paper discusses research findings relating of the use of the
machine that provides isolated, specific exercise and testing
for the muscles that extend the lumbar spine (lumbar extension
). The function of the machine is explained, and its reliability
and validity examined. The effects of various lumbar extension
training protocols on lumbar strength and low back pain are then
explored, and practical implications and future research
directions discussed. We conclude that that the lumbar extension
machine provides reliable and accurate measures of lumbar
extension strength and can produce very large increases in low
back strength in a relatively short time period. Perhaps more
importantly given the huge costs of low back problems, it is a
very effective tool for preventing or eliminating low back pain
in most chronic patients.
costs of LBP to Western industrialised societies are enormous.
For example, the estimated direct health care costs of lower
back pain in the
in 1998 totalled 1632 million pounds1. The direct cost of back
pain is insignificant compared to the cost of informal care and
the production losses related to it, which according to
Maniadakis and Gray1 totals 10668 million pounds. In addition,
Aylward and Sawney2 state that in the UK up to 50 million
working days are lost each year and up to half a million people
receive a long term state incapacity benefit because of back
pain. In addition to the impact on individuals and their
families back pain is estimated to cost the
economy up to 5 billion pounds a year.
there are many causes of LBP, it has been claimed that these are
often related to weakness of the muscles that extend the lumbar
spine3-5. Therefore, resistance training is often
prescribed for the prevention and treatment of LBP6,7. Clearly,
the importance of lumbar strength to lower back health
necessitates a reliable and valid measure of the strength of
these muscles, as well as an effective way of increasing their
strength. In 1986, a machine was developed to perform both
functions, the lumbar extension machine (MedX,
). Much research has been conducted with this machine, producing
some very interesting findings and implications for strength
testing, training and rehabilitation. Though this research has
been published in a wide variety of scientific journals, the
practices of many doctors and physiotherapists we have observed
suggest to us that they are unaware of these important findings.
Given this, and given that there has never before been a
systematic review of this line of research, our aim was to bring
all these findings together to present an overview of the
functions of the machine and relevant findings in peer-reviewed
journals, with practical implications and suggestions for future
research. Firstly, the function of the lumbar extension machine
will be described, and its validity and reliability will be
explored. Research examining the effect of lumbar extension
training on muscle strength, low back pain and other outcomes
will be examined, and practical implications discussed. Finally,
possible future research directions with this tool will be
explored. Please note that when we use the terms ‘lumbar
extension training’, ‘lumbar extension exercise’ or
‘lumbar extension machine’, these all relate specifically to
the machine mentioned above that is the subject of this review,
and not to any other ‘lower back’ machine or training
method, unless otherwise stated.
strategy and selection criteria
literature search strategy used recognised academic search
engines such as Science Direct, Sports Discus, Pubmed, Ingenta
and Taylor and Francis online journals. The additional search
engines used included journal websites (e.g., Journal of
Strength & Conditioning Research and Spine). Also, searches
were conducted of the reference lists of all the articles read,
and internet searches were also performed through Google and
Google Scholar. To be included in the review, studies had to be
peer-reviewed and published within the last 35 years, and had to
use appropriate statistical analysis (i.e. purely qualitative
studies were not included).
machine was developed to enable specific exercise and testing of
the muscles that extend the lumbar spine. To achieve these
aims, it is essential to stabilise the pelvis so that the
muscles that cause backward rotation of the pelvis (i.e. the
gluteal and hamstring muscles) cannot contribute. These muscles
enable the trunk to extend through a range of motion (ROM) of
approximately 180°, in contrast to the lumbar extensor muscles
that have a range of motion of only 72°5. The gluteal and
hamstring muscles are much larger than the lumbar extensors and
have a longer moment arm8, and therefore will contribute much
greater force to trunk extension movements.
of the most important aspects of this machine, therefore, is its
pelvic restraint system. This prevents movement of the pelvis
using the femurs. A thigh restraint is placed over the thighs
and tightened to prevent vertical movement of the pelvis or
thighs. A knee restraint is placed above and behind the patella.
