Effects of postural and visual stressors on myofascial trigger point development and motor unit rotation during computer work
From: J Electromyogr Kinesiol. 2011 Feb;21(1):41-8. Epub 2010 Jun 26
The nature of modern work is changing and physically demanding jobs are now being replaced with many more service oriented jobs that require work at low levels of physical loading. More specifically, computer work at visual display terminals is becoming much more prominent in the workplace and at home. According to the Bureau of Labor Statistics (BLS), 77 million Americans use a computer at work. This represents over half of the total employed American public. In addition, with continual technological advances, future work trends indicate that this type of work is expected to represent an even greater percentage of jobs in the future.
Despite this shift, musculoskeletal complaint rates continue to be high among computer users. Studies have reported musculoskeletal disorder prevalence rates of 20% to over 75% among these types of workers. However, our understanding of the causal mechanisms leading to such high prevalence rates among computer users is lacking.
It is known that the physical demands for computer work are much different than those required during typical manufacturing and industrial tasks. Computer tasks typically require much lower levels of physical force and more mental processing than industrial work. In terms of physical demand, computer work imposes low-level static exertions on the musculoskeletal system. An important aspect of these types of exertions is that the muscle is rarely (if ever) able to relax completely; therefore, the duration of sustained contraction is thought to be a critical component for musculoskeletal disorder risk. Originally, it was thought that these low-level static exertions could be maintained for an unlimited amount of time. However, experience and research may contradict this belief.
There is growing concern that low-level static exertions (at any level) pose risk to workers, but there is no consensus as to ‘‘how much” force can be maintained for ‘‘how long”. This lack of consensus is believed to be due to the poor understanding of the underlying mechanisms through which the health effects occur.
In addition to physical demand, computer work also imposes high mental demands on users. Visual information must be processed, interpreted, and reacted to in a very short period of time, resulting in high cognitive demands on workers. Visual parameters such as glare, lighting, screen resolution, or text legibility may directly impact cognitive demands during computer work. However, it is not clear how these visual and mental demands might impact the musculoskeletal system, and translate into physical symptoms. Studies have shown that increased mental demand may result in greater muscle co-contraction and sustained muscle activation. However, such results do not fully explain the casual pathway for pain and discomfort during computer work.