Musculoskeletal Risks: RULA Bibliometric Review

The objective of this study was to reveal RULA method applications in terms of the knowledge, country, year and journal categories. The search was performed using the “Web of Science Core Collection”. The period from 1993 to April 2019 was selected. Eight hundred nine results were obtained, of which 226 were used. The largest number of publications was determined to be in the fields of industry and health and social assistance, which coincides with the OWAS and Standardized Nordic Questionnaire methods. By country, the USA stands out for its greater number of research studies and categories that are encompassed. By date, 2016 was the year when more studies were carried out, again coinciding with the Standardized Nordic Questionnaire. By journal, “Work—A Journal of Prevention Assessment and Rehabilitation” is highlighted, as it is for the REBA method as well. It was concluded that RULA can be applied to workers in different fields, usually in combination with other methods, while technological advancement provides benefits for its application.


Musculoskeletal Disorders (MSD)
One of the most common work diseases in Europe are musculoskeletal disorders. These appear in various areas of the body, the most common developing in the back and upper extremities [1].
Among the causes that stand out for their appearance are the physical (manual, forced or frequently repeated movements, harmful postures and vibrations, etc.) and those relating to work organisation (high work rate, schedule, routine work, etc.) [2].
This type of disorder has numerous consequences for the affected worker, but also for businesses and countries (at the economic level) [3].
To prevent this occupational disease, it is necessary to identify all the risk factors that occur during work. Once determined, preventive measures should be taken to avert them, or actions taken to reduce them [2]. Some authors propose measures such as rotating workers between different jobs [4], providing ergonomic training to workers [5], designing ergonomic tools for MSD analysis in the workplace [6], redesigning work equipment from the ergonomic perspective [7], etc.

Assessment Methods
There are numerous methods for assessing musculoskeletal disorders. These can be classified into three main groups: direct, semi-direct and indirect (Table 1 [8]). Table 1. Types of MSD assessment methods [8].

Direct Semi-Direct Indirect
Placing sensors on workers' bodies as they perform tasks.
Observing the task being carried out and using software to analyse it. Employing questionnaires.
Of the three groups above, the most economical methods are the indirect ones since they are based solely on completing questionnaires. The opposite is true in the other two cases as software licenses are required and sensors have to be purchased. Direct methods are the most accurate because they provide virtually automatic information. In terms of complexity, direct and indirect methods stand out-in the former because the use of sensors can be a nuisance for the worker and, in the latter, because of the subsequent statistical analysis [8].
When selecting a method for a particular study, it is advisable to consider several criteria (cost, accuracy, complexity, application time, etc.) and to analyse the advantages and disadvantages of each.

Rapid Upper Limb Assessment (RULA) Method
The RULA method was designed in 1993 by McAtamney and Corlett. Its objective is to know if workers are exposed to MSD risk factors in the upper extremities during the performance of their work [20].
The method assesses three factors: the posture of the different areas of the body, the load or force exerted and the muscle activity (static posture or repetitive movements). The body regions which RULA focuses on are divided into two groups [31]:

Rapid Upper Limb Assessment (RULA) Method
The RULA method was designed in 1993 by McAtamney and Corlett. Its objective is to know if workers are exposed to MSD risk factors in the upper extremities during the performance of their work [20].
The method assesses three factors: the posture of the different areas of the body, the load or force exerted and the muscle activity (static posture or repetitive movements). The body regions which RULA focuses on are divided into two groups [31]: Group A: arm, forearm, wrist and wrist turn. Group B: neck, torso and legs.
Three main stages [20,31] are performed to carry out the assessment using this method: Observation of postures. This is done while the worker performs the task and can be realised in three ways: direct observation or by taking images or videos. The postures to be assessed (those most repeated, those performed for more than 10% or 15% of the task and those that are most harmful) are selected. Only one side of the body is analysed, namely the one which suffers most harm; however, if they are very different, then both sides are assessed. Scores. For the postures to be assessed, the angle must be measured between each of the body areas and the vertical. The lower extremities are not measured, although it is taken into account whether the posture is balanced and supported. Using these data, which are modified by different criteria and considering the load factors and muscle activity, the RULA scores are calculated ( Figure 3). Action levels. From the final scores, one obtains the action level. RULA differentiates four levels: Level 1 (Score: [1][2]. No action is needed. Level 2 (Score: [3][4]. Measures should be taken, but not in the short term. Level 3 (Score 5-6). Measures should be taken in the short term. Level 4 (Score 7). Urgent action must be taken.

Advantages
Some advantages of the RULA method include: It is a reliable method to use for repetitive tasks, mainly in the upper limbs [31]. It has been applied to workers across very different areas [31]. The assessor needs no experience in order to apply it during the observation phase [20]. It is not very complex to apply. The method is simple to use [32]. It can be applied with the help of software [31,32].

Limitations
Among the disadvantages of the RULA method are the following: It results in a high-level risk for non-permanent jobs [31]. The left and right side of the body are assessed independently [32]. It does not take into account the time the worker takes to carry out the task [32].

Objective
The aim of this work is to review all the studies in which the RULA method has been applied from 1993 to April 2019 and to analyse them according to the following categories: knowledge, country, year and journal.

Materials and Methods
To search for information about the different RULA method applications, the University of Almería's library website was accessed. There, we used the "Web of Science" (WoS) database, the license of which is managed by the Spanish Foundation for Science and Technology (FECYT).
The search was done by selecting the "Web of Science Core Collection" and the advanced search option, in which "so = Applied Ergonomics" was introduced. The "Create Citation Reports" option was selected. In this way, the total number of available citations was consulted for the original article proposing the RULA method by McAtamney and Corlett [20].
The number of studies obtained was 809, in the period from 1993 to 29 April 2019. Of these, using the title and abstract of each study, we finally selected a total of 226 results, discarding those that did not include the method's application. The final studies were from 1998 to 2019.
It should be noted that the main limitation of the information search is that we only used the Web of Science Core Collection; no other databases were accessed. Therefore, some studies may have been overlooked with the search method used.

Results and Discussion
The studies obtained from the search have been analysed and classified according to the categories of knowledge, location (countries), publication date (years) and journals.

