Causes of repetitive strain injury (RSI)

Repetitive strain injury (RSI) is most commonly related to the overuse and strain on the muscles, tendons and soft tissues of the upper part of the body like the wrists, forearms, shoulders, elbows, back or neck. (1-6)

The cause of RSI lies in repetitive microscopic trauma that occurs due to strain on the muscles and joints. This repeated trauma at the microscopic level leads to tendonitis or inflammation of the tendons, tenosynovitis or inflammation of the tendons and synovial sleeve or sheath covering the muscles and tendons.

Mechanism that leads to RSI

The actual underlying mechanism that leads to inflammation is not clear.

Factors that lead to RSI

Common factors that lead to RSI deep within the muscles and tendons include:

• Fatigue of the muscles and ligaments, tendons and muscles due to over strain and stretching
• Strain may lead to lack of blood supply and damage to the nerves. This is called ischemia
• Depletion of energy giving adenosine triphosphate (ATP) due to ischemia
• Psychosocial factors related to work conditions

Activities that raise the risk of RSI

Activities that can raise the risk of RSI include:

• repetitions
• doing the same activity over a long period of time without rest
• working with force such as lifting heavy objects
• maintaining a poor or awkward posture or position for a long time without rest

Working in cold climates, with instruments that vibrate and stress also raises the risk of RSI.

RSI tends to worsen by pressure related movements like twisting, hammering and pounding, squeezing, pushing, pulling, lifting or reaching.

Other factors are too fast or excessive workloads, long hours and lack of rest in between.

When does RSI occur?

Commonly the affected persons are unable to pin point the exact time when their condition began. This makes RSI different from an acute or sudden injury to a muscle or tendon due to an accident.

The inflammation affects the lining around tendons that hurts when the wrist and fingers are straightened or bent but usually not when they are at a neutral position.

Jobs associated with RSI

Jobs commonly associated with RSI include:

• heavy computer workers
• typists
• clerks and data entry professional
• workers of an assembly line
• ultrasonographers
• surgeons
• nurses
• dentists
• tailors
• cooks
• cleaners
• drivers
• carpenters
• road maintenance staff
• workers with heavy machinery
• equestrian athletes
• swimmers
• golfers
• martial artists
• musicians (instrument players) etc.

Classification of RSI risk

Risk of RSI thus can be classified as awkward or static posture, force, repetition of movements, and vibration.

Awkward or Static Posture

An awkward posture occurs when the body remains at a position different from its neutral position. This includes:

• twisting
• bending
• reaching above the level of shoulders
• stooping
• reaching behind the body
• bending backward and side to side movement of the wrist etc.

When the body is in a neutral position there is maximum work efficiency with the least amount of energy use. Static posture refers to being in the same position neutral or awkward for long periods of time.

Continuous use of the same set of muscles cause them to develop fatigue. Examples are constant standing, or twisting the neck to see a poorly placed computer monitor. Prolonged static phase of muscles leads to affected blood supply to the muscles and RSI.

Force

All work requires force. However, if the force required to perform the activity overloads the muscles, joints, tendons etc. there may be excessive strain on the tissues leading to RSI.

This could be due to reaching more than an arm’s reach, handling heavy objects, improper or tight gripping or high amounts of force applied over a small area leading to pressure points.

Excessive force, like repetitive movements does not allow time for the muscles to fully recover between movements.

Repetition of movements

These are dangerous when they use the same joints and muscle groups over and over. This leads to muscle fatigue that is unable to rest in between two movements. Eventually, it takes more effort to perform the same actions.

Vibration

Vibrations responsible for RSI are of two major types: hand or arm vibrations or whole body vibrations.

Hand/arm vibration affects people who operate power driven hand tools like drills, jack hammers, air guns, chain saws etc.

Total Body Vibration is seen among heavy equipment operators, heavy vehicle drivers etc. This type of vibration injury often contributes to low back pain.

Further Reading

• Repetitive strain injury (RSI) – What is Repetitive strain injury?
• Symptoms of repetitive strain injury (RSI)
• Diagnosis of repetitive strain injury (RSI)
• Treatment of repetitive strain injury (RSI)