Electromyographic activity of the erector spinae: The short-effect of one workday for welders with nonspecific chronic low back pain,an observational study

Abstract

OBJECTIVE:

This study aimed to evaluate the effect of one workday on pain and perceived exertion, muscular strength, and electromyographic activity of the erector spinae muscles in welders with and without low back pain. This is an observational cohort study.

PARTICIPANTS:

Twenty-two welders, metallurgical shipbuilding, were equally divided into 2 groups: low back pain and no low back pain. Pain and perceived exertion. Muscular strength by maximal voluntary contractions and electromyographic activity of right and left erector spinae muscles during maximal voluntary contractions and in the 3 welding positions for 2 periods of the workday (in the morning and at the end of the workday).

RESULTS:

At the end of workday, the pain increased significantly for the low back pain group (t(22) $=$ 2.448; $P=$ 0.023). The perceived exertion also increased significantly for both groups at the end of workday groups (F(1,22) $=$ 8.570, $P=$ 0.000) and periods (F(1,22) $=$ 8.142, $P=$ 0.000). There were no significant differences between groups and workday periods for muscular strength and electromyographic activity during maximal voluntary contractions of the erector spinae. There was no significance difference for electromyographic activity between groups and workday period and in the 3 welding positions.

CONCLUSION:

Although the pain and perceived exertion increased at the end of the workday, these results did not interfere in muscular strength and electromyographic activity of right and left erector spinae muscles. Thus, we can conclude that welders with chronic low back pain had a good physical capacity (muscular strength) and that muscle performance was maintained.

Keywords

Occupational biomechanics electromyographic workplace low back pain ergonomics

1. Introduction

Low back pain (LBP) is a significant public health problem with an estimated global prevalence of 11.9 $\pm$ 2.0% on average or 23.2 $\pm$ 2.9% in 1 month with a tendency to increase in the coming decades as a result of population aging [1]. Additionally, LBP is the most common work-related musculoskeletal disorder (WRMSD) occurring mainly during productive age and ranking in the top 10 causes of years lived with disability [2]. An integration of several factors, such as personal, occupational, and psychosocial, have been appointed with determinant to occur LBP [3]. The potential predictors for an increase of LBP incidence in workers are load lifting, monotonous tasks [4, 5], and an interrelation between physical and psychosocial factors [3, 6]. In addition, risk for the onset and course of LBP at the workplace involves spontaneous breaks, stiffness in procedures and work routines, static forces, and repetitive movements in spinal flexion and rotation [1, 4, 7].

A longitudinal study demonstrated that 51% of welders and metalworkers have been absent from work because of musculoskeletal complaints, LBP being the major cause [8]. Welders adopt some awkward postures and remain in these postures for long periods of time during the workday when performing their job [9, 10]. Trunk flexion movements that are necessary to perform welding [11], such as excessive bending and twisting postures in confined spaces, are considered risk factors for LBP [12, 13]. This can be explained by specific characteristics of the welder’s job, which should be related to the occurrence of back pain. Because of the demands of welding work, the adoption of ergonomic interventions to mitigate the problem of LBP is often impossible [6].

Thus, it appears that the most appropriate intervention is monitoring the workers to diagnose early in order to prevent further complaints, maintain the functional capacity of the worker, and preserve health. The surface electromyographic has been described as a potential tool to directly measure both the diagnosis [14, 15] and prognosis of patients with LBP after therapy [15]. Individuals with LBP present asymmetries or decreases of the electromyographic signal (SEMG) when compared with healthy individuals [14]. This suggests that the muscle fatigue [16] response is a strong predictor of functional capacity, allowing the monitoring of individuals with LBP to avoid a worsening of clinical conditions [14]. In addition, electromyographic variables seem to correlate with changes in trunk muscle recruitment patterns in individuals with nonspecific LBP [15, 17, 18].

The prognosis of LBP depends on various factors [19], although the majority of patients with acute or persistent LBP will be better in six weeks independent of the therapies used [20]. On the other hand, workers’ lack of physical fitness may lower the functional capacity of workers in rehabilitation compared with those who stay at work with chronic nonspecific musculoskeletal LBP [21], and consequently, physical deconditioning [22]. Thus, sick leave workers at work have lower physical fitness, higher perceived workload, fear avoidance, and life control which increase the chances of acute pain becoming a chronic condition [22, 23, 24].

