Comparing Electromyographic Muscle Activities and Kinematics During Sit-to-Stand Transitions in Patients with Adult Spinal Deformity Versus Healthy Controls

<b>Background/Objectives:</b> Adult spinal deformity (ASD) affects sit-to-stand (STS) transitions due to abnormal spinal alignment, influencing muscle function. This study investigated lower-extremity electromyographic activity and kinematic parameters during STS transitions in ASD patients. <b>Methods:</b> A cross-sectional study was conducted with ASD patients scheduled for corrective surgery. The STS task was divided into three phases, and electromyographic activity, temporal parameters, and joint kinematics were compared between ASD patients and controls. Surface electromyography measured muscle activity, and a high-speed camera recorded phase durations and joint movements. <b>Results:</b> Compared to 17 controls, 17 ASD patients exhibited significantly increased %MVIC (ASD, controls, <i>p</i>-value) in the biceps femoris during the flexion momentum phase (23.7 ± 26.5, 12.3 ± 8.6, <i>p</i> = 0.048) and extension phase (48.6 ± 25.8, 32.8 ± 40.5, <i>p</i> = 0.011), and in the soleus during the flexion momentum phase (16.2 ± 7.5, 8.5 ± 2.9, <i>p</i> = 0.001). The ASD group also showed greater joint motion and longer phase durations during STS transitions. <b>Conclusions:</b> ASD patients display increased lower limb muscle activation, prolonged phase durations, and more joint motion during STS transitions. These findings highlight neuromuscular and biomechanical differences, though whether these are pathological, adaptive, or compensatory remains unclear.