A survey of high school students with ubiquitous access to tablet PCs.

This paper presents findings of a study of high school students participating in a tablet PC (TPC) programme. Primary areas of interest were students' experiences with and attitudes about the TPCs, physical discomfort associated with use of TPCs and temporal and task-driven patterns of TPC use. Data were collected via questionnaire and computer use-monitoring software. Results showed students' attitudes were generally quite positive towards the TPCs, although they did not tend to think TPCs had improved their grades, few disagreed that TPCs were a distraction in class, and visual and musculoskeletal discomfort was prevalent. Understanding how to use the TPC and recognizing its organizational capacity were associated with several positive attitudes towards the TPC, including making school more enjoyable. Children's exposure to computers will only increase, so study of the many dimensions of their impact is critical in order to understand what is effective, constructive and healthful for children.

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.

A field evaluation of monitor placement effects in VDT users.

Appropriate visual display terminal (VDT) location is a subject of ongoing debate. Generally, visual strain is associated with higher placement, and musculoskeletal strain is associated with lower placement. Seeking resolution of the debate, this paper provides a comparison of results from previous lab-based monitor placement studies to recommendations and outcomes from viewing preference and neutral posture studies. The paper then presents results from a field study that addressed two outstanding issues: Does monitor placement in a workplace elicit postures and discomfort responses similar to those seen in laboratory settings? Results showed placements in the workplace elicited postures similar to those in lab studies. Additionally, preferred VDT location generally corresponded to the location in which less neck discomfort was reported, though that trend requires further investigation. Overall, there seems to be consistent evidence to support mid-level or somewhat higher placement, as a rule-of-thumb, considering preferred gaze angle and musculoskeletal concerns. However, optimal placement may be lower for some individuals or tasks.

An investigation of the effects of touchpad location within a notebook computer.

This study evaluated effects of the location of a notebook computer's integrated touchpad, complimenting previous work in the area of desktop mouse location effects. Most often integrated touchpads are located in the computer's wrist rest, and centered on the keyboard. This study characterized effects of this bottom center location and four alternatives (top center, top right, right side, and bottom right) upon upper extremity posture, discomfort, preference, and performance. Touchpad location was found to significantly impact each of those measures. The top center location was particularly poor, in that it elicited more ulnar deviation, more shoulder flexion, more discomfort, and perceptions of performance impedance. In general, the bottom center, bottom right, and right side locations fared better, though subjects' wrists were more extended in the bottom locations. Suggestions for notebook computer design are provided.

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.

A method for developing biomechanical profiles of hand-intensive tasks.

OBJECTIVE: To develop a methodology for generic, comprehensive biomechanical profiling of hand-intensive tasks. DESIGN: Based on a multifactorial model of work-related musculoskeletal disorder development, a method was developed for continuous, simultaneous measurement of relevant variables (wrist and finger joint position, force, muscle activity, and carpal tunnel pressure). Joint dynamics and tendon travel were derived. BACKGROUND: Few generic dose-response relationships have been identified for work-related musculoskeletal disorders. This may improve if methodologies are developed that quantify multiple factors along several dimensions (means, cumulative exposure, etc.). This requires continuous, simultaneous measurements, and facilitates examination of interactions. METHODS: Five touch-typists were instrumented to quantify their biomechanical profiles using the methodology, and to evaluate the sensitivity of the method to various work organization/design conditions. RESULTS: The method captured individual and group responses to design conditions and revealed interactions and trade-offs between response variables. Carpal tunnel pressure was found to be sensitive to radial-ulnar wrist posture. CONCLUSIONS: Multi-variable biomechanical profiling can provide insight into effects of work design on workers; however, to achieve statistical significance large numbers of subjects are needed.

A quantitative description of typing biomechanics.

One approach to combating work- related upper extremity musculoskeletal disorders (UEMSDs) is to improve understanding of MSD risk factors through quantitative biomechanical characterization of manual tasks, including joint postures, joint dynamics, and force exertion. This paper describes a methodology employed to quantitatively assess professional typing in a workplace setting, and the results of that assessment. Results are compared between different kinds of typing tasks, and between typing and hand- intensive industrial tasks, based on nontask- specific biomechanical terms. Quantitative, biomechanical characterizations of manual tasks will lead to identification of appropriate ranges for joint kinematics and force exertion, which will, in turn, facilitate proper design of manual tasks. Additionally, the methodology could be used to assess manual performance of skilled tasks for proper (healthy) technique, or be used to evaluate progress through a course of rehabilitation (when do an impaired worker's motions begin to resemble motions of healthy workers?).