The thigh restraint acts as a fulcrum redirecting the upwards
force on the knees downwards at the pelvis. This downwards force
locks the pelvis into position, preventing backward pelvic
rotation. When the muscles of the buttocks and hamstrings
contract, this pushes the pelvis against the pelvic restraint
pad. This pad is free to rotate on its own axis. If the patient
is correctly restrained, when he or she moves from flexion to
extension the restraint pad should not rotate. If it does, then
the pelvis is rotating backwards.
neutralize the effects of gravity acting upon the head and
torso, the center-line of the torso mass of the patient is
established, and a counterweight is connected to the resistance
arm of the machine so that it is 180° out of phase with the
patient’s center-line. This is important because in the flexed
position of a lumbar extension movement, the patient must lift
his or her torso weight, whereas in the extended position torso
weight assists the patient. If this influence is not corrected
for, torque readings will be produced that are too low in the
flexed position and too high in the extended position. The
movement arm of the machine is attached to a load cell
interfaced to a computer.
that some individuals may have weaknesses at specific points in
a muscle’s range of motion, it is important to be able to
measure strength through a full range of motion. Due to
acceleration and deceleration occurring at the beginning and end
of a movement, dynamic tests cannot measure strength through a
full ROM9. Also, impact forces and kinetic forces can be
recorded (incorrectly) as torque, giving an inaccurate measure
of muscular strength10,11. In contrast, isometric strength tests
can measure strength through a full ROM if multiple joint angles
are tested4. Therefore, the lumbar extension machine uses an
isometric testing method. Testing can be conducted at 3°
intervals throughout a full range of lumbar extensor motion, but
it is most common to test at intervals of 6°.
well as testing lumbar strength, the machine is also used for
dynamic exercise of the lumbar muscles (lifting and lowering a
selected level of weight stack resistance). The use of a cam
ensures that the resistance varies in line with changes in
strength that occur throughout the range of motion12.
validity of the pelvic restraint system used in the machine has
been established by several studies. One study using radiography
showed that when participants were properly restrained in the
machine, backward rotation of the pelvis was less than 3°13.
Also, Graves et al.14, in comparing the effects of training on
the lumbar extension machine with training on commercially
available lower back machines that do not stabilise the pelvis
(Nautilus, Cybex), found that the no-stabilization groups did
not increase their lumbar extension strength, whereas the former
group enhanced their strength significantly at all joint angles.
Therefore, the pelvic restraint system is effective in achieving
the necessary isolation of the lumbar extensors.
same research group also found that the test-retest reliability
was very high at all angles (r = .94-.98; 4). Interestingly,
this and other studies7,15 have found that lumbar extension
strength is greatest at full flexion, in contrast with studies
using other methods of lumbar extension strength measurement,
which have tended to find that it decreases towards this
position16,17. This is probably because of a lack of correction
for the effects of gravity in these studies. As the lumbar spine
moves towards full flexion, the effect of gravity acting upon
the torso mass becomes greater, and this will reduce observed
torque values. This emphasises the importance of valid gravity
correction procedures when testing the strength, not only of the
lumbar spine, but of all muscle groups where gravity exerts an
effect. To test the validity of the counterweighting procedure,
a lateral version of the lumbar extension machine, which enables
testing in the transverse plane, was constructed. Testing
strength in this position removes the effects of gravity, and
Pollock et al.18 found that the isometric torque values in the
sagittal plane with upper body mass counterweighted were
identical to those recorded in the transverse plane without
counterweighting. These data, therefore, strongly support the
effectiveness of the counterweighting procedure.
of specific and non-specific lumbar extension exercise on lumbar
is well-established that pelvic stabilization is necessary to
achieve optimal recruitment of lumbar extensor muscles during
lumbar extensor exercise. This has been shown with both
dynamic19 and isometric20 exercise modalities. In addition,
traditional trunk extension exercises that do not stabilise the
pelvis have been shown to produce low levels of
electromyographic (EMG) activity in the lumbar extensor
muscles21. Therefore, these authors suggested that healthy
people would not receive a significant strengthening effect from
such exercises. This view was confirmed by Mayer et al.22, who
found that roman chair exercises, which do not stabilize the
pelvis, did not increase lumbar extension strength. In addition,
Daneels et al.23 found that traditional lumbar stabilization
exercises were insufficient to significantly challenge the
multifidi muscles. In an interesting case study, Johnston24
found that a participant who had had his lumbar strength
measured in 1995, had lost an average of 42% of this strength
when measured 10 years later, despite regularly performing heavy
deadlifts, squats, bent-over rows and other exercises that load
the lumbar spine. This strongly suggests that specific, isolated
exercise for the lumbar spine is needed to maintain and increase
lumbar extension strength. This is also clearly shown by the
Graves et al. study described in the previous section14, where
groups that trained on “lower back” machines that do not
stabilize the pelvis did not increase their lumbar extension
strength, in contrast to a group who trained on the lumbar
extension machine. Interestingly, although training without
pelvic stabilization did not increase torque production of the
lumbar extensors, dynamic trunk extension strength did increase,
presumably due to an increase in strength of the muscles that
derotate the pelvis, i.e. the gluteal and hamstring muscles.
