Spinal muscle characteristics during three different types of locomotion activities among college students with idiopathic scoliosis

Abstract

Background context

Physical activities such as walking and climbing stairs are pervasive in human daily life. Individuals with scoliosis frequently encounter dysfunction in their muscle recruitment. Multiple studies have corroborated the presence of muscle dysfunction in individuals diagnosed with scoliosis. However, there is currently a noteworthy research gap regarding the exploration of changes in muscle characteristics and disparities from those observed in individuals without scoliosis during everyday activities, specifically stair climbing.

Purpose

This study aims to examine the unique patterns of muscle activity during daily life in individuals with scoliosis and distinguish the specific differences between scoliosis patients and the healthy controls. The findings of this study are significantly important for the future accurate assessment of scoliosis and the development of rehabilitation treatment plans.

Study design

Case–control study.

Sample size

Twenty eight idiopathic scoliosis patients and twenty eight controls.

Outcome measures

Root Mean Square(RMS), Maximum Voluntary Isometric Contraction(MVIC)%, RMS ratio(RMS convex / RMS concave).

Methods

The surface electromyography (sEMG) device used in this study was the Delsys Trigno, with a sampling frequency of 1500 Hz. It recorded the activation level, peak contraction, and average activation level of the erector spinae (at T6, T10, and L3 levels), gluteus maximus, gluteus medius, external oblique, and rectus abdominis muscles during three different types of locomotion for both the 28 individuals with idiopathic scoliosis and the 28 control participants.

Results

The movement patterns of the idiopathic scoliosis patients significantly differ from those of the normal population during level walking and ascending or descending stairs. In level walking, there is an asymmetry in the activation levels of the T6 and L3 erector spinae muscles, with lower activation on the convex side compared to the concave side. Similarly, during stair ascent, the activation of the T6 and T10 erector spinae muscles is asymmetric, with higher activation on the convex side than the concave side. Moreover, during stair descent, the activation of the T6 erector spinae muscle is asymmetric, with higher activation on the convex side than the concave side.

Conclusions

During level walking and stair activities, idiopathic scoliosis patients exhibit pronounced abnormal movement patterns that significantly differ from those of the control group. Under different activity conditions such as level walking, ascending and descending stairs, idiopathic scoliosis patients demonstrate abnormal muscle activation in different segments of the spine. It is crucial for clinicians to prioritize the symmetry of muscle activation in the spinal region of idiopathic scoliosis patients and consider incorporating symmetry training for these muscles.

Introduction

Scoliosis is a three-dimensional deformity of the spine characterized by its deviation from the central axis in the coronal, sagittal, and horizontal planes. The Scoliosis Research Society (SRS) defines scoliosis as having a Cobb angle greater than 10°. Idiopathic scoliosis (IS) accounts for 80% of all scoliosis cases [1, 2], with a global prevalence rate ranging from 0.93% to 12% [1]. IS refers to cases where the cause is unknown, potentially associated with abnormalities in the central nervous system, hormones, growth and development, bone density, platelets, and skeletal muscles [3]. The prevalence of scoliosis among college students in China ranges from 1.38% [4] to 3.15% [5] based on epidemiological studies. Furthermore, a significant number of college students with scoliosis exhibit Cobb angles falling between 10° and 30° [6]. Our study aims to examine the unique muscle activity patterns in the daily lives of individuals with scoliosis, identifying specific differences between scoliosis patients and healthy controls. This analysis seeks to establish an objective foundation for the subsequent clinical evaluation of scoliosis.

Research has indicated that individuals with IS experience notable impairments in motor function [7], with a prevalence of 85% [8]. Walking and ascending or descending stairs are typical daily activities for individuals, but they can pose significant challenges to maintaining spinal equilibrium and stability. Numerous studies have consistently shown that patients with IS exhibit heightened electromyographic activity in the convex side of erector spinae, quadratus lumborum, and gluteal muscles on the convex side during physical activities compared to healthy controls [9–11]. Studies reveals that asymmetric inactivation of paraspinal muscle is associated with IS [12–14]. The training aimed at achieving symmetrical alignment of the trunk is esteemed as a fundamental approach for remedying coronal plane imbalance of the scoliosis [15].The impairment of spinal muscles in individuals with IS has the potential to hinder their overall performance in daily activities while also elevating the risk of injuries and falls [16]. Presently, numerous studies predominantly emphasize the functional aspects of walking on flat surfaces in individuals with scoliosis, while neglecting the heightened spinal challenges presented by activities like stair climbing in daily routines. Ascending and descending stairs are typical daily tasks for individuals, demanding increased trunk engagement compared to walking on level ground. These activities not only consume more energy and challenge the trunk muscles significantly [17] but also elevate the risk of falls [16]. Proficiency in stair negotiation is crucial for upholding a high quality of life [17, 18]. However, few studies have specifically examined the muscle functions associated with the stair activities in scoliosis. Previous studies have shown asymmetrical muscle activation in the quadratus lumborum, erector spinae, and gluteus medius during level walking [9], as well as asymmetric muscle activities in the paraspinal muscles when performing the superman position—an exercise involving prone spinal extension to lift the arms and legs off the floor [19]. Consequently, it is crucial to investigate the muscle patterns of individuals with IS during stair-related activities to assess their daily function accurately.