Occupational risk factors associated with soft tissue disorders of the shoulder: a review of recent investigations in the literature.

Cumulative trauma illness currently accounts for over half of all occupational illness in the United States. From 1987 to 1989 there was a 100% increase in the reported number of cases of cumulative trauma illness (Bureau of Labor Statistics 1990). Shoulder region pain ranks second only to low back and neck pain in clinical frequency, and the occurrence of occupational shoulder illness is on the rise. This paper summarizes findings of a subset of recent epidemiologic, laboratory, and field studies conducted in order to identify occupational risk factors for cumulative trauma disorders (CTDs) of the shoulder region. These studies have identified the following risk factors as being associated with particular shoulder pain syndromes: awkward or static postures, heavy work, direct load bearing, repetitive arm movements, working with hands above shoulder height, and lack of rest. The paper begins with a discussion of several shoulder disorders, includes problems in studying cumulative trauma, presents results of recent studies, and concludes with suggested ergonomic controls that could help to reduce the incidence of shoulder disorders, by eliminating or reducing exposure to the associated risk factors.

Temporal patterns of trunk muscle activity throughout a dynamic, asymmetric lifting motion.

This study examined the effects of trunk speed and exertion level on temporal aspects of trunk muscle activity patterns during dynamic, asymmetric lifting. Electromyographic (EMG) data from eight trunk muscles were collected along with trunk torque output, position, and velocity data during several repetitions of four speed/loading combination conditions. During analysis, each muscle's EMG record was reduced to three key events: a start, a peak, and an end point. For each subject, temporally ordered event lists were constructed for each test condition. Networks of events that consistently occurred regardless of loading or speed levels were constructed for each subject. Two event pairs occurred consistently for all subjects under all conditions, whereas some pairs occurred in association with specific speed or resistance levels. Temporal information related to muscle activity could be used in biomechanical models in order to predict changes in spinal loading during the course of workplace tasks.

A three-dimensional motion model of loads on the lumbar spine: I. Model structure.

Traditionally most biomechanical models that are used to estimate the loading experienced by the spine during work focus on static, two-dimensional representations of the work. However, most work tasks impose loads on the lumbar spine under dynamic, three-dimensional conditions. The objective of this study was to describe the structure and logic of a model that is capable of producing estimates of spine loading under three-dimensional motion conditions. This model is intended for use primarily under laboratory conditions. The model was designed initially for workplace simulation in which the trunk is moving under symmetric and asymmetric constant velocity lifting conditions. Future embellishments may enable the model to be used under free dynamic conditions. The model predicts lumbar spine compression, shear, and torsional forces as well as trunk torque production continuously throughout the exertion. This information may be compared with spine tolerance limits so that the risk of causing a vertebral end-plate microfracture by workplace requirements could be determined.

A three-dimensional motion model of loads on the lumbar spine: II. Model validation.

A three-dimensional motion model has been developed that estimates loads on the lumbar spine under laboratory conditions that simulate manual materials handling conditions. Eleven subjects experienced spinal loading during an experiment in which conditions of trunk velocity, trunk torque output, and trunk asymmetric posture were varied in a series of isokinetic velocity trunk extensions. The electromyographic activity of 10 trunk muscles, subject anthropometry, and trunk kinetics were used as input to a biomechanical simulation model described in Part I of this study. The model calculated estimates of compression, shear, and torsion loading in the lumbar spine, as well as the torque production of the trunk, continuously throughout the exertion. Trunk torque estimates derived from this model were compared with measured trunk torque. The effects of trunk motion, posture, and torque level on spine loading as estimated by the model are discussed. It was concluded that this approach provides a straightforward means of assessing loading of the spine attributable to laboratory simulations of workplace conditions.

The effects of preview and task symmetry on trunk muscle response to sudden loading.

The effect of warning time (preview) and task symmetry on the trunk muscular response to sudden loading conditions was investigated. Eleven subjects were asked to catch falling weights with four levels of preview (0, 100, 200, and 400 ms) in saggitally symmetric posture and asymmetric posture. For each of the eight muscles sampled with surface electrodes, the integrated electromyographic (EMG) signal was interpreted in terms of its peak value, mean value, onset rate, and lead/lag time with reference to the weight drop. Results show linear relationships between preview times and peak EMG, preview times and mean EMG, and preview times and lead times. The results show significant change when going from symmetric to asymmetric conditions across most dependent measures. Analysis of peak changes in compression were performed across all conditions but yielded unexpected results.