Work Related Factors of Upper Limb Musculoskeletal Disorders

An Obervation Based Evaluation System

Copyright © 2002

Thomas J. Armstrong
University of Michigan
Ann Arbor, MI 48109


Musculoskeletal disorders are multifactorial, that is, they are often associated with more than one causal factor.

Work Related Risk Factors

Numerous observation schemes, check lists, numerical methods, and instrmental methods have been proposed for observing and characterizing risk of work related musculoskeletal disorders of the upper limb. Often it is the case that these systems are more sensitive to one factor than anther and consequently will be found to work better in one situation than another, which probably explains why each investigator has his or her favorite system. It is important that users understand the factors that are present in each situation before conducting a detailed analysis. Often these factors can be assessed through evaluation of work factors such as production standards and tool and equipment attributes. They also may be assessed through observation of the job. The purpose of this page is to provide a systemmatic method that can be used to assess presence and magnitude of the most commonly cited work related factors. We have found this to be useful starting point that provides insight into the possible causes of problem situation and helps the investigator determine how to procede with possible interventions or additional analyses.

Observations may be performed on site or from video tapes. In either case it is recommended that:

  1. the analysis include a thorough documentation of what the worker uder study does.
  2. video tapes of selected jobs be saved as bench marks for each attribute.
  3. The jobs periodically be rated by a team of 2 to 5 people so that they can discuss and agree on the important factors affecting each factor.

    The following scales are provided to help investigators with this work.

Reference: Latko, W., Armstrong, T., Foulke, J., Herrin, G., Rabourn, R., Ulin, S. Development andevaluation of an observational method for assessing repetition in hand tasks. Am. Ind. Hyg. Assoc. J. 58(4):278-285, 1997.


Documentation: Documentation Procedures

Repetition or Activity: Additional information on repeated and sustained exertions

Repetition is an index of the frequency of movement or exertions, the speed of the motion, and the recovery time. At one extreme the hands are idle with almost continuous recovery time. At the other extreme the hands are moving a rapidly as imaginable with no recovery time.

Low
Medium
High
0
Idle most of the time
2
Frequent long pasuses; may have brief rapid burst of activity
4
Slow steady motion, or frequent breaks
6
Steady motion; occassional breaks
8
Rapid steady motion, infrequent pauses
10
Rapid steady motion or continusous exertion, difficulty keeping up


Force: Additional information on Force

Force is an index of the effort exterted get, hold, or use a work object or to support the weight of the body. Both averate and peak forces should be assessed. 15% is considered the maximum force that can be exerted for a prolonged period of time without exhaustion. Higher forces may be exerted for shorter periods of time. Both average and peak forces should be rated. Force can be assess from observations of the worker and from consideration of task factors.

Force (average & peak)

Most Keyboard
Upholstery work
Low
Medium
High
0
%MVC
0.5
1.0
1.5
2
4
6
8
10
100%MVC
%MVC= Percentage of Maximum Voluntary Contraction


Contact stress: Contact stress is the force per unit area acting between the body and an external object. While it can be expressed as pounds per square inch or Newtons per square meter, so it is necessary to assess the force and the area of contact. Here contact stresses is rated from nothing to the greatest imaginable. Nothing correspondes to the situation in which there is not contact with the body. The greatest imaginable corresponds to the maximum that could be tolerated for a very short period. Both averaage and peak stresses should be rated.

 

Contact Stress - Fingers (average & peak)

Low
Medium
High
0
None
2
4
6
8
10
Greatest imaginable

   

Contact Stress - wrist/palm (average & peak)

Low
Medium
High
0
None
2
4
6
8
10
Greatest imaginable

Contact Stress - Forearm/elbow (average & peak)

Low
Medium
High
0
None
2
4
6
8
10
Greatest imaginable


Posture: Consider both position and time

Wrist - flexion/extension (average & peak)


0
Neutral

2
4
6
8
10
Max Flx/Ext

Wrist - radial/ulnar deviation (average & peak)


0
Neutral
2
4
6
8
10
Max rad/ul dev

Forearm rotation - inward/outward (average & peak)
0
Semi-pronated

2
4
6
8
10
Max pronation or supination

Elbow - flexion/extension (average & peak)
0
straight

2
4
6
8
10
Max flex

Shoulder - elbow elevation/rotation (average & peak)
0
elbow at side
2
4
6
8
10
Maximum elevation


Low Temperature (average & peak)

Skin temperatures less than 70 deg F adversly affected sensitivity and dexterity. Skin temperature is related to the air temperature, the temperature and conductivity of work objects, and clothing.

0
2
4
6
8
10


Vibration (average & peak)
0
2
4
6
8
10


Summarize stresses and apportion causes
StressRatingWork factorsFixes
Repetition   
Force   
Contact Stress
Fingers   
Wrist/palm   
Forearm/elbow   
Posture
Wrist   
Forearm   
Elbow   
Shoulder   
Temperature   
Vibration