Factors involved in repetitive work injuries

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As I have discussed on previous posts, repetitive or Gillette type injuries can be caused from a variety of work factors. These types of injuries can develop within a matter of minutes or within a matter of years. The courts have not set a rule as to the duration of time it takes to develop a repetitive injury.

ErgoRehab Blog recently posted an article concerning some of the occupational ergonomic risk factors involved in possible repetitive or Gillette type injuries. The risk factors are as follows:

  1. High Task Repetition and Inappropriate Work / Rest Cycles: A job is classified as highly repetitive if the cycle time is less than 30 seconds, or if a task or motion is performed more than 50% of the time it takes to complete the work cycle. Work and rest cycles are the intervals of time measured during one complete task revolution or cycle. The more repetitive the task or cycle, the less recovery time there is for the muscles and tendons. Inappropriate rest/work cycles are work cycles that do not allow time for sufficient recovery and micro trauma can accumulate, leading to cumulative trauma disorders.
  2. Forces and Forceful Exertions: Both static and dynamic loading increases muscle contraction strength and duration, thus reducing circulation to the muscle fibers and increasing recovery time requirements. Static loading is a greater risk factor than dynamic loading, since static loading results in increased muscle fiber recruitment and fatigue and decreased blood perfusion. Forceful exertions produce increased muscle effort in response to high task load, leading to more rapid muscle fatigue and overuse which can lead to upper extremity injuries.
  3. Positions of the Wrist and Arm and Awkward Postures: Repetitive wrist flexion and extension increase intra-carpal tunnel pressures in the wrist. In addition, awkward postures overload muscles and tendons and load joints in an asymmetrical manner, imposing a static load to the musculature thus reducing nerve and muscle blood flow. Activities that use repetitive finger motions with the wrist in an extended position in constrained postures, such as playing a musical instrument, typing or the use of pinch grips also increases intra-carpal tunnel pressures and thus reduces nerve and muscle blood flow which may lead to upper extremity injuries.
  4. Mechanical Stress Concentrations / Contact Trauma: Weight bearing with the wrist in an extended position such as gymnastic sports or bicycle riding. Direct pressure contacting the base of the palm or the palmar surface of the fingers such as in frequent or continuous use of tools with hard or sharp edges, or short handles can cause direct compression against peripheral nerve fibers, leading to upper extremity symptoms.
  5. Vibration: Vibrating hand-held tools can cause toxic vibration reflex and constrict blood vessels, which may damage nerve fibers in the upper extremity.
  6. Exposure to Cold: Working in cold environments and/or handling cold tools affect the circulation to the upper extremity.
  7. Gloves: Use of gloves reduces tactility, increasing the amount of force required to hold or manipulate a given object. This risk increases with poor fitting of the gloves and with glove thickness.
  8. Lead: Constant contact or exposure to lead has been shown to impair maximal motor and sensory nerve conduction velocities of the medial nerve which may cause Carpal Tunnel Syndrome of the wrist.
  9. Work Stress and Job Satisfaction: The perception of the workload, work pressures and job satisfaction may alter the individual’s response to early signs of fatigue and discomfort.

The risk of developing upper extremity cumulative trauma disorders and injuries increases with the number of ergonomic risk factors present. Jobs that combine high force and high repetition pose the greatest risk.

It is important that you discuss your job duties with your doctor if you believe you have a work injury. Also, it is important that you notify your employer of your injury, as failing to notify your employer may cause you lose out on work comp benefits. It may be necessary to consult with an attorney to assist you in determining whether you have a work related injury.

Costs & Causes of Injuries to the Upper Extremity| ErgoRehab Blog