Our objective was to employ surface electromyography (sEMG) technology to investigate muscle activity and bilateral symmetry of spinal muscles in college students with scoliosis while walking on level ground and ascending/descending stairs. Through identifying distinct differences between individuals with idiopathic scoliosis (IS) and the general population, the research endeavors to offer dependable evidence for upcoming clinical investigations and functional management of IS.

Materials and methods

Ethics statement

This study has obtained approval from the Ethics Committee of the Affiliated Rehabilitation Hospital of Fujian University of Traditional Chinese Medicine in accordance with the Declaration of Helsinki (Approval No: 2020KY-015–02). Additionally, it has been registered with the Chinese Clinical Trial Registry on July 13, 2020, under the registration number ChiCTR2000034580.

Participants

The participants for this study were selected from the Fuzhou University City area using a questionnaire screening process. They were required to meet specific criteria related to their medical history, symptoms, signs, and imaging examinations. Normal volunteers were also recruited from the Fuzhou University City area.

Inclusion criteria for participants with IS:①Meeting the diagnostic criteria for IS [20]: The patient underwent a standing position X-ray (full-spine view) to measure a coronal Cobb angle greater than 10°. Subsequently, the Adam Forward Bend Test was performed, during which the patient stood with both knees extended and slowly bent forward. The therapist conducted a thorough observation of the spine from top to bottom, assessing for differences in height, asymmetry on both sides, and the presence of a rib-hump;②College students aged between 18 and 20, irrespective of gender;③X-ray screening showing a Cobb angle between 10° and 30° (excluding 10° and 30°);④Willingness to sign an informed consent form and voluntarily participate in the experiment.

Exclusion criteria with IS:①Severe spinal deformities, including congenital, neuromuscular, neurofibromatosis, interstitial lesions, and traumatic types;②Severe osteoporosis or other diseases unsuitable for manual therapy;③Suspected or diagnosed cases of lumbar joint, soft tissue, or intra-spinal tumors;④Severe skin injuries, bleeding, or skin diseases in the spinal area;⑤True leg length discrepancy exceeding 2 cm on both sides;⑥BMI > 25. Any participant meeting any of these criteria would be excluded from the study.

Inclusion criteria for healthy controls:①Meet the diagnostic criteria for the normal population: no history of musculoskeletal system diseases or trauma in the past 6 months;②Aged between 18–20 years, regardless of gender;③Able to walk on flat ground and climb 8 steps of stairs without assistance.

Outcome measures

The root mean square (RMS%) values, normalized for each muscle amplitude, were calculated throughout the full gait cycle, including level walking and stair climbing. These calculations were performed using Visual3D, a software that offers kinematics and kinetics (inverse dynamics) calculations for biomechanical analysis of 3D motion capture data. These values provide insights into the average variation in discharge over time, serving as an indicator of the average level of muscle activation and demonstrating the extent of motor recruitment and rhythmic excitation [21]. The bilateral RMS values ratio can further reveal the symmetry of muscle activation [22].

Selection of trunk and lower limb analysis side: Based on the study, IS divided into convex side and concave side analysis [22], and controls are analyzed on the right and left sides [23].

RMS ratio (Indicator of symmetry): Normal-Right side RMS/Left side RMS; IS-Convex side RMS/Concave side RMS.

Data collection

The participants will first be acquainted with the experimental procedures, including walking on level ground and ascending and descending stairs. After a minimum of three repetitions, the participants will be instructed to walk at a self-perceived comfortable walking speed on a flat corridor measuring 10 m in length (with a data collection valid length of 4 m) and 2.4 m in width. For stair activities, an adjustable staircase consisting of eight steps, each with a height of 20 cm and depth of 30 cm, will be used. sEMG electrodes will be securely placed on the bilateral erector spinae muscles at T6, T10, L3, as well as on the gluteus maximus, gluteus medius, external oblique, and rectus abdominis muscles. The EMG signals will be captured using a sEMG system (Delsys Trigno, USA) with a sampling frequency of 1500 Hz. During the maximal voluntary isometric contraction (Biering Sorensen test, BST), the activation level, peak contraction, and average activation level will be recorded for each muscle. Prior to the test, the maximum voluntary isometric contraction (MVIC) will be measured and utilized for data normalization. The MVIC values will serve as indicators of muscle strength, and all walking parameters will be standardized to MVIC (%MVIC).

