Adapted exercises versus general exercise recommendations on chronic low back pain in industrial workers: A randomized control pilot study

Abstract

BACKGROUND:

Exercise has been demonstrated as effective for the treatment of low back pain (LBP) in workers.

OBJECTIVE:

The purpose of this study was to investigate whether an exercise program adapted to the characteristics of the workplace is a useful supplement to general exercise recommendations in assembly line workers with chronic LBP.

METHODS:

Workers were randomly assigned to intervention group-adapted exercises plus general exercise recommendations (n = 10), and control group-general exercise recommendations (n = 8). Both received 8-week exercise program through a mobile application (APP) to manage the intervention. Outcome was based on lumbar disability (Oswestry Disability Index), interference and lumbar pain intensity (Brief Pain Inventory), and kinematic parameters.

RESULTS:

Significant differences were obtained for the intervention group in the “pain interference” variable, in the “mood” and “enjoyment” sub-variables, as well as in “flexion angle” variable. For the control group, significant differences occurred in the “pain intensity” variable. Adapted exercise plus general recommendations seems more effective than the general recommendations for the improvement of lumbar flexion.

CONCLUSIONS:

An adapted exercise program for assembly line workers with chronic LBP could be an effective treatment. Future studies with a larger sample size and with an exhaustive control of the exercise adherence are required to confirm the findings of this pilot study.

Keywords

Assembly line mobile application occupational health physical activity

1 Introduction

Low back pain (LBP) is one of the most frequent work-related musculoskeletal disorders. According to the Sixth European Working Conditions Survey, almost half of European workers suffers from work-related musculoskeletal disorders, and 44.7% of the workers reported back pain [1].

Several authors have published systematic reviews examining the efficacy of the LBP treatment on workers. Among the most effective strategies are: early return to work/modified work, graded exposure to workstation after an acute episode, physiotherapy treatments, lumbar belts, ergonomic changes in workstation and educational sessions [2, 3] as well as phy-sical exercise (PE) [2 , 4–7] and multidisciplinary interventions in treatment [5].

PE has been demonstrated as an effective strategy for the treatment and prevention of low back pain in several studies with workers from different companies, within the manufacturing industry [8 –12]. The lack of consensus on the type of exercise and protocols of action makes it necessary for the scientific community to continue investigating which exercises are the most appropriate for the treatment and prevention of low back pain in different population groups [13].

The analysis of work place and the control of the total burden that the worker suffers are considered as strategies to deal with occupational low back pain [14], but no previous study has proposed the possibility of designing an exercise program adapted to the characteristics and demands of the work place. Assembly line workers are exposed to different physical load, depending on the characteristics of their job, so not everyone would need the same type and amount of exercise to prevent musculoskeletal disorders.

On the other hand, the American College of Sport Medicine (ACSM), recommends a program of reg-ular exercise that includes cardiorespiratory, resistance, flexibility, and neuromotor exercise training beyond activities of daily living to improve and maintain physical fitness and health [15]. Therefore, an interesting proposition would be that exercise programs to prevent and treat chronic LBP in assembly line workers, could be adapted to meet the physical demands of each worker, compensating for the overloads caused in their workday, and compensating for the lack of strength, flexibility, coordination or resistance of each individual, according to the general recommendations of the ACSM.

Mobile applications (APP) are a resource increasingly used by society to manage the performance of PE and to promote health habits, and specifically for the self-management of low back pain [16, 17]. Adapted exercise program management through an APP would allow maintaining control of follow-up and adherence to the program [18]. The APP would facilitate the organization of the recommended exercises for each worker and would help to the subject to be autonomous in the execution of the exercises without having to go to any authorized facility and without established schedules.

The main purpose of the present pilot study was to investigate whether adapted exercises recommendations are a useful supplement to general exercise recommendations in assembly line workers with chr-onic low back pain. Our hypothesis was that a general exercise recommendation would be less effective in reducing patient self-reported pain, disability and lumbar function than PE program adapted to the characteristics and demands of the work place combined with general exercise recommendations.

2 Material and methods

2.1 Study design

A double-blinded randomized pilot study was performed. Subjects were randomly assigned to 1 of the 2 treatment groups: 1) the control group received general exercise recommendations based on ACSM's approach, and 2) the intervention group received general exercise recommendations in addition to an exercise program adapted to the work activity done during the week.

