Abstracts

INTRODUCTION

Low back pain is one of the major public health issues in several industrialized and developing countries, not only due to its high prevalence and incidence, but also because of the labor incapacity it generates, the intensive use of health services it causes and the number of missed working days. Therefore, it is an important cause for the concession of disability insurance¹1. Hoogendoorn WE, Bongers PM, de Vet HC, Ariens GAM, van Mechelen W, Bouter LM. High physical work load and job satisfaction increase the risk of sickness absence due to low back pain: results of a prospective cohort study. Occup Environ Med 2002; 59(5): 323-8. ^{, 2}2. Soucy I, Truchon M, Côté D. Work-related factors contributing to chronic disability in low back pain. Work 2006; 26(3): 313-26..

In many countries, the urban cleaning activity is performed manually, thus exposing the worker to a series of occupational risks, especially those related to physical work overload, as in the case of musculoskeletal impairment³3. Camada IMO, Pataro SM, Fernandes RC. Heavy physical work under time pressure: the garbage collection service- a case study. Work 2012; 41(Suppl 1): 462-69. ^{, 4}4. Poulsen OM, Breum NO, Ebbehøj N, Hansen AM, Ivens UI, van Lelieveld D et al. Collection of domestic waste. Review of occupational health problems and their possible causes. Sci Total Environ 1995; 170(1-2): 1-19.. The role of the physical load caused by frequent trunk flexion and rotation, lifting and/or carrying load, whole body vibration and heavy physical work in the occurrence of low back pain has been widely documented. In the past few years, studies have focused on the psychosocial demands at the workplace⁵5. National Research Council/Institute of Medicine [NRC & IM]. Musculoskeletal disorders and the workplace: low back and upper extremities. Washington DC: National Academy Press; 2001..

Epidemiological studies in different occupational categories have been conducted in different countries, however, there is a gap when it comes to studies that approach the prevalence of low back pain with clear case definition, especially those performed with active individuals. Inconclusive epidemiological studies are also due to the lack of contrast required in the exposure to risk factors, which makes it difficult to determine the associations in more homogeneous occupational groups. Besides, the inadequate control of confusing factors and the inaccurate categorizations of exposure may mask the results⁶6. Burdorf A, Sorock G. Positive and negative evidence of risk factors for back disorders. Scand J Work Environ Health 1997; 23(4): 243-56..

Therefore, an epidemiological study was conducted with the objectives of estimating the prevalence of low back pain, and specifying its frequency, severity and duration of pain, besides the sociodemographic, occupational, extra-occupational characteristics and the factors associated with low back pain in a population of urban cleaning workers.

METHODS

This is a cross-sectional study involving a population of 657 urban cleaning workers (UCW) in Salvador. It was chosen to conduct a census with the maintenance and operation staff from the company that provides the service to the city.

A questionnaire was used for data collection, and direct measurements of weight and height were taken in the beginning, during and at the end of the work shift in a reserved place. The used questionnaire, elaborated by Fernandes⁷7. Fernandes RCP. Distúrbios músculo-esqueléticos e trabalho industrial [tese de doutorado]. Salvador: Instituto de Saúde Coletiva da Universidade Federal da Bahia; 2004., was adapted for the population of UCW, considering their own characteristics. This questionnaire was composed by the following items: sociodemographic aspects; current and former occupational history; habit of smoking; intake of alcohol; use of medications; presence of comorbidities; practice of physical exercises and sports; household chores; questions about musculoskeletal symptoms; and issues related to physical and psychosocial demands at work.

The questionnaire incorporates the amplified version of the Nordic Musculoskeletal Questionnaire (NMQ)⁸8. Kuorinka I, Forcier L. Work related musculoskeletal disorders (WMSDs): a reference book for prevention. London: Taylor & Francis; 1995., which is an instrument that assesses the presence of pain or discomfort in the previous 12 months in anatomic regions of the musculoskeletal system, as well as its severity, duration and frequency.

