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Wrist and forearm postures and motions during typing
1Piziali and Associates, Inc., San Carlos, CA 94070, USA.
Ergonomics
|July 29, 1999
Summary
Typing frequently involves awkward wrist postures, with many individuals exceeding 15 degrees of extension and 20 degrees of ulnar deviation. These rapid wrist motions may contribute to musculoskeletal disorders.
Area of Science:
- Ergonomics
- Occupational Health
- Biomechanics
Background:
- Awkward upper extremity postures and repetitive wrist motions are potential risk factors for musculoskeletal disorders during keyboard work.
- Accurate data on typists' body postures and joint motions at standardized workstations are lacking.
Purpose of the Study:
- To continuously measure wrist and forearm postures and motions of subjects typing at a standardized computer workstation.
- To analyze joint angles, velocities, and accelerations during typing tasks.
Main Methods:
- A laboratory study involving 25 subjects typing for 10-15 minutes.
- Continuous recording of wrist and forearm angles using electrogoniometers.
- Calculation of joint angular velocities and accelerations from postural data.
Main Results:
- Typing resulted in sustained non-neutral wrist postures: mean wrist extension of 23.4° (left) and 19.9° (right); mean ulnar deviation of 14.7° (left) and 18.6° (right).
- Over 73% of subjects exhibited wrist extension >15°, and >20% showed ulnar deviation >20°.
- Joint angles and motions varied widely, were unpredictable by anthropometry or typing speed, and exhibited rapid velocities comparable to high-risk industrial jobs.
Conclusions:
- Typing on adjusted workstations involves significant non-neutral wrist postures and rapid motions.
- These dynamic wrist joint motions may be a critical risk factor for developing musculoskeletal disorders.
- Further evaluation of wrist joint dynamics is recommended for understanding typing-related cumulative trauma disorders.