1Department of Rehabilitation Medicine, Seoul National University Hospital, Seoul National University College of Medicine, Seoul, Korea
2Department of Rehabilitation Medicine, Seoul National University Bundang Hospital, Seoul National University College of Medicine, Seongnam, Korea
Correspondence: Ju Seok Ryu Department of Rehabilitation Medicine, Seoul National University Bundang Hospital, Seoul National University College of Medicine, 82 Gumi-ro 173beon-gil, Bundang-gu, Seongnam 13620, Korea. Tel: +82-31-787-7739 Fax: +82-31-787-4051 E-mail: jseok337@hanmail.net
• Received: October 26, 2025 • Revised: January 2, 2026 • Accepted: January 26, 2026
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (https://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
To identify the asymmetric spinal stabilizing exercise (ASSE) postures that selectively activate the multifidus (Mu) relative to the erector spinae (ES) in patients with adolescent idiopathic scoliosis (AIS), thereby supporting the development of curve-specific exercise programs for three-dimensional spinal deformities.
Methods
Surface electromyography recordings were obtained bilaterally from the ES and Mu muscles during ASSE postures. Signals were normalized to the maximal voluntary isometric contraction. The asymmetry ratio, Mu/ES ratio, and additional asymmetric contraction of the Mu were analyzed.
Results
The study included 40 patients with AIS. The Mu demonstrated greater ipsilateral activation in the side-lying posture, whereas greater contralateral activation was observed during unilateral lower extremity lifting and combined upper–lower extremity lifting in the prone posture, as well as during combined upper–lower extremity lifting in the bird-dog posture. In the prone and bird-dog postures, the Mu/ES ratio exceeded 1.0, indicating relatively stronger Mu recruitment under rotational loading. Additional asymmetric contraction of the Mu was greatest in the side-lying posture (47%), with differences<15% in all other postures.
Conclusion
ASSE induces posture-specific asymmetric activation of the paraspinal muscles in patients with AIS. Although the side-lying posture produced the largest asymmetry, this reflected increased ES activity for trunk elevation rather than true selective Mu contraction. In contrast, the prone and bird-dog postures demonstrated a greater Mu contribution relative to the ES under rotational loading. These findings suggest that ASSE can be adapted to target specific paraspinal muscle components: side lying for lateral bending and bird-dog variations to enhance rotational stability.
Scoliosis, the most common spinal deformity, affects 2%–3% of adolescents. Adolescent idiopathic scoliosis (AIS) is defined as a structural, three-dimensional curvature of the spine that combines lateral bending and axial rotation [1,2]. Clinically, AIS is often categorized according to the curve morphology into single thoracic, thoracolumbar, and lumbar patterns, and double thoracic and major patterns [3,4].
Paravertebral muscle morphology has long been implicated in scoliosis development and progression. Histological and imaging findings have revealed marked asymmetry between the convex and concave sides of the curve, with a larger cross-sectional area, greater proportion of type I fibers, and richer capillary network on the convex side, and smaller fibers and greater fat infiltration on the concave side [5-7] Most of these findings were derived from thoracic paraspinal biopsies obtained near the apical vertebrae; direct evidence from the lumbar region remains limited.
In the lumbar region, the erector spinae (ES), comprising the longissimus thoracis and iliocostalis lumborum, primarily contributes to ipsilateral bending. The multifidus (Mu), with its short segmental fibers, generates contralateral rotation and provides intersegmental stabilization [8,9]. These distinct biomechanical roles suggest that muscle adaptation may vary by curve type, with thoracic curves tending to exhibit convex-side hyperactivation and lumbar curves more likely to demonstrate concave-side weakness, reflecting different underlying asymmetrical mechanisms [3,10].
Surface electromyography (sEMG) in patients with scoliosis has consistently demonstrated convex-side hyperactivity during maximal contractions or postural tasks [10-12]. However, most previous studies have focused on the ES, with limited analysis of the Mu, despite its critical role in rotational control and segmental stability.
Because scoliosis involves both bending and rotation, with the balance of these components dependent on the curve pattern, exercise strategies should be tailored accordingly [11,13]; selective or preferential activation of the ES or Mu may be required.
The asymmetric spinal stabilizing exercise (ASSE) was originally proposed by Ko et al. [11] as a rehabilitation approach for idiopathic scoliosis that intentionally introduces postural asymmetry to facilitate selective activation of the paraspinal muscles on the convex or concave sides of the curve. The protocol consists of side-lying, prone, and quadruped postures designed to induce targeted activation of the ES and trunk muscles according to the curvature pattern. However, that study did not evaluate the Mu, which plays a crucial role in rotational control and intersegmental stabilization.
