Semester

Summer

Date of Graduation

2014

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Industrial and Managements Systems Engineering

Committee Chair

Ashish Nimbarte

Committee Co-Chair

Majid Jaridi

Committee Member

Xiaopeng Ning

Abstract

Shoulder musculoskeletal disorders (MSDs) are a major cause of morbidity and pain in the modern working population. Epidemiological literature suggests that forceful arm exertions pose an increased risk for shoulder MSD development. Although several previous studies have reported a significant stress-strain relationship for the shoulder complex during physically demanding exertions, a clear assessment method to evaluate the risk of injury to the shoulder complex currently does not exist. The objective of this study was to develop and validate a new shoulder strain index to evaluate strain placed on the shoulder during work-related forceful arm exertions. Specifically, the concept of the concavity compression mechanism of the glenohumeral joint was used to develop the proposed strain index. Nine strain indices were developed using different biomechanical measurements that characterize the concavity compression mechanism. The highest correlation (r=0.70) between the strain index scores and ratings of perceived exertion was observed for a strain index which comprised of three normalized components: (1) angular deviation between the resultant force vectors (external load and shoulder muscles) in the frontal plane, (2) resultant reaction force acting on the glenohumeral joint due to the shoulder muscles, and (3) contact pressure between the humeral head and glenoid produced as a result of external force. The scores for this strain index were found to be significantly affected by the direction and level of force exertion and indicated that the force exertions performed in the mediolateral direction are more strenuous than the other directions. The proposed stress index could potentially have application in the occupational setting for the assessment of forceful arm exertions that may increase the risk of shoulder MSDs.

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