Cases of low-back Musculoskeletal Disorders (MSD) were defined as the sensation of pain in the past 12 months lasting over one week or minimum monthly frequency, not caused by acute lesion, associated with one or more of the following criteria: level of severity > 3 in a scale from 0 to 5, with anchors on the extremities (no discomfort to unbearable discomfort); search for medical care due to the problem; absence at work (official or not); changing work due to health restrictions⁸8. Kuorinka I, Forcier L. Work related musculoskeletal disorders (WMSDs): a reference book for prevention. London: Taylor & Francis; 1995. ^{, 9}9. Fernandes RC, Carvalho FM, Assunção AA. Prevalence of musculoskeletal disorders among plastics industry workers. Cad Saúde Pública 2011; 27(1): 78-86.. Cases of low-back pain referred to complaints about pain in this region in the past 12 months, without the aforementioned severity criteria. Besides the low-back region, the questionnaire included the following body segments: fingers, hands, fists, forearms, elbows, neck, shoulders, upper back, hips and thighs, knees, legs and ankles. The prevalence of musculoskeletal pain referred only to the presence of pain in one or more of the cited regions in the previous 12 months and, in the case of MSD, pain in the respective body segment that met the aforementioned criteria.

The inclusion of issues related to the severity of symptoms aimed at increasing the specificity of the pain case. However, considering that some studies described in literature do not adopt such criteria, it was also chosen to register pain in the last 12 months for comparison purposes⁹9. Fernandes RC, Carvalho FM, Assunção AA. Prevalence of musculoskeletal disorders among plastics industry workers. Cad Saúde Pública 2011; 27(1): 78-86..

The questionnaire investigated the physical demand at work by means of questions answered by the workers as to frequency, duration or intensity of exposure, in a scale from 0 to 5, with anchors on the extremities, about the work posture, repetitive movements and handling loads.

The psychosocial demands at work were measured by the incorporation of the Job Content Questionnaire (JCQ)¹⁰10. Karasek R. Job Content Instrument: Questionnaire and User's guide. Massachusetts: University of Massachusetts Amhers; 1985. ^{, 11}11. Araújo TM, Karasek R. Validity and reliability of the job content questionnaire in formal and informal jobs in Brazil. Scand J Work Environ Health Suppl 2008; 6: 52-9.. In the analysis, the scores were obtained for psychological demand, control social support and dissatisfaction at work.

For measures of weight and height, obtained with the objective of calculating the body mass index, a portable scale and a stadiometer were used as instruments.

In the statistical approach of data, the prevalence of low-back MSD was analyzed (dependent variable), as well as the means and their respective standard-deviations for most of the independent variables and the percentage of exposure for the other variables. After the descriptive stage, a multivariate logistic regression analysis was conducted using the Epi-Info 6.04 and the R statistical software, respectively.

All of the independent variables in this study were dichotomized. The schooling variable was stratified as lower than complete high school and higher or equal to complete high school. Marital status was identified as married or living together and single or living alone; the presence of children was analyzed as children aged less than two years old and older than two years old or no children; body mass index (BMI) was considered as overweight or obesity and normal or low weight.

The intake of alcohol at least once a week was adopted as the cutoff point. With regard to physical activity, individuals were asked about what they did while not working in the company or at home. "Sedentary" subjects (exposure) were those who reported activities such as reading the newspaper or a magazine, watching television and studying. The report of competitive sports activity or actions like running, doing gymnastics, walking, bike riding, swimming, fishing and gardening were considered as non-exposure ("active"). The variables overtime, smoking and vibration were dichotomized as to the presence or not of the exposure registration.

Variables related to physical demands were summarized into three indexes. The first one refers to the posture in trunk flexion and rotation. The second one refers to dynamic work and includes the variables walking, running, standing up, crouching, and jumping from different levels. In both cases, median was established as the cutoff point. The third index, for handling load, was created from the variables lifting, pushing and pulling loads, with the adoption of the cutoff point above the first quartile, since it would better discriminate this variable. The sitting work was stratified by mean.