Classification by Knowledge Categories
A particular classification [33] has been used to order the RULA studies according to the knowledge categories. Table 2 shows the different areas presented, the designated nomenclature and the number of published studies. Other scopes not previously included * 25 * The category "Other areas not previously included" is not part of the classification used; it is a section that encompasses studies that have not been considered in the other fields.
In total, 19 categories are differentiated. One can observe that "Manufacturing" stands out as having more studies than the rest, a total of 74. This is followed by 38 and 25 publications corresponding to "Human health and social work activities" and "Other areas not previously included ", respectively ( Table 2).
In contrast, two fields are differentiated in which only one research study is recorded-"Water supply, sewerage, waste management and remediation activities" and "Financial and insurance activities" (Table 2). Figure 4 shows the different areas of knowledge based on the frequency of the published studies. Below is a description of each of these categories [33].
3.1.1. Agriculture, Forestry and Fishing Table 3 summarises the studies related to this category. Crop and Animal Production, Hunting and Related Service Activities The RULA method has been used for the ergonomic assessment of farm workers working on various crops or specific tasks.
In fruit crops, Thetkathuek et al. [38] applied it together with the Nordic Musculoskeletal Questionnaire and a tasks checklist. In total, 861 farm workers took part in Thailand. They showed that men with more than 10 years of experience had their necks most affected and women their lower backs. In blueberry harvesting, Kim et al. [36] used it in conjunction with the Borg CR10 scale, electromyography, the Cumulative Trauma Disorders (CTD) index and NIOSH (National Occupational Institute for Safety and Health). They concluded that the risk was reduced by carrying out the work with the help of machinery.
Three studies were carried out on oil palm harvesting. In two of them, other ergonomic tools were also used. In the first study, 109 workers were assessed, while three and seven were assessed in the other two. The results for all three showed that most workers were exposed to a very high level of risk when carrying out the tasks. Changes were required as a matter of urgency [46][47][48].
Three other studies were conducted into rice cultivation. Pal and Dhara [37] studied 166 workers in India. They also used other methods such as REBA (The Rapid Entire Body Assessment), OWAS (The Ovako Working Analysis System), etc. The results showed the frequent appearance of MSD, with the most affected areas being the lumbar, hip, wrist, shoulder and knee regions. In the other two studies, farm workers were assessed when using machinery during the tasks: in one case using threshing machines and in the other using a cultivator. For both, it was concluded that there was a high risk of MSD [44,49].
In olive cultivation, Pardo-Ferreira et al. [40] assessed farm workers performing pruning with a chainsaw. Other methods were also used, in particular REBA and OWAS. They determined that change was needed, as workers were exposed to ergonomic risks.
Another series of studies was conducted using the RULA method to assess different tasks. Jain et al. [39,41] carried out two studies focusing on manual tasks, also using a questionnaire. The first concluded the frequent development of musculoskeletal disorders in workers; this coincided with the second, which indicated a score (RULA) of 5 or above for 92% of the workers.
Vazquez-Cabrera [45] investigated farm workers during crop stringing. They simulated different ways to do it in a laboratory according to the height, crop weight and guides used. Among other findings, heights of 1.4 m were shown to be acceptable, with 1.2 and 1.6 m heights also being possible. Weights over 2 kg were found not to be suitable.
Finally, some authors set out specific objectives. Kong et al. [42] used RULA to assess Korean farm workers as they adopted 96 postures. The aim was to apply RULA along with the REBA, OWAS and ALLA (Agricultural Lower Limb Assessment) methods in order to compare the last one with the previous three, proving it to be the most correct. Di Gironimo et al. [50] set out to redesign and improve the ergonomics of an agricultural tractor's driver space. In addition to RULA, this was done using Catia V5 software (as well as other ergonomic tools) to design a 3D model. Some devices in the cab needed to be corrected to provide better ergonomics.

Forestry and Logging
Studies in this category using the RULA method have only been carried out in forestry. Several authors focused on rubber harvesting workers (tappers). Meksawi et al. [51] also used a survey and a form. According to the RULA results, an action Level 3 was obtained, so changes needed to be made to the work. Pramchoo et al. [35] assessed the ergonomics of a new knife designed for tapping. Two groups participated, one of them using the new knife. In each group, half of the workers suffered discomfort related to the carpal tunnel syndrome. The Boston Carpal Tunnel Syndrome Questionnaire (BCTQ) was also applied. The new knife, among other advantages, reduced the discomfort from carpal tunnel syndrome in sufferers and improved the wrist posture.
Regarding forestry activity, two studies were performed to assess workers. Cremasco et al. [34] focused on tasks performed with a wood-chipper; they also used REBA in their assessment. Unver-Okan et al. [43] focused on forestry nurseries; they also employed REBA, OWAS and QEC (Quick Exposure Check). In both cases, it was determined that the RULA method was the most suitable for such assessments. Table 4 presents the only two studies related to this category. Table 4. Mining and quarrying.

Reference
Year Country Study Objective [52] 2010 India Use of REBA, RULA, OCRA and other ergonomic tools on stone carving workers. [53] 2016 Malaysia Application of RULA on mine workers.
In this field of knowledge, there are only two studies available in which the RULA method was applied-one for the ergonomic assessment of mine workers and the other, together with the REBA and OCRA (Occupational Repetitive Action) methods, in stone-carving workers. Both studies concluded that very high risks existed that required immediate changes [52,53]. Table 5 sets out the different publications available in the field of manufacturing.

Reference
Year Country Study Objective [54] 2019 Turkey The design of a cell in an industry using virtual reality and an ergonomic study with RULA. [55] 2019 Malaysia Application of RULA and interviews on workers in a car factory. [56] 2018 India Application of a questionnaire, RULA and REBA on brick kiln workers. [57] 2018 Tunisia Application of RULA and REBA on milling, turning and drilling workers. [58] 2018 Canada Use of the RULA method and certain devices on baristas responsible for tamping the espresso coffee. [59] 2018 Iran Application of a questionnaire and RULA on assembly workers in an electronic components factory. [60] 2018 Malaysia Use of the modified Nordic questionnaire, REBA and RULA on assembly workers in an electronics factory. [61] 2018 Iran Use of RULA, LUBA (Loading on the Upper Body Assessment) and NERPA (New Ergonomic Posture Assessment) on automotive, pharmaceutical and assembly workers.
[62] 2018 United Kingdom Design and analysis of a system allowing workers to control an industrial robot. RULA was also used for its design.
[63] 2017 Malaysia A car seat was designed with CATIA and then RULA was used for the ergonomic assessment.
[64] 2017 Iran Use of RULA and another computer tool on sugar factory workers who manually moved the bags.

Manufacture of Motor Vehicles, Trailers and Semi-Trailers
The RULA method was used in four research studies to ergonomically assess automotive workers. Each focused on various tasks such as painting, assembly and others. One of the studies used a human digital model, obtaining some benefits from its use [124]. In the others, in addition to the RULA method, other assessment tools were applied. It was concluded that the risk of musculoskeletal disorders existed. Two of them yielded high-level risks [55,75,123]. On the other hand, Mat et al. [63] used RULA to ergonomically assess a car seat. The seat was analysed after being designed with CATIA software and optimisation was performed. This showed a decrease in the level of risk.

Manufacture of Other Non-Metallic Mineral Products
Sain and Meena [56] used RULA, REBA and a questionnaire to perform an ergonomic analysis on brick furnace personnel. They concluded that some tasks needed to be modified as there was a risk of musculoskeletal disorders. Coinciding with this need to take action, Monteil et al. [115] employed RULA via a digital human model on roof slate manufacturing workers.

Manufacture of Fabricated Metal Products, Except Machinery and Equipment
The RULA method was used by Boulila et al. [57] along with REBA and a survey on milling, turning and drilling workers. Twelve postures were determined to negatively influence job performance. In relation to this, other authors redesigned a CNC milling machine to take worker ergonomics into account. They used RULA to analyse the postures assumed in the initial machine and those in the new design, with the latter being less harmful [90].
In addition, two studies found high risk levels according to the RULA method. The first was carried out on workers performing manual handling work in a metal stamping business. The Cornell Musculoskeletal Discomfort Questionnaire (CMDQ) [96] was also used. The second study focused on cutlery polishing workers [116].
Finally, some authors [126] studied the relationship between ergonomics at work and product quality in the metallurgical industry. RULA was used and, as a result, the work carried out was modified. Quality improvements were identified in the newly-produced products.

Food Product Manufacture
The RULA method was used in conjunction with REBA in the food industry. It was concluded that workers adopted postures that could lead to musculoskeletal disorders [65]. Similar results were obtained by applying RULA together with other assessment tools on pineapple peeling workers, obtaining a risk Level 3 assessment [76]. It was also applied in a sugar factory assessing the bag movement task. A high-risk level was determined [64].
In two other cases, negative results were shown for certain body regions. One of them applied the method to a frozen food business, along with other tools such as the Nordic Questionnaire. This was applied to both production and office workers. The greatest discomfort appeared at the elbow [77]. The other focused on workers in a meat packing factory. RULA, a human body diagram and anthropometric measurements were used. The shoulder was shown to be at risk. It was concluded that corrective measures were required [104].
Other authors used 3D simulation and the I-DEAS programme to replace the work of a robot (used for processing fruits and vegetables) with a worker. RULA and LBA (Lower Back Analysis) were employed for the ergonomic analysis. The results found a particular posture that the seated worker could adopt to avoid a high risk to the lower back and upper limbs [105].
Finally, a study was carried out on baristas tasked with tamping espresso coffee. RULA was used in conjunction with sensors placed on the column and a force plate. Lower scores were shown when using a flat tamper rather than a traditional one [58].

