Rectus Abdominis –friend or foe?
Rectus abdominis has got a lot of bad publicity lately.
Training of this particular muscle has been ridiculed and regarded as out-dated and part of a non-functional body-building culture. I say that training Rectus Abdominis is as important as any other muscles.
“Modern abdominal training”
New training theories for the abdominals have emerged in the last couple of years consisting of exercises resisting deviations of the trunk like Planks, Stirring the Pot, Ab-Wheels and different versions of Cable Pulls. These exercises are great, but are not necessarily training the abdominals better than anything else. Despite the fact that these new generation of abdominal/core exercises only work the surrounding layers of the core, they have been promoted as the new generation of core stabilization exercises.
Core activation has to be developed from the inside out and is dependent upon proper activation of the diaphragm. The abdominal wall supplies resistance against the diaphragm’s activity and thereby increases the Intra-Abdominal Pressure (IAP). Tensing the abdominal wall without filling the Core-Center inside the abdominal cavity is only training the abdominal wall - not the function of the core. To get better effect out of all these new-core/abdominal exercises we have push the diaphragm down, thereby increasing the IAP, and learn to maintain normal breathing while we do so (diaphragm’s dual function). The empty space inside the tensed abdominal wall has to pressurized. Too much or too early activation of the abdominal wall will actually decrease the core stabilization since the diaphragm cannot contract properly. Synchronized function of the diaphragm and the entire abdominal wall has to be achieved to develop ideal trunk stabilization.
Bracing and tensing the abdominal wall is good for improving muscle activity but only as component training. Core training can be divided into core-function (where all components are being trained together) or the components can be strengthened separately through their functional action. The diaphragm can and should be trained separately and so should all other components of the abdominal wall. Resisting deviation of the trunk in both rotation and lateral flexion will strengthen the involved core-components and so will specific training of rectus abdominis. Ideally we train the abdominals (both the Obliques and Rectus) with an active core (diaphragm activity) to develop a good function of the core simultaneously. A six-pack is not going to decrease the strength of the core but the Rectus Abdominis is only one of the muscles involved in the abdominal wall.
Function of Rectus Abdominis
I have seen some new descriptions of the function of Rectus Abdominis where it is said not to be a trunk flexor but to resist extension of the trunk. All muscles have got these dual functions of creating movement in one direction and also restricting the opposite action by isometric or eccentric contractions. For example the elbow flexors are also involved in resisting elbow extension. This enables a delicate balance of muscle work making it possible for us to perform fine motor skills. We can move the hand to the mouth without knocking ourselves out. Rectus is trunk flexor which also participates in lateral flexion and rotation of the trunk.
As far as I can tell the rectus Abdominis is still a trunk flexor and the reason it has got its peculiar structure of beaded muscle bellies separated by ligamentous tissue is because of its other important function of compressing the abdominal content into the cavity. Even during flexion of the trunk the abdominal muscles are able to compress the abdominal content. This is an important feature in assisting us to maintain IAP even when we are moving the trunk.
Posture and Rectus Abdominis
Another argument that has been raised for not training the rectus abdominis is that it causes bad posture. Most individuals spend too much time in a slouched sitting position, and since rectus is a trunk flexor it is said to pull the body more forward.
In all my years working as a Chiropractor I have seen a lot of slouched (hyper-kyphotic) backs, but I have never seen one caused by too much strength in the abdominal wall. A strong rectus abdominis will create a bigger resistance in the abdominal wall and thereby increase the intra-abdominal pressure when we sit. The intra-abdominal pressure induces an extension straightening moment in the lumbar spine which actually reduces the Thoraco/lumbar kyphosis. Weak abdominal muscles result in increased curves of both the lumbar and thoracic spine. The claim that the rectus will pull the ribcage downwards and thereby cause the slouching is not true. A stiff elevated position of the chest is dysfunctional and prevents the diaphragm from proper activation. The ideal position of chest for proper core activation is with the lower ribs in lower (caudal) position without any thoracic spine flexion.
One of the first things I often have to do when I treat people to restore their normal diaphragm function is to improve the flexibility of the ribcage (chest-wall). There is often a movement restriction in the rotation between the lower ribs and their thoracic vertebrae. The lower ribcage should be able to move independent of the thoracic spine in ideal circumstances. Ribcages that cannot be moved without thoracic spine involvement are dysfunctional and need to be worked on. The joints between ribs and the vertebrae have to be mobilized and the individuals given exercises to improve the downwards movement of the ribcage.
Training the rectus abdominis is not the complete answer to core stabilization but it is not detrimental to the core or the posture either. Strengthening all components of the abdominal wall as well as the diaphragm and the pelvic floor will have beneficial effects on core stability.
The key strategy in core stabilization is to synchronize the activity of all the core components.