Composition, Function & Approach to Core Training

By Leo Shveyd, Co-Owner of Advanced Wellness (with consultation from Brett Jones)

During the two-and-half decades that I have been involved in fitness, the definition of “the core” and consequently, core training has evolved. Part of the evolution is subjective (meaning I have learned more about the topic) and part is objective (as a profession there is more and better information about the subject area). With so many great minds in the rehab and fitness arena contributing daily in the information age, a good deal of terrific data exists about the “the core”. In this article, I will attempt to define what makes-up the core, its functions and suggest an approach to core training.

Core Composition

My introduction to the core occurred in fourth grade during the Presidential Physical Fitness Test (PPFT). If memory serves me correctly, the test consisted of dead-hang body weight pull-ups, push-ups, a one-mile run for time, a bent knee sit-up test (with a partner holding your feet) for maximum repetitions in 60 seconds, etc. According to my fourth grade Physical Education teacher, the PPFT’s sit-up portion tested the “abs” and this was my first introduction to a definition of the “core”. With little guidance about the quality of the movement, and quantity being king, the goal was to do as many repetitions as possible with no regard for how each one was performed. What I didn’t comprehend at the time was that each one of the activities in the PPFT tested the core. Soon thereafter, the fitness industry professed that sit-ups were bad (but nobody ever explained why). Sit-ups were then substituted by crunches as core training supposedly evolved to a safer, more effective way to strengthen your core! One of my friends, who was a high level collegiate athlete, would literally do hundreds of crunches per day. If you saw this guy without his shirt, you would notice his “six pack” and assume he has a strong core, right? Not so fast my friend…this highly conditioned individual had such severe back pain that he had to give up his sport as he was preparing to tryout for the US Olympic team. So what gives? How could someone who looks like Hercules, and have a “core” that appears as though it is made of steel, have back pain?

To answer this question, one must understand the composition of the core and its interplays with the entire body. The core consists of many parts and layers, initiating at the muscles that surround and protect the spine. Kyle Kiesel, citing Bergmark (4), hypothesized the presence of two muscle systems responsible for maintaining stability of the spine. “The global or superficial musc[ular] system” (outer core) consists of large torque producing muscles that act on the spine without directly attaching to it. These muscles provide general trunk stabilization without the capacity to control intersegmental motion. The “local or deep muscle system” (inner core) is made up of muscles that directly attach to the lumbar vertebra and are responsible for providing segmental stability and control. In addition, I believe the core is also comprised of the stabilizer muscles of every joint of the extremities when under load. Categorizing muscles as stabilizers is tricky because the same muscle can be either a “stabilizer” or a “mover” depending on whether a joint is under load in a particular movement pattern. In my opinion, the sum of these parts (spine [inner and outer level]; plus the stabilizers of the hip, shoulder, elbow, ankle, wrist and out to the extremities when under load), collectively comprise the core. Below are the muscles of the core, broken down by segments of the body or the respective joints.

Muscles of the Inner Core of the Spine

  1. Spinal extensors (multifidus) muscles
  2. Deep neck flexors (longus capitas, longus colli)
  3. Abdominal wall (transverse abdominis)
  4. Diaphram
  5. Pelvic floor

Muscles of the Outer Core of the Spine

  1. External Olique
  2. Rectus abdominis
  3. Erector Spinae
  4. Lattissimus Dorsi

Joint Stabilizers

  1. Hip Stabilizers
  2. Shoulder Stabilizers
  3. Knee Stabilizers
  4. Elbow Stabilizers
  5. Ankle Stabilizers
  6. Wrist Stabilizers

These parts that comprise the core are the foundation of posture, efficient movement and athletic performance. As the definition of core has evolved, so too has our understanding of its function and how to improve it.

Core Function

The functions of the core are respiration (breathing), continence, postural control, joint/segment stabilization, movement generation and energy transfer (Keisel). In order to efficiently perform the most basic movements, in addition to high-level athletic fetes, an individual must have a functioning inner core. The inner core must be in balance with the exterior muscles of the outer core of the spine. Moreover, the stabilizer muscles of any joint located on an extremity must counter-balance mover muscles (i.e. vastus medialis (knee stabilizer and rectus femoris [prime mover]) of a given joint under load. This enables the core to be both mobile and stable in the appropriate segments through the entire system. In Mike Boyle’s book, Advances in Functional Training and Gray Cook’s book Movement ( both authors lay out a concept that originated from a conversation between the two: the joint-by-joint approach. In short, the joint-by-joint approach states that joints have a primary function, either mobility or stability, with each alternating joint trading function. For example, the ankle joint is a mobile joint, the knee stable, the hip mobile, the lumbar stable, the thoracic mobile, the cervical stable. While the joints each have a primary responsibility (mobility or stability), should that joint be unable to function optimally, the joint above or below provides added support. Take the thoracic spine, a mobile joint, as an example. When it become stiff, the body will provide mobility in the joint above (cervicals), below (lumbars) or both. This is one of the magical aspects of the human system. It is a survival mechanism, a short-term secondary solution, so-to-speak. These adjustments are a way to keep your body functioning until it has a chance to reboot, up regulating the primary system (mobility in thoracic spine), while down regulating the secondary system (excess mobility in the cervical and lumbar spine). Your core works much in the same way. When dysfunction occurs at different levels of the core, the body recruits nearby partners, whether joints, ligaments, tendons or muscles that weren’t primarily designed for segmental stabilization in order to assist with fortifying a particular region. This stability is artificial and a mere safety mechanism. For instance, when a person is incapable of diaphragmatic breathing, the inner core is not optimally activated. As a counter measure, the body will rely on the larger exterior muscles such as the hamstrings, for example, to stabilize the core. While it is true the hamstrings have some postural responsibility, their primary role is hip extension and knee flexion. When asked to stabilize the core in addition to their primary role, they often fatigue and become prone to injuries. Said another way, asking the hamstring to play both roles is like asking a point guard to handle the ball and play center at the same time. It is not impossible to do, but hard for the average Joe’s hamstring to thrive in that role. If my memory serves me correct, only the great Magic Johnson was able to do so successfully (play Center in the 1980 NBA Playoffs when Kareem Abdul-Jabbar got hurt). But I digress. Interestingly enough, most elite level athletes have unparalleled compensation pattern abilities. Many have the ability to use their secondary systems and do so successfully.

