Factors related to working posture and its assessment among keyboard operators

Cumulative Trauma Disorders: Behavioral Injury Prevention at Work

The purpose of this study was to decrease the risk of carpal tunnel syndrome (CTS) during keyboard entry tasks through a combination of training, self-monitoring, feedback, goal-setting, and reinforcement. Technologies from biomechanics, ergonomics, and behavioral psychology were combined effectively to construct a powerful training package. As the subjects entered text on a keyboard, their postures and hand-wrist positions were recorded. After baseline data were gathered, subjects received training and self-monitored either posture or hand-wrist position. Feedback, goal-setting, and reinforcement were given later on both behaviors in a staggered fashion. The results indicate dramatic increases in the percentages of correctly performed postures and neutral hand-wrist positions, for all subjects. The training components used are reviewed in detail and the impact of these results is discussed.

Influence of laptop computer design and working position on physical exposure variables

OBJECTIVE

To evaluate the impact of two laptop designs (with or without palm rest) and two work situations (on desk or lap) on neck and upper limb posture, muscle activity and productivity.

DESIGN AND METHODS

Eight healthy subjects performed a standardized typing task of 15 min duration. During the last 5 min of each test, the neck, upper arm and trunk postures were captured by a three-dimensional video system, wrist motion was measured by a biaxial electrogoniometer and muscle activity of four neck and upper limb muscles was recorded.

RESULTS

Only minor differences in postures, wrist positions and productivity were observed when comparing the two laptop designs in the same situation. Larger differences were found when comparing the two situations (desk or lap). In the desk situation, the subjects bent their heads forward less, had less backward trunk inclination and wrist extension, but more elevation of the upper arm. Higher electromyographic (EMG) levels in the trapezius and deltoid muscles and lower EMG levels in the wrist extensors were also found in the desk situation.

CONCLUSIONS

Our findings do not favor one particular laptop design because only small differences in physical exposure were found. However, the workstation set up influenced the physical exposure variables, and was pinpointed as the main determinant to be considered when doing laptop work even-though no ideal situation was found. Greater physical (muscular and articular) constraints seem to be imposed to the shoulder region in the desk situation whereas the head-neck and wrist segments appear to be more stressed in the lap situation.

RELEVANCE

Laptop computers are often used although the physical exposure in laptop work and the impact of different laptop designs have not been systematically assessed. A better understanding of these factors may help formulate some recommendations for laptop users.

Effects of armrests on workload with ten-key operation

The constrained posture used for work using a visual display terminal (VDT), such as data entry, can produce static muscular fatigue. Based on the application of ergonomic principles, we conducted an experiment using a prototype VDT chair designed with an armrest adjustable to heights from 22 to 28 cm. The experiment--conducted to assess the static muscular strain based on varying heights of the armrest and distance from the keyboard--was performed with male subjects. The subjects were asked to input five-figure numbers using the 10 keys arranged on the right side. Using a surface electromyogram, we measured the strain imposed on the arm and the shoulder. This was followed up with a performance, weight-loading onto the armrests and a questionnaire. Results show that use of armrests is effective for the alleviation of muscles in one-handed keyboard operation where operators work on a desk whose height is unadjustable according to their body height or where operators are unable to rest their wrist on the desk. A chair with height-adjustable armrests is considered desirable when used by several people.

Microcomputer video image processing technology in working posture analysis: application to seated postures of keyboard operators

A new two-dimensional video-based technique for the recording and analysis of working posture has been developed and applied to seated work. After initial set-up of the portable equipment in the workplace, and attachment of small adhesive retroreflective joint markers on the subject, an operator is not required for the remainder of the recording session. Analysis of the video recording is conducted in the laboratory using custom-written software and a commercially available image-processing package running on an IBM AT-compatible computer. After interactive set-up of a reference frame, the system is able to analyse the full video tape automatically, extracting video frames for analysis at approximately 30-s intervals. Poor image quality may occasionally necessitate interactive analysis. The system is capable of determining postural angles to an accuracy of 1-2 degrees , and thus represents a substantial improvement on other postural analysis systems which are able to be used readily in the workplace.