Maximum voluntary isometric contraction (MVIC)

The Biering Sørensen test (BST) was utilized to evaluate the maximum voluntary isometric contraction (MVIC) of the patients' trunk muscles. The patients lied in supine position and instructed to extend the hips and knees, while placing both hands on the body to elevate the upper body off the bed surface until the scapulae are lifted, maintaining this position for a duration of 3 s. This measurement is repeated three times and the average value is computed to evaluate the Maximum Voluntary Isometric Contraction (MVIC) of the abdominal muscle chain, including the rectus abdominis and external oblique muscles.

Next, the patient lies prone with the upper body protruding over the edge of the bed, while the tester utilizes their own manual force to stabilize the lower limbs. The patient is directed to position their hands at the sides of the body and raise the upper body above the horizontal plane, sustaining this position for 3 s. This measurement is conducted thrice, and the average value is determined to assess the MVIC of the posterior muscle chain, specifically the erector spinae muscles at T6, T10, and L3, as well as the gluteus maximus and gluteus medius muscles.

The surface electromyography electrode placement is shown in the Fig. 1 [24–26]:

Fig. 1.

L T6 ES: Left Erector Spinae muscle at the sixth thoracic vertebra R T6 ES: Right Erector Spinae muscle at the sixth thoracic vertebra L T10 ES: Left Erector Spinae muscle at the tenth thoracic vertebra R T10 ES: Right Erector Spinae muscle at the tenth thoracic vertebra L L3 ES: Left Erector Spinae muscle at the third lumbar vertebra R L3 ES: Right Erector Spinae muscle at the third lumbar vertebra L OA: Left External Oblique muscle R OA: Right External Oblique muscle L RA: Left Rectus Abdominis muscle R RA: Right Rectus Abdominis muscle L Gmax: Left Gluteus Maximus muscle R Gmax: Right Gluteus Maximus muscle L Gme: Left Gluteus Medius muscle R Gme: Right Gluteus Medius muscle

Data analysis

Surface EMG data processing: Visual 3D is used to sequentially perform baseline correction, full-wave rectification, 50 ms RMS linear envelope, and amplitude/time normalization on the raw EMG signals [27].

①Baseline correction: Due to various factors such as experimental environment, the participants’ skin condition, temperature and the EMG raw signal deviates from the 0 point. It is necessary to perform baseline correction on the original EMG signal.

②Bandpass filtering: The 0-20 Hz range of the EMG raw signal is mainly caused by signal instability and motion artifacts. Generally, the original data needs to be filtered. However, the equipment used in this study includes a 20-450 Hz filter, so the EMG signal was not filtered again.

③Full wave rectification: The original EMG signal is smoothed and rectified.

④Linear envelope: The rectified signal is subjected to RMS envelope using a 50 ms time window [28].

⑤Amplitude/time normalization: The frequency and energy of muscle fiber discharge vary. EMG signals collected from the same person at different time points and from different people at the same time point will have differences. In this study, MVC maximum amplitude is chosen to standardize the amplitude of EMG signals for level and stair climbing tasks.

Statistical analysis

The original data was recorded to EXCEL 2013 and data analysis was conducted using SPSS 24.0 software. For continuous data that follows a normal distribution, it is expressed as $\overline{\mathrm{x}}\pm s$ . Between-group comparisons were performed using independent sample t-test. The significance level for hypothesis testing was set at P < 0.05. Non-parametric tests were used for data that did not follow a normal distribution.

Results

Participants

Among 200 individuals, 28 IS patients who met the inclusion criteria were selected, and 28 healthy participants who met the criteria were included in the control group. Out of the 28 participants with IS, 13 presented with a single curve, while 15 exhibited a double curve. Specifically, 21 affected spinal segments were located in the thoracolumbar region, 6 in the thoracic region, and 1 in the lumbar region. The results presented in Table 1 reveal that within the IS group, the Cobb angle was significantly greater (IS: 16.00°) compared to the control group (control: 5.00°) (P < 0.05). No statistically significant variations were observed between the two groups concerning age, height, weight, and BMI (P > 0.05). Table 1 illustrates the fundamental characteristics of the participants.

Table 1.

Demographics between group analysis $\left[\overline{x},\pm ,\mathrm{s},,,,\mathrm{M},(\mathrm{P}25,\mathrm{P}75)\right]$ 

	IS (n = 28)	Control(n = 28)	t/Z	P Value
Gender
Female	15(53.6%)	15(53.6%)	/	/
Male	13(46.4%)	13(46.4%)
Cobb angle(°) a	16.00 ± 0.89	5.00 ± 0.35	-4.199	< 0.001***
Age	19.50(18.00, 20.00)	19.50(18.25, 20.00)	-0.668	0.504
Height(m)	1.70(1.63,1.74)	1.64(1.60,1.77)	-0.837	0.402
Weight(Kg) a	59.25 ± 7.63	60.13 ± 12.74	0.311	0.757
BMIa	20.73 ± 2.51	21.28 ± 2.75	0.783	0.437