Researchers who participated in the design of the exercise program and who assessed the patient and analyzed the data were blinded. The study was registered in the Clinical Trial database (ID:PTDLEF1) at https://clinicaltrials.gov/ (USNLN, Bethesda, MD, USA).

The development of the project was based on the Declarations of the World Medical Association of Helsinki and the Code of Ethics of the Association of Medical Associations and Physiotherapists of Spain. Each subject was informed about the nature of the study, voluntary participation in the study, the propo-sed objectives, as well as possible adverse effects that might occur in its implementation. Each subject sig-ned a written informed consent to participate in the study. The study could be suspended at any time, if de-sired by the subject. This project was approved by the Ethical Committee of Clinical Research of Aragon.

Voluntary workers with chronic lumbar pain were recruited from an assembly line of a manufacturing industry. A total of 34 participants would be required (17 in each group) to detect a clinically significant minimal difference between the groups of two points in the Brief Pain Inventory Form [19], accepting an alpha risk of 0,05 and a power of 80% in a bilateral contrast, and assuming a standard deviation of re-sponse of 2 points in this questionnaire [19]. The recruitment of the sample was carried out by the medical service of the company. The randomization was carried out using the Microsoft Excel 2010 program by an independent researcher who was not involved in the recruitment process. The subjects had to be assembly line workers with previous or current chronic low back pain, diagnosed by a physician (for at least the previous three months), who were not incapacitated in terms of job performance. They must have owned a smartphone. All those subjects with a lumbar lesion which did not allow them to perform their work or undertake a PE program, or who did not have a mobile device compatible with the APP, designed for the management of the exercise program, were excluded from the study. The subjects who did not collaborate with the completion of the PE program or who started a new treatment program for their lower back pain during the study period had to leave the study. In addition, patients were free to withdraw from the study on their own volition at any time or because of sickness absenteeism.

Measurement variables were assessed before starting the study and after eight weeks at the end of the exercise program. The medical service was requested to provide the following characteristics of the subjects through their company number: age, sex, height and weight, specific diagnosis of chronic low back pain as well as associated chronic diseases. The main variables were:

Lumbar disability, interference and lumbar pain intensity: To assess lumbar disability, the questionnaire “Oswestry Disability Index” (ODI) was used [20]. Intensity and pain interference were assessed using the “Brief Pain Inventory. Short Form” (BPI Short Form), Spanish version [21, 22]. The authors had permission from MD Anderson University to use this questionnaire.

Angle, bending speed, and flexion-extension ratio (FER): A functional assessment of the lumbar spine was performed using the flexion relaxation (F/R) test measuring kinematic parameters (angle and flexion or bending speed) and a lumbar paraspinal muscle surface electromyography (EMG). The ratio between the root mean square (RMS) value in volts of the spinal erector in maximal lumbar flexion and in standing position (flexion/extension ratio or FER) was calculated. In order to simplify the results interpretation, an inverse ratio (1/FER) was used as has been done in some previous studies [23].

The most frequently repeated movement patterns were: 1. Displacement in the workplace (the worker takes more than one step or not). 2. Cervical movement (cervical flexion or cervical rotation). 3. Spinal movement (forward flexion or left and right rotation). 4. Handle loads (the worker doesn't handle loads or handles load heavier than 1 kg: raise, bring near or push loads). 5. Range of shoulder movement (flexo-abduction <60° or flexo-abduction >60°). 6. Use of tools (gun grip or fist grip).

A series of compensatory exercises were propo-sed for each of the patterns, with the objectives of strengthening the muscle groups that were not active during the day and stretching the ones that are worked on continuously. Exercise were also developed to de-compress and mobilize the lumbar spine for lack of joint movement, as well as increase cardiovascular exercise in case of remaining static in the workplace, and improve motor control in case of performing excessive lumbar movement. For each movement pat-tern described by the workers, exercises were proposed with three levels of difficulty: starting level (for the first 3 weeks of the program), average level (for the 4th and 5th weeks) and advanced level (for the 7th and 8th weeks). The program had a total duration of 8 weeks.

An initial biomechanical assessment was perfor-med by an external laboratory collaborator with the F/R test and ODI, BPI Short Form questionnaires were administered for self-completion. In the F/R test, the electrodes were placed at four points, over the muscles iliocostal erector spinae (right and left), longissimus lumborum (right and left), in two spinal segments (L1-L2 and L4-L5), longitudinally to the muscle fibers. Seven reflective markers were placed in two spinal segments (D12-L1 and S1 level), as well as in both trochanters and in the tips of the third fingers. A complete cleaning of the skin with alcohol and exfoliating was carried out before the placement of the electrodes.

