Computer mouse use and cumulative trauma disorders of the upper extremities

The computer mouse is now present in virtually every office environment because of the recent adoption of the graphical user interface. However, Karlqvist et al. (1994) pointed out that there still remains a paucity of work on the musculoskeletal problems associated specifically with computer mouse use. Likewise, there have been no published data on the magnitude of upper extremity musculoskeletal disorders associated with computer mouse use. In order to ascertain this magnitude, claims data from the Liberty Mutual Group were reviewed for the years 1986 to 1993, inclusive. Count, total cost and average cost per claim for all claims associated with computer use and computer mouse use were determined for the years in question. It was concluded that although there are few claims related to computer mouse use, it appears to be a growing problem, and therefore, perhaps, deserves more research and intervention attention. However, the present magnitude is less than for other musculoskeletal disorders.     

Power hand tool vibration effects on grip exertions

Operation of vibrating power hand tools can result in excessive grip force, which may increase the risk of cumulative trauma disorders in the upper extremities. An experiment was performed to study grip force exerted by 14 subjects operating a simulated hand tool vibrating at 9.8 m/s² and 49 m/s² acceleration magnitudes, at 40 Hz and 160 Hz frequencies, with vibration delivered in three orthogonal directions, and with 1.5kg and 3.0kg load weights. Average grip force increased from 25.3 N without vibration to 32.1 N (27%) for vibration at 40 Hz, and to 27.1N (7%) for vibration at 160 Hz. Average grip force also increased from 27.4 N at 9.8 m/s² acceleration to 31.8 N (16%) at 49m/s². Significant interactions between acceleration x frequency, and frequency x direction were also found. The largest average grip force increase was from 25.3N without vibration to 35.8N (42%) for 40 Hz and 49 m/s² vibration. The magnitude of this increase was of the same order as for a two-fold increase in load weight, where average grip force increased from 22.5N to 35.0N (56%). A second experiment studied hand flexor and extensor muscle responses using electromyography for five subjects holding a handle vibrating at 8 m/s² using ISO weighted acceleration, with frequencies of 20 Hz, 40 Hz, 80 Hz and 160 Hz, and grip forces of 5%, 10% and 15% of maximum voluntary contraction. Muscle responses were greatest at frequencies where grip force was affected, indicating that the tonic vibration reflex was the likely cause of increased grip exertions.     

Adaptation in Observers During Television Quality-Grading Tests I. Adaptation as a Function of the Conditioning Situation

The results of subjective quality-grading tests aro affected by ‘ adaptation ’ in the sense that observers become more critical when the quality of the tost material is generally high, and vice versa- The phenomenon has been investigated for tests with television pictures impaired by random noise and by a long-delayed echo. The magnitude of the effect of adaptation as a function of the ‘ conditioning situation ’ is described in terms of ‘ adaptation coefficients ’; it is greater for random noise.     

The future of research in understanding and controlling work-related low back disorders

Our knowledge of low back disorder (LBD) causation has progressed well over the years with in-depth understanding accelerating in the traditional disciplines of biomechanics, psychology, psychophysics, psychosocial, physiology, genetics, organizational psychology and rehabilitation. However, each of these disciplines has studied LBD causality in isolation of other disciplines. The underlying assumption is that each discipline can fully explain causality and each discipline is treated as if it were mutually exclusive and exhaustive of the other disciplines. Hence, the body of knowledge has progressed along research silos where we have in-depth knowledge along given research tracks that are defined by the boundaries of the discipline. Furthermore, a wealth of knowledge has been amassed within each of these research silos. How can they all be correct if they are indeed mutually exclusive and exhaustive? The answer is: they cannot be. This brief review of the state-of-the art in LBD research applied to ergonomics, suggests that instead of observing LBD through the myopic lens of each discipline, we need to begin to view LBD causality as a system. Recent work attempting to understand the interaction between these traditional disciplines has demonstrated that many of the findings along these silos are really interrelated and can be explained in terms of changes in the biomechanical loading at the tissue level. It is argued that further efforts to understand these interactions represent the next level of understanding causality of LBDs.     

A case study of Taiwanese custom-beverage workers for their musculoskeletal disorders symptoms and wrist movements during shaking task

This study administered the Nordic Musculoskeletal Questionnaire to a convenience sample of 106 workers at custom-beverage vendors in Taiwan (who prepare drinks through manual shaking) to explore their work-related musculoskeletal disorders (WMSDs) and identify risk factors for these disorders symptoms. Wrist posture for twenty workers were also measured for three shaking methods using an electrogoniometer. The prevalence of musculoskeletal discomfort in the past year among the respondents was 88.6%. Most of them reported discomfort in their hands/wrists (67.9%), followed by the lower back/waist (44.3%), knees (39.6%), and shoulders (38.7%). Hands/wrists and low back/waist discomforts varied significantly by the worker's gender and the number of working days per week, and hands/wrists discomfort also by the shaking method. Knee discomfort was affected by age and whether rest periods at work were scheduled, whereas shoulder discomfort by work experience, number of working days per week, and number of drink orders prepared per day. Measurements in wrist postures exhibited that repetitive activity for each wrist was as high as 4 time/s for a cup preparation (10 s). Among shaking methods, curve swing can constrain the shakers' wrists in a relatively neutral position and a smaller range of movement than others, regardless of the sex.Relevance to industryBecause of the nature of shaking-based beverage preparation work, the respondents have a higher prevalence of discomfort in the hands/wrists, lower back/waist, knees, and legs/ankles than their counterparts in other industries. These findings are expected to inform the prevention and alleviation of musculoskeletal discomfort in custom-beverage workers.