This is an excerpt from Dance Anatomy and Kinesiology 3rd Edition With HKPropel Access by Karen Sue Clippinger.
In analyzing movements of the spine, it is important to realize that in functional movement, they are often linked with movements of the pelvis and may involve various regions of the spine moving in isolation, together, or in opposite directions. For purposes of simplicity, this text focuses on the basic movements of the spine and related sample conditioning exercises.
To understand what muscles are producing a given movement of the spine, it is helpful to think of the spine as a flexible column with the muscles acting like guy ropes relative to the spine (Houglum and Bertoti, 2012). When the vertebral column leans off the vertical, the guy ropes (e.g., muscles) opposite to the direction in which the spine is leaning must contract to control or prevent the falling of the spine in that direction. Muscles of the spine are also often used together (cocontraction) in a coordinated manner to create a stable desired position of the spine. As previously described, the spine as a whole is capable of flexion, extension, lateral flexion, and rotation. A summary of the muscles capable of producing these movements of the spine is provided in table 4.2, and an illustration of the movements of the spine has been given in figure 4.7. To help readers focus on the more important muscles, the following movement descriptions list just the primary muscles. However, key secondary muscles are also listed in table 4.2 for those desiring a more detailed analysis.
Remember that spinal flexion involves bringing anterior surfaces of the vertebrae and trunk closer together. Spinal flexion that involves concentric use of the spinal flexors (table 4.2)—the rectus abdominis, external oblique abdominal muscles, and internal oblique abdominal muscles—occurs when the spine flexes or the pelvis posteriorly tilts against gravity or another external resistance as in the up phases of the curl-up (see table 4.3 and table 4.4A), curl-back (table 4.4B), pelvic tilt (table 4.4C), and hip lift (table 4.4D). These latter two exercises emphasize the lower (inferior) attachments of the abdominal muscles as the moving end, helpful for improving some spinal alignment issues. In the first two exercises, the emphasis is on the upper (superior) attachments of the abdominal muscles as the moving end, and the hip flexors are also used to bring the thigh closer to the pelvis. Spinal flexion involving a concentric contraction where both superior and inferior attachments move toward each other to create a C curve (see Concept Demonstration 4.1) is commonly used to raise the trunk from a supine position during floor work in jazz or modern dance.
During standing in an erect position, the situation gets more complex, since once the spine is slightly flexed, gravity will tend to produce more flexion. In a roll-down, after initiation of the movement by the spinal flexors, the spinal extensors are actually what would be the most important muscles working (eccentrically) to control the spinal flexion produced by gravity. In contrast, for the standing contraction shown in figure 4.22, concentric contraction of the spinal flexors would principally be used to posteriorly tilt the pelvis, flex the spine, and pull the abdominal wall inward.
Concept Demonstration 4.1
Creating a C Curve
Start lying supine with the knees bent to about 90 degrees and the feet resting on the floor.
- Emphasizing upper spinal flexion. While maintaining the back of the sacrum in contact with the floor, use your hands, which are positioned behind your thighs, to help pull the upper spine into flexion. Focus on pulling the bottom of the sternum and the bottom of the anterior rib cage down and back to further increase spinal flexion. Then, let go with the hands and focus on keeping the low ribs back and the same height of the upper torso (angle of spinal flexion).
- Emphasizing lower spinal flexion. Gently pull the pubic symphysis toward the lower rib cage, creating a small tuck (posterior pelvic tilt) and rounding the lumbar spine.
- Emphasizing the transverse abdominis. Slowly exhale and pull the abdominal wall inward and around toward the spine, decreasing the girth of the abdomen as a corset would.
- Putting it all together. Beginning from a supine position, pull the ribs and pubic bone toward each other and scoop the abdomen inward as the torso curls up.