This study therefore aimed to identify ASSE postures that differentially activate the Mu and ES in patients with AIS. By analyzing the relative muscle activation ratios across ASSE postures, positions that emphasize bending or rotation were explored to support the development of individualized curve-specific exercise programs for the treatment of three-dimensional spinal deformities.
Methods
Study design
This prospective, single-center, cross-sectional study was conducted at a tertiary university hospital. Patients with AIS were enrolled in the study between December 21, 2016, and December 31, 2019. The study was registered at ClinicalTrials.gov (NCT03497520). All study procedures were approved by the Institutional Review Board of the Seoul National University Bundang Hospital (No. B-1701/378-103) and conducted in accordance with the principles outlined in the Declaration of Helsinki. Written informed consent was obtained from all participants or their legal guardians. Participants under 18 years of age provided consent through their guardians, and those aged 18 years or older provided their own written consent.
Participants
Participants were recruited from among patients with AIS who visited the Department of Rehabilitation Medicine at the Seoul National University Bundang Hospital for periodic follow-up or adjunctive therapy. Patients who met the eligibility criteria were included in the study regardless of race or socioeconomic status.
The inclusion criteria were as follows: (1) diagnosis of idiopathic scoliosis with a Cobb angle≥10°, as confirmed by standing radiography; and (2) aged 8–20 years. The exclusion criteria were as follows: (1) history of spinal surgery; (2) scoliosis secondary to cerebral palsy, neuromuscular disease, poliomyelitis, or congenital spinal abnormality; (3) Cobb angle<10° or >40°; and (4) acute back pain or inability to maintain the required postures.
Of the 109 patients with AIS enrolled in the study, 40 completed both the baseline assessment and sEMG recordings and were included in the final analysis.
Electromyographic measures
Muscle activation was assessed using sEMG. Measurements were obtained bilaterally from the ES at the 7th and 12th thoracic (ES_T7 and ES_T12, respectively) and 3rd lumbar (ES_L3) levels and from the Mu at the 3rd lumbar level (Mu_L3). Electrodes were placed 2 cm lateral to the spinous process for ES_T7, ES_T12, and Mu_L3 and 4 cm lateral to the spinous process for ES_L3. The skin was cleaned with alcohol prior to application of the disposable Ag/AgCl electrodes.
Signals were recorded using a wireless 8-channel FREEEMG 1000 system (BTS Bioengineering). Data were sampled at 1,024 Hz with a 20–500 Hz band-pass filter. The root mean square (RMS) value of muscle activation was calculated over a 10-second acquisition period for each posture. Outliers in terms of raw sEMG amplitude (top and bottom 1%) were excluded before normalization and statistical analysis.
Postures
The participants performed the ASSE postures, as described by Ko et al. [11], during sEMG. Each posture was explained to the participants and practiced before data acquisition; a single examiner provided verbal corrections to ensure proper alignment. All postures were performed sequentially in the fixed order shown in Fig. 1. Each posture was measured twice in the same order for all participants, and sufficient rest periods were provided between postures to minimize fatigue accumulation.
Side-lying position
The participants were instructed to lie on one side with the trunk and pelvis maintained in the same vertical plane, ensuring no trunk rotation. The upper arm was positioned vertical to the floor, and the shoulder and pelvis were vertically aligned (Fig. 1A).
Prone position
In the prone posture, the participants were asked to lie face down with both arms and legs fully extended. From this position, they performed one of three movements: lifting a unilateral upper extremity (Pr_Upper), lifting a unilateral lower extremity (Pr_Lower), or lifting one arm and the contralateral leg simultaneously (Pr_Upper/Lower) (Fig. 1B).
Bird-dog position
In the quadruped posture, participants again lifted one arm (Bd_Upper), one leg (Bd_Lower), or one arm and the opposite leg (Bd_Upper/Lower) while keeping the supporting arm and leg perpendicular to the floor and the lifted limbs parallel to the ground. The trunk was maintained as close to the horizontal as possible throughout (Fig. 1C).
Superman position
The participants were instructed to lie prone with both arms and legs simultaneously extended and lifted off the ground to induce bilateral maximal contraction of the paraspinal muscles (Fig. 1D). This posture, which is not a part of the ASSE protocol, was included to serve as a reference for maximal voluntary isometric contraction (MVIC).
Normalization
sEMG data were normalized to minimize the influence of physiological and individual factors on the absolute amplitude. Variations in subcutaneous tissue thickness, muscle fiber type and diameter, and local blood flow may alter sEMG magnitude even under identical contraction conditions [14,15]. Because these intrinsic properties cannot be experimentally controlled, normalization enables reliable comparison of muscle activation across individuals and muscle groups [14-16].