only evidence to date that challenges the view that such pelvic
stabilisation is necessary to effectively exercise the lower
back was provided by Walsworth25, who compared the use of the
MedX lumbar extension with the Cybex dynamic
variable resistance trunk extension machine in healthy
electromyographic activity was recorded bilaterally from the
L3-4 paraspinal region during trunk extension exercises. In
contrast to the studies mentioned above, their results showed no
significant differences between lumbar paraspinal
electromyographic activity during trunk extension on the MedX
compared to the Cybex dynamic variable resistance trunk
extension machine. However, the effect of the two machines on
lumbar extension strength was not compared, and the low
participant numbers in the Walsworth study (n =13) suggest that
the statistical power may have been too low to achieve
statistically significant differences anyway. These issues
should also be taken into account when interpreting these
findings, and we conclude that, overall, the evidence strongly
suggests that the pelvic stabilisation provided by the lumbar
extension machine is necessary to provide effective exercise for
the lumbar extensor muscles.
The necessity of stabilizing the pelvis to provide meaningful
exercise for the lumbar extensors may partially explain the
large strength increases that can be achieved from isolated
lumbar extension training in a relatively short period of time.
et al.5, Carpenter et al.12 and Pollock et al.15 have all shown
increases in isometric lumbar extension strength of more than
100% in the fully flexed position from one set of 8-12
repetitions of lumbar extension exercise performed to volitional
fatigue once per week for 10-12 weeks. Strength increases in the
extended position tend to be lower, with average increases in
peak torque of 37 to 41% found by
et al.26 from 12 weeks of lumbar extension training. This
compares favourably with the typical strength increases of
between 20 and 30% reported by Fleck and Kraemer27 for
resistance training programs of 10-12 weeks. Graves et al.5 and
Pollock et al.15 speculated that this may be due to the lumbar
extensors initially being very weak. As the lumbar extensors are
not isolated during normal daily activities, they receive no
exercise effect from such activities, and therefore exist in a
state of chronic disuse atrophy in those who do not perform
isolated lumbar extension exercise.
et al.5 compared training frequencies of 1x/week, 2x/week,
3x/week and 1x/2weeks, with each group performing one set of
dynamic lumbar extension exercise to volitional fatigue during
each exercise session for 12 weeks. All groups significantly
increased isometric strength, with no significant between-group
differences, but dynamic training weight increased less in the
1x/2weeks group than in the other group. Therefore, optimal
training responses can be elicited with as little as one
exercise session per week. Interestingly, the 3x/week subjects
complained of chronic fatigue, and one of the subjects in this
group became progressively weaker. In addition, individuals who
trained more than 1x/week experienced orthopaedic discomfort.
Therefore, frequent high-intensity training of the lumbar
extensors (>1x/week) is contraindicated for some individuals,
and a training frequency of once per week is generally
recommended. This is supported by the findings of Carpenter et
al.12, who also found no significant differences in lumbar
extension strength increases between groups training at
frequencies of 1x/week, 2x/week, 3x/week and 1x/2 for 12 and 20
weeks. Once lumbar extension strength has been built up by
regular training, the increases in strength can be maintained by
performing a reduced frequency of training. This is shown by the
findings of Tucci et al.28 who observed significant increases in
lumbar extension strength following 10 or 12 weeks training when
using single-set training. Tucci et al. also observed that this
increase in strength can be maintained for an additional 12
weeks by reducing the training frequency to either once every 2
weeks or once every 4 weeks, compared to a 55 % reduction in
lumbar strength in subjects who stopped training altogether.
of specific lumbar extension exercise on low-back pain and other
the high prevalence and costs of LBP, the question naturally
arises as to the effectiveness of the lumbar extension machine
in helping to reduce this problem. A wealth of evidence suggests
that muscle weakness contributes significantly to LBP. For
example, Kader et al.29 found multifidus atrophy in 80% of LBP
patients, and Daneels et al.30 found multifidus weakness and
atrophy is related to LBP. Sinaki et al.31 found a significant
negative relationship between lumbar extension strength,
thoracic kyphosis and the number of vertebral fractures in
osteoporotic patients. Also, individuals with high muscular
strength and endurance are less likely to suffer back
problems32. Therefore, logically we would expect that the lumbar
extension machine could be a valuable ally in the fight against
LBP, and in fact many studies show that this is the case.
