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The effect of typing posture on wrist extensor muscle loading.
Peter J Keir1, Richard P Wells
1School of Kinesiology and Health Science, York University, Toronto, ON, Canada. pjkeir@yorku.ca
Human Factors
|December 28, 2002
Summary
Keying tasks cause high forearm extensor loading. Wrist extension increases this load, mainly due to passive finger flexor muscle forces, potentially explaining office worker pain.
Area of Science:
- Biomechanics
- Ergonomics
- Human Factors
Background:
- Forearm extensor musculature experiences high static loading during repetitive keying tasks.
- Understanding contributing factors is crucial for reducing this occupational strain.
Purpose of the Study:
- To simulate human finger mechanics during static index finger key presses.
- To quantify muscle force contributions across various wrist postures.
- To determine exertion demands on wrist extensor muscles.
Main Methods:
- Developed a planar model of the human finger, incorporating active and passive forces of intrinsic and extrinsic muscles.
- Expanded the model to include passive forces from adjacent fingers and hand weight.
- Analyzed muscle force contributions at different wrist postures, focusing on index finger key presses.
Main Results:
- Wrist extensors require over 25% of maximal exertion at 30 degrees of wrist extension.
- Passive forces from extrinsic finger flexor muscles significantly contribute to increased wrist extensor demand.
- Findings align with previous electromyographic (EMG) studies.
Conclusions:
- Passive muscle forces play a critical role in forearm extensor loading during keying.
- This mechanism may explain forearm extensor pain experienced by office workers.
- Results support applications in ergonomic modeling for preventing work-related upper limb disorders.