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Revista Latino-Americana de Enfermagem

On-line version ISSN 1518-8345

Rev. Latino-Am. Enfermagem vol.22 no.3 Ribeirão Preto May/June 2014 

Original Articles

Low back pain characterized by muscle resistance and occupational factors associated with nursing1

Rafael de Souza Petersen 2  

Maria Helena Palucci Marziale

2MSc. Scholarship holder from Coordenação de Pessoal de Nível Superior (CAPES)

3PhD, Full Professor, Escola de Enfermagem de Ribeirão Preto, Universidade de São Paulo, WHO Collaborating Centre for Nursing Research Development, Ribeirão Preto, SP, Brazil



to identify the occupational factors associated with low back pain using a surveillance tool and to characterize the low back pain by the resistance of the extensor muscles of the vertebral column among nursing professionals at an Intensive Care Unit.


Cross-sectional study. The workers answered a questionnaire about occupational factors and participated in a resistance test of the extensor muscles of the vertebral column. Associations were established through Student's T-test or Mann-Whitney's U-test and correlations using Pearson's test.


Out of 48 participants, 32 (67%) suffered from low pain. For the resistance test, the subjects suffering from low back pain endured less time in comparison with asymptomatic subjects, but without significant differences (p=0.147). The duration of the pain episode showed a significant negative correlation (p=0.016) with the results of the resistance test though. The main factors identified as causes of low back pain were biomechanical and postural elements, conditions of the muscle structure and physical and organizational conditions.


the main occupational factors associated with the low back pain were the posture and the characteristics of the physical and organizational conditions. In addition, the extensor muscles of the column showed a trend towards lesser resistance for workers in pain. This evidence is important when considering prevention and treatment strategies.

Key words: Intensive Care Units; Nursing; Low Back Pain; Human Engineering; Physical Endurance; Occupational Health


Low back pain (LBP) has been characterized as a condition related to nursing staff (NS) in intensive care units (ICU) when analyzed from an ergonomic point of view, due to exposure to occupational risks that contribute to LBP. However, the ergonomic risk factors related to LBP in NS have been less understood even though there is still a high prevalence of LBP symptoms( 1 - 2 ).

The ICU exhibits important risks for NS in relation to the organization, the conditions of work and the social and professional relationship( 2 ). Moreover, the fact that the ICU areas have been designated for the care of unstable patients and with risk of death( 2 ), contributes to a correlation between stress and the appearance of cardiovascular, digestive, and musculoskeletal system symptoms for NS( 3 ).

Among the causes of work-related LBP, individual factors (gender, age, stature, obesity, muscular strength related to the work requirements, endurance of the back musculature and smoking) and organizational factors (heavy, vigorous lifting movements, bending and twisting the vertebral column, vibration of the entire body, and work that is physically tiring) have been highlighted( 4 ). The most useful way to understand the occupational risks of LBP is based on the application of questionnaires related to the theory of the surveillance model( 5 ), in which the detection of work factors that contribute to LBP are based on the declaration of the workers involved. Therefore, the model is based in the early detection and control of musculoskeletal disorders related to work through the identification of musculoskeletal symptoms and risk factors which can contribute for the occurrence of the musculoskeletal disorders. In addition, this kind of approach will be effective for the best cost-benefit of the company and the employee, through an early detection of the problem for the prevention of musculoskeletal disorders( 5 ). In this way, the information obtained by the worker is more useful and specific for the detection of the problem and the early action for resolution( 5 ). This kind of questionnaire has been applied to health professionals( 6 ) but it has not been applied to NS.

Additionally, there is a relationship between LBP and the reduced endurance of the extensor muscles of the vertebral column( 7 ), as measured by the Sorensen test( 8 ). The lower the time an individual achieves in the test, the higher the probability of that individual being affected by an LBP episode( 7 ). Moreover, the Sorensen test has been applied to NS( 9 ) and has shown to be a good tool for the diagnosis and prognosis for treatment and ergonomic changes in the workplace.

Thus, the study had the following objectives: to identify the work factors associated with LBP through the use of a surveillance tool, and characterize LBP by the endurance of lumbar extensor muscles among female NS in the ICU.


