Archives of Physical Medicine and Rehabilitation
Volume 89, Issue 9 , Pages 1675-1685, September 2008

Isolated Lumbar Extensor Strengthening Versus Regular Physical Therapy in an Army Working Population With Nonacute Low Back Pain: A Randomized Controlled Trial

  • Pieter H. Helmhout, MSc

      Affiliations

    • Department of Training Medicine and Training Physiology, Personnel Command, Royal Netherlands Army, Utrecht, The Netherlands
    • Corresponding Author InformationReprint requests to Pieter H. Helmhout, MSc, Dept of Training Medicine and Training Physiology, Personnel Command, Royal Netherlands Army, PO Box 90004, Utrecht, 3509 AA, The Netherlands
    • ,
  • Chris C. Harts, MSc

      Affiliations

    • Department of Training Medicine and Training Physiology, Personnel Command, Royal Netherlands Army, Utrecht, The Netherlands
    • ,
  • Wolfgang Viechtbauer, PhD

      Affiliations

    • Department of Methodology and Statistics, Maastricht University, Maastricht, The Netherlands
    • ,
  • J. Bart Staal, PhD

      Affiliations

    • Department of Epidemiology and Caphri Research Institute, Maastricht University, Maastricht, The Netherlands
    • ,
  • Rob A. de Bie, PhD

      Affiliations

    • Department of Epidemiology and Caphri Research Institute, Maastricht University, Maastricht, The Netherlands

published online 04 August 2008.

Article Outline

Abstract 

Helmhout PH, Harts CC, Viechtbauer W, Staal JB, de Bie RA. Isolated lumbar extensor strengthening versus regular physical therapy in an army working population with nonacute low back pain: a randomized controlled trial.

Objective

To evaluate the effectiveness of specific lumbar extensor training compared with regular physical therapy (PT) in workers with nonspecific nonacute low back pain (LBP).

Design

A multicenter randomized controlled trial with 1-year follow-up.

Setting

PT department in (military primary care) health centers.

Participants

Predominantly male soldiers (N=129) with 4 weeks or more of low back complaints who were referred by the health center's general practitioner for PT (mean age, 35.9±10.8y; range, 20–56y), of whom 127 randomized participants were included in the analyses. One patient withdrew because of adverse effects during treatment.

Interventions

Participants were assigned to 1 of 2 treatment programs: (1) a 10-week device-supported isolated lumbar extension training, twice a week, or (2) regular PT, mainly consisting of exercise therapy and aerobic activities.

Main Outcome Measures

Functional status (Roland-Morris Disability Questionnaire, Patient-Specific Functional Scale) and global perceived effect were assessed in the short term (5wk, 10wk) and long term (6mo, 12mo).

Results

Both groups showed a favorable development in main outcomes over time: short-term improvements (after 10 weeks of treatment) remained stable or even slightly increased throughout the 12-month follow-up. No significant differences between the 2 groups were shown for any of the outcome measures, at any time.

Conclusions

Consistent with prior evidence, specific back strengthening does not seem to offer incremental benefits in LBP management compared with regular PT care that mainly consists of general exercise therapy. (ISRCTN identifier ISRCTN19334317.)

Key Words: Exercise, Low back pain, Rehabilitation

List of Abbreviations: GP, general practitioner, GPE, global perceived effect, LBP, low back pain, 1-RM, 1-repetition maximum, PSFS, Patient-Specific Functional Scale, PT, physical therapy, RMDQ, Roland-Morris Disability Questionnaire, TSK, Tampa Scale for Kinesiophobia

 

LOW BACK DISORDERS have become a major medical and socioeconomic problem among working populations in industrialized countries.1, 2 Recent-onset LBP often recurs intermittently, sometimes resulting in persistent disabling symptoms. Once chronic, the back pain condition can significantly impact an injured worker's quality of life and productivity,3, 4 generating substantial costs related to medical service use, sick leave compensation, disability pension, and replacement costs.5, 6, 7, 8

The Royal Netherlands Army is a major professional organization in the Netherlands, employing approximately 25,000 military and civilian personnel. The diverse workforce is involved in a wide range of jobs, making the Dutch army comparable to other organizations with a high degree of physically straining job activities, such as the police force, fire brigade, health service, or construction industry. Military occupations that involve heavy physical training programs (eg, special forces, infantrymen) and/or frequent manual material handling tasks (eg, construction equipment operators, heavy vehicle mechanics) are associated with higher-than-average risk of disability.9 These types of jobs may expose workers to occupational risk factors that have been specifically associated with low back disability, such as repetitive lifting, frequent bending and twisting, pushing and pulling, and awkward body postures.10, 11, 12

Back-related disorders represent one of the most prevalent sources of disability in personnel of the Dutch army (P. Helmhout, unpublished data, 1998). Acute LBP is the primary reason for Dutch soldiers to visit the general practitioner at a military health center. Chronic nonspecific LBP, defined as having complaints for at least 12 weeks, is 1 of the 3 most diagnosed disorders during GPs' consulting hours; managing care-seekers with LBP takes up to 15% of the military company doctor's weekly consulting hours time (P. Helmhout, unpublished data, 2003).