The subject should be at least fifteen seconds static standing to record the initial muscle activation, then the subject should perform flexion-lumbar extens-ion for six seconds, maintaining a second in the position of maximal lumbar flexion. The measurement was repeated three times in a row.

The motion analysis system SMART-DX (BTS Bioengineering, Italy) with BTS FREEEMG 300 electromyographic probes, six BTS Bioengineering - SDX-C2 3D and two video cameras BTS VISTA were used.

The evaluation of the study variables was performed again at eight weeks, once the PE program was completed.

2.2 Statistical analysis

In the statistical analysis, in order to characterize the samples, the variables were described in number and percentage, or mean and standard deviation depending on whether they were quantitative or qualitative respectively. The Shapiro-Wilk test was used to analyze data normality and distribution. A Student T test was used to assess the existence of signifi-cant differences between the variables for independent samples as a parametric test and Mann-Whitney U test as a nonparametric test. Furthermore, a correlation of the variables has been performed applying the Spearman test. Statistical significance was accepted for P-Values <0,05. The analysis was conducted with IBM SPSS Statistics 21 software.

3 Results

Finally, the intervention group consisted of 10 subjects and control by 8 subjects. The flowchart outlines the progress of patients throughout the trial (Fig.1). Table 1 shows the clinical and demographic characteristics of the sample. There were no significant differences in the variables measured before treatment between the control and intervention groups.

Fig. 1

Flowchart outlining the progress of patients throughout the trial.

Table 1

Subjects’ characteristics at baseline

	N = 18	N = 10	N = 8
Characteristics	Total	Intervention	Control
Age (years), Mean (SD)	42,22 (6,19)	42,25 (7,28)	42,20 (5,59)
Gender, N (%)
Male	12 (65)	8 (80)	4 (50)
Female	6 (35)	2 (20)	4 (50)
Lumbar pain diagnosis, N (%)
Nonspecific lumbar pain	13 (72)	7 (70)	6 (75)
Degenerative disc disease	5 (28)	3 (30)	2 (25)
Sick-leave days from last year, Mean (SD)	7,5 (24,05)	3,8 (12,01)	12,12 (34,29)
Years of service in the company, Mean (SD)	13,70 (6,42)	13,15 (7,04)	14,14 (6,24)
Height (meters), Mean (SD)	1,69 (0,75)	1,69 (0,05)	1,68 (0,09)
Weight (kg), Mean (SD)	70,76 (14,31)	72,75 (15,79)	68,27 (12,80)
Body Mass Index, Mean (SD)	24,53 (3,79)	25,12 (4,69)	23,80 (2,34)
<25, N (%)	8 (44)	4 (40)	4 (50)
25–30, N (%)	8 (44)	4 (40)	4 (50)
>30, N (%)	2 (11)	2 (20)	0 (0)

In the analysis of the change produced in the variables before and after treatment within each group, significant differences were obtained for the intervention group in the “pain interference” variable (P < 0,01), and in the “mood” sub-variable (P < 0,05), and “enjoyment” sub-variable (P < 0,05), as well as in “flexion angle” variable (P < 0,05). For the control group significant differences occurred in the “pain intensity” variable (P < 0,05) (Table 2).

Table 2

Change in mean and standard deviation of the principal variables and sub-variables by group before and after the treatment