^aParametric tests were used as the data followed a normal distribution

Body Mass Index

^***Compared to the control group, P < 0.001

IS Idiopathic Scoliosis

RMS(%MVC) and RMS ratio during level walking

The results presented in Table 2 showed that, during level walking, the Root Mean Square (RMS) values of the external oblique muscle on the convex side (IS: 8.02; Control: 4.96%MVC; P < 0.0001) and the erector spinae muscle on the convex side at the tenth thoracic vertebra (IS: 7.28; Control: 4.94%MVC; P = 0.02) were higher compared to the control group (P < 0.05). Conversely, the RMS values of the rectus abdominis muscle on the concave side (IS: 2.51; Control: 3.13%MVC; P = 0.012) and the erector spinae muscle on the concave side at the tenth thoracic vertebra (IS: 9.09; Control: 16.81%MVC; P < 0.001) were lower than those observed in the control group (P < 0.05).

Table 2.

RMS (%MVC) between group analysis (level walking) $\left[\overline{x},\pm ,\mathrm{s},,,,\mathrm{M},(\mathrm{P}25,\mathrm{P}75)\right]$ 

Outcomemeasure	Concave/Convex side	muscle	IS (n = 28)	Control(n = 28)	t/Z	P Value
RMS(%MVC)	Concave side	Gmax	2.40(1.00,4.45)	3.33(2.04,6.99)	-1.605	0.109
		Gme	12.93(8.96,18.90)	12.16(7.68,23.68)	-0.500	0.617
		RA	2.53(1.91,4.52)	2.79(1.57,5.10)	-0.380	0.704
		OA	8.02(5.41,12.25)	4.96(2.40,6.61)	-4.938	< 0.001***
		L3 ES	7.00(3.95,11.04)	7.08(4.46,10.06)	-0.168	0.866
		T6 ES	6.34(4.48,10.98)	5.61(3.32,8.38)	-1.192	0.233
		T10 ES	7.28(4.85,10.45)	4.94(3.98,7.52)	-2.331	0.020*
		Gmax	7.01(3.06,17.15)	9.83(4.29,20.85)	-1.168	0.243
	Convex side	Gme	10.88(5.14,23.26)	11.81(5.37,22.73)	-0.010	0.992
		RA	2.51(1.58,3.38)	3.13(1.69,7.20)	-2.500	0.012*
		OAa	9.00 ± 5.37	7.71 ± 7.58	-1.105	0.272
		L3 ES	8.35(4.48,15.79)	9.91(6.41,18.44)	-1.274	0.203
		T6 ES	6.50(3.65,12.02)	6.29(3.52,10.86)	-0.718	0.473
		T10 ES	9.09(5.74,14.83)	16.81(11.70,24.85)	-3.482	< 0.001***

Gmax Gluteus Maximus, Gme Gluteus Medius, RA Rectus Abdominis, OA Obliquus externus Abdominis, L3 ES Third Lumbar Spine Erector Spinae, T6 ES Sixth Thoracic Spine Erector Spinae, T10 ES Tenth Thoracic Spine Erector Spinae, RMS Root Mean Square, MVC Maximum Voluntary Contraction, IS Idiopathic Scoliosis

^aParametric tests were used as the data followed a normal distribution

^*Compared to the control group, P < 0.05

^***Compared to the control group, P < 0.001

The results presented in Table 3 indicate that when walking on a level surface, the RMS ratio of the erector spinae muscle on the third lumbar vertebra (IS: 2.11; Control: 4.43; P = 0.008) and the sixth thoracic vertebra (IS: 1.42; Control: 2.89; P = 0.037) in the IS group are significantly lower compared to the control group (P < 0.05).

Table 3.

RMS Ratio between group analysis (level walking) $\left[\overline{x},\pm ,\mathrm{s},,,,\mathrm{M},(\mathrm{P}25,\mathrm{P}75)\right]$ 

	Muscle	IS (n = 28)	Control(n = 28)	Z	P Value
RMS Ratio (Convex / Concave)	Gmax	0.82(0.21,2.24)	1.63(0.40,3.54)	-1.871	0.061
	Gme	2.47(0.84,8.75)	3.67(0.90,14.08)	-0.956	0.339
	RA	1.46(0.87,2.59)	1.84(0.96,3.11)	-1.178	0.239
	OA	1.75(0.94,4.64)	2.26(1.09,5.25)	-1.003	0.316
	L3 ES	2.11(0.68,4.58)	4.43(0.96,8.48)	-2.658	0.008**
	T6 ES	1.42(0.56,5.44)	2.89(1.17,6.31)	-2.082	0.037*
	T10 ES	1.39(0.64,6.26)	3.30(0.27,5.45)	-0.356	0.722

Gmax Gluteus Maximus, Gme Gluteus Medius, RA Rectus Abdominis, OA Obliquus externus Abdominis, L3 ES Third Lumbar Spine Erector Spinae, T6 ES Sixth Thoracic Spine Erector Spinae, T10 ES Tenth Thoracic Spine Erector Spinae, RMS Root Mean Square, IS Idiopathic Scoliosis

