The four main abdominal muscle groups that combine to completely cover the internal organs include:
• transversus abdominis – the deepest muscle layer. Its main roles are to stabilise the trunk and maintain internal abdominal pressure
• rectus abdominis – slung between the ribs and the pubic bone at the front of the pelvis. When contracting, this muscle has the characteristic bumps or bulges that are commonly called ‘the six pack’. The main function of the rectus abdominis is to move the body between the ribcage and the pelvis
• external oblique muscles – these are on each side of the rectus abdominis. The external oblique muscles allow the trunk to twist, but to the opposite side of whichever external oblique is contracting. For example, the right external oblique contracts to turn the body to the left
•internal oblique muscles – these flank the rectus abdominis and are located just inside the hipbones. They operate in the opposite way to the external oblique muscles. For example, twisting the trunk to the left requires the left side internal oblique and the right side external oblique to contract together.
Transversus abdominis is the deepest of the abdominal muscles and wraps around the abdomen between the lower ribs and top of the pelvis, functioning like a corset.
When transversus abdominis contracts the waist narrows slightly and the lower abdomen flattens.
The function of the transversus abdominis is to stabilize the low back and pelvis BEFORE movement of the arms and/or legs occurs. This function is critical if wear and tear of the joints in your low back/pelvis (degeneration) is to be prevented.
Mind control with deep breathe will create a strong deep contraction of transversus abdomens contraction.
Note: Top of transverses abdominis there are there more layers, Internal oblique muscles, external oblique muscles then rectus abdominis.