Since the 1990s, passive forms of PT treatments such as massage and electrophysical treatments have become less popular, while exercise therapy has grown in popularity. Recent reviews conclude that exercise is an effective conservative treatment for persistent LBP in terms of restored function, reduction of sick leave, and alleviation of pain, although improvements in outcomes such as pain and functional limitations are generally small and brief.13, 14, 15, 16, 17, 18 Efficacy studies on exercise therapy generally show a lack of treatment specificity of different exercise modalities such as aerobic exercise, muscle strengthening, or stabilization.19, 20, 21 Recent reviews by Slade and Keating14 and Hayden et al15 indicate that the optimal type of exercise for LBP may not be known because the effects of specific exercises have not been systematically assessed. Another explanation for the nonspecific effects of exercise therapy could be the heterogeneity in demographic and clinical characteristics of many study populations.22, 23

For the last 10 years, clinical researchers of the Royal Netherlands Army have studied the potential of physical training modalities in preventing and alleviating nonspecific LBP in their working population. This research has led to a minimal intervention program existing of no more than approximately 10 minutes of specific training of the isolated lumbar extensors on a training device, while adhering to sports medicine principles. An extensive elaboration on the rationale for the use of this approach has been published elsewhere.24 In short, physical fitness can be seen as a critical aspect of military preparedness and an inherent part of military service. The necessary high levels of physical fitness needed by armed forces can only be achieved through systematic, repeated, general, and task-specific physical exercise. From the initial military education, soldiers are exposed to unit physical fitness training programs, including progressive resistance training on exercise machines. In our experience, this repeated occupational exposure to physical exercise shapes the beliefs, attitudes, and coping behavior of, for instance, a soldier with chronic pain toward a strong physical orientation. In an earlier study we found that service members with chronic LBP perceived their health problems as mainly physically disabling.25 Interventions such as isolated lumbar extensor training, which predominantly focus on physical reconditioning using devices, may therefore be especially appropriate for our target population. The limited dimensions of our exercise program are expected to be highly appreciated in a military setting of constant change.

Earlier studies on isolated lumbar extension training suggest that this type of progressive exercise can be of value for back pain management.26, 27, 28 Overall, promising results were reported regarding strength improvements and pain relief. However, several methodologic shortcomings hinder solid interpretation of these findings. Most encountered problems were small population size, lack of randomization, and inadequate or missing control groups. In a review, Miltner et al29 have stressed the need for randomized trials to assess further the efficacy of isolated lumbar extension exercise in LBP management.

Literature from the early 1990s showed some evidence for a dose-response effect of exercise for chronic LBP.30, 31 In 2 previous trials at our department in Utrecht, The Netherlands, we compared the efficacy of a high-intensity versus low-intensity training protocol for the lumbar extensors in a group of workers with nonspecific LBP. Total intervention time of both minimal intervention programs was limited to 10 to 14 sessions of approximately 10 minutes each, over a period of 12 weeks (first trial) or 8 weeks (second trial). In the first trial,25 we were unable to demonstrate that either of the 2 training programs was superior in alleviating back complaints in a group of 81 workers. The magnitude of the improvements in back function found in this study were in line with those reported in studies that used more extended multidisciplinary exercise programs. Moreover, the results of our first trial indicated that some people with LBP might benefit more from an aggressive approach, showing a trend toward a higher self-assessed percentage decrease in complaints directly after the minimal intervention treatment, as well as a higher compliance to the treatment and a higher willingness to participate in physical exercise in the longer term. The second study,32 which also included a waiting list group, showed that for most outcome measures, the point estimates were slightly in favor of the 2 exercise groups compared with the waiting list group. Effects were small and mostly not statistically significant, possibly because of the low number of participants (65 workers distributed over 3 intervention arms).

On the basis of our previous work, we concluded that further exploration was needed into the optimal type, intensity, and frequency of lumbar extensor training in LBP. Other factors like the mediating role of pain-related fear, degree of physical activity, and/or job characteristics could be explored. We therefore set up a randomized controlled trial in which different military health centers participated, in an attempt to overcome previous problems of underpowering. Moreover, we slightly modified our test and training protocol based on previous experience (eg, 10-wk program, 2 times a week, 1 training set). Because the population under study (soldiers visiting a military GP for their back trouble) generally had more acute symptoms than our previous study populations, we extended our inclusion criterion from 12 to 4 weeks of LBP. This article reports the results of the multicenter trial, in which the effectiveness of isolated lumbar extensor training compared with regular PT is evaluated in workers with nonspecific nonacute LBP. An extensive description of the design of the trial (registered as ISRCTN19334317) was published in 2004.24