The high exposure for psychosocial demand was defined as high psychological demand, low control and low social support¹⁰10. Karasek R. Job Content Instrument: Questionnaire and User's guide. Massachusetts: University of Massachusetts Amhers; 1985.. The registration of at least two of these criteria characterizes high exposure to psychosocial demand at work. Fulfilling at least two of the following criteria, psychological low demand, high control and high social support, characterizes low exposure¹²12. Devereux JJ, Vlachonikolis IG, Buckle PW. Epidemiological study to investigate potential interaction between physical and psychosocial factors at work that may increase the risk of symptoms of musculoskeletal disorder of the neck and upper limb. Occup Environ Med 2002; 59(4): 269-77..

For occupation, performing the activity of waste collection was considered as exposure, and not performing this activity, as non-exposure. The other variables were dichotomized by the mean.

The pre-selection of independent variables to enter the multivariate logistic regression model was based on the biological plausibility criteria of the associations, as well as on the univariate logistic regressions, considering a p-value of 0.25 in the likelihood ratio test for the significance of the coefficient¹³13. Hosmer DW, Lemeshow S. Applied logistic regression. Wiley Interscience: New York; 2000..

The backward model was adopted for the selection of variables. In this exploratory study, α equals to 0.16 was used to enter the model. The choice of a value between 0.15 and 0.20 for the inclusion of variables in this stage is highly recommended, considering that the choice of more rigorous significance levels can exclude important variables from the model¹³13. Hosmer DW, Lemeshow S. Applied logistic regression. Wiley Interscience: New York; 2000..

Since it is a census, and knowing that the methods of statistical inference apply only to the analysis of results obtained from a random sample¹⁴14. Silvany Neto AM. Bioestatística sem segredos. Edição do autor: Salvador; 2008. ^{, 15}15. Conceição MJ. Leitura Crítica dos Dados Estatísticos em Trabalhos Científicos. Ver Bras Anestesiol 2008; 58(3): 260-6., even though the intermediate stages of the logistic regression model required the adoption of alpha values for the selection and permanence of variables, the final results of the model were presented only through the measure of association, without considering confidence intervals.

This study was approved by the Research Ethics Committee of Hospital São Rafael, protocol n. 48/09.

RESULTS

From the total of 657 workers, there was a 5.02% loss, which corresponded to losses and workers on leave with disability insurance, who were not found for interview. The total population of the study was then comprised of 624 workers, all of whom were male. The 624 workers held the following occupations: 367 waste collectors, 118 drivers, 84 cleaning agents and 55 maintenance workers.

The prevalence of pain or discomfort in the past 12 months and of cases of MSD, both considering any segments of the body, was of 77.4 and 62.8%, respectively, in this category. For low-back pain and low-back MSD, according to the specificity criteria that were previously defined, prevalence of 45.5 and 37.0% was found, respectively, superior to the ones found for pain and MSD in other body segments (Table 1). Among the cases of low-back MDS, it was observed that 62,8% of the workers had pain in the last 7 days.

The mean age of the interviewed workers was of 33.9 years old. Out of these, 55.3% were black, 72.0% were married, 18.0% had children younger than 2 years old and 63.1% had not completed high school. The mean of weekly hours destined to household chores was of 4.9 (Table 2).

The intake of alcohol at least once a week was reported by 57.3% of the workers, and the habit of smoking was present among 14.6% of them. BMI was normal for 51.8% of the workers (Table 2).

With regard to occupational aspects, about 96.5% of the workers performed their activities in a fixed shift, and 85.1% did overtime. The total work time was of 19.1 years, and the mean time in the company was of 56.6 months. The mean weekly working hours was of 54.8 hours (Table 2).

The variables for physical demands are presented in Table 3. The work standing up or performing dynamic activities walking, running and jumping from different levels, as well as postures in trunk flexion and rotation, conducting repetitive movements with the hands and raising the arms above the shoulders are frequent among collectors. Besides, a higher exposure to handling load was registered among them when compared to the other occupations. Among drivers, the exposure to the work sitting down and to whole body vibration is frequent, being the latter also referred by collectors due to the truck movements.

