Abstract
［Purpose］In the present study, it was hypothesized that the instantaneous center of rotation (ICR) from the head side gradually shifted to the caudal side from the head side as the rotational motion of the head and sternum strongly occurred by obtaining the segmentality of the spinal column .[Subjects and Methods]Twelve healthy males were included.In the sitting-up motion from the supine position, the initial motion of the head was defined as two conditions of head flexion and cervical flexion. The coordinates of the ICR of the head and sternum under each condition were calculated using a three-dimensional motion analyzer VICON-MX.［Result］Both the head and the sternum had head flexion located on the head side in the first half of the operation.［Conclusion］It was suggested that head flexion movement contributes to the construction of the segmental nature of cervical vertebrae and thoracic vertebrae.