Manufacture of Computer, Electronic and Optical Products
According to RULA, assembly tasks in the electronics industry indicate high levels of risk for the workers who perform them. Two studies demonstrated this, the first applied the RULA method along with a questionnaire while carrying out an intervention to achieve more comfortable postures. The other supplemented it with REBA and the modified Nordic Questionnaire. Both agreed that the body areas most affected by MSD were the lumbar region and the wrists. However, one of them also included the hands and neck while the other included the shoulders [59,60].
Other authors set out to reduce neck discomfort in mobile phone assembly workers. To do this, they performed an ergonomic intervention. An assessment, using the RULA method and other tools, was carried out before and after the intervention. Improved worker ergonomics were achieved following the intervention [106,117].
Something similar was done during the manufacture of laptops. Materials were reused and two carts were created, one for refuse collection and the other for sorting and distributing labels. An assessment was carried out with RULA before and after using the new carts. Better ergonomic and work results were obtained [107].

Manufacture of Other Transport Equipment
The RULA method was used in three studies developed in the same year which looked into aircraft manufacturing. The purpose was to assess worker ergonomics. One of the studies also used the Strain Index demonstrating a relationship among work design, performance and ergonomics [66]. In another, RULA was used in conjunction with REBA to assess aircraft wing component assembly using immersive virtual reality to perform the task [67]. Finally, a maintenance work analysis tool was developed using CATIA software. RULA, OWAS and LBA [68] were employed together.

Manufacture of Machinery and Equipment N.E.C.
In this area, the RULA method was used in a single study. It was concluded that high-risk postures were present in pump assembly workers diving into wells [69].

Manufacture of Leather and Related Products
There has been repeated use of the RULA method for the postural assessment of shoe factory workers. In some studies, it has been combined with the OWAS method and in others with the Nordic Musculoskeletal Questionnaire. In all the cases studied, negative results were obtained for some of the postures adopted [70,78,92].
These conclusions coincided with those obtained in a study on manual shoe-sewing workers. The RULA method was used together with a questionnaire. The need for postural correction was demonstrated; in some cases, it was required immediately [91].

Manufacture of Basic Pharmaceutical Products and Pharmaceutical Preparations
Two studies were developed in the pharmaceutical industry using the RULA method and the Nordic Questionnaire. One concluded that RULA was not a very successful method for assessing this type of industry. The other aimed to assess lumbar and neck discomfort [71,79].

Textile Manufacture
In the textile industry, two research studies were carried out using the RULA method and questionnaires. Approximately 380 workers participated. The results concluded that MSD was common. One of the studies found that the body areas suffering the greatest discomfort were the neck, knees and lumbar region [81,97]. Using the same ergonomic tools, Dianat et al. [87] also established that the neck and back were the body regions most affected in sewing machine workers. They also pointed to other areas such as the shoulders, wrists and hands.
Other authors also employed RULA in the textile industry along with the Nordic Musculoskeletal Questionnaire, or an adaptation of it. They assessed 566 workers in one study and 283 in the other. Both studies concluded that high levels of risk were present in their results and therefore there was a need to take corrective actions, in some cases immediately. They agreed that the affected body areas included the torso, neck and arms, amongst others [108,113].
Other assessments were carried out in industries located in Indonesia and Cambodia. In the first of these, a virtual space with a human model was used and four tasks were analysed: cutting, sewing, putting on buttons and finishing. The Posture Evaluation Index (PEI) was used, which includes the LBA, OWAS and RULA scores. The second was performed using interviews and RULA. In both cases, workers could develop musculoskeletal disorders [83,114].
Analysis was also carried out on people working in rug-fixing workshops. They usually performed their tasks squatting. Using a survey, it was possible to deduce the most affected body regions, and then to design a new work posture from this information. This posture was subsequently assessed with RULA, demonstrating it to be less harmful [125].
Other authors found a way to organise clothing assembly tasks at particular workstations. To do this, they assessed both productivity and ergonomics; RULA was used for the latter [99].
Using the same ergonomic tools, Dianat et al. [80] concluded from the studies described above that there is a high onset rate of musculoskeletal disorders among sewing workers.
Finally, several ergonomic studies have also been carried out in the batik cap industry. One demonstrated the emergence of MSD among the workers, and the other two determined new work postures for specific tasks that were less harmful [82,88,98].

Manufacture of Basic Metals
Garcia-Garcia et al. [95] used RULA and REBA along with virtual simulation to assess workers in a metal factory. Kushwaha and Kane [74] utilised the method to ergonomically assess two crane cabs (the usual one and a new design) in the steel industry. The new cab was designed with CATIA software and was shown to improve worker ergonomics.

Manufacture of Chemicals and Chemical Products
The Nordic Musculoskeletal Symptoms Questionnaire (NMSQ) and the RULA method were used to study ergonomics in chemical industry workers when performing various tasks. RULA showed that they were suffering from MSD. Automation and work modification [73] were proposed as a solution.

Repair and Installation of Machinery and Equipment
The risks that occur during the maintenance of a REHM V8 furnace were analysed using a modification of the NTP 330 method. The ergonomic risks were also contemplated using the RULA method and interviews. It was concluded that the ergonomic risks, amongst others, were detrimental to workers [86].

Manufacture of Electrical Equipment
At a transformer factory in Brazil, worker ergonomics were studied using RULA and a questionnaire. Risk factors were shown to be related to the posture adopted and the work rate. Immediate changes to the tasks [93] were required.

Manufacture of Paper and Paper Products
CATIA P33 V5R14 software was used to recreate the posture adopted by workers in a packaging business. RULA was used for the ergonomic assessment. Certain harmful postures were determined, mainly in tasks where heavy loads were lifted, or tasks which included bending [100].

Manufacture of Rubber and Plastic Products
In total, 25 rubber sheet manufacturing workers were ergonomically assessed using RULA, REBA and OWAS, specifically looking at nine9 different tasks. Most of the postures adopted were repeated continuously and the job was not particularly comfortable for the workers. High scores for these working postures [109] were determined according to the methods applied.

Manufacture of Wood, and Wood and Cork Products, Except Furniture; Manufacture of Articles Made from Wicker and Plaiting Materials
Several research studies were conducted on sawmill workers, using RULA in conjunction with other assessment methods and ergonomic tools. The objective was to compare the results using the different methods to find if there was any agreement among them [118,120,121].

