The pain syndromes, also known as diffuse RSI, are some of the most common conditions, especially for RSI amongst computer users. The explanation below of how this condition arises and is sustained is based upon some of the latest medical opinions on the subject.
Muscles and tendons get blood through capillaries passing between the muscle fibres. A tense muscle squeezes on these vessels and they collapse, slowing the flow of blood. Blood flow restriction begins when the muscle exerts 5% of full power, and is stopped completely at 50% of full power.
When blood flow stops, the muscle has enough stored energy to cope with brief periods of tension. When this is used up, the muscle switches to an inefficient form of energy supply. However this is quickly exhausted and leads to a buildup of acid wastes in the muscle (lactic acid). These acid products cause pain and fatigue in the muscle. This pain and fatigue is similar to that felt when lifting weights at the gym.
The muscle pain can cause neighbouring muscles to tense up in sympathy by a reflex reaction (called the splinting reaction). This is a normal reaction to injury, and is good where bracing is needed for acute injuries like a broken bone, or an infection. In overuse syndrome, however, a self-sustaining pain cycle can develop. This pain fluctuates in intensity, from being mild to intolerable. The pain can also migrate from one part of the affected limb to another. Over time the muscles can become hyper-sensitive, with pain being caused by relatively low levels of activity, and the muscles developing specific tender points (myofascial trigger points).
An inadequate blood supply to nerves may also cause numbness and tingling. If larger nerves passing between muscles are squeezed, more definite tingling and numbness may result.
This description, illustrated by the diagram above, explains one of the main mechanisms behind the development of RSI symptoms, however it is by no means the only one. In the development of localised conditions (e.g. tendinitis) other factors such as repetition and vibration are also involved. That said, however, muscle tension is currently regarded as one of the primary causes of RSI. It is for this reason that the name Repetitive Strain Injury is no longer the preferred term (see list of other names for RSI)
This description of the mechanism behind RSI helps to explain why micropauses are so critical and so effective in its treatment and prevention. Micropauses, together with longer breaks, are intended to regularly refresh the muscles and thereby prevent the buildup of waste products and fatigue.
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