^*Compared to the control group, P < 0.05

^**Compared to the control group, P < 0.01

RMS(%MVC) and RMS ratio during ascending stairs

The results from Table 4 indicate that during ascending stairs, the RMS of the external oblique muscle on the convex side in the IS group measured 6.83 (Control: 4.34% MVC; P < 0.001), whereas the RMS of the external oblique muscle on the concave side in the IS was 6.36 (Control: 5.00% MVC; P = 0.001). These values were both higher than those observed in the control group (P < 0.05). Additionally, the RMS of the gluteus maximus muscle on the convex side in the IS registered 5.78 (Control: 7.29% MVC; P = 0.006), while the RMS of the gluteus maximus muscle on the concave side in the IS measured 7.76 (Control: 10.41% MVC; P < 0.001). These values were both lower than those observed in the control group (P < 0.05). Moreover, the RMS of the erector spinae muscle on the convex side at the third thoracic vertebra in the IS was 9.78 (Control: 11.02% MVC; P = 0.004), the RMS of the erector spinae muscle on the convex side at the sixth thoracic vertebra in the IS was 4.33 (Control: 5.75% MVC; P = 0.033), and the RMS of the erector spinae muscle on the concave side at the tenth thoracic vertebra in the IS was 9.00 (Control: 9.86% MVC; P = 0.006). All of these values were lower than those observed in the control group (P < 0.05).

Table 4.

RMS (%MVC) between group analysis (ascending stairs) $\left[\overline{x},\pm ,\mathrm{s},,,,\mathrm{M},(\mathrm{P}25,\mathrm{P}75)\right]$ 

Outcomemeasure	Concave/Convex side	muscle	IS (n = 28)	Control(n = 28)	Z	P Value
RMS(%MVC)	Concave side	Gmax	5.78(1.88,8.84)	7.29(4.94,10.70)	-2.755	0.006**
		Gme	16.54(9.58,26.65)	18.63(13.35,24.35)	-1.866	0.062
		RA	2.81(1.58,5.81)	3.12(1.67,5.12)	-0.027	0.978
		OA	6.83(3.94,10.96)	4.34(2.57,6.42)	-5.791	< 0.001***
		L3ES	9.78(8.04,12.36)	11.02(9.06,13.18)	-2.861	0.004**
		T6ES	4.33(3.37,7.35)	5.75(3.90,7.45)	-2.137	0.033*
		T10 ES	8.79(6.43,11.54)	8.01(5.79,10.54)	-1.896	0.058
	Convex side	Gmax	7.76(3.90,17.02)	10.41(8.17,15.17)	-3.807	< 0.001***
		Gme	17.67(12.77,28.64)	23.28(9.50,36.71)	-0.844	0.399
		RA	2.98(1.64,5.86)	3.34(2.07,5.79)	-0.716	0.474
		OA	6.36(3.99,9.88)	5.00(3.17,6.96)	-3.253	0.001**
		L3 ES	9.53(7.42,13.44)	10.40(8.48,12.48)	-0.648	0.517
		T6 ES	3.93(3.13,7.25)	4.80(3.44,6.32)	-0.709	0.478
		T10ES	9.00(6.99,11.08)	9.86(8.17,12.17)	-2.761	0.006**

Gmax Gluteus Maximus, Gme Gluteus Medius, RA Rectus Abdominis, OA Obliquus externus Abdominis, L3 ES Third Lumbar Spine Erector Spinae, T6 ES Sixth Thoracic Spine Erector Spinae, T10 ES Tenth Thoracic Spine Erector Spinae, RMS Root Mean Square, MVC Maximum Voluntary Contraction, IS Idiopathic Scoliosis

^*Compared to the control group, P < 0.05

^**Compared to the control group, P < 0.01

^***Compared to the control group, P < 0.001

The findings presented in Table 5 reveal that during the activity of ascending stairs, the RMS ratio of the erector spinae muscle on the sixth thoracic vertebra (IS: 1.37; Control: 1.18; P = 0.029) as well as the tenth thoracic vertebra (IS: 1.23; Control: 0.83; P < 0.001) in the IS group are higher in comparison to the control group (P < 0.05).

Table 5.