Other
This section includes studies that are also within the scope of industry, but which cannot be included in any of the classification groups used.
Most of these studies were carried out in the past 17 years. The first one performed aimed to establish the QEC method action categories. To do this, several industry jobs were analysed using QEC and RULA, and then the results were compared [127]. RULA was also compared to other methods (OWAS and REBA) by analysing 301 worker postures in industries such as the electronics, steel, chemical and automotive industries, as well as in a hospital. OWAS and REBA ranked 21% of the postures in Categories 3 and 4, while RULA ranked 56% of them [122]. This method was also compared to seven others by performing an ergonomic assessment of 567 industrial tasks. The results were shown to be different for the same work post depending on the method used. RULA determined a high risk for nearly 80% of the jobs [111].
Eswaramoorthi et al. [119] used RULA with CATIA V5 software to assess assembly line workers. This assessment led to changes in job design to reduce or eliminate waste, as these could cause an increase in the heavy physical burden on the worker. The method was also used in another assessment of this type, but in this case on a humanoid robot arm with similar postures to those adopted by a human. The goal was to assess the robot arm's configurations [112]. Related to the above, a method was developed allowing one to configure the manipulation of articulated robots which moved similarly to humans. RULA was used to analyse the coincidence between the robot and the human [110]. Continuing in the field of robotics, one study focused on the design and analysis of a system based on gesture control. The goal was to allow workers to control an industrial-type robot. The RULA [62] method was also used for its design.
Moreover, RULA was combined with other advanced tools to carry out new research. To improve industrial production, an ergonomic study was combined with virtual reality. The design of a cell was carried out to reduce worker fatigue [54]. Conversely, RULA was combined with Kinect to collect information on the movements made by workers during mounting and assembly tasks [72,103]. Likewise, an ergonomic assessment was performed using the DELMIA (Digital Enterprise Manufacturing Interactive Application) simulation tool for assembly tasks in the robotics industry. RULA determined the harmful postures and the necessary redesign of the work to improve them [85]. Finally, a system was developed using sensors placed on the workers' bodies. RULA was used by a computer in real time, displaying the results on a screen. When these were very harmful, acoustic and visual signals were initiated. It was concluded that this system, which showed the information to the worker, reduced the occurrence of MSD [101].
Rivero et al. [89] carried out an assessment of industrial and construction workers using RULA. They explained that increased productivity is closely linked to good worker ergonomics. Other authors also used it in conjunction with OSHA and the NIOSH equation. They concluded that rapid changes were required in 65% of the industrial tasks [84,94].
Baptista et al. [102] conducted three studies with three methods, including RULA. In total, 109 factory workers participated. The results showed that there were workers suffering from MSD, although no indications were presented. Finally, Yazdanirad et al. [61] also used three assessment methods to assess 210 people in three industries (the automotive, pharmaceutical and assembly industries). The results concluded that RULA was the most suitable method.
3.1.4. Water Supply; Sewerage, Waste Management and Remediation Activities Table 6 presents a single study belonging to this category. Table 6. Water supply; sewerage, waste management and remediation activities.

Reference
Year Country Study Objective [128] 2015 Turkey RULA and REBA assessment of workers in waste collection.
Cakit [128] conducted a study to analyse waste collection workers. A programme was used to assess the postures adopted during loading and unloading. In addition, the RULA and REBA methods were used. They concluded the need for urgent changes in the postures adopted. Table 7 presents studies conducted in the construction field using RULA.

Reference
Year Country Study Objective [129] 2019 Canada Development of a 3D system to simulate the working environment in the construction field. Use of RULA in the ergonomic assessment. [130] 2018 Canada Development of a 3D visualisation tool for the construction field. Use of RULA in ergonomic assessment. [131] 2016 Canada Development of a new way to measure the angles that form the postures to apply RULA. [132] 2013 Canada Assessment with RULA, REBA and the Strain Index on construction workers.
Shanahan et al. [132] analysed the usefulness of three assessment methods (RULA, REBA and the Strain Index) when used in non-fixed tasks and comparing them with four psychophysical scales from Borg 10. Fourteen construction workers without MSD were followed up. They concluded that the best method for this type of task was the Strain Index.
Another study proposed a more accurate way of measuring the angles in the postures adopted by construction workers in order to use the RULA method [131].
Finally, Li et al. [129,130] also focused on the field of construction. They developed a 3D system that allows one to simulate the working environment and perform an ergonomic assessment. They also applied REBA and RULA for the analysis.

Wholesale and Retail Trade; Repair of Motor Vehicles and Motorcycles
In this category, only three studies are presented (Table 8).

Wholesale and Retail Trade and Repair of Motor Vehicle and Motorcycles
Risk factors and the onset of MSD were studied in car repair mechanics. In total, 191 workers participated. The modified Nordic Questionnaire was used with RULA, in addition to other tools. Most workers were shown to have this type of disorder [133].

Retail Trade, Except Motor Vehicles and Motorcycles
Capodaglio [134] conducted an ergonomic study on 70 clothing store vendors. RULA, REBA, the Strain Index and OCRA were used. The results showed a high risk in the upper extremities for the postures adopted. Another study was carried out at supermarket check-outs. A tool was developed to carry out a postural assessment of the workers. It was a portable and wireless system based on RULA and the Strain Index. It allowed the assessment to be performed as the task was being undertaken [135]. Table 9 contains the studies available in the Transportation and Storage category. Land Transport and Transport via Pipelines

Transportation and Storage
The RULA method was used in various studies to analyse drivers of different vehicles, such as garbage trucks and road-cleaning trucks. In total, 77 workers participated. The study concluded that the neck was the most affected area. The scores obtained varied depending on whether an adjustable seat was used [147]. Drivers of dangerous goods vehicles also suffered discomfort in the neck region, as well as in the feet, ankles, hands, etc. According to RULA, immediate changes to the tasks were required [136]. Similarly, car drivers were assessed, but this time RULA was used along with other methods such as OWAS and CORLETT. Goniometry was applied on some workers. The results showed different levels of discomfort in various parts of the body [145]. The method was used together with OCRA to assess workers in five transport company posts. In addition, a group interview was carried out. RULA demonstrated action Levels 1 and 2 [143].
Hoy et al. [146] studied the vibrations and postures to which forklift drivers were exposed. RULA, OWAS and a questionnaire were applied, and the vibrations were measured. The posture test results showed frequent lumbar discomfort. The highest risk level postures were those comprising a bent or twisted torso.
Another such study focused on wheelchair-support bus drivers. The assessment involved four workers and one passenger. Three different wheelchairs were used. The RULA, REBA, PLIBEL and iLMM methods were employed. High-level risks were determined during this task [144].
Balaji and Alphin [140] focused on drivers of industrial vehicles. Their objective was to optimise the worker's area in the vehicle in order to reduce discomfort from the postures adopted. The software analysis was performed using RULA and REBA. Nearly half of the workers performed the task at a high-risk level. The areas most affected were the arm, wrist and torso.
Lastly, a new type of nozzle was developed for fuel refilling hoses. One hundred people were assessed using RULA while putting fuel in their vehicles. The postures were shown to be less harmful with the new design [139].

Warehousing and Support Activities for Transportation
In total, 92 workers from a supermarket warehouse were ergonomically assessed, specifically in two tasks-lifting boxes and pulling them. RULA was used in conjunction with other tools. Lifting the boxes affected the workers' lower back, while the other task affected the lower arm and wrist [142]. Using the same method in the same workplace, they assessed the effect caused by a new storage tool. They concluded that it allowed for better work completion and resulted in less back and shoulder risks [141].
Finally, material handling workers were assessed. Sensors capable of measuring angles during a work task were used and, from these data, RULA was applied. The results showed high levels of risk in the postures adopted [137].

Air Transport
Some authors performed a study in which a new RULA method was developed. This allowed astronauts to be posturally assessed [138].

Accommodation and Food Service Activities
Three studies are differentiated in this field of knowledge (Table 10). Workers in an industrial kitchen, chefs at a Chinese restaurant and pub workers were assessed. RULA was used in all of these along with other ergonomic methods or tools. In the first case, RULA obtained more harmful results than for the other methods applied. The second showed that repetitive actions were performed on the upper extremities. The third concluded that very harmful tasks existed that required corrective actions [148][149][150]. Table 11 is composed of the different studies that have been carried out in the area of Information and Communication. Several studies have been carried out on people who work regularly on a computer. One of these studies investigated whether the position where the mouse was placed with respect to the keyboard influenced the arm and shoulder postures adopted. RULA and surface electromyography were used. Some results showed that the position taken by right-handed people was less damaging if the number keyboard was not used [159]. Another similar analysis was performed on 10 workers who were also visually impaired. Harmful postures were identified for all the participants, and several recommendations [156] were made. Ekinci et al. [151] carried out an assessment very similar to the previous cases, using other tools in addition to RULA. The objective was to check the effectiveness of pre-use ergonomic computer training. Ergonomic risk was shown to decrease as a result. One of the workers carrying out this same task was followed up. They indicated discomfort in the neck and upper right extremity. They received physiotherapy sessions and ergonomic intervention, after which RULA indicated an improvement in the results [154].

