There are four abdominal muscles—Rectus Abdominis, transverse abdominis, internal oblique, external oblique. These four muscles, which are paired in the body, are all connected through a network of tendon and fascia as you can see in the image above. The tendons of the transverse abdominis muscles and the oblique muscles wrap around the rectus abdominis.
The rectus abdominis, the muscle we use to do sit ups or crunches tends to dominate all of the other abdominal muscles. It is a surface muscle that often has more resting tone than the other abdominal muscles and as results it frequently tries to do the work for those muscles even if it is not their job.
Nothing in the body works in isolation—muscles work in chains, and it is rarely one muscle that accomplishes any task. Each muscle in the body has a specific function but they are not limited to that function. Any time the body needs to do something the brain and nervous system go into action and recruit muscles to accomplish a task. The problem is that very often a stronger muscle gets recruited to compensate for a weaker muscle and correct function flies out the window.
Creating a healthy and balanced body does not happen by osmosis. Building a body that works as designed is a science project that requires a very conscious approach to building muscles.
When it comes to the abdominals the transverse abdominis is the muscle to focus on first. Of the four abdominal muscles it is the one that provides the most support to the lumbar spine. The transverse abdominis doesn’t actually attach to the spine but its connection into the thoracolumbar fascia is the closest the abdominals get to the spine. When it comes to back pain this is the first muscle to focus on, followed at a close second by the pelvic floor.
When working with clients I try to help them isolate muscles that I want them to build. My standard way to introduce people to the transverse abdominis is an exercise called Feet Three Inches off the Floor (creative,no?). If you are lying on your back with the knees bent and the feet to the floor, and then lift the feet up off the floor (one at a time) you will feel abdominal muscles engage to support the weight of the legs lifting off the floor.
Nine out of ten times I ask someone to do this exercise the rectus abdominis acts first as the belly pushes up and often the spine goes with it. The function of the rectus abdominis is to draw the ribs towards the pelvis and the pelvis towards the ribs depending on what part of the body is mobile and what part of the body is fixed. But if you think about the fact that in this exercise the trunk is flat on the floor and the act of lifting the feet should not change the position of the ribs and pelvis. There is no need for the rectus to engage in this exercise yet for so many people it is doing the most work.
Doing Feet Three Inches off the floor until it is easy and the trunk is solid is a great way to begin the science project of building a functional body.