Internal Obliques in Yoga - Anatomy of Muscles
We recently explored the rectus abdominis and the external obliques which are just two of your four abdominal muscles. Use of your internal obliques in yoga is similar to your external obliques with one major difference: the internal obliques cause your trunk to rotate to the same side (whereas the external obliques cause your trunk to rotate to the opposite side). Your internal obliques are just deep to your external obliques. That is, if you peel your external obliques away you will discover your internal obliques.
Origin = iliac crest (the top part of the pelvic bone), the inguinal ligament (a ligament in the groin area), and the fascia or connective tissue that covers the mid and low back.
Insertion = Ribs 9-12 and the linea alba (the tendinous tissue that runs down along the center of the abdomen).
You have internal obliques on either side of the abdomen and the action created by these muscles varies depending on whether one or both contract. When both internal obliques (the right and the left) work together, they work much like the rectus abdominis. That is, with a concentric contraction (See What Muscles Work in Yoga), they cause forward bending (trunk flexion), and/or a posterior pelvic tilt. As described with the rectus abdominis and external obliques, the action created will depend on which end of your body is free to move. If your pelvis is stabilized (which is generally true when you are standing), your ribs will move towards the pelvis and your spine will fold forward. If your ribs are stabilized (which is generally true when lying down with your feet lifted off the floor), your pelvis will move towards the ribs. This causes your pelvis to tilt backwards. This is the action that happens when you work on abdominal exercises that involve “tucking your tailbone” and lifting your pelvis off the mat.
Both your right and left internal oblique also work to stabilize your spine and to increase pressure on your abdominal cavity (where your digestive organs are) and the thoracic cavity (where your heart and lungs are). The increased pressure from your abdominal muscles provides tension to aid in digestion and respiration.
What about when only one set of your internal obliques contracts? Remember that the insertion moves towards the origin during a concentric contraction. When your internal obliques shorten, your ribs will move towards the pelvis. In the image above of the right internal obliques, notice the oblique lines created by the muscles. Muscles that run diagonally (or in an oblique direction) cause rotation when they contract and shorten. The internal obliques cause rotation to the same side. That is, when your left internal obliques contract concentrically, they cause your left ribs to move towards the left side of your pelvis and trunk rotation to the left. When you do an abdominal exercise and rotate towards the left leg, your left internal obliques contract to create rotation to the left.
Your internal obliques are also responsible for sidebending. With a concentric contraction of just your left internal obliques, your left ribs (where the insertion of the internal obliques is) moves towards the left side of your pelvis (where the origin is) to cause a left side bend in your body.
What about eccentric contractions of the internal obliques? Stand up and take yourself into a left sidebend. In order to initiate that movement, you concentrically activate your left internal obliques. However, your right internal obliques lengthen out. In order for you to control yourself into the left sidebend (without letting gravity sweep you to the floor), your right internal obliques contract eccentrically. Once you are holding your sidebend, both the left and right internal obliques work isometrically to hold the sidebend. As you release back up to neutral, your right internal obliques contract concentrically. Even though you only go to neutral, you have to go towards right sidebending to get out of left sidebending (or back to neutral).
In review, when both internal obliques contract together they create a forward fold and increase the pressure in the abdomen and thorax. When one contracts alone (i.e. only the right internal obliques), it creates rotation to the same side (i.e. right internal obliques rotate the body to the right) and side bend to the same side (i.e. right internal obliques sidebend to the right side).
In order to stretch a muscle you must lengthen it in a passive manner (different from an eccentric contraction). The best way to stretch your obliques is with a supported sidebend. Take a comfortable seat and place your left hand on the mat beside you and lean over to the left,. You will stretch your right internal and external obliques. Because your trunk is supported with your left hand, your muscles do not need to work eccentrically to control the movement into the sidebend, and can therefore stretch passively. Lean heavily into your left hand, feel that awesome stretch through your right side body. Yes, that is your obliques. Stay there and breath. Repeat on the other side. The more you relax, the more you may feel your obliques being stretched.
As mentioned, the description of the external obliques and internal obliques are quite similar with the major differences being the origins and insertions and their function in rotation. In actuality, your external obliques and internal obliques usually work in synchronization to create the actions of forward bend, posterior pelvic tilts ("tucking the tailbone") and rotation of the trunk. It is nearly impossible to move your trunk without involving both your internal and external obliques as well as the rectus abdominis. The trunk is a large part of your body and therefore the ability to use multiple muscles to move and support it is of great benefit. Consider the many ways you might use your external and internal obliques in yoga practice. Similarly, when you move throughout the day or throughout your practice, think of the many ways you ask your spine to move. Aren't you glad you have several muscles to help you do that?
Trish Corley is a Baptiste certified yoga teacher and a licensed doctor of physical therapy.
Trish leads several Baptiste inspired and anatomy related workshops and yoga teacher trainings.