There is strong evidence that the longer the worker stays away from work, the more difficulty he will have returning to work [25]. The hypothesis of this study is that individuals with LBP who continue to actively work can preserve their muscular trunk strength and electromyographic activity even with pain. Therefore, staying at work contributes to workers maintaining muscle capacity as they perform their occupational activities.

This study aimed to evaluate the effect of one workday on pain and perceived exertion, muscular strength, and electromyographic activity of the erector spinae muscles in welders with and without LBP.

2. Methods

This is a comparative cohort study, conducted from July to December 2013. The research was approved by the local Ethics Committee (process number 011673/ 2013), and all the participants signed an informed consent form.

2.1 Participants

The participants were selected from 123 right-handed male welders who worked at a metallurgical shipbuilding company in the city of Santos, São Paulo, Brazil. All workers were interviewed and responded questionnaire about on their sociodemographic and occupational characteristics, musculoskeletal diseases, physical activity level (Baecke Questionnaire [26]), perception of the relationship between job risk factors and musculoskeletal diseases (Job Factor Questionnaire [27, 28]), and fatigue self-perceived association with psychosocial job factors (Need for Recovery Scale [29]).

The inclusion criteria for the LBP group were active welders at work with at least 1 year of experience, who had an episode of acute LBP lasting more than 24 hours after a period of 30 days without pain [30] and without musculoskeletal complaints in other body regions. According to the European Low Back Pain Guidelines [31], several diagnostic classification systems for acute low back pain are suggested; however, because none of these classification systems has been critically validated [32], data history and clinical examination were considered [33]. The exclusion criteria were workers who had a clinical diagnosis of disc herniation with symptoms of nerve root impairment, such as diminished reflexes, paresthesia in the lower limbs, or decreased sensation and pain with a visceral origin or rheumatic pain were excluded from the LBP group, as were those with a previous history of surgery on the lumbar spinae.

The amount welders ( $n=$ 123) after applied all eligibility criteria, only 11 welders with low back pain (LBP) diagnosis were included in this study. To evaluate effect of one workday in electromyographic activity of the erector spinae our comparative were welders no low back pain (No LBP) group ( $n=$ 11). The pairing of the No LBP group ( $n=$ 11) was based on age, sex, and body mass index (BMI) of the LBP group.

2.2 Equipment

Three devices with channel synchronization were used. A lumbar dynamometer TFL-200 EMG System® Brazil model with a maximum capacity of 300 kg/f was used to test maximum muscle strength. For the acquisition of the SEMG of the bilateral erector spinae muscles, the EMG System ${}^{\@setsize{\scriptsize}{8pt}{\viipt}{\@viipt}\textregistered}$ Brazil [34] EMG-800RF was used, consisting of 16 channels with a digital-analog conversion card and 16-bit resolution, an amplifier with 2000X total amplification, input impedance of 109 Ohms, common-mode rejection ratio more than 120 dB, noise ratio less than 3 $\mu$ V, and a second order Butterworth filter band-pass with a 10–1000 Hz band. Active (Ag/AgCl) bipolar rectangular surface electrodes (4.5 $\times$ 3.5 cm) were used. An electrogoniometer (EMG System ${}^{\@setsize{\scriptsize}{8pt}{\viipt}{\@viipt}\textregistered}$ Brazil), consisting of fixed and mobile arms and an axis, was also used to adjust the trunk position before data acquisition.

2.3 Experimental conditions

The job of the welder is to weld pre-cut pieces of metal from the weld shop sector using a welding electrode or gun. Thus, the work can be performed in workshops or while building on a ship.

The three welding positions used in this study were: P1) standing with horizontal trunk flexion; P2) semi-kneeling (left knee flexion with the knee on the floor and right foot flat on the surface with the trunk flexed); and P3) kneeling with both knees on the floor with flexion of the trunk (Fig. 1). The angle of the trunk was initially placed at approximately 30 degrees for each welding position using the electrogoniometer, with the axis positioned at the right side of the trunk in the anterosuperior iliac spinae line.

