J Can Chiropr Assoc 1999 (Jun); 43 (2): 75–88 ~ FULL TEXT
Stuart M McGill, PhD
Faculty of Applied Health Sciences,
Department of Kinesiology,
University of Waterloo,
Waterloo, Ontario, Canada N2L 3G1.
This paperformalizes stability in a clinician-friendly way
and then discusses waysfor chiropractors to ensure
stability ofspinaljoints that may have their stability
KEY WORDS: lumbar stability, chiropractic, exercise, manipulation.
From the FULL TEXT Article:
The purpose of this paper is to develop a scientific foundation
and formalize the notion of stability as it pertains to
the spine, and then discuss some implications of stability
for advancing spine rehabilitation and clinical practice.
The intention was to write a reader-friendly synthesis
where only minimal references were provided. This invited
review will complement my last review written for
this journal 10 years ago. Over the intervening time we
have established the UW-CMCC Chiropractic Research
Clinic and have been conducting research with CMCC
researchers. While we have been investigating the
biomechanical effects of manipulation, we will need to
perform additional experiments to provide a synthesis of
sufficient utility for chiropractic practice. Look forward to
this report in another couple of years.
A major theme developed here pertains to the stability
of spinal joints which are directly affected by chiropractic
treatment. Can chiropractors be more effective at stabilizing
a joint with exercise after they have decreased its stability
with manipulation - and if so, how?
On stability: the foundation
Ask ten different clinicians to define stability and chances
are there will be ten different responses. Much progress
has been made recently on the formulation and operationalization
of stability in musculoskeletal linkages and
joints. These concepts are now being employed in the
clinic and have resulted in enhanced rehabilitation outcome
together with more biomechanically justifiable injury
prevention strategies. This section shall formalize the
notion of stability from a spine perspective.
During the late 1980's, Anders Bergmark, a professor of
solid mechanics at the University of Lund in Sweden, very
elegantly formalized stability in a muscular system using a
very simplistic model of the spine.  With an extremely
simplified linkage, and only a few muscles, he was able to
formalize mathematically, the concepts of "energy wells",
stiffness, stability and instability. For the most part, this
classic work went unrecognized largely because the engineers
who understood the mechanics did not have the biological
- clinical perspective, while the clinicians were
unable to interpret the engineering-mechanics. This pioneering work, together with embellishment by several others
will be synthesized here. The following forms a brief
tutorial for clinicians to understand the mechanical formulation,
and implications of stability for musculoskeletal
First, one must understand the concept of potential energy,
which for the purposes here, comprise two basic
forms. In the first form, objects have potential energy by
virtue of their height above a datum. An apple has potential
energy while still on the tree since this energy will be
transformed into kinetic energy if it were to fall.
PE = m*g*h
In the second form, elastic bodies may possess potential
energy by virtue of their elastic deformation under load,
storing potential energy which is then recovered when the
load is removed - such as what would happen when loading
and unloading any elastic band. Let's begin with the
first form of potential energy to describe the notions of
energy wells and minimum potential energy. If we place
the ball into a bowl it is stable. We know this because if one
were to apply a force to the ball (or a perturbation) the ball
will rise up the side of the bowl but then come to rest again
in the position of least potential energy - or the bottom of
the bowl. We can make this system more stable by deepening
the bowl and/or by increasing the steepness of the sides
of the bowl (see Figure 1). Conversely, a ball placed on a
flat surface or at the top of hill (an upside down bowl) is
unstable since any perturbation would cause the ball to roll
away. So one can see that the objective in creating stability
with this analogy is to create a bowl shaped potential energy
surface or an energy well. The ball will seek the
position ofminimum potential energy (or mass times gravity
times height - height being the variable to minimize).
This corresponds to a stable situation. Thus, the notion of
stability requires the specification of the unperturbed state
of a system followed by study of the system following
perturbation, which in turn indicates the stability of the
The previous analogy is a two dimensional example.
This would be analogous to a hinged skeletal joint that
only has the capacity for flexion/extension. Some ball and
socket joints can rotate in three planes requiring a 4 dimensional
bowl. Obviously, this is a theoretical bowl since a
real bowl has only 3 dimensions - mathematics allows us
to examine a 15 dimensional bowl. If one were to decrease
the height of the bowl in any one of these 15 dimensions,
the ball would roll out. In clinical terms, a single muscle
force having an inappropriate magnitude will cause instability.
