Abstract
BACKGROUND:
Musculoskeletal disorders are one of the most important problems faced by ergonomists today.
OBJECTIVE:
This study was conducted with the aim of investigating the effect of weather conditions, working conditions and mental workload on musculoskeletal disorders of rescuers and water and sewage company accidents in hot and cold seasons.
METHODS:
The present study was a longitudinal study that was performed on all employees of rescue and disaster teams of Shiraz Water and Sewerage Company in Iran (184 people) by census. Demographic and Nordic questionnaires, NASA Load Index (NASA-TLX), work environment assessment with temperature screening checklist and workplace ergonomic risk factor (WERA) assessment method were performed by the researcher. The collected data were analyzed using SPSS version 23 software and parametric and non-parametric statistical tests.
RESULTS:
The results showed that the highest and lowest prevalence of musculoskeletal disorders related to knee and back in winter and thigh in summer with prevalence of 57.1, 55.4 and 6%. The comparison of exposure to heat stress factors in summer and winter seasons showed that the temperature factors and work clothes of the workers in both seasons are in worse conditions than other factors (P < 0968). The results of the mental workload of people in two seasons showed that the highest and lowest mental workload is related to physical changes in the winter season and frustration in the summer season, and this relationship was significant (P < 0.001). Using multiple logistic regression model, the potential risk factors for musculoskeletal injuries including age, height, BMI, level of education and work experience in both hot and cold seasons were compared. The results showed that in summer, work experience (OR = 1.16 (1.06–1.28.)) and height (OR = 1.03(0.98–1.08) had a direct effect on the prevalence of pain and discomfort arranged in the back areas. One year of increase in work experience significantly increases the chance of a disorder in the back by 16% and a one centimeter increase in height increases the chance of a disorder in the lumbar region by 3%, although this relationship is significant.
CONCLUSION:
It is recommended that suitable solutions such as using appropriate and up-to-date mechanical tools, reducing activity time, increasing rest time, increasing the number of personnel in order to reduce mental workload, using work clothes suitable for the season and type of work, and ergonomics training for workers are on the agenda of company officials. Water and sewage should be placed.
Introduction
Musculoskeletal disorders are one of the most important problems faced by ergonomists today. These disorders are multifactorial and are affected by various factors [1]. These factors include four groups of genetic factors, morphological factors, psychosocial factors and biomechanical factors. Risk factors that cause or cause these disorders are inappropriate or unstable posture: Excessive posture, Excessive force, Repetition, Lifting and carrying a load, Contact pressure, Vibration or localization, Low temperature, and finally Light Less that leads to a bad situation [2].
Stable supply of basic drinking water needs and collection, transfer, treatment and sanitary disposal of produced wastewater is the responsibility of the Water and Sewerage Company. In this regard, the relief and accident unit of the Water and Sewerage Company repairs the defects of water and sewage networks, including broken and burst pipes and main and secondary water branches with different diameters, as well as clogging and removal of clogged water and sewage networks. Is responsible. Depending on the type of activity of the relevant workers, including manual drilling according to the place of operation, shoveling, digging in drilled trenches, transporting and moving pipes, fittings and sometimes heavy tools such as electric pickaxes, floor pumps, grinding, etc. Which alone creates unfavorable situations during these activities and also due to water and mud leakage, which inevitably causes the work clothes of these people to get wet. Doing work in unpredictable conditions due to the nature of work on the other hand causes workers to face different climatic conditions, unfavorable working conditions and psychological pressures in terms of the importance of quality and time of work and assigned tasks [3].
As mentioned above, there are several risk factors for musculoskeletal injuries, one of which is the work environment (heat and cold). In Iran, due to hot and dry weather, workers in various industrial sectors are exposed to heat [4]. In many industries, in addition to the natural heat of the region, industrial processes may intensify it [5]. Heat stress from working in a hot environment can be associated with early mental effects and physical responses. A combination of mental and physical responses has been shown to affect performance by reducing work efficiency, reducing work skills, increasing fatigue, reducing concentration, and thus rapidly increasing errors [6].
