Association Between Postural Balance and Muscle Activity of the Lumbar and Lower Limb Muscles in Female With or Without Adolescent Idiopathic Scoliosis (AIS) During Standing Balance Tasks With Upper Limb Movement

Adolescent idiopathic scoliosis (AIS) is the most common type of three-dimensional deformity of the spine in adolescence with a clear female predominance at a prevalence rate of 3.5% in Hong Kong. AIS increases the risk of spinal degeneration, back pain, and cardiorespiratory dysfunction. These impairments caused by AIS can be related to the abnormal lateral deviation, axial rotation, and reduction of sagittal curves of the spine. AIS has been associated with asymmetrical muscle activity and impaired postural balance performance. AIS who had convex side of the major curves to the right demonstrated an increase in right side thoracic and lumbar erector spinae muscle activity during pelvic anterior, posterior, and left tilting on an unstable sitting board as measured by electromyography (EMG).

Postural balance is defined as the act of maintaining, achieving and restoring a state of balance during any posture or activity. The ability of maintaining postural balance in AIS is influenced by multiple factors including spinal deformities, asymmetrical muscle activities, alteration in sensory input, central integration or motor response. Previous studies have investigated the motor response in young adults. They were found to depend more on ankle strategy than hip strategy during a balance perturbation on a movable platform. Increased lateral gastrocnemius muscle activity was also observed when centre of gravity falls forward during an EMG measurement in quiet stance. In a study of low back pain patients, training regime involving single rapid arm movement in flexion and extension was found to promote the activation of the transversus abdominis muscle and improved the feedforward postural adjustment. There are limited studies to investigate the association between somatosensory input and motor response particularly lower limb muscle activity and upper limb movement on balance control in AIS. Recent evidence also suggested that AIS tend to overestimate the severity of their spinal deformity but their perception of their body schema and spinal curvature can be improved by enhancing motor skills. Therefore, training of postural balance that involved enhancing motor skills and stimulating somatosensory system will have the potential to improve motor response as well as improve self-perceived body schema in AIS.

Ten female subjects aged 10 to 16 will be recruited if they are diagnosed with AIS by standard standing long X-ray examinations, with Cobb angle larger or equal to 15°, without prior treatment for their AIS and been cleared for physical activity by their doctors. Subjects were excluded if they had (i) Cobb angle larger or equal to 40°, (ii) scoliosis with any known aetiologies such as congenital, neuromuscular, metabolic, and skeletal dysplasia, (iii) known endocrine and connective tissue abnormalities, (iv) known heart condition or other diseases that could affect the safety of exercise, (v) eating disorders or gastrointestinal malabsorption disorders, and (vi) currently taking medications that affecting their bone or muscle metabolism. Ten healthy female subjects with matched for age, height and weight will be recruited as control. All subjects will be recruited in the community.

All subjects will participate voluntarily in this study. Informed consent will be signed by subject in the presence of their parents after thorough explanation by research personnel before data collection. This study will be carried out with Low/Negligible Risk Human Research Ethics Approval issued by TWC Research Ethics Committee (REC).

Study Procedures This cross-sectional study will be carried out at Physiotherapy laboratory, School of Medical and Health Sciences, Tung Wah College between October 2021 and May 2022.

The experiment environment will be maintained at 25 degrees Celsius. Subjects should not perform any vigorous exercise before testing time.

Subjects will be asked to complete 3 questionnaires: The Chinese University of Hong Kong: Physical Activity Rating for Children and Youth (CUHK-PARCY), Tanner Scale and Trunk Appearance Perception Scale (TAPS) prior to the experiment for determining their physical activity level, sexual maturity and self-perception of spinal deformity respectively. Bioelectric Impedance Analysis (BIA) will be done to collect body composition data. Anthropometric parameters and spinal deformity data will be collected by female student investigators.

Surface EMG (sEMG) electrodes will be used for detection of muscle activity during balance tasks. According to the Surface EMG for Non-Invasive Assessment of Muscles (SENIAM) guidelines, skin preparation with hair removal by single-use razor and alcohol swab will be done before applying electrodes to reduce the skin impedance below 5k Ohm. sEMG electrodes will be positioned on muscle bellies of erector spinae (ES) at lumbar level (largest muscle mass lateral to L3 spinous process). For gluteus medius (GM), electrodes will be placed at proximal 1/3 of the distance between iliac crest and the greater trochanter. For lateral gastrocnemius (LG), electrodes will be placed at most prominent part of muscle belly during resisted plantar flexion.

After placing the sEMG for muscle activity measurement, balance performance of subjects will be tested on a proprioceptive-stabilometric assessment machine. Four tasks will be carried out, including: 1) open eyes fixing at a set point (170 cm height and 200 cm away) on a wall with relaxed arm aside; 2) eyes closed with relaxed arm aside; 3) eyes open with arm movements and 4) eye closed with arm movements. The arm movements are unilateral shoulder flexion and and extension of both arms with two frequencies (40 bpm and 120 bpm). The tempo will be given using a metronome. Each task will be tested twice with at least fifteen seconds rest between trials.

Balance Functions Performance for each balance test will be recorded by proprioceptive-stabilometric assessment machine (ProKin 252, TecnoBody®, Italy). The outcome will be analysed in terms of Ellipse area (mm2), Perimeter (mm), Forward-backward standard deviation (mm), Medial-lateral standard deviation, Average center of pressure in the medial-lateral direction on X-axis projection (mm), Average center of pressure in the anterior-posterior direction on Y-axis projection (mm), Standard deviation of forward-backward displacement (mm), Standard deviation of medial-lateral displacement (mm), Average velocity for forward-backward displacement (mm/s), Average velocity for medial-lateral displacement (mm/s) and Standard deviation of Trunk sway (o).

sEMG Muscle Activity The muscle activity will be measured by surface electromyography and recorded by the Noraxon wireless TELEmyo Direct Transmission System (TELEmyo DTS) with product code of 580 (Noraxon, USA Inc., USA). The sampling frequency will be of 1000Hz and bandwidth of 10-500Hz. Bipolar silver chloride electrodes of 15mm diameter will be used for EMG signals collection, the interelectrode distance will be fixed at 20mm. Electrodes will be attached to surface of 3 groups of muscles bilaterally, namely the lumbar erector spinae (LES), gluteus medius (GM) and lateral gastrocnemius (LG). Placement of electrodes will be based on previous studies to reduce inconsistency and inter-subject variability in normalizing the sEMG signal \[21\]. Normalization procedure will be done by asking subjects to perform isometric maximum voluntary contractions (MVC). The MVC will be measured by Lafayette hand-held dynamometer connected to flat stirrup. MVC will be tested as listed below. For LES, resisted lumbar extension against belt on lower thoracic area (T12) in prone lying. For GM, resisted hip abduction against belt in side-lying. For LG, resisted ankle plantarflexion in sitting position against belt in 90º dorsiflexion.

The sEMG signals during each experiment will be normalized to the sEMG at isometric MVC and expressed as percentages of the maximum sEMG activity (%EMG_max) for comparison with normalization signal processing program in Noraxon System.

Eligibility Criteria:
Inclusion Criteria:

(i) Cobb angle larger or equal to 40° (ii) scoliosis with any known aetiologies such as congenital, neuromuscular, metabolic, and skeletal dysplasia (iii) known endocrine and connective tissue abnormalities (iv) known heart condition or other diseases that could affect the safety of exercise (v) eating disorders or gastrointestinal malabsorption disorders (vi) currently taking medications that affecting their bone or muscle metabolism

Exclusion Criteria:

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