Having understood these analogies incorporating potential
energy by virtue of height, we can now consider potential
energy as a function of stiffness and storage of the
elastic energy, which is much more useful for musculoskeletal
application. Elastic potential energy can be calculated
from the formula:
PE = 1/2*k*x2
In other words the greater the stiffness (k) the greater the
steepness of the sides of the bowl (from the previous analogy), and the more stable the structure. Thus stiffness creates
stability (see Figure 2). Active muscle, produces a
stiff member and in fact the greater the activation of the
muscle the greater this stiffness. Furthermore, joints possess
inherent joint stiffness, ligaments contribute stiffness
in different ranges of motion. Nonetheless the motor control
system is able to control stability of the joints through
intentional muscle activation and to a lesser degree by
placing joints in positions which modulate passive stiffness
contribution. A faulty motor control system leads to
inappropriate magnitudes of muscle force, and stiffness,
allowing a "valley" for the "ball to roll out" or, for ajoint to
buckle or undergo shear translation.
In a complex system such as the lumbar spine one must
analyze the bowl which will have many dimensions - 6
dimensions or degrees of freedom per joint (3 rotational
and 3 translational) multiplied by the number of joints
chosen for the analysis. This is done by forming a matrix
where each dimension is represented by a number (or
eiganvalue) and the magnitude of that number represents
its contribution to forming the height of the bowl in that
particular dimension. One then simply scans the matrix for
eigenvalues less than zero indicating instability, and furthermore,
by observing the eigenvector can then identify
the mode in which the instability occurred.
The next concept that clinicians must understand is the
link between muscle activation and stiffness. Activating a
muscle increases stiffness, both within the muscle and to
the joint(s). Activating a group of muscle synergists and
antagonists in the optimal way now becomes a critical
issue. From a motor control point of view, we often use the
analogy of an orchestra - we must get the orchestra to play
together, or in clinical terms we must get the full complement
of the stabilizing musculature to work together to
achieve stability. One instrument out of tune ruins the
sound - one muscle with inappropriate activation amplitude
can produce instability, or at least unstable behaviour
will result at lower applied loads. Figure 3 shows a few of
the stabilizers of the spine which we appreciate to be very
Clinicians are very aware of patients who co-contract in
order to stabilize a joint - this type of behavior makes
sense and in fact it is the only way to stabilize a joint.
However the clinical question then becomes how much
stability is necessary - obviously insufficient stiffness will
not achieve the necessary stability for the joint but on the
other hand too much stiffness and co-activation imposes
massive load penalties on the joints and skeletal system.
We must now develop the concept of "sufficient stability".
In order for a joint to bear larger loads, more stability is
required. However, in most situations only a modest
amount of stability is required to stabilize the joint. Too
much stiffness from muscle activation imposes a severe
load penalty on the joint, and would over-stiffen the joint
impeding motion. In normal joints, with fit motor control
systems, appropriate stability is achieved. Individual joints
have passive stiffness. If the joint is not at the end range
and passive tissues cannot create a mechanical stop to
motion, the joint will most likely be unstable without additional
muscular stiffness. The role of the motor system is to
add stiffness required to make the joint stable. Post injury,
the motor system has been documented to loose its fitness
and it chooses abnormal muscle activation sequences. Furthermore,
the passive stiffnesses are disturbed decreasing
the force required for unrestricted rotations and translations.
The Biomechanist's contribution is to quantify the
loss of passive tissue stiffness and determine how much
muscular stiffness is necessary for stability. Once this
amount of stability is determined, the clinician will then
wish to add a modest amount of extra stability to form
a margin of safety, and this is known as "sufficient
The stability concept is revolutionizing rehabilitation.
New insight into the pathogenesis of injury is obtained -
we are now able to explain how people can sustain a back
injury picking up a pencil. In this situation, the general
demand of the task is relatively low, muscular forces are
low, and stiffness is low. If the motor system committed a
small error in activation sequence and/or muscle magnitudes
resulting in a temporary loss of stiffness, in a single
mode from a single muscle, instability could result.  In
other words, the ball would roll through the side of the
bowl formed by the contributions of the particular muscle
stiffness (bowl sides are created by systems of muscles,
not only single muscles that contribute to the particular
direction of joint motion). The resulting rotation and/or
translation at the joint overloads a passive tissue to the
point of damage. In fact we observed such an instability on
videoflouroscope records in a single spine motion segment
that resulted in injury.  We are also beginning to provide
clinicians with specific target levels of activation in order
to achieve sufficient stability.