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Methods 

Recruitment and Randomization of Study Group 

The source population consists of military employees of the Royal Netherlands Army (N=23,000). Participants were recruited in 6 military (primary care) health centers during regular GP consulting hours. Patient recruitment commenced in April 2002 and continued until December 2005. Inclusion criteria were military employees of the Dutch army between the age of 18 and 54 years, at least 4 weeks of continuous or recurrent (at least 3 times a week) episodes of LBP, pain localized between posterior iliac crests and angulus inferior scapulae, with or without radiation in the legs, availability in duty time to visit the local military health center 2 times a week during 10 consecutive weeks, with no more than 2 sessions of absence because of job-related activities (eg, military exercise, course, leave), and willingness to abandon other treatment interventions for the lower back during the intervention period. Exclusion criteria were spinal surgery in the last 2 years; specific treatment for LBP in the last 4 weeks (eg, PT, manual therapy); severe LBP that hindered performing maximal isometric strength efforts; and specific LBP, defined as herniated disk, ankylosing spondylitis, spondylolisthesis, or other relevant neurologic diseases.

After physical examination by the physician, eligible patients received information about the study and a referral to the military physiotherapist. In 2 physiotherapist consults, participants underwent a trial measurement and a baseline measurement, respectively, consisting of a compound questionnaire and an isometric back strength test. The main purpose of the trial measurement was that participants could get accustomed to the testing procedure, in particular the isometric back strength test. In a previous test-retest reliability study, we found that reproducibility of this test was lower between an initial and second measurement than between a second and third measurement (C. Harts, P. Helmhout, unpublished data, 1998). Written informed consent was obtained from all participants. At the third visit, patients were randomized into 2 groups: an intervention group receiving an isolated lumbar extensor training program, and a reference group receiving regular PT. Randomization was done by means of a computer-generated table of random numbers per study center, using a block size of 10. Prestratification was applied for the duration of the back complaints, with a cutoff point of 12 weeks, with suspicion of duration of complaints to influence the individual response to the program. Randomization was concealed by means of a computer program. After the name and military registration number of the patient were entered by the physiotherapist, the program provided the allocated treatment. Directly after randomization, the first treatment session started. The study protocol was approved by the Medical Ethics Committee of The Netherlands Central Military Hospital, Utrecht.

Study Interventions 

Lumbar extensor strength training program 

The lumbar extensor strength training program was a highly standardized, progressive resistance training of the isolated lumbar extensor muscle groups, covering 10 weeks of training. The program was provided by physiotherapists from the military health center. The program included 14 training sessions twice a week, and 3 isometric back strength tests (in weeks 1, 5, and 10). The program aimed at both strength and endurance gain of the back muscles, in that the protocol allowed 15 to 20 repetitions every session on the lower back machine, which is equivalent to approximately 50% and 70% of the 1-RM, respectively.33 If the subject was able to perform more than 20 repetitions of slow and controlled back extension (2s) and flexion (4s) movements, 2.5kg was added in the next training session. Vice versa, if the subject was unable to perform 15 repetitions, the training load was lowered 2.5kg next time. This training protocol is based on both existing protocols34, 35, 36, 37 and our own clinical experiences. A more extensive description of the training protocol can be found elsewhere.24 Training sessions were carried out on a Total Trunk Rehab machine.a This lower back machine is equipped with a knee-lock system and a thigh-restraining belt to immobilize both hips and thighs, allowing the participant to move only the isolated lower back. All training sessions were conducted as much as possible by the same physiotherapist, who paid special attention to the execution of the training in terms of execution (hollowing and flattening of the lumbar lordosis), pace (relatively slow), and movement (full range). The weight load used and the number of repetitions completed during each training session were recorded. Patients were not allowed to undergo cotreatments beside the lumbar extensor strength training program during the treatment period.

Regular PT program 

Subjects allocated to the regular PT program received regular PT for their lower back for 10 weeks, or less when the patient was free of complaints. The therapy was provided by physiotherapists from the military health center. Based on the physiotherapists' judgment, this could include hands-on treatment (eg, passive mobilizing and pain-cushioning techniques, manual therapy) and/or hands-off treatment (eg, exercise therapy, individual education, instruction on the back function). In the Dutch army, active therapy forms are favored. To increase the contrast between both intervention programs, physiotherapists were not allowed to use the lower back machine in their usual care. Patients were also not allowed to undergo cotreatments besides the regular PT program during the treatment period, nor exercise on equipment that mimicked the specific components of the lower back machine. Therapeutic activities in every therapy session as well as the number of sessions were written on a form.

