Repetitive strain injury, or RSI, is the name given to a range of musculoskeletal disorders, usually caused by work in some way. One study by the TUC reckoned that one in 50 UK workers suffered some form of RSI. Those injuries most pertinent to the IT industry are associated with keyboard and mouse use, such as Carpal Tunnel syndrome. They can be worsened by poor ergonomics and posture. Some conditions are acute and very noticeable, while others can be less immediately obvious and worsen over time.
The term RSI is not a medical one -- it refers to how you got the injury, rather than the type of injury sustained. As well as repetitive motion, RSI can be caused by using excessive force, or by bad posture. Some symptoms include numbness, tingling, pain and stiffness. Some conditions can be diagnosed and treated, and some even qualify as industrial diseases, Non-specific Pain Syndrome (NSPS), also known as diffuse RSI, is another term used to describe musculoskeletal problems that are not focused on a specific part of the body. This can be harder to treat medically.
The keyboard and mouse are often associated with Carpal Tunnel syndrome, a condition where a nerve running through the wrist is compressed. This can be caused by bending the wrist too far, and often by the tendons passing through the carpal tunnel becoming inflamed and swollen. This can be treated using anti-inflammatory drugs or painkillers, or in more extreme cases a splint can be used to restrict wrist movement.
Other problems associated with PC use include back pain through incorrect posture: if your seat, keyboard and screen aren't in a straight line, the tendency is to twist your back, shoulders or neck.
The consequences of RSI can affect people personally, and the companies they work for. It can get so serious that people need to take time off work. This means that a company’s interests are served by ensuring it minimises the risk of RSI among staff. Research cited by the RSI Association estimates the cost of RSI conditions to UK industry to be between £5bn and £20bn, although not all this is related to PC use.
Problems that people working with or in IT are likely to face are related to keyboard and mouse use. Rather ironically, trained typists are more likely to suffer problems than two-finger typists, since the latter rarely move their hands quickly or often enough to do serious damage. Regular typists are at risk because of the position of the hands while typing: A standard keyboard forces you to bend your wrists outward, a movement known as ulnar deviation. The usual solution to this is an ergonomic keyboard, where the keys are split into two halves that are then angled outwards. Realistically this won't be an issue if you’re a "two finger typist", as you won't be trying to fit your hands to the rows of keys.
Mouse use will affect far more people. For a decade now, the mouse has been the dominant method of issuing commands to PCs, replacing the command line within windowing environments and menu keys in applications. Just gripping a mouse tends to put the wrist in a strained position, even ergonomic mice. This is made worse by most people's habit of using only the wrist to move the mouse, rather than the whole arm.
Another issue with using a mouse is that it's often positioned too far to the right, especially if you have your keyboard in the correct position for typing. This makes you over-reach for it, straining your shoulder. Since most people only ever do this motion with one hand, the strain can be worse than with tasks performed with both hands. Ironically, left-handed users should be in a better situation, since virtually all keyboards have the keypad on the right, leaving a clear space on the left to put the mouse in.
While it's difficult to narrow down what effects you're likely to suffer from using a PC, the causes are well enough understood that it is possible to reduce your risk of suffering RSI, provided you take some care.
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