On the other hand, exposure to cold is a significant risk in the workplace and can cause injury. In such a way that the cooling of tissues causes discomfort, reduces function and thus increases error and can affect various organs of the body. Cold is mentioned as one of the aggravating factors of work-related musculoskeletal disorders. However, it can be difficult to identify cold exposure as one of the main causes of symptoms of musculoskeletal disorders. According to the relevant data, the main reasons for workers’ complaints and work-related musculoskeletal diseases include the type of work as well as psychosocial factors. Studies have shown that the symptoms of neck, shoulder and back pain are more common among employees who have been exposed to colds due to colds [7]. In a study by Chiang et al., Carpal tunnel syndrome was associated with frequent wrist movements associated with cold exposure [8]. According to another study, lumbar disc disease is an annoying problem and an expensive treatment in Western countries. Lumbar disc disease appears to be a high risk for workers due to exposure to cold at work due to reduced motor and musculoskeletal function in cold environments [9].
One of the stressors that can affect the behavior and performance of employees in the workplace is mental workload. The mental burden of work, defined as “the level of intellectual and cognitive need or analytical effort required by the worker or employees to meet the physical temporal and environmental physical needs of a given job” [10], has a multidimensional and complex structure influenced by external work needs., Environment, organizational and psychological factors and administrative and cognitive abilities of the individual [11]. Various studies have shown that in jobs where there is a lot of mental load due to fatigue and poor programming, efficiency is reduced and memory is impaired [12]. Numerous psychological and physical factors affect people’s perceptual capacities and concentration and cause human error. Some of these factors include mental and physical stress in the workplace, job fatigue, stress, poor employee relations and poor information processing. Epidemiological studies have identified these factors in combination with physical activity as a risk factor for musculoskeletal disorders, especially in the neck area [13].
According to the above, this study was conducted to determine the effect of environmental factors, working conditions and mental workload on the musculoskeletal disorders of rescuers and accidents of Shiraz Water and Sewerage Company in Iran.
Materials and methods
Participants
The present study was a longitudinal study that was performed on all employees of rescue and disaster teams of Shiraz Water and Sewerage Company in Iran (184 people) by census. The study was conducted in 2021 and for 9 months.
Inclusion criteria
Conscious desire to participate in the study and signing of the informed consent form. Worked in the relief and accident teams of the Water and Sewerage Company for more than the last 12 month. Ability to speak, listen and be literate. No underlying diseases (acute musculoskeletal disorders).
Exclusion criteria
Reluctance to continue participating in the study. changing the job of the person being studied. Occurrence of non-occupational musculoskeletal injuries during the study.
Data collection tools
The research tools in this study are divided into two parts. The first part includes questionnaires that were completed by the subjects and the second part is the evaluation of the working environment of individuals that was done by the researcher.
Demographic characteristics questionnaire
In this questionnaire, demographic and work information of the subjects including age, sex, work experience, working hours per day, number of working days per week, marital status, history of specific disease, work environment characteristics were evaluated.
Nordic questionnaire
Using this questionnaire, the prevalence of musculoskeletal symptoms in different parts of the body was assessed one month before and at the time of the study. This questionnaire was developed by Kornika et al. (1987) during a study on the standardization of the Nordic questionnaire to analyze the symptoms of musculoskeletal disorders [14] and its psychometric properties in the Iranian population by Choobineh et al. (2015) during the study of skeletal symptoms. Ergonomics related to ergonomic factors in the Iranian hand-woven carpet industry and general guidelines for designing workstations have been approved [15].
NASA workload index (NASA-TLX)
The NASA Workload Index is a multidimensional questionnaire that aims to evaluate and measure perceptual volume and pressure to evaluate a particular task or activity, a system, the efficiency and effectiveness of a team, or other aspects of performance. Is. The tool was developed at NASA’s Ames Research Center over three years and performed more than 40 laboratory simulations, with the help of more than 550 studies. In this method, the total workload of an activity is divided into six subscales and they are evaluated by this method, and finally a general evaluation of people is done whether they are under high workload or not. These 6 subscales are: 1) mental stress 2) physical stress 3) time pressure 4) efficiency 5) effort 6) frustration. Mental stress is related to perceptual activities such as thinking, decision making, and calculation, memorization, searching, while physical stress is related to physical activities such as pushing, pulling, controlling and acting. Time pressure is related to time and performance related to achieving personal goals. Effort is associated with energy consumption to perform a level of performance, and ultimately frustration is associated with feelings of insecurity, discouragement, stress, and unhappiness. The questionnaire questions are designed in two parts and in the first part, the amount of workload is presented in 6 dimensions and during 6 questions, they are measured on a scale of 0 to 100; Except for the axis of performance and efficiency which is evaluated between two levels of good and bad, other axes are evaluated between two levels of high and low. In the second part of the 15-item questionnaire, the importance of each of the six dimensions is compared and marked in pairs, the axis that has had the most impact and importance on the individual is determined by the individual. In this study, the first part of this questionnaire (rating) was used [16]. Validity and reliability of NASA questionnaire in Iran was conducted by Mohammadi et al. [17].
