External Obliques in Yoga - Anatomy of Muscles
There are four different abdominal muscles (rectus abdominis, external obliques, internal obliques, and the transverse abdominis). While each plays a vital role in stabilizing your core with yoga poses and life's activities, each one functions to move the body differently. The external obliques share many of the same functions as the rectus abdominis.
The external obliques also play a key role in rotating and sibebending the trunk. Whether you are using your abdominal muscles to twist deeply into parivrtta parsvakonasana (revolving lunge), working on abdominal strengthening exercises with a twist, or moving into or out of a sidebend pose, you engage your external obliques in yoga.
The origin of the external obliques is on the sides of the 4th to 12th ribs. (See image below). Have you ever done an intense ab workout and felt sore on the outside of your rib cage? Perhaps you were using your external obliques (along with the other abdominal muscles). The external obliques insert onto the iliac crest (the top of the pelvis bone) and the linea alba (the tendinous tissue that runs down along the center of the abdomen). There are external obliques on either side of the abdomen and the action created by these muscles varies depending on whether one or both contract. When both external obliques (the right and the left) contract simultaneously, 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 ("tailbone descends"). As described with the rectus abdominis, the action created will depend on which end of the body is free to move. If the pelvis is stabilized, the ribs will move towards the pelvis and the spine will fold forward. If the ribs are stabilized, the pelvis will move towards the ribs. This causes a posterior pelvic tilt which is often what is referred to as a lengthened or "tucked" tailbone.
Both the right and left external oblique also work to stabilize the spine and to increase pressure on the abdominal cavity (where your digestive organs are) and the thoracic cavity (where heart and lungs are). The increased pressure from the abdominals provides tension to aid in digestion and respiration.
What about when only one of the external obliques contracts? Remember that the insertion moves towards the origin during a concentric contraction. Look at the alignment of the muscles fibers in the image of the Right External Obliques. Notice the slanted lines created by the muscles. Because the muscles are slanted (or run in an oblique line), they cause rotation when they contract. The rotation occurs to the opposite side of the muscles. That is, when the right external obliques contract, they cause the trunk to rotate to the left. When you do a twisting abdominal exercise and rotate towards the left leg, the right external obliques contract to create that rotation.
The external obliques do all that is described above and still one more action. They are also responsible for sidebeding. With a concentric contraction of just the left external obliques, the left side of the pelvis (where the insertion of the external obliques is) moves towards the left ribs to cause a left side bend in the body. However, in many cases you are standing or sitting and your pelvis is fixed to the floor (or to your leg that is fixed to the floor). Only the free end can move. In this case, it is the ribs that move. So what you see happen is the left ribs move towards the left pelvis. What about eccentric contractions of the external obliques? Stand up and take yourself into a left sidebend. In order to initiate this movement, you concentrically activate your left external obliques. However, the right external obliques lengthen out. In order for you to control yourself into the left sidebend (without letting gravity sweep you to the floor), your right external obliques contracted eccentrically. Once you are holding your sidebend,both the left and right external obliques work isometrically to hold the sidebend.
As you release back up to neutral, the right external obliques contract concentrically. Even though you only go to neutral, you have to go towards right sidebending to get out of left sidebending.
In conclusion, your external obliques are busy muscles. When both contract together they create a forward fold and increase the pressure in the abdomen and thorax. When one side contracts alone (i.e. only the right external obliques), it creates rotation to the opposite side (i.e. right external obliques rotate the body to the left) and side bend to the same side (i.e. right external obliques sibebend to the right side). Now get on your mat and explore how you use your external obliques in yoga!
--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.