Entries in Core Stability (3)


The Function of the Mid-Torso In Sports Activities

By: Adrian Faccioni.
Lecturer in Sports Coaching, University of Cabberra, Australia.
From: Published in Track Coach: No133 - Fall 1995.
Site Link: Coachr.

1. Anatomy & Kinesiology.



Most sports encompass relatively large movements of the trunk. Since the trunk segment has a large mass, great demands are exerted on the trunk musculature, particularly if the trunk movements are to be performed with high accelerations. Also the trunk has a critical role in the maintenance of stability and balance when performing movements with the extremities.

Sporting activities requiring running or jumping place pressure on the lumbo-pelvic region (that includes the 4th and 5th lumbar vertebra), the pelvis and the hips as this region becomes the hub of weight bearing. The superior forces (from torso, head and arms) meet the inferior forces transmitted from the ground through the lower extremity.

No part of the body is more vulnerable to tissue strains and sprains. This point is the center of all body movements and efficient body movements (as required in sprinting) can be critical in maintaining the stability of an anatomically correct body position, that of the Abdominal muscle groups, erector spinae (making up the mid-torso region) and the gluteus maximus (Porterfield 1985).

A study by Comerford, et al. (1991) analyzed the mid-torso muscle groups to see which group had the greatest impact on lumbo-pelvic stabilization. Results indicated that oblique muscle groups were the most important for this stabilization (especially from pelvic rotation forces) as found in high-speed sprint movements.

To assist in sprint acceleration, powerful arm drive will allow for a more rapid and powerful leg extension. The limitation with this technique is that large rotational forces can be placed upon the mid-torso musculature. If there is inadequate stability in this region, rotation of the pelvis will occur to counteract shoulder rotation resulting in poor technique and inefficient force application; therefore a slower athlete will be the result.

At an elite level, upper body strength is emphasized in sprint athletes out with a concurrent development of mid-torso strength to allow efficient usage of this additional strength during high-speed sprinting movements.

The naturally occurring wide pelvis of the mature female also leads to the above problem and mid-torso strength is absolutely vital if the coach wishes to maximize efficient technique at maximal speed in his/her female sprint athletes. Hip rotation is required to maximize stride length, but if excessive, then poor technique will result and if combined with a poor pelvic tilt, then major inefficiencies will result, leading to either poor performance, injuries or both.

Apart from resistance to rotational forces, there must be support of the pelvis to minimize excessive anterior pelvic tilt. An excessive anterior tilt indicates poorly toned mid-torso musculature and this can increase the lordotic curve (lower back arch) in the lumbar region. This can increase the strain on the facet joints in the vertebral column and can result in the iliopsoas going into spasm to protect the lower core from injury.

Also increased pressure on the neural plexus from the lumbar region can result in nerve irritation (e.g. sciatic nerve) which can then affect the optimal functioning of lower limb musculature that can have deleterious effects if maximal effort work (e.g., 100% sprinting) is performed (such as hamstring strains).

Excessive anterior tilt of the pelvis can limit hip range of motion leading to excessive hip extension and limited hip flexion. This technical position limits stride length and increases ground contact time (which is undesirable for increases in speed performance) due to the athlete's center of gravity being lower than required for maximal sprinting speed.

The demands of sprinting require the abdominals to function in a way that leads to optimal torsional stabilization during explosive contractile sequences, matching the needs of performing up to 5 strides per second (such as that which occurs in an elite sprint race). During sprinting at this rate, the lower limb velocity can reach 80km/h; therefore the stresses placed upon the pelvic stabilizers are extreme and can only be accommodated for with extremely well-developed abdominal (including oblique) musculature (Francis 1992).


The development of a strong mid-torso should be the goal of all speed/power athletes and the preferred procedures for maximizing strength in this region is by the common sit-up. Kinesiologically, the sit-up and its many variations are the ideal exercises to develop the vertebral flexor and rotational muscles (namely the RA, EO & IO).

The mid-torso musculature consists of postural muscles with a high percentage of slow-twitch muscle fibers. Their function is to be able to hold contractions for long periods to maximize trunk stability (Nordel and Frankel 1989, p. 104).

