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Twenty Years Of Specific, Isolated Lumbar Extension Research: A Review

 Dave Smith *, Stewart Bruce-Low **,  Gary Bissell #

* Manchester Metropolitan University , UK
** Southampton Solent University , UK
# ProPhysio UK .

Address for Correspondence:  

Dave Smith, Ph.D.
Department of Exercise and Sport Science
Manchester Metropolitan University
Stoke-on-Trent ST7 2HL, UK
Tel. 44 1270 883067


This 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 machine, MedX, Ocala , FL ). 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.

J.Orthopaedics 2008;5(1)e14


The costs of LBP to Western industrialised societies are enormous. For example, the estimated direct health care costs of lower back pain in the UK 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 UK economy up to 5 billion pounds a year.

Though 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, Ocala , FL ). 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.   

Search strategy and selection criteria

The 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).           

Lumbar extension machine

This 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.

One 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.

To 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.

Given 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°.

As 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 and reliability

The 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.

The 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.      

Effect of specific and non-specific lumbar extension exercise on lumbar strength

It 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.

The 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 subjects. Surface 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. For example, Graves 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 Graves 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.

Training frequency

Graves 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.  

Effect of specific lumbar extension exercise on low-back pain and other clinical outcomes

Given 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.

Possibly 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.   

As 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 in the US , 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 patients.

The 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.

A 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.  

Implications of research findings.

Lumbar 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.


In 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.

Some 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 to LBP.

Finally, 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, Ocala , FL ) 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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This is a peer reviewed paper 

Please cite as : Dave Smith : Twenty Years Of Specific, Isolated Lumbar Extension Research: A Review  

J.Orthopaedics 2008;5(1)e14





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