	Intervention group		Control group
	PRE^d treatment	POST^e treatment	PRE treatment	POST treatment
	Mean (SD)	Mean (SD)	Mean (SD)	Mean (SD)
ODI^a	17 (16,42)	18,6 (14,67)	16,75 (13,09)	12,25 (12,98)
BPI short form^b
Pain intensity in last 24 hours (total)	3,9 (2,05)	2,85 (2,3)	4,75 (1,16)	3,44 (1,19)^*
Maximum pain	5,2 (2,74)	4 (2,91)	7,63 (2)	5,5 (2,33)
Minimum pain	2,3 (1,89)	1,8 (1,99)	3,13 (2,03)	2 (1,77)
Average pain	4,2 (2,3)	3,3 (2,67)	5 (1,41)	3,63 (1,51)
Pain at time of completion	3,9 (2,18)	2,3 (2,36)	3,25 (1,67)	2,63 (1,77)
Pain interference (total)	3,23 (2,48)	2,03 (2,11)^**	3,91 (3,21)	2,82 (2,04)
General activities	4,9 (3,18)	2,9 (2,85)	4,38 (3,2)	2,75 (2,66)
Mood	3,4 (3,06)	1,8 (2,44)^*	4,88 (4,29)	3,38 (3,54)
Walking	1,1 (1,91)	0,6 (1,07)	3,5 (3,85)	1,38 (2,5)
Usual work	4,2 (3,26)	3,1 (3,14)	3,88 (2,95)	3,13 (1,64)
Relations with others	2 (2,67)	1 (1,94)	3,38 (3,85)	1,75 (2,76)
Sleep	3,6 (3,75)	2,9 (3,21)	3,5 (2,83)	3,88 (3,36)
Enjoyment	3,4 (3,13)	1,9 (2,47)^*	3,88 (3,91)	3,5 (3,63)
F/R test^c
Flexion angle (°)	68,38 (9,47)	75,94 (8,34)^*	74,32 (13,89)	72,86 (12,56)
Flexion speed (°/sg)	31,33 (8,47)	31,33 (9,25)	33,69 (10,47)	22,56 (6,63)
FER^e spinalis (uV)	1,10 (0,97)	0,90 (0,60)	0,95 (0,33)	1,07 (0,32)

^aODI: Oswestry Disability Index. ^bBPI: Brief Pain Inventory.^cF/R test: Flexion-Relaxation test. ^eFER: Flexion/extension ratio. ^dPRE: Before the program. ^ePOST: After 8 weeks of exercise program. ^*p < 0,05; ^**p < 0,01.

If we compare the difference of changes produced before and after the treatment between groups, it seems that significant differences were only recorded in the “flexion angle” variable (P < 0,05) (Table 3). No correlations were found between variables.

Table 3

Mean and standard deviation of the variable differences before and after treatment by group, and between groups mean differences (IC 95%) and significance

	Intervention group	Control group	Between groups
	PRE-POST^e	PRE-POST	mean differences
	Mean (SD)	Mean (SD)	(IC 95%)
ODI^a	1,6 (5,15)	–4,5 (8,6)	–6,1 (–13,01 to 0,81)
BPI short form^b
Pain intensity (total)	–1,05 (1,75)	–1,31 (1,22)	–0,26 (–1,81 to 1,29)
Pain interference (total)	–1,2 (1,6)	–1,09 (2,67)	0,11 (–2,03 to 2,26)
F/R test^c
Flexion angle (°)	7,56 (10,28)	–1,46 (3,54)	–9,02 (–16,65 to –1,4)^*
Flexion speed (°/sg)	–0,01 (9,48)	–11,12 (13,8)	–11,12 (–23,6 to 1,36)
FER^d spinalis (uV)	0,2 (0,45)	–0,11 (0,18)	0,31 (–0,05 to 0,67)

^aODI: Oswestry Disability Index. ^bBPI: Brief Pain Inventory. ^cF/R test: Flexion-Relaxation test. ^dFER: Flexion/extension ratio. ^ePRE-POST: Differences between before and after 8 weeks of exercise program. ^*p < 0,05.

4 Discussion

The results of the pilot study show that, after eight weeks of adapted PE plus general recommendations of PE, subjects in the intervention group showed a significant decrease in lumbar pain interference as well as a significant improvement in the angle of lumbar flexion. In the control group, after eight weeks of performing a PE program based on general recommendations, the subjects improved their lumbar pain intensity. When comparing the two PE programs, we observed that the adapted exercise program plus general recommendations seems more effective than the simple general recommendations for the improvement of lumbar flexion movement.

Despite the lack of significance in some cases, both exercise programs generated a decrease in the means of intensity, interference and disability produced by pain, except for the ODI variable in the intervention group (Table 2), which coincides with the results obtained in previous studies performed with workers in whom PE was used as a treatment for chronic low back pain [6 , 27–29].

In the literature it seems that core stability exercise was more effective than general exercise for decreasing pain and increasing back-specific functional status in patients with LBP [30], but there is no clinically important difference between motor control exercises and other forms of exercise in terms of pain and disability in the short term [31].

