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Observational Methods for Assessing Ergonomic Risks for Work-Related Musculoskeletal Disorders. A Scoping Review

Introduction: Work-related musculoskeletal disorders (wrmsds) are one of the most common causes of absence from work. Exposures in the work environment can cause or aggravate the impact of these musculoskeletal disorders and the identification of ergonomic exposures are essential in risk assessment. It is important to assess all three key indicators of these exposures (intensity, frequency and duration) for being able to estimate the risk level for the development of wrmsds. Aim: This paper aims to give an overview of some of the observational methods that can be used for assessment of ergonomic risks at the workplace. Methods: This study was conducted as a scoping review of the 1 Karolinska Insitutet, Department of Neurobiology, Caring Sciences and Society, División of Physical Therapy. * Corresponding author: Wim.Grooten@ki.se 2 University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciencies; Centre for Musculoskeletal Research. E-mail: elin.johansson@ki.se Rev. Cienc. Salud. Bogotá, Colombia, vol.16 (especial): 8-38, junio de 2018 ARTÍCULOS DE INVESTIGACIÓN CLÍNICA O EXPERIMENTAL

medical and ergonomic literature and official governmental webpages in Sweden, U.S.A. and the Netherlands. Results: In total, 19 different observational methods were identified. We summarize our findings based on the body parts that were studied and what key indicators were assessed: 1) intensity of the work load (posture and force production), 2) frequency of the work load (e.g. repetitive movements), and 3) the duration of the work load (e.g. static work). In an appendix we include a brief presentation of these methods together with the work sheet (if available) and the source reference of the observational method. Conclusion: For ergonomists that perform risk assessments, there is a large number of observational assessment tools available and it is important to understand that different methods can be used simultaneously to be able to estimate the objective risk levels for wrmsds.

Background Ergonomics
E rgonomics involves the interaction between human, technology and organization in the purpose of optimizing health, well-being and performance (1). Deficiencies in the working environment affect the individual, the company and the community. Therefore, well planned ergonomic working environment not only implies health benefits for the individual but also lead to increased quality and productivity gains for the company (2) and for society (3). A specific part within the field of ergonomics is, according to the international ergonomics association (iea), the compatibility among human anatomical, anthropometric, physiological and biomechanical characteristics and the static and dynamic parameters of physical work (4). Relevant issues are thus working postures, materials handling, repetitive movements, static work, work-related disorders and safety and health (4), aiming to prevent the occurrence of injuries of the musculoskeletal system. These injuries are one of the most common causes of absence from work, leading to individual suffering and enormous costs for society. The most common body-parts that are affected are neck/shoulder and low back (5). Biomechanical exposures in the work environment can cause (6) or aggravate (7) the impact of these injuries, therefore the term work-related musculoskeletal disorders (wrmsds) is often used to describe these injuries (4).
Prevention of wrmsds is less costly than rehabilitation and preventive measures aim to detect the potentially harmful ergonomic work situations at an early stage, before wrmsds occur (2). This process of identifying and classifying the risk levels for wrmsds is called risk assessment. Risk assessment should be performed systematically by the employer, but there is often a need for an ergonomists with more extensive knowledge about workenvironmental conditions. Although risk assessment often is used on an individual level, for example in the investigation if the msd of a specific worker could be related to his/her specific workplace, risk analyses should analyze the work task rather than focusing on the individual. Moreover, risk assessments should be performed by using methods that are objective and correct, in other words, reliable and valid. It is of great importance that risk assessment is performed before the work task is taken into production, for example, during the planning stage or when reconstructing existing workplaces. By assessing the wrmsd risk in this stage, it is easier to specify the individual demands that are needed to perform the specific task. Ergonomic risk analyses can also be performed when one aims to evaluate Observational Methods for Assessing Ergonomic Risks for Work-Related Musculoskeletal Disorders aim to evaluate the reduction of wrmsds (8), but this approach is shadowed with a large number of methodological difficulties and it seems to be more feasible to study the effect on ergonomic exposures, rather than the occurrence of injuries.
Using an assembly line as example, workers are exposed to multiple concurrent factors that could lead to wrmsds, such as the speed and height of the assembly line, the amount of products that are handled, the weight and shape of the products, the weight of the tools used, the duration of the working cycles and the number of pauses. The number of workers on the work site, the number of joints involved, the movement quantity and quality, the ability to alter body positions, psychological stress, time pressure, working hours, time of day, environmental factors (light, temperature, noise, vibrations), and the psychosocial work environment, etc. In a risk assessment of such a complex workplace it is important to structure the exposures into different components based on the pathophysiological mechanisms for wrmsds. In the best of worlds, a risk assessment should cover all aspects, but often one need to focus on the two or three most important risks in order to find suitable interventions. In a multifactorial environment, one could use one specific assessment method that is perfectly constructed to assess one specific risk in one specific work task over a short time period, or use a general risk assessment method that assesses the total load over a longer time period.
So the question is: which approach should be used?

