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Upper Extremity Muscle Activity During In-Phase and Anti-Phase Continuous Pushing Tasks
Kristina M Gruevski1, Joanne N Hodder2, Peter J Keir3
1University of Waterloo, Waterloo, ON, Canada.
Human Factors
|June 13, 2017
Summary
Continuous, anti-phase pushing tasks increase upper extremity muscle activity and injury risk. These findings highlight the physical demands of asymmetrical pushing, especially at lower frequencies.
Area of Science:
- Ergonomics and Occupational Health
- Biomechanics
- Muscle Physiology
Background:
- Limited research exists on symmetrical (in-phase) and asymmetrical (anti-phase) pushing exertions in industrial settings.
- Pushing tasks are prevalent in various industries, necessitating an understanding of their biomechanical demands.
Purpose of the Study:
- To investigate the effects of anti-phase, in-phase bimanual, and unimanual simulated industrial pushing tasks on upper extremity muscle activity.
- To determine the influence of different pushing frequencies on muscle activation patterns.
Main Methods:
- Fifteen female participants performed five distinct pushing tasks at three frequencies (15 cpm, 30 cpm, self-selected) using a dual handle apparatus.
- Surface electromyography (EMG) was used to measure muscle activity in key upper extremity and torso muscles.
- EMG data was normalized to maximum voluntary effort for comparative analysis.
Main Results:
- A significant task by frequency interaction was observed for the anterior, middle, and posterior deltoid (AD, MD, PD) and right trapezius (RT) muscles.
- Muscle activity in AD, MD, and PD was highest during the continuous anti-phase task at 15 cpm.
- The continuous task exhibited the lowest muscle activity coefficient of variation across all frequencies.
Conclusions:
- Continuous, anti-phase pushing tasks and constrained, in-phase pushing tasks impose the highest muscle activity demands.
- These tasks also demonstrate the least variability in muscle activity, suggesting a potentially elevated risk of musculoskeletal injury.
- Anti-phase pushing, particularly when performed continuously, presents greater physical demands compared to in-phase exertions.
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