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Question: How does a trackball compare ergonomically to the more standard computer mouse? It seems the trackball might be better since it requires moving only the thumb or hand instead of repetitive movements of the whole arm.
Answer: There is almost no research available on the comparative ergonomics of trackballs and mouses, so the answer to this question must be based on ergonomic theory. Ergonomists say the trackball may offer some advantages over a computer mouse, but they caution that the trackball may just present a different set of problems for the computer user.
There is not enough evidence at this point to indicate whether trackballs are a better alternative to mouses, says Roberta Carson, MSIE, CPE, an ergonomist with ErgoFit, an ergonomics consulting company in Newton, MA. But she says lots of people who have problems with the traditional mouse are trying the new trackballs. At least until more is learned from formal research, Carson says workers should consider trackballs a legitimate alternative that may relieve the repetitive motion stress that can come from using a mouse.
The evidence for injuries from using a mouse is substantial, showing that long-term, repetitive use of the computer mouse can be detrimental.1 In one study, researchers from Sweden studied 12 office workers who normally use a mouse and 12 who normally use only a keyboard. The subjects worked to enter corrections in text as ergonomic factors were measured.
Mouse users spent 64% of the working time with the operative wrist deviating more than 15% toward the ulnar side, which can lead to injury, compared with non-mouse users who spent 96% of the time with their wrists in the neutral position. Mouse users worked with the shoulder rotated outward more than 30 degrees 81% of the time, while non-mouse users kept the shoulders in a neutral position at all times.
The researchers concluded that the use of a computer mouse causes the worker to maintain awkward, twisted postures that can lead to discomfort after long periods of work. They suggest redesigning work stations so mouse pads can be placed as close as possible to the operator.
Other research has suggested workers typically grip the mouse too hard, increasing the chance of injury. In a report from the Center for Workplace Health Information in Haverford, PA, ergonomists say the average person applies 10 pounds of pressure when gripping the mouse, which puts 100 pounds of pressure on the joint at the base of the thumb.
That means that using a computer mouse can be riskier than using only a keyboard, even though long-term keyboard use poses its own risk of repetitive motion disorders. Part of the problem is that instead of using eight fingers and one thumb to type, the mouse requires clicking the button with only the index finger while gripping with the rest of the hand. Moving the pointer requires sustained, fine movements, which requires the worker to continually contract the muscles in the hand.
The ergonomists advise placing the mouse on a surface next to the keyboard and at the same height, to prevent awkward reaching. The mouse should be held loosely, and the whole arm should be used to move the mouse, not just the wrist. The mouse buttons should be clicked lightly to avoid excessive tension in the hand.
Carson says many of those problems may be avoided by using a trackball because the design of the device requires a different type of body movement from the worker. With a mouse, the entire device must be moved across a surface and buttons clicked usually with just one finger. But with trackballs, the device remains stationary and a large ball is moved by moving the entire hand, or sometimes just the thumb, across it.
Using a trackball can eliminate one of the major hazards of a mouse, Carson says. Many workers rest their wrists on the work surface when using a mouse, which makes them move the mouse with a back and forth motion like a windshield wiper. That creates extreme stress on the wrist. But with a trackball, the design usually forces the worker to move the ball with motions of the entire arm. In theory at least, that’s better because it usually is ergonomically better to use larger and stronger muscles instead of smaller, weaker muscles for repetitive motions.
"But some functions can be more difficult with a trackball, like drag-and-click," Carson says. "With a mouse, you hold the button down and move the mouse. But with some trackball designs, it can be very awkward to hold a button down and move the entire palm."
The design of the trackball can make a difference in how ergonomically sound it is, Carson notes. There are many designs on the market, with some using a large ball that is moved with the palm and some using a smaller ball that is moved only by the thumb. In general, Carson says the larger trackballs probably are better because they require movement of the entire hand and sometimes the whole arm.
"With the smaller balls that use only the thumb, you run into the same problem of using one digit for repetitive motions all day long," she says. "Using the thumb is better than using the forefinger for repetitive motion with the mouse, but in the long run, you’re much better off if the design requires the user to move the entire arm."
The bottom line, Carson says, is trackballs are ergonomically good tools only in a theoretical sense. The good news is that many trackballs can be purchased for $50 or less, so there is no great expense in allowing workers to try them if they find the traditional mouse to be uncomfortable.
"It wouldn’t be a bad idea to supply both the mouse and a trackball so the worker can use either one," Carson says. "Or the worker could use the mouse in the morning and switch to the trackball at lunch so that you give your body a break from doing either of the motions all day long."