RMS Ratio between group analysis (ascending stairs) $\left[\overline{x},\pm ,\mathrm{s},,,,\mathrm{M},(\mathrm{P}25,\mathrm{P}75)\right]$ 

	Muscle	IS (n = 28)	Control(n = 28)	Z	P Value
RMS Ratio (Convex / Concave)	Gmax	0.97(0.66,3.24)	1.07(0.52,4.28)	-0.518	0.604
	Gme	1.16(0.65,3.24)	1.58(0.49,12.86)	-0.038	0.970
	RA	1.22(0.61,1.88)	1.22(0.57,2.13)	-0.844	0.398
	OA	1.31(0.83,2.35)	1.21(0.73,2.26)	-1.244	0.213
	L3 ES	1.15(0.79,5.73)	1.10(0.83,4.03)	-0.059	0.953
	T6 ES	1.37(1.01,3.81)	1.18(0.76,2.91)	-2.184	0.029*
	T10 ES	1.23(0.89,4.80)	0.83(0.62,3.71)	-3.725	< 0.001***

Gmax Gluteus Maximus, Gme Gluteus Medius, RA Rectus Abdominis, OA Obliquus externus Abdominis, L3 ES Third Lumbar Spine Erector Spinae, T6 ES Sixth Thoracic Spine Erector Spinae, T10 ES Tenth Thoracic Spine Erector Spinae, RMS Root Mean Square, IS Idiopathic Scoliosis

^*Compared to the control group, P < 0.05

^***Compared to the control group, P < 0.001

RMS(%MVC) and RMS ratio during descending stairs

The results from Table 6 showed that during descending stairs, the root mean RMS of the gluteus maximus muscle on the concave side in the IS group measured 5.55 (Control: 3.99% MVC; P = 0.033), the RMS of the external oblique muscle on the convex side in the IS was 7.56 (Control: 4.50% MVC; P < 0.001), and the RMS of the external oblique muscle on the concave side in the IS was 7.46 (Control: 5.01% MVC; P < 0.001). These values were all higher than those observed in the control group (P < 0.05). Conversely, the RMS of the gluteus medius muscle on the convex side in the IS measured 10.14 (Control: 12.56% MVC; P = 0.033), and the RMS of the rectus abdominis muscle on the concave side in the IS was 2.85 (Control: 3.46% MVC; P = 0.03). Both of these values were lower than those observed in the control group (P < 0.05).

Table 6.

RMS (%MVC) between group analysis (descending stairs) $\left[\overline{x},\pm ,\mathrm{s},,,,\mathrm{M},(\mathrm{P}25,\mathrm{P}75)\right]$ 

Outcomemeasure	Concave/Convex side	muscle	IS (n=28)	Control (n=28)	Z	P Value
RMS(%MVC)	Concave side	Gmax	4.39(1.88,8.66)	3.42(2.69,5.26)	-1.332	0.183
		Gme	10.14(6.45,14.08)	12.56(7.90,21.49)	-2.137	0.033*
		RA	3.41(2.18,5.88)	3.39(1.93,5.35)	-0.261	0.794
		OA	7.56(4.86,11.15)	4.50(3.66,7.42)	-4.055	<0.001***
		L3 ES	5.34(3.68,9.70)	6.13(4.47,8.13)	-0.843	0.399
		T6 ES	4.68(3.28,7.02)	4.53(2.53,5.57)	-1.609	0.108
		T10 ES	5.76(4.37,8.36)	5.98(4.39,7.54)	-0.273	0.785
	Convex side	Gmax	5.55(3.08,12.87)	3.99(2.18,5.97)	-2.127	0.033*
		Gme	10.59(7.05,16.20)	11.67(5.82,21.26)	-0.494	0.622
		RA	2.85(2.04,4.62)	3.46(2.38,6.12)	-2.170	0.030*
		OA	7.46(4.85,10.41)	5.01(3.88,6.26)	-3.628	<0.001***
		L3 ES	5.12(3.68,8.93)	4.71(2.97,6.22)	-1.591	0.112
		T6 ES	3.81(2.42,6.07)	4.28(2.96,5.58)	-0.319	0.750
		T10 ES	6.62(4.38,8.43)	6.77(4.81,11.00)	-1.022	0.307

Gmax Gluteus Maximus, Gme Gluteus Medius, RA Rectus Abdominis, OA Obliquus externus Abdominis, L3 ES Third Lumbar Spine Erector Spinae, T6 ES Sixth Thoracic Spine Erector Spinae, T10 ES Tenth Thoracic Spine Erector Spinae, RMS Root Mean Square, MVC Maximum Voluntary Contraction, IS Idiopathic Scoliosis

^*Compared to the control group, P<0.05

^***Compared to the control group, P<0.001

The results presented in Table 7 demonstrate that while descending stairs, the RMS ratio of the erector spinae muscle on the sixth thoracic vertebra (IS: 1.95; Control: 1.35; P = 0.016) in the IS group is significantly greater than that of the control (P < 0.05).

Table 7.