The scores for psychosocial demands are presented in Table 4. A higher score was observed for the psychological demand among collectors. A higher control over work was registered among drivers and maintenance workers, and more social support was seen among cleaning agents. The latter, as well as collectors, had higher scores for dissatisfaction at work.

Table 5 reveals the results of the multivariate analysis. It is observed that low back pain was 1.65 times more frequent among those who were mostly exposed to trunk flexion and rotation. Those who performed more dynamic work were more protected for low back pain in relation to those who did not perform those activities. Workers exposed to a higher psychosocial demand had 1.63 times more low back pain than the ones who were not exposed.

It was also observed that workers who had more time of activity inside the company and with lower schooling had more low back pain in comparison to those with less time and higher schooling. Waste collectors had 1.66 times more low back pain than the ones who were not collectors (Table 5).

DISCUSSION

The prevalence of low back MSD among UCWs was high, given the severity criteria adopted in this study. The high prevalence of pain in the past seven days was also noticed among the cases of low back MSD, which demonstrates that many workers perform their work activities at the presence of considerable symptoms. The results of most studies about the prevalence of musculoskeletal symptoms, especially in the low back segment, show the presence of pain in the last 12 months, without adopting severity criteria, thus finding moderate to high values for the prevalence of low back pain in different populations¹⁶16. Hartvigsen J, Bakketeig LS, Leboeuf-Y C, Engberg M, Lauritzen T. The association between physical workload and low back pain clouded by the "healthy worker" effect: population-based cross-sectional and 5-year prospective questionnaire study. Spine (Phila Pa 1976) 2001; 26(16): 1788-92. ^{, 17}17. Mehrdad R, Majlessi-Nasr M, Aminian O, Sharifian AS, Malekahmadi F. Musculoskeletal disorders among municipal solid waste workers. Acta Medica Iranica 2008; 46(3): 233-38.. In this study, the inclusion of questions related to the severity of cases enabled to reduce the classification error of the disease with the purpose of an epidemiological analysis and improved the specificity of the evaluation¹⁸18. Baron S, Hales T, Hurrel J. Evaluation of symptom surveys for occupational musculoskeletal disorders. Am J Ind Med 1996; 29(6): 609-17..

Studies about the prevalence of low back MSD among UCWs are rare not only in Brazil, but also in other countries. A cross-sectional study conducted with workers of this category found a 45.6% prevalence of low back pain, which is similar to this study (45.5%). With regard to musculoskeletal pain in one or more of the nine defined regions of the body in the past 12 months, studies observed prevalence of 65¹⁷17. Mehrdad R, Majlessi-Nasr M, Aminian O, Sharifian AS, Malekahmadi F. Musculoskeletal disorders among municipal solid waste workers. Acta Medica Iranica 2008; 46(3): 233-38. and 54.7%¹⁹19. Oliveira MG. Características organizacionais e acidentes ocupacionais em empresas de limpeza urbana de Salvador-BA [tese de doutorado]. Salvador: Instituto de Saúde Coletiva da Universidade Federal da Bahia; 2008., which were inferior to those in this investigation.

Studies with workers from the industry found different values of low back pain prevalence, being 52% among workers of the assembly line and the petrochemical industry²⁰20. Ijzelenberg W, Burdorf A. Risk factors for musculoskeletal symptoms and ensuing health care use and sick leave. Spine (Phila Pa 1976) 2005; 30(13): 1550-6., and 28.9% for workers in the plastic industry⁹9. Fernandes RC, Carvalho FM, Assunção AA. Prevalence of musculoskeletal disorders among plastics industry workers. Cad Saúde Pública 2011; 27(1): 78-86., and these results are inferior to the ones found in this study.