A cross-sectional survey was conducted from August till October 2011 in a private and a public adult ICU in Ribeirão Preto, Brazil. The inclusion criteria were female, working in an ICU for more than six months, and no professional occupation outside nursing. The exclusion criteria were males, prior back surgery, herniated disk, spondylolisthesis, rheumatic or prior neurological illness, acute spinal infection, tumor or any other type of neoplasm or past treatment of the spinal column, LBP with symptoms of radiating pain, and pregnancy. All ethical requirements were respected, and the study was approved by the Research Ethics Committee of the Ribeirão Preto School of Nursing at the University of São Paulo. The NS were initially approached in their workplaces, and all provided a signed consent form.

The sample of this study was obtained through convenience sampling. In this way, all the subjects who complied with the inclusion criteria were invited to participate. Thus, of the 112 workers who work in the investigated ICU, 48 (43%) accepted to participate in this study. The procedures established for data collection had been previously tested in a pilot study involving NS from a pediatric ICU in June-July 2011.

For the data collection, all workers who participated were taken to a medical office that contained a stretcher. The data collection room was near the work place, free from external interferences. All participants were conducted to the data collection room during the work period and received instructions about the Sorensen test and the questionnaires applied. For the Sorensen test, they were placed in a prone position on the examining table with their iliac crest aligned to the edge of the table, and their lower limbs were fixed to the examining table( 8 ). Additionally, two rods were positioned on either side of the subject, at the height of the seventh thoracic vertebra, and a cord linked to the rods remained over the subject's trunk to determine the tactile feedback( 10 ). During the test, the subjects supported their trunk aligned with the horizon, and touched the tactile feedback cord, until they were exhausted. The endurance of the extensor muscles was determined by how long they could remain in this position.

After the test, the effort spent was measured by the Borg RPE Scale, on a scale from six to 20, with six indicating "no exertion at all" and 20 indicating "maximal exertion", and the reason for stopping the test was recorded. The utilization of the Borg RPE Scale was to ensure that the effort realized in the Sorensen test was appropriate. The workers received an envelope containing the demographics questionnaire, with questions about age, ethnic classification, role in the nursing team, description of principal activity, marital status, practice of domestic or sports activities, and the presence and characterization of LBP in the last year by the number of episodes per year, episode duration and the length of time since the last LBP episode. They also received an adapted questionnaire of work-related activities (QWRA) that may contribute to job-related pain and/or injury, translated and adapted to Brazilian Portuguese( 11 ). This questionnaire was used to identify 15 work-related factors, which factor contributed to the appearance of LBP by applying a score from zero to 10, with zero being "no problem" and 10 being "serious problem" for the occurrence of LBP, based on the theory of the surveillance model( 5 ) and ergonomics( 11 ). All factors that were scored higher than two were considered indicative of a factor that positively contributed to the occurrence of LBP( 12 ). The scores were divided into three broad strata: zero to one as no problem related to that factor, two to seven as a minimal to moderate problem, and eight to 10 as an important problem related to that factor( 12 ). The factors evaluated were posture, work rhythm, organizational and environmental factors, and physical condition.

We analyzed the data using the SPSS statistical software version 16.0 and Microsoft Office Excel Home and Student 2007 software was used to produce the correlation ratio. The Kolmogorov-Smirnov test was applied to test the normality of distribution for the Sorensen test, the Borg Scale and the QWRA (Questionnaire of Work related activities that may contribute to job-related pain and/or injury). To evaluate the differences between individuals with LBP and those without, Student's T-test or the Mann-Whitney U-test were applied. The alpha value adopted was 0.05. Correlations were made with the variables 'episodes of LBP in the year', 'length of episodes of LBP', and 'most recent episode of LBP' with the result from the Sorensen test by applying Pearson's correlation coefficient or Spearman's correlation coefficient.


Of the 112 nursing professionals approached, 48 (43%) subjects participated. They were: 16 (33%) registered nurses, 12 (25%) nursing technicians and 20 (42%) nursing assistants. Sixty-four (57%) subjects were excluded: men (n=36.56%), refusal to participate in the research (n=13.20%), being on leave or on holiday (n=7.11%), signs and/or symptoms described in the exclusion criteria (n=7.11%) and pregnancy (n=1.2%).

The mean age of the workers was 35 (sd=9.5) years and 38 (79%) were between 20 and 40 years old. The majority of the workers, 36 (75%), were Caucasian. There were 20 (42%) single, 21 (44%) married, and seven (14%) separated workers.

