The core is made up of every muscle except for those related to the extremities (arms and legs). Some will even argue that the muscles attaching the extremities to the torso are also included as core muscles. One way to classify the muscles of the core are in the terms of outer and inner core muscles. Another classification is anterior, posterior, and rotational muscles.
Out of the many functions of the core, respiration is the most important. The diaphragm is the main muscle of respiration. Contraction of the diaphragm increases the volume of the thoracic cavity drawing air into the lungs. When the diaphragm is impaired it can compromise breathing patterns. The diaphragm activates the inner core and stabilizes the spine to allow the outer core to activate properly, thus allowing postural stability and control to allow prime movers to support movement generation in the proper sequence without a loss in energy transfer.
Many like to train the core as a prime mover in crunching and twisting motions, however, the core must also be able to resist flexion, extension, and rotation of the spine. In my opinion this is the second most important function of the core; to protect the vertebrae of the spine. Functional movements such as deadlifts and squats work the posterior core by resisting flexion of the spine while the anterior core is better trained with push-ups and plank variations by resisting extension of the spine.
Many athletes develop a strong posterior core but neglect to train the anterior core. A weak anterior core can result in back pain and can give lead to developing an anterior pelvic tilt which can bring on further complications. Plank variations are a great starting point for someone looking to develop the anterior core.
Start with a simple plank on the elbows. Brace the core and tuck the hips under by squeezing the glutes and quads forcefully, mimicking a hollow position. You should be able to hold this position for a minimum of 40 seconds. The next progression would be a plank on an unstable surface such as a stability ball. This can be progressed even further with extension of the arms, placing the ball closer to the wrist rather than the elbows or by lowering the angle to the floor with a smaller stability ball. Barbell rollouts or an ab wheel would be the next step with TRX band or ring fallouts being an even further progression. Remember stay braced and don’t let the spine extend.
The core must also be able to resist rotation before properly being able to produce it. A good place to start is with anti-rotation exercises.
Pallof Press (kneeling or standing) – Hold a cable or band at the bottom of the sternum and rib cage (mid-section) with the origin of the band/cable perpendicular to your body (to the side). Chest tall, stomach (abs) tight, shoulders back. Slowly control the band/cable away from your body out front, staying in line with your mid-section until your elbows are almost locked out. Pause and return to start slowly.
Single arm bench press and different variations of the single arm row.
Single leg deadlifts Once stabilization is established within the body, the use of rotational exercises can be applied in the training program. The thoracic spine and hips should be the area from which the greatest amount of rotation should occur with limited rotation in the lumbar spine. Rotational training of the core is mainly performed as chopping, flexion with rotation (overhead to ground across the body), and lifting, extension with rotation (ground to overhead across the body or rotational push press).
When the core doesn’t function properly, secondary systems take over to compensate for failed primary function. These secondary systems create artificial stability and take up the slack as a safety mechanism. The more elite the athlete is the more chance of success they will have with the secondary systems. That being said, these athletes would be even more elite with proper use of the primary systems and less prone to injury. As goes the same for any athlete or person in everyday movement, not just in a sport or gym setting.