Interestingly enough, large
muscular forces are rarely required. Rather low levels of
activation are required for long periods of time. In our
recent paper,  stabilization exercises were quantified and
ranked for muscle activation magnitudes together with the
resultant spine load. Furthermore, Cholewicki and
McGill,  and Cholewicki et al.  have demonstrated that
sufficient stability of the lumbar spine is achieved, for a
neutral spine, in most people with modest levels of coactivation
of the abdominal wall. This means that a patient
must be able to maintain sufficient stability getting on off
the toilet, in and out of the car, up and downstairs etc. The
amount of "Sufficient stability" over these types of tasks
depends on the health of the joints and their passive stiffness
This argument suggests that the margin of
safety when performing tasks, particularly the tasks of
daily living, is not compromised by insufficient strength
but rather insufficient endurance. We are now beginning to
understand the mechanistic pathway of those studies
showing the efficacy of endurance training vs. strength
for the muscles that stabilize the spine. Having strong
abdominals do not provide the prophylactic effect that had
been hoped for - but recent work suggests that endurable
muscles reduce the risk of future back troubles (e.g. ).
Joint stability and chiropractic practice
Stiffness, and stability, of a spinal motion segment is due
to both muscle stiffness and the inherent passive stiffness
of the joint. Chiropractors attempt to identify spinal segments
that are not moving correctly, or are "blocked" or
"stiff'. Interestingly enough, stiffjoints are, by definition,
quite stable or would require a very large perturbation to
become unstable. The goal of manipulation is to restore
more normal motion, but more motion means less joint
stiffness and stability. This may increase the need for more
stability from muscular sources. Furthermore, there may
be a peril in overmanipulation producing too much
motion, which compromises stability and can produce
another set of concerns.
In my opinion, some chiropractors are lagging in the
practice and prescription of stabilization exercises for
their patients. While some progressive chiropractors
have employed stabilization programs for their patients,
many manipulate without due consideration of enhancing
spine stability through exercises specifically designed to
increase the effectiveness of the motor control system to
activate the stiffening muscular "guy wires". The next section
is designed to assist the chiropractor in prescribing
optimal stabilizing exercises.
Exercise for the low back: general concepts
A lot of the notions that clinicians consider to be principles
for exercise prescription may not be as well supported with
data as one may think. For example, we have all heard to
perform sit ups with bent knees. Why? Further, many clinicians
emphasize performing a pelvic tilt when performing
many types of low back exercise. What is the scientific
evidence for such a recommendation? An examination of
the literature will reveal that the scientific foundation upon
which many exercise notions are based is extremely thin.
Rather "clinical wisdom" appears to prevail and, in fact,
dominates the decision process when choosing the most
appropriate exercise for an individual situation. This observation
is not intended to belittle clinical wisdom but
rather to emphasize that choosing an optimal exercise
challenge requires the blend of "clinical art" and "science".
The foundation for specific exercises will be briefly
developed here. Chiropractors interested in more detail
should consult the American College of Sports Medicine
textbook  in which I was asked to develop a program emphasizing
enhancement of stabilizing motor patterns and
muscle endurance performance.
The traditional objective of most exercise prescription is
to stress both damaged tissue and other healthy supporting
tissues to foster tissue repair, while avoiding further excessive
loading which can exacerbate an existing structural
weakness. However, a relatively recent development is to
meet these objectives, while also enhancing the ability of
the motor control system to optimize stability. Furthermore,
certain types of low back injuries are characterized
by very specific tissue damage which may require quite
different exercise rehabilitation programs for different
people. For example, the posterior herniated disc would do
well to avoid full spine flexion manoeuvres, particularly
with concomitant muscle activity causing significant
compressive loading since this is a potent way to herniate
the annulus. Yet this spine posture is often unknowingly
adopted by patients or consciously advocated by clinicians
who demand a full pelvic tilt! Consider an example that
addresses the- mechanically unstable spine which may be
associated with a musculature and motor control system
that is very "unfit" whereby the individual makes all sorts
of inappropriate muscle activation sequences (cf. ).
well documented that, following injury, the motor system
loses its ability to optimally sequence motor patterns to
muscles. These motor control "errors" appear to lead to
brief spine buckling situations and a high risk of injury.  It
is imperative that clinicians understand what are the stabilizers
of the spine - and what is the safest, and most effective
way to train them. While an entire textbook could be
written to describe ideal exercise programs for the entire
population including chronic low back pain sufferers,
children, men and women of all ages, through to
elite athletes, the focus of the exercises discussed here is
on developing the safest exercise for enhancing stability
and the daily maintenance of low back health that is
of utility for the chiropractic office.
