Exercises of The Trunk
Sit Up (from supine lying down position):
1.Lumbar and thoracic spine flexed by concentric action of rectus abdominus, and all four abdominal oblique muscles.
2.After first few centimeters, psoas major can also be involved. Its origin and insertion are reversed so it can pull lumbar spine into further flexion. At this stage, psoas major will tend to lift feet off floor unless firmly fixed. This is opposed by synergistic activity of hamstrings which hold legs against floor. But this action tends to flex knees, which must then be opposed by quadriceps to keep knees extended.
3.When body returns to lying position from sitting, hips and trunk require to be extended. The same muscles as before work eccentrically to control the downward movement, which is produced by gravity.
4.In a sit-up with hands behind the neck, and trunk rotation also included, so for instance right elbow moves towards left knee, then left internal oblique and right external oblique work strongly to aid rotation.
Toe Touching and straightening
1.Starting from anatomical position, a brief contraction of trunk and hip flexors moves trunk forward. Then gravity takes over as the force producing the movement. Thus erector spinae and quadratus lumborum of the spine contract eccentrically to control further movement, as do gluteus maximus and hamstrings for the hip. Thus thoracic and lumbar spine as well as hip joint muscles are involved.
2.The trunk is extended when returning to anatomical position, by concentric contraction of all the above muscles
Sideways Bending (lateral flexion)
1.Starting in full lateral flexion to the left, the trunk is raised to upright position by concentric contraction of right external and internal obliques, rectus abdominus, quadratus lumborum and erector spinae. When the trunk moves past upright into right lateral flexion, gravity continues the movement, with the corresponding muscles of the left side working eccentrically to control the movement.