Normalization was also performed to correct for curve-specific differences in paraspinal muscle activation. Because peak and RMS amplitudes may vary depending on scoliosis type and morphology, sEMG values obtained during each ASSE posture were normalized to the MVIC of each participant, as recorded in the superman position [17-19]. This allowed relative activation patterns to be compared among different muscles independent of individual strength or curve characteristics.
Statistical analysis
All statistical analyses were conducted using IBM SPSS software version 23.0 (IBM Corp.). Normalized sEMG data were averaged for the ipsilateral and contralateral sides in each posture. Paired t-tests were used to assess side-to-side differences in activation, with p<0.05 considered statistically significant. Paired t-tests were performed to compare bilateral muscle activities under each posture. Bonferroni correction was applied to adjust for multiple comparisons within each muscle across seven postures. Effect sizes were calculated using Cohen’s dz, and 95% confidence intervals (CIs) for mean differences were reported.
The asymmetry ratio was calculated by dividing the normalized ipsilateral sEMG values by the normalized contralateral sEMG values of each muscle [10].
To compare the Mu and ES activation at the 3rd lumbar level, the Mu/ES ratio was computed as follows:
Paired t-tests were used to evaluate the differences in the Mu/ES ratio between the sides for each posture. Additional asymmetric contraction of the Mu (%) was defined as the absolute percentage difference between the contralateral and ipsilateral Mu/ES ratios and calculated as follows:
Ipsilateral and contralateral sides were determined based on the direction of the elevated limb. When a single upper limb or lower limb was elevated, the T7, T12, and L3 on the same side as the elevated limb were defined as ipsilateral. In the Pr_Upper/Lower and Bd_Upper/Lower postures, where the upper limb and contralateral lower limb were both elevated, T7 and T12 were defined as ipsilateral to the elevated upper limb, while L3 was defined as ipsilateral to the elevated lower limb. In the Side-Lying position, the T7, T12, and L3 on the same side as the upper arm, which provides vertical support against the floor, were defined as ipsilateral.
RESULTS
Participant characteristics
The baseline participant characteristics are presented in Table 1. The mean age of the 40 patients with AIS included in the study was 14.3±4.0 years; 8 patients were male and 32 were female. The mean Cobb angles for each curve group were as follows: thoracic, 16.6±2.3°; thoracolumbar, 20.9±6.0°; lumbar, 20.3±5.5°; double major, 22.8±8.1° (thoracic) and 23.5±6.6° (lumbar); and double thoracic, 31.5±7.7° (thoracic) and 32.2±4.6° (thoracolumbar). Orthoses were used by 40% of the participants.
Asymmetric contraction of paraspinal muscles during the ASSE protocol
The normalized sEMG data for each paraspinal muscle, as recorded during the ASSE protocol, are summarized in Table 2. The asymmetry ratios, which represent the relative activation of the ipsilateral and contralateral sides of each muscle (ipsilateral/contralateral), are presented in Fig. 2, illustrating the degree of lateral activation difference for each paraspinal muscle.
Side-lying position
Normalized sEMG values for all recorded muscles were higher on the ipsilateral side than on the contralateral side. Significant asymmetry was observed in the T12 ES, L3 ES, and L3 Mu (all p<0.001).
After Bonferroni correction, significant side-to-side differences remained in the L3 ES (mean difference=0.50, 95% CI 0.41–0.60, p<0.007, Cohen’s dz=1.32), T12 ES (mean difference=0.18, 95% CI 0.09–0.26, p<0.007, dz=0.51), and L3 Mu (mean difference=0.36, 95% CI 0.28–0.44, p<0.007, dz=1.13), indicating large effect sizes.
Prone position
In the single-arm-lift posture (Pr_Upper), ipsilateral activation was significantly greater than contralateral activation in the T7 ES (p<0.001) and T12 ES (p=0.025), whereas the L3 ES showed stronger contralateral contraction (p=0.009). After Bonferroni correction, the asymmetry in the T7 ES remained significant (p<0.007, dz=1.65), whereas the difference in the T12 ES did not retain statistical significance (p=0.175). The contralateral dominance of the L3 ES was not significant after correction (p=0.063).
In the single-leg-lift posture (Pr_Lower), contralateral dominance was observed in the T7 ES (p<0.001), T12 ES (p<0.001), and L3 Mu (p=0.020). Following Bonferroni correction, significant contralateral dominance persisted in the T7 ES (p<0.007, dz=0.59) and T12 ES (p<0.007, dz=0.43), whereas the L3 Mu did not remain significant (p=0.140).