Instability as a cause of injury
The ability of the joints of the lumbar spine to bend in any
direction is accomplished with large amounts of muscle
cocontraction. Such coactivation patterns are counterproductive
to generating the torque necessary to support the
applied load in a way that minimizes the load penalty imposed
on the spine from muscle cocontraction. In fact a
ligamentous spine will fail under compressive loading at
about 20 Newtons in a buckling mode.  From the first
section of this paper, the reader understands that muscle
activity around the spine acts like the rigging on a ship's
mast, and while the spine ultimately experiences more
compression it is able to bear a much higher compressive
load as it stiffens and becomes more resistant to buckling.
A number of years ago we were investigating the mechanics
of powerlifter spines while they lifted extremely heavy
loads using video fluoroscopy viewing the sagittal plane.
We happened to film and record one injury. The view of
the powerlifter spines was calibrated for full flexion by
first asking them to flex at the waist and hang the upper
body against gravity with no load in the hands.
their lifts, even though they outwardly appeared to fully
flex their spines in fact their spines were two to three degrees
per joint from full flexion, thus explaining how they
could lift magnificent loads without sustaining injury
which we suspect is linked with full flexion. However, one
lifter dropped the weight and complained about pain (apparently
injured). Upon examination of the video fluoroscopy
records a local instability was noted: specifically
only at L3 /L4 where this joint approached the full flexion
calibrated angle and exceeded it by one-half a degree,
while all other joints maintained their static positions. 
This is the first observation reported in the scientific literature
documenting the presence of a local instability occurring
at a single lumbar joint that we know of. This
motivated the work of my former graduate student Dr.
Jacek Cholewicki, now a professor at Yale University, to
first define mathematically lumbar stability and then continuously
quantify stability of the lumbar spine throughout
a reasonably wide variety of loading tasks.
speaking it appears that the spine is most prone to instability
failure when the loading demands are low and the major
muscles are not activated to high levels. (In the case of
the powerlifter the loading was extreme). Nonetheless it
appears that the chance of the motor control error which
results in a short and temporary reduction in activation, to
one of the intersegmental muscles would cause rotation of
just a single joint to a point where passive or other tissues
become irritated or possibly injured. In fact at this point it
is interesting to discuss the very small intersegmental muscles,
the rotators and intransversarri. There is evidence to
suggest that these muscles are highly rich in muscle spindles
(at least four to seven times higher than multifidus). 
It would seem that these organs are not functioning to
produce force given their minimal cross sectional area, but
are rather position transducers for each lumbar joint enabling
the motor control system to control overall lumbar
posture and avoid injury. Once again these findings are
relevant to those responsible for injury management and
exercise prescription - spine stability and motor control
issues appear to be important considerations.
Toward developing the stabilization program - more evidence
Choosing the best exercise requires evidence on tissue
loading and on the knowledge of how injury occurs to
specific tissues (described in [12-14]). The ideal exercise
will challenge muscle, impose minimal joint loads to spare
the spine, and do this in a way that enhances joint stability
in a neutral posture, and that requires additional elements
of whole body stabilization. The following section addresses
certain selected exercise issues beginning with an
example to illustrate the need for quantitative analysis for
evaluating the safety of certain exercises.
Situps with bent knees?
We have all been aware of the principle to perform situps
and other flexion exercises with the knees and hips flexed.
Several hypotheses have suggested that this disables the
psoas and/or changes the line of action of psoas to reduce
the low back compressive load. Recent MRI based data 
demonstrated that the psoas line of action does not change
due to lumbar or hip posture (except at L5/S 1) as the psoas
laminae attach to each vertebrae and "follow" the changing
orientation of spine, not of the hip or knees. There is no
doubt that psoas is shortened with the flexed hip, modulating
force production. But the question remains, is there a
reduction in spine load with the legs bent? Recently
McGill  examined 12 young men, with the laboratory
technique described previously, and observed no major
difference in lumbar load as the result of bending the knees
(average moment of 65 Nm in both straight and bent knees,
Compression: 3230N-straight legs, 3410N-bent knees;
Shear: 260N-straight legs, 300N-bent knees). Compressive
loads in excess of 3000N certainly raises questions of
safety for some patients. This type of quantitative analysis
is necessary to demonstrate that the issue of performing
situps using bent knees or straight legs is probably not as
important as the issue of whether to prescribe situps at all!
The pelvic tilt
Many clinicians universally recommend performing a pelvic
tilt when prescribing exercise. One what evidence?
Flexing the spine consistent with the "pelvic tilt", preloads
the annulus and posterior ligaments  which appears
to be associated with an increase in the risk of injury.
