The Inner Core
The inner core is made up of four muscle groups: pelvic floor on the bottom, transversus abdominus on the front, thoracic diaphragm on top, and the multifidi on the back. When these groups of muscles fire together they pull the pelvis and spine tightly together and help to prevent the skeleton from sliding out of neutral alignment. I think of this inner core as the center or core of a tree. The more strongly you contract or fire your inner core, the more solid you will keep your core trunk.
Author inside huge tree washed up on coastline in Washington State
Firing the inner core while the body is holding still is a good place to start. Lying down with your hands on your belly while you fire the pelvic floor muscle group you should be able to feel the stomach flatten. If you cannot feel this, bring your fingertips out more to the side but staying on the front of the stomach muscles. Angle your fingertips to 45 degrees and push down into your stomach while firing the pelvic floor muscle group. You may be able to feel this muscle tighten or flatten under your fingertips. This muscle you are feeling is the transversus abdominis. You may recall I likened this muscle to the saran wrap around the boxes on top of the pallet at the warehouse stores. The pelvic floor is the screws and the bones of the pelvis are the wood to the pallet. By firing the pelvic floor the pelvis now becomes a solid unit. The coolest thing I have found is that the deepest stomach muscle, transversus abdominis, typically kicks in automatically when contracting the pelvic floor muscle group. So these work together as a unit.
The thoracic diaphragm
The thoracic diaphragm is the large dome-shaped muscle that sits underneath the lungs and on top of the abdominal cavity. This muscle assists in breathing. There are other diaphragms in the body that are flat structures, but when I refer to the diaphragm, I am talking about the thoracic diaphragm in the trunk. The diaphragm pulls down and flattens creating a larger volume of space causing pressure like a vacuum in the lungs which causes air to rush into the lungs. When the diaphragm relaxes it moves back up and the air leaves the lungs. The most important thing you can do when firing the inner core is to breathe. The most common thing patients hear me say when they are learning strengthening exercises is BREATHE! This will engage the diaphragm.
When contracting a muscle it is common to hold your breath. I find people often hold their breath or cut off their air supply and bear down causing increased pressure in the abdomen. This is called a Valsalva's maneuver which is done while forcing a bowel movement or during childbirth. This increases the pressure in the abdomen and that pressure can cause you to push outward making a hernia possible. A hernia is an organ pushing through a weak muscle or tissue that typically holds it in place. The most common place to find a hernia is the abdomen. When you are holding your breath and lifting something, with a weak muscle the organs of the abdomen can push through weak muscles. I have found it common to see a bulging through the lower belly when someone who is quite weak is trying to get out of bed. It is also possible to bear down so hard with such force while having a bowel movement that you can herniate or rupture a disc between the bones of the spine. So the most important thing you can do to prevent a hernia is to breathe and hold your inner core while exercising. When getting in and out of bed, remember to fire the inner core and breathe.
The multifidi are tiny muscles in the back along the side of the spine. They span 3-4 bones of the spine and are critical is assisting in spinal stabilization. These muscles also kick in automatically when firing the pelvic floor muscle group. Yipee! So all you have to do to fire the inner core is to contract the pelvic floor muscle group and breathe.
As I said above, practicing firing the inner core lying on your back is really the best. Just lie on the bed, you do not have to get on the floor. With your knees bent and feet on the bed take a deep breath in and while letting the breath out fire the inner core, or hold the pelvic floor muscles as if holding back urine or gas. When all of the breath is out relax the inner core and repeat. Do this four times. Repeat this twice a day every day for a week. Next practice firing the inner core and then keep breathing in and out while holding the inner core for 10-15 seconds. Make sure not to stop the air from coming in and out.
Once you are confident in breathing while holding the inner core you are ready to progress. Now fire the inner core while lying down or sitting and raise one arm overhead while breathing. Then practice it while raising both arms overhead. For the next progression, it is best to lie on your back on the bed. Put your fingers at the front of the front of the pelvis feeling the bones off to each side close to the top of a pocket. This bone is kind of pointy and easy to find if you are slender. This point on the bone is known as the anterior, inferior iliac spine or ASIS. If you are not slender then it is more difficult to find but you can rest your hand on the side of the abdomen still staying on the front but off to the side toward the hip. Keep knees bent and fire the inner core. You can feel the abdomen tighten as you do this.
Next, bring one foot off the bed raising the knee toward the chest slowly. While you do this feel the pelvis on the opposite side from the leg you lifted. You should feel the bone not moving while holding the inner core. If you are not sure, practice not holding the inner core and raise the leg. The pelvis is like a bowl and when you push down on one side the other side raises up. So you can typically feel the pelvic bone or the abdomen raise on the side opposite of the leg that is raising. Then fire the inner core and raise the leg again. This time you should feel no movement under the opposite hand. Practice this until you can raise the foot off the bed with no motion in the pelvis. Some people are so weak in the inner core they can only lift the heel off the bed before they feel the motion in the opposite hand. This indicates that the weight of the leg is too much for the inner core to stabilize against.
Holding the body still and moving the arms and legs is a great place to practice becoming an expert at firing the inner core. When you feel like you are understanding this and getting better at it try doing it in sitting. Hold your inner core and raise one leg while feeling the pelvis under the opposite hand. Ideally, there will be no motion of the pelvis. I like to have a patient put their hand on my back and spread their fingers about 1″ apart so they can feel the bones of my lower back. Then I demonstrate raising both arms, one leg at a time, and bending forward both while not firing and again while firing the inner core. This allows them to feel motion during the movements without the inner core compared to a solid position of the spine during firing the inner core. Again, firing the inner core I simply squeeze the pelvic floor muscles and breathe.
The most difficult progression is to move the body while holding the pelvic floor. It is the most important thing I think you can do to prevent pain. Firing the inner core while changing positions with the body will help maintain neutral alignment of the pelvis and spine. The nice benefit of doing this exercise is improving or preventing incontinence.
I cannot recall a patient over the past 20 years who returned to see me as their physical therapist because their pain had returned who was remembering to hold their inner core. Every patient I have seen have a regression they had forgotten about holding the inner core. They moved wrong and their skeletal alignment slid out of place and eventually, their pain returned.
I tell patients to learn about the inner core, even if they learn nothing else from me. My pelvic floor is so strong it keeps me in neutral alignment even when I forget to fire it while changing positions. I beg of you, please learn to fire the inner core, but don’t forget to avoid overuse.