Core Stability and Rib Stacking: Common Questions relating to the Core

By: Dr. Brooke Munion

Most people have heard it’s important to strengthen up the core-but why?  When asked that most people aren’t entirely sure,  its just something they’ve heard and know they need to work on.  Having a strong core is not just aesthetics!  Having a strong core is essential for everyday life.  It helps us maintain optimal posture when lifting, so that we can lift more with ease/ less stress on our body.  Less stress = less chance for injury/ strain. 

What muscles make up the core?

Hint: it’s not just the abdominals! 

The core is comprised of 4 major muscles that form a “cylinder”: diaphragm, multifidi, transverse abdominus, and pelvic floor.  The cylinder is “pressurized” and that pressure in the cylinder is referred to as “intra-abdominal pressure”.  The best way to explain the core muscles is to think of it as a soda can.  There is a top/bottom and a side. 

Core muscles and can analogy of a stable cylinder. 

What’s the deal with rib stacking?

Ribs are an important part to ensuring the core is in an optimal position to use!  Stacking the ribs mean that the ribs are directly on top and in line with the pelvis or anterior superior iliac spine (ASIS)- otherwise known as hip bones.  They need to be “stacked” to ensure that the core is in an optimal position for maintaining intra-abdominal pressure.  When they are “flared” open, there is already a weakness in maintaining a strong core when lifting and there is biomechanical compensation in the lumbar spine. When there is flaring in the ribs the chest comes up to expand on inspiration. This means that the traps are mainly used to bring air in and diaphragm is secondary when it should be reversed.  On inspiration the diaphragm should contract and air should enter “into the belly” instead of shallow breathing into just the chest.

  Depicts A) Optimal Positioning/ Activation and B) Shows Rib        Flaring

What happens when you breathe?

Biomechanically, when you take a breath of air in the chest expands outward and the diaphragm contracts down.  This creates the start of intra-abdominal pressure.  When breathing out, the chest contracts, and diaphragm relaxes by going up.  You can feel this when you breathe in (belly goes up), and exhale (belly relaxes or goes in).

What happens when the ribs aren’t in optimal position?

When the ribs are in the correct position and stacked- the core is like a soda can that is un-popped. It can withstand a lot of force without crushing or breaking.  However, when there is a weakness in the can or the pressure is released- cracking the can, it is not able to sustain similar forces.  This is why it is important and useful for everyone to understand-especially labourers, moms, and weightlifters.  If there is a weakness in the core, there is a greater chance of injury and biomechanical compensation elsewhere.  On the opposite end of the spectrum, if there is too much intra-abdominal pressure, we can get leakages (urine) through the pelvic floor, bulging of organs (hernia), or disc bulges from compensation.

What is the pelvic floor?

Its role is to stabilize the pelvis and spine and to support abdominal organs, including maintaining continence of flatulence, faeces, and urine.  The pelvic floor is comprised of 3 muscle layers: urogenital triangle, urogenital diaphragm, and pelvic diaphragm (which is often torn during childbirth).  The main muscles in those layers are The main muscles consist of: levator ani, pubococcygeus, puborectalis and iliococcygeus.  This group has 2 paired groups of muscles.  The other muscle is the coccygeus and there is only 1 muscle.

How does the pelvic floor work with the diaphragm?

The diaphragm and pelvic floor work as a piston. They are dependent on each other. The pressure that we manage in our intra-abdominal cavity will go to the area of weakest support. the front abdominal wall commonly begins to lengthen and without proper counterpressure, that can lead to increased stress to the tissues surrounding our linea alba where our abs attach. If this is left unchecked, this can lead to a diastasis recti (DR), hernias, pelvic floor dysfunction, low back pain, and hip instability.