Therefore a "neutral" spine (neutral lordosis) is emphasized
to reduce the risk of injury while the spine is under
load - neither hyperlordotic or hypolordotic. A general
rule of thumb is to preserve the normal low back curve
(similar to that of upright standing) or some variation of
this posture that minimizes pain. While in the past performing
a "pelvic tilt" when exercising has been recommended,
this is not justified as the "pelvic tilt" increases
spine tissue loading as the spine is no longer in staticelastic
equilibrium, in fact the "pelvic tilt" preloads the
spine - it would appear to be unwise to recommend the
"pelvic tilt" when challenging the spine.
Issues of flexibility
The amount of emphasis on spine flexibility depends on
the person's injury history, exercise goal, etc. Generally,
for the back injured, spine flexibility should not be emphasized
until the spine has stabilized and has undergone
strength and endurance conditioning - some may never
reach this stage! Despite the notion held by some, there is
little quantitative data to support a major emphasis on
trunk flexibility to improve back health and lessen the risk
of injury. In fact some exercise programs that have included
loading of the torso throughout the range of motion
(in flexion-extension, lateral bend, or axial twist) have had
negative results (cf [18, 19]) and greater spine mobility has
been, in some cases, associated with low back trouble
(cf [20, 21]). Furthermore spine flexibility has been shown to
have little predictive value for future low back trouble. [20, 22]
The most successful programs appear to emphasize trunk
stabilization through exercise with a neutral spine (e.g. )
but emphasize mobility at the hips and knees (Bridger
et al.  demonstrate mobility advantages for sitting and
standing while McGill and Norman  outline advantages
Issues ofstrength and endurance
While it is well documented that those with previous back
injuries have lower muscle strength and endurance performance,
very few studies (longitudinal) have linked reduced
strength and endurance with the risk of a subsequent
first time low back injury. The few studies available suggest
that endurance has a much greater prophylactic value
than strength.  Furthermore, it would appear that emphasis
placed on endurance should precede specific strengthening
exercise in a gradual progressive exercise program
(i.e., longer duration, lower effort exercises).
The mounting evidence supporting the role of aerobic exercise
in both reducing the incidence of low back injury 
and also in the treatment of low back patients  is compelling.
Recent investigation into loads sustained by the low
back tissues during walking  confirm very low levels of
supporting passive tissue load coupled with mild, but prolonged,
activation of the supporting musculature. Epidemiological
evidence also sheds light on the effects of
aerobic exercise. A large study  examined age related
changes to the lumbar spines of elderly people as a function
of life long activity level, those who were runners had
no differences in spine changes measured from MRI
images while weight lifters and soccer players were
characterized with more disc degeneration and bulges.
The abdominals (anterior and lateral)
First, there is no single abdominal exercise that challenges
all of the abdominal musculature - requiring the prescription
of more than one single exercise. Calibrated intramuscular
and surface EMG evidence [12, 14] suggests that the
various types of curl-ups challenge mainly rectus abdominis
as psoas and abdominal wall (internal and external
oblique, transverse abdominis) activity is low. Situps (both
straight-leg and bent-knee) are characterized by higher
psoas activation and higher low back compression while
leg raises cause even higher activation and also spine compression
(the interested reader is directed to reference 
for actual data).
Several relevant observations were made regarding abdominal
exercises in our investigations. The challenge to
psoas is lowest during curl-ups, followed by higher levels
during the horizontal isometric side support, while bent
knee situps were characterized by larger psoas activation
than straight leg situps, through to the highest psoas activity
observed during leg raises and hand-on-knee flexor
isometric exertions. It is interesting to note that the "pressheels"
sit-up which has been hypothesized to activate
hamstrings and neurally inhibit psoas,  actually increased
psoas activation. Normalized electromyographic data in Table 1 is provided for comparative purposes. (We note
here that some clinicans intentionally wish to train psoas
and will find this data informative). One exercise not often
performed, but that appears to have merit is the horizontal
side support as it challenges the lateral obliques without
high lumbar compressive loading. 