To best condition this region, variations on the sit-up can be used. To maximize abdominal development and minimize stress placed upon the lower back, exercises should be performed slowly (1-4 seconds per repetition) while working on all muscle groups in the mid-torso region.

These exercises should also be performed through a range of motion that minimizes lower back strain, and maximal control is required. When compared to the stress placed upon the lumbar region when standing (assume this is measured as 100%), the full sit-up (Figure 5), even with knees bent and feet flat on the floor, creates a stress equal to 200%.

This load can be decreased if the sit-up is only partial (first 30' from floor) and lessened even more if a reverse sit-up is performed (pelvis lifted off the floor) (Figure 6).

The reverse curl has been shown to increase the activation on the EO and IO as well as the RA (Nordin & Frankel 1989, p. 202). A modification to maximize load and minimize stress upon the lumbar region is to perform a partial crunch as well as a reverse sit-up concurrently (Figure 7) and hold each maximal contraction for four seconds. This minimizes the use of assistant muscle groups and quickly fatigues the musculature targeted in only 5-15 repetitions.

Sit-ups performed fast and or with the feet supported have:

  1. The relative contribution of the hip flexors increasing while the relative contribution of the abdominal muscles decreasing (Sevier 1969).
  2. Increased stress placed upon the lumbar region of the spine.
  3. Decreased load on the abdominal musculature due to increased momentum from the upper body.

The major limitation of the sit-up is the functional application of mid-torso strength transferable from a sit-up routine to the pelvic stabilization required under the stresses of a sprint or any high-speed movement performance. Personal observation of a variety of athletes has highlighted that even the development of very strong mid-torso regions from situps and squat type activities do not automatically transfer to the pelvic and mid-torso positions required to maximize sprinting performance.

Many athletes are strong enough through their mid-torso region but have not developed correct motor patterns to be able to stabilize the body while having rapid upper and lower limb movements (e.g., arm and leg movements in sprinting). To develop the specific strength qualities or transfer mid-torso strength to the required strength positions can be achieved both in a weight room and the field/court/ track situation.


The best adaptation in the mid-torso musculature results from slow isotonic training in combination with isometric training in a range of nonspecific and sprinting-specific body positions.

Once the athlete can perform acceptable slow isotonic (with movement) mid-torso exercises, more sprint specific positioning can be introduced that requires the athlete to place his hips in the necessary posterior tilt position while placing stress upon the mid-torso musculature. Examples of these exercises are:

  1. Abdominal hollowing (Figure 8)
  2. Isometric prone (Figure 9)
  3. Single leg raise with lumbar support (Figure 10).

Abdominal hollowing

To perform abdominal hollowing the athlete can be either in a supine position or standing. The technique is to contract the abdominals "INWARDS" as hard as possible while maintaining normal rib cage positioning. This can be assisted by placing a finger into the belly button and try to push the abdominal wall inwards while maximally contracting. The athlete should continue to breath as normally as possible throughout the exercise; each contraction can be held for up to 60 seconds.

Isometric prone

To perform an Isometric prone exercise the athlete begins on elbows and knees and then takes the knees off the ground while trying to maximally contract the abdominal musculature upwards. If any stress is felt on the lower back, this is an indication that the abdominal wall is not being totally contracted. This position should be held 15-60 seconds depending upon the condition of the athlete.

Single leg raise with lumbar support

To perform a single leg raise with lumbar support, the athlete places the tips of his fingers under the lower back and maximally contracts the back against the fingers. Then one leg at a time is slowly lowered (up to 10 seconds per leg) while maintaining a constant pressure on the fingers. As soon as the pressure decreases, this indicates that the abdominal musculature is beginning to fail and the hip flexors have been activated. At this point if the pressure cannot be regained, the athlete either finishes that repetition or brings the leg slowly back to the starting position until lower back pressure can be regained and then continues the repetition.

These are still "PASSIVE" isometric exercises (done slowly) that once a high competency is reached can be followed by "ACTIVE" isometric exercises that are highly sprint specific.

