Document Type

Dissertation

Date of Degree

Fall 2014

Degree Name

PhD (Doctor of Philosophy)

Degree In

Industrial Engineering

First Advisor

Nathan Fethke

Second Advisor

Geb Thomas

Abstract

Epidemiological evidence suggests an association between exposure to non-neutral working postures and work-related musculoskeletal disorders (MSDs) of the low back and shoulder. Accurate and precise quantitative estimation of exposure to non-neutral working postures is, therefore, essential for evaluating worker risk, developing and testing ergonomic interventions, and improving worker health and well-being. Current methods used to directly estimate occupational exposure to non-neutral postures may be obtrusive, often lack sufficient portability for field use, and have limited accuracy and precision when used to measure dynamic or complex motions.

Inertial measurement units (IMUs) are emerging instrumentation devices that measure and report an object's orientation and motion characteristics using multiple electromechanical sensors (i.e., accelerometers, gyroscopes, and/or magnetometers). They have been observed to accurately monitor body kinematics over periods of relatively short duration in comparison to laboratory-based optical motion capture systems. Limited research, however, has been performed comparing exposure information obtained with IMUs to exposure information obtained with other field-capable direct measurement exposure assessment methods. Furthermore, insufficient information on the repeatability of IMU-based estimates over a substantial time period (e.g., a full work shift) and inadequate knowledge regarding the effects of different IMU sensor configurations and processing methods on the accuracy and repeatability of estimates of exposure obtained with IMU systems contributes to a lack of their use in epidemiological field studies.

This thesis was designed to address these issues and expand upon the current scientific literature regarding the use of IMU sensors as direct measurement devices for assessing exposure to non-neutral working postures in the field. Chapter I provides a background and justification for the work. Chapter II presents the findings of a laboratory-based, manual material handling study that was performed to compare estimates of thoracolumbar trunk motion obtained with a commercially available IMU system with estimates of thoracolumbar trunk motion obtained with a field-capable reference system, the Lumbar Motion Monitor (LMM). The effects of alternative sensor configurations and processing methods on the agreement between LMM and IMU-based estimates of trunk motion were also explored. Chapter III presents the results of a study performed to evaluate the accuracy and repeatability of estimates of trunk angular displacement and upper arm elevation obtained with the IMU system examined in Chapter II over the course of an eight-hour work shift in both a laboratory and field-based setting. The effects of alternative sensor configurations and processing methods on the accuracy and repeatability of estimates of trunk angular displacement and upper arm elevation obtained with the IMU system were also studied. Chapter IV presents the results of a randomized, repeated measures intervention that demonstrates the utility of the IMU system examined in Chapters II and III as a direct measurement instrument for comparing "ergonomic" and conventional examination equipment commonly used by ophthalmologists. Finally, Chapter V summarizes the major findings, discusses their practical implications, and provides suggestions for future research.

Public Abstract

Low back pain and disorders of the shoulder are among the most common and expensive of all occupational injuries and illnesses. Gaining a better understanding of how and why workers develop these conditions is important for protecting worker safety, health, and well-being. Current methods used to measure occupational exposure to non-neutral working postures, a common risk factor associated with low back pain and shoulder disorders, in a real work environment are lacking. Novel technology has recently become available that may be better suited for measuring occupational exposure to non-neutral working postures than previous methods. However, limited research has been conducted to evaluate this technology for use in real work environments.

The aims of this thesis were, therefore, to (i) evaluate the accuracy and repeatability of the novel technology designed to estimate exposure to non-neutral working postures, (ii) explore the effects of wearing the technology in slightly different configurations and using different data processing options on its accuracy and repeatability, and to (iii) demonstrate the effectiveness of the technology by applying it in a study comparing old work equipment with innovative work equipment designed to reduce the development of disabling low back and shoulder conditions in healthcare workers. Results of the thesis showed that the novel technology may be used to accurately and repeatedly estimate exposures to non-neutral working postures in studies involving real work environments. Researchers can now more confidently use this technology in studies designed to better understand the reasons why people develop disabling low back and shoulder conditions.

Keywords

publicabstract, inertial measurement, low back pain, musculoskeletal disorders, posture, shoulder disorder

Pages

xii, 117 pages

Bibliography