In addition this exercise
produces high activation levels in quadratus lumborum
which appears to be a significant stabilizer of the
spine.  Graded activity in rectus abdominis and each of
the components of the abdominal wall changes with each
of these exercises demonstrating that there is no single best
task for the collective "abdominals". Clearly, curl-ups excel
at activating the rectus abdominis but produce relatively
lower oblique activity. A very wise choice for
abdominal exercises, in the early stages of training or rehabilitation,
would consist of several variations of curl-ups
for rectus abdominis and isometric horizontal side support
(or side bridge), with the body supported by the knees and
upper body supported by one elbow on the floor to challenge
the abdominal wall in a way that imposes minimal
compressive penalty to the spine. The level of challenge
with the isometric, horizontal side support can be increased
by supporting the body with the feet rather than the
Quadratus lumborum and spine stabilization
Several other clinically relevant findings from these two
data sets include notions that: psoas activation is really
determined by hip flexion demands and that psoas activity
is not consistent with either lumbar sagittal moment or
spine compression demands - we question the often cited
notion that psoas is a lumber spine stabilizer; quadratus
lumborum activity is consistent with lumbar sagittal moment
and compression demands suggesting a larger role in
stabilization; in fact when compression is applied to the
spine, in an upright posture with no bending moments,
quadratus lumborum is the muscle whose activation is
most closely related to the increasing need for stability
more than any other torso muscle;  and psoas activation is
relatively high (greater than 25% MVC) during pushups
suggesting cautious prescription of this exercise for the
low back injured. As noted in the previous section, the
horizontal side support appears to be a wise choice of exercise
for training quadratus lumborum for enhancing spine
The back extensors
Most traditional extensor exercises are characterized with
high spine loads which result from externally applied
compressive and shear forces (either from free weights or
resistance machines). We have been searching for methods
to activate the extensors with minimal spine loading. 
It appears that the single leg extension hold, while on the
hands and knees minimizes external loads on the spine but
produces spine extensor moment (and small isometric
twisting moments) which activates the extensors. Activation is sufficiently high on one side of the extensors to
facilitate training but the total spine load is reduced since
the contralateral extensors are producing lower forces
(lumbar compression is less than 2500N) (see Table 2).
Switching legs trains both sides of the extensors (one side
of lumbar approximately 18% of MVC).
extension with contralateral arm raise ("birddog") increases
the unilateral extensor muscle challenge (approximately
27% MVC in one side of lumbar extensors and
45% MVC in other side of thoracic extensors) but also
increases lumbar compression to well over 3000N. The
often performed exercise of laying prone on the floor and
raising the upper body and legs off the floor is contraindicated
for anyone at risk of low back injury - or re-injury. In
this task the lumbar region pays a high compression penalty
to a hyperextended spine (approximately 4000N)
which transfers load to the facets and crushes the interspinous
ligament (noted earlier as an injury mechanism).
Once again, these data are provided for the exercise professional
who must design programs for a wide range of
The beginner's program for stabilization
Specific recommended low back exercises have been
shown. We recommend that the program begin with the
flexion-extension cycles (Figure 4) to reduce spine viscosity,
followed by hip and knee mobility exercises. We have
found that 5-6 cycles is often sufficient to reduce most
viscous stresses. This is followed by anterior abdominal
exercises, in this case the curl-up with the hands under the
lumbar spine to preserve a neutral spine posture (Figure 5)
and one knee flexed but with the other leg straight to lock
the pelvis-lumbar spine. Then, lateral musculature exercises
are performed - namely isometric side support, or
side bridge, for quadratus lumborum and the obliques of
the abdominal wall for optimal stability (Figure 6). The
upper leg-foot is placed in front of the lower leg-foot to
facilitate longitudinal "rolling" of the torso to challenge
both anterior and posterior portions of the wall. The extensor
program consists of leg extensions and the "birddog" (Figure 7).
We have recently established "normal" ratios of endurance
times for the torso flexors relative to the extensors
(0.98) And for the lateral musculature relative to the extensors
(0.73)  to assist clinicians to identify endurance deficits.
Finally, as patients progress with these isometric
stabilization exercises, we recommend conscious simultaneous
contraction of the abdominals (hollowing - drawing
the navel towards the spine) to enhance motor control and
stability using the deeper abdominal wall (transverse
abdominis and internal oblique) after Richardson et al. 
Some general caveats
While there is a common belief among some "experts" that exercise sessions should be performed at least 3
times per week, it appears low back exercises have the
most beneficial effect when performed daily. 
The "no pain-no gain" axiom does not apply when exercising
the low back, scientific and clinical wisdom
would suggest the opposite is true.
While specific low back exercises have been rationalized
in this chapter, general exercise programs that also
combine cardiovascular components (like walking)
have been shown to be more effective in both rehabilitation
and for injury prevention.  The exercises shown
here only focus on the stabilization component of the
Diurnal variation in the fluid level of the intervertebral
discs (discs are more hydrated early in the morning after
rising from bed), changes the stresses on the disc
throughout the day. It would be very unwise to perform
full range spine motion while under load, shortly after
rising from bed (e.g. 17).
