Rectus Abdominis in Yoga: Anatomy of Muscles
Understanding the location and function of the rectus abdominis in yoga postures will allow you to better understand your own body. As you better understand your body, you can go deeper with your own yoga practice (and teaching).
You have undoubtedly identified the location of your abdominal muscles while practicing yoga or participating in other fitness programs. The abdominals are the muscles that cover the front of your belly. These muscles allow you to hold your spine stable in poses such as navasana (boat pose). And yet they do so much more too! There are actually 4 different abdominal muscles (rectus abdominis, external obliques, internal obliques, and the transverse abdominis). While each plays a vital role in stabilizing your core with all yoga poses and life's activities, each one functions to move the body differently.
The first of the four abdominal muscles is the rectus abdominis. This muscle originates at the pubic bone. It inserts on the cartilage of the middle ribs. (As the ribs come around the front of the body, they become cartilage (connective tissue that is relatively flexible)). When the rectus abdominis undergoes an active shortening of the muscle or a concentric contraction (see What Muscles Work in Yoga), the pubic symphysis (origin) moves towards the ribs (insertion). This may lead to rounding of the spine which is known as flexion. Flexion of the spine is commonly associated with forward folds. A shortening contraction of the rectus abdominis in yoga, also causes the front of the pelvis to be pulled up towards the ribs. This causes the entire pelvis to tilt backwards. In other words, the tailbone tucks down. The best way to feel this is with a type of abdominal exercise common in yoga. Lie down on the floor with thighs perpendicular to mat and hands clasped behind back. Tuck your tailbone, lifts your hips off the floor, and send knees or feet up to the to sky. This will require activation of the rectus abdominis and will allow the pubic bone to move closer to the ribs and the pelvis to rotate backwards/tailbone to tuck. Another very common abdominal exercise in the fitness world is a basic sit up. Lie on your back with feet on the floor and bring your chest up off of the floor to come to a seated position. In this case, the origin (ribs) moves towards the insertion (pubic symphysis). Why does the origin move towards the insertion rather than following the rule (see What Muscles Work in Yoga) of insertion towards origin? In the case of a sit up, the feet and pelvis remain stationary on the floor and therefore, only the top of the body moves. In this case, the ribs are free to move towards the stationary pelvis. In both exercises described, a concentric contraction occurs.
Do we ever use the rectus abdominis eccentrically? Of course! In fact we do every time each of the two exercises described above is performed. After lifting your pelvis off of the floor and your feet/knees up to the sky, you must lower your pelvis back down. In order to do this safely and with control, the rectus abdominis peforms an eccentric contraction to lower the pelvis down against gravity. The muscle is lengthening out, but it is still active. Similarly, after performing a sit up, you must lower your chest back down to the floor to either rest or perform another sit up. When lowering yourself to the floor, the rectus abdominis must contract eccentrically to control the speed at which you lower down to the floor.
What type of contraction of the rectus abdominis occurs in Navasana (boat pose)? Since you are maintaining the pose without moving (or at least trying to keep those legs lifted, spine long, and chest up), an isometric contraction occurs. Neither a shortening or lengthening of the muscle occur. The rectus abdominis is stationary and therefore isometric.
What types of poses allow the rectus abdominis to stretch? Essentially any backbends that bring the pubic bone away from the ribs will allow the abdominals to stretch. In reality, it is not very common for the abdominals to be so tight that they require a lot of stretching. Additionally, limitations in range of motion of other joints and decreased flexibility of other muscles often limit the expression of a pose before the rectus abominis reaches full length. For example, in Urdhva Dhanurasana (full wheel), the rectus abdominis is stretched, but limitations in the shoulders and spine probably occur before the full length of the rectus abdominis may be felt.
It is always a good idea (and feels so good!!) to stretch the rectus abdominis after doing abdominal exercises. A simple stretch willl work. Lie down on your back, reach your arms overhead and legs out long, take a big inhale into your belly and let that awesome stretch in your abs wake you up!
As mentioned above, the rectus abdominis helps stabilize the spine. It is considered one of the "core" muscles. Developing strong abdominals helps create an internal corset which is the best thing to protect the spine from injury. The rectus abdominis (along with the other three abdominal muscles) also plays a key role in maintaining pressure on the abdominal cavity (where your digestive organs are) and the thoracic cavity (where heart and lungs are). The increased pressure from the abdominal muscles provides tension to aid in digestion and respiration.
You may be wondering what those white lines (tendinous intersections and linea alba) are. The rectus abdominis is a long muscle with very little bony attachment. Therefore, it requires attachment to something else in order for it to be able to create forces large enough to lift your chest or pelvis off the mat. These white lines are made of tendinous tissue which is a strong connective tissue. The intersections that run horizontally are actually what cause the appearance of a "six pack" when someone is lean and has a well developed rectus abdominis. The line that runs vertically down the center is the linea alba. In Latin, linea alba means "white line". This line also contributes to the appearance of a "six pack".
The rectus abdominis has several important roles in the health of your body. There are many exercises to strengthen your rectus abdominis in yoga and other activities. Next time your yoga teacher says "it is time for abs" smile and thank yourself. Your body will thank you for years to come!
Trish Corley is a Baptiste certified yoga teacher and a licensed doctor of physical therapy.