According to the statements on activities performed, all three categories (single, married and separated) performed activities involving direct care of critically ill patients and because of this, we analyzed all the workers together. There were 43 (89%) workers performing domestic activities and the majority of the participants (31 (64%)) did not participate in sports activities.

Workers affected by LBP (n=32,.67%)* reported a mean 57.7 (sd=105.4) LBP episodes during the year, with a median of 6.0 episodes (Table 1).

Table 1. Absolute, relative and accumulated frequency of LBP episodes per year of nursing professionals suffering from LBP pain (n=32.67%)* in two hospitals in Ribeirão Preto, SP, Brazil, 2011 

Number of episodes per year Absolute frequency of nursing professionals Relative frequency (%) Relative accumulated frequency (%)
1 2 6.4 6.4
2 1 3.2 9.6
3 5 16.2 25.8
4 3 9.8 35.6
5 3 9.8 45.4
6 3 9.8 55.2
10 2 6.4 61.6
12 2 6.4 68.0
30 1 3.2 71.2
40 2 6.4 77.6
100 2 6.4 84.0
150 1 3.2 87.2
200 1 3.2 90.4
300 1 3.2 93.6
360 2 6.4 100
Total 31 100 100

* One worker suffering from LBP did not declare the number of episodes per year

The mean duration of the episodes of LBP was 63.9 (sd=63.94) hours, with a median of 54 hours. The mean number of days since the last episode of LBP at the time of the Sorensen test was 41.7 (sd=54.64) days ago, with a median of 22.5 days.

For the Sorensen test, the LBP subjects remained less time, mean 93.06 (sd=54.32) seconds, in the position, whereas the non-LBP subjects remained in the test position for a mean of 116.5 (sd=44.98) seconds, but there were no significant differences (Kolmogorov-Smirnov test, p=0.534; Student's T-test, p=0.147) between groups. The Borg Scale after the Sorensen test was 15.8 (sd=3.18) for LBP workers and 14.7 (sd=1.89) for non-LBP with no significant differences (Kolmogorov-Smirnov test, p=0.291; Student's T-test, p=0.143) and this indicated an intensive effort on the Borg Scale for both groups.

The main reasons for ending the test were pain in the lumbar region (23 (33%) mentions), followed by feelings of cramping, weight, muscular contraction, lack of resistance, tiredness and sweating (20 (29%) mentions), and pain in the legs, thighs and feet (8 (11%) mentions).

All of the LBP characteristics were correlated with the time achieved pm the Sorensen test. Only the average duration of the LBP symptoms presented a negative, significant correlation (Pearson correlation, r=-0.421, p=0.016) (Figure 1).

Figure 1. Correlation of time achieved on the Sorensen test, according to average duration in hours of episodes of LBP among ICU NS in two hospitals in Ribeirão Preto, SP, Brazil, 2011(n=32, 67%) 

In relation to the factors that could cause LBP, both groups showed similar opinions, with no significant difference (Mann-Whitney U-test, p-value varied between 0.062 and 0.982) between the groups. Accordingly, the workers were grouped into a single analysis of the factors.

The principal factors identified as causing LBP were related to biomechanical and postural elements, conditions of the muscular structure, and physical and organizational conditions. These factors presented average values of greater than or near 8.0, with a higher concentration of responses in the third column of Table 2. Subsequently, the factors that were grouped in the range from two to seven were "working without receiving training", "working in a hot, cold, humid or wet environment" and "using tools (shape, weight, vibration, etc.)". The average value for these factors was between 4.39 and 5.64. Finally, the only factor that obtained a maximum number of marks in the band of zero to one was "having to handle or hold small objects". Thus, this factor was considered not to contribute to the appearance of LBP.