Outcome Measurements 

In this study, we have chosen low-back specific functional status as our primary outcome, which was measured with the validated Dutch 24-item version of the widely used RMDQ.38, 39 Patient-specific functional status was measured by the PSFS, in which patients selected at baseline the 3 most important activities of daily living that were hampered by their back pain, and rated them on a 100-mm visual analog scale at each test moment.40 GPE was measured by self-assessment on a 7-point scale (1=completely recovered, 2=much improved, 3=slightly improved, 4=no change, 5=slightly worsened, 6=much worsened, 7=vastly worsened).41

The following demographic variables were registered during the intake: age, height, weight, duration of current back complaints, earlier episodes of LBP, pain radiation, change of work, and work absenteeism because of LBP in the last year.

As a potential effect modifier, fear of movement or reinjury was measured using the Dutch version of the TSK, a 17-item scale to obtain a score for the extent to which a back patient fears physical damage caused by physical activity.42, 43, 44 Moreover, individual back extension strength progression was evaluated using repeated isometric measurements on the lower back training and testing machine. A detailed description of these measurements can be found elsewhere.24

Patient satisfaction was measured at the end of the treatment program by two 3-level items and one 5-level item in which the degree of satisfaction with the allocated treatment was assessed: (1) “Were you satisfied with the allocated treatment at the start of the program?” (2) “Has your opinion about the treatment changed during the program?” (3) “How satisfied are you now about the treatment that was given to you?”

Short-Term and Long-Term Follow-Up 

Follow-up data were collected at 2 short-term intervals at 5 and 10 weeks after randomization, respectively, and 2 long-term intervals at 6 and 12 months after the end of the intervention, respectively. At every test moment, participants filled in a compound questionnaire on a stand-alone personal computer, and they underwent an isometric back strength measurement on the lower back machine.

Blinding 

Blinding of patients was not possible because of the nature of the interventions. However, in an attempt to minimize potential novelty effects (ie, allocation to the new lumbar extensor strength training program treatment causes temporary improvements in perceived complaints),45 both lumbar extensor strength training and regular PT were introduced to the patient as potentially equally effective treatments in restoring back function, with the relative efficacy of both programs as the main focus of the study. Patients were informed at baseline about the opportunity they had to continue with a treatment modality of their choice, including our training device, after finishing the treatment period. Patient satisfaction with the allocated treatment was measured directly after the treatment period. Moreover, training sessions and strength measurements were as much as possible administered by different physiotherapists. Knowledge on individual training progression could not influence the process of measurement and vice versa. An independent data manager, who had not been involved in the study thus far, collected data from all study locations and recoded patients and locations to unique codes before handing the database to the researchers.

Statistical Analysis 

We intended to include 100 participants a treatment arm, which should be sufficient to detect a 2-point difference in our primary outcome variable RMDQ between both intervention groups.46 According to Resnik and Dobrzykowski,47 a 2-point to 3-point change can be considered clinically important in RMDQ values that are less than 9 points at baseline. For the calculation of the sample size, we further used an SD of 4.8 (based on our first trial), a dropout rate of approximately 10%, an α of .05, and power of 80%.

Differences between lumbar extensor back strength training and regular PT in the development of the outcome measures RMDQ, PSFS, and GPE were separately described for the study treatment period and the follow-up period, respectively. We performed longitudinal linear regression analysis for repeated measurements using mixed effects models. Analyses were carried out with the nlme library48 under R, version 2.5.0.49,b

To avoid model overfitting and multiple testing,50 models for the 3 dependent variables were chosen a priori on the basis of theoretical considerations and prior empirical findings, such as the following: baseline differences were not expected because of randomization; trends over time were assumed to be linear; slopes were allowed to differ between the treatment phase and follow-up phase, as well as between both treatment groups; and random intercepts and slopes were modeled, with treatment location as a fixed effect.

Before fitting the a priori models, a so-called unconditional means model and unconditional growth model were both fitted to the data for all 3 dependent variables. The unconditional means model allowed us to assess how much variability existed at the between-person and within-person levels. The unconditional growth model modeled the trend over time without including predictors that might account for differences in the intercepts and slopes across treatment groups, locations, or subjects. Next, the a priori models were fitted by including the treatment group and location variables, in an attempt to account for some of the variability in person-specific intercepts and slopes of the unconditional growth model.

In the models for RMDQ and PSFS, the main (null) hypothesis to be tested was as follows: the average slope of the linear trend in the treatment phase and the follow-up phase, respectively, is the same for lumbar extensor back strength training and regular PT. In the model for GPE, the main (null) hypotheses to be tested were as follows: (1) lumbar extensor back strength training and regular PT do not differ with respect to the average at the beginning of the follow-up phase, and (2) the average slope of the linear trend in the follow-up phase is the same for lumbar extensor strength training and regular PT. Finally, an additional effect modifier model was fitted by including 2 potential effect modifiers: duration of current complaints11, 51 and baseline TSK score.52, 53, 54 The values of these potential effect modifiers were adjusted prior to their inclusion in the model by subtracting the median value from each value in order to give a more natural interpretation to the model parameters.

