BackCare

Testing and training the muscles that extend the lumbar spine

2010 Author: Dave Smith, Stewart Bruce Low and Gary Bissell

A review of lumbar extension research. The three authors summarised research to date examining the usefulness of a machine designed to measure the strength of the lumbar extensor muscles.

Testing and training the muscles that extend the lumbar spine:

In this article, the three authors summarise research to date examining the usefulness of a machine designed to measure the strength of the lumbar extensor muscles, and to train these muscles. They examine its validity and reliability, its effect on lumbar strength and on prevention and rehabilitation of low back pain (LBP). They also give a brief overview of their own work with this machine and conclude by offering suggestions for future research.

Introduction
During the past several years we have been involved in a research project examining the effects of isolated lumbar extension exercise on lumbar strength and LBP

The lumbar extension machine (MedX, Orlando, FL) was developed specifically to exercise and test the muscles that extend the lumbar spine, and since its development in 1986, much research using this equipment has been published in various scientific journals.

However, in our discussions with physiotherapists and others involved in back care, it has been made clear that many involved in this field are unaware of this programme of research. Given that the findings to date have important implications for evaluation of lumbar strength, strength training of the lumbar extensors and rehabilitation of chronic LBP, we present a brief overview of the key literature on this topic (we refer interested readers to Smith, Bruce-Low and Bissell' for a much more detailed analysis), concluding with an explanation of our own recent work and future research directions.

Lumbar extension machine
The 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. 

The gluteal and hamstring muscles are much larger than the lumbar extensors and have a longer moment arm,2 and therefore will contribute much greater force to trunk extension movements. Therefore, in the machine a pelvic restraint system prevents movement of the pelvis using the femurs.

To neutralize the effects of gravity acting upon the head and torso, the centre-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 centre-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.

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 ROM.3 Also, impact forces and kinetic forces can be recorded (incorrectly) as torque, giving an inaccurate measure of muscular strength.4. 5

In contrast, isometric strength tests can measure strength through a full ROM if multiple joint angles are tested.6 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.

 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 motion.7

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°8 Also, Graves et al.,9 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. Testtretest reliability of the machine is very high at all angles (r = .94-.986), and data also support the validity of the gravity correction procedures.10

Effects of lumbar extension training on strength
When exercised in this manner, the lumbar extensors in most participants are capable of rapid and large increases in lumbar strength. For example, Graves et aI., 11 Carpenter et al. 7 and Pollock et al. 12 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.13 from 12 weeks of lumbar extension training. This compares favourably with the typical strength increases of between 20 and 30% reported by Fleck and Kraemer14 for resistance training programs of 10-12 weeks. Graves et al. 11 and Pollock et al. 12 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 little exercise effect from such activities. 

Amount of training required
Optimal training responses in these muscles can usually be elicited through one exercise session per week, consisting of one set of dynamic exercise to volitional fatigue. More frequent or higher volume training does not produce greater effects and can produce orthopaedic discomfort.7,11

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 (once every 2 or 4 weeks15).

Effect on low-back pain and other clinical outcomes
Though the above findings may be interesting, ultimately most readers will be more interested in potential uses in prevention and rehabilitation of LBP. A wealth of evidence suggests that muscle weakness contributes significantly to LBP.16.17,18 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. 19 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.

Lumbar extension exercise also appears effective in aiding the rehabilitation of patients with low-back problems. For example, Leggett et al.20 conducted a study at two clinics in the US, finding that one year after completion of an exercisee 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.21 found that just four weeks of post-operative lumbar extension training reduced lumbar pain and disability, and improved spinal function of LBP patients. Holmes et al.22 found that geriatric women with symptoms of LBP had significant reductions in pain after regular lumbar extension exercise. More recently, Choi et al.23 administered a 12-week post toperative 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.24 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.25 on 895 patients, with a one-year follow-up. Patients had tried an average of six 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.