Breathing is the first thing we do when we enter this world. It goes without saying that breath is a perquisite to life…and also the foundation of core function and performance. Without proper breathing patterns, your inner core cannot optimally activate and sequence. By sequence, I mean the inner core of the trunk and the stabilizers must turn on before the outer core and prime movers, specifically with a precise level of activation. This centers your joints, providing postural support and stability at each engaged joint. In turn, the muscular system becomes the primary system of support for movement. When sequencing is inefficient, ligaments, tendons and joint structures must act as stabilizers and bear the brunt of segmental force transfer through the body. Therefore, proper breathing is the prerequisite that sequentially and efficiently activates the inner core of the spine. Therefore, proper breathing is the first function of the core! Once this is properly activated, the job of the inner core is to stabilize and allow for segmented movement of the spine. Along with the inner core, the main responsibility of the outer core of the spine is to prevent flexion, extension and rotation according to Dr. Stuart McGill. Essentially, your trunk is made to stabilize, allowing you to transfer force from your limbs bottom-up or top down. This is the core’s secondary function. In sum, the function of the core is first, respiration and second, controlling movement. For example, when you watch a high level sprinter at top speed, you will see very little movement at the belly-button region, while her limbs propel her forward. Moreover, her joints are stable in the frontal (side-to-side) and rotational plane (i.e. little rotational movement at the knee). This principle applies to much of athletics, and life in general. Therefore, training the core must focus on activation of the respiration mechanism and preventing flexion, extension and rotation of the spine!

Approach to Training the Core

Reflexive Core (Stability) Activation Feed-forward Core Development

A. Reflexive Core (Stability) Activation Approach

Reflexive Core Stability is the precursor to optimal core strength and power development. Reflexive core training is also known as motor control (stability), and core strength and power core is also known as “feed-forward”. Understanding whether or not a reflexive core stability deficiency exists is the first step. Using the Functional Movement Screen (FMS) or the Selective Functional Movement Assessment (SFMA) to examine whether or not a client has reflexive core instability is one effective approach. If so, the client must address this fault in the appropriate developmental position, with joints centered (neutral), while maintaining diaphragmatic breathing, while using appropriate stimulus to activate the inner core, before considering any feed-forward core training.

a. Developmental Positions

One of Gray Cook’s strongest attributes is his ability to take very complex ideas, simplify them and articulate them to many others. Cook’s simplification of the human neuro-developmental process is one example. While there are many levels and stages of development, Cook narrowed the process to four main positions: supine (face-up), prone (face-down), kneeling and standing. Within those four positions, there are variations. For example, kneeling can be balanced on one or two knees. The key is to establish a strong level of reflexive core (stability) in each of the four main developmental positions, as well as transitional positions (i.e., rolling from supine to prone), prior to progressing to strength and power development. At a minimum, it is imperative that the client own reflexive core stability in the position you intend to train. In other words, training a loaded squat with a client that has inadequate reflexive core stability in a body-weight squat is, at best, counterproductive and, at worst, dangerous.