After this adjusted position, the welders could make fine and small adjustments to reach the most comfortable body position for their work. Then, the final angle of the trunk that was adopted by each worker in the morning was also used for the evaluation at the end of the workday. The welding positions used in this study were established by company managers according to physical demands.

2.4 Procedures

Data collection was performed twice during the workday: in the morning (first hours of the day) and at the end of the workday (the last hour of an 8-hour shift). The evaluations were conducted in a welding laboratory, where the three welding positions were reproduced as men welded steel sheets.

For the maximum voluntary contraction (MVC) evaluation, the participants were positioned on the dynamometer platform with their feet in a comfortable position and both hands holding the handle. Then, the trunk of the volunteers was maintained in a position with 30 degrees of flexion using the adjustable height device when necessary to ensure the angulation. The volunteers were instructed to pull a lever up to the maximum possible strength when a verbal command was given. Data were gathered 3 times during a period of 10 seconds; the dynamometer provided resistance and recorded the amount of strength in kg/f.

For the SEMG evaluation of the simulated activities, 3 trials were collected. Each trial lasted 10 seconds with a 30-second interval between assessments. Electrodes were placed according to the recommendations of the SENIAM [35] project (Surface Electromyography for the Non-Invasive Assessment of Muscles). The volunteers were placed in a standing position with the lumbar region free of clothing; the mounting location of the electrodes was cleaned with cotton and 70% alcohol. Electrodes were placed bilaterally at L1 on the skin over the erector muscles of the lumbar spinae with a distance of 20 mm between the electrodes. The attachment of the EMG electrode was accomplished after alcohol evaporation to avoid interference. In cases in which volunteers had hair on the region of the electrode attachment, shaving was performed with disposable razors.

Participants from both groups indicated the intensity of pain and perceived exertion using the Borg CR10 scale [36, 37]. This modified scale rated from 0 to 10 points, with 0 being no pain/no perceived exertion and 10 being much pain/much perceived exertion.

2.5 Data analysis

For data analysis, electromyographic and dynamometric signals underwent a digital filtering process using the software EMGLAB V1.1 (EMG System ${}^{\@setsize{\scriptsize}{8pt}{\viipt}{\@viipt}\textregistered}$ Brazil, version 2010). For the EMG signal, a Butterworth band-pass filter was used (fourth order, with cutoff frequencies between 10 and 500 Hz). After obtaining the signals, files were saved as text for posterior analysis.

Data from each trial were then loaded into MATLAB software (MathWorks 7.0) to determine the root mean square (RMS) of the strength and electromyographic signals. The maximum value of the RMS obtained from the 3 trials of MVC was used to normalize the electromyographic data from the 3 trials of each welding position. The mean of the 3 trials at each position assessed in the morning and at the end of the workday were used for statistical analysis.

2.6 Statistical analysis

SPSS software (version 22.0) was used for statistical analysis. A t-test was used to compare pain during the 2 periods of the workday, only in the LBP group. Analysis of variance (ANOVA) for repeated measures with 1 factor (periods of the workday) was used to compare muscular strength and exertion perception scores between the groups. ANOVA with 2 factors (period of the day and muscle strength) was used to analyze EMG activity during MVC, and a 3-factor ANOVA (welding position, 2 periods of the workday, muscle strength) was used to verify the existence of significant differences in the EMG activity between the groups. A significance level of 5% was considered and post hoc Bonferroni adjustments were performed when necessary.

3. Results

The 11 participants in the LBP group had an average time in job of 41.56 (SD 56.33) months, age of 31.09 (SD 12.25) years, BMI of 23.86 (SD 2.25) kg/m ${}^{2}$ , and 51.32% has active lifestyle. The 11 workers in the No LBP group had an average time in job of 47.34 (SD 54.71) months, age of 29.08 (SD 8.39) years and BMI of 24.65 (SD 2.48) kg/m ${}^{2}$ , and 41.78% has active lifestyle. More than 76% of workers in both groups were married or living with a partner.