During the combined arm and contralateral leg lift (Pr_Upper/Lower), ipsilateral activation was greater than contralateral activation in the T7 ES (p<0.001) and T12 ES (p<0.001), whereas the L3 ES and L3 Mu exhibited significant contralateral dominance (p=0.020 and p=0.003, respectively). All of these differences remained statistically significant after Bonferroni correction (all p<0.007 for T7 ES and T12 ES; p=0.021 for L3 Mu), with moderate-to-large effect sizes (dz=0.36–2.48).
Bird-dog position
With one arm lifted (Bd_Upper), ipsilateral dominance was again observed in the T7 ES (p<0.001) and T12 ES (p<0.001). These differences remained significant after Bonferroni correction (both p<0.007), with large effect sizes in the T7 ES (dz=2.05) and T12 ES (dz=1.22). Conversely, in the single-leg-lift posture (Bd_Lower), contralateral activation was predominant in the T7 ES (p<0.001) and T12 ES (p<0.001). Both effects remained significant after correction (p<0.007), with large effect sizes (dz=0.96–1.00).
In the combined arm and contralateral leg lift (Bd_Upper/Lower), marked asymmetry was present in all muscles examined, with ipsilateral dominance in the T7 ES (p<0.001) and T12 ES (p<0.001) and contralateral dominance in the L3 ES (p=0.002) and L3 Mu (p=0.015). After Bonferroni correction, significant asymmetry persisted in the T7 ES and T12 ES (both p<0.007) and in the L3 ES (p=0.014), whereas the L3 Mu did not retain statistical significance (p=0.105).
Comparison of L3 Mu and L3 ES activation during the ASSE protocol
Fig. 3 shows the Mu/ES ratios, calculated as the normalized sEMG value of the L3 Mu divided by that of the L3 ES on the same side. This ratio was used to identify the postures that preferentially activated the Mu, independent of the ES.
In the side-lying position, the Mu/ES ratio was significantly higher on the contralateral side than on the ipsilateral side (1.38±0.56 vs 0.91±0.48, p<0.001). This difference remained statistically significant after Bonferroni correction and was associated with a large effect size, supporting preferential contralateral Mu activation in the side-lying posture. No significant side-to-side differences were observed in the prone and bird-dog postures, although a trend toward higher Mu/ES ratios was observed.
Additional asymmetric contraction of the Mu
Fig. 4 shows the additional asymmetric contraction of the Mu across the ASSE postures. Additional asymmetric contractions were most pronounced in the side-lying posture, reaching 47%, representing a Mu/ES ratio 47% higher on the contralateral side than on the ipsilateral side. Although smaller in magnitude, measurable side-to-side differences were also observed in the prone and bird-dog postures. Among these, the Bd_Upper/Lower posture exhibited an additional asymmetric contraction of 14%, followed by Pr_Upper at 10%, Pr_Upper/Lower at 7%, Bd_Lower at 6%, and Pr_Lower and Bd_Upper at 4% and 2%, respectively. Consistent with the statistical analyses, these additional asymmetric contractions outside the side-lying posture were relatively small and were not always maintained after correction for multiple comparisons.
Overall, apart from the side-lying position, the differences in the additional asymmetric contraction of the Mu were relatively small.
DISCUSSION
This study investigated paraspinal muscle activation in patients with AIS during ASSE. While Ko et al. [11] demonstrated that ASSE can induce asymmetric activation of the ES in healthy individuals, the contribution of the Mu, which is crucial for rotational stability, remains unclear. Therefore, this study aimed to identify postures that could selectively activate the Mu relative to the ES in patients with AIS. The results of the study confirm that asymmetric activation of the paraspinal muscles occurs across multiple ASSE postures in patients with AIS. The Mu showed significant asymmetric activation on the ipsilateral side in the side-lying position and on the contralateral side in the Pr_Lower, Pr_Upper/Lower, and Bd_Upper/Lower positions. In addition, Mu/ES ratio and asymmetric contraction analyses revealed posture-specific differences in the relative contributions of the Mu and ES, supporting our efforts to identify ASSE postures that selectively activate the Mu.
Significant asymmetric contraction of the paraspinal muscles was observed in all the ASSE postures, indicating that selective muscle activation can occur in AIS. Mu activation was stronger on the ipsilateral side in the side-lying posture and on the contralateral side in the prone and bird-dog variations involving limb elevation. These findings are consistent with those of Ko et al. [11], who reported that ASSE can generate side-specific muscle recruitment through controlled postural asymmetry. By including the Mu, which primarily contributes to rotational control, the present study extends the previous findings and confirms that asymmetric recruitment is not limited to the ES [9,20,21].
