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

"Proprioceptive-stabilometric assessment machine (ProKin 252, TecnoBody®, Italy) Balance performance of subjects will be tested on the proprioceptive-stabilometric assessment machine.~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. 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.~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."