"Core" Concepts, Part 1 - What is the Core, Really?

Core training is the bee's knees right now. A Google search of "core training" comes up with 604,000,000 hits (soon to be +1), countless lists of the top 10 exercises for core strength, and a mind-boggling number of uses of the word "shredded." Unfortunately, the ubiquity of internet users' desires for a strong and well-exercised core overshadows the presence of any good definition of what the "core" really is, any real clarity on what it means to have a strong one, and any good explanation of why we should care.

(By U.S. Navy photo by Photographer's Mate Airman Lamel J. Hinton. [Public domain], via Wikimedia Commons)

So what is the "core?" 
Of those 604 million Google hits, I'd be willing to bet that about half of them are using "core" synonymously with "abs," and that to many people a "strong core" means visible and well-defined (see: SHREDDED) rectus abdominis muscles with very little body fat. While there's nothing inherently wrong with having a visible 6-pack, and while the rectus abdominis muscles are indeed part of the core, they are only a small piece of the whole ensemble.

I propose we define the core as:

The system of muscles and connective tissues surrounding the spine, including both deep and superficial muscles, which directly contributes to the positioning and stability of the spine and aids in the positioning of the rib cage and the shoulder & hip joints, including the pelvis and the scapulae; and which allows for (and in some cases contributes to) the transfer of force (muscle force) from the limbs to some external point(s) of resistance (resistive force) which is not a point on the force-producing limb (particularly in a closed-chain movement). 

This definition of core has two tiers: anatomical and functional. The anatomical definition, which could be generally summed up as "the torso," is quite general and really only sets the stage for the more precise and function-based definition. Because we are talking about the core in the context of human movement and performance, we need the specificity of function.

The functional demands on the trunk in the context of basic movement, sport, optimal force production, etc. provide us with a pretty accurate view of what tissue groups make up the core. The core is aptly named in that it is at the "center," both anatomically and with regard to movement. The arms, legs, and head are all attached to and anchored in your torso--your core. Most all multi-joint movements, and particularly those which could be deemed "functional" movements, are produced through a limb that has proximal insertions in the torso. And unless you believe competitive typing or staring contests are sports, all sport movements are anchored in, and in some ways originate from, the core.

In order to get a clear view of what the core is in the context of function, let's look at a few examples of common movements and the demands on the core in each. For the sake of variety and thoroughness, the movements I have chosen span a wide range of intensities and complexities:

- Walking: Probably the most "basic" and common of all human movements is walking. It is a low-force, low-speed movement. While the prime movers in walking are muscles of the legs and butt, the limbs which generate the movement are attached at the hip joint, and many of these muscles have insertions (i.e., where the muscle attaches to bone) in the torso, and therefore require a stable base (the core). Generation of force at the distal end (away from the center) of a joint requires stability at the proximal end (close to the center) of the joint.

- Swinging a baseball bat: Swinging a baseball bat is a low-resistance, high-speed, rotational movement. Force is generated primarily by the legs and hips and contributed to by the arms, shoulders, and trunk. The back leg generates a strong force against the ground and weight is transferred forward; that force is then translated through the rotation of the hips and subsequent rotation of the trunk and shoulders; the shoulders and arms add additional accelerative forces which are then transmitted to the bat. Ultimately, the swinging of a baseball bat involves the generation of a large force against the ground and transmission of this force through the trunk. In the swinging of a baseball bat, the core is involved in force transmission, acceleration, and deceleration. The core is involved in force transmission in that the enormous forces generated against the ground and through the legs and hips require rigidity in the torso in order to transmit said forces to the shoulders; the core is involved in acceleration in that the muscles of the core (particularly the obliques) contribute to the rotational force that is transmitted to the shoulders; and the core is involved in deceleration in that it must slow down and stop the rotation of trunk in the follow-through.

- Blocking/Form-tackling: A standard block or form tackle is a high-speed, high-resistance, high-impact movement. Force from the legs and hips and momentum are transmitted through the torso to the shoulder or arms, and subsequently to the opposing player. When blocking or tackling, the primary point of contact between the blocking/tackling player and the other player is generally the shoulder or the forearms and hands, while the legs and hips are continually driving into and accelerating against the ground. The torso is the connection between the two points of resistance (the player being blocked/tackled and the ground), and therefore must exhibit great stability in order for the accelerative forces against the ground to be transmitted to the opposing player. This is the job of the core. The core is also required to resist rotation (as blocks/tackles are generally on one side or another, not straight on) and sometimes to generate rotational force. Football hits can involve in excess of 1500lbs of force (sources 1,2). Without a strong, rigid core, a player attempting to block or tackle would just fold in half.

- Bench pressing: The bench press (when performed with maximal or near-maximal loads) is a very high-resistance, lower speed, low-impact, and primarily upper-body movement. However, the core is still an absolutely essential element in performing the bench press. One of the prime movers in the bench press, the pectoralis major, is proximally attached at the rib cage and distally attached at the humerus of the upper arm. When the muscles contracts, it pulls on both the insertion at the rib cage and the insertion on the humerus. If the rib cage were not stabilized and rigid, the forces generated by the muscles would pull the rib cage towards the arm and would not allow transmission of nearly as much force through the arms. In the bench press, the core is responsible for stabilization of the proximal insertions to allow transmission of forces. In addition, the core is responsible for creating and maintaining optimal positioning of the back, chest, shoulders, and hips, and is necessary for creating leg drive and maintaining stability against the bench.

These examples should demonstrate that the core is more than just the rectus abdominus muscles. It is all of the muscles, front and back, surrounding your spine. Yes, your back is your core too (I'm looking at you, Six Pack Shortcuts). Do cut/chiselled/shredded abs look better than flab? Yes. Do they necessarily prevent you from destroying your spine when you help a friend push his stalled car? No. Strength is not always what you see in the mirror.

Why does it matter?
It should be pretty apparent by now why it's important to have a strong core; but, I'll offer a brief summary and explanation in case you're not tired of reading yet.

Think about trying to push someone off of a diving board. Not too hard if they're not expecting it, right? Now think about trying to push someone off of a diving board with a pool noodle. How's that going for you? The pool noodle is a weak, unstable core. You have plenty of strength to push your foe, but the limp pool noodle is sapping all of your force production and turning it into a floppy, bendy, comical dud. Now think about pushing someone off of a diving board with a concrete pylon. Much more effective. The concrete pylon is a strong, stable core. All of the force you generate is being transmitted through the pylon and too the unsuspecting victim.

The core has a unique job in that it is required to both produce stability as well as express mobility around the spine. The core’s job is very precise: it needs to allow mobility of the trunk and limbs around the spine (think about swinging a baseball bat), but it also must prevent excessive mobility (think wrestling or deceleration in a golf swing), and be able to create stability under extreme forces (think football tackle). Most back injuries (and joint injuries, for that matter) occur when joint stability is lost and when a joint is pushed beyond its active range of motion. A strong core is the main player in keeping your back/spine happy and healthy, and in allowing optimal force production and sports performance. 

(By U.S. Navy photo by Mr. Damon J. Moritz [Public domain], via Wikimedia Commons)

Willing to bet there are some strong cores in that mix.

Stay swole.

In the next post, I'll discuss some exercises you can do to optimally train your core. (Hint: it's probably not crunches 'til the cows come home)