The mean age found among the UCWs in this study was compatible with the mean of other studies in the same category¹⁷17. Mehrdad R, Majlessi-Nasr M, Aminian O, Sharifian AS, Malekahmadi F. Musculoskeletal disorders among municipal solid waste workers. Acta Medica Iranica 2008; 46(3): 233-38. ^{, 21}21. Miglioransa MH, Rosa LC, Perin C, Ramos GZ, Fossati GF, Stein A. Estudo epidemiológico dos coletores de lixo seletivo. Rev Bras Saúde Ocup 2003; 28(107-018): 19-28., thus showing the relatively Young profile of this category, which can reflect on physical demands of the developed tasks, leading to overload for the body.

The low schooling was observed in this category, which is in accordance with data referring to the population from Bahia (only 3.8% are have 15 or more schooling years). Besides, little more than half of the assessed population was composed of black people, who were considered as the ones with less schooling years when compared to other ethnicities²²22. Instituto Brasileiro de Geografia e Estatística [Internet]. Síntese de Indicadores Sociais 2010. Disponível em: http://www.ibge.gov.br. (Acessado em 26 de setembro de 2010).
Disponível em: http://www.ibge.gov.br... . Other studies with UCWs had similar results concerning schooling¹⁷17. Mehrdad R, Majlessi-Nasr M, Aminian O, Sharifian AS, Malekahmadi F. Musculoskeletal disorders among municipal solid waste workers. Acta Medica Iranica 2008; 46(3): 233-38. ^{, 23}23. Dos Santos Mabuchi A, de Oliveira DF, de Lima MP, da Conceição MB, Fernandes H. The use of alcohol by workers of the garbage collection service. Rev Lat Am Enfermagem 2007; 15(3): 446-52.. According to Ilário²⁵25. Palmer KT, Syddall HE, Cooper C, Coggon D. Smoking and musculoskeletal disorders: findings from a British national survey. Ann Rheum Dis 2003; 62(1): 33-6., the UCWs represent disqualified work force, whose occupational background is usually related to construction or other sort of manual labor. These data reflect the low schooling of this category and the difficulty and the difficulty to enter the work market in other fields. The possible consequence for that is the submission to difficult conditions in this activities and the low interlocution with the management for better work conditions.

The intake of alcohol among these workers is very high²¹21. Miglioransa MH, Rosa LC, Perin C, Ramos GZ, Fossati GF, Stein A. Estudo epidemiológico dos coletores de lixo seletivo. Rev Bras Saúde Ocup 2003; 28(107-018): 19-28. ^{, 23}23. Dos Santos Mabuchi A, de Oliveira DF, de Lima MP, da Conceição MB, Fernandes H. The use of alcohol by workers of the garbage collection service. Rev Lat Am Enfermagem 2007; 15(3): 446-52. ^{, 24}24. Ilário E. Estudo de morbidade em coletores de lixo de um grande centro urbano. Rev Bras Saúde Ocup 1989; 17(66): 7-13.. This study demonstrated high frequency of alcohol intake at least once a week, and this result is compatible with other studies in the same category, which indicate the stressful activity of public waste collection as the precursor of the onset of alcohol intake, calling the attention to the risk of alcoholism among waste collectors²³23. Dos Santos Mabuchi A, de Oliveira DF, de Lima MP, da Conceição MB, Fernandes H. The use of alcohol by workers of the garbage collection service. Rev Lat Am Enfermagem 2007; 15(3): 446-52. ^{, 24}24. Ilário E. Estudo de morbidade em coletores de lixo de um grande centro urbano. Rev Bras Saúde Ocup 1989; 17(66): 7-13..

A low frequency was found with regard to the habit of smoking in this study, when compared to others in this category¹⁷17. Mehrdad R, Majlessi-Nasr M, Aminian O, Sharifian AS, Malekahmadi F. Musculoskeletal disorders among municipal solid waste workers. Acta Medica Iranica 2008; 46(3): 233-38. ^{, 24}24. Ilário E. Estudo de morbidade em coletores de lixo de um grande centro urbano. Rev Bras Saúde Ocup 1989; 17(66): 7-13.. The prevalence of smoking can be related to the socioeconomic status, being more common among workers who perform manual work and those who are unemployed²⁴24. Ilário E. Estudo de morbidade em coletores de lixo de um grande centro urbano. Rev Bras Saúde Ocup 1989; 17(66): 7-13. ^{, 25}25. Palmer KT, Syddall HE, Cooper C, Coggon D. Smoking and musculoskeletal disorders: findings from a British national survey. Ann Rheum Dis 2003; 62(1): 33-6..