Examples of these exercises are:

  • Rapid hip extension/hip flexion (Figure 11)
  • Modified Russian Twist with/ without arm swing. The 'MRT' is accomplished while reclining with the buttocks on a raised, fixed seat and with the toes/feet hooked under a rigid padded bar. In this position, the back, shoulders and head are not supported. Then twist at the waist while swinging an arm in the direction of the rotation. (Figure 12)



The weight room training is purely a precursor to what must be achieved at the "on field" situation. This is where true application of the strength gain can be both assessed and true transfer can be completed.

This goal can be achieved in two parts.

  • The correct body positioning can be further applied by several "running drills" that are aimed at correct running form (which usually means correct body posture through the mid-torso).

The "A", modified single leg "A", "B", heel flick and high knee drills (Figure 13) are all aimed at increasing the tilting and rotational stresses that are placed upon the mid-torso musculature. These drills can be done slowly at first and progressively sped up as the athlete's ability to hold the correct position improves.

 The modified single leg "A" places high levels of stress upon the mid-torso region to hold the pelvis in place while the athletes perform very explosive hip flexion and extension movements in a single leg form.

  • The most specific transfer to sprinting is to have the athlete sprint while concentrating on the positioning drilled previously. Sprints should be less than maximal at first, progressing only as the athlete is able to maintain the correct running position. As soon as pelvic stability decreases, the drill should be stopped.

External resistance to increase learning can be in the form of a towing device that the athletes place around their mid-torso and the pressure on this region through each repetition reinforces the control required and increases the level of control as the athlete is having to work harder to maintain good body position under this increased resistance. (Figure 14)

It is important that the resistive load be small enough so that the athlete is able to maintain proper sprint acceleration posture. Bending forward at the waist should be avoided.

In summary, the mid-torso is the link between the upper and lower body and must allow the transfer of strength movements and allow powerful movements of both the upper and lower body to complement each other. The best way to achieve this is to develop mid-torso strength through traditional ways (situps) but ensure functional strength (by more specific mid-torso training methods) is being attained throughout the athlete's training year.



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.


Core Stability: The Outer Unit

By: Paul Chek.
From: IAAF/NSA 1-2.00.
Site Link: Coachr.
Article Link: The Outer Unit.


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 stated that abdominal exercises can be performed in various ways and asks if the common exercises really improve the functionality of the abdominal muscles. In this article the author explains first, the anatomy of the outer unit, second, he describes the function of the four sling systems of the outer unit and, finally, he demonstrates exercises targeting one or all of the sling systems in a methodical manner.

In the previous article titled The Inner Unit A New Frontier In Abdominal Training, we discussed the function of the transversus abdominis, multifidus, diaphragm and pelvic floor musculature with regard to their significant functions as stabilizers of both the spine and extremities. The main message of this article was that stabilization of the core via the inner unit must always precede force generation by the core or extremities.

The scope of this article will be, first, to explain the anatomy of the outer unit, second, to describe the function of the four sling systems of the outer unit and, finally, to demonstrate exercises targeting one or all of the sling systems in a methodical manner.   

Functional Anatomy of the outer unit

The outer unit consists primarily of phasic muscles (Table 1), although there are many muscles such as the oblique abdominals, quadratus lumborum, hamstrings and adductors which serve a dual role, acting in a tonic role as stabilizers and a phasic role as prime movers. To be technically correct, we may say that outer unit functions are predominantly phasic functions (geared toward movement).  

Superficial to the musculature of the inner unit are the outer unit systems, sometimes referred to as slings. The Deep Longitudinal System (DLS) is composed of the erector muscles of the spine and their investing fascia. The spinal erectors communicate with the biceps femoris through the sacrotuberous ligament of the pelvis and to the lower extremity via the peroneus longus muscle (Figure 1).

The Posterior Oblique System (PS) or sling consists primarily of the latissimus dorsi and the contralateral gluteus maxim us (Figure 2).    

