More on the Core

Hopefully we're all on the same page now, with a good understanding of the relationship between core strength and core stability. I assume everyone now knows that core stability refers to the stability of the spine, NOT to the stability of the muscles themselves. And remember that core stability is attained through the strength and endurance of the muscles of the core. In other words, core strength allows for core stability.

"What? What are you talking about, 'stabilizing my spine?' I thought core exercises were meant to give me a good 6-pack."

Good question: why do we need to have a stable core, a.k.a., stable spine? Having the strength to stabilize your spine is vital because on its own, the spine is inherently unstable. As a complex of vertebrae and intervertebral discs, the spine would buckle under compression loads of as little as 2 kg. So you can see that a strong and stable core is vital for more reasons than having a good 6-pack.

Okay, so we've moved beyond the infomercials' emphasis on the aesthetics of the core. I can only assume that means you want to know more about the "real" core, right? Here is a basic overview:

The core musculature can be generally defined as the 29 pairs of muscles that support the lumbo-pelvic-hip complex in order to stabilize the spine, pelvis, and kinetic chain during functional movements. A stable core can be considered the foundation of all limb movements.

The Inter-related Subsystems of the Core

The core can be thought of as 3 inter-related subsystems: passive, active, and neural. (We will not address the neural system today, as more research is needed to determine how to best train neural involvement.)

The Passive Subsystem

The "passive" core is made up of the vertebrae, intervertebral discs, joints, and ligaments, all structures which have no ability to act.

The Active Subsystem

The "active" core includes the muscles and tendons surrounding and acting upon the spinal column. The active core can be divided into "local" muscles and "global" muscles. Let's look a little deeper here, as local vs. global will come into play in program design (which means in your training!).

Active "Local" Muscles
The local muscles (primarily the transverse abdominus and multifidi) activate approximately 100ms prior to limb movement to stabilize the spine for that movement. The local core muscles do not create movement, although they likely contribute secondarily to the movement of the spine.

Active "Global" Muscles
Global core musculature, on the other hand, produce movement and torque in (and secondarily stabilize) the core. Global muscles include the rectus abdominus (muscles of the 6-pack), lateral fibers of external obliques, psoas major, and erector spinae.

Implications for Training

Now that we understand the subsystems of the core, we can talk training. Functional progression is the most important aspect of the core strengthening program. Progression of training of core musculature works from the inside out. You may have guessed that that means from the local to the global system.

Core training generally optimizes function of the local system before emphasizing movements that utilize the global system. Specifically, trainers might begin with local system exercises that involve little to no motion through the spine and pelvis, low resistances, and slow movements.
Examples: prone bridge, side bridge, side bridge abduction

Because most isolation (local) exercises are in nonfunctional positions, exercise training must shift to more functional positions and activities, which is, of course, the global system. These exercises emphasize movement of the spine, and involve more dynamic eccentric and concentric movement of the spine through a full range of motion. These will be done with rapid movement and higher resistance.
Examples: T rotation, twist on ball, cable wood chop

In addition to all this strength talk, there is growing evidence in the research to support that endurance may be the more important training variable when it comes to the core musculature. You should expect your trainer to include longer, less demanding exercises to target core endurance.

Feeling a lot more motivated about doing the plank now? Good, me too!

Faries, M.D., and M. Greenwood. Core Training: Stabilizing the Confusion. Strength and Conditioning Journal. 29:10-22. 2007.