The work compatibility improvement framework: preliminary findings of a case study for defining and measuring the human-at-work system.

Although researchers traditionally examined the 'risk' characteristics of work settings in health studies, few work models, such as the 'demand-control' and 'motivation-hygiene theory', advocated the study of the positive and the negative aspects of work for the ultimate improvement of work performance. The objectives of the current study were: (a) to examine the positive and negative characteristics of work in the machining department in a small manufacturing plant in the Midwest USA, and, (b) to report the prevalence of musculoskeletal and stress outcomes. A focus group consisting of worker experts from the different job categories in the machining department confirmed the management's concerns. Accordingly, 56 male and female workers, employed in three shifts, were surveyed on the demand/energizer profiles of work characteristics and self-reported musculoskeletal/stress symptoms. On average, one-fourth to one-third of the workers reported 'high' demand, and over 50% of the workers documented 'low' energizers for certain work domains/sub-domains, such as 'physical task content'/'organizational' work domains and 'upper body postural loading'/'time organization' work sub-domains. The prevalence of workers who reported 'high' musculoskeletal/stress disorder cases, was in the range of 25-35% and was consistent with the results of 'high' demands and 'low' energizers. The results of this case study confirm the importance of adopting a comprehensive view for work improvement and sustainable growth opportunities. It is paramount to consider the negative and positive aspects of work characteristics to ensure optimum organizational performance. The Work Compatibility Improvement Framework, proposed in the reported research, is an important endeavor toward the ultimate improvement and sustainable growth of human and organizational performance.

Biomechanical evaluation of nursing tasks in a hospital setting.

A field study was conducted to investigate spinal kinematics and loading in the nursing profession using objective and subjective measurements of selected nursing tasks observed in a hospital setting. Spinal loading was estimated using trunk motion dynamics measured by the lumbar motion monitor (LMM) and lower back compressive and shear forces were estimated using the three-dimensional (3D) Static Strength Prediction Program. Subjective measures included the rate of perceived physical effort and the perceived risk of low back pain. A multiple logistic regression model, reported in the literature for predicting low back injury based on defined risk groups, was tested. The study results concluded that the major risk factors for low back injury in nurses were the weight of patients handled, trunk moment, and trunk axial rotation. The activities that required long time exposure to awkward postures were perceived by nurses as a high physical effort. This study also concluded that self-reported perceived exertion could be used as a tool to identify nursing activities with a high risk of low-back injury.

Ergonomics and human factors: the paradigms for science, engineering, design, technology and management of human-compatible systems.

This paper provides a theoretical perspective on human factors and ergonomics (HFE), defined as a unique and independent discipline that focuses on the nature of human-artefact interactions, viewed from the unified perspective of the science, engineering, design, technology and management of human-compatible systems. Such systems include a variety of natural and artificial products, processes and living environments. The distinguishing features of the contemporary HFE discipline and profession are discussed and a concept of ergonomics literacy is proposed. An axiomatic approach to ergonomics design and a universal measure of system-human incompatibility are also introduced. It is concluded that the main focus of the HFE discipline in the 21st century will be the design and management of systems that satisfy human compatibility requirements.

Musculoskeletal outcomes in multiple body regions and work effects among nurses: the effects of stressful and stimulating working conditions.

This study investigated the various stressors encountered by the nursing profession. In particular, the following hypotheses were tested: (1) working conditions of nurses significantly affect perceived risk of injury and illness, work dissatisfaction, work satisfaction, energy state at the end of workday, the effort exerted by the registered nurse (RN), psychosomatic outcomes, and musculoskeletal symptoms (in multiple body regions); (2) both intermediate work effects (i.e., effort, perceived risk of injury/illness, work satisfaction/dissatisfaction, energy state at end of workday) and psychosomatic outcomes significantly affect musculoskeletal outcomes (in multiple body regions); (3) both working conditions and effects significantly affect musculoskeletal outcomes. In a preliminary study conducted on 34 registered nurses, results show that: (1) stressful working conditions affect musculoskeletal outcomes in multiple body regions, and (2) physical maladies such as lower back problems are not only associated with physical factors but also with a complex interaction of working conditions. Further research is warranted to obtain a better understanding of the complex interaction and the synergistic effects of the various nursing working conditions.

LUBA: an assessment technique for postural loading on the upper body based on joint motion discomfort and maximum holding time.