The Mu/ES ratio was used to identify the postures that preferentially activate the Mu over the ES. In the side-lying posture, the Mu exhibited greater ipsilateral activation. However, the Mu/ES ratio was paradoxically higher on the contralateral side. This apparent discrepancy may be explained by the biomechanical characteristics of the posture. Maintaining vertical trunk alignment in a side-lying position requires ipsilateral trunk elevation, which strongly engages the ES for lateral bending, while contralateral ES activity decreases, allowing the Mu to dominate. Conversely, in the prone and bird-dog postures, which involve axial rotation, the Mu/ES ratio exceeded 1.0 bilaterally, suggesting a greater contribution of the Mu relative to the ES. These results indicate that Mu activation is more prominent under rotational loading, whereas ES activation predominates during lateral bending tasks [9,20,21].
In the present study, the additional asymmetric contraction of the Mu was markedly higher in the side-lying posture than in the other positions. However, this asymmetry should be interpreted with caution. The large difference observed in the side-lying position likely reflects a relative reduction in contralateral ES activity, given its primary role in bending, rather than true selective Mu activation. In contrast, the Bd_Upper/Lower posture showed moderate, but more physiologically meaningful, asymmetry, suggesting that contralateral Mu recruitment was associated with postural compensation during limb elevation.
In the conservative management of AIS during growth, recent international guidelines, including those from the International Society on Scoliosis Orthopaedic and Rehabilitation Treatment, emphasize the role of physiotherapy scoliosis-specific exercises (PSSE), which incorporate curve-specific, asymmetric exercise strategies aimed at three-dimensional correction and postural stabilization [22]. PSSE commonly relies on selective muscle recruitment to maintain corrected spinal alignment, although the neuromuscular characteristics underlying individual exercise components remain incompletely understood [23,24]. In this context, the present findings provide mechanistic insight into posture-dependent paraspinal muscle activation that may inform the selection of asymmetric stabilization tasks within curve-specific rehabilitation programs.
PSSE primarily conceptualizes scoliosis as a three-dimensional postural deformity and focuses on macroscopic correction through active self-correction, rotational breathing, and postural feedback to maintain global spinal alignment [23,24]. In contrast, the present ASSE framework targets microscopic neuromuscular activation patterns, particularly the relative contributions of the Mu and ES during posture-specific stabilization tasks. Rather than directly addressing three-dimensional alignment, ASSE modulates segmental stability and rotational control by selectively emphasizing muscle recruitment under specific biomechanical loading conditions, as quantified by sEMG. The present findings show that postures involving axial rotational loading, such as prone and bird-dog variations, preferentially increase Mu contribution relative to the ES, whereas side-lying postures are characterized by dominant ES activation associated with lateral bending demands. This posture-dependent neuromuscular specificity distinguishes ASSE from PSSE, which primarily relies on postural correction strategies rather than muscle-specific activation targets. Clinically, these approaches may be considered complementary: ASSE-based prone or bird-dog tasks may be prioritized in rotationally dominant curves to enhance Mu-mediated rotational control, whereas side-lying ASSE postures may be more appropriate in curves dominated by lateral bending. In mixed deformity patterns, PSSE may provide the primary framework for three-dimensional self-correction, with ASSE serving as an adjunct to refine segmental stabilization according to curve-specific biomechanical demands (Fig. 5).
In conclusion, this study demonstrated that ASSE elicits posture-specific asymmetric activation of the paraspinal muscles in patients with AIS. By incorporating a detailed analysis of Mu activation, the present findings extend previous ES-focused research and indicate that ASSE protocols may be further refined according to the rotational characteristics of the scoliotic curve—emphasizing side-lying postures for lateral bending and bird-dog variations for enhancing rotational stability.