Another investigated characteristic was the body mass index, which proved to be normal for more than half of the workers, which can reflect the dynamic character of the urban cleaning activity.

Among the occupational characteristics, it was observed that the total work time demonstrates, based on the mean age of these individuals, the early insertion in the work market, and many of them began in the informal market, in little qualified activities. Besides, the mean time of 4.7 years in the company may reflect the high workforce turnover in this category²⁴24. Ilário E. Estudo de morbidade em coletores de lixo de um grande centro urbano. Rev Bras Saúde Ocup 1989; 17(66): 7-13..

The number of working hours per week among the UCWs is above the predicted working hours by the Federal Constitution of 1988 and by the labor legislation. Even though the workday determined by the company is of eight hours, the workers cannot fulfill the predicted working hours, given the volume of work. This is even more evident by the frequency of overtime reported by the workers. It is known that, due to the characteristics of production, the variability of working conditions and the means to execute the task, that the daily workload is extrapolated, even if paid as overtime³3. Camada IMO, Pataro SM, Fernandes RC. Heavy physical work under time pressure: the garbage collection service- a case study. Work 2012; 41(Suppl 1): 462-69..

The mean hours spent in household chores in the previous week was similar to that found among men in the plastic industry²⁶26. Fernandes RCP, Assunção AA, Silvany Neto AM, Carvalho FM. Muskuloskeletal disorders among workers in plastic manufacturing plants. Rev Bras Epidemiol 2010; 13(1): 11-20.. The little workload found in this study is probably due to the sociocultural construction of a behavior in which the household chore is seen mostly as a female activity, and also because of the hard working hours outside of the house, which is a characteristic of this category.

The high exposure to physical demands, such as handling load and trunk postures in flexion and rotation, is compatible with the one found among nursing workers²⁷27. Ribeiro NF, Fernandes RCP, Solla DJF, Junior ACS, Junior ASS. Prevalência de disturbios osteomusculares relacionados ao trabalho em profissionais de enfermagem. Rev Bras Epidemiol 2012; 15(2): 429-38. and superior to that registered among workers in the plastic industry²⁶26. Fernandes RCP, Assunção AA, Silvany Neto AM, Carvalho FM. Muskuloskeletal disorders among workers in plastic manufacturing plants. Rev Bras Epidemiol 2010; 13(1): 11-20. using the same instrument.

The self-registration of repetitive movements was high for all of the UCWs, which is a similar result to the one found in the aforementioned studies in other categories²⁶26. Fernandes RCP, Assunção AA, Silvany Neto AM, Carvalho FM. Muskuloskeletal disorders among workers in plastic manufacturing plants. Rev Bras Epidemiol 2010; 13(1): 11-20. ^{, 27}27. Ribeiro NF, Fernandes RCP, Solla DJF, Junior ACS, Junior ASS. Prevalência de disturbios osteomusculares relacionados ao trabalho em profissionais de enfermagem. Rev Bras Epidemiol 2012; 15(2): 429-38.. However, based on a repetitive task concept, which is characterized by work cycles smaller that lasts less than 30 seconds, or fundamental cycles constituting more than 50% of the total work cycle²⁸28. Kilbom A. Assessment of physical exposure in relation to work-related musculoskeletal disorders-what information can be obtained from systematic observations? Scand J Work Environ Health 1994; 20: 30-45., an activity that is much more globally dynamic than repetitive is observed in this category, especially among collectors. But this reflects the difficulty to use the repetitiveness question, mostly interpreted as repetitive gestures of distal extremities and others, such as a work situation that is repeated on working days.