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Results 

Figure 1 shows the progress through the different phases of the trial. We enrolled 127 subjects into the study before ending our recruitment activities. Mainly practical reasons underlay the decision to end the recruitment before meeting the prespecified sample size calculation, such as a declining recruitment rate (<3 enrollments a month toward the end), a long recruitment period (nearly 4y), and the fact that one of the major military health centers was about to close.

Our final database consisted of 5 repeated measurements on 127 predominantly male subjects with moderate chronic back complaints, who were clustered in 6 different treatment locations (health centers) and randomly assigned to the 2 treatment groups lumbar extensor strength training or regular PT within each location. Table 1 shows baseline characteristics of the subjects in both treatment arms. The lumbar extensor strength training group contained relatively more subjects with chronic back complaints (>3mo) compared with the regular PT group. One subject was randomized in regular PT but incorrectly received lumbar extensor strength training; he was analyzed in the regular PT group, according to the intention-to-treat principle. Because of planning difficulties at the health centers, our trial showed some variability between subjects in time of measurement, although not significantly different between locations: the 5-week intermediate assessment was planned, on average, in week 6 (SD=1.5; range, 4–13), the 10-week posttreatment assessment in week 12 (SD=2.2; range, 8–18), the 36-week short-term follow-up in week 39 (SD=7; range, 25–60), and the 62-week long-term follow-up in week 70 (SD=12.9; range, 50–100). For this reason, the actual individual measurement week was included as a timing variable in the analyses.

Table 1. Baseline Demographic and Clinical Characteristics and Baseline Outcome Measures of Trial Participants in Both Treatment Groups
CharacteristicsLumbar Extensor Strength Training (n=71)Regular PT (n=56)
Demographic characteristics
Age (y)37±11(20–53)35±11(21–56)
Height (cm)183±8(157–196)182±7(165–198)
Weight (kg)85±12(50–116)86±11(65–108)
Male sex (n)6954
Clinical characteristics
Duration current back complaints(%)(n=59)(n=44)
<4wk02
4–6wk816
6–12wk2027
3–6mo209
6–12mo157
≥1y3639
Earlier episode(s) of back complaints(%)76(n=64)74(n=51)
Pain radiation in legs(%)10(n=63)10(n=51)
Change of work because of back complaints(%)0(n=48)0(n=38)
Work absenteeism in last year because of back(%)10(n=48)8(n=38)
Outcome measures
RMDQ score(0–24 points)8.3±4.8(0–19)7.9±4.4(0–18)
PSFS score(0–300 points)178±65(38–272)178±52(43–277)
TSK(17–68 points)38.2±6.9(27–57)38.5±6.3(24–55)
NMT(Nm)214±64(81–332)212±65(71–370)

NOTE. Values are mean ± SD (range) or as otherwise indicated.

Abbreviation: NMT, isometric (net) muscular torque of the lumbar extensors (mean of 3 positions).

The average number of treatment sessions (± SD) in the lumbar extensor strength training program was 13.9±3.7, and in the regular PT program it was 10.8±4.7. The participating physiotherapists reported mean intervention times a treatment session of 10 to 15 minutes in the lumbar extensor strength training group and 25 to 30 minutes in the regular PT group.

All therapeutic activities during treatment sessions in the regular PT program had to be written down by the physiotherapists in order to obtain information about the content of the program. Although not every provider fully complied with this registration duty (about 1/5 of the treatment forms of participants in the regular PT program were not sent back), locations reported overall similar proportions of regular PT activities: approximately 65% of the activities recorded were exercise therapy (eg, trunk and leg strengthening exercises, core stability exercises, stretching exercises, specific McKenzie exercises), 25% aerobic activities (eg, walking on treadmill, cycling), and 10% instruction and advice (eg, safe lifting instruction, advice on proper techniques for crunches), and less than 1% were passive modalities like massage and kinesiotaping.

Despite the fact that we requested physiotherapists not to use specific devices for the lumbar extensors in the regular PT program, 2 of 6 centers reported an incidental use of standard low back machines during individual training sessions. It was not possible to quantify this any further.

Two cases of cointerventions were reported in the lumbar extensor back strength training group, both providing additional manual therapy to the subject during the treatment phase. Data from these subjects were excluded from the analyses. Moreover, 1 adverse event was reported in the lumbar extensor back strength training group, which concerned an acute lumbago during one of the first training sessions; the subject involved decided to discontinue the program. No adverse events were reported in the regular PT group.

Plots of the individual profiles for each outcome variable in time indicate that considerable noise is present in the data: we see a large variability in baseline values, and profiles differed substantially in their form (not presented here). For example, some subjects exhibited an RMDQ profile that looked like a slanted L; others had an almost linear line with a positive slope, and others with a negative slope. For each outcome variable, the plots shown in figure 2 present averages for the 5 measurement occasions for lumbar extensor back strength training and regular PT separately. It is evident that, on average, the treatment groups do not differ with respect to their average baseline value or the trend in time. For RMDQ and PSFS we see a slanted L-shaped pattern, with a changing slope once the follow-up phase begins. The pattern for GPE is essentially flat.