Regarding the biomechanical variables, the subjects in the intervention group obtained a significant improvement in the maximum angle of lumbar flexion, they maintained the average of speed flexion, and they reduced the FER of the spinal erectors in a non-significant way, whereas the control group obtained a decrease in the angle and speed flexion values, and an increase in the FER of the erectors, all in a non-significant way. Several studies state that subjects with low back pain tend to have a lower range of lumbar motion, and move the spine with slower velocity during flexion movements [32 –34]. For this reason, maybe we could interpret the results obtained in the intervention group as signs of improvement of the functionality of the lumbar spine. In addition, it has been shown that the changes produced in the FER pattern are signs of improvement in relation to pain and function [35, 36]. However, in the present study no correlations were found between FER changes and any disability index change.

The results obtained in the present pilot study are in line with several interventions. Improvements were obtained in the FER values with chronic lumbar pain patients, in which different PE programs were applied [36, 37], as well as training with bio-feedback [37, 38].

Despite the fact that none of the studies perfo-rmed on industrial workers with low back pain used FER in assessing patients’ functionality, it was observed that the application of combined programs with strengthening exercises, flexibility, balance and cardiovascular exercise for two months [27], as well as the application of programs of aerobic exercise of high intensity [8], increased flexibility and nonspecific quantity of movement (distance of fingers-tip to floor).

One of the major limitations was the high number of dropouts during the study. Only 18 of 42 recruited subjects completed the exercise program and performed post-intervention assessment. The power of the study was reduced to 51% and it was not possible to infer the results to the working population with chronic lumbar pain in general.

The APP as a management and self-management tool was a solution to the complex logistics of the company to carry out the PE programs, but in some cases generated technical problems: older versions of smartphone operative system or not enough memory on the device SD card. Other problem was the difficulty in using the APP, especially for older workers, who had limitations with the new technologies. In addition, in the intervention group, the APP sometimes proposed an excessive number of exercises ba-sed on the description of the characteristics of the workstation, so a limit of a maximum number of exercises should be used in future versions of the APP in order to avoid the dropouts for this reason.

Despite having considered in the present study the lumbar disability, the pain level and the pain interference, beliefs and fears of the patient with lumbar pain have not been analyzed. These variables are closely related to chronic low back pain [39] and future studies should take these variables into account.

The self-administered programs had the advantage of not conditioning the subject to a specific schedule or installation, adapting to their possibilities and giving them flexibility in completing the program. Al-though it has been shown that a self-administered exercise program can lead to improvement in patients with chronic low back pain [40], it is considered that a program guided by a professional on site would have greater monitoring and control of the activity performed and as has been demonstrated in some studies, better results in terms of the decrease of pain [41].

Although F/E test as a pain-provoking test has been shown to be reliable for assessing subjects with low back pain [42, 43], it may be insufficient when the pain-inducing factor is lumbar extension or rotation positions as well as axial compression.

5 Conclusion

The implementation of a physical exercise program adapted to the characteristics of the work place, for assembly line workers with chronic low back pain, could be an effective treatment to reduce the interference of pain and to improve the functionality of the lumbar spine. Future studies with a larger sample of subjects and with exhaustive control of the completion of the work-adapted PE program should be performed to confirm the findings of this pilot study.

Conflict of interest

None declared.

Footnotes

Acknowledgments

This research was performed thanks to the support of the Cátedra “Empresa Sana” signed between BSH/E, MAZ and Universidad San Jorge. This work was supported by the Operative Program ERDF Ar-agon 2014–2020, “Building Europe from Aragon”, Research Group Valora.

References

Parent-Thirion

, Fernández

, Hurley

, Vermeylen

. Fourth European Working Conditions Survey. Dublin: European Foundation for the Improvement of Living and Working Conditions; 2007.

Williams

, Westmorland

, Lin

, Schmuck

, Creen

. Effectiveness of workplace rehabilitation interventions in the treatment of work-related low back pain: a systematic review. Disabil Rehabil. 2007;29(8):607–24.

Koda

, Nakagiri

, Yasuda

, Toyota

, Ohara

. A follow-up study of preventive effects on low back pain at worksites by providing a participatory occupational safety and health program. Ind Health. 1997;35(2):243–8.

Bell

, Burnett

. Exercise for the primary, secondary and tertiary prevention of low back pain in the workplace: a systematic review. J Occup Rehabil. 2009;19(1):8–24.

Tveito

, Hysing

, Eriksen

. Low back pain interventions at the workplace: a systematic literature review. Occup Med (Lond). 2004;54(1):3–13.

Kang

, Lee

, Park

, Cynn

. Effect of 6-week lumbar stabilization exercise performed on stable versus unstable surfaces in automobile assembly workers with mechanical chronic low back pain. Work. 2018;60(3):445–54.