Temperature stress screening checklist
This questionnaire was developed by Malchir et al. (1999) and was used for qualitative evaluation of thermal stress. This questionnaire includes six parameters affecting the feeling of heat stress in the workplace, including air temperature, humidity, radiant temperature, air flow, workload and clothing. In addition, in this method, the worker’s opinion is taken into account in order to evaluate the thermal stress. Also, the effect of wetting temperature index (WBGT) as a valid indicator in assessing the weather conditions of the workplace on the prevalence of musculoskeletal disorders in the study population in winter and summer was investigated. This index was measured by WBGT meter. Psychometric properties of this checklist have been confirmed by Dehghan et al. (A = 0.91) [18].
Workplace ergonomic risk assessment method (WERA)
This method was developed in 2011 by the Indonesian University of Technology for ergonomic evaluation of construction activities and has high validation. It is a pen-paper method without the need for complex tools and interference in the work of the individual. In order to assess the risk of ergonomic factors in the work environment, the WERA assessment method was used. And legs). Intensity counting is from 2 to 6, which indicates the severity of the risk for areas of the body. Finally, the total risk in WERA, which includes posture, contact stress, vibration, payload, and duration of activity, is summed, and if it is between 18 and 27, the risk is negligible, and if it is between 28 and 44, the risk is moderate. Between 45 and 54 is also a high risk [19].
Procedure
In this study, first with the approval of the ethics committee of Shiraz University of Medical Sciences and the issuance of a letter of introduction from the Vice Chancellor for Research and obtaining permission from the officials of the Water and Sewerage Company, the research environment was referred to registration and obtaining consent from workers to participate in the process. The study was conducted to include those who have the inclusion criteria (184 people) in the study sample. Before distributing the questionnaires among the workers, they were given complete explanations about the questionnaires so that they could complete them more accurately and accurately. Also, in order to evaluate the posture during the work (Fig. 1), by observing the work process, the researcher completed it. It is worth mentioning that the steps of completing the questionnaire and posture evaluation by the researcher in two seasons of winter and summer with the aim of comparing environmental factors, work postures, mental workload and prevalence of musculoskeletal disorders in the workers in question. Due to the quality of the heat stress screening checklist, it was completed by placing the researcher in the research environment.
Common working situation.
In order to respect people’s rights and ethical principles in this research, all people gave their consent before entering the study. If a person did not want to participate in the study, he was excluded from the study. In the process of completing the data collection questionnaires, the details of the study were explained to the individuals for a better understanding in completing the information. Also, all information received from people was kept confidential until the end of this study.
Data analysis method
The collected data were analyzed using SPSS software version 23. For this purpose, first the data distribution was normal (Smirnov-Kolmogorov test). Then, the frequency of the studied variables was reported using descriptive statistics such as mean and standard deviation through tables and pie charts. If the parameters of parametric analysis are not met, non-parametric methods (U-Mann-Whitney statistic) were used and hypotheses were tested using logistic regression model, Pearson correlation coefficient, ratio comparison test, independent t, dependent t and statistics. Key square was checked along with the relevant confidence intervals.
Results
Demographic characteristics
In the present study, 184 male workers of the Water and Sewerage Company were in the age range of 23 to 58 years with an average age of 35.8±6 6.11 years (Table 1).
Demographic characteristics of the subjects (n = 184)
Demographic characteristics of the subjects (n = 184)
The results of the prevalence of musculoskeletal disorders in the study population in the past month and the current time in the two seasons of summer and winter are shown in Table 2. As can be seen in the table, the highest and lowest prevalence of musculoskeletal disorders in the studied employees are related to the knee area in winter and the thigh area in summer with a prevalence of 57.1% and 6%, respectively. Be. In addition, the results showed that during the past year, the highest increase in prevalence was related to the wrist and hands in winter, so that in the past year, the prevalence has increased by 14.1%.