  • View full-size image.
  • Fig 2. 

    Means (with point-wisely constructed 95% confidence intervals) of the main outcomes over the course of the study. *RMDQ range, 0–24 (high score indicates greater disability). †PSFS range, 0–300 (high score indicates greater disability). ‡GPE range, 1–7 (high score indicates worsening of complaints).

For both groups, the observed mean changes over time of the 3 outcomes are presented in table 2. The results of the back strength measurements are also presented in table 2, indicating that back strength progression was comparable in both groups. The frequency distribution over time of the GPE items is presented in table 3.

Table 2. Average Value for the 3 Outcome Variables and for Back Strength per Repeated Measurement per Treatment Group
WeekLumbar Extensor Strength TrainingRegular PT
No.RMDQPSFSGPENMTNo.RMDQPSFSGPENMT
0718.3±4.8178±65ND214±64567.9±4.4178±52ND212±65
5645.8±4.8119±70ND23±62464.2±4.2116±67ND246±74
10593.4±4.685±722.4±0.8244±66473.5±4.297±742.4±0.7247±73
36573.2±4.374±722.5±1.0264±64372.7±3.864±592.3±0.9254±73
62612.6±4.469±712.2±1.0267±62452.5±3.965±692.3±1.0249±74

NOTE. Values are mean ± SD.

Abbreviations: ND, no data; NMT, isometric (net) muscular torque (mean of 3 positions).

Table 3. Frequency Distribution for GPE per Repeated Measurement per Treatment Group
WeekLumbar Extensor Strength TrainingRegular PT
No.1⁎234567No.1234567
10597612010200464612411000
3662154427130104815502312000
626427392760105020461812400

NOTE. Values are percentages.

⁎GPE scores: 1=completely recovered, 2=much improved, 3=slightly improved, 4=no change, 5=slightly worsened, 6=much worsened, 7=vastly worsened.

Table 4 shows the most important results of the a priori models for the 3 outcome variables. In particular, we see that the slopes of the lumbar extensor strength training and regular PT groups are significantly different from 0 in the treatment phase. For RMDQ, 10 weeks of treatment are estimated to yield on average a 3.80-point (ie, 10 × –.38) drop for the lumbar extensor strength training group and a 3.55-point drop for the regular PT group. Analogously, for PSFS, 10 weeks of treatment are estimated to yield on average a 75.11-point and a 69.03-point drop for the lumbar extensor strength training and regular PT groups, respectively. While these values indicate a slight advantage for the lumbar extensor strength training group, the between-group differences (treatment effect) are not significant (RMDQ, P=.66; PSFS, P=.57).

Table 4. Output of Mixed Effects Model for the Main Outcomes in the Lumbar Extensor Strength and Regular Program
Outcome⁎PhaseParameterSlope95% CI
RMDQTreatmentWithin-group average slope LEST program−0.380†−0.450to−0.302
Within-group average slope regular program−0.355†−0.441to−0.270
Between-group effect (slope difference)−0.025−0.134to0.085
Follow-upWithin-group average slope LEST program−0.013−0.030to0.004
Within-group average slope regular program−0.013−0.033to0.006
Between-group effect (slope difference)0.000−0.025to0.026
PSFSTreatmentAverage slope LEST program−7.511†−9.096to−5.927
Average slope regular program−6.903†−8.619to−5.187
Between-group effect (slope difference)0.608−2.693to1.477
Follow-upAverage slope LEST program−0.286−0.600to0.028
Average slope regular program−0.442†−0.786to−0.059
Between-group effect (slope difference)0.136−0.344to0.616
GPEFollow-upAverage slope LEST program−0.004−0.009to0.001
Average slope regular program−0.002−0.008to0.003
Between-group effect (slope difference)−0.002−0.010to0.006

Abbreviations: CI, confidence interval; LEST, lumbar extensor strength training.

⁎For the RMDQ, a negative slope reflects improvement; for the PSFS, a negative slope reflects improvement; and for the GPE, a positive slope reflects improvement.

†P<.05.

For the follow-up phase, the estimated slopes indicate no significant change for RMDQ and GPE in both groups. During the 52 follow-up weeks, RMDQ is estimated to change on average by −.676 points (ie, 52 × –.013) for both groups. The estimated between-group difference was essentially 0, and we can therefore conclude that there was no significant treatment effect (P=.99). GPE is estimated to change by −.208 points (lumbar extensor back strength training) and −.104 points (regular PT) during the 52 follow-up weeks, respectively, with again no significant difference between the 2 groups (P=.66). For PSFS, the estimated change was −14.872 for the lumbar extensor back strength training and −22.984 for the regular PT group. The change for the regular PT group was significantly different from 0 (P=.02) but just failed to be significant for the lumbar extensor strength training group (P=.08). Nevertheless, a direct test of the between-group difference indicated no significant treatment effect (P=.58).

