Sagittal Kinematics and Muscular Activities of Torso and Hip during Trunk Flexion and Extension

The aim of this study was to investigate the kinematical movements and electromyographic activities of the trunk and hip during trunk flexion and extension at different velocities. Thirteen male subjects performed trunk flexion and extension movements for 5 times at three different velocities of 1 s, 3 s, and 5 s in the standing position. Sagittal angular displacements of the lumbar spine, pelvis, and hip as well as the surface electromyogram of the trunk and hip muscles were recorded. The kinematic characteristic was normalized, and the electromyogram was integrated and normalized separately in cycles of flexion and extension. During flexion, the lumbar spine range was significantly larger during 5 s than during 3 s and 1 s, whereas the hip range was significantly larger during 1 s than during 5 s (p<0.01). During extension, the normalized electromyogram values of the iliocostalis and longissimus were significantly greater during 1 s than during 5 s (p<0.05). Increase in the movement velocity during extension produced greater activity in the trunk extensors, while the activities of the flexors showed minimal change. The results suggest that there is a kinematic and kinetic strategy among the lumbar, pelvis and hips in order to accomplish task-oriented movements.