Shipton

. Physical Therapy Approaches in the Treatment of Low Back Pain. Pain Ther. 2018.

Murtezani

, Hundozi

, Orovcanec

, Sllamniku

, Osmani

. A comparison of high intensity aerobic exercise and passive modalities for the treatment of workers with chronic low back pain: a randomized, controlled trial. Eur J Phys Rehabil Med. 2011;47(3):359–66.

Rasmussen

, Holtermann

, Mortensen

, Søgaard

, Jørgensen

. Prevention of low back pain and its consequences among nurses aides in elderly care: a stepped-wedge multi-faceted cluster-randomized controlled trial. BMC Public Health. 2013;21(13):1088.

10.

Park

, Lee

, Ko

. The Effects of the Nintendo Wii Exercise Program on Chronic Work-related Low Back Pain in Industrial Workers. J Phys Ther Sci. 2013;25(8):985–8.

11.

White

, Dionne

, Warje

, Koehoorn

, Wagner

, Schultz

, et al. Physical Activity and Exercise Interventions in the Workplace Impacting Work Outcomes: A Stakeholder-Centered Best Evidence Synthesis of Systematic Reviews. Int J Occup Environ Med. 2016;7(2):61–74.

12.

Shariat

, Cleland

, Danaee

, Kargarfard

, Sangelaji

, Tamrin

SBM

. Effects of stretching exercise training and ergonomic modifications on musculoskeletal discomforts of office workers: a randomized controlled trial. Braz J Phys Ther. 2018;22(2):144–53.

13.

van Middelkoop

, Rubinstein

, Verhagen

, Ostelo

, Koes

, van Tulder

. Exercise therapy for chronic nonspecific low-back pain. Best Pract Res Clin Rheumatol. 2010;24(2):193–204.

14.

Agencia Europea para la Seguridad y la Salud en el Trabajo. Introducción a los trastornos musculoesqueléticos de origen laboral: European Agency for Safety and Health at Work; 2007 [cited 2017]. Available from: http://www.insht.es/portal/site/Ergonomia2/menuitem.a31300b4f8e0827cd614c46a280311a0/?vgnextoid=309b96ac6a914310VgnVCM1000008130110aRCRD&vgnextchannel=67c096ac6a914310VgnVCM1000008130110aRCRD.

15.

Garber

, Blissmer

, Deschenes

, Franklin

, Lamonte

, Lee

, et al. American College of Sports Medicine position stand. Quantity and quality of exercise for developing and maintaining cardiorespiratory, musculoskeletal, and neuromotor fitness in apparently healthy adults: guidance for prescribing exercise. Med Sci Sports Exerc. 2011;43(7):1334–59.

16.

Chhabra

, Sharma

, Verma

. Smartphone app in self-management of chronic low back pain: a randomized controlled trial. Eur Spine J. 2018.

17.

Machado

, Pinheiro

, Lee

, Ahmed

, Hendrick

, Williams

, et al. Smartphone apps for the self-management of low back pain: A systematic review. Best Pract Res Clin Rheumatol. 2016;30(6):1098–109.

18.

Johnston

, Hoffman

, Thornton

. Mobile health: a synopsis and comment on “Increasing physical activity with mobile devices: a meta-analysis”. Transl Behav Med. 2014;4(1):4–6.

19.

Mathias

, Crosby

, Qian

, Jiang

, Dansey

, Chung

. Estimating minimally important differences for the worst pain rating of the Brief Pain Inventory-Short Form. J Support Oncol. 2011;9(2):72–8.

20.

Fairbanck

, Couper

, Davies

, O’Brien

. The Oswestry low back pain disability questionnaire. Physiotherapy. 1980;66(8):271–3.

21.

de Andres

, Cruces

, Canos

, Penide

, Del Valle

, Herdman

,et al.. Validation of the Short Form of the Brief Pain Inventory (BPI-SF) in Spanish Patients with Non-Cancer-Related Pain. Pain Pract. 2015;15(7):643–53.

22.

Cleeland

. The Brief Pain Inventory User Guide. Houston University of Texas M. D. Anderson Cancer Center; 2009.

23.

Owens

Jr , Gudavalli

, Wilder

. Paraspinal muscle function assessed with the flexion-relaxation ratio at baseline in a population of patients with back-related leg pain. J Manipulative Physiol Ther. 2011;34(9):594–601.