The results for the effect modifier models indicate that baseline TSK score can account for some of the variability in baseline RMDQ and PSFS values, but not in slopes. The expected RMDQ value at baseline increased on average by .285 points for each point increase in TSK (P<.001). The expected PSFS value at baseline increased on average by 2.323 points for each point increase in TSK (P<.01). Nevertheless, adding this effect modifier to the model does not change the overall conclusion that both treatment groups do not follow significantly different patterns during treatment and follow-up. The other potential effect modifier in this model, duration of complaints at baseline, appears to have no influence on baseline values or slopes of either main outcome.

Table 5 shows how many participants in both intervention groups were satisfied with the treatment allocation at baseline and whether this opinion had changed during the treatment phase. Moreover, the degree of satisfaction with the intervention at the end of the treatment period is presented. Finally, scores on questions about back pain episodes, back treatment, medication, and work absenteeism during the 6-month and 12-month follow-up periods are presented. No clear differences between the 2 groups were seen in these items.

Table 5. Self-Reported Degree of Satisfaction With Treatment Program and Self-Reported Back Pain Evaluation in 6-Month and 12-Month Follow-Up Periods, Respectively
Pretreatment and PosttreatmentScore ItemLEST (n=56)Regular PT (n=46)
Satisfied with the allocated treatment program at baseline?Satisfied7070
Neutral2328
Not satisfied72
Opinion has changed during the program?Yes, positively3737
No6359
Yes, negatively04
Final degree of satisfaction at the end of the treatment program?(Very) satisfied8989
Neutral119
Not satisfied (at all)02
6-Month Follow-UpScore ItemLEST (n=56)Regular PT (n=40)
Back pain in first half year after the end of the treatment period?No, not at all918
Yes, incidentally5763
Yes, monthly113
Yes, weekly2318
Back treatment in first half year after the end of the treatment period?No, not at all3025
Yes, fitness/back training3458
Yes, PT147
Yes, specialist60
Yes, other treatment1610
Back pain medication in first half year after the end of the treatment period?No9583
Yes517
Work absenteeism because of back pain in first half year after the end of the treatment period?No9590
Yes510
12-Month Follow-UpScore ItemLEST (n=61)Regular PT (n=46)
Back pain in second half year after the end of the treatment period?No, not at all2522
Yes, incidentally5550
Yes, monthly211
Yes, weekly1817
Back treatment in second half year after the end of the treatment period?No, not at all4235
Yes, fitness/back training3430
Yes, PT515
Yes, specialist10
Yes, other treatment1819
Back pain medication in second half year after the end of the treatment period?No9587
Yes513
Work absenteeism because of back pain in second half year after the end of the treatment period?No9591
Yes59

NOTE. Values are percentages.

Abbreviation: LEST, lumbar extensor strength training.

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Discussion 

In this study, 2 potentially effective treatment programs for LBP were compared. To our knowledge, this is the first controlled trial comparing isolated lumbar extensor training of such limited dimensions (about twenty 10-minute to 15-minute sessions) to regular PT in a predominantly male population with moderate nonspecific subacute to chronic LBP. In both intervention arms, main outcomes showed a favorable development over time: short-term effects (after 10 weeks of treatment) remained stable or even slightly improved throughout the 12-month follow-up. However, no significant differences were found between the 2 intervention programs, both in the short-term and the long-term. Specific back strengthening using a lumbar extensor isolation device does not seem to offer incremental benefits compared with regular PT that mainly consists of general exercise therapy.

How can these results be interpreted? The results show that the observed mean short-term and long-term changes in the main outcome variables RMDQ and PSFS are, in both treatment groups, 3 to 5 times larger than expected because of background noise alone.55 Fifty-nine percent to 68% of the participants rated their complaints on the GPE as completely recovered or much improved over time, which are indicated in the literature as qualifications for clinically important improvements.40 However, these changes cannot be automatically considered treatment effects but may also reflect natural history of recovery. We compared the outcomes of 2 active treatments without the inclusion of a nontreatment or placebo group. It was not considered ethically or practically feasible to include a nontreatment arm because the study relied on voluntary participation of subjects who visited the GP's office hour for their back pain. This precludes an adequate insight in the natural course of LBP over time in both groups. Definitive inferences about the effectiveness of either one of the treatments are, therefore, hard to make.

