Shoulder moments and angles during single and combined manual material handling tasks

Abstract

Shoulder musculoskeletal disorders due to manual material handling tasks are common workplace injuries. Here we investigated the difference in shoulder biomechanics (moments and angles) between a single task of removing a box from a shelf (or depositing a box on a shelf) and the equivalent part of a combined task that consisted of removing, carrying and depositing boxes; that is, a single removing [depositing] task was compared with the removing [depositing] part of a combined task. We found that the peak and cumulative shoulder moments were larger during the single-task paradigm than during the equivalent part of the combined task by 26.3 and 25.5%, respectively. The two paradigms also differed in terms of shoulder angles. It is likely that the main contributors to this overestimation were differences between the single and combined tasks in terms of the lever arm (i.e. horizontal distance), the shoulder angle, and the task duration.

Practitioners’ Summary: We investigated shoulder moments during single and combined manual material handling tasks. Shoulder moments were found to be smaller during combined tasks. Practitioners should consider that analysing combined tasks using estimations based on single tasks could result in an overestimation of 26.3 and 25.5% in peak and cumulative shoulder moments, respectively.

Abbrevaitions: MSDs: musculoskeletal disorders; MMH: manual material handling; LMM: linear mixed model

Keywords:

• Shoulder moment
• shoulder angle
• manual material handling
• shoulder injury
• musculoskeletal disorders

Acknowledgements

The authors would like to thank Prof. Yisrael Parmet for his statistical consultancy and Mor Topaz and Yarden Avrahami for their assistance in the data collection.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the following: The Israel Science Foundation under grant No. [899/18]; The Helmsley Charitable Trust through the Agricultural, Biological and Cognitive Robotics Initiative and the Marcus Endowment Fund, both at Ben-Gurion University of the Negev.