Intensity, Frequency and Duration
W hen assessing the ergonomic risks, three key indicators of ergonomic exposure should be taken into account: I) the "intensity" of the work load; e.g. awkward posture of the trunk and/or extremities (posture) 3 and force production during lifting, pushing and pulling (due to lifting, pushing and pulling tasks), F) the "frequency" of the work load; e.g. repetitive movements, and D) the "duration" of the work load; e.g. static work, lack of changes in posture (9). Using these categories, many of the common ergonomic risks can be identified: manual handling (I), awkward posture (I/D), repetitive work (F), and static work (D) can be observed. Table 1 provides examples of how these three key indicators of biomechanical exposure can be clustered against the aforementioned ergonomic risks for wrmsds. This table also shows that many of the common wrmsds, due to combinations of risks (6, 7), can be described by more than one key indicator. Moreover, different and similar categories could be expressed in different or similar measures, making it difficult to know which risk or key indicator is observed. For example, by measuring the inclination degree of the back during a lifting task (expressed in degrees and in Newtons) in combination with the time spent in this angle (expressed in percentage of working time or in seconds), one could assess the risk level for wrmsds for the combination of awkward postures and static work. Previous researches show that the combination of risk factors is an especially important factor to consider in a risk assessment [6]. There is in addition a need for observing concurrent risk factors for wrmsds. Table 1. Classification of biomechanical loading into the three key indicators (Intensity, Frequency, and Duration) of the ergonomic risks for wrmsds, their measures and some of the common wrmsds associated with these exposures.

Risk
Measure Common wrmsds I: Intensity Manual handling Kg or newton Injuries in the vertebras and discs 4 , Injuries in tendons 5 Injuries in muscles 6 Awkward posture Degrees

Ergonomic Risk Assessment and Intervention
E rgonomic risk assessment is part of the risk management process that will be included in a systematic analysis of potential hazards to ill-health and accidents. The purpose of making an ergonomic risk assessment is to eliminate work-related health risks by identifying existing or potential risks that may lead to msds. When risk factors are identified, interventions to reduce or minimize them must be carried out. Risk assessments can also be useful to evaluate an intervention performed at the workplace. To successfully implement ergonomic improvements in the work environment, it is important to identify key persons who have the power and obligations to take action at the workplace at an early stage (10). It is of the outmost importance that the risk assessment is well imbedded in the organization and the key persons are employed by the organization.
External consultants could be involved in the ergonomic risk assessment, but the intervention should be initiated from within the organization. Moreover, the employees should be included from the beginning. This so called participatory approach, i.e. where the employees are actively involved in the risk assessment and intervention development, has been proved successful in earlier studies (3).

Four Steps in an Ergonomic Risk Analysis
T here are four steps involved in an ergonomic risk analysis. First, the physical working situation should map all performed tasks. There are several methods for this, but the hierarchical task analysis (hta) is a recommended method for this mapping procedure [11]. The next step is to rank the tasks. This can be based on, for example, the time spent on a specific work task, or the severity of the ergonomic problems. This step is followed by an objective assessment of the three key indicators (intensity, frequency and duration) for each work task. Based on the assessment, a decision of the severity of the risk should be taken. A traffic light model -green (no obvious ergonomic problems), yellow/orange (minor/major ergonomic problems) and red (serious ergonomic problems, many workers are at risk of developing wrmsds)-can be used for this. The fourth and final step is risk management.
In this paper, we focus on the second step, the objective assessment of the ergonomic exposures.
The methods available for the observation of risks can be divided into three categories: questionnaires, observation methods, and technical measurement methods.

Questionnaires:
Here, the employee assesses the organization ergonomic risks during work using a questionnaire with pre-defined answers, e.g. the Dutch Musculoskeletal Questionnaire (12). This method is easy to use with large groups of workers and enables comparisons over time and between groups. However in workers with wrmsds, there could be validity problems since they experience their work with a higher perception in terms of intensity, frequency and duration compared to those with no wrmsds, thus introducing a serious form of bias, i.e. differential exposure assessment bias (13).

Observational Methods:
These methods have to be based on concepts of an external observer (preferably an ergonomist) who fills in a predefined scoring sheet while watching a worker performing his/her work. These methods are more time-consuming  (15), as well as different types of accelerometers (16)(17)(18) and inclinometers (19,20), smart clothing (21), and video-based systems (www.vidarweb.se), etc. that could be used for ergonomic risk assessment.
These instruments are usually very accurate, but with some disadvantages: they are more expensive than observational methods, they need to be handled by experts and they interfere with the organization's work.
It is important to choose the most accurate and cost-effective method. We believe that weighing all the pros and cons of these three methods observational methods using pre-defined score sheets seem to be the most useful for ergonomists that work with daily ergonomic risk assessment in work environments.

Aim
T he aim of this paper is to give an overview of observation methods that can be used in the assessment of ergonomic risks for wrmsds at the workplace.