Study Limitations 

Several methodologic limitations that may have influenced the outcomes can be considered, such as trial power, intervention contrast, and loss to follow-up. First, our strict inclusion and exclusion criteria (especially availability in duty time and LBP >4wk), as well as a slow recruitment rate, resulted in a lower sample size than expected. This inevitably reduces the power of this study and, consequently, the robustness of our findings. Second, the intervention contrast between the lumbar extensor strength training and regular PT program may not have been large enough to detect clinically relevant changes with the chosen outcome measures. The results show that strength progression in the lumbar extensor back strength training group was comparable to the regular PT group, indicating that both interventions provided an equally strong strength training stimulus. Specific (isolated) lumbar extensor strengthening exercises were excluded from our regular PT program, but some general back strengthening exercises were allowed; the regular PT treatment would otherwise not have been a realistic representation of usual back pain management in the Dutch army. Moreover, 2 locations reported that they had used the low back training device incidentally in the regular PT program, despite our request not to do so. This may have influenced the results of the regular PT program in some way. Third, the treatment frequency differed somewhat between both groups: 4 more treatment sessions, on average, were planned in the lumbar extensor back strength training group compared with the regular PT group. The average time of a treatment session was, on the other hand, 50% shorter in the lumbar extensor strength training group. Fourth, the loss to follow-up in this trial may have influenced the results. With 8% dropouts (lumbar extensor strength training, regular PT) during the treatment period and 13% (lumbar extensor back strength training) and 18% (regular PT) overall dropouts, respectively, we had a follow-up rate comparable or favorable to what has been reported in other studies on exercise therapy in outpatient settings.18, 21, 56, 57, 58, 59, 60 The greater part of the loss to follow-up was a result of factors unrelated to the study, such as military mission or leaving military duty. Dropouts were evenly distributed over both treatment groups, which supports the stability of our findings. The problem of relatively high numbers of missing values in our database was tackled by applying random coefficient analysis, a statistical technique that includes both complete and incomplete longitudinal data.

Next, one cannot disregard that the use of a new low back training device in the lumbar extensor strength training program as opposed to general exercises in the regular PT program had an added psychologic impact on outcomes (novelty effect). As in most exercise therapy interventions, neither participants nor providers could be blinded for the type of intervention used in this study. Although it was not possible to blind participants from expectation bias about the efficacy of the allocated treatment, we took great care in maximizing the treatment credibility of both programs when explaining the intervention to each participant. The degree of satisfaction with the allocated treatment throughout the intervention period appeared to be rather similar across the treatment groups, indicating that neither of the 2 treatment programs was seen as more or less credible than the other.

Finally, to evaluate validly the lumbar extensor strength training concept in its future setting, we chose regular visitors of our military health centers as our target population. This study population of predominantly male, young, and physically active subjects might have influenced the outcomes. Because both interventions mainly focused on exercising and strengthening the lumbar region, they might have been more effective and efficient in groups of patients (older, unfit, female) with a higher strength development potential.

The results of this study corroborate earlier studies19, 20, 21 and reviews13, 14, 15, 16, 17, 18 on the same topic, indicating that many therapeutic exercise interventions exist, but none seem to be clearly superior to others. In a recent review, Slade and Keating14 conclude that the optimal type of exercise for chronic LBP is still unknown because the effects of specific exercises have not been systematically assessed. Exercise interventions that make use of a singular concept need to be studied. In our trial, we compared a unimodal back strengthening program using a test and training device with a treatment program that included a wide range of therapeutic exercises. Our back strengthening program included elements that have recently been identified as important intervention characteristics to decrease back pain and improve function, such as exercises that are individually designed, that contain muscle strengthening, and that are supervised.61

The results of this study can be extrapolated to other working populations with a predominance of male employees (eg, construction workers, police squads, fire brigades). We do not expect the long recruitment process to have influenced the generalizability of this study significantly, because the military population at risk can be considered relatively stable and homogeneous. In our opinion, our inclusion and exclusion criteria were well defined, leaving no room for GPs of different health centers to refer certain subgroups of patients more often to the study. Subjects in this study were selected from a patient group normally considered suitable for progressive resistance training inasmuch as all patients with clinical contraindications (eg, affected nerve root) were excluded.

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Conclusions 

Our study indicates that neither specific isolated lumbar extensor training with a training device nor regular PT that mainly consists of general exercise therapy is more effective than the other in a predominantly male population with moderate nonspecific subacute to chronic LBP.

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Acknowledgments 

We thank Peter de Putter and Wim Veenman for their efforts in the development and maintenance of the ALBATROS software program, as well as in the management of all data. We thank Colonel René Roelofs, MD, former Surgeon General Royal Netherlands Army (RNLA), and Colonel Cees IJzerman, MD, former Director Occupational Health & Safety Service RNLA, for authorizing this multicenter study within the military setting.

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  • a Technogym Inc, Via G. Perticari, 20, Gambettola (FC), Italy 47035.
  • b R Foundation for Statistical Computing. Available at: http://www.R-project.org.

 No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit on the authors or on any organization with which the authors are associated.

PII: S0003-9993(08)00389-4

doi:10.1016/j.apmr.2007.12.050

Archives of Physical Medicine and Rehabilitation
Volume 89, Issue 9 , Pages 1675-1685, September 2008

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