Prevalence of symptoms of musculoskeletal disorders in winter and summer (n = 184)
Prevalence of symptoms of musculoskeletal disorders in winter and summer (n = 184)
*Summer: the month of August (2021) –Winter: the month of February (2022).
In the present study, the level of risk of ergonomic factors in the workplace was assessed using the physical factor risk assessment (WERA) method for each individual. Table 3 shows the frequency of results related to risk assessment of 5 ergonomic physical factors in the workplace of the surveyed employees in summer and winter.
Results of risk assessment of ergonomic factors of work environment of employees in summer and winter (n = 184)
Results of risk assessment of ergonomic factors of work environment of employees in summer and winter (n = 184)
*Summer: the month of August (2021) –Winter: the month of February (2022).
In order to determine the level of risk of musculoskeletal disorders, the total acquired score related to ergonomic factors of the workplace was used, so that if the acquired score related to ergonomic factors of the workplace for each worker is in the range of 18–27 indicates the low risk of musculoskeletal disorders, in the range of 28–44 indicates the moderate risk level and if the acquired score is in the range of 45–54 as a high risk level of musculoskeletal disorders Estimated.
Table 4–6 shows the results related to the evaluation of the workload level of the studied employees in summer and winter by applying a coefficient of 5 and also a comparison between the two seasons. As can be seen in Table 4, the highest and lowest workload scores are related to the components of physical stress in winter and frustration in summer with average scores of 89.42 and 58.39, respectively.
Results of assessment of mental workload level and level of comparison in summer and winter of the studied employees using NASA-TLX standard questionnaire (n = 184)
Results of assessment of mental workload level and level of comparison in summer and winter of the studied employees using NASA-TLX standard questionnaire (n = 184)
*Summer: the month of August (2021) –Winter: the month of February (2022).
Results of completing the checklist of thermal stressors in the study environment in the two seasons of summer and winter and the level of significance of comparison between the two seasons (ratio comparison test) (n = 184)
*Summer: the month of August (2021) –Winter: the month of February (2022).
Results of WBGT in two seasons of summer and winter and the level of significance of the results in two seasons (n = 184)
*Summer: the month of August (2021) –Winter: the month of February (2022).
Using this checklist, the variables of air temperature, relative humidity, radiant temperature, air flow velocity and the characteristics of employees’ work clothes were examined. Details of the results of completing the temperature stress screening checklist in the two seasons of summer and winter and the significant level of their differences are presented in Table 5. Also, in Table 6, the results of the study of the wetland temperature index (WBGT) in the two seasons of summer and winter are shown.
Comparison of the relationship between the prevalence of symptoms of musculoskeletal disorders and the level of risk
Table 7 compares the results of examining the relationship between the overall prevalence of disorders in each individual (total disorders in 9 areas of the body) and the level of risk of related musculoskeletal disorders (WERA method results).
Results of the study between the overall prevalence of disorders and the level of risk of musculoskeletal disorders in the studied workers (n = 184)
Results of the study between the overall prevalence of disorders and the level of risk of musculoskeletal disorders in the studied workers (n = 184)
In Table 8, the results of the study between the prevalence of symptoms of musculoskeletal disorders in different areas of the body in the current situation with the level of risk of musculoskeletal disorders of the studied workers in two seasons, summer and winter and the level of significance of the results based on different seasons using the model of Logistic regression is shown.
Results of the study on the relationship between the prevalence of symptoms of musculoskeletal disorders in different areas of the body and the level of risk of musculoskeletal disorders in the studied workers (n = 184)
Using multiple logistic regression model, the potential risk factors for musculoskeletal injuries including age, height, BMI, level of education and work experience in both hot and cold seasons were compared. The results showed that in summer, work experience (OR = 1.16 (1.06–1.28.)) and height (OR = 1.03(0.98–1.08) had a direct effect on the prevalence of pain and discomfort. Arranged in the back and waist areas. One year of increase in work experience significantly increases the chance of a disorder in the back by 16% and a one centimeter increase in height increases the chance of a disorder in the lumbar region by 3%, although this relationship is significant. Is not. Also in winter, independent variables such as height (OR = 1.07 (0.957–1.218) and work experience (OR = 1.04 (0.1–98.19), each of which increases by one unit. Respectively increased the chances of pain and discomfort in the lumbar region by 7 and 4%, respectively.