RMS Ratio between group analysis (descending stairs) $\left[\overline{x},\pm ,\mathrm{s},,,,\mathrm{M},(\mathrm{P}25,\mathrm{P}75)\right]$ 

	Muscle	IS（n=28）	Control（n=28）	Z	P Value
RMS Ratio （Convex / Concave）	Gmax	1.46(0.58,6.63)	1.51(0.85,3.26)	-0.600	0.548
	Gme	2.63(0.74,10.30)	1.72(0.49,9.94)	-0.748	0.455
	RA	1.90(1.10,3.76)	1.55(0.77,2.91)	-1.662	0.097
	OA	2.35(1.00,6.05)	1.48(0.91,4.68)	-1.444	0.149
	L3 ES	1.88(1.03,4.82)	2.25(0.98,5.33)	-0.368	0.713
	T6 ES	1.95(1.24,5.04)	1.35(0.55,4.08)	-2.413	0.016*
	T10 ES	2.18(0.96,5.75)	1.25(0.70,5.07)	-1.895	0.058

Gmax Gluteus Maximus, Gme Gluteus Medius, RA Rectus Abdominis, OA Obliquus externus Abdominis, L3 ES Third Lumbar Spine Erector Spinae, T6 ES Sixth Thoracic Spine Erector Spinae, T10 ES Tenth Thoracic Spine Erector Spinae, RMS Root Mean Square, IS Idiopathic Scoliosis

^*Compared to the control group, P<0.05

Discussion

This study uncovers unique movement patterns in college students with IS during level walking and ascending/descending stairs, in comparison to the healthy population. In level walking, asymmetrical activation is observed in the erector spinae muscles at T6 and L3, with lower activation levels on the convex side compared to the concave side. When ascending stairs, there is asymmetric activation in the erector spinae muscles at T6 and T10, with higher activation levels on the convex side than the concave side. Likewise, during descending stairs, the erector spinae muscle at T6 shows asymmetrical activation, with higher activation on the convex side compared to the concave side.

These findings suggest that, during level walking, individuals with IS experience heightened activation in the erector spinae and abdominal muscles on the convex side, while displaying diminished activation in the paravertebral and abdominal muscles on the concave side at the thoracic and lumbar levels. Ng PTT’s review [29] highlighted that increased activity on the convex side compared to the concave side was frequently observed in scoliosis patients during postural tasks, consistent with our findings. Muscle imbalance has been proved to be associated with IS and thought to be a contributing factor to the progression of IS [12, 30]. The surrounding muscles of the spine endeavor to bring the spine into a neutral position [31]. The erector spinae muscles have been identified to possess corrective functions by attempting to straighten the thoracic vertebrae as a compensatory mechanism against increasing instability. In support of this compensatory role, the application of electrical stimulation around the spine [32] has been demonstrated to partially correct the curvature associated with IS. When the paravertebral muscles are unable to compensate and stabilize spinal rotation, it leads to the progression of scoliosis [33].

The erector spinae muscles and abdominal muscles play a role in controlling inertia and gravity to enhance the dynamic stability of the spine in level walking [34, 35], additionally, they help maintain balance during gait by controlling the swinging and rotational movements of the trunk [34, 36, 37]. There is a phenomenon of reverse coupling motion between lateral bending and rotation in the spine. The vertebral bodies of the scoliotic curve rotate towards the convex side, and the activation of the external oblique muscles on the convex side is greater, in alignment with this mechanism. Conversely, the activation of the erector spinae muscles on the concave side is smaller. Other studies have also reported significant asymmetrical electromyographic responses in the muscles on the concave and convex sides among patients with IS [38]. The rotational strength of the convex side in the primary curve is greater than that of the concave side, indicating that factors such as soft tissue tension and limited range of rotational motion contribute to the disparities in rotational muscle strength [39]. Morphological and histological research indicates that the increase in fibrosis, fatty degeneration, and the proportional increase of type II fibers may contribute to the decline in muscle strength on the concave side. These studies have consistently demonstrated the presence of abnormal characteristics such as muscle asymmetry or imbalance in patients with IS. Consequently, in the development of rehabilitation intervention plans, it is crucial to prioritize the relaxation of the convex side muscles and the strengthening of the concave side muscles. This approach promotes the restoration of muscular imbalance in the bilateral spinal muscles and sustains the external stability of the spine. Morphological and histological studies have provided evidence that fibrosis, fatty degeneration, and an elevated proportion of type II fibers may contribute to the decreased muscle strength on the concave side [40]. These studies have consistently confirmed the presence of abnormal muscle asymmetry or imbalance in patients with IS. As a result, when devising rehabilitation intervention plans, simultaneous consideration should be given to the coordinated contraction and coordination of the abdominal muscles and erector spinae.

