Figure 1. A) The normal squat posture (NSP): The shoulder joint was abducted as an external rotation and the middle finger was placed on the temple. The center of the foot pressure (COP) was between the left and right feet, but the subjects did not focus on the sagittal plane. B) The forward-shifted posture (FSP): Subjects looked at the front monitor, lifted their upper limbs and shifted the COP forward.