Discussion
The present study uses the Nordic Questionnaire, NASA TLX Job Load Index, Heat Stress Screening Checklist, and Ergonomic Workplace Risk Assessment (WERA) to assess the impact of weather conditions, occupational conditions, and mental workload on the incidence and prevalence of disorders. The results of the present study showed that the highest sensation of musculoskeletal discomfort in the subjects was related to the lower back and knees. In winter, 102 (55.4%) employees felt discomfort in the lower back and 105 (57.1%) in the knee. In summer as in winter, but with less prevalence in the lumbar region and knees with 51.1% and 49.5%, respectively, had the highest prevalence of musculoskeletal disorders. It is worth noting that during the last year, the highest increase in the prevalence of musculoskeletal disorders was related to the wrists and hands in winter, so that during the last year, there was a 14.1% increase in the prevalence of disorders and pain in this area.
As it was found in the results of the present study, the highest feeling of pain and discomfort of the workers of the Relief and Accidents Unit of the Water and Sewerage Company is related to the back and knee area. They put their backs and knees in an awkward position while engaging in repetitive activities and exerting force, which justifies the feeling of discomfort and pain in the lower back and knees in most people. A study by Coelho et al. assessing the psychological and ergonomic condition of workers in the Portuguese Water and Sewerage Repair and Accident Unit found that workers who were mainly engaged in repairing sewer lines were in a worse psychological condition than repair workers.
The results of this study showed that the most musculoskeletal discomfort of the studied workers was in the lumbar and knee area so that 28% and 66% of the studied workers felt discomfort in the lumbar and knee area, respectively. In this study, we concluded that repetition of physical activity along with applying force and lifting the load in an inappropriate position, has a significant role in the occurrence of discomfort in the subjects’ back, which is consistent with the present results. Study. The interesting thing about this study is that the results showed that in a similar job, people involved in sewage repairs feel more muscle pain and discomfort than similar workers who are responsible for repairing the water channel, so that the unpleasant smell of sewage affects the mood. And psychologically affects. They have had an adverse effect on the musculoskeletal disorders of workers [20]. In a study that examined the prevalence of musculoskeletal disorders in miners using the WERA method, the results showed that miners in the upper extremities feel more discomfort than the lower extremities and its average score is in the moderate or warning range (with the average The score was 40.89). In this study, it was found that poor posture and long working time are the main causes of musculoskeletal disorders in the studied workers, and lifting the load and repeating the operation (10 to 8 times per minute) with force (more than 10 kg) leads to increased pain. And workers’ discomfort in the lower back and knees [21].
In order to compare the risk of musculoskeletal disorders in different parts of the body in both hot and cold seasons, the results of Physical Risk Factor Assessment (WERA) were evaluated. The results showed that the highest risk in summer was related to poor posture (with an average of 5.19), poor posture of the legs (with an average of 5.1) and working time (with an average of 4.95). Also in winter, the highest risk is related to these cases and with averages very close to summer. Based on this, it can be said that in general, the risk of musculoskeletal disorders in cold and hot seasons is not much different from each other, and in both seasons, the back and legs are in poor condition and have the greatest potential for musculoskeletal disorders. It should be noted that due to the same working time in both test seasons, it was not possible to compare working time. Also, the comparison between the overall prevalence of disorders (total number of disorders per person) and the risk of musculoskeletal disorders in the studied workers in the cold and hot seasons of the year confirms a direct relationship between high-risk levels and increased prevalence of pain and discomfort in the body. Based on this, it can be claimed that the results of the Nordic questionnaire are consistent with the results of the WERA assessment method. In a study conducted by Saedpanah et al. Using the WERA method to examine the risk factors for physical factors among construction industry workers, the results showed that more than 94% of workers were considered to be in poor working condition and felt in the lower back. They were in pain and upset. The study found that people who exercised or used shovels for work felt more back and knee pain than others, while those in charge were bricklayers carrying the load. They kill. They feel more pain in the shoulder and elbow area than others and the type of tool used plays an important role in the prevalence of musculoskeletal disorders in the upper limbs [22].
Also, in the results of the present study, it was found that the general level of physical factors affecting the musculoskeletal disorders of the studied workers in the summer and winter seasons is in the moderate range or warning for action (with an average of 34.74 and 37.85).