The findings from level walking revealed a significantly higher RMS ratio between sides in the erector spinae muscles at T6 and L3 in the control group (P < 0.05). Additionally, during ascending stairs activity, IS patients exhibited significantly higher RMS asymmetry ratios in both the erector spinae muscles at T6 and T10, compared to the control group (P < 0.05). For the control group, individuals may have distinct walking patterns on flat surfaces, potentially leading to asymmetrical bilateral muscle contractions stemming from differences in dominance [41, 42]. The research revealed that the control group displayed greater asymmetry in bilateral spinal muscle contractions during level walking in comparison to individuals with scoliosis. Interestingly, the scoliosis group exhibited even more pronounced asymmetry than the control group during stairs ascent. It is hypothesized that individuals with scoliosis may experience heightened asymmetry in response to increased spinal challenges due to compromised muscle coordination, whereas the control group demonstrates better adaptation to such challenges, representing a significant distinguishing factor between the two groups. Previous research has also confirmed that IS patients exhibit significant asymmetrical muscle activity in the T10 and L3 muscles when resisting external perturbations [38]. Moreover, patients with IS have been found to have concave-convex asymmetry in muscle length, muscle tension angles, proportions of type I and type II muscle fibers [22, 43], muscle volume [44], skinfold thickness [45]. This asymmetry during dynamic activities can lead to imbalanced mechanical forces on the spine. Stair ascent necessitates enhanced trunk control, presents greater balance challenges, and imposes higher muscular demands in comparison to walking on level ground. Numerous individuals experiencing low back pain report heightened discomfort during stair climbing [18], which may be linked to this mechanism. The pattern of stair climbing intensifies spinal instability and potentially exacerbates muscular imbalances. Further research is warranted to explore the correlation between lower back pain in individuals with IS and these alterations in kinematics.

This study unveiled a statistically significant augmentation in the bilateral RMS of the thoracic and external oblique muscles among IS patients during stair descent, in comparison to the control group (P < 0.05). These findings signify an escalated level of activation in the bilateral oblique muscles of IS patients during stair descent. In the sagittal plane, during the process of descending, the spine has a propensity to extend posteriorly in order to safeguard body equilibrium and prevent potential falls. Consequently, the abdominal muscles are required to perform significant eccentric contractions to uphold the body's extension angle and ensure optimal balance. The results of this study demonstrate an augmented activation of the bilateral external oblique muscles in IS patients in comparison to the control group. The findings of this study suggest that IS patients require greater effort from their trunk muscles to maintain spinal extension and stability. This increased demand leads to heightened activation of the external oblique muscles. We propose that this phenomenon may be due to the increased need for eccentric control of the spinal muscles during stair descent, in order to ensure whole body stability. The stability of descending stairs is lower compared to level walking or ascending stairs. The compensatory muscle strategies employed by patients are insufficient in ensuring spinal stability, leading to minimal compensatory effect on the spine. Research has shown a higher risk of falls during stair descent [46], thus confirming the reduced stability of patients with IS during this activity. These findings recommend prioritizing stair descent in rehabilitation training for IS.

Limitations

This study has several limitations. Firstly, it only included individuals with Cobb angle below 30° and aged between 18–20 years. To improve the study's generalizability, future research should consider including participants from different age groups and increasing the sample size. Additionally, not classifying the affected segments of the spinal curvature may have masked certain disease characteristics. Therefore, it is recommended that further analysis be conducted, focusing on different subtypes of spinal curvature. The unclear etiology of scoliosis necessitates comparative analysis with normal populations in clinical research to determine potential factors linked to its pathogenesis. Moving forward, we hope to harness big data and employ predictive models to identify the key factors associated with IS, thereby offering objective evidence to inform the prevention and treatment strategies for IS.

Conclusions

Walking and stair climbing are prevalent everyday tasks that possess substantial practical significance for comprehending the variations in muscle activity during dynamic activities. During level walking and stair activities, IS patients exhibit pronounced abnormal movement patterns that significantly differ from those of the control group. Under different activity conditions such as level walking, ascending and descending stairs, IS patients demonstrate abnormal muscle activation in different segments of the spine. When formulating rehabilitation intervention plans, it is crucial to simultaneously consider the coordinated contraction and coordination of the abdominal muscles and erector spinae. The act of stair climbing can heighten spinal instability and potentially aggravate muscular imbalances; therefore, we suggest focusing on stair descent as a priority in rehabilitation training for individuals with impaired posture due to IS.

Authors’ contributions

Data curation: Yanyun Gou, Jing Tao, Yifan Sun, Xiang Chen. Formal analysis: Yanyun Gou, Xiangbin Wang. Funding acquisition: Yanyun Gou. Investigation: Xiangbin Wang, Yifan Sun. Methodology: Meijin Hou, Jing Tao, Jia Huang. Project administration: Yanyun Gou. Visualization: Yanyun Gou, Jing Tao. Writing – original draft: Yanyun Gou Writing – review & editing: Yanyun Gou, Xiangbin Wang.

Funding

Project supported by the National Natural Science Foundation of China (Grant No. 82205306), Guangzhou Science Technology Project (Grant No. 2022FX7).

Data availability

All data generated or analyzed during this study are included in this article.

Declarations

Ethics approval and consent to participate

Informed consent to participate was obtained from all participants and/or their legal guardian(s).

Consent for publication

Informed consent to participate was obtained from all participants and/or their legal guardian(s).

Competing interests

The authors declare no competing interests.