Table 2. Work-related factors that may contribute to the occurrence of symptoms of LBP, according to ICU NS from two hospitals in Ribeirão Preto, SP, Brazil, 2011 (n=48) 

Work-related factors Mean score 0-10 (sd)* 0-1 (No problem) 2-7 (Minimum or moderate problem) 8-10 (Major problem)
Working in an uncomfortable/unsuitable position or in a very small space. 8.92 (1.98) 2.1 8.3 89.6
Working in the same position for long periods (standing, leaning, sitting down, kneeling, etc). 8.92 (2.01) 2.1 12.5 85.4
Carrying, lifting or moving heavy materials or equipment. 8.69 (2.06) 2.1 14.6 83.3
Bending or twisting one’s back in an uncomfortable way. 8.58 (1.93) 0 20.8 79.2
Continuing working when in pain or hurt. 8.33 (2.75) 4.1 16.7 79.2
Working close to or at one’s physical limit. 7.98 (2.51) 2.1 25.0 72.9
Carrying out the same task repeatedly. 7.56 (2.66) 2.1 35.4 62.5
Workday (length of work, overtime). 7.44 (2.59) 4.2 33.3 62.5
Insufficient breaks or pauses during the workday. 7.14 (3.02) 10.4 31.3 58.3
Reaching up to, or working, at a level above head-height, or away from the body. 7.08 (3.10) 6.3 39.6 54.1
Working quickly for short periods. 6.29 (3.16) 10.4 43.8 45.8
Working without receiving training. 5.64 (3.52) 14.6 50.0 35.4
Working in a hot, cold, humid or wet environment. 5.16 (3.60) 16.7 52.1 31.2
Using tools (shape, weight, vibration, etc). 4.39 (3.83) 33.3 37.5 29.2
Having to handle or hold small objects. 2.56 (2.97) 50.0 39.6 10.4

*Standard deviation †Percentage by each broad strata score


This study showed us that a surveillance tool is an excellent way to identify the work factors associated with LBP in NS staff in the ICU, as all factors highlighted are consistent with the literature and all workers, with or without LBP, have the same opinion about the risks. Moreover, the endurance of the extensor muscles of the vertebral column showed a tendency towards less resistance for workers with LBP in comparison to workers without LBP, especially when the duration of the LBP episode was longer, and this evidence is important when prevention strategies are considered.

The LBP episode is a reality for the nursing working and Brazilian( 3 , 13 ) and international( 1 ) studies reinforce this idea. However, the approach utilized in this study showed its novel nature, as there were no studies that combined the instruments selected which enable the contextualization of the research problem in a broader sense.

To ensure a strong methodology, we chose only women because there are differences between the musculature vertebral column endurance in men and women. Men have shown to be less resistant compared to women, because of variations in the morphology of the lumbar tissues relative to the proportion of type 1 and type 2 fibers( 14 ). If we had not made this choice, the characterization of the workers by muscle resistance would be biased. On the other hand, we did not perform a sample calculation. Our sample was by convenience and we observed great variability in some variables. Because of this, we could not discard the possibility of a type II error. The characteristics of workers selected ensured that we selected a group of LBP risk. The age of workers who participated in our study belonged to a young group and who have shown a higher percentage of pain in the vertebral region( 15 ). Additionally, the majority of workers participating in this study performed domestic tasks, which associated with bad posture during domestic activities, coupled with professional activity, can increase the probability of LBP( 16 ). Moreover, we found a low frequency of workers who participate in sports activities, and considering that sports activities would be an important factor in LBP prevention( 17 ), this factor could contribute to the appearance of LBP. We categorized the workers in the LBP and non-LBP groups by self declaration and this could be a limitation because the workers might have underreported symptoms out of fear of losing their job, reprisal, and believing pain to be an expected consequence of work and age( 18 ). It is known that the Sorensen test is affected by individual factors such as motivation, tolerance, pain, fear and competitiveness( 10 ), so we used the Borg RPE Scale and the tactile feedback to evaluate the fatigue in the execution of the test and, thus, to ensure its reproducibility( 10 , 19 ). It is important to say that the majority of LBP workers who participated claimed to have performed the endurance test during a pain-free period. We did not investigate the psychological factors and their contribution to LBP but one recent research shows us an association between LBP and psychological factors( 20 ), and we suggest that future research should investigate this variable.