In the present study, workload levels in winter and summer were compared using the NASA Workload Index (NASA-TLX) test. The mental results of the subjects in the two relevant chapters showed that the highest and lowest scores of mental load of rescuers and water and sewage company accidents were related to the variables of physical pressure in winter and failure and frustration in summer (respectively). With an average of 42.89 and 39.58). Therefore, the results show that the change of seasons and related conditions has its own effects on changing the level of mental workload of individuals. Water and Sewerage Company rescuers in winter due to burst water pipes, especially in areas with old and worn network due to reduced water consumption and as a result of increased water pressure and freezing in the pipes and in summer due to increased water consumption and needs Adjusting the main and secondary valves to provide safe and stable drinking water in all parts of the city and increasing accidents and leaks in sewer pipes have a high working pressure due to increased water consumption among customers. It is worth mentioning that the average score of psychological stress of the studied workers in summer and winter was equal to 80.76 and 84.40, which indicates the high psychological pressure of people while performing work. In general, the results of the present study indicate that the mental and physical burden of workers in both seasons is high and can lead to increased human error at work and aggravation of musculoskeletal disorders of rescuers and water and sewage accidents.
In a study by Kalantari et al., Which examined the relationship between mental workload (using the NASA-TLX questionnaire) and the prevalence of low back pain (musculoskeletal discomfort questionnaire) in car assembly line workers, it was found that the average score of the questionnaire It was 72.41 and was lower than the average score obtained in the present study (81.47 and 77.35) and 43.37% of the assembly line workers felt uncomfortable, which is still less than the results of the present study (55.4%). It is worth noting that assembly workers do not use physical force, and therefore the force on their spine is less than the relief forces and water and sewage accidents, which have more unfavorable physical conditions and use physical force while working. In their study, it was found that the volume of mental-physical work has a significant direct effect on the prevalence of pain and discomfort in employees (P < 0.05). They also concluded that reducing work speed, improving the ergonomic condition of the workstation, as well as increasing the duration of daily rest can reduce the prevalence of pain and musculoskeletal discomfort of workers [23].
Exposure to heat and cold stress reduces job productivity, harms human health, and exacerbates musculoskeletal disorders. It has also been shown that the incidence of human error in hot and cold environments increases and the incidence of occupational accidents in hot and cold environments is much higher than in environments with suitable climatic conditions [24]. The results of comparing the exposure to thermal stressors in summer and winter showed that the variables of air temperature, workload and work clothes of rescuers and water and sewage company accidents in both summer and winter in more unfavorable conditions than other factors. The opinion of most of the workers was that in both summer and winter, the working conditions of their work environment are unfavorable (for summer and winter, 75.5% and 71.7%, respectively). Inadequate work clothes for work, limited work space, physical and hard work, use of vibrating tools and open work environment of rescuers and water and sewage company accidents cause unfavorable weather conditions in their work environment. Therefore, due to the complementarity of the questionnaire results for each of the factors, the utility ratio comparison test was not significant due to the proximity of the results in both chapters. As the results show, about 80% of workers in summer and winter do handicrafts at high speed, for a long time and in poor condition, which can lead to workers’ dissatisfaction with the working conditions of their work environment. The results of Pidrahita et al.’s study showed that weather conditions are one of the most important variables affecting workers’ job satisfaction with the work environment and the incidence of musculoskeletal disorders. In their study, they concluded that physical activity in a cold work environment increased pain and discomfort in the wrists and lower back compared to the control group and increased pressure on the body’s muscular system [25]. One of the most important variables affecting the incidence of disability and musculoskeletal disorders in hot and cold environments is the duration of work, so that by increasing the time of exposure, the ability of the hand muscles, gaining strength, reducing the ability to maintain proper posture And seek to reduce the ability to remember [26].On the other hand, working in a hot environment increases sweating, decreases body water level and reduces the mental tolerance of the worker, which can lead to decreased muscle strength, increased risk, decreased ability to think and memory, and ultimately lead to increased Be human errors [21]. In a study by Marrosi et al., Which examined the effect of air temperature on job satisfaction of workers in open environments using WBGT indices, the average estimated vote and the percentage of forecasted dissatisfaction, it was found that a decrease of 5 degrees C-temperature in winter reduces the job satisfaction of workers in the open environment by 25% [27].