the most dramatic example of the efficacy of specific lumbar
extension exercise as a tool to prevent low-back injury was a
study by Mooney et al.33. After using a lumbar extension machine
for six months at a strip mine that had been plagued by low-back
injuries in its employees and as a consequence was in danger of
going out of business, injuries dropped from 2.94 per 200,000
employee hours to .52. Also, the average workers compensation
liability decreased from $14,430 per month to $380 per month.
well as being an effective tool for prevention of low-back
injuries, lumbar extension exercise also appears effective in
aiding the rehabilitation of patients with low-back problems.
For example, Leggett et al.34 conducted a study at two clinics
, finding that one year after completion of an exercise-only
(lumbar extension) treatment for LBP, only 12% of patients
needed to re-enter the health care system for treatment of
spinal problems. In a similar vein, Dolan et al.35 found that
just 4 weeks of post-operative lumbar extension training reduced
lumbar pain and disability, and improved spinal function of LBP
patients. Holmes et al.36 found that geriatric women with
symptoms of LBP had significant reductions in pain after regular
lumbar extension exercise. More recently, Choi et al.37
administered a 12-week post-operative lumbar extension training
programme to patients who had suffered a herniated disc.
Following the training, patients increased lumbar extension
strength, muscle mass in the longissimus and multifidus, and
decreased their pain scores on a visual analog scale. Most
impressively, 87% of exercising participants returned to work
following the 12-week period compared to only 24% of controls.
Similar findings were reported by Risch et al.38 who found that
a 10-week program of lumbar extension exercise significantly
reduced pain and improved psychosocial function in chronic LBP
largest study to date of the effects of specific lumbar
extension exercise on LBP was conducted by Nelson et al.7 on 895
patients, with a 1-year follow-up. Patients had tried an average
of 6 other treatments prior to participation, and 89% of them
had failed a supervised exercise program. Treatment was
continued until the patient was pain-free or was not making any
additional gains in spinal function. 76% of patients rated their
results as “good or “excellent”, and for 70% these were
lasting at follow-up. Given that almost all the patients had
previously tried more ‘low-tech’ exercise solutions (home
exercise or use of health clubs) and that these had universally
failed, this study clearly demonstrates that the use of home
exercise or health club equipment that does not stabilize the
pelvis is of little or no use in alleviating chronic LBP.
Therefore, though the equipment required for intensive, specific
exercise of the lumbar spine is relatively expensive, this must
be set against the huge costs to industry and the healthcare
system of having large numbers of people who are unable to work
effectively due to chronic LBP and who require long-term
healthcare as a result. Nelson et al. concluded that aggressive,
exercise is valuable and cost-effective in treating LBP.
further study by Nelson and colleagues39 examined whether spinal
surgery could be prevented by lumbar or cervical extension
exercise. Out of 46 patients who were initially recommended for
surgery and completed the program, only 3 required surgery upon
completion. Therefore, lumbar extension exercise can greatly
reduce the need for costly and dangerous spinal surgery.
In a randomised controlled study examining the effect of
resistance training on bone mineral density (BMD) in heart
transplant recipients40, Braith et al. compared a resistance
training group, who performed lumbar extension once per week and
other variable resistance exercises (Nautilus) twice per week
for six months, with a control group. BMD was measured by dual
X-ray absorbiometry prior to heart transplantation, two months
post-transplantation and after three and six months of
resistance training. BMD did not differ between groups prior to
transplantation, and two months post-transplantation it had
decreased significantly in both groups. After the six months of
resistance training, BMD in the total body, femur neck and
lumbar spine (L2 to L3) had increased significantly to within
1%, 1.9% and 3.6% of pre-transplantation levels respectively,
whereas the control group did not improve. Therefore, resistance
training can increase BMD, and of particular interest to this
paper, resistance training that includes lumbar extension
exercise can significantly increase BMD in the lumbar spine.
