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