Core Muscle Function
By Fitness Atlantic Writer: Brian Cannone

In understanding the anatomy of the core we looked at the different muscles that are involved with the core. Now we can begin to talk about their function and exercises to target these areas. The determining factor of how a muscle will work is it's attachment to either bone or soft tissue, and the alignment of the fibers. Muscles work to bring bones together; to resist/control bones moving away from each other, and to stabilize or neutralize the movement of bones will other muscles work. With this concept in mind, we will examine the muscles involved during some "core exercises".

The rectus abdominus is one muscle and not divided into upper and lower abdominals. It has no direct attachment to the femur (thigh bone) and therefore does not directly control hip motion. The primary function of the rectus is to flex the trunk. This action occurs in the simple crunch where the shoulders barely raise off the ground. The chest moves towards the pelvis.

Since the rectus does not connect to the thigh bone, moving the legs has no direct effect on the abdominals! When the legs are moving (as in a leg raise), the rectus only contracts to stabilize the pelvis and is not being targeted directly. Leg movements primary action is on the hip flexors. Abdominal activity is felt due to the the rectus stabilizing function as well as the fact that one of the hip flexors (psoas) begins on a vertebrae of the back, goes through the abdomen to insert on the femur.

To target the rectus, hip motion should be eliminated. A better way to perform exercises such as leg lifts or hanging ab exercises, is to begin with the legs bent so that the hip forms a 90 degree angle. The starting position should mimic sitting in a chair. Now, the movement focus is to bring the pelvis up towards the chest. This movement will be need to be more controlled, and you will notice a smaller range of motion.

Extreme back hyper-extension is not necessary when targeting the back muscles. Often, exercisers will use a weighted hyper-extension machine, or a roman chair (pads on thighs, face down, lean over and lift upper body) in an attempt to strengthen the back extensors.

Great care must be taken when performing any exercise with back hyperextension. Better control and muscle targeting can be attained with focused movements that only take the trunk back to neutral. Using the roman chair means that the trunk would be bent towards the ground and then only raised until the spine is straight again.

It is best to not do this with additional weights as the potential for injury greatly increases. Usually, as the resistance increases dramatically, there is a tendency to use assisting muscles of the arms, and hip. Resistance may be added by maintaining the arms overhead (biceps on ears) throughout the movement. Supermans are also great for back extensors. This is done by laying face down on the ground and then raising the quads and upper body off the ground. Hyperextension will be very limited by the ground.

Twist and extend motions greatly involve the obliques. The internal and external obliques work in opposites. The internal obliques rotate and bend the trunk to the same side while the external obliques have similar actions but on the opposite side. Bending or twisting the trunk to the right involves the right internal obliques and the left external obliques.

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Again it is important to remember that the abs do not have any connection to the femur, so ab action should focus challenging the muscle based on its intended action. We will be discussing twisting motions and their effect on performance at a later time.

Lastly, we turn our attention to the transverse abdominus. This muscle is activated when one thinks about drawing the bellybutton towards the spine. Forceful exertion, as occurs when one is having difficulty using the restroom, also activates the TVA. The TVA creates a lot of the stability in exercises such as the plank.

Failure to activate the TVA during heavy lifting can result in injury so it is important to ensure that the TVA is engaged during weight lifting. Popular weight lifting belts perform the function if the TVA by creating increased internal pressure and increasing spinal stability. It is not the thick back part of the belt that causes the stability.

The abdominal muscles and organs push against the front of the belt and when resistance meets them they get shoved towards the back. The thick back part provides resistance and the result of these opposing forces creates the spine stability. Although there is debate amongst fitness professionals, it has been stated that a properly engaged TVA provides enough stability to ensure most strength training can be safely done without the use of a weight belt.

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