The core is the collective term used to describe the muscles that control your spine, specifically your abdominals, waist and lower back. Many exercisers spend workout time focusing on their core muscles in the hope of developing a six-pack midsection. In addition to being aesthetically pleasing, a well-developed core also provides essential spinal stability and can contribute to good posture. Both spine stability and good posture will help minimize back pain.
The rectus abdominus, abs for short, is the most well-known of the core muscles. Running from the bottom of your sternum and ribs down to the front of your pelvis, your abs are responsible for flexing your spine forward and also to the side. The abs are also involved in forceful exhalation, which is achieved by compressing your abdominal cavity to drive air out of your lungs. Your abs are bisected by fibrous tissue called the linea alba -- literally white line. These linea alba give the abs their distinctive six-pack appearance that is visible on very lean people.
You have three sets of oblique muscles: internal, transverse and external. Arranged in diagonal layers, these muscles are located on the side of your torso and cover parts of your lower back and ribs. They are responsible for rotating your spine, for flexing it laterally and also for forceful exhalation by compressing your abdominal cavity. Exercises that target these muscles include twisting crunches, cable Russian twists and side planks.
The erector spinae is the collective term used to describe the eight muscles that run up either side of your spine from the base of your sacrum to the base of your skull. When both sides of the erector spinae contract together, they pull your spine back into extension or maintain an upright position. When one side contracts and the other side relaxes, they bend your spine sideways into lateral flexion. Many cases of back pain are due to weakness and subsequent injury of the lower erector spinae muscles that cross and control the lumbar vertebrae. These muscles often become weakened as a result of prolonged sitting.
The transverse abdominus, TVA for short, is a thin, wide muscle that runs horizontally around your abdominal cavity. The main role of the TVA is to create intra-abdominal pressure. When your TVA contracts, it compresses your abdominal organs and increases pressure within your abdominal cavity. This pressure helps to support your spine from within. Performing this action voluntarily during exercise is commonly called bracing. Pilates places a great emphasis on bracing and increasing the strength of your TVA. To brace your TVA, contract your midsection as though you were protecting yourself from a blow to the stomach, pull up your pelvic floor muscles and then inhale. You should feel your midsection become more solid and stable.
The quadratus lumborum is a deep muscle that runs from your bottom ribs and first to fifth lumbar vertebrae to the top of your pelvis. When the left and right quadratus lumborum muscles, QL for short, contract simultaneously, they work with your erector spinae to extend or stabilize your lower spine. Singularly, the QL helps to laterally flex your spine. Tightness in your QL can result in a side-to-side deviation in your spine, which is commonly called scoliosis. Bending sideways while keeping your hips level will stretch this small but important core muscle.