Design
This study was designed as a scoping review of the literature on ergonomic risk assessment.
PUBMED, ARBLINE and GOOGLE SCHOLAR databases were searched using combinations of key words such as 'ergonomic risk', 'assessment/measurement/methods', 'wrmsds', 'intervention', together with the three biomechanical exposure categories, intensity, frequency and duration. Moreover, websites from different national institutions (Sweden) and international (the Netherlands, US) were searched as well. The two authors (WG and EJ) searched for methods using a "snowball method", which means that bibliography of papers also were used to find methods. Special focus was put on papers published after 2008, to add methods that were developed after the systematic review of Takala, et al. (2010) (14).
Included were original papers that present the assessment method of the ergonomic risk exposures at work. Only papers in English, Dutch or Swedish that were available in full text were included. Moreover, only methods that use objective assessment measures were included; that is, an external assessor performs the risk assessment based on a pre-defined scoring sheet without the use of technical equipment.

Results
I n total 19 methods were found that met the inclusion criteria, and for each method, the body part that is assessed together with the key indicators are presented in Table 2. In Appendix 1, the methods are described very briefly. In general, those methods had been found easy to use and provided useful information for the ergonomist to communicate the risk to the employer/employee in terms of green, yellow and red, and gave directions for ergonomic interventions.

Discussion
T his study maps a large number of instruments that can be used in the assessment of ergonomic wrmsd risk factors. Table 2 shows an overview of which body parts and key indicators (I, F, D) are assessed by these instruments. All of the instruments assess posture (intensity), but the other two key issues of biomechanical exposure (frequency and duration) were not included in all observational methods. Considering the instruments, only six assess all three key indicators: SI, HARM, kim I-II and kim III, RAMP and wera, and among these, only wera measures the biomechanical wrmsd risk for all body parts.
For ergonomists that perform risk assessments, there is a large number of observational assessment tools available, it is important to understand that different methods can be used simultaneously in order to estimate the objective wrmsd risk levels.

Appendix 1. Short description of the observational methods
Agricultural Lower Limb Assessmentalla alla is a diverse and segmented ergonomic lower limb assessment tool developed for farm assessing farmers at work. alla is especially useful for studying lower limb burdening work [22,40].

Hand Activity Level
This method intends to assess the msd risk in the hand and forearm in repetitive work that is performed for at least four hours. The method is based on two variables that are judged by simple observations and estimates of the person performing the work: 1) hand activity level (hal), that indicates how often the movements are performed (assessed on a vas scale), and 2) hand force, in which the produced force is estimated with a Borg cr-10 scale. These variables are placed on two axes in a chart with marked areas for red, yellow and green for identification of action and threshold limit values (tlv) (25). In a similar way, kim II is used for assessment of work that involves pushing and pulling.
The procedure is similar to kim I. First, a time point is given, based on the distance that the load is moved (more or less than 5 m). Then, the weight of the load and how it is moved is

Loading on the Upper Body Assessmentluba
In luba, a score is calculated for the posture of each body part. The combined individual score for the neck, shoulders, upper back, lower back, elbows and wrists/hands gives a postural load index (pli). This pli score shows how musculoskeletal loading is associated to the worker's posture. luba classifys the risk of musculoskeletal disorders into four action categories (29). is a simplified version, as a preliminary screening tool is intended for special sectors (e.g. craftwork, small business, agriculture, etc.) in which the work is not organized according to precisely defined rates, times and cycles as it is in industry, 2) the ocra checklist for initial risk assessment, and 3) the ocra index for precise and analytical risk assessment (30).

Duration multiplier
Ocra Checklist

Additional factors Posture Force Frequency
The calculation procedure for the OCRA Checklist.  Posture, Activity, Tools, and Handlingpath path has a work sampling-based approach, it was developed specifically to characterize the ergonomic hazards of heavy highway construction work. path is based on the owas definitions and uses the same risk levels [32].

Rapid Upper Limb Assessment Methodrula
A single page worksheet is used to evaluate required body posture, force, and repetition.
Based on the evaluations, scores are entered for each body region in section A) for the arm and wrist, and section B) for the neck and trunk. After the data for each region is collected and scored, tables on the form are then used to compile the risk factor variables, generating a single score that represents the level of msd risk. The rula was designed for easy use without the need for advanced ergonomic knowledge or expensive equipment. By using the rula worksheet, an evaluator will assign a score for each of the following body regions: upper arm, lower arm, wrist, neck, trunk, and legs. After the data for each region is collected and scored, tables on the form are used to compile the risk factor variables, generating a single score that represents the level of msd risk (37).

Strain Indexsi
The methodology involves the measurement or estimation of six task variables (intensity of exertion, duration of exertion per cycle, efforts per minute, wrist posture, speed of exertion, and duration of task per day), the assignment of an ordinal rating for each variable according to exposure data, and then the assignment of a multiplier value for each variable. The strain index is the product of these six multipliers (38).

Observational Methods for Assessing Ergonomic Risks for Work-Related Musculoskeletal Disorders
Workplace Ergonomic Risk Assessmentwera wera provides a quick method for screening the working task for assessing the physical risk factors associated with wrmsds. The wera tool covers six physical risk factors including posture, repetition, force, vibration, contact stress and task duration and it involves the five main body regions: shoulder, wrist, back, neck and leg. It has a scoring system and contains action levels, which provide a guide to the level of risk and the possible need for action to conduct more detailed assessments (39).