A. Genaidy

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.

Spinal compression tolerance limits for the design of manual material handling operations in the workplace

Spinal compression tolerance limits (SCTL) have been widely used by ergonomists in setting work tolerance limits for manual materials handling (MMH) operations. Thus, the effect of personal and experimental factors on spinal compression tolerance limits (SCTL) is reviewed with the aid of regression and correlation analyses performed on data compiled from the published literature. Tables of SCTL from various sources utilizing large number of specimens and personal factors are presented so that they can be accessed by ergonomists easily. Integrated biomechanical guidelines based on SCTL are provided for the design of MMH operations in the workplace. It is suggested that, in order to reduce the probability of MMH injuries, biomechanical tolerance limits should be set at the damage load instead of the load at fracture. The damage load is the weight which causes the first gross signs of damage such as tissue fluid and blood. An algorithm is described to demonstrate the use of a biomechanics approach to the design of MMH operations.

An epidemiological appraisal instrument – a tool for evaluation of epidemiological studies

In recent years, ergonomics practices have increasingly relied upon the knowledge derived from epidemiological studies. In this regard, there is limited research devoted to the exclusive evaluation of the methodological qualities of ergonomics epidemiological studies. The aim of this study was to develop and test a general purpose ‘epidemiological appraisal instrument’ (EAI) for evaluating the methodological quality of existing or new ergonomic epidemiological studies using a critical appraisal system rooted in epidemiological principles. A pilot EAI version was developed and tested by a team of epidemiologists/physicians/biostatisticians, with the team leader being both epidemiologist and ergonomist. The pilot version was further tested with regard to other raters with/without a background in epidemiology, biostatistics and ergonomics. A revised version was evaluated for criterion validity and reliability. An assessor with a basic background in epidemiology and biostatistics would be able to correctly respond on four out of five questions, provided that subject matter expertise is obtained on specific items. This may improve with the articles quality. Training may have an effect upon assessors with virtually no background in epidemiology/biostatistics, but with a background in ergonomics. In this latter case, the inter-rater degree of agreement is largely above 90% and assessors can resolve their differences in a subsequent round. The EAI proved to be a valid and reliable appraisal instrument that may be used in various applications, such as systematic reviews and meta-analyses.

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.

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.

Active microbreak effects on musculoskeletal comfort ratings in meatpacking plants

This study was conducted to examine whether a system of active microbreaks can reduce the discomfort perceived by employees in a meatpacking plant. Moreover, the relationship between the discomfort perceived on the job and musculoskeletal capability was investigated. Twenty-eight men employed in a local meatpacking plant participated in a study conducted over a period of four weeks. Results indicated that active microbreaks significantly reduced the level of discomfort perceived by employees during the course of the working day. The subjective ratings of perceived discomfort correlated significantly with anthropometric, strength and background information (R2 = 0.66). The physical characteristics of Caucasian employees were higher than those of their Hispanic counterparts. Moreover, the physical characteristics of meatpacking employees were significantly lower than those reported in the literature for employees engaged in manual handling tasks.

Cumulative spinal loading exposure methods for manual material handling tasks. Part 1: is cumulative spinal loading associated with lower back disorders?

Objective: To critically appraise the observational studies linking cumulative spinal loading and lower back disorders (LBD) among workers engaged in manual material handling and to explore the association between cumulative spinal loading and LBD through a meta-analysis of papers reported in the published literature. Background: Although studies have indicated a definitive relationship between long-term exposure to manual materials handling and LBD, little is generally known about the validity of the cumulative exposure assessment methods used for predicting the risk of LBD. Methods: A comprehensive electronic search on the subject was conducted. The articles found from the search were critically appraised from an epidemiological standpoint. The strengths and weaknesses of the studies were documented. A quantitative assessment was performed for the meta-analysis estimate using the fixed-effect and random-effects (Dersimonian and Laird method) models. The assessments were conducted in two ways: with a standard approach that does not consider study quality and with a modified method that allows weighting scores to be calculated based on the rating of the quality of each study. Results: The electronic search resulted in identification of four epidemiological papers, three of which provided sufficient information for an assessment of epidemiological quality and two of which provided sufficient data to conduct a meta-analysis. The results showed that the methodological quality of the studies ranged from poor to marginal. Without considering the overall study quality for the exposure data, (1) there were substantial differences between the three studies that were rated for epidemiological quality as evidenced by the significant heterogeneity testing at the 10% level and (2) the difference in the mean exposure values between the study and control groups (i.e. summary mean difference) was significant at the 5% level for both the fixed-effect and random-effects models. After accounting for overall study quality, the heterogeneity was reduced but still significant at the 10% level and the summary mean difference was greater than that without the quality score. The meta-odds ratio for LBD outcomes was 1.66 (95% confidence interval using quality scores = 1.46–1.89). Conclusions: The preliminary findings suggest that there likely is an association between cumulative spinal loading and LBD. Further, there are considerable differences among the studies in terms of exposure assessment techniques. A subsequent paper (Part II of this research) provides an in-depth analysis of cumulative spinal loading exposure methods and discusses critical issues related to their reliability and validity for estimating force distribution and practicality for field measurement.

Effects of a job-simulated exercise programme on employees performing manual handling operations

This study investigated the effects of physical training on employees performing manual handling operations in three manufacturing plants. Employees from two plants were trained using progressive resistance exercise (PRE) while employees in the third plant were trained using PRE and trunk flexibility exercises (TFE). The results were: (1) a combined TFE and PRE programme significantly improved muscular endurance (124%), dynamic (86%) and static (back: 59%; arm: 25%; shoulder: 23%) muscular strength, and trunk flexibility (low back flexibility: 11%; total trunk rotation: 48%); (2) a dynamic PRE programme did not improve static strength (arm: 3%; shoulder: 8%; back: 14%; composite: 7%) as much as dynamic strength (71%); (3) endurance time at a fixed workload increased without changing job demand perception, but daily operations were performed more easily.

Ranking of static non-neutral postures around the joints of the upper extremity and the spine

Constrained body postures are usually cited as the major cause of musculoskeletal static loading. Thus, the main goal of the present study was to develop a ranking system for the stressfulness of the non-neutral static postures around the wrist, elbow, shoulder, neck and lower back. This was based on the ratings of perceived discomfort. Sixteen men participated in the study. The results indicated that static postural stresses yielded varying effects on the discomforting rating levels. On the basis of these preliminary findings, a ranking system was developed for the stressfulness of non-neutral postures around the joints of the upper extremity and the spine.

Physical training: a tool for increasing work tolerance limits of employees engaged in manual handling tasks

The lack of physical fitness is a contributing factor to the etiology of musculoskeletal disorders resulting from the manual handling of material in industry. Thus the major objectives of this paper were (1) to discuss the role of physical fitness in the control of occupational injuries; (2) to review techniques available in the exercise physiology literature for increasing human physical capacity in industry; and (3) to review and evaluate studies on the effects of physical training on individuals engaged in manual handling tasks.