Nelson et al.25 concluded that aggressive, exercise is valuable and cost-effective in treating LBP. A further study by Nelson and colleagues26 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.

Finally, in a randomised controlled trial Braith et al. 27 found that lumbar extension training significantly increased bone mineral density in heart transplant patients.

Our recent research
Our recent work has focused on the use of lumbar extension training in low back rehabilitation, particularly focusing on how best to perform such training to optimise clinical outcomes.

Our first study, which we presented at the Society for Back Pain Research in 2008, confirmed the importance of pelvic stabilisation when attempting to increase lumbar strength and decrease self reported LBP. A group of chronic LBP patients that performed fully restrained lumbar extension training increased their lumbar strength and decreased in LBP following a 12-week training programme, but a group that performed an identical training programme but whose pelvises were not restrained did not increase their strength or decrease their LBP ratings.

Our most recent study, kindly funded by BackCare, is examining the effects of an additional weekly light, 'mobilisation' session on the machine in chronic LBP patients. We are almost ready to report our findings and, once again, these appear very interesting so far and we believe will be of interest to all those involved in spinal rehabilitation.

Conclusions
The lumbar extension machine provides a valid and reliable mean of quantifying low-back strength, an effective means of strengthening the low-back muscles, and preventing and treating many cases of chronic LBP.

There are still many interesting questions that remain unanswered. For example, comparisons of lumbar extension exercise with other forms of treatment for LBP would be very valuable. Also, no research has yet examined the effect of lumbar extension exercise on low-back problems in children.

Finally, a 'lower-tech' exercise-only version of the lumbar extension machine (MedX, Orlando, FL) is now available, but there is 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 this machine. We hope that this article may stimulate some of this future work, ultimately to aid those suffering from debilitating lower back problems. 

References

(1) Smith D, Bruce-Low S, Bissell G. Twenty Years Of Specific, Isolated Lumbar Extension Research: A Review. J.Orthopaedlcs 2008; 5(1)e14

(2) Farfan HF. Muscular mechanism of the lumbar spine and the position of power and efficiency. Orthopedic Clinics of North America 1975; 6:135-44.

(3) Mayhew & Rothstein. Measurement of muscle periormance with instruments. In Rothstein J (ed.), Measurement In physical (4)therapy, 1985. New York: Churchill Livingstone.

(4) Bemben MG, Grump KJ, Massey BH, Assessment of technical accuracy of the Cybex II isokinetic dynamometer and analog recording system. J Orthopedic and Sports Physical Therapy 1988; 10: 12-17.

(5) Murray, D. Optimal filtering of constant velocity torque data. Medicine and Science in Sports and Exercise 1986; 18, 603-611

(6) Graves JE, Pollock ML, Jones AE, Colvin AS, Leggett SH. Specificity of limited range of motion variable resistance training. Medicine and Science in Sports and Exercise 1989; 21: 84-89.

(7) Carpenter DM, Graves JE, Pollock ML, Leggett SJ. Foster D, Holmes S, Fulton MN. Effect of 12 and 20 weeks of resistance training on lumbar extension torque production. Physical Therapy 1991; 71 :580-588.

(8) Inanami H. Iwai Orthopedic Hospital rehabilitation pr09ram. Paper presented at the International Spinal Rehabilitation Update 1991 Symposium. Daytona: Sept 12-14, 1991.

(9) Graves J, Webb 0, Pollock ML, Matkozich J, Le9gett SH, Carpenter OM, Foster ON, Cirulli J. Pelvic stabilization durin9 resistance training: its effect on the development of lumbar extension strength. Archives of Physical Medicine and Rehabilitation 1994' 75: 210-215

(10) Pollock ML, Graves JE, Leggett SH et al. Accuracy of counter weighting to account for upper body mass in testing lumbar extension strength. Medicine and Science in Sports and Exercise 1 991 ; 23: S66.

