PILATES KINESIOLOGY
Anterior lateral abdominal wall
Content
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Anatomy review
Exercise analysis Side over box Single leg stretch Spine twist Spinal stability Discussion: The abdominal muscles and spinal stabilization Self study questions
Image two, external oblique showing the inferior-and-medial fiber direction
The internal oblique is located deep to the external oblique muscle, forming the second layer of the lateral abdominals. (See Image 3) Fibers originate from the iliac crest and blend with the adjacent thoracolumbar fascia. From this lateral attachment point, the fibers course in a cranial-and-medial direction toward the linea alba and lower ribs. The inferior attachments of the internal oblique muscle extend to the inguinal ligament. The average fiber direction of the internal oblique muscle is nearly perpendicular to the average fiber direction of the overlying external oblique muscle
Image 3, the internal oblique fibers, as they course in a cranial-and-medial direction toward the linea alba and lower ribs.
Image 5, the abdominal muscles fuse at the midline of the abdomen through a blending of connective tissues
Flexion
Actions of the Abdominal Muscles
Bilateral action of the rectus abdominis and oblique abdominal muscles reduces the distance between the xiphoid process and the pubic symphysis. (see image 6) An example would be a standard sagittal plane sit-up. The opposing axial rotation and lateral flexion tendencies of the oblique abdominal muscles are neutralized by opposing right and left muscles.
Image 6, flexion muscles reduces the distance between the xiphoid process and the pubic symphysis
Lateral flexion Contracting unilaterally, the abdominal muscles laterally flex the trunk. The external and internal obliques are particularly effective in this action owing to their relatively favorable leverage (large moment arms) and cross sectional area 3. Lateral flexion of the trunk often involves activation of both trunk flexor and extensor muscles. For example, lateral flexion against resistance to the left in an exercise like “side lift over box” (see image below) requires a contraction from the left external and internal oblique, left erector spinae, and left transversospinal muscles.
Rotation The external and internal oblique muscles are the primary axial rotators of the trunk. 4 They are assisted by the ipsilateral (on the same side) latissimus dorsi, the more oblique components of the ipsilateral iliocostalis lumborum, and the contralateral (on the opposite side) transversospinal muscles. These synergists also neutralize the trunk flexion potential of the oblique abdominal muscles. Unopposed, the oblique muscles could create an undesirable flexion bias to the base of the spine. (This is important to look out for when teaching rotation and side flexion exercises) The external oblique muscle is a contralateral rotator, and the internal oblique muscle is an ipsilateral rotator. During active axial rotation in one direction, the external oblique muscle on one side functions synergistically with the internal oblique on the other side. (See image 7) This functional synergy produces a diagonal line of force that crosses the midline through the muscles’ mutual attachment into the linea alba. Contraction of the two muscles therefore reduces the distance between one shoulder and the contralateral iliac crest.
In Brief The external and internal obliques are the prime movers in side lifting and lowering the trunk. If the concentric action is toward the left, synergists include left erector spinae, quadratus lumborum and left transversospinal muscles. Coactivation of both trunk flexor and extensor muscles stabilizes the trunk within the coronal plane, preventing any flexion tendency created by the oblique abdominal muscles. The gluteus medius, minimus, tensor fascia Lata and possibly rectus femoris all assist in rotating the pelvis laterally during “side over box.�
References 1 McGill SM, Patt N, Norman RW: Measurement of the trunk musculature of active males using CT scan radiography: implications for force and moment generating capacity about the L4/L5 joint, J Biomech 21:329-341, 1988. 2 Kumar, S: Moment arms of spinal musculature determined from CT scans, Clin Biomech (Bristol, Avon) 3:137-144, 1988.
Spine twist
The Spine Twist involves axial rotation of the trunk in the transverse plane. (See image 1) The internal and external oblique muscles are the most effective axial rotators (prime movers) of the trunk because of their relatively large cross-sectional area and favorable leverage. The external oblique muscle is a contralateral rotator, (rotates to the opposite side), and the internal oblique muscle is an ipsilateral rotator (rotates to the same side.) When twisting to the right in the example below, the external oblique muscle on the left side function synergistically with the internal oblique on the right side. This functional synergy produces a diagonal line of force. Contraction of the two muscles therefore reduces the distance between one shoulder and the contralateral(opposite) iliac crest.
Image one, the external oblique muscle on the left side function synergistically with the internal oblique on the right side. This functional synergy produces a diagonal line of force.
Cylindrical support including the diaphragm and pelvic floor For the most effective stabilization, the cylinder-like abdominal cavity must also be simultaneously compressed from both its cranial and caudal ends. This is normally accomplished by concurrent activation and descent of the diaphragm muscle—the roof of the abdominal cavity—and activation and ascent of the pelvic floor muscles— the ultimate floor of the abdominal cavity. Although sparse, evidence does exist from both animal and human subjects that these muscular interactions do indeed occur in a coordinated manner, with a resulting increased stiffness in the lumbar spine. 9 (see image 5)
Image 5
Chronic low back pain Hodges and colleagues used a similar experimental protocol to study the sequential muscle activation in persons with chronic low back pain. 10 Remarkably, this research showed a consistent, short delay in the onset of EMG signals from the transversus abdominis—the activation of this muscle occurring most often after the activation of the prime movers of the rapid limb motion. Whether a short delay in abdominal muscle activation can create sufficient reactive stress in the lumbopelvic region to ultimately cause low-back pain is not known, although it is an intriguing question. Cadaveric studies have indeed shown that axial rotation of as little as 2 to 3 degrees per intervertebral lumbar junction can potentially injure the apophyseal and interbody joints. Although a single “unprotected” stress event may not be significant, multiple events that accumulate over many years may predispose the region to injury.
Self-study questions Please note, the answers to these questions are provided in the previous material. If you are stuck, re-read your material! You can also go to the Pilates Kinesiology website and take the online quiz, where the correct answers are provided. www.pilateskinesiology.com Finally, you are encouraged join the Facebook group and discuss any queries with the group. https://www.facebook.com/pilatesanatomy/
Side over on box
In the Side over on box, the _______________________________________muscles contract unilaterally and concentrically to lift and laterally flex the trunk, in the coronal plane. The combined cross-sectional area of the _______________________________________ muscles at the level of the L4-L5 junction is almost twice that of the rectus abdominis muscle. Coactivation of synergists amplifies the total coronal torque while simultaneously stabilizing the trunk within the sagittal plane. Synergists for lateral flexion include ______________________________________________________ __________________________________________________________________________________________ The following muscles below the iliac crest ______________________________________________________ _________________________________________________________________________________________ __________________________________ assist in rotating the pelvis laterally. Contracting unilaterally, the _________________________________ has very favourable leverage as a lateral flexor of the lumbar region