Abstract
Cartographers were studied to determine if they were exposed to those risk factors that may lead to a work related musculoskeletal disorder. As part of the workstation evaluation, the investigators conducted a literature search, observed the normal job functions of the cartographers, assessed the layout of the cartographers’ workstation, and administered a body part discomfort diagram. The results indicated that the work performed by cartographers has high static demands to the neck, back, and upper extremities, and only the fingers performed repetitive work to operate the pointing device. The cartographers operated the pointing device once every 4-5 seconds and the required force needed to operate the device is over twice the amount dictated in the military standard for human factors criteria. Additionally, the results of the body part discomfort diagram indicated that on average the cartographers suffered from discomfort at eight different body parts with the neck, back, and shoulder being the most prevalent.
Introduction
The ancient Egyptians, renaissance Italians, and more recently corporate America have documented work-related musculoskeletal disorders (WMSDs). Work related musculoskeletal disorders refer to a category of physical signs and symptoms due to chronic musculoskeletal injuries in which the causes appear to be related to some aspect of repetitive work. In 1936, Klockenburg determined that the layout of the keys on a typewriter put the wrists in non-neutral postures. Typewriter and keyboard manufacturers as well as other researchers ignored these findings until the proliferation of upper extremity injuries associated with use of these products surfaced during the 1980s. These increased injury rates associated with keyboard use has set off a flurry of studies with researchers focused on the ergonomic evaluation of keyboard designs, among these studies are ones performed by Chen et al; Grandjean, Nakaseko et al.; Lopez; Kroemer; and Tittiranonda et al.
Matching the propagation of keyboard users is a new segment of the VDT user population, the “pointing device user.” Examples of commonly used pointing devices are trackballs, mouses, and joysticks. The “pointing device user” is different from the traditional computer user in that he/she uses the pointing device the majority of the time to enter data and operate computer software. Furthermore, the user maintains a more static upper extremity posture whereas keyboard users perform more repetitive motions. This difference in computer hardware choice created a new set of problems. Unfortunately there has been little research which has documented injuries associated with pointing device use. Telephone conversations with U.S. Army ergonomics experts (Lopez, Rice, and Tannen), U.S. Air Force ergonomics experts (Klingenberg and Cogburn), and others (Rempel and White) did not yield any research evidence suggesting problems between pointing device use and user injury. A literature search linking pointing device use to injuries yielded two references. The first was a study performed by Liberty Mutual Insurance Company published in the Human Factors and Ergonomics Society Journal. The second was in the WMSD News which used the Liberty Mutual study as its source. Currently, research articles devoted to the mouse are dedicated to mouse design criteria and wrist posture. Liberty Mutual’s research showed mouse related injuries jumping from zero in 1988 to 326,099 in 1993. Interestingly these injuries only account for .58 percent of all claims and .71 percent of all claims paid out by Liberty Mutual. Conversely, over the same period of time injuries suffered at a computer workstation (predominately injuries associated with keyboard use) rose from 292,359 to 15.1 million over the same time period.
The cartographers main job function was to digitize a map by connecting contours via computer software. This is accomplished with the help a puck. The puck is a specially designed pointing device that acts as a mouse. It has a viewing lens with a cross hair on the top which aids the cartographer in properly aligning the puck on any section of the map and to digitize the map quickly. This job incorporated many factors associated with WSMD. Major tasks included aligning the puck on the map and clicking on the puck once every four to five seconds to initiate a software command. Aside from the repetitive finger motions the task also involved static loading of the shoulder when the puck is operated. Finally, the size of the map being digitized and the depth of the work surface caused the worker to assume poor upper extremity and back postures. The problems faced by mouse users are documented but are not on as large a scale as the rest of the computer workstation. However, it is important to note that pointing device use has mushroomed over the past 10 years and is continuing to grow. The increased use of window based software has ensured this. Therefore without changes involving employee work practices and the equipment being used by the employees, the magnitude of injuries associated with the pointing device may equal that of today’s keyboard user. It is possible that cartographer development of WMSDs could foretell possible trends we will see in the population of users of windows systems.
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