Low back exercises performed for maintenance of
health need not emphasize strength, with high-load low
repetition tasks, rather more repetitions of less demanding
exercises will assist in the enhancement of endurance
and strength. There is no doubt that back injury can
occur during seemingly low level demands (such as
picking up a pencil) and that the risk of injury from
motor control error can occur. While it appears that the
chance of motor control errors, resulting in inappropriate
muscle forces, increase with fatigue there is also
evidence documenting the changes in passive tissue
loading with fatiguing lifting.  Given that endurance
has more protective value than strength,  strength gains
should not be overemphasized at the expense of endurance.
There is no such thing as an ideal set of exercises for all
individuals. For the specific case of chiropractors who
wish to enhance spine stability following a manipulative
regimen, we recommend the "Big 3" described here (in
Figures 5, 6 and 7). In other situations, an individuals'
training objectives must be identified, (be they rehabilitation,
specifically to reduce the risk of injury, optimize
general health and fitness, or maximize athletic performance),
and the most appropriate exercises chosen.
While science cannot evaluate the optimal exercises for
each situation, the combination of science and clinical
experiential "wisdom" must be utilized to enhance low
Be patient and stick with the program. Increased function
and reduction pain may not occur for 3 months. 
The rehabilitation field is continuing to embrace techniques
that consider notions of stability. Past emphasis, in
some cases, was on issues such the production of torque,
enhancing range of motion etc. Fortunately, the laws of
physics, and techniques of engineering, are being recognized
by clinicians who can then ensure that first a system
must be stable before presented with a physical challenge.
Furthermore of particular importance to chiropractic, is
the need to consider the role of stabilizing exercise when
joint stability may be altered from treatment. We will continue
our work to understand the contributions to stability
of various components of the anatomy at particular joints -
and the ideal ways to enhance their contribution; to understand
what magnitudes of muscle activation are required to
achieve sufficient stability; to identify the best methods to
re-educate faulty motor control systems to both achieve
sufficient stability and reduce the risk of inappropriate
motor patters occurring in the future. Our challenge for the
future, as clinicians like yourselves and scientists like myself,
is to tackle in a collaborative and scientifically substantiated
way, the pain and mobility problems that are so
important for quality of life.
The author wishes to acknowledge the contributions of
several colleagues who have contributed to the collection
of works reported here: Daniel Juker, M.D., Craig Axler,
M.Sc., and Jack Callaghan, Ph.D. and in particular Professor
Jacek Cholewicki who I consider to be the premier
scientist in the world regarding the engineering analysis of
spine stability. Also the continual financial support from
the Natural Science and Engineering Research Council,
Canada has made this series of work possible.
Stability of the lumbar spine: A study in mechanical engineering.
Acta Orthop Scand 1989; 60:3-53.2
Biomechanics of low back injury: Implications on current practice and the clinic.
J Biomech 1997; 30:465-475.
Cholewicki J, McGill SM.
Lumbar posterior ligament involvement during extremely heavy lifts estimated from fluoroscopic measurements.
J Biomech 1992; 25(1): 17-28.
Low Back Exercises: Evidence for improving exercise regimens.
Physical Therapy, 78:754-765.
Cholewicki J, McGill SM.
Mechanical stability of the in vivo lumbar spine: Implications for injury and chronic low back pain.
Clin Biomech 1996; 11(1):1-15.
Cholewicki J, Panjabi MM, Khachatryan A.
Stabilizing function of trunk flexor-extensor muscles around a neutral spine posture.
Spine 1997; 22(19):2207-2212.
Luoto S, Heliovaara M, Hurri H, Alaranta M.
Static back endurance and the risk of low back pain.
Clin Biomech 1995; 10(6):323-324.
Low back exercises: Prescription for the healthy back and when recovering from injury.
In: Resource manual for guidelines for exercise testing and prescription,
American College of Sports Medicine. 3rd ed.
Baltimore, Williams and Wilkins, 1998.
McGill SM, Sharratt MT, Sequin JP.
Loads on spinal tissues during simultaneous lifting and ventilatory challenge.
Ergonomics 1995; 38:1772-1792.
Lucas D, Bresler B.
Stability of the ligamentous spine.
Technical Report number 40, Biomechanics Laboratory,
San Francisco, University of California.
Nitz AJ, Peck D.
Comparison of muscle spindle concentrations in large and small human epaxial muscles acting in parallel combinations.
The American Surgeon 1986; 12:273-277.