Information and Communication
Other authors used RULA [158] to assess workers carrying out two specific tasks, one based on entering data using VDT (Visual Display Terminal) screens and another on document classification and sorting. The results showed that the first task required further assessment. The second had to be modified after identifying harmful postures. Another group of VDT workers had the ergonomic training they received assessed using the method. The results improved after this, reducing the action levels [153]. To this end, RULA was used in conjunction with the Visual Analog Scale (VAS) to test the benefits of ergonomic training and physiotherapy sessions. VDT operators from the Software Corporation participated. It was observed that the methods were beneficial as they decreased the risk factors and the development of musculoskeletal disorders [157].
Other authors ergonomically assessed workers at a technology company, focusing on programming, management, administration and marketing tasks. RULA deduced high action levels with no risk-free postures [155]. Lastly in this area, the RULA method was applied, along with a modified version of it (mRULA), on 29 people working in computer science. The goal was to know if mRULA was valid for ergonomic assessment. They concluded that it could be used, and that it was only necessary to make an observation [152].

Reference
Year Country Study Objective [160] 2012 Brazil Application of the RULA method on workers in the financial department of a hospital.
An ergonomic study was carried out in the financial department of a hospital using the RULA method. The results showed the need for ergonomic actions. This could reduce the grounds for absenteeism due to work-related accidents and increase well-being at work [160].

Professional, Scientific and Technical Activities
Publications relating to this category are presented below (Table 13). Table 13. Professional, scientific and technical activities.

Reference
Year Country Study Objective [161] 2016 Spain Application of OWAS and other tools to evaluate veterinarians. [162] 2008 China Ergonomic analysis using software based on the RULA method of people who perform their work on desktops.

Other Professional, Scientific and Technical Activities
A study was carried out to establish a procedure for product design managers to perform an ergonomic assessment at the start of the design. This was developed for work carried out on desktops. To this end, information on the movement of workers was collected and a digital human model was created. Software incorporating the RULA method was used to perform the ergonomic analysis [162].

Veterinary Activities
The work of 12 veterinarians was assessed while performing four different tasks. Several tools were used, including a modification of RULA, to assess the wrist. It was concluded that, of the four tasks, only the posture adopted for suturing was not detrimental to the wrist [161].

Administrative and Support Service Activities
In this field of knowledge, 12 studies have been analysed (Table 14). Table 14. Administrative and support service activities.

Reference
Year Country Study Objective [163] 2019 Iran Assessment of the benefits of an ergonomic programme performed on office workers in a petrochemical company using a questionnaire and RULA.

Building Services and Landscape Activities
Two studies were carried out on cleaning workers using the RULA method. The first was used in conjunction with the REBA method and the Standardized Nordic Questionnaire. The results indicated risks ranging from medium to very high [166]. The second also made use of the Manual Task Risk Assessment (ManTRA) and QEC and the cleaning task was assessed. The results showed that the staff developed musculoskeletal disorders [172].

Office Administration, Office Support and Other Business Support Activities
Several research studies were conducted on the risks of MSD for office workers. One of these focused on computer staff. The workers were divided into two groups, one of which contained workers already suffering from discomfort. The ROSA (Rapid Office Strain Assessment), RULA and Maastricht questionnaire methods were used. RULA indicated worse scores for workers suffering discomfort [165]. Two similar studies were performed (one of which was determined with RULA) showing that more than half the workers suffered from musculoskeletal disorders and that the most injured areas of the body were the back and upper limbs. The other study proposed corrective actions for the work carried out [169,174]. Administrative workers were ergonomically studied in the same way. In addition to using RULA, measurements were taken of the workers and the office furniture. The study concluded that the subjects were developing MSD. Corrective actions were necessary over the short term [170].
Two further studies were carried out with RULA using an intervention group and a control group. In one of them, two groups were created containing 100 workers, and lighting data and information were collected. It was determined that the use of adjustable lights improved both the ergonomics and vision while the tasks were carried out [167]. In the other study, the intervention group used a particular keyboard, mouse and touchscreen. RULA showed a decrease in harmful upper limb postures although this worsened for the hands [168].
Several works were also carried out, the objective of which was to assess ergonomic programmes. One of them was performed in Iran on office workers in a petrochemical business. A questionnaire and the RULA method were used for the assessment. Improvements were made to the postures affecting the neck, shoulders, upper back and lumbar area thanks to the ergonomic programme [163]. With the same purpose in mind, Taieb-Maimon et al. [173] assessed three groups of workers who used computers in offices, one the control group and two that had received different types of training. Workers were assessed with RULA before, during and after the training. It was observed that the two groups with training improved their postures in a short period of time. Dalkilinc and Kayihan [171] also demonstrated that ergonomic training improved the postures adopted by office workers; they used RULA and surveys. In this case, it was web training.
Finally, in this field of knowledge, Cavalini et al. [164] verified an upper extremity assessment questionnaire called the Upper Extremity Work Demand (UEWD-R). The assessment was carried out using RULA with the help of office workers who used computers. The results indicated that the questionnaire was valid for assessing postural load on upper extremities. Table 15 presents the research developed in this field. Nam et al. [175] assessed the postural load on soldiers when cleaning cannons in two different ways: manually and with an automated tool. OWAS, RULA and REBA were applied. They concluded that there was a lower risk (Level 2) when using the tool than with manual cleaning (Level 4). Another assessment of this type was developed for firefighters and emergency physicians. RULA, REBA and the NIOSH equation were used. The results showed high risks, indicating the need for corrective action [176]. Table 16 consists of 12 studies developed in education.