(11) Graves JE, Pollock ML, Foster D, Leggett SH, Carpenter DM, Vuoso R, Jones A Effect of training frequency and specificity on isometric lumbar extension strength. Spine 1990; 15:5044509.

(12) Pollock ML, Leggett SH, Graves JE, Jones A, Fulton M, Cirulli J. Effect of resistance training on lumbar extension strength. American Journal of Sports Medicine 1989; 17:624-629.

(13) Graves JE, Fix CK, Pollock ML, Leggett SH, Foster ON, Carpenter OM. Comparison of two restraint systems for pelvic stabilization during isometric lumbar extension strength testing. J Orthopedic and Sports Physical Therapy 1992; 15: 37-42.

(14) Fleck SJ, Kraemer WJ. Designing resistance training programs (2nd edition), Champaign, IL: Human Kinetics, 1997.

(15) Tucci JT, Carpenter DM, Pollock ML, Graves JE, Leggett SH. Effect of reduced frequency at training and detraining on lumbar extension strength. Spine 1992; 17:1497-1501.

(16) Kader OF, Wardlow 0, Smith FW. Correlation between changes in the lumbar multifidus muscles and leg pain. Clinical Radiology 2000; 55: 145-149.

(17) Daneels LA, Coorevits PA, Cools AM, Vanderstraeten GG, Cambier DC, Witwrouw EE De CH. Differences in electromyographic activity in the multifidus muscle and the iliocostalis lumborum between healthy subjects and patients with acute and chronic low back pain. European Spine Journal 2002; 11: 13-19.

(18) Sinaki M, Itoi E; Rogers J; Bergstralh, EJ; Wahner, HW Correlation of back extensor strength with thoracic kyphosis and lumbar lordosis in oestrogenndeficient women. American Journal of Physical Medicine and Rehabilitation 1996; 75: 370-374.

(19) Mooney V, Kron M, Rurnrnerfield P, Holrnes B. The effect of workplace based strengthening on low back injury rates: a case study in the strip mining industry. Journal of Occupational Rehabilitation 1995; 5: 157-167.

(20) Leggett S, Mooney V, Matheson LN, Nelson B, Creisinger T, Van Zytveld, Vie L. Restorative exercise for clinical low back pain: a prospective two-centre study with 1-year follow-up. Spine 1999; 24: 889-898.

(21) Dolan P, Greenfield K, Nelson RJ, Nelson IW Can exercise therapy improve the outcome of microdisectomy? Spine 2000; 15: 1523-1532.

(22) Holmes S, Mooney V, Negri S, Leggett S, Nichols J, Hoeyberghs A. Comparison of female geriatric lumbar extension strength. Journal of Spinal Disorders 1996; 9: 106-15.

(23) Choi G, Raiturker PP, Kim MJ, Chung OJ, Chae YS, Lee SH. The effect of early isolated lumbar extension exercise program for patients with herniated disc undergoing lurnbar discectorny. Neurosurgery. 2005 Oct; 57(4):764-72; discussion 764-72.

(24) Risch SV, Norvell NK, Pollock ML, Risch ED, Langer H, Fulton M et al. Lurnbar strengthening In chronic low back pain patients. Spine 1993; 18:232-238.

(25) Nelson BW, O'Reilly E, Miller M, Hogan M, Wegner JA, Kelly C. The clinical effects of intensive, specific exercise on chronic low back pain: a controlled study of 895 consecutive patients with 1-year follow up. Orthopedics 1995; 18: 971-981.

(26) Nelson BW, Carpenter DM, Dreisinger TE, Mitchell M, Kelly CE, Wegner JA Can spinal surgery be prevented by aggressive strengthening exercise? A prospective study of cervical and lumbar patients. Archives of Physical Medicine and Rehabilitation 1999; 80: 20-25, 

(27) Braith RW, Mills RK, Welsch MA, Keller JW, Pollock ML, Resistance training restores bone mineral density in heart transplant patients, Journal of the American College of Cardiology 1 996; 28:1471-1477.