This paper presents a technique for postural loading on the upper body assessment (LUBA). The proposed method is based on the new experimental data for composite index of perceived discomfort (ratio values) for a set of joint motions, including the hand, arm, neck and back, and the corresponding maximum holding times in static postures. Twenty male subjects participated in the experiment designed to measure perceived joint discomforts. The free modulus technique of the magnitude estimation method was employed to obtain subjects' discomforts for varying joint motions. The developed postural classification scheme was based on the angular deviation levels from the neutral position for each joint motion. These were divided into groups with the same degree of discomforts based on the statistical analysis. Each group was assigned a numerical discomfort score relative to the perceived discomfort value of elbow flexion, which exhibited the lowest level among all joint motions investigated in this study, and, therefore, was set as a reference point. The criteria for evaluating stresses of working postures were proposed based on the four distinct action categories, in order to enable practitioners to apply appropriate corrective actions. The proposed scheme can be used for evaluating and redesigning static working postures in industry.

The boundaries for joint angles of isocomfort for sitting and standing males based on perceived comfort of static joint postures.

This study presents data for the joint angles of isocomfort (JAI) in sitting and standing males based on perceived comfort ratings for static joint postures maintained for 60 s. The JAI value was defined as a boundary indicating joint deviation (an angle) from neutral posture, within which the perceived comfort for different body joint postures is expected to be the same. An experiment for quantifying perceived comfort ratings was conducted using the free modulus method of magnitude estimation. Based on experimental results, regression equations were derived for each joint posture, to represent the relationships between different levels of joint deviation/joint posture and corresponding normalized comfort scores. The JAI values were developed for nine verbal categories of joint comfort. The JAIs with the marginal comfort levels, one of the nine verbal categories used, for most joint postures around the wrist, elbow, neck and ankle were similar to the maximum range of motion (ROM) values for these joints. However, the JAIs with the marginal comfort category for back and hip postures were much smaller than the maximum ROM values for these joints. There were no significant differences in JAI expressed in terms of the percentage of the corresponding maximum ROM values between sitting and standing postures. The relative 'marginal comfort index', defined as the percentage of JAIs for the marginal comfort relative to the corresponding maximum ROM values, for the hip was the smallest among all joints. This was followed, in an increasing order of the marginal comfort index, by the lower back and shoulder, while the marginal comfort index for the elbow joint was the largest. The results of this study suggest that static postures maintained for 60 s cause greater discomfort for the hip joint than for the other joints studied, and less discomfort for the elbow than for the other joints. The data about JAIs can be used as guidelines for enhancing postural comfort when designing a variety of human-machine tasks where static postures cannot be eliminated.

A heart rate evaluation approach to determine cost-effectiveness an ergonomics intervention.

This paper describes a hear-rate methodology to determine the cost-effectiveness of an ergonomics intervention to reduce workload and improve working conditions. This is a practical approach as opposed to the energy expenditure technique that is difficult to implement in natural settings. This was a laboratory study using a large excavator cabin with devices to simulate excavation operations. Mean heart rate was used to calculate the required rest time during a shift with or without air-conditioning. The criterion for evaluation was differences in required rest time during a shift under these 2 conditions. The simplicity and objectivity of this approach invites use to solve the problem of the economic evaluation of ergonomics interventions.

A classification system for characterization of physical and non-physical work factors.

A comprehensive evaluation of work-related performance factors is a prerequisite to developing integrated and long-term solutions to workplace performance improvement. This paper describes a work-factor classification system that categorizes the entire domain of workplace factors impacting performance. A questionnaire-based instrument was developed to implement this classification system in industry. Fifty jobs were evaluated in 4 different service and manufacturing companies using the proposed questionnaire-based instrument. The reliability coefficients obtained from the analyzed jobs were considered good (0.589 to 0.862). In general, the physical work factors resulted in higher reliability coefficients (0.847 to 0.862) than non-physical work factors (0.589 to 0.768).

Beyond psychophysics: the need for a cognitive engineering approach to setting limits in manual lifting tasks.

The classical psychophysical approach to setting limits in manual lifting tasks is discussed in view of experimental procedures used, non-linearity of human perception of load heaviness, and the related experimental outcomes. The results of two studies investigating the human assessment of load acceptability and safety are presented. The first study compares the classical concept of the maximum acceptable weight of lift (MAWL) to the alternative concept of the maximum safe weight of lift (MSWL). The second study utilizes the linguistic magnitude estimation (LME) method to mathematically model human assessment of four categories of lifted loads, including the concepts of acceptable, safe, not-too-heavy, and too-heavy loads for continuous lifting. It is shown that the concepts of the lifted load acceptability and safety are non-linear, and can be modelled with great accuracy using the third degree polynomials. This study also introduces and investigates the concept of the load indifference in assessment of load heaviness, and shows that lack of a cognitive benchmark introduces inconsistency in subjects' perception of load acceptability and safety compared to the concept of too-heavy load for continuous lifting. It is concluded that a new research approach to manual lifting tasks based on cognitive engineering is needed to improve the quality of research methodologies currently utilized in this field. This unexplored area of research should lead to greater understanding of human capacities and limitations in manual lifting tasks in the context of cultural and linguistic anthropology.