The relationship between the prevalence of symptoms of musculoskeletal disorders in different parts of the body (Nordic questionnaire results) and the risk of these disorders (WERA results) in hot and cold seasons of the year was compared. The results of the present study showed that the feeling of pain and discomfort in the hands, back and legs of the studied workers in both seasons had a significant relationship with the score of musculoskeletal disorders in these areas. It should also be noted that the results of comparing the prevalence of symptoms of musculoskeletal disorders in different areas of the body with the risk of musculoskeletal disorders by logistic regression method also confirmed a significant relationship between these disorders and the risk in these cases (P > 0.05). In a study aimed at investigating the effects of posture, speed of movement and load carrying on shoulder muscle activity, it was found that carrying a weight of 0.5 kg leads to a 4% increase in the maximum voluntary stimulation of the shoulder muscles. Shoulder muscles the strength of the shoulder muscles decreases. In their study, it was found that repetitive activities, holding the load with the hand, increasing the angle of the arms from the trunk and increasing the speed of repetition of manual activity lead to a decrease in isometric and dynamic stimulation of the shoulder muscles [28]. Previous studies have shown that the most important causes of pain and discomfort in the lower back and knees are inappropriate posture, strenuous physical activity, exercise, inappropriate and static posture and exposure to vibration [29, 30].
Finally, using multiple logistic regression model, the potential risk factors for musculoskeletal injuries including age, height, BMI, education level and work experience in both hot and cold seasons were compared. Due to the fact that the activity of the examined workers is often in a sitting position, twisted in a static position with the application of force and standing with the application of force, with increasing weight or depth of the abdomen, the spinal support has a longer longitudinal distance. This causes an increase in the load on the lower part of the spine and damage to the components of the spine, including the disc between the vertebrae of the spine, and therefore it can be said that by increasing the weight and depth of the abdomen, during physical activity In sitting and static postures, the load on the lower back increases and the amount of pain and discomfort in the lower back increases. In the WERA method, the bending angle of the waist is classified into three categories: 0–20 degrees, 21–60 degrees and above 60 degrees. The section is awarded because it leads to an increase in the load on the lower back (23, 24). In a study by Choobineh et al., Which examined the musculoskeletal disorders of rubber workers, it was found that the age and work experience of workers play an important role in the feeling of musculoskeletal disorders related to their jobs. However, in this study, it was found that the weight and height of workers did not affect the prevalence of musculoskeletal disorders among the workers [31].
Conclusion
The results of the present study showed that the type of activity of the studied workers is physical activity, static, repetitive with force and sometimes direct exposure to water, sewage and vibrating equipment. The results of the Nordic questionnaire showed that the highest prevalence of musculoskeletal disorders was in the lumbar and knee area of workers. According to the type of job duties of the studied workers, the volume of physical work and the effort of the workers during the work, the most important factors of the workload of the workers were identified. In the present study, it was shown that exposure to cold in winter (low temperature, direct exposure to water, high relative humidity and cold air flow) leads to aggravation of joint pain including workers’ knees, elbows and wrists compared to summer. Due to the fact that workers work outdoors, in the summer due to exposure to heat radiation, high ambient temperatures and inappropriate work clothes, people sweat more than usual, which can cause dehydration and exacerbate muscle pain. Due to other occupational factors (such as unfavorable situation, repetition of activities, use of force, duration of activity, duration of rest) in the workers of the relief and accident unit of the Water and Sewerage Company. It is recommended to prevent the spread and occurrence of musculoskeletal disorders in the workers under study appropriate strategies such as the use of appropriate and up-to-date mechanical tools, reducing the duration of activity, increasing the rest time, increasing the number of people wearing work clothes appropriate to the season and The type of work and teaching ergonomic principles to workers should be on the agenda of the officials of the Water and Sewerage Company.
Study limitations
1- Since the type of job of the workers under study requires them to be sent to the accident site in the shortest possible time, in some cases, due to the absence of workers, the completion of questionnaires was postponed to another time, which caused the investigation to take time.
2- Due to the dispersion of possible accidents in the area covered by each relief and accident group and the need for the researcher to be present at their place of activity in order to assess the posture and weather conditions, it causes time and traffic problems to the desired locations.
Ethical approval
This study has been approved with the ethics code IR.SUMS.REC.1398.408 and design number 18619-04-01-97 in Shiraz University of Medical Sciences.
Informed consent
All participants provided informed consent prior to enrollment. No identifying information is presented in this work.
Conflict of interest
Not applicable.
Footnotes
Acknowledgments
We feel it necessary to express our gratitude to all the professors, colleagues, and friends and especially to the officials of the water and sewage department who helped us in all stages of this project.
Funding
Not applicable.