b. Joint Centration and Diaphragmatic Breathing

Once a developmental position has been determined and joint centrated position assumed, proper breathing is necessary in order to activate the spine’s inner core, which is imperative for proper reflexive core stability. This approach helps to maintain the centering and stabilization of all loaded joints and enables the execution of a movement pattern. Because breath is the foundation of the core (and many other things), it is important to determine whether or not a person can well….,breath. I know this sounds simple, but it never ceases to amaze me how difficult diaphragmatic breathing is for many. Individuals may be able to maintain diaphragmatic breathing in a lower developmental position (i.e. laying on their back), but not in a higher developmental position (i.e., standing) or vice-versa. Furthermore, breathing can also be disrupted by making an activity more challenging/strenuous (i.e. training a higher developmental position; or training a body weight squat versus a weighted squat). Therefore, training in a position where breath cannot be maintained is counter-productive! There are many techniques to assess breathing as well as many techniques to coach the reestablishment of proper breath. While that subject is worthy of much greater analysis, I will try to summarize it here. When we coach breathing (specifically with respect to reflexive core) training at Advanced Wellness, we first help the client achieve a joint neutral position. We then ask the client to imagine a deflated balloon inside their trunk, with their nose being the opening of the balloon. While drawing air in through their nose, we ask the client to direct (focus) their breath to their pelvic floor, the bottom of the balloon. Once the inhaled air hits the pelvic floor, we coach having the breath expand in all 360˚ as it travels up the sides of the balloon on its way back to the opening. With the balloon fully inflated, we ask the client to keep the balloon inflated (eccentrically contracted) while maintaining their breath. With every subsequent repetition, the goal is to expand the balloon a tiny bit more, yet do so in a relaxed fashion. Once breathing is proficient in that position, you have re-established the first function of the inner core: respiration in that developmental position.

In sum, reflexive core activation is done by assuming any developmental position with joints centered, while maintaining diaphragmatic breathing with or without an outside stimulus or a part of the body creating a perturbation. In addition to the video above, another example would be the half-kneeling hold, or the chop and lift.

Assuming that an adequate level of reflexive core function exists, feed-forward core training is appropriate. One way to delineate reflexive core training from feed-forward core is that reflexive core training focuses on the things you are not able to do, while core strength and power is about how much load, how many reps and sets (volume) one can handle. When the focus changes to feed-forward core training, the positions expand beyond the developmental positions (i.e. pull-ups). Furthermore, breathing strategies evolve beyond continuous diaphragmatic breathing, to whatever strategy in effective for the activity (see valsalva maneuver, a different for of diaphragmatic breathing). Resistance and intensity also increases. Moreover, I believe good quality movement based feed-forward core training will, in most cases, continue to support good activation of the inner core. However, the reverse is not necessarily true: good reflexive core training will only enhance feed-forward core strength and power output in those that lack inner core activation. In short, the approach is activate the inner core and then, develop core feed-forward core strength and/or power as appropriate.

It should be noted that excessive or inappropriate feed-forward core training can disrupt the balance between the inner and outer core, causing the central nervous system to rely on the bigger muscles of the outer core. This is one example of what is known in the FMS community as “putting fitness on top of dysfunction”. It is theorized that this can lead to undue compressive forces on the spine, over-use injuries and should obviously be avoided.

c. Reflexive Core Training Example

Here is an example of how you train your core reflexively in the supine position: start by laying on your back with feet elevated, knees bent to 90˚ and externally rotated (turned-out); hands above the shoulders with palms-up to the ceiling and elbows off the ground. Rotate your bottom two ribs (right underneath your chest) down towards feet and floor, gently externally rotate the shoulders, while pulling the elbows away from your body; finally, try to press your chin to the back of your neck, flattening your spine. Once in the supine developmental position, see if you can maintain diaphragmatic breathing as described previously in this article. If not, practice this. Once you have this down, begin by adding single limb body movements. Extending one leg away from the body, one arm above your head, mixing ipsilateral and/or contralateral limb simultaneous flexion or extension, or synchronizing leg flexing with arm extending. This must be done while you maintain the original starting (neutral position) and diaphragmatic breathing. This is one example of reflexive core training in the supine position.

Once motor control proficiency is established in this activity, adding resistance, by way of a weighted stability ball, for instance, is appropriate for feed-forward core strength and power development.

B. Feed-forward Core Development Approach and Example Exercise

C. Attacking Core Training: Where to Start?

Here is the step-by-step approach to core training:

  1. Determine if a reflexive core deficiency exist?
    1. Use FMS or SFMA (or whatever tool you have to make that determination).
  1. If the reflexive core is not functioning properly, select the appropriate developmental position with centrated joints, use diaphragmatic breathing and add the appropriate stimulus to retrain the reflexive core.
  1. If the reflexive core properly activates, move on to feed-forward core training. Use positional variety including and extending beyond the four main developmental positions, while maintaining joint centration, appropriate breathing strategies, adding resistance, intensity and volume (as dictated by the training goal) to develop feed-forward core strength and power.
  1. As a maintenance/prehab measure, continue to recheck reflexive core function on a regular basis (see FMS & SFMA). At Advanced Wellness, we program corrective based reflexive core activation drills into pre-workout warm-up, mid-workout and post-workout-cool-down for every client; as well as rescreen our clients on monthly basis.

Core training is, in essences, part of everything we do, every position and every movement. So yes, core training includes doing sit-ups just like the PPFT in the 1980’s. Doing crunches like my friend used to do–to no end– is also core training. (I am speculating here, but I believe it is likely that he had to give up his athletic career due to back pain because his inner core never functioned properly after a high school knee injury). Therefore, making sure that your core is functioning and training in a way that promotes good core function (both reflexive and feed forward) is core training in 2012. It will be interesting to see how this subject evolves in the future.