The job factors self -perceived for occurrence of musculoskeletal disease were respectively 6.21 (SD 3.00) and 6.70 (SD 2.94) for LBP and No LBP group in a likert scale (0 to 10 points). Regarding perceived fatigue associated with psychosocial job factors the average percentage for LBP group was 34.87 (SD 15.49) and No LBP group was 33.30 (SD 13.67) on a scale ranging from 0 to 100 points.

The pain increased significantly at the end of the workday for the LBP group (t(22) $=$ 2.448; $P=$ 0.023). The pain score for the No LBP group was 0 for both periods; statistical analysis was not performed to compare groups or periods. The perceived exertion was significantly different between the groups (F(1,22) $=$ 8.570, $P=$ 0.000) and between the periods of the workday (F(1,22) $=$ 8.142, $P=$ 0.000). This difference is a result of the greater perceived exertion score for the LBP group, specifically at the end of the workday (Table 1).

Table 1
Average and standard deviation of LBP and physical exertion perceived by workers with LBP ( $n=$ 11) and No LBP ( $n=$ 11) during the morning and at the end of the workday

Likert scale	Morning		End of the day
(0–10)	LBP	No LBP	LBP	No LBP
	Average (SD)		Average (SD)
Pain	4.91 (2.21)	0	6.36 (1.86)	0
Perceived	0.27 (0.64)	0	4.18 (1.47)	2.36 (1.56)
exertion

SD – Standard Deviation.

The maximum muscular strength during the MVC evaluation was not significantly different between the groups and periods of the workday (F(1,20) $=$ 2.627, $P=$ 0.121) and (F(1,20) $=$ 0.060, $P=$ 0.810), respectively. The muscular strength had decreased at the end of the workday for the LBP group, unlike the No LBP group, who demonstrated greater muscular strength at the end of the workday (Fig. 1).

Figure 1.

Average muscle strength (kg/f) assessed by maximal voluntary contraction (MVC) in workers with LBP ( $n=$ 11) and No LBP ( $n=$ 11) in the morning and at the end of the workday.

The RMS of SEMG activity averaged during MVC was similar between groups and periods (F(1,20) $=$ 0.043, $P=$ 0.838) and (F(1,20) $=$ 1,634, $P=$ 0.216), respectively. However, the muscles on the non-dominant side of the LBP group showed a greater increase in the SEMG activity between the 2 periods (Fig. 2).

Figure 2.

Normalized electromyographic activity of erector spinae muscles (average and standard deviation) during maximal voluntary contraction in welders with LBP ( $n=$ 11) and No LBP ( $n=$ 11) in the morning and at the end of the workday. Data presented in arbitrary units (a.u.).

The comparison of the RMS of SEMG activity of the erector spinae muscles between groups during the 3 simulated welding positions in the morning and at the end of the workday revealed a significant interaction across the groups, welding positions, and period factors (F(2,40) $=$ 5.31, $P=$ 0.009), but significant differences were not found by the post hoc analysis using a Bonferroni adjustment.

In a further analysis, however, the comparison of the RMS of SEMG activity of the erector spinae muscles between groups during the evaluation of the 3 simulated welding positions for each period separately indicated a significant difference between groups by welding position interaction only for the first evaluation (F(2,42) $=$ 5.084, $P=$ 0.011). This interaction was due to the differences across positions only for the No LBP group ( $P<$ 0.05). The RMS of SEMG activity of the No LBP group in the morning was influenced by the simulated positions, where the electromyographic activity in the P1 position was higher when compared to the other 2 welding positions (Fig. 3).

Figure 3.

Normalized electromyographic activity of erector spinae muscles of the right and left side (average and standard deviation) in welders with LBP ( $n=$ 11) and No LBP ( $n=$ 11) in 3 different welding positions in the morning (A) and at the end of the workday (B). Data presented in arbitrary units (a.u.).

4. Discussion

LBP did not influence the muscular strength and electromyographic activity during the MVC or P1, P2, or P3 postures in the morning and at the end of the workday, although the pain was significantly greater for the LBP group between the 2 assessment times. This was not expected because maintaining certain postures for long periods, in welders, as well as in many other professional activities, is frequently reported as a cause of LBP [7].

