Sharon Joines

Use of surface electromyography to estimate neck muscle activity

This paper reviews the literature concerning the use of surface electromyography (sEMG) for the study of the neck musculature in response to work and workplace design during light work and semi-static tasks. The paper also draws upon basic research and biomechanical modeling in order to provide methodological recommendations for the use of surface electromyography in this region of the body and to identify areas which require further investigation. The paper includes review and discussion of electrode site location, methods of normalization, data reliability, and factors that can affect sEMG signals from this region, including noise, physiologic artifact, stress, visual deficiencies, and pain. General guidance for maximum exertions with the neck musculature, for sEMG normalization or other purposes, is also included.

Effects of computer monitor viewing angle and related factors on strain, performance, and preference outcomes.

A model of visual and musculoskeletal strain associated with computer monitor placement was developed. The main premise of which is that monitor placement decisions must take into consideration development of both visual and musculoskeletal strains. Certain factors in the model that were thought to affect one or both types of strain, or that were considered important to rule out for effect, were tested in a lab setting. These factors were viewing angle (eye level, midlevel, low level), monitor size (14 in., 19 in.), keyboard familiarity (touch typist, nontouch typist), and task (reading, mousing, typing). Outcomes included indicators of visual and musculoskeletal strain, preference, and performance. Muscle activity was generally greater for the low viewing angle, for the standard monitor (14 in.), and for non-touch typists. Participants preferred the midlevel placement. Task performance was slightly diminished with eye-level placement. Results are interpreted in relation to the model and to several hypotheses that were formed to focus the inquiry. Actual or potential applications of this research include monitor placement decisions in the design or modification of computer workstations

The Effect of Personality Type on Muscle Coactivation during Elbow Flexion

A great deal of interest has been generated recently regarding the influence that psychosocial factors may have on the reporting of and disability associated with work-related musculoskeletal disorders. The current study considers the potential influence of one psychosocial factor - personality type - on basic neuromuscular control strategies and biomechanical loading. The study investigated the hypothesis that Type A people exhibit increased muscular antagonism relative to their Type B counterparts. Volunteers participated in an EMG-based biomechanical study to investigate the co-activation patterns of the major muscles that span the elbow joint during elbow flexion exertions. Results showed that, averaging across all conditions, the antagonist muscle activity was significantly higher for Type A individuals than for their Type B counterparts (10% of maximum for Type A, 5.5% of maximum for Type B). Although the study was somewhat limited in its size and scope, the results indicate that certain psychosocial factors may be more than a filter in postinjury response and may directly influence biomechanical loading. A potential application of this research is an increased awareness that certain individuals may be at greater risk of developing work-related musculoskeletal disorders.

Technical Note The use of mirrors during an assembly task: a study of ergonomics and productivity

Industrial assembly tasks often require awkward, sustained neck and/or shoulder postures that can lead to increased musculoskeletal discomfort and reduced productivity. The aim of this study was to investigate the effects of mirror and periscope visual aids as ergonomic interventions designed to eliminate awkward postures of the cervicobrachial region during assembly tasks. Participants simulated a simple assembly task by using a cordless screwdriver to drive screws into a pre-tapped aluminium block. Trials of 15 min were run for each of four distinct assembly workstation configurations: industry standard (in-line screwdriver, work at elbow height, no visual aid); pistol grip (pistol grip screwdriver, work at shoulder height, no visual aid); mirror (in-line screwdriver, work at elbow height, single mirror visual aid); and periscope (in-line screwdriver, work at elbow height, two-mirror visual aid system). Muscular activity, discomfort, body posture, productivity and operator subjective assessment were recorded to determine the effects of the visual aid interventions. The results show that when comparing the interventions to the industry standard condition, there was a 45% reduction in average cervical erector spinae activity, a 90% reduction in average neck flexion angle and a 72% reduction in neck discomfort with the interventions. When comparing these interventions to the pistol grip condition there was an 80% reduction in activity of the dominant side deltoid, a 92% reduction in shoulder flexion angle and an 81% decrease in shoulder discomfort with the interventions. Productivity was greatest in the industry standard configuration followed by the pistol grip (9% lower), the periscope (13% lower) and the mirror (23% lower) configurations. A follow-up study that compared the productivity of the periscope configuration with that of the industry standard configuration showed that within a 4-h work period this productivity differential decreased by over 33%.

Effects of VDT Viewing Angle on User Biomechanics, Comfort, and Preference

A study was conducted to characterize effects of computer monitor viewing angle on operators. The study was conducted in two phases: controlled laboratory experiment followed by field verification. Lab results are discussed here. Three viewing angles were studied: 0, -17.5, and -35 deg to center of screen. Effects of monitor size and keyboard familiarity were also investigated. Muscle activity, body posture, visual acuity, performance, discomfort, and preference data were collected. In general, muscle activity was greater at -35 deg than at 0 deg; and greater for a smaller monitor than a larger one. Only head postures were affected by viewing angle. The eye-ear line was angled higher for touch typists. Mousing performance slowed slightly at 0 deg. Subjects preferred the -17.5 deg angle most and the -35 deg angle least. Results suggest there could be benefits to using a larger monitor with viewing angle between -17.5 to 0 deg for screen-intensive work.