Limitations
This study had several limitations. First, maintaining precise trunk alignment and preventing unintended body-axis rotation during ASSE was challenging, particularly for younger participants. Because the study population included children and adolescents, variations in compliance may have occurred despite the use of clear and simplified instructions. To minimize this variation, all participants received comprehensive training, and a single examiner supervised each measurement to ensure consistency. In addition, the RMS values, rather than peak amplitudes, were used to reduce the bias caused by inconsistent effort levels. Second, the degree of limb elevation during ASSE was not standardized. As greater elevation increases balance demands and alters paraspinal recruitment patterns, this may have influenced the results. In addition, the order of task presentation was neither randomized nor counterbalanced, and each posture was performed repeatedly in a fixed sequence. Therefore, potential learning effects associated with repeated task performance cannot be completely excluded. Third, breathing patterns during ASSE performance were neither controlled nor recorded. Given that respiratory phase (inhalation/exhalation) can influence trunk muscle activation and is considered an important component in both PSSE and stabilization-based exercise paradigms, the lack of respiratory control may have introduced additional variability in paraspinal muscle activation. Future studies should incorporate standardized or monitored breathing conditions as part of a more rigorously controlled protocol. Fourth, due to limitations in the current data structure, additional normalization analyses, such as task-specific peak normalization or cross-validation using alternative reference voluntary contractions, could not be performed. However, because all EMG data were normalized using the same reference condition, the primary outcome measures reflect relative, posture-dependent differences rather than absolute activation levels [25]. Therefore, the interpretation of side-to-side asymmetry and Mu-to-ES ratios is expected to be minimally affected by the choice of normalization method. Additionally, although surface electrodes were placed symmetrically at standardized anatomical landmarks to minimize crosstalk, the use of surface EMG for L3 Mu assessment carries inherent limitations, and electrode reattachment reliability and skin impedance were not formally evaluated in this study. Finally, the use of orthotics and their wear time were not controlled in this study. Although the presence of orthotics may have affected paraspinal muscle activation patterns, no subgroup analysis or covariate control was performed to account for this factor. Future studies should evaluate the impact of orthotics use and wear time on paraspinal activation. Additionally, the effect of limb-elevation angle on paraspinal activation should be examined to refine and individualize ASSE protocols based on AIS curve characteristics and muscle imbalance.
CONFLICTS OF INTEREST
No potential conflict of interest relevant to this article was reported.
FUNDING INFORMATION
None.
AUTHOR CONTRIBUTION
Conceptualization: Ryu JS. Methodology: Kim S, Ryu JS. Data collection: Kim S, Ryu JS, Suh JH. Formal analysis: Kim S, Ryu JS. Supervision: Ryu JS. Writing – original draft: Kim S, Ryu JS. Writing – review & editing: Kim S, Ryu JS, Suh JH. Approval of final manuscript: all authors.
ACKNOWLEDGMENTS
The authors would like to thank all participants for their involvement and cooperation in this study.
Fig. 1.
Postures adopted for surface electromyography. (A) Side-lying position. (B) Prone position, involving three movements: lifting unilateral upper extremity, lifting unilateral lower extremity, and lifting unilateral upper extremity and opposite side lower extremity. (C) Bird-dog position, involving three movements: lifting unilateral upper extremity, lifting unilateral lower extremity, and lifting unilateral upper extremity and opposite lower extremity. (D) Superman position.
Fig. 2.
Asymmetry ratios of paraspinal muscle activation during asymmetric spinal stabilizing exercise postures. Significance was determined using paired t-tests. *p<0.05, **p<0.01, and ***p<0.001. Pr, prone; Bd, bird-dog; T7 ES, 7th thoracic erector spinae; T12 ES, 12th thoracic erector spinae; L3 ES, 3rd lumbar erector spinae; L3 Mu, 3rd lumbar multifidus.
Fig. 3.
Mu/Erector spine ratios during asymmetric spinal stabilizing exercise postures. Data are presented as mean±standard deviation. Postures are grouped according to their dominant mechanical characteristics (lateral bending–dominant vs. rotational stabilization–dominant). Mu, multifidus; ES, erector spinae; L3, 3rd lumbar;ip, ipsilateral side of lifted limb; con, contralateral side of lifted limb; Pr, prone; Bd, bird-dog; UE, upper; LE, lower.
Fig. 4.
Additional asymmetric contraction of the Mu during asymmetric spinal stabilizing exercise postures. The bars indicate the magnitude of the additional asymmetric contraction of the Mu muscle. Pr, prone; Bd, bird-dog.
Fig. 5.
Conceptual framework for integrating physiotherapy scoliosis-specific exercises (PSSE) and asymmetric spinal stabilizing exercise (ASSE) based on scoliosis curve characteristics.
Table 1.
Demographic and baseline participant characteristics
Characteristic
AIS patients
Age (yr)
14.3±4.0
Sex (male:female)
8:32
Height (cm)
158.7±10.9
Weight (kg)
48.7±12.7
BMI (kg/m2)
18.8±3.2
Orthosis (%)
22.5
Curve type
Thoracic
2
Thoracolumbar
6
Lumbar
11
Double major
19
Double thoracic
2
Cobb’s angle (°)
Thoracic
16.6±2.3
Thoracolumbar
20.9±6.0
Lumbar
20.3±5.5
Double major
Thoracic
22.8±8.1
Lumbar
23.5±6.6
Double thoracic
Thoracic
31.5±7.7
Thoracolumbar
32.2±4.6
Values are presented as mean±standard deviation or number only.
AIS, adolescent idiopathic scoliosis; BMI, body mass index.