Juker D, McGill SM, Kropf P, Steffen T.
Quantitative intramuscular myoelectric activity of lumbar portions of psoas and the abdominal wall during a wide variety of
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Med Sci Sports Ex.
Callaghan JP, Gunning JL, McGill SM.
Relationship between lumbar spine load and muscle activity during extensor exercises.
Physical Therapy 1998, 78:8-18.
Axler CT, McGill SM.
Low back loads over a variety of abdominal exercises: Searching for the safest abdominal challenge.
Med Sci Sports and Exerc 1997; 29:804-811.
Santaguida L, McGill SM.
The psoas major muscle: a three dimensional mechanical modelling study with respect to the spine based on MRI measurement.
J Biomech 1995; 128(3):339-345.
The mechanics of torso flexion: situps and standing dynamic flexion manoeuvres.
Clinical Biomechanics 1995; 10(4):184-192.
Adams MA, Dolan P.
Recent advances in lumbar spine mechanics and their clinical significance.
Clin Biomech 1995; 10(1):3-19.
Malmivaara A, Hakkinen U, Aro T, Heinrichs M, Koskenniemi L, Kuosma E, Lappi S, Hernberg S.
The treatment of acute low back pain - bed rest, exercises, or ordinary activity?
N Eng J Med 1995; 332:35 1.
Newest knowledge of low back pain: a critical look.
Clin Orthop Rel Res 1992; 279:8-20.
Physical measurements as risk indicators for low back trouble over a one year period.
Spine 1884; 9:106-119.
Burton AK, Tillotson KM, Troup JDG.
Variation in lumbar sagittal mobility with low back trouble.
Spine 1989; 14(6):584-590.
Battie MC, Bigos SJ, Fischer LD, Spengler DM, Hansson TH, Nachemson AL, Wortley MD.
The role of spinal flexibility in back pain complaints within industry: a prospective study.
Spine 1990; 15(8):768-773.
Saal JA, Saal JS.
Nonoperative treatment of herniated lumbar intervertebral disc with radiculopathy: An Outcome Study.
Journal Missing 1989; 14(4):431-437.
Bridger RS, Orkin-D, Henneberg M.
A quantitative investigation of lumbar and pelvic postures in standing and sitting: interrelationships with body position and hip muscle length.
Int J Ind Ergonomics 1992; 9:235-244.
McGill SM, Norman RW.
Partitioning of the L4/L5 dynamic moment into disc, ligamentous, and muscular components during lifting.
Spine 1986; 11:666-667.
Cady LD, Bischoff DP, O'Connel ER, Thomas PC, Allan JH.
Strength and fitness and subsequent back injuries in firefighters.
J Occup Med 1979; 21(4):269-272.
Aerobic exercise in the treatment and prevention of low back pain.
State Art Rev Occup Med 1988; 3:137-145.
Callaghan JP, Patla A, McGill SM.
Low back three dimensional joint forces, kinematics and kinetics during walking.
Clin Biomech. 1999; in press.
Videman T, Sarna S, Crites-Battie M, Koskinen S, Gill K, Paananen H, Gibbons L.
The long term effects of physical loading and exercise lifestyles on back-related symptoms, disability, and spinal pathology among men.
Spine 1995; 20(b):669-709.
Kraft-Theorie und praxis.
1990. Thieme, Stuttgardt.
McGill SM, Juker D, Kropf P.
Quantitative intramuscular myoelectric activity of quadratus lumborum during a wide variety of tasks.
Clin Biomech 1996; 11(3):170-172.
McGill SM, Childs A, Leibenson C.
Endurance times for stabilization exercises: clinical targets for testing and training from a normal database.
Arch Phys Med Rehab 1999.
Richardson C, Jull G, Toppenberg R, Comerford M.
Techniques for active lumbar stabilization for spinal protection: a pilot study
Australian Physiotherapy; 38(2): 105-112.
Mayer TG, Gatchel RJ, Kishino N, Keeley J, Capra P, Mayer H, Barnett J, Mooney V.
Objective assessment of spine function following industrial injury: a prospective study with comparison group and one-year follow up.
Spine 1985; 10(6):482-493.
Potvin JR, Norman RW. Can fatigue compromise lifting safety?
Proc. NACOB II, The Second North American Congress on Biomechanics, 1992;
August 24-28, pp.513-514.
Manniche C, Hesselsoe G, Bentzen L, Christensen I, Lundberg E.
Clinical trial of intensive muscle training for chronic low back pain.
Lancet 1988; Dec. 24-31, pp.1473-1476.
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