The Anterior Oblique System (AS) consists of a working relationship between the oblique abdominal muscles and the contralateral adductor musculature and the intervening anterior abdominal fascia (Figure 3).   

The Lateral System (LS) (Figure 4) consists of a working relationship between the gluteus medius, gluteus minimus and ipsilateral adductors (1,3). Porterfield and DeRosa (3) indicate a working relationship between the gluteus medius and adductors of one leg with the opposite quadratus lumborum. The author's clinical experience strongly suggests that the oblique musculature is synergistic with the quadratus lumborum during lateral sling functions such as those seen in Figure 4.  



The deep longitudinal and posterior systems

 To better understand how the DLS and PS function, we will explore their actions in what is certainly one of our most primal movement patterns, gait (walking). While walking, there is a consistent low level activation of the inner unit muscles to provide the necessary joint stiffness to protect the joints and support the actions of the larger outer unit muscles. Recruitment of the inner unit muscles will fluctuate in intensity as needed to maintain adequate joint stiffness and support, as the inertial forces of limb movement, kinetic forces and intradiscal pressures increase.  

As we walk, we swing one leg and the opposite arm forward in what is termed counter rotation. Just prior to foot strike, the hamstrings become active . The DLS, uses the thoracolumbar fascia and paraspinal muscle system to transmit kinetic energy above the pelvis, while using the biceps femoris as a communicating link between the pelvis and lower extremity. For example, Vleeming shows that the biceps femoris communicates with the peroneus longus at the fibular head, transmitting approximately 18% of the contraction force of the biceps femoris through the fascial system into the peroneus longus.  

Interestingly, the anterior tibialis, like the peroneus longus, attaches to the plantar side of the proximal head of the first metatarsal. The significance of this relationship is appreciated when considering that there is recruitment of the biceps femoris and the anterior tibialis just prior to heel strike in concert with the peroneal muscles, which act as dynamic stabilizers of the lower leg and foot. Dorsiflexion of the foot and activation of the biceps femoris just prior to heel strike, therefore, serves to "wind up" the thoracolumbar fascia mechanism as a means of stabilizing the lower extremity and storing kinetic energy that will be released during the propulsive phase of gait (4). 

As you can see by observing Figure 2, just prior to heel strike the gluteus maximus reaches maximum stretch as the latissimus dorsi is being stretched by the forward swing of the opposite arm. Heel strike signifies transition into the propulsive phase of gait, at which time the gluteus maximus contraction is superimposed upon that of the hamstrings. Activation of the gluteus maximus occurs in concert with activation of the contralateral latissimus dorsi, which is now extending the arm in concert with the propelling leg. The synergistic contraction of the gluteus maximus and latissimus dorsi creates tension in the thoracolumbar fascia, which will be released in a pulse of energy that will assist the muscles of locomotion, reducing the metabolic cost of gait.

The anterior oblique system

The concept of the Anterior Oblique System (AS Figure 3) appears to have become popular very recently. A review of the literature shows that spiral concept of muscle-joint action was understood as integral to human movement and corrective exercise by Robert W. Lovett, M.D. and by anatomist Raymond A. Dart in the early 1900's.  

To clarify the point that movement originates in the spine (core), Gracovetsky describes torque generation by an S-shaped spinal column. He exemplifies the point that the legs are not responsible for gait, but merely instruments of expression, by showing that a man with no legs whatsoever can walk. In both the examples of what Gracovetsky calls the spinal engine, it is evident that the kinetic and potential energies of the oblique abdominal musculature, in concert with other core muscles, are primarily responsible for creating the torque that drives the spinal engine; the oblique abdominal being best situated to create rotary torque.  

The oblique abdominals, like the adductors, serve to provide stability and mobility in gait. When looking at the EMG recordings of the oblique abdominals during gait and superimposing them upon the cycle of adductor activity in gait demonstrated by Inman, it is clear that both sets of muscles contribute to stability at the initiation of the stance phase of gait, as well as to rotating the pelvis and pulling the leg through during the swing phase of gait. As the speed of walking progresses to running, activation of the anterior oblique system becomes more prominent.  

