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Core Stability: The Inner Unit

By: Paul Chek.
From: A new frontier in abdominal training: IAAF/NSA 4.99.
Site Link: Coachr.
Article Link: The Inner Unit.

ALSO SEE: Core Stability: The Outer Unit.

A new frontier in abdominal training


Paul Chek is an expert in the fields of corrective exercise and high performance conditioning and is the founder of the C.H.E.K Institute in San Diego, California. For over fifteen years he has traveled around the world lecturing, consulting and giving seminars. Paul Chek has been a consultant to the Los Angeles Chiropractic College, the Chicago Bulls, the Denver Nuggets, the US Army Boxing team, Australia's Canberra Raiders and the US Air Force Academy. 


The author states that abdominal exercises can be performed in various ways and asks if the exercises commonly practiced really improve the functionality of the abdominal muscles. From his own studies with patients and clients who performed a high volume of abdominal routines, he concludes that the usual theories of explanation and treatment for back pain are wrong. He recommends the concept of "The Inner Unit", which is a term describing the functional synergy between specific abdominal muscle groups. He describes ideas for Inner Unit conditioning and concludes that Inner Unit training provides the essential joint stiffness and stability needed to give the large prime movers of the body a working foundation.

How many ways can you do an abdominal exercise? Well, if you have been reading the muscle tabloids for the past 20 years you could probably come up with well over 100. Today we have classes devoted to nothing but TRASHING people's abdominal muscles, complete with every variation of crunch, jack knife, side bend and leg raise exercise known to man. Are these classes, or these exercises, really improving the way you look or function, or reducing your chances of back pain?

To find the answers to these questions, in 1992 I began investigating the correlation between abdominal exercises performed, exercise volume and the postural alignment, pain complaints and overall appearance of my clients. To ensure objective observations of postural alignment and responses to specific exercises, I designed and patented calibrated instruments to measure structural misalignment.
In the first year of recording such information as forward head posture, rib cage posture, pelvic tilt and overall postural alignment, it became evident that those performing high volume sit-up/crunch exercise programmes were not showing promising results (see Figure 1)! Those attending "Ab Blast" classes and/or performing high repetition/high volume abdominal routines were not only having a harder time recovering from back pain, they were also showing little or no improvement in their postural alignment.

While studying patients and clients who performed high volume abdominal routines, it became very evident that there was a common link. About 98% of those with back pain had weak lower abdominal and transversus abdominis muscles, while those with no history of back pain were frequently able to activate the transversus abdominis and scored better on lower abdominal strength and coordination tests. To alleviate back pain, I frequently had to suggest that clients stay completely away from any form of sit-up or crunch type exercises. When this advice was adhered to, and exercises for the lower abdominal and transversus abdominis were practiced regularly, back pain either decreased or was completely alleviated and posture routinely improved.

One can always find some "experts" in the health and fitness industries who state that "there is no such thing as lower abdominal muscles," while others suggest that the best treatment for back pain is to exercise on machines that isolate the lower back muscles. My clinical observations lead me to believe both theories are wrong.

In 1987, "Clinical Anatomy of the Lumbar Spine" by Nikolai Bogduk and Lance Twomey was published. This book is important because it was Bogduk who made the first clinical observations of how the abdominal and back muscles worked together as a functional unit. This occurs via the connection of the transversus abdominis and internal oblique muscles to the envelope of connective tissue (thoraco-Iumbar fascia) surrounding the back muscles (Figure 2).

A few years ago, Australian researchers Richardson, Jull, Hodges and Hides began making significant headway in understanding how the deep abdominal wall worked in concert with other muscles, creating what they would later call THE INNER UNIT.

The Inner Unit

The Inner Unit became accepted as a term describing the functional synergy between the transversus abdominis and posterior fibers of the obliquus intern us abdominis, pelvic floor muscles, multifidus and lumbar portions of the longisssimus and iliocostalis, as well as the diaphragm (Figure 3). Research showed that the inner unit was under separate neurological control from the other muscles of the core. This explained why exercises targeting muscles such as the rectus abdominis, obliquus extern us abdominis and psoas, (the same muscles exercised in traditional abdominal conditioning programmes common all over the world) were very ineffective at stabilising the spine and reducing chronic back pain.

Exercising the big muscles (prime movers) was not providing the correct strengthening for such essential small muscles as the multifidus, transversus abdominis and pelvic floor muscles. When working properly, these muscles provide the necessary increases in joint stiffness and stability to the spine, pelvis and rib cage to provide a stable platform for the big muscles. In a sense, as the big muscles (outer unit) become stronger and tighter, the delicate balance between the inner and outer units becomes disrupted. This concept is easier to understand using the pirate ship model (Figure 4).

The mast of the pirate ship is made of vertebra which are held together (stiffened) by the small guy wires running from vertebra to vertebra. just like the role of the multifidus (a member of the inner unit) in the human spinal column.

Although the big guy wires (representing the outer unit) are essential to hold up the mast of the pirate ship (our spine), they could never perform this function effectively if the small segmental stabilizers (inner unit) were to fail. By viewing the pirate ship's large guy wires, it becomes easy to see how developing too much tension from the overuse of exercises such as the crunch, could disrupt the posture of the mast, or spinal column in the case of a human.

To better apply the concept of the pirate ship, let's examine how the inner and outer units work in a common situation such as picking dumbbells up from the floor in the gym (Figure 5). Almost in synchrony with the thought, "Pick up the weights from the floor," the brain activates the inner unit, contracting the multifidus and drawing in the transversus abdominis. This tightens the thoraco-Iumbar fascia in a weight belt-like fashion (Figure 2). Just as this is happening, there is simultaneous activation of the diaphragm above and the pelvic floor below. The effect is to encapsulate the internal organs as they are compressed by the transversus abdominis. This process creates both stiffness of the trunk and stabilises the joints of the pelvis, spine and rib cage, allowing effective force transfer from the leg musculature, trunk and large prime movers of the back and arms to the dumbbells.

When the inner unit is functioning correctly, joint injury is infrequent, even under extreme loads such as pushing a car, tackling an opponent in football or lifting large weights in the gym. When it is not functioning correctly, activation of the large prime movers will be no different than a large wind hitting the sail of the pirate ship in the presence of loose guy wires running from vertebra to vertebra in the mast. Any system is only as strong as its weakest link!

Inner Unit Conditioning Tips

The first and most important step towards reducing back pain, improving posture and the general visual appearance, is to stop all crunch and/or sit-up type exercises until you become proficient at activating your inner unit! Although the assessment procedures for the inner unit are beyond the scope of this article, the interested reader may find detailed information in the video series "Scientific Core Conditioning". With inner unit dysfunction being extremely common in today's working and exercising population, it is safe to assume that everyone needs to start with novice exercises, even the most elite of athletes.

To begin conditioning the transversus abdominis, use the 4 Point Transversus Abdominis Trainer (Figure 6). For conditioning of the multifidus and related stabiliser and postural muscles, the Horse Stance exercises may be used (Figures 7-9).

 ALSO SEE: Core Stability: The Outer Unit.

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