**1. Introduction**

Scoliosis is a three-dimensional deformity of the lateral curvature and rotated vertebrae, among which adolescent idiopathic scoliosis (AIS) is the most commonly diagnosed. The prevalence of AIS is reported as high as 1.02–2.4% among primary and secondary school students [1,2]. The deformed spine in patients with AIS leads to asymmetric paraspinal muscles that show higher electromyographic (EMG) activity on the convex side than that of the concave side of the scoliotic curve [3–5]. This asymmetry could be due to a lower proportion of oxidative slow-twitch (type 1) fibers on the concave side, which induced a decrease in tonic activity and the ability to sustain contractions, resulting in sustained postural deficits [5,6]. The imbalance and asymmetry in the paraspinal muscles have been suggested to be related to the development and progression of spinal deformity [4] and decreased quality of life in AIS patients [7], which warrants further efforts to identify and validate the appropriate treatment.

**Citation:** He, C.; Yang, J.-T.; Zheng, Q.; Mei, Z.; Ma, C.Z.-H. How do Paraspinal Muscles Contract during the Schroth Exercise Treatment in Patients with Adolescent Idiopathic Scoliosis (AIS)? *Bioengineering* **2022**, *9*, 234. https://doi.org/10.3390/ bioengineering9060234

Academic Editors: Andrea Cataldo and Stuart Goodman

Received: 1 April 2022 Accepted: 25 May 2022 Published: 27 May 2022

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Treatment of the musculature is one of the main objectives in AIS, as the effect of the correction in posture needs to be maintained by the musculature. Different treatment exercises have been proposed, and the muscle responses to these exercises have been investigated in a number of previous studies. Schmid et al. (2010) assessed the surface electromyography (sEMG) activity of paraspinal muscles during four back strengthening exercises on patients with AIS, and found that the asymmetric exercises of the front press at the lumbar level and the roman chair and bent-over barbell row at the thoracic level were superior in increasing sEMG amplitudes in the concave side [8]. Chwala et al. (2014) compared sEMG activity symmetry during two symmetric and four asymmetric exercises in girls with AIS, and found that most cases generated an increase in the predominance of sEMG activity at the convex side during symmetric and asymmetric exercises than in the resting position [9]. Strasse et al. (2018) validated the application of sEMG in monitoring the neuromuscular activity after an exercise treatment lasting for 12 weeks. They found improved balance in the recruitment of motor units for the production of muscle strength after exercise, especially at the right side of the spine [10]. Tsai et al. (2010) investigated the difference in bilateral paraspinal muscle activities during resistance isokinetic exercises in people with and without scoliosis [11]. They found that the paraspinal muscle tended to shift sEMG activities from the convex to the concave side, and the lumbar paraspinal muscle supplied the major action in healthy subjects, while thoracic paraspinal muscle compensated to supply actions in patients with a larger scoliosis curve. As a result, they recommended more midback protection during exercises on patients with AIS.

The Schroth exercise is a common approach for paraspinal muscle training for patients with AIS in clinical practice. It was developed by Katharina Schroth in 1920 [12]. The scoliosis-specific exercise is specifically designed to train patients to bring their asymmetric posture into alignment and restore a correct upright position. The repetitive training of the skeletomuscular system could reinforce the effect, so that patients could consciously maintain the corrected posture in daily living activities [13]. The Schroth method also provides sensorimotor and breathing exercises aimed at the recalibration of static/dynamic postural control, spinal stability, and breathing patterns [14]. It has been reported that the Schroth exercise slows curve progression [15], reduces curve severity [16] and reduces scoliosis related pain (>50% intensity and frequency) [17]. Furthermore, the Schroth exercise was also reported to improve the performance capacity of the paraspinal muscles, such as strengthening the musculature, better exploiting muscle activity [12], improving erector spinae activation strategies [6], and correcting the postural defects [18]. These benefits may be presented by a more symmetric sEMG activity on the concave and convex side of the paraspinal muscles.

However, to the best of the authors' knowledge, few previous studies have investigated the sEMG activity while performing the Schroth exercise in patients with AIS. Therefore, this study aimed to address this issue and applied sEMG innovatively to investigate the paraspinal muscles activity before, during and after the Schroth exercise in AIS patients. The muscle performance in the Schroth exercise, as revealed via sEMG signal, will provide evidence and contribute to the individualized and case-specific training of the Schroth exercise for patients with AIS in future clinical practice.

#### **2. Materials and Methods**