The AS is very important, particularly in sprinting, where the limbs and torso must be accelerated. The demands on the AS are great in multi-directional sports such as tennis, soccer, football, basketball and hockey. In such sporting environments the AS must not only contribute to accelerating the body, but also to changing direction and decelerating it. One need not see an EMG study to appreciate the strong contribution of the AS; just ask anyone that has experienced an abdominal strain! Accelerating, decelerating and changing directions are all activities that result in immediate pain in the presence of both abdominal and groin strains or tears.  

AS functions can be appreciated when running in sand. Because sand gives away during the initiation of the stance and propulsive phases of gait, the impulse timing of ground reaction forces is disrupted, resulting in poor use of the thoracolumbar fascia, or what Margaria calls the smart spring system. The result is that you must muscle your way through the sand. Many athletes having performed sand sprints, will note abdominal fatigue in the following day or two after the sand sprints. This is due to the increased activation of the AS to compensate for the lost kinetic, potential and muscular energy, which is usually stored and released in part by the thoracolumbar fascia system. Gracovetsky states that wearing soft soled sporting shoes, as athletes often do today, can easily disrupt the body's timing mechanism, which could very well result in increased work and may result in injury.  

During explosive activities, such as swinging a sledge hammer (Figure 5), the AS serves critical function, stabilizing as in gait, yet assisting in propelling the hammer. Trunk flexion and rotation, as a closed chain movement atop of the lead leg, is generated by the adductors as they assist in trunk flexion and internal rotation of the pelvis and assisted by gravity. Activation of the adductors occurs in concert with activation of the ipsilateal (stance leg side) internal oblique and contralateral (throwing arm side) external oblique, pulling the trunk in the necessary direction to propel the shoulder/arm complex. The forces of the shoulder/arm unit summate with those of the legs and trunk below to produce a powerful hammer swing. Here one can clearly see the phasic functions of the AS at work.

 The lateral system

Porterfield and De Rosa (3) suggest that functional anatomy dictates that the lateral system provide essential frontal plane stability. While walking, the LS will be active at heel strike (initiation of stance phase), providing frontal plane stability. This is accomplished by a force-couple action between the gluteus medius and minimus pulling the iliac crest toward the stable femur while the opposite quadratus lumborum and oblique abdominal musculature assist by elevating the ilium. This action is necessary to help create the freeway space needed to swing the leg in gait, particularly when you consider the terrain we ambulated across during developmental years. 

During functional activities such as participating in Step class (Figure 4) or simply walking up stairs (Figure 6), the LS plays a critical role, stabilizing the spine in the frontal plane. Stability in the frontal plane is very important to the longevity of the lumbar spine because frontal plane motions of the lumbar and thoracic spine are mechanically coupled with transverse plane motions; excessive amounts of either will quickly aggravate spinal joints.    

The LS provides stability that not only protects the working spinal and hip joints, but is a necessary contributor to overall stability of the pelvis and trunk. Should the trunk become unstable, the diminished stability will compromise ones ability to generate the forces necessary to move the swing leg quickly, as required by many work and sports environments. Attempts to move the swing leg, or generate force with the stance leg during gait and other functional activities, can easily disrupt the sacroiliac joints and pubic symphysis and cause kinetic dysfunction in joints throughout the entire kinetic chain.     

A classic example of distal expression of LS dysfunction was illustrated by Sahrmann. She described a lateral shift of an athlete's center of gravity over the subtalar joint while going through the stance phase of gait (Trendelenburg's Sign) resulting in an inversion ankle sprain. Since attending her course in 1992, the author has found gluteus medius weakness and contralateral low back pain due to quadratus lumborum overload common among athletes exhibiting recurring ankle sprain.  


Although the outer unit is thought of as a phasic system, (a system for moving the body) by most, it does provide crucial stabilizer functions. We must remember that the muscles of the inner unit are relatively small, with less potential to generate force than the large outer unit muscles.