24.

Keyserling

, Chaffin

. Occupational ergonomics–methods to evaluate physical stress on the job. Annu Rev Public Health. 1986;7:77–104.

25.

Burdorf

, Laan

. Comparison of methods for the assessment of postural load on the back. Scandinavian Journal of Work, Environment & Health. 1991;17(6):425–9.

26.

Kee

, Karwowski

. A comparison of three observational techniques for assessing postural loads in industry. Int J Occup Saf Ergon. 2007;13(1):3–14.

27.

Nassif

, Brosset

, Guillaume

, Delore-Milles

, Tafflet

, Buchholz

,et al.. Evaluation of a randomized controlled trial in the management of chronic lower back pain in a French automotive industry: an observational study. Arch Phys Med Rehabil. 2011;92(12):1927–36 e4.

28.

Sadeghi-Abdollahi

, Eshaghi

, Hosseini

, Ghahremani

, Davatchi

. The efficacy of Back School on chronic low back pain of workers of a pharmaceutical company in a Tehran Suburb. COPCORD stage II study. Int J Rheum Dis. 2012;15(2):144–53.

29.

Bertozzi

, Villafane

, Capra

, Reci

, Pillastrini

. Effect of an exercise programme for the prevention of back and neck pain in poultry slaughterhouse workers. Occup Ther Int. 2015;22(1):36–42.

30.

Coulombe

, Games

, Neil

, Eberman

. Core Stability Exercise Versus General Exercise for Chronic Low Back Pain. J Athl Train. 2017;52(1):71–2.

31.

Saragiotto

, Maher

, Yamato

, Costa

, Menezes Costa

, Ostelo

,et al.. Motor control exercise for chronic non-specific low-back pain. Cochrane Database Syst Rev. 2016;1:CD012004.

32.

Sanchez-Zuriaga

, Lopez-Pascual

, Garrido-Jaen

, de Moya

, Prat-Pastor

. Reliability and validity of a new objective tool for low back pain functional assessment. Spine (Phila Pa 1976). 2011;36(16):1279–88.

33.

Laird

, Gilbert

, Kent

, Keating

. Comparing lumbo-pelvic kinematics in people with and withouy back pain. BMC Musculoskelet Disord. 2014;10(15):229.

34.

McGregor

, McCarthy

, Doré

, Hughes

. Quantitative assessment of the motion of the lumbar spine in the low back pain population and the effect of different spinal pathologies of this motion. Eur Spine J. 1997;6(6):308–15.

35.

Mayer

, Neblett

, Brede

, Gatchel

. The quantified lumbar flexion-relaxation phenomenon is a useful measurement of improvement in a functional restoration program Spine (Phila Pa 1976). 2009;34(22):2458–65.

36.

Marshall

, Murphy

. Changes in the flexion relaxation response following an exercise intervention. Spine (Phila Pa 1976). 2006;31(23):E877–83.

37.

Neblett

, Mayer

, Brede

, Gatchel

. Correcting abnormal flexion-relaxation in chronic lumbar pain: responsiveness to a new biofeedback training protocol. Clin J Pain. 2010;26(5):403–9.

38.

Marchand

, Nougarou

, O’Shaughnessy

, Descarreaux

. Neuromechanical responses after biofeedback training in participants with chronic low back pain: an experimental cohort study. J Manipulative Physiol Ther. 2015;38(7):449–57.

39.

Shirado O

, Doi

, Akai

, Hoshino

, et al. Multicenter randomized controlled trial to evaluate the effect of home-based exercise on patients with chronic low back pain: the Japan low back pain exercise therapy study. Spine (Phila Pa 1976). 2010;1(35(17)):E811–9.

40.

Jakobsen

, Sundstrup

, Brandt

, Jay

, Aagaard

, Andersen

. Effect of workplace- versus home-based physical exercise on musculoskeletal pain among healthcare workers: a cluster randomized controlled trial. Scand J Work Environ Health. 2015;41(2):153–63.

41.

Wei

, Zhu

, Wang

, Fan

, Zhou

. Clinical utility of flexion-extension ratio measured by surface electromyography for patients with nonspecific chronic low-back pain. J Chin Med Assoc. 2019;82(1):35–9.

42.

Colloca

, Hinrichs

. The biomechanical and clinical significance of the lumbar erector spinae flexion-relaxation phenomenon: a review of literature. J Manipulative Physiol Ther. 2005;28(8):623–31.