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7. Mannion AF, Meier M, Grob D, Müntener M. Paraspinal muscle fibre type alterations associated with scoliosis: an old problem revisited with new evidence. Eur Spine J 1998;7:289-93.
10. Park Y, Ko JY, Jang JY, Lee S, Beom J, Ryu JS. Asymmetrical activation and asymmetrical weakness as two different mechanisms of adolescent idiopathic scoliosis. Sci Rep 2021;11:17582.
11. Ko JY, Suh JH, Kim H, Ryu JS. Proposal of a new exercise protocol for idiopathic scoliosis: a preliminary study. Medicine (Baltimore) 2018;97:e13336.
12. Cheung J, Halbertsma JP, Veldhuizen AG, Sluiter WJ, Maurits NM, Cool JC, et al. A preliminary study on electromyographic analysis of the paraspinal musculature in idiopathic scoliosis. Eur Spine J 2005;14:130-7.
13. Lee JG, Yoon SY, Kim J, Lim J, Ryu JS. Analysis of the mechanism and clinical classification of thoracolumbar scoliosis using three-dimensional EOS and surface electromyography. Heliyon 2023;9:e19510.
15. Rainoldi A, Galardi G, Maderna L, Comi G, Lo Conte L, Merletti R. Repeatability of surface EMG variables during voluntary isometric contractions of the biceps brachii muscle. J Electromyogr Kinesiol 1999;9:105-19.
16. Knutson LM, Soderberg GL, Ballantyne BT, Clarke WR. A study of various normalization procedures for within day electromyographic data. J Electromyogr Kinesiol 1994;4:47-59.
17. Yang JF, Winter DA. Electromyographic amplitude normalization methods: improving their sensitivity as diagnostic tools in gait analysis. Arch Phys Med Rehabil 1984;65:517-21.
20. Hodges PW, Richardson CA. Inefficient muscular stabilization of the lumbar spine associated with low back pain. A motor control evaluation of transversus abdominis. Spine (Phila Pa 1976) 1996;21:2640-50.
21. Ward SR, Kim CW, Eng CM, Gottschalk LJ, Tomiya A, Garfin SR, et al. Architectural analysis and intraoperative measurements demonstrate the unique design of the MU muscle for lumbar spine stability. J Bone Joint Surg Am 2009;91:176-85.
23. Berdishevsky H, Lebel VA, Bettany-Saltikov J, Rigo M, Lebel A, Hennes A, et al. Physiotherapy scoliosis-specific exercises - a comprehensive review of seven major schools. Scoliosis Spinal Disord 2016;11:20.
24. Thompson JY, Williamson EM, Williams MA, Heine PJ, Lamb SE. Effectiveness of scoliosis-specific exercises for adolescent idiopathic scoliosis compared with other non-surgical interventions: a systematic review and meta-analysis. Physiotherapy 2019;105:214-34.
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Fig. 3. Mu/Erector spine ratios during asymmetric spinal stabilizing exercise postures. Data are presented as mean±standard deviation. Postures are grouped according to their dominant mechanical characteristics (lateral bending–dominant vs. rotational stabilization–dominant). Mu, multifidus; ES, erector spinae; L3, 3rd lumbar;ip, ipsilateral side of lifted limb; con, contralateral side of lifted limb; Pr, prone; Bd, bird-dog; UE, upper; LE, lower.
Fig. 4. Additional asymmetric contraction of the Mu during asymmetric spinal stabilizing exercise postures. The bars indicate the magnitude of the additional asymmetric contraction of the Mu muscle. Pr, prone; Bd, bird-dog.
Fig. 5. Conceptual framework for integrating physiotherapy scoliosis-specific exercises (PSSE) and asymmetric spinal stabilizing exercise (ASSE) based on scoliosis curve characteristics.
Graphical abstract
Fig. 1.
Fig. 2.
Fig. 3.
Fig. 4.
Fig. 5.
