM and activity of EO, IO, and LM muscles measured in static lifting position. Further studies are needed to investigate the activity and thickness of trunk muscles during dynamic stoop lift.

5. Conclusion

This study aimed to compare the percent change of thickness and activity of the trunk muscles during static stoop lifting depending on the different loads between the subjects with and without LBP. The result showed that the activity of EO muscle was significantly increased with increasing lifting loads in subjects with LBP ( $p<$ 0.05), whereas there was no significant difference in EO and IO muscles activity among three lifting loads in subjects without LBP. The activity of the LM muscle was significantly increased in response to lifting loads in both groups ( $p<$ 0.05). Also, the activity of the LM in subjects without LBP was greater than those in subjects with LBP at all three lifting loads. The percent change of TrA and LM muscles thickness was significant difference between two groups ( $p<$ 0.05). Whereas, there was no significant differences in the percent change of the IO muscle thickness between two groups. And the percent change of TrA and LM muscles thickness in subjects without LBP was greater than those in subjects with LBP at all three lifting loads. Therefore, the results of this study suggest that more activation of EO muscle in subjects with LBP compared to subject without LBP may contribute to increase the compressive force on the lumbar spine and disk during static stoop lifting. Also, less activation of TrA and LM muscles in subjects with LBP compared to subject without LBP may contribute to decrease the lumbar stabilization during static stoop lifting. Further, there is a need to study the effect of the long-term strengthening exercise of the deep muscles (TrA and LM) on the lumbar stability and function during static stoop lifting at different lifting loads in subjects with LBP.

Footnotes

Conflict of interest

None to report.

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Difference of the thickness and activation of trunk muscles during static stoop lift at different loads between subjects with and without low back pain

Abstract

BACKGROUND:

OBJECTIVE:

METHODS:

RESULTS:

CONCLUSIONS:

Keywords

1. Introduction

2. Method

2.1 Subjects

2.2 Strain gauge

2.3 Surface electromyography

2.4 Ultrasonography

Table 1 Descriptive characteristics for subjects without and with LBP (N = 56)

2.6 Statistical analysis

3. Results

3.1 Descriptive characteristics

Table 2 The muscle activity (% RVC) of EO, IO, and LM depending on different loads in the subjects without and with LBP

3.3 The percent change of muscle thickness of trunk muscles at different lifting loads

4. Discussion

5. Conclusion

Footnotes

Conflict of interest

References

Table 1
Descriptive characteristics for subjects without and with LBP (N $=$ 56)

Table 2
The muscle activity (% RVC) of EO, IO, and LM depending on different loads in the subjects without and with LBP