The main functions of the abdominal musculature are to permit movement through the trunk, transfer power from the upper to lower extremities (and vice versa) and lastly to protect the spine and nervous structures in the trunk (spinal cord and peripheral nerves).
The movements produced by the abdominal musculature are bending forward (flexion), leaning backwards (extension), bending to the side (side bending/lateral flexion), twisting (rotation) and combinations of all these movements. But they also resist gravitational forces imposed on the body that result in no movement such as keeping you upright when you're standing on the bus for example.
When we talk about the abdominal musculature we refer to the area from the lower ribs -both front and back - to those muscles that attach to the top of the pelvis -both front and back.
Rectus abdominis - this muscle is located on the front of your body and is responsible for the much-desired "6 pack" appearance. It's not justf or aesthetics though and is the main muscle responsible for trunk flexion or forward bending. It is the most superficial (outer most) layer of the absominal wall and extends from the 5th, 6th, 7th ribs and the bottom of the sternum downward to the public symphysis, a strong joint at the front of the pelvis. Another important structure for the rectus abdominis is the Linea alba, this is a strip of strong connective tissue called fascia that divides the left and right rectus abdominis fibres - it is this tissue among others that becomes slack during pregnancy to allow the abdominal cavity to increase in size.
External & internal oblique – these muscles are located more laterally to the rectus abdominis and are mainly responsible for rotation. They run in a diagonal fashion and work with one another during movement; hypothetically during right rotation the right internal oblique and left external oblique contract together to achieve the movement - the opposite is true during left rotation. They are imperative for transmitting force in sports such as golf, tennis and hockey and as such, any programme designed at enhancing performance in rotation sports must have an emphasis on these muscles/movements.
Transversus Abdominis - this muscle is described as being the muscular corset that braces the trunk and exists as its deepest layer. It spans the entire abdominal wall and starts and finishes on each side at the lumbar spine, the back of the pelvis and the inguinal ligament. It has received a lot of attention over the last 5 years and although it is essential for the muscle to be conditioned it is important to remember that it is still just one component of the abdominal wall. Some authors have hypothesized that there is a strong connection between weak TVA and back pain but as the research progresses it becomes evident that pain in itself is a much more multisystem experience than we may have previously thought and thus, blaming one muscle in one body system (musculoskeletal system in this case) is naïve. But that does not mean it is not worth isolating and nor does it mean it might not be the source of your pain! However, it is just one element so make sure you spend equal time elsewhere in your exercise programme.
Multifidus - here is an incredibly important muscle for a multitude of movements that centre around stabilising your in rotatory and extension movements. It has fibres in the lumbar, thoracic and cervical spine and each fibre spans 2-4 spinal segments to aid fluidity of movement. Whereas the previous muscles we spoke about provide movement and bracing forces, the multifidus' main function is to steady the ship so to speak, to keep the spine in a manner that displaces pressure equally among its segments. It is also a very important player in the gait cycle and along with glute medius is responsible for ensuring the hips don't "drop" when you're supporting your bodies weight on one leg.
Quadratus Lumborum - is muscle is often forgotten but provides a strong connection from your lowest rib to your lumbar vertebra and pelvis. The movements it can produce are bending to the side (lateral flexion) and it also works with the obliques to reinforce rotation. Keeping this muscle healthy is very important to ensure that the intervertebral discs in your lumbar spine distribute weight evenly. If the QL is tight on one side in a sport that is bilateral, meaning you use each side of your body as much as the other (running etc), it can cause all manner of problems in the hip joint, sacro-iliac joint and further down, as well as reduce the expandable nature of the ribcage.
Key Points
- The abdominal wall has various components, neglect them at your peril!
- Rectus abdominis; flexes the trunk and provides 6 pack appearance.
- Obliques; rotates the trunk and is essential in rotatory sports.
- TVA: braces the abdominal wall and is a key player in supporting the lumbar spine in heavy lifting.
- Multifidus; not limited to the trunk however stabilizes the lumbar spine especially.
- Quadratus lumborum; situated on the back of the abdominal wall and works with the oblques to reinforce rotation and side bending.