Graphical abstract
Differential Activation of the Multifidus and Erector Spinae During Asymmetric Spinal Stabilizing Exercise in Adolescent Idiopathic Scoliosis
Characteristic
AIS patients
Age (yr)
14.3±4.0
Sex (male:female)
8:32
Height (cm)
158.7±10.9
Weight (kg)
48.7±12.7
BMI (kg/m2)
18.8±3.2
Orthosis (%)
22.5
Curve type
Thoracic
2
Thoracolumbar
6
Lumbar
11
Double major
19
Double thoracic
2
Cobb’s angle (°)
Thoracic
16.6±2.3
Thoracolumbar
20.9±6.0
Lumbar
20.3±5.5
Double major
Thoracic
22.8±8.1
Lumbar
23.5±6.6
Double thoracic
Thoracic
31.5±7.7
Thoracolumbar
32.2±4.6
Side-lying
Pr_Upper
Pr_Lower
Pr_Upper/Lower
Bd_Upper
Bd_Lower
Bd_ Upper/Lower
L3 ES_ip
0.70±0.32
0.51±0.25
0.55±0.27
0.60±0.18
0.34±0.30
0.32±0.18
0.55±0.17
L3 ES_con
0.19±0.19
0.64±0.52
0.58±0.24
0.66±0.17
0.27±0.31
0.32±0.18
0.40±0.15
Asymmetry ratio
3.68
0.80
0.95
0.91
1.26
1.00
1.38
Difference
0.50±0.38
-0.13±0.52
-0.03±0.31
0.06±0.16
0.07±0.30
0.01±0.17
0.15±0.21
95% CI
0.41, 0.60
-0.25, -0.01
0.02, 0.10
0.02, 0.10
-0.03, 0.17
-0.05, 0.06
0.09, 0.22
p-value
<0.001***
0.009**
0.180
0.020*
0.183
0.641
0.002**
p (Bonf.)
<0.007
0.063
1.000
0.140
1.000
1.000
0.014
Cohen’s dz
1.32
0.25
0.10
0.38
0.23
0.06
0.71
T12 ES_ip
0.44±0.28
0.68±0.31
0.45±0.21
0.72±0.21
0.50±0.28
0.21±0.12
0.67±0.20
T12 ES_con
0.27±0.28
0.55±0.22
0.55±0.23
0.56±0.22
0.17±0.09
0.34±0.17
0.35±0.18
Asymmetry ratio
1.63
1.24
0.82
1.29
2.94
0.62
1.91
Difference
0.18±0.35
0.13±0.39
-0.10±0.23
0.16±0.27
0.33±0.27
-0.13±0.13
0.32±0.24
95% CI
0.09, 0.26
0.04, 0.23
-0.16, -0.05
0.09, 0.23
0.25, 0.41
-0.17, -0.09
0.25, 0.39
p-value
<0.001***
0.025*
<0.001***
<0.001***
<0.001***
<0.001***
<0.001***
p (Bonf.)
<0.007
0.175
<0.007
<0.007
<0.007
<0.007
<0.007
Cohen’s dz
0.51
0.33
0.43
0.59
1.22
1.00
1.33
T7 ES_ip
0.43±0.33
1.08±0.38
0.26±0.23
1.05±0.25
1.00±0.34
0.19±0.22
0.87±0.31
T7 ES_con
0.33±0.26
0.36±0.22
0.45±0.24
0.33±0.15
0.24±0.16
0.41±0.21
0.26±0.15
Asymmetry ratio
1.30
3.00
0.58
3.18
4.17
0.46
3.35
Difference
0.10±0.35
0.71±0.43
-0.19±0.32
0.72±0.29
0.76±0.37
-0.22±0.23
0.61±0.35
95% CI
0.01, 0.19
0.61, 0.83
-0.27, -0.11
0.64, 0.81
0.63, 0.88
-0.30, -0.13
0.59, 0.73
p-value
0.086
<0.001***
<0.001***
<0.001***
<0.001***
<0.001***
<0.001***
p (Bonf.)
0.602
<0.007
<0.007
<0.007
<0.007
<0.007
<0.007
Cohen’s dz
0.29
1.65
0.59
2.48
2.05
0.96
1.74
L3 Mu_ip
0.59±0.31
0.53±0.27
0.55±0.20
0.65±0.17
0.29±0.14
0.34±0.17
0.56±0.17
L3 Mu_con
0.23±0.14
0.55±0.20
0.59±0.23
0.70±0.17
0.24±0.14
0.35±0.20
0.46±0.17
Asymmetry ratio
2.57
0.96
0.93
0.93
1.21
0.97
1.22
Difference
0.36±0.32
-0.01±0.31
-0.04±0.16
0.05±0.14
0.04±0.14
-0.01±0.18
0.10±0.19
95% CI
0.28, 0.44
-0.08, 0.05
-0.08, 0.00
0.02, 0.09
0.00,0.08
-0.07, 0.04
0.04, 0.16
p-value
<0.001**
0.97
0.020*
0.003**
0.054
0.359
0.015*
p (Bonf.)
<0.007
1.000
0.140
0.021
0.378
1.000
0.105
Cohen’s dz
1.13
0.03
0.25
0.36
0.29
0.06
0.53
Table 1. Demographic and baseline participant characteristics
Values are presented as mean±standard deviation or number only.
AIS, adolescent idiopathic scoliosis; BMI, body mass index.