What is 'heavy'?

One of the work practices frequently taught to employees is to estimate the heaviness of load before it is actually handled. If it is 'heavy', then one should ask for help. However, limited information can be found in the ergonomics literature about what a person perceives as a 'heavy load'. This study was conducted on 20 male and 20 female workers in the package delivery industry to estimate the amounts of load that correspond to various levels of load heaviness (e.g. 'somewhat heavy'). Experienced employees were used for this purpose. The distribution of loads within each heaviness level was developed using fuzzy sets theory. The maximum load (i.e. 23 kg) defined by the US National Institute for Occupational Safety and Health represents a 'somewhat heavy' load based on the analysis of load distribution (corresponding to a 1.0 certainty factor). Also, the 40 kg considered in the 1981 NIOSH guidelines may be classified as a 'very heavy' load. A comparative analysis of the results of this study with norms established in prior research indicates that one should be more careful in the interpretation of statistical norms for human perception of load handling. A 'moderate' level of load heaviness (i.e. 14 kg) can be handled by 85% of the worker population.

A comprehensive lifting model: beyond the NIOSH lifting equation.

A comprehensive lifting model (CLM) for the evaluation and design of manual tasks was developed in two stages using 11 task, personal and environmental variables. In the first stage, the model was built using the psychophysical data. In the second stage, discounting factors of various variables were tested and adjusted using the physiological and biomechanical data. Two lifting indices are proposed to evaluate lifting tasks for a group of workers (relative lifting safety index or RLSI) and for an individual worker (personal lifting safety index or PLSI).

A neural network-based system for classification of industrial jobs with respect to risk of low back disorders due to workplace design.

Despite many years of research efforts, the occupational exposure limits of different risk factors for development of low back disorders (LBDs) have not yet been established. One of the main problems in setting such guidelines is the limited understanding of how different risk factors of LBDs interact in causing the injury, as the nature and mechanism of these disorders are relatively unknown phenomena. The task of an industrial ergonomist is complicated because the potential risk factors that may contribute to the onset of LBDs interact in a complex way, and require an analyst to apply elaborate data measurement and collection techniques for a realistic job analysis. This makes it difficult to discriminate well between the jobs that place workers at high or low risk of LBDs. The main objective of this study was to develop an artificial neural network-based diagnostic system which can classify industrial jobs according to the potential risk for low back disorders due to workplace design. Such a system could be useful in hazard analysis and injury prevention due to manual handling of loads in industrial environments. The results show that the developed diagnostic system can successfully classify jobs into the low and high risk categories of LBDs based on lifting task characteristics.

Comprehensive manual handling limits for lowering, pushing, pulling and carrying activities.

The objective of this study was to develop a set of mathematical models for manual lowering, pushing, pulling and carrying activities that would result in establishing load capacity limits to protect the lower back against occupational low-back disorders. In order to establish safe guidelines, a three-stage process was used. First, psychophysical data was used to generate the models' discounting factors and recommended load capacities. Second, biomechanical analysis was used to refine the recommended load capacities. Third, physiological criteria were used to validate the models' discounting factors. Both task and personal factors were considered in the models' development. When compared to the results from prior psychophysical research for these activities, the developed load capacity values are lower than previously established limits. The results of this study allowed the authors to validate the hypothesis proposed and tested by Karwowski (1983) that states that the combination of physiological and biomechanical stresses should lead to the overall measure of task acceptability or the psychophysical stress. This study also found that some of the discounting factors for the task frequency parameters recommended in the prior psychophysical research should not be used as several of the high frequency factors violated physiological limits.

Ergonomic investigation of letter-carrier satchels: part I. Field study.

A field study was conducted to compare four satchels designed for the purposes of manually carrying and delivering mail. The satchels differed primarily in the presence/absence of a waist belt, the number and design of the shoulder strap(s) and the number of pouches. The evaluation consisted of questionnaires and interviews of slightly more than 300 letter carriers employed by the United States Postal Service. The questionnaires focused on 10 main areas of interest; ease of adjustability and handling, comfort, suitability and durability of materials, anthropometric applications, impact on other activities, ease of motion in retrieving mail, ease of motion in carrying the satchel, versatility of use in diverse climates, protection of mail from damage due to rain and snow, and defense against dog attacks. The primary conclusion was that the satchel with two shoulder straps and two pouches, which results in more symmetric loading than the other satchels, is the most desirable of the satchels tested. However, there are problems with the satchel that need to be addressed, such as concerns about the use of the satchel for defense from dog attacks.