Therefore, lumbar extension training may be very beneficial for
patients suffering from conditions where bone mineral density
tends to decline, such as heart transplantation patients and
osteoporotic patients. Research, however, is clearly needed with
this latter group to test this hypothesis.
of research findings.
extension research has produced many interesting findings of
great importance to doctors, physiotherapists, exercise
physiologists and others. Possibly the most important of these
is that specific, isolated exercise is necessary to enhance
lumbar extension strength. When the pelvis is free to move, it
is impossible to meaningfully exercise the lumbar spine.
Therefore, most commercially available “low-back” machines,
which do not isolate the lumbar extensors, are worthless for
their intended purpose; they can increase the strength of the
gluteal and hamstring muscles but cannot improve lumbar
function. Specific, isolated exercise, on the other hand, can
increase lumbar extension strength to a large degree in a
relatively short space of time. The lumbar extension machine is
unique in its ability to isolate the lumbar extensors through
pelvic stabilization. In addition, this strengthening can also
greatly reduce LBP, protect people from the risk of future
low-back injury, increase bone mineral density and even
eliminate the need for spinal surgery in the vast majority of
patients. Therefore, we contend that isolated lumbar extension
exercise should be tried as a matter of course for prevention
and treatment of LBP, and should always be tried prior to spinal
surgery. It is particularly interesting that almost all the
participants in the LBP studies cited above had tried various
other treatments prior to isolated lumbar extension exercise,
including various home- and health-club based exercise programs,
and none of these treatments had proved successful. We concur
with Carpenter and Nelson41 that the tendency among many
clinicians to prescribe gentle, calisthenic-type exercises is
unfortunate, given that they lack the requirements to produce
adaptive responses in atrophied tissue and also do not exercise
the low back muscles. They note that athletes do not improve
their condition by merely lying on the floor and moving their
limbs about, and neither do chronic LBP patients. It is
important for clinicians and exercise physiologists not to view
all exercise therapy programs for the lower back as equal;
isolated lumbar extension exercise appears far more effective
than any other type of exercise in tacking low-back problems.
Even traditional low-back exercises such as deadlifts and roman
chair exercises are not effective in enhancing low back
strength. Strength and conditioning professionals, therefore,
need to ensure that specific, isolated exercise for the lumbar
extensors is included in athletes’ training to increase lumbar
strength and guard against low back problems; traditional
weight-lifting exercises will not be an effective substitute.
conclusion, the lumbar extension machine provides not only a
valid and reliable mean of quantifying low-back strength, but
also provides a very effective means of strengthening the
low-back muscles, and preventing and treating most cases of
chronic LBP. In our view, it is unfortunate that most therapists
appear to eschew such treatment in favour of passive and
non-specific active treatment modalities, which may provide
short-term relief from LBP but are unlikely to be effective in
dealing with chronic LBP.
people have questioned the need for expensive, computerised
testing equipment for lumbar spine rehabilitation, believing
that the costs are not justified, and that low-cost exercise
with low-tech equipment or home exercise programmes is
preferable. However, the enormous costs to taxpayers and
employers from LBP must be set against the relatively small
costs of such equipment. Given that roughly 80% of chronic LBP
patients respond well to isolated lumbar extension exercise,
decreasing their reutilisation of the health care system and
increasing the likelihood of their return to gainful employment,
then such treatment appears very cost effective. We agree with
Nelson et al.7, who note that whether the expense is
considered justified depends upon the values placed by society
on the treatment of chronic LBP. Do we believe that this is a
problem worth dealing with, knowing that there is strong
scientific evidence that a high-tech exercise solution to most
cases of LBP exists, or do we prefer to carry on as at present,
with most LBP treatments currently used providing short term
relief from pain at best, while the healthcare costs of chronic
LBP continue to escalate? This is the key question that
government and employers should be asking themselves with regard
it is important to note that there are still many interesting
questions that remain unanswered. For example, direct
comparisons of lumbar extension exercise with other forms of
treatment for LBP would be useful. Also, no research has yet
examined the effect of lumbar extension exercise on low-back
problems in children. The issue of detection of malingering is
also of interest; research examining the effectiveness of the
lumbar extension machine in this regard would be of great help
to employers and healthcare providers seeking to distinguish
between genuine and faked low-back problems. Also, an
exercise-only version of the lumbar extension machine (MedX,
) is now available, but there are no data available on the
effectiveness of this machine in enhancing lumbar extension
strength and treating low-back problems. Such data would be very
useful for those interested in using the exercise-only machine
for any purpose.
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