The time in the Sorensen test was on average 93.06 seconds for LBP workers, which was similar to the values found in other studies( 21 ). For the asymptomatic workers however, the time found in the present study (116.3 seconds) was less than in another study( 21 ), in which the time was 220 seconds. Nevertheless, we could classify our asymptomatic workers as 'best performance' and those with LBP as "average performance'( 7 ). Therefore, despite no significant differences between our groups of workers, literature research and the present results, we can say that there exists a trend towards less endurance of the extensor muscles in individuals with symptoms of LBP. The results of the Sorensen test were effective because all workers who performed the test reached an intense effort (15) on the Borg Scale, which has shown good sensitivity and reliability to evaluate intensive effort among healthy persons and those with LBP( 19 ). Furthermore, the main reason to finish the test revealed symptoms of fatigue, which strengthened the quality of the results. Moreover, the use of the Sorensen test is valid because the test utilizes the individuals' own body weight to create the postural resistance. Thus, the strength of the individuals is reasonably related with their body weight, and the load offered to the individuals tested is proportional to their vitality most of the time( 22 ). The correlation between the average duration of an episode of LBP and the Sorensen test time showed that, the longer the duration of the lumbar episode, the shorter the time achieved n the Sorensen test and, consequently, the lesser the endurance of the low back extensor muscles. We did not find any studies in the literature that correlated these two characteristics and further research, especially longitudinal studies, are needed to confirm the occurrence of this behavior, and to better understand the contribution of muscle resistance and appearance of LBP.

All workers associated the same factors that contributed to the appearance of LBP as posture, physical condition and organizational characteristics. Moving patients, bending and twisting the vertebral column, repetitive movements caused by the constant changes in the lying position of patients, handling loads, difficulty reaching objects and the lack of space around the bed caused by the quantity of equipment present, and obliging the NS to assume a poor posture in their activities, established the causal factors for LBP pain( 2 , 17 , 23 ), and thus reflected the opinions indicated by the workers surveyed in this study. Working when one has some injury or pain was mentioned by the workers as a cause of LBP. In addition, working with an injury or symptoms of pain also jeopardized the quality of the services provided and promotes limitation in productivity of about 4.87%( 24 ). In terms of organizational issues, the rhythm of work in ICUs, such as the speed with which tasks are completed and the long shifts with lack of breaks for relaxing in the normal work day of NS are evidence found in the literature that contributes to LBP( 25 ). Thus, they are in consonance with the subjective impressions given by the workers in the present research. This research indicated a minimum or moderate association between factors related to working without prior training and in an uncomfortable environment and the characteristics of tools and the appearance of LBP. It is known that, while training related to care and procedures is offered to nursing professionals in ICUs, there is a lack of training focusing on the recognition of the health risks in performing their activities and injury prevention( 2 ). Such training is important to prevent LBP, and the training has to be accompanied by structural changes and the use of technological apparatus to be successful in the treatment and prevention of LBP( 23 ). Although no studies were found in the literature evaluating the role of temperature factors in the appearance of LBP in ICU NS, the exposure of a part or all of the body to the cold may be a contributing factor in the appearance of musculoskeletal disorders in the lumbar column( 26 ). Therefore, future research should be undertaken to better understand how this relationship would contribute to the appearance of LBP in these professionals.


Overall, LBP appears to be linked to a wide variety of associated elements, such as environmental, biomechanical, organizational, personal, genetic, psychosocial, physiological and financial factors in ICU nursing professionals and these relationships support our findings. The reorganization of work through ergonomic studies is necessary to improve the work environment and to prevent LBP among NS. Thus, the application of surveillance tools is very useful because they are easy to apply, raise the opinions of workers, direct the ergonomic changes and evaluate the interventions. Moreover, the trend towards less endurance of spinal column extensor muscles being associated with LBP highlights the need to consider the physical conditions of workers and the implementation of exercises for the treatment and prevention of LBP, but these hypotheses need to be better investigated. Therefore, the outcomes of this study add relevant information to the areas of worker health, physiotherapy and nursing, and we believe that our results will promote projects aimed at the treatment, prevention and protection of NS in ICUs.


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1 Paper extracted from master's thesis "Work-related factors associated to nonspecific low back pain characterized by the resistence of lumbar extensor muscles among female nursing workers of intensive care units" presented to Escola de Enfermagem de Ribeirão Preto, Universidade de São Paulo, WHO Collaborating Centre for Nursing Research Development, Ribeirão Preto, SP, Brazil

Received: June 05, 2013; Accepted: September 23, 2013

Corresponding Author: Maria Helena Palucci Marziale Universidade de São Paulo. Escola de Enfermagem de Ribeirão Preto Departamento de Enfermagem Geral e Especializada Av. Bandeirantes, 3900 Bairro: Monte Alegre CEP: 14040-902, Ribeirão Preto, SP, Brasil E-mail:

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