Analysis of Alternative Keyboards Using Learning Curves

Objective : To quantify learning percentages for alternative keyboards (chord, contoured split, Dvorak, and split fixed angle) and understand how physical, cognitive, and perceptual demand affect learning. Background: Alternative keyboards have been shown to offer ergonomic benefits over the conventional, single-plane QWERTY keyboard design, but productivity-related challenges may hinder their widespread acceptance. Method: Sixteen participants repeatedly typed a standard text passage using each alternative keyboard. Completion times were collected and subsequent learning percentages were calculated. Participants were asked to subjectively rate the physical, cognitive, and perceptual demands of each keyboard, and these values were then related to the calculated learning percentages. Results: Learning percentage calculations revealed the percentage for the split fixed-angle keyboard (90.4%) to be significantly different ( p < .05) from the learning percentages for the other three keyboards (chord, 77.3%; contour split, 76.9%; Dvorak, 79.1%). The average task completion time for the conventional QWERTY keyboard was 40 s, and the average times for the fifth trial on the chord, contoured split, Dvorak, and split fixed-angle keyboards were 346, 69, 181, and 42 s, respectively. Conclusions: Productivity decrements can be quickly regained for the split fixed-angle and contour split keyboard but will take considerably longer for Dvorak and chord keyboards. The split fixed-angle keyboard involved physical learning, whereas the others involved some combination of physical and cognitive learning, a result supported by the subjective responses. Application: Understanding the changes in task performance time that come with learning can provide additional information for a cost-benefit analysis when considering the implementation of ergonomic interventions.

Collaborating with cardiac sonographers to develop work-related musculoskeletal disorder interventions

Abstract For more than two decades, surveys of imaging technologists, including cardiac sonographers, diagnostic medical sonographers and vascular technologists, have consistently reported high prevalence of work-related musculoskeletal discomfort (WRMSD). Yet, intervention research involving sonographers is limited. In this study, we used a participatory approach to identifying needs and opportunities for developing interventions to reduce sonographers’ exposures to WRMSD risk factors. In this paper, we present some of those needs. We include descriptions of two interventions, targeted for cardiac sonographers, that were developed, through an iterative process, into functional prototypes that were evaluated in pilot tests by practicing sonographers. One of these interventions is now in daily use. We would like other engineers and ergonomists to recognise this area of opportunity to apply their knowledge of biomechanics and design in order to begin to address the high prevalence of WRMSDs in sonographers, by working with sonographers to develop useful and usable interventions. Practitioner Summary: This paper discusses needs, opportunities and methods for working with sonographers in order to develop interventions to reduce their exposure to risk factors for work-related musculoskeletal discomfort. Results from field tests of two novel interventions targeting cardiac sonographers are also presented.

Developing a Framework of Guiding Interface Design for Older Adults

Many design recommendations have been provided for designing user interfaces for older adults. Existing design recommendations over the last twenty years were reviewed. Most of the design recommendations focused on older adults’ age-related changes in physical, sensory, and cognitive abilities, from an aging perspective or aging-oriented approach. Few design recommendations have been generated focusing on older adults’ prior knowledge and experience from a generation perspective or generation-oriented approach. The comparison of the two approaches is provided and the significance of taking into account both approaches during the design process is discussed. A framework guiding interface design for older adults systematically combining both the aging-oriented approach and the generation-oriented approach is proposed. This paper describes the framework which aims to assist developing user interfaces for maximum usability and accessibility for older adults.

Participatory Ergonomics Applied to Sonographers’ Work

A participatory ergonomics process has been initiated, the aim of which is to work with cardiac, vascular, and diagnostic medical sonographers to develop interventions that will improve their work conditions and reduce their occupational exposure to risk factors for musculoskeletal discomfort. Numerous surveys have been conducted that have identified sonographers as experiencing high rates of work-related musculoskeletal disorders. However, intervention research involving them is limited. The presentation describes the research methodology and results from the first stages of the intervention process.

Comparison of self-assessment and partnered-assessment as cost-effective alternative methods for office workstation evaluation

Abstract A study was conducted in order to determine if anthropometric and office workstation measurements could be accurately collected individually by the employees who worked as those stations, or alternatively by two-person teams consisting of the employee and a co-worker. An iterative process was used to develop a method that would: (1) require a minimum number of measurements to be made by the employees, (2) produce an acceptable level of accuracy, and (3) provide useful information for analyzing employee–workstation fit. Results of the study showed acceptable accuracy when using a combined assisted and unassisted data collection approach. Relevance to industry Office workstation assessment can be a challenge for companies with large numbers of employees working in office settings, particularly if those settings are distributed across a country or the globe. Developing a formulaic method for accurately measuring those workstations by someone other than the companys expert (ergonomist or other) has several benefits, including: (1) ability to measure more workstations in the same time period; (2) freeing the expert to perform tasks and analyses that require his/her expertise; and (3) inducing active involvement of employees in the companys health and safety (or ergonomics) efforts.