A cross-validation of the NIOSH limits for manual lifting.

The psychophysical, biomechanical, and physiological criteria used in establishing the NIOSH limits for manual lifting were cross-validated against the data published by different researchers in the subject literature. Assessment of the 1991 NIOSH lifting equation indicated that: (1) NIOSH-based limits are significantly different from the psychophysical limits in the (i) low and high frequencies of lift, and (ii) small and large horizontal distances; (2) NIOSH limits are highly correlated with the data of Snook and Ciriello (1991) in the low frequency range, with the Recommended Weight Limit (RWL) protecting about 85% of the female population and 95% of the male population; (3) the 3.4kN limit for compression on the lumbosacral joint cannot protect the majority of the worker population on the basis of damage load concept; and (4) energy expenditure limits used in development of the RWL index can be sustained by 57 to 99% of worker population when compared to the physiological limits based on previous fatigue studies. Results of the cross-validation for psychophysical criterion confirmed the validity of assumptions made in the 1991 NIOSH revised lifting equation. However, the results of cross-validation for the biomechanical and physiological criteria were not in total agreement with the 1991 NIOSH model.

Postural stress analysis in industry.

Both observational and instrumentation-based techniques have been used to conduct postural stress analysis in industry. As observational methods are more widespread than instrumentation-based techniques and can be used as a practical tool in the workplace, this study reviews and assesses the scientific literature on observational techniques. Techniques are classified into macropostural, micropostural and postural-work activity. The basis for each classification is outlined and evaluated. Postural recording is performed either continuously or intermittently. Intermittent postural recording procedures lack the criteria for determining the optimum number of observations for low and high repetitive jobs. Research is warranted to examine the sources and magnitudes of errors associated with postural classification. Such information is required to train job analysts in the ergonomics of working postures.

The effects of computer interface design on human postural dynamics.

The main objective of this study was to examine the effects of human-computer interface design on postural dynamics, i.e., changes in working postures and postural discomfort exhibited by operators of the computer-based remote bar coding (RBC) system. In addition, the effects of different work/rest schedules on postural dynamics were evaluated. Twelve subjects participated in the laboratory experiment, which consisted of twelve scenarios utilizing two cognitive task requirement factors, i.e., (1) information presentation mode, defined through the letter image preview on the computer screen (none or one preview image); and (2) the information processing mode, defined through the specific keying method (key all characters or key 5 digits only). The third experimental factor was the work/rest schedule (50 min work/10 min break, 2 h of work/15 min break, or flexible schedule). The results showed that requirements of human-computer interface design significantly affected the operators' postural dynamics. It was concluded that not only the physical, organizational, or psychosocial work environment characteristics, but also the cognitive task characteristics are important for assessment of postural effects in the VDT work. The relationship between interface design, mental workload and postural dynamics should be carefully considered in future studies aimed at optimizing the human-computer data entry tasks.

Analysis of working postures in hammering tasks on building construction sites using the computerized OWAS method.

The main objectives of this study were to identify the most problematic postures in hammering tasks performed at building construction sites through application of the computerized OWAS method, and to develop recommendations for improvement of working method and workplaces. Eighteen construction workers, with mean age of 41.6, from three construction companies participated in the field study. The hammering tasks observed during the two-month period included roof boarding, concrete form preparation, clamping support braces, assembling roof frames, roof joisting, shelter form preparation, and fixing fork clamps. Three different types of hammer, including a small Fiskar's hammer, a Fiskar's construction hammer, and a Rocket hammer, were used by the workers. Of all the observations, poor working postures were observed most frequently in roof joisting (12.4% of all observations within the task), followed by concrete form preparation (8.6%), and construction of frames for the roof (7.5%). Overall, out of 593 different postures analysed, a total of 7.8% of postures adopted by the workers during various hammering tasks were classified into OWAS categories III or IV, indicating that these postures should be corrected either soon or immediately. The computerized OWAS method for postural data analysis proved to be a very useful way to reduce postural load of dynamic hammering tasks, and allowed for efficient application of the original OWAS method.

The effects of neutral posture deviations on perceived joint discomfort ratings in sitting and standing postures.

There is a pressing need to rank body deviations from neutral postures which occur due to variety of body movements around different joints. Such knowledge is needed to better understand potentially adverse effects of poor working postures on the industrial population. The main objective of this study was to examine the effects of postural deviations on perceived joint discomfort ratings assessed under similar working conditions. Twelve males and seven females participated in the laboratory study. The results revealed several distinct classes of joint deviations from neutral postures, which need to be assigned different weights of postural stress. A preliminary ranking system for assessment of stressfulness of human body deviations about different joints was proposed.