Article

How well do you know your internal obliques?

If you’re a Pilates instructor, you know that the core muscles are the foundation of healthy movement. You know that the “core” can be thought of as a canister around the center of the body.

by Kristine @mat.pilates

The diaphragm forms the lid, the pelvic floor forms the base.  The transverse abdominis stabilizes the muscles that flex the spine, and the multifidus is a deep spinal muscle important for stabilizing the joints between each of your vertebrae.  Together, these four muscles (diaphragm, pelvic floor, transverse abdominis, multifidus) are generally thought of as the foundation for core stability.  But what about the rest of the muscles in your midsection? To understand how the core functions, we really have to think of the core as a complex – a network of layers that synergistically stabilize our lumbopelvic region.

Going over all these muscles would, of course, be a little overwhelming to cover in one shot, so I’ll begin the discussion with the core muscle I realized I knew the least about: the internal obliques.  Often overshadowed by their more attractive sibling (the external obliques) your internal obliques deserve their moment in the spotlight, too! Here are the top ten things you should know about the internal obliques:

1. Where they are: Your internal obliques are the middle layer of abdominals located on each side of the abdominal cavity.  They sit directly on top of the transverse abdominals and underneath the external obliques.

2. How the muscle fibers run: To visualize their location, place all four fingers on the bottom 4 ribs towards your midline.  Let the fingers fan out as you trace a diagonal line down to the top of the hips (iliac crest).  The anterior fibers (closest to your pointer fingers) attach centrally to connective tissue called the rectus sheath.  The posterior fibers (closest to your pinky fingers) blend with more connective tissue called the thoracolumbar fascia.

3. They make an “X” pattern with the external obliques: The average internal oblique fiber runs almost perpendicular to the average fiber of the overlying external oblique muscle fiber1.

4. When both sides contract together: The obliques stabilize the core by increasing tension on the thoracolumbar fascia and assist in trunk flexion.

5. When a single side contracts: The internal obliques flex the trunk laterally on the same side and rotate the trunk on the same (ipsilateral) side.

6. They are the primary axial rotators of the trunk: Without contraction of the latissimus dorsi, transversospinal muscles, and multifidi to offset the trunk flexion potential of the internal obliques, the trunk would lean forward every time you twist your ribs(1).

7. Motor control: Strutton and colleagues provide evidence that the simulation of the left motor cortex resulted in greater muscle activation for both sides of the obliques(2).  In other words, the left side of the brain may have greater control over the internal obliques and could be a consideration for individuals who are rehabilitating from stroke or other brain lesion.

8. Stabilizing function:  In healthy subjects without reported back pain, the internal obliques and the transverse abdominis (TvA) activate before the deltoid or hip flexors during respective arm or leg raises(3).  This means that the internal obliques (and TvA) fire first during arm and leg movements.

9. Low back pain management: Abdominal muscle recruitment patterns differ for individuals who have nonspecific, chronic low back pain.  Study subjects who trained their abdominals with leg raises and an “abdominal scoop” exercise improved their internal oblique (and TvA) activity after 10-weeks of practice(4).

10. During Pilates exercises: A recent study by Pereira and colleagues measured trunk muscle activity during three Pilates exercises in beginners(5).  The internal obliques were 78% active during a dead bug exercise, 90% active during single leg stretch, and 101% active during criss-cross (a 100% activation means a muscle is turned on to its maximum contraction).  Since a muscle activation even as low as 35-45% can create strength gains in muscles, these three Pilates exercises are very effective for training the internal obliques.

References
1. Neumann (2017). ISBN: 978-0-323-28753-1
2. Strutton et al. (2004). DOI: 10.1007/s00221-004-1939-5
3. Urqurhart et al. (2005). DOI: 10.1007/s00586-004-0799-9
4. O’Sullivan et al. (1998). DOI: 10.2519/jospt.1998.27.2.114
5. Pereira et al. (2017). DOI: 10.1016/j.jmpt.2017.02.010