The rise of RSI is generally attributed to the small repetitive motions such as the action of typing on a computer keyboard and clicking a mouse. While there have been reports of RSI in the workplace since the 17th century, the short and fast motions associated with computer use have become a predominant feature of modern working life. More that 150 million people in Europe and America now use computers at work. When looking at the cause of RSI it is also necessary to look at the strain on muscles of sitting for long periods in a fixed position as well as the stresses of repeated arm, hand and finger action.
Arm muscles of computer users have the same reaction to stress as muscles of athletes. Athletes train wisely to avoid injury, so should computer workers.
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The muscles of the arms are type IIB which not ideally suited to cope with short and fast motions for long periods of time. The blood flow diminishes in IIB muscles when they are contracted. They also require large supplies of energy in the form of stored glycogen. When the glycogen is depleted, arm muscles work very inefficiently. If these muscles are forced to continue functioning without sufficient rest required to replace the glycogen stores, then they will fatigue very quickly. Such forced action not stresses the muscle but causes tiny tears in some of the small muscle fibers called fibrils. The same thing happens in athletes' muscles during training or competing. However,a conscientious athlete knows the signs of a strain and will take steps to rehabilitate it. For computer users this type of strain is rarely diagnosed until large numbers of fibrils have suffered. When the muscle continues to be used without adequate steps being taken to ensure healing, the process of fatigue and strain is accelerated.
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While this explains the basis of repetitive strain injury there is still more to the story. RSI has become an umbrella term for all conditions derived from repetitive actions. This is a bit of a misnomer. For instance tendonitis (irritation and swelling of a tendon) is not technically a strain injury. Rather is is an extension of the category of conditions created or made worse by repetitive actions. So the label 'RSI' serves the purpose of recognizing the origin of problems, but due to its lack of accuracy is not a complete diagnosis. A good diagnostician may state, for example, that “from the patient’s history of prolonged periods of typing and the findings of pain and swelling over the tendon the RSI appears to be tendonitis”. Other disorders such as muscular adhesions, muscular tension, nerve entrapment and vascular disorders may be at the root of many of these RSIs. The key for the doctor is to recognize the signs, symptoms and findings of each.
If we consider the initial point of RSI, where prolonged typing causes micro strains of the muscle fibrils, each of these fibrils will remain shortened leaving the muscle slightly shorter and tighter (secondary theory: It may also occur due to lactic acid build-up). If the body does not recover from this, more and more fibrils will be affected and the muscle will get shorter and tighter still. This usually happens in one muscle group but not the opposing muscles. In the example of the typist, the muscles used to press the keys (on the inside of the forearm) would shorten more than the opposing muscles. This imbalance of muscles will in itself cause a great number of problems. Firstly, the ‘neutral position’ of the wrist joint will shift to the inside (potentially putting stress into the carpal tunnel). The stability of the joint may be compromised leaving the person more susceptible to other injuries from pulling or twisting motions.
Already we can see how repetitive activity that exceeds the muscle’s recovery time will strain the muscle, and then affect the muscular balance and joint stability. When a joint becomes unstable, the articulating bones move against one another in a compromised way. This may mean that the motion is restricted; wearing one part of the joint cartilage more or the instability could allow the joint to move in abnormal vectors causing the joint surface to wear prematurely. Wear and tear of the articular surface of bones is called (osteo) arthritis. Prolonged muscular imbalance accelerates the development of osteoarthritis, yet it must be remembered that RSI is not the only thing that causes muscular imbalance.
The right amount of muscle tone is very important for joint flexibility. Too much muscle tone will limit the range of motion and keep the joint under excessive tension, potentially wearing it prematurely. Too little muscle tension will allow the joint to be hyper flexible and not properly supported. This can have negative long term effects on the ligaments of the joint. Abnormal flexibility, either too little or too much is a sign for your doctor that attention should be paid to the tone of the muscles supporting the particular joint.
Repetitive strains and long term muscle tension can lead to something called adhesions. In a healthy muscle the small fibers (fibrils) that make up a muscle glide over one another during contraction. With repetitive strain and muscle tension, these fibers stay shortened and start to form adhesions which limit the gliding action. Limited flexibility is one sign of this but there are often small painful bumps in the muscle as well. Adhesions are a sign of a chronically irritated muscle. They can be treated effectively through deep massage, slow and deep stretching and careful rehabilitation.
Tendons and ligaments are other non-contractile tissues that fill important roles in the musculoskeletal system. Tendons are the rope-like ends of muscles that attach the muscle to the bones. Tendons can be quite long especially when a muscle is far away from the joint it is moving. Most of the muscles that control the fingers are in the forearm and various tendons travel down through the wrist and attach to the bones of the fingers. It is kind of like a puppet on a string scenario but all the strings are forced through a relatively small space (called the ‘carpal tunnel’) with a bunch of other things like arteries and nerves. One of the issues with the tendons of the wrist is that they can undergo a lot of friction especially with certain positions of the wrist. Regular and repeated friction can cause micro tears and will cause the tendons to become irritated and start an inflammatory response (tendonitis). Tendons heal very slowly but there are many effective therapies to support recovery. Tendon damage is often a later consequence of inefficient muscles, poor ergonomics and consistent abuse.
Ligaments are the strong fibrous bands that hold joints together. Ligaments are generally under very little stress in the neutral position of a joint. They become very effective at the end ranges of a joint’s motion. Muscles and ligaments work together to stabilize joints and when one of them fails to work efficiently, it shifts the load to the other. An under-active set of muscles will shift more of the joint stability load to the ligaments. Over time this can create laxity or even tearing of the ligaments. Ligaments are damaged by a joint moving beyond its normal range of motion such as the excessive motion associated with whiplash. Ligaments also heal very slowly and are often left weaker post-injury.
The nerve damage attributed to repetitive strain injuries is often due to compression. As nerves pass between tense muscles and through bone foramina they are susceptible to chronic pressure which could damage the insulating and protective myelin sheath. Chronic compression generally affects large diameter fibers leaving the smaller pain and temperature fibers unscathed. The affected fibers are often those of fine touch, proprioception (joint position sense), vibration and the motor fibers. This often produces the classic numbness, tingling and weakness scenario. When the compression can be identified and the source removed, nerve fibers have a relatively good capacity to heal but this may take a considerable amount of time and requires significant support.
Blood flow compromise in the limbs may be another source of numbness, tingling and weakness as the nerves need blood to function. The leg that falls asleep and becomes weak and tingling is a good example of this scenario. Long term compromises to blood flow either into or out of the limb can create a great number of secondary disorders such as swelling or pitting of the skin, cold limbs and even pain. Vascular disorders can be very severe and have serious consequences.
From the seeming insignificance of a few overworked muscle fibrils multiplied over time, a whole host of rather complex chronic disorders can arise. Thankfully even at the most advanced stages there are many excellent therapies available quite capable of assisting the individual toward restoring their health.
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Awareness is the first and most important step on the path to a safe and healthy work practice. If we all looked at our daily activity as a series of athletic events, we might more carefully consider how we prepare for such an event. A jogger would not run ten miles without properly warming up and so too we should not run our fingers across our keyboards without preparation. Athletes pay attention to what they eat and drink and so should we. An athlete will be careful not to overexert their body and we too should monitor our activity, rest and stretch.
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