Reference
Year Country Study Objective [177] 2018 South Africa Use of RULA and a questionnaire on students using the computer. [178] 2018 Philippines Application of RULA and REBA on students in a chemistry laboratory.
[179] 2015 South Africa Use of RULA and VAS to assess ergonomic training carried out with school students who used a computer. [180] 2014 Australia Ergonomic assessment with RULA of children using ICT (Information and Communications Technology) to ascertain if the assessor's experience is relevant in this method. [181] 2014 Iran Use of the Nordic Musculoskeletal Questionnaire, the RULA method and other methods as well as interviews on people who used computers at two universities.
[182] 2014 Malaysia The use of RULA and other tools on elementary school students.
[183] 2012 Iran Assessing a training programme using RULA and other tools on university workers using computers. [184] 2012 Malaysia Application of a questionnaire, REBA and RULA on students between 13 and 15 years old.
[185] 2011 Indonesia Use of a virtual environment for ergonomic analysis of a bicycle. PEI was used, containing methods such as RULA. [186] 2009 USA Application of the modified RULA method and the University of California Computer Use Checklist on university students using computers. [187] 2009 Ireland The RULA method and other tools were used on high school students using computers. [188] 2007 Ireland Application of RULA, the body discomfort chart and VAS on school children using computers.
Breen et al. [188] and Kelly et al. [187] used RULA and other tools to study the postures adopted by students on the computer. Some authors focused on primary schools and others on high schools. They concluded that about 60% of the postures belonged to action Level 2. Sellschop et al. [177,179] provided ergonomic training to students with the same characteristics. They assessed effectiveness using two groups (the intervention and control groups) with the same method and other tools. In the intervention group, the risk decreased according to RULA, with action Level 4 disappearing. Other authors found that the assessor's experience of using RULA and task observation was not relevant. They demonstrated this by assessing children while they took part in ICT. The study was performed by two groups of assessors, one of them experienced in applying the method [180]. Some authors [181,186] ergonomically analysed students at the university level, also while using computers. Two studies are differentiated, one using the RULA method and the other a modification of it (mRULA) in addition to other tools. It was shown that, at an engineering university, 30.8% of participants were exposed to a Level 3 risk. In medicine, 42.9% were exposed to a Level 2 risk. On the other hand, when employed at the Qazyin University of Medical Sciences on workers using the computer, it was intended to assess a training programme. This was done in stages, through a control group and an intervention group. RULA, VAS and the Nordic Questionnaire were used. The intervention group improved. The programme proved beneficial to the workers [183].
Furthermore, in the field of education, other ergonomic analyses were carried out using RULA and other tools. They focused on students at different levels. In some cases, harmful postures were adopted due to, among other causes, the furniture used. New furniture designs were required [178,182]. Students aged between 13 and 15 were also assessed in a total of 104 positions. It was concluded that the 13-year-olds were more at risk [184].
Finally, other authors used a virtual environment to perform an ergonomic analysis on a folding bike. This was designed at the University of Indonesia. RULA was used along with other methods. The goal was to obtain the best design, which was completed when the handlebars were 32 cm high and the saddle at 83 cm [185]. Table 17 presents the studies according to the "Human health and social work activities" category. Table 17. Human health and social work activities.

Reference
Year Country Study Objective [189] 2019 Canada To check the usefulness of a training course for ophthalmologists on the placement of a slit lamp, using RULA. [190] 2019 Netherlands Use of RULA, among other tools, on operating room nurses using the da Vinci robot. [191] 2019 Iran Assessment using RULA of workers performing a task in a traditional way and with a newly designed instrument. [192] 2018 USA Application of RULA on otolaryngologists. [193] 2018 Ireland Use of RULA and other tools on ICU nurses. [194] 2018 United Kingdom Use of RULA and statistical analysis on dental students. [195] 2018 Netherlands To check if it was effective to give ergonomic training to surgical personnel in using robots, performed with RULA and other tools. [196] 2017 United Kingdom Ergonomic assessment with RULA on plastic surgeons who used magnifying glasses. [197] 2017 India Postural assessment of surgeons during a laparoscopic operation. [198] 2017 Italy Use of RULA and another method on dentists while carrying out an operation. [199] 2017 USA The RULA method was used to assess postures adopted by otolaryngologists. [200] 2016 USA Ergonomic assessment (including the RULA method) on gynaecology surgeons using 4 different chairs and several tools. [201] 2016 France Use of RULA together with a tool to assess the use of a new instrument designed for use by surgeons. [202] 2016 United Kingdom Study on the methods used, such as RULA, to analyse ergonomics in health-related jobs. [203] 2016 Iran Ergonomic assessment of dental students using RULA and a questionnaire. [204] 2016 Portugal Ergonomic study of workers in a hospital laboratory, using RULA. [205] 2016 Brazil Ergonomic assessment using 3 methods, including RULA, of emergency pharmacy workers.  [219] 2011 Taiwan RULA assessment of one of the tasks performed during blood tests.
[220] 2010 USA Application of RULA and three-dimensional imaging on surgeons who perform laryngeal microsurgery. [221] 2010 Spain Data collection using CyberGlove (R) and assessment using an adapted RULA method. [222] 2008 United Kingdom Application of the RULA method on mammogram radiologists. [223] 2007 United Kingdom Ergonomic assessment using RULA on dental students using two different armchairs. [224] 2005 USA Use of the Job Strain Index and RULA to assess surgeons performing an endoscopy manually and with the help of a robot. [225] 2001 Canada Use of an optoelectronic system to collect posture data on surgeons, and then assessing them with a modified RULA. [226] 2000 Ireland Ergonomic intervention in biomedical workers. RULA was used in the ergonomic assessment, among others. This field is divided into different specialties to show the available studies in a more ordered fashion.

• Ophthalmology
Ratzlaff et al. [189] tested the usefulness of an ergonomic training course given to 10 ophthalmologists. They focused on a task that consisted of positioning a slit lamp. It was assessed before and after training, using RULA applied with software. Risk levels were shown to be lower after training.
• Radiology In the United Kingdom, mammogram radiologists were ergonomically assessed. Three work posts were analysed, one for digital mammograms, one for film mammograms and the third for both. The RULA method was used. It was determined that no more MSDs developed as a result of performing the mammograms digitally [222].
• Nursing Sezgin and Esin [207] evaluated 1,515 intensive care nurses. They mainly used the RULA method. They showed that the hardest-hit areas of the body were the back and legs. They also concluded that the scores for this method were lowered by giving the Ergonomic Risk Management Programme (ERMP) to workers [193].
Sung et al. [219] decided to use an armrest and mirror to observe the tubes after each blood test. These proposals reduced the RULA score from 7 to 2. Therefore, the postures of the workers improved, mainly in the neck and shoulders.
As a last study, Garosi et al. [191] designed and developed a new instrument for a nursing task that used to be done manually. According to RULA, the level of risk decreased from 3 to 2 in the upper extremities when using this new tool.

• Otolaryngology
Goyil et al. [192,199] analysed the postures adopted by the otolaryngologists when the patient was placed in position (sitting or lying on their back). The RULA method was used. Higher risk levels were determined for sitting patients.