With regard to psychosocial demands, high scores were observed for the psychological demand and social support among cleaning workers, higher than the ones found in industry²⁶26. Fernandes RCP, Assunção AA, Silvany Neto AM, Carvalho FM. Muskuloskeletal disorders among workers in plastic manufacturing plants. Rev Bras Epidemiol 2010; 13(1): 11-20. and in the health sector²⁷27. Ribeiro NF, Fernandes RCP, Solla DJF, Junior ACS, Junior ASS. Prevalência de disturbios osteomusculares relacionados ao trabalho em profissionais de enfermagem. Rev Bras Epidemiol 2012; 15(2): 429-38.. This reflects the high demand and the accelerated rhythm found in this service, as well as the essentially collective work, especially inside the collection and cleaning teams. In these activities, there is the need for group cohesion, such as collective competence, so that they can perform their work and administrate situations of task variability²⁹29. Vasconcelos RC, Lima FPA, Camarotto JA, Abreu ACMS, Coutinho Filho AOS. Aspectos de complexidade do trabalho de coletores de lixo domiciliar: a gestão da variabilidade do trabalho na rua. Gest Prod São Carlos 2008; 15(2): 407-19. ^{, 30}30. Santos MCO, Lima FPA, Murta EP, Motta GMV. Desregulamentação do trabalho e desregulação da atividade: o caso da terceirização da limpeza urbana e o trabalho dos garis. Produção 2009; 19(1): 202-13.. More work dissatisfaction at work and less control over it were registered among collectors and cleaning agents. In the collection service, drivers have more autonomy and decision making abilities over the activity³3. Camada IMO, Pataro SM, Fernandes RC. Heavy physical work under time pressure: the garbage collection service- a case study. Work 2012; 41(Suppl 1): 462-69..

Physical and psychosocial demands at work were positively associated with cases of low back pain in this population. Besides these, other occupational factors, such as time of work in the company and being a waste collector were also positively associated. Among the non-occupational variables, the low schooling remained associated with low back pain.

The activity of waste collection is essentially manual³3. Camada IMO, Pataro SM, Fernandes RC. Heavy physical work under time pressure: the garbage collection service- a case study. Work 2012; 41(Suppl 1): 462-69., which requires from the worker constant trunk flexion and rotation movements in the manipulation of waste volumes. Yang et al.³¹ 31. Yang CH, Chang WT, Chuang HY, Tsai SS, Wu TN, Sung FC. Adverse health effects among household waste collectors in Taiwan. Environ Res 2001; 85(3): 195-99. found 2.16 times more low back pain among collection workers than among the ones in other activities in the same company, when adjusted by age, gender, education, smoking and time in the company, which corroborates the result of this study, in which low back pain was 1.66 times higher in this occupation when compared to the others.

The movement of throwing garbage bags during collection generates high shear strength over the low back region⁴4. Poulsen OM, Breum NO, Ebbehøj N, Hansen AM, Ivens UI, van Lelieveld D et al. Collection of domestic waste. Review of occupational health problems and their possible causes. Sci Total Environ 1995; 170(1-2): 1-19.. Besides, extreme flexion postures and the torsion of the trunk that are present in some activities related to handling waste are described in literature as being associated with low back pain complaints⁵5. National Research Council/Institute of Medicine [NRC & IM]. Musculoskeletal disorders and the workplace: low back and upper extremities. Washington DC: National Academy Press; 2001. ^{, 6}6. Burdorf A, Sorock G. Positive and negative evidence of risk factors for back disorders. Scand J Work Environ Health 1997; 23(4): 243-56., and proved by the results in this study. Risk estimates for frequent flexion and rotation movements range from 1.3 and 8.1, and this interval is higher than the one found for load lifting (1.1 to 3.5) in a literature review⁵5. National Research Council/Institute of Medicine [NRC & IM]. Musculoskeletal disorders and the workplace: low back and upper extremities. Washington DC: National Academy Press; 2001.. Excessive posture desensitizes mechanoreceptors, which are in charge of neuromotor control, with consequent loss of the reflex contraction of stabilizing muscles and the increased load over the spine³²32. Pope MH, Goh KL, Magnusson ML. Spine ergonomics. Annu Rev Biomed Eng 2002; 4: 49-68..

