Shoulder muscular activity in individuals with low back pain and spinal cord injury during seated manual load transfer tasks^*

* The study was approved by the University of Michigan Health Sciences Institutional Review Board and was conducted in the University of Michigan, Department of Industrial and Operations Engineering.

Abstract

This study aimed to compare the activity of four shoulder muscles in individuals with low back pain (LBP), spinal cord injuries (SCI) and a control group, during one-handed load transfer trials. Nine individuals with minimum one-year of LBP, eleven with thoracic/lumbar SCI and nine healthy controls participated in this study. The activations of anterior deltoid, upper trapezius, infraspinatus and pectoralis major were recorded by surface EMG during one-handed transferring of a cylinder from a home shelve to six spatially distributed target shelves. The integrated EMG values were compared using repeated measure ANOVA. Both LBPs and SCIs had higher anterior deltoid activation and LBPs required more upper trapezius activation than controls (p < 0.05). The spatial position of the targets also significantly influenced demands for these two muscles. The anterior deltoid and upper trapezius in LBP and SCI individuals are under higher demand during occupational load transfer tasks.

Practitioner Summary: This study aimed to compare the activation of four shoulder muscles in individuals with low back pain, spinal cord injuries and healthy condition. EMG analysis showed that the injured groups required more upper trapezius and anterior deltoid activation during load transfer tasks, which may predispose them to muscle overexertion.

Keywords:

• Shoulder
• load transferring tasks
• spinal cord injuries
• low back pain
• workplace design

Abbreviations:

• EMG: electromyography
• iEMG: integrated electromyography
• LBP: low back pain
• LSD: least significant difference
• MVC: maximal voluntary contraction
• RMS: root mean square
• SCI: spinal cord injury
• SD: standard deviation

Acknowledgements

The assistance of Charles Woolley and Nancy Womack in data collection and reduction are acknowledged.

Notes

* The study was approved by the University of Michigan Health Sciences Institutional Review Board and was conducted in the University of Michigan, Department of Industrial and Operations Engineering.