The inner unit muscles are concerned with providing joint stiffness and segmental stability. They work for extended periods of time at low levels of maximal contraction. The outer unit muscles, while very well oriented for moving the body, are also very important to stability, often serving to protect the inner unit muscles, spinal ligaments and joints from damaging overload. For example, consider this common scenario:

The coach instructs two football players to engage in an oblique medicine ball toss drill. One player is much bigger and stronger than the other, as the other player finds out as he attempts to catch the 8 kg. (17.5 lbs.) medicine ball traveling at him at over 60 kph (40mph)! The smaller player does not have the strength in his outer unit to decelerate the ball and is forced into end-range trunk flexion and rotation, traumatizing his lower lumbar discs, ligaments and intrinsic spinal muscles (multifidus, rotatores, intertransversarii and interspinales).

Regardless of how well conditioned the inner unit of the smaller player may have been, lack of strength in his outer unit relative to his partner, or the demands of the task at hand resulted in inner unit overload and injury! With careful scrutiny of most activities in the work or sports environment, you will find that good eccentric strength in the outer unit systems is critical to protecting the inner unit from damage. Protection of the inner unit through proper conditioning of the outer unit is a worthy goal when one considers that optimal proprioception is dependant upon the health of the inner unit muscles and the joints they protect!   


Now that we have taken a detailed look at the anatomy and function of the outer unit, it should be clear that modern exercise technology has taken us a long way from conditioning the outer unit systems the way they were designed to work! For example, can you see any way the following exercises condition the outer unit systems in such a way that they could provide carryover to most functional work or sport activities?    

  • Crunch on Floor
  • Crunch Machines of all types
  • Sit-up
  • Hanging Leg Raises of All Types
  • Bench Press
  • Leg Press
  • Seated Row Machines?

I could go on, filling the page with exercises that do very little to enhance function. Many of you will no doubt recognize the above exercises as traditional bodybuilding exercises. What has happened? Only a few years back in the days of Bill Pearl, bodybuilders were building beautiful physiques with functional exercises like squats, lunges, barbell rows, cable rows, deadlifts and the like. Today, we are overrun by the machine era, the era of the aesthetic emotional hook so carefully used by the machine manufacturers to convince you that you will look better using their machines.    

Our bodies were not designed to exercise on machines, they were designed to function in the wild. We are designed for three-dimensional freedom, not two dimensional guided, unrealistic exercise that encourages muscle imbalance between those muscles used to stabilize and those used in a phasic manner for any given movement. The motor programs developed on machines are of little use to the body for anything other than pushing or pulling the levers of that very machine during that very exercise. This limits functional carryover to those that operate cranes, excavators, bulldozers, and buses for a living; they are about the only people that must apply force to levers in a seated, supported, two-dimensional environment.    


Using your new understanding of the outer unit systems, carefully analyze such functional pushing and pulling exercises as the single arm standing cable row (Figure 7) and standing single arm cable push (Figure 8). You will see all outer unit systems being conditioned simultaneously, jU5t as they are used in most of our work and sport environments. 



Medicine ball exercise, like free weight training, was much more popular in the 40s, 50s, 60s, and 70s than it is today. Great athletes of those decades used exercises such as the oblique medicine ball toss and push-pass, not to mention almost 100 other variations of medicine ball exercises.  

The Swiss Ball can be used to effectively condition the outer unit systems in three-dimensional movement while providing unloading opportunities for those recovering from injury. For example, analyze the Supine Lateral Ball Roll (Figure 9) and see if you can determine which outer unit systems are being used and categorize them in the order of demand during this exercise. This will be a great start toward a better understanding of functional exercise.  



The outer unit consists of four systems, the deep longitudinal, posterior oblique, anterior oblique and lateral. These systems are dependent upon the inner unit for the joint stiffness and stability necessary to create an effective force generation platform. Failure of the inner unit to work in the presence of outer unit demand often results in muscle imbalance, joint injury and poor performance. The outer unit cannot be effectively conditioned in patterns of movement that carryover to function when using modern bodybuilding machines. Effective conditioning of the outer unit should include exercises that require integrated function of the inner and outer units, using movement patterns common to any given client's work or sport environment.