Among the UCWs in this study, it was observed that the dynamic occupational work functioned as a protective factor for low back pain. This finding seems to be supported by literature, since the static activity is more damaging to the spine than the dynamic activity. The postural variation enables better disc nutrition, thus preventing its degeneration. Besides, physical aptitude components, such as muscular resistance, which are a characteristic of the dynamic activity, are pointed out as being important protective factors³³33. Toscano JJO, Egypto EP. A influência do sedentarismo na prevalência de lombalgia. Rev Bras Med Esporte 2001; 7(4): 132-7..

Consistent results in different study designs have been found for the relationship between low back pain and psychosocial aspects of work³⁴34. Hoogendoorn WE, Bongers PM, de Vet HCW, Houtman ILD, Ariens GAM, van Mechelen W, et al. Psychosocial work characteristics and psychological strain in relation to low-back pain. Scand J Work Environ Health 2001; 27(4): 258-67. ^{, 35}35. Fernandes RCP, Carvalho FM, Assunção AA, Silvany Neto AM. Interactions between physical and psychosocial demands of work associated to low back pain. Rev Saúde Públ 2009; 43(2): 326-34.. The psychosocial demand has been associated with low back pain in the studied population, even after the adjustment for the other variables.

Some possible explanations of the relationship between psychosocial aspects and low back pain are the fact that the psychosocial characteristics of work may increase psychological tension, and, therefore, muscular activity and excretion of hormones, which contributes with the development or worsening of the symptoms⁵5. National Research Council/Institute of Medicine [NRC & IM]. Musculoskeletal disorders and the workplace: low back and upper extremities. Washington DC: National Academy Press; 2001. ^{, 34}34. Hoogendoorn WE, Bongers PM, de Vet HCW, Houtman ILD, Ariens GAM, van Mechelen W, et al. Psychosocial work characteristics and psychological strain in relation to low-back pain. Scand J Work Environ Health 2001; 27(4): 258-67.. Psychosocial aspects can also decrease the pain threshold, thus causing increased report of symptoms³⁴34. Hoogendoorn WE, Bongers PM, de Vet HCW, Houtman ILD, Ariens GAM, van Mechelen W, et al. Psychosocial work characteristics and psychological strain in relation to low-back pain. Scand J Work Environ Health 2001; 27(4): 258-67.. Likewise, low back pain can affect the perception about work or the way it is performed.

Other variables associated with low back pain were time of work in the company and schooling. The time of exposure to this activity contributes with low back pain, possibly due to the effect of cumulative trauma, which is very discussed in MSD studies⁵5. National Research Council/Institute of Medicine [NRC & IM]. Musculoskeletal disorders and the workplace: low back and upper extremities. Washington DC: National Academy Press; 2001.. As to schooling, no associations were found in studies with UCWs¹⁷17. Mehrdad R, Majlessi-Nasr M, Aminian O, Sharifian AS, Malekahmadi F. Musculoskeletal disorders among municipal solid waste workers. Acta Medica Iranica 2008; 46(3): 233-38.. Some studies that reveal such an association usually do not present adjusted estimates for the physical work load⁶6. Burdorf A, Sorock G. Positive and negative evidence of risk factors for back disorders. Scand J Work Environ Health 1997; 23(4): 243-56..

This study points out to the need for preventive and control measures concerning low back pain at work, through a multifactorial approach that includes adaptation in the physical environment and changes in aspects related to work organization. To provide an adequate physical environment, with proper equipment, tools and technology for the performance of tasks can contribute to reduce the need for extreme movements or the adoption of anomalous trunk postures. It is also important to introduce strategies that promote the expression of capacities, autonomy over the work chore, temporal management of the activity and group support in the context of organizational management.

REFERENCES

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