A design tool to estimate maximum acceptable manual arm forces for above-shoulder work

Area of Science:

• Ergonomics and Occupational Health
• Biomechanics and Human Factors Engineering
• Industrial Safety and Design

Background:

• Above-shoulder work poses significant risks for shoulder fatigue and injuries, including supraspinatus impingement.
• Existing ergonomic tools lack the detailed design criteria necessary for evaluating manual arm forces in above-shoulder tasks.
• There is a clear need for quantifiable design guidelines to mitigate risks associated with overhead work activities.

Purpose of the Study:

• To develop and present a novel tool for estimating maximum acceptable manual arm forces (MAF) for tasks performed at or above shoulder height.
• To provide detailed, location-specific design criteria for above-shoulder work environments.
• To enhance the safety and reduce the risk of injury for workers performing overhead tasks.

Main Methods:

• A new tool was developed using 25th percentile female manual arm strength (MAS) as a base, with adjustments for supraspinatus tendon impingement and shoulder fatigue.
• Equations for estimating MAF were derived and presented.
• Maximum acceptable forces were calculated and tabulated for 77 distinct 3D locations within the reach envelope of a 50th percentile female.

Main Results:

• The largest acceptable anterior force was 140.3 N at shoulder height, 0.5 m anterior to the shoulder.
• The largest acceptable superior force was 84.4 N at shoulder height, 0.1 m anterior and 0.2 m medial to the shoulder.
• Sensitivity analyses confirmed the tool's robustness to variations in parameter assumptions.

Conclusions:

• The developed tool offers a higher level of detail for arm exertion criteria compared to previous ergonomic tools, making it valuable for engineers.
• The tool provides practical design criteria for engineers to create safer above-shoulder work environments.
• The tool enables the design of acceptable above-shoulder work that can be safely performed by a majority of the workforce.