More recently it has been confirmed that biomechanical, individual, and psychosocial risk factors increased the risk of low back disorder referring to the discussion of causal factors for LBP [13, 38]. However, the groups LBP and No LBP presented very similar sociodemographic, occupational, physical activity level, and fatigue associated with psychosocial job risk. Regardless, it seems that more studies assessing the relationship between back pain and specific occupational postures as performed in this study still are needed to evaluate these correlations. In addition, the muscular strength and electromyographic activity of the erector spinae muscles in the LBP group was expected to decrease at the end of the workday when compared to that measured in the morning.

Thus, with increased pain and exertion perceived, workers would use fewer lumbar muscles to perform the activities, which would increase back pain. These hypotheses confirm that individuals with LBP exhibit asymmetries and decreases of electromyographic signals during certain activities, causing increased pain or pain exposure to other soft tissues, such as the ligaments of the lumbar spinae [14]. However, a modulation of the muscle activity seems to be related to specific positions adopted only for the No LBP group.

Furthermore, in relation to muscle strength, it was not possible to identify a distinct correlation between the 2 groups. For the LBP group, lumbar muscle strength decreased at the end of the workday, while in the No LBP group, there was an increase in lumbar muscle strength in relation to the first measurement period. However, the initial level of the LBP was higher in the morning compared to those with No LBP. Thus, the hypothesis that the group would have less back pain and more muscle strength than those with No LBP at the end of the workday was nil.

It is possible that pain and perceived exertion may have influenced the decrease in muscle strength because the pain reported by the workers in the LBP group, as well as perceived exertion, increased by 30% at the end of the workday. In addition, it is possible that this has also happened because they were more tired than workers without pain (i.e., the No LBP group) at the end of the workday. Thus, they could not achieve or sustain a maximum contraction during the requested time that was similar to that obtained in the first collection. Despite workers staying at work reporting lower levels of perceived workload, higher pain acceptance compared with sick-leave workers in rehabilitation [21, 23].

Thus, even with decreased strength in the LBP group, the electromyographic signal of the erector spinae muscles of these workers showed no significant change. This indicates that the worker maintained the recruitment of motor units but failed to sustain the same strength [39]. Another hypothesis is that the workers in the No LBP group are more active due to work that does not have the same response as patients with LBP [8]. There are studies showing that patients with acute and sub-acute LBP are more active than those with chronic LBP [40]. It is likely that workers with LBP who continue in their work activities [41] can maintain strength, functional capacity, and muscle activation pattern. For a worker having difficulty returning to normal occupational duties within 4–12 weeks, there is strong evidence that the longer the worker is off work with LBP, the lower the chances are of ever returning to work. Most clinical interventions are quite ineffective at returning people to work once they have been off work for a protracted period with LBP [30].

Our study reinforces the multiple benefits that physical therapy care can have in workplaces with employees who experience LBP [42]. In addition, this is the first study that evaluated the electromyographic strategic analysis in a real work condition.

5. Limitations

The limitation in this study was the impossibility of developing continuous analysis in the workplace. We choose to evaluate a normal workday with moderate demands; this may have been a limitation of the study. Therefore, considering the care to be taken with EMG electrodes, next studies should consider on randomized workdays analysis with different demands. Cohort studies are necessary to evaluate the work demand effect in muscle strength and electromyographic activity allowing early diagnosis and better prognosis of LBP among workers. Future studies should prioritize the assessment of the risk factors prognosis of LBP in workers. In addition, also to investigate job exposure factors, which contribute to management the pain, disability, maintaining of functional and work capacity, and avoiding absence from work. Finally, to evaluate the influence of stress on the work and the engagement of the workers for the prognosis of low back pain.

6. Conclusion

The present study demonstrated that muscle strength and electromyographic activity do not change for either group during the workday. The group with pain had decreased strength at the end of the workday, but there were no major changes in electromyographic activity for either group.

Footnotes

Conflict of interest

All authors confirm that there are no known conflicts of interest associated with this publication, and there has been no significant financial support for this work that could have influenced its outcome.

References

Hoy

Bain

Williams

March

, et al. A systematic review of the global prevalence of low back pain. Arthritis Rheum 2012 Jun; 64: 2028-37.