• Ultrasounds
Workers performing ultrasounds were assessed because they often suffer from musculoskeletal discomfort. RULA was used on five participants and on 24 ultrasounds; other parameters were also taken into account. The results showed awkward postures for the upper limbs [213].
• Laboratory Some authors found that lab workers in hospitals developed MSD from performing their tasks. In these studies, they applied RULA, sometimes with other methods or tools [204,212].
• Surgery The use of robots in surgery does not always lead to correct postures in the workers. Several authors assessed surgical personnel during their work using RULA and other tools. They found detrimental results and the need to modify the tasks [190,215]. One solution could be to provide ergonomic training to workers who perform surgery with robots. According to RULA, this improved the levels of risk [195]. The use of robot in other cases led to ergonomic improvements. One of these was when performing endoscopies. Surgeons obtained lower RULA scores when using robots than when performing the operation manually [224].
Other authors focused their studies (using the RULA method) on surgeons performing laparoscopies.
They showed that there was a risk regarding the postures the surgeons developed [197]. In some cases, they combined these studies with the use of new technologies. For example, Youssed et al. [218] used a virtual reality simulator in this type of study, whereas Sanchez-Margallo et al. [221] used a glove called a CyberGlove (R). This glove allowed one to measure the movements made by the wrist, which can then be applied to an adapted RULA method. Bensignor et al. [201] designed a robotic needle holder for this type of surgery. Using RULA, they demonstrated that surgeon's postures were less harmful than when performing the technique in the traditional way.
Other ergonomic analyses were performed on surgeons carrying out various tasks. Li et al. [196] used RULA to assess plastic surgeons who used magnifying glasses, and who suffered discomfort in the upper extremities. They indicated that modifying the height of the table or the distance of the magnifying glass from the workplace could lessen these problems. Person et al. [225] used an optoelectronic system to take posture data and obtain results using a modified RULA. They found harmful results mainly at the wrist. Hermandon and Choi [217] agreed that the wrist was one of the hardest-hit areas. They used RULA and other tools on office-based surgery (OBS) workers. They concluded that these workers were at high risk of musculoskeletal disorders. In addition, they highlighted other areas of the body that were harmed such as the arms, shoulder, neck and back.
Other authors assessed surgeons' postures using RULA when they performed the same procedure in different ways. For example, Statham et al. [220] focused on laryngeal microsurgery surgeons. They assessed them while performing the task adopting three different postures, one with the arms unsupported and the other two with different supports. They deduced the levels of risk to which the surgeons were exposed. Singh et al. [200] assessed gynaecology surgeons using four different chairs. They determined a medium-to-high risk in the neck and shoulders. They showed that the chairs did not influence the scores.
Finally, some authors presented the idea of integrating different ergonomic methods and tools to assess nursing and surgery workers. OWAS, REBA, RULA and NIOSH were used, amongst other methods [209].
• Dentistry Several authors focused on ergonomically assessing dental students while they were doing their internships. This was done using RULA, sometimes together with other methods or questionnaires. They concluded that there was a high level of risk regarding musculoskeletal disorders [203,211,214]. Ergonomic improvements in this area showed that using a Bambach Saddle armchair resulted in lower risk than when using a conventional chair [223], and that using magnifying glasses was beneficial for adopting lower-risk postures [194].
This type of study was also conducted on dentists to assess their postures. RULA was used in conjunction with other methods in most cases. Marcon et al. [198] compared the difference between using a magnifying glass, a microscope or not using anything at all during operations. They showed that using a microscope led to more harmful postures. In addition, these dentists are usually harmed by the postures they adopt during their tasks. Therefore, it is necessary to establish changes, some of which are required immediately. The most affected parts of the body are the lumbar region and neck [206]. This coincides with that determined by Tirgar et al. [208], although they added that another area affected was the shoulders, as inferred by Rafie et al. [210].
To conclude this group, the ergonomics of dental hygienists were also studied. They used RULA, REBA and the Strain Index. It was concluded that the postures the hygienists adopted contributed to the onset of musculoskeletal disorders [216].
• Other An ergonomic assessment of workers in an emergency pharmacy was carried out using three methods, including RULA. This led to some improvements in their work [205]. Another series of improvements was made for women workers in the biomedical field. An intervention was carried out based on changes to the workplace and recommendations. According to RULA, this was beneficial as it led to lower scores for more than half of the postures [226]. Finally, methods for analysing ergonomics in health-related jobs were studied. It was concluded that RULA could be used to attain more accurate results [202]. Table 18 includes only three studies. Table 18. Arts, entertainment and recreation.

Reference
Year Country Study Objective [227] 2013 India The modified Nordic Questionnaire, REBA and RULA were applied to potters and sculptors.
[228] 2011 Israel RULA and questionnaires were used on orchestral musicians. [229] 2010 India RULA, REBA, OVAKO, OCRA and the Strain Index were applied to craft workers.
In the field of music, some authors demonstrated, with RULA and other tools, that musicians often suffer MSD mainly in the upper extremities. The risk is higher in those who play string instruments [228]. The development of such disorders was also confirmed in potters, sculptors and craft workers in India. They made use of RULA and other assessment methods. For all cases, harmful postures were deduced as well as the need to make changes to avoid them, immediately for the crafts workers [227,229].

Other Service Activities
Only three studies are presented in this category as well (Table 19). Table 19. Other service activities.

Reference
Year Country Study Objective [230] 2017 USA Use of a survey and the RULA method on tattooists.
[231] 2015 India REBA, RULA and OCRA were used on bicycle repair workers.
[232] 2011 Portugal An ergonomic study using RULA and QEC was conducted on workers from four spas.

Repair of Computers, and Personal and Household Goods
An ergonomic assessment was carried out on bicycle repair workers. The RULA, REBA and OCRA methods were used, along with other parameter measurement. The tasks assessed were shown to be at a high-risk level, and that immediate improvement actions were required [231].
Other Personal Service Activities Some authors focused on spa workers, with the aim of preventing them from developing MSD during three of their tasks. An assessment was carried out with RULA and QEC. The results showed that ergonomic information and training would improve the postures adopted [232]. A similar study, using only RULA and a survey, was conducted on tattooists. It was concluded that 71% of the postures adopted had a high level of risk and therefore urgent corrective measures were needed [230].
3.1.18. Activities of Households as Employers; Undifferentiated Goods-and Services-Producing Activities of Households for Own Use Table 20 summarises the publications in this category. Table 20. Activities of households as employers; undifferentiated goods-and services-producing activities of households for own use.

Reference
Year Country Study Objective [233] 2016 Ecuador Assessment of people in wheelchairs who performed some domestic or work activity, using the RULA method and MAPFRE. [234] 2012 Italy 5 ergonomic methods or tools were used, including RULA, on people performing household chores.
Domestic workers are also exposed to the onset of musculoskeletal disorders, although, according to Apostoli et al. [234], at a medium or low level. This was deduced by research in which RULA and other assessment methods or tools were applied. Another similar study was carried out using the RULA and MAPFRE methods, but in this case the workers were in wheelchairs. It was inferred that there were risks caused by the postures that had to be adopted in the chair in order to carry out the tasks [233].

Other Areas Not Previously Included
Finally, a category (Table 21) is presented that is not covered by the classification used but has applications that cannot be included in the above fields of knowledge. Table 21. Other scopes not previously included.

Reference
Year Country Study Objective [235] 2019 Ecuador New way to perform ergonomic analysis using the Kinect V2 sensor together with the RULA method. [236] 2018 Brazil RULA and the deformation rate (SI) were studied, and the analysis of various jobs was carried out. [237] 2018 Malaysia Conducting a study to assess the utility of the RULA-Kinect (TM) system. [238] 2018 Malaysia Research to compare the RULA method with the RULA-Kinect system. [239] 2018 Thailand Ergonomic study using a questionnaire and the RULA method on people who use mobile phones.
[ The different studies available are divided into groups according to the topic covered: • Sensors The Kinect sensor has been used in several studies together with the RULA method for ergonomic analysis. Some of them have compared the results by performing the assessment without the sensor and were similar. With Kinect, you can reduce the assessment time or subjectivity with professional analysis [235,244].

•
Use of mobile phones and computers Some authors assessed people who sent SMS using their mobile phones. They used a questionnaire and the RULA method. The latter exposed a risk Level 3 for the right and left area of the body, so modifications [239] were required. Employing the same method, other authors assessed the postures of children using computers or other ICT devices. They deduced risk categories of Level 2 or higher for the latter. In the case of computers, it was inferred that the RULA method was not recommended for applying to girls under eight years of age [245,251].

• Methods
Can and Figlali [241] developed a new assessment method from RULA, called ARULA (Advanced RULA). This was characterised as improving the advantages of the initial method, such as its high pre-observation time, assessment, etc.
One assessment was carried out using various methods such as the State of Washington method, OCRA, RULA, the Strain Index, etc. A high or very high level of risk for the upper limbs [256] was obtained with all. Two of the above methods, the Strain Index and RULA, were also studied from the perspective of validity, reliability, etc. The analysis of various jobs that included static positions or repetitive tasks was carried out, concluding that training was necessary to apply the [236] methods. Finally, a study was conducted on perceived discomfort in the different postures of the upper extremities. The RULA method [248] was used. •

Technological Evolution
Technology was used to apply the RULA method in several studies. Manghisi et al. [242] developed software called K2RULA capable of assessing workers during the task or with subsequent analysis. Goncalves and Fernandes [253,255] developed a semi-automatic system for performing ergonomic assessments using the RULA method. It was based on two synchronised video recording cameras for observing the worker's tasks. From these recordings, RULA automatically calculated the scores, obtaining the action level for each of the observations. Plantard et al. [246] developed a method for performing ergonomic assessments using a virtual mannequin and RULA scores. They noted that the results of this new method coincided with those that had actually been obtained. Finally, Schlette and Rossmann [252] adapted the RULA method with Virtual Human in order to control human movements. The goal was to control the movements of a humanoid robot that are similar to those performed by a human.