Bovenzi M, Apostoli P, Allessandro G, et al. Changes over a workshift in aesthesiometric and vibrotactile perception thresholds of workers exposed to intermittent hand transmitted vibration from impact wrenches. Occ and Envir Med 1997; 54:577-587.
The use of impact wrenches can cause a deterioration of tactile perception in the fingers, according to this study from the Institute of Occupational Medicine at the University of Trieste in Italy. The deterioration can occur even when the worker’s daily exposure to the impact wrench’s vibration is at a level generally considered to pose little risk.
An impact wrench is a power tool that delivers significant amounts of vibration to the worker’s hands. Occupational exposure to vibration from hand tools is associated with an increased risk of neurological, vascular, and musculoskeletal disorders of the upper arms. Early symptoms include intermittent tingling and numbness in the fingers and hands. Workers may have reduced tactile function, meaning they have reduced senses of touch, temperature, pain, and dexterity.
The researchers studied 30 workers who used impact wrenches in their daily work, plus 25 controls who performed manual labor but did not use impact wrenches or other tools that deliver substantial vibration to the hands. The tactile function of the workers’ hands was measured before and after work, and the results showed that those using impact wrenches lost tactile function.
"A significant temporary threshold shift in vibration perception at all test frequencies was found in the workers exposed to vibration but not in the controls," the researchers report. "A significant increase in depth sense perception thresholds was found in the men exposed to vibration."
The degree to which the tactile function was impaired was directly related to the amount of vibration received from the impact wrench over a workshift. Tactile function can be diminished even when the worker is not exposed to what is considered an excessive degree of vibration.
"The loss of tactile sense can also disturb the manual control of power tools, increasing the risk of accidents at the workplace," the researchers say. "It is a matter of concern for the occupational health physician that objective signs of acute tactile dysfunction could be detected in workers exposed to an energy equivalent acceleration at a level that is considered to be associated with a minimal risk of vibration-induced adverse health effects."
Krause N, Ragland DR, Greiner BA, et al. Psychosocial job factors associated with back and neck pain in public transit operators. Scand J Work Environ Health 1997; 23:179-186.
Nonphysical factors such as job dissatisfaction have a significant effect on back and neck pain, according to this research from the University of California at Berkeley.
The researchers addressed the issue because the role of psychosocial risk factors in the development of spinal disorders is still being debated. The study was designed to take into account the physical stressors that could lead to nondisabling back and neck pain, but also the psychosocial factors. A total of 1,449 transit vehicle operators in San Francisco participated in the study, undergoing a medical examination and completing a questionnaire.
By using the questionnaire results and looking at the employees’ personnel files, the researchers were able to assess each worker’s uninterrupted driving periods, frequency of job problems, job dissatisfaction, supervisory support, and other psychosocial demands.
Workers experienced more back and neck pain when they drove vehicles for long, uninterrupted periods, such as normal shifts or longer. They also experienced more back and neck pain if they had high job dissatisfaction, low supervisory support, and high psychosocial demands such as those that might accompany family disputes or financial problems.
The most significant finding, according to the researchers, is that nearly all the associations between psychosocial job factors and back and neck pain remained strong even after controlling for past and current work load, age, gender, height, weight, and vehicle type.
Melamed S, Froom P, Kristal-Boneh E, et al. Industrial noise exposure, noise annoyance, and serum lipid levels in blue collar workers The Cordis Study. Arch Envir Health 1997; 52:292-298.
Noise in the workplace may be a threat to more than just a worker’s hearing, according to this study. It also may increase cholesterol levels and increase the risk for cardiovascular disease.
The authors studied the association between industrial noise exposure, noise annoyance, and serum lipid/lipoprotein levels in 1,455 men and 624 women, all blue collar workers. They found that young men, those under 45, who were exposed to high noise levels had higher total levels of cholesterol and triglycerides, as well as a higher cholesterol ratio, than men exposed to low noise levels.
High noise levels were considered at least 80 decibels. With women and men older than 45, high noise levels did not affect the serum lipid/lipoprotein levels. Noise annoyance (how much the worker was annoyed by the noise level) also appeared to increase total cholesterol and high-density lipoprotein levels in young men and in women, while also increasing triglyceride levels in women.
"The findings of this study, conducted on a large cohort of male and female blue collar workers, support the hypothesis that exposure to high industrial noise levels may be a risk factor for [cardiovascular disease] via increased plasma lipids," the authors write.