Vos

, et al. Global, regional, and national incidence, prevalence, and years lived with disability for 301 acute and chronic diseases and injuries in 188 countries, 1990-2013: A systematic analysis for the Global Burden of Disease Study 2013. The Lacet 2015; 386: 743-800.

Govindu

Babski-Reeves

. Effects of personal, psychosocial and occupational factors on low back pain severity in workers. Int J Ind Ergon 2014 March; 44: 335-341.

Driscoll

Jacklyn

Orchard

, et al. The global burden of occupationally related low back pain: Estimates from the Global Burden of Disease 2010 study. Ann Rheum Dis 2014; 73: 975-81.

Matsudaira

Konishi

Miyoshi

Isomura

, et al. Potential risk factors for new onset of back pain disability in Japanese workers: Findings from the Japan epidemiological research of occupation-related back pain study. Spine 2012; 37: 1324-33.

Silva

Barros

Cunha

Carnide

Santos

. Prevalence of back pain problems in relation to occupational group. Int J Ind Ergon 2016; 52: 52-58.

Kwon

Roffey

Bishop

Dagenais

, et al. Systematic review: Occupational physical activity and low back pain. Occup Med 2011; 61: 541-8.

Burdorf

Jansen

. Predicting the long term course of low back pain and its consequences for sickness absence and associated work disability. Occup Environ Med 2006; 63(8): 522-9.

Chunga

Leeb

Keec

. Effect of stool height and holding time on postural load of squatting postures. Int J Ind Ergon 2003; 32: 309-317.

10.

Lowe

Wurzelbacher

Shulman

Hudock

. Electromyographic and discomfort analysis of confined-space shipyard welding processes. Appl Ergon 2001; 32: 255-269.

11.

Vieira

Kumar

. Occupational risks factors identified and interventions suggested by welders and computer numeric control workers to control low back disorders in two steel companies. Int J Ind Ergon 2007; 37: 553-561.

12.

Fethke

Gant

Gerr

. Comparison of biomechanical loading during use of conventional stud welding equipment and an alternate system. Appl Ergon 2011; 42: 725-734.

13.

Ferguson

Allread

Burr

Heaney

, et al. Biomechanical, psychosocial and individual risk factors predicting low back functional impairment among furniture distribution employees. Clin Biomech 2012; 27(2): 117-23.

14.

Reger

Shah

Adams

Endredi

, et al. Classification of large array surface myoelectric potentials from subjects with and without low back pain. J Electromyogr Kinesiol 2006; 16: 392-401.

15.

van Damme

Stevens

Perneel

Van Tiggelen

, et al. A surface electromyography based objective method to identify patients with nonspecific chronic low back pain, presenting a flexion related movement control impairment. J Electromyogr Kinesiol 2014; 24(6): 954-964.

16.

Geisser

Ranavaya

Haig

Roth

, et al. A meta-analytic review of surface electromyography among persons with low back pain and normal, healthy controls. J Pain 2005; 6(11): 711-26.

17.

Heydari

Nargol

AVF

Jones

APC

Humphrey

, et al. EMG analysis of lumbar paraspinal muscles as a predictor of the risk of low-back pain. Eur Spine J 2010; 19: 1145-1152.

18.

Kwok

Tse

Luk

. Time-varying surface electromyography topography as a prognostic tool for chronic low back pain rehabilitation. Spine 2014; 14(6): 1049-56.

19.

Hayden

Chou

Hogg-Johnson

Bombardier

. Systematic reviews of low back pain prognosis had variable methods and results: Guidance for future prognosis reviews. J Clin Epidemiol 2009 Aug; 62(8): 781-796.

20.

da C Menezes Costa

Maher

Hancock

McAuley

, et al. The prognosis of acute and persistent low-back pain: A meta-analysis. Can Med Assoc J 2012 Aug 7; 184(11): E613-24.

21.

Soer

, de Vries

Brouwer

Groothoff

Geertzen

Reneman

. Do workers with chronic nonspecific musculoskeletal pain, with and without sick leave, have lower functional capacity compared with healthy workers? Arch Phys Med Rehabil 2012; Dec; 93(12): 2216-22.

22.