• Gestures
One study used RULA in conjunction with another method called Quick Rating (QRating) to ergonomically assess people who made typical gestures when communicating. Physical discomfort during these gestures should be controlled [243].
In another study, gestures were required for 18 commands used in the movement of objects in a virtual environment. To do this, they were determined using Korean sign language and others created by the user. All these gestures were analysed and the RULA method [250] was used for this purpose.

•
Other works Razavi and Behbudi [247] ergonomically analysed box office workers with the RULA method, following the adoption of a series of improvements. It was concluded that there was a reduced level of risk. The same type of study was carried out on workers at a gas bottle company. It determined the existence of postures with an action Level 3 risk, and the need for changes in a short period of time [249]. It was also carried out on workers who used machines and other equipment during their work. Anthropometric information and the OCRA method were also used [254].
On the other hand, Ward et al. [257] used RULA to assess the ergonomics of postures adopted in the use of biometric devices (fingerprints and veins on the palm of the hand). They concluded that the positions in which they were placed (angles and heights) influenced the postures adopted. McGorry and Lin [258] studied the influence on grip strength of the orientation and placement (height and distance) of tool handles. They used RULA to carry out an ergonomic assessment.
Finally, several authors developed two assessment methods, one that considered frequent and harmful postures and the other the time. An assessment was made, using these methods and a modified RULA method, of the postures adopted by a group of people. They deduced that there was no coincidence between the methods [259].

Country-by-Country Ranking
The revised applications are also classified according to their location, taking into account the fields of knowledge ( Figure 5).
There are 34 countries where the RULA method has been used. The USA stands out with 23 studies, followed by Iran with 21, Malaysia with 17, India with 16, Portugal with 15, Brazil with 12 and Canada and the United Kingdom with 11. All other countries have 10 or fewer research studies. Eight locations have a single publication: Saudi Arabia, Japan, Mexico, Poland, Slovenia, Sweden, Tunisia and Venezuela ( Figure 5).
In addition to the USA having the largest number of studies, it is also the country where the most knowledge categories have been covered. This comprises a total of 10 areas. "Human health and social work activities" stand out with nine studies, followed by "Manufacturing" with three ( Figure 5). Both categories match the ones that have the most published studies at the general level ( Figure 4 and Table 2).
The places following the USA are Turkey, Italy, Iran, India and Brazil, with seven different locations. In all of them, except Italy, the largest number of publications also corresponds to "Manufacturing". Iran stands out with 11 studies in this category. Countries such as Venezuela, Tunisia, Sweden South Africa, Slovenia, Poland, Mexico, Japan and Saudi Arabia only cover one area ( Figure 5).
The United Kingdom is the location where the RULA method originated. However, it is not a place where it has been most applied, as only 11 studies have been performed there. The method originated with assessments carried out on workers in the industry [20]. Despite this, RULA has not been widely used in industry in the United Kingdom; it presents only three studies. "Human health and social work activities" stands out with five publications ( Figure 5).    The RULA method was created in 1993; however, according to the review carried out, it was not until 1998 that it was first applied.

Classification by Years
From 1998 to 2019, the method has been applied every year. It should be noted that the year 2019 includes only the studies developed up until April.
The Over the past 10 years, there has been an increase in such research. This may be due to the importance and awareness that occupational hazard prevention has received in recent times. In addition, it might be linked to the development of new technologies. These allow the method to be applied more quickly and efficiently (Figure 7).
It is noted (Figure 7) that over the past 10 years, the number of categories investigated has also increased compared to the previous 12 years. The year 2016 is characterised not only as having the largest number of publications, but also by the largest number of areas studied (11). "Manufacturing" stands out for representing 13 of the 32 research studies, followed by "Human health and social work activities" with 6. There are seven years with a single category (1998-2002, 2004 and 2006). Table 22 presents all the journals available in this review, the number of articles published in each, knowledge categories (Web of Science), impact factor, rank and quartile. In total, 163 studies are differentiated. The rest of those that have been reviewed do not correspond to journal articles.   Of all the journals, there are four with a greater number of articles published: "Work-A Journal of Prevention Assessment & Rehabilitation" with 26 studies, followed by "Applied Ergonomics" with 16, "International Journal of Industrial Ergonomics" with 12 and "International Journal of Occupational Safety and Ergonomics" with 8 (Table 22).

Comparing Results with Other Methods
Some bibliographic reviews similar to this one have already been carried out. They have focused on other indirect and semi-direct assessment methods. Some matches are presented in the results obtained.
The RULA method matches the OWAS method and the Standardized Nordic Questionnaire in the most common knowledge categories. The field of industry and health and social assistance are the most researched, with one or the other being highlighted depending on the method [8,260]. The REBA method has also been highlighted in industry, although the health-related field ranks fourth [261].
For countries with the highest number of publications, none of the methods coincided with RULA, since REBA excelled in India, OWAS in Finland and the Nordic Questionnaire in Iran. However, for REBA, the second country with the most studies was the USA [8,260,261].
By date, the Nordic Questionnaire matches RULA. The year 2016 was when more studies were published for both [260].
Finally, with regards to journals, information is only available for the REBA method. The journal with the largest number of publications on this method is "Work-A Journal of Prevention Assessment & Rehabilitation"; this is also the case for RULA [261].
It should be noted that this comparison is general since the date range selected in each of the studies is not the same.

Sustainability and the RULA Method
By integrating ISO 45001 with ISO 9001 and ISO 14001, organisations seek to implement quality management, occupational safety and health and the environment in a single system (Figure 8). The three systems, operating together, allow the organisation to optimise: The quality of the product or service Customer satisfaction The disposal of waste that has an impact on the environment The efficiency of the processes The health and safety of workers  Sustainability is a set of three fundamental parts: economic, social and environmental [262]. Sustainability, therefore, is not only focused on natural resources, but also plays a very important role in companies and contracted staff [263]. It fosters a relationship between healthy living and caring for nature [262]. For this reason, it is very important to also focus on the care of workers, carrying out assessments in order to obtain improvements in their health and safety [264].
The RULA method pursues this objective, as it focuses on the study of musculoskeletal disorders. Therefore, the use of this method contributes to the production of sustainable products.

Limitations
The country classification in this document has been based on the origin of the authors, as not all studies are clear about their location. The locations selected in each study have been those to which the greatest number of authors belong. In cases where it was not possible to follow this criterion, the location of the first author was selected.

Conclusions
The RULA method has been used in two main areas, "Manufacturing" and "Human health and social work activities". However, it has been found not to be a sector-specific method. It can be applied to workers in any field.
Its use has been increasing over the last 10 years, perhaps indicating it is an effective method which is being tested more and more. This is also coupled with a growing awareness of workers' health and safety. The year that stands out for the number of studies published is 2016 with a total of 32, followed by 2018 with a total of 28.
Countries such as the USA and Iran excel at applying the method and encompassing numerous fields of knowledge. The journal with the most publications is "Work-A Journal of Prevention Assessment & Rehabilitation", with a total of 26. This journal is followed by "Applied Ergonomics" with 16 published studies.
RULA is usually used in combination with other ergonomic methods or tools to provide better and more reliable results. In this way, it is possible to contemplate different risk factors and evaluate numerous body areas. In addition, technological advancement is also appreciated in all sectors, since in many studies the method is combined with the use of sensors, software, virtual reality, etc.