Evaluation of shoulder strain during multi- directional forceful arm exertions

Abstract

Background

Forceful exertions of the arm/shoulder are common during material handling and many other industrial tasks. Determination of how the risk of shoulder injury changes in conjunction with direction of force exertion could provide useful guidance on the design of workplaces and tasks.

Objective

This research was conducted to determine how direction of force exertion and muscle recruitment algorithm effect shoulder strain computed by musculoskeletal modeling.

Methods

Musculoskeletal modeling software was used to perform simulations of static force exertions of the right upper limb. A series of 36 force exertions in directions at 30° intervals in the transverse, sagital, and frontal planes were performed using three muscle recruitment optimization algorithms. A previously validated strain index equation was used to calculate risk injury for each force exertion based on the magnitude and direction of the resultant glenohumeral force.

Results

Generally, highest strain values were found in the downward, backward, and leftward direction and lowest strain values were found in the upward, forward, and rightward direction, or, in other words, during force exertions opposing forces in those directions.

Conclusions

When designing workplace tasks that involve forceful exertions of the shoulder, pulling and downward pushing exertions should be given preference over pushing and lifting exertions.