Bousema

Verbunt

Seelen

Vlaeyen

Knottnerus

. Disuse and physical deconditioning in the first year after the onset of back pain. Pain 2007; 130: 279-86.

23.

De Vries

Reneman

Groothoff

Geertzen

JHB

Brouwer

. Workers Who stay at work despite chronic nonspecific musculoskeletal pain: Do they differ from workers with sick leave? Journal of Occupational Rehabilitation 2012; 22(4): 489-502. doi: 10.1007/s10926-012-9360-6.

24.

Lin

McAuley

Macedo

Barnett

, et al. Relationship between physical activity and disability in low back pain: A systematic review and meta-analysis. J Pain 2011; 152(3): 607-13.

25.

Airaksinen

Brox

Cedraschi

Hildebrandt

, et al. COST B13 Working group on guidelines for chronic low back pain. Eur Spine J 2006 Mar; 15(Suppl 2): S192-300.

26.

Florindo

. Latorre MRDO: Validation and reliability of the Baecke questionnaire for the evaluation of habitual physical activity in adult men. Rev Bras Med Esporte 2003; 9: 121-12827.

27.

Coluci

Alexandre

Rosecrance

. Reliability and validity of an ergonomics-related job factors questionnaire. Int J Ind Ergon 2009; 39: 995-1001.

28.

Comper

MLC

Padula

. Ergonomic risk assessment in textile industry workers by two instruments: Quick exposure check and job factors questionnaire. Fisioter Pesq 2013; 20: 215-21.

29.

Moriguchi

Alem

MER

Veldhoven

, et al. Cultural adaptation and psychometric properties of Brazilian Need for Recovery Scale. Rev Saude Publica 2010; 44: 131-9.

30.

de Vet

Heymans

Dunn

Pope

, et al. Episodes of low back pain: A proposal for uniform definitions to be used in research. Spine 2002; 27(21): 2409-16.

31.

Burton

Balagué

Cardon

Eriksen

, et al. European guidelines for prevention in low back pain. Eur Spine J 2006 15(Suppl 2): S136-S168.

32.

Kamper

Maher

Koes

Croft

, et al. Treatment-based subgroups of low back pain: A guide to appraisal of research studies and a summary of current evidence. Best Pract Res Cl Rh 2010 Apr; 24(2): 181-91.

33.

van Tulder

Becker

Bekkering

Breen

, et al. European guidelines for the management of acute nonspecific low back pain in primary care. Eur Spine J 2006; 15(Suppl 2): S169-S191.

34.

Watari

Sartor

Picon

Butugan

Amorim

Ortega

, et al. Effect of diabetic neuropathy severity classified by a fuzzy model in muscle dynamics during gait. J Neuroeng Rehabil 2014; 11(1): 1.

35.

Surface ElectroMyoGraphy for the Non-Invasive Assessment of Muscles (SENIAM). Avaiable in www.seniam.org. Accessed in 20/09/2012.

36.

Borg

. Psychophysical bases of perceived exertion. Med Sci Spor Exer 1982; 14: 377-381.

37.

Morishita

Yamauchi

Fujisawa

Kazuhisa

. Rating of perceived exertion for quantification of the intensity of resistance exercise. Int J Phys Med Rehabil 2013; 1(9): 172.

38.

Widanarko

Legg

Stevenson

Devereux

, et al. Prevalence and work-related risk factors for reduced activities and absenteeism due to low back symptoms. Appl Ergon 2012; 43: 727-737.

39.

Tucker

Falla

Graven-Nielsen

Farina

. Electromyographic mapping of the erector spinae muscle with varying load and during sustained contraction. J Electromyogr Kinesiol 2009; 19: 373-379.

40.

Dahm

Brurberg

Jamtvedt

Hagen

. Advice to rest in bed versus advice to stay active for acute low-back pain and sciatica. Cochrane Database Syst Rev 2010; 16(6).

41.

Padula

Carregaro

Melo

Silva

. Low Back pain disability and stay at work: Contradiction or necessity? Work 2012; 41: 2417-2419.

42.

Nassif

Brosset

Guillaume

Delore-Milles

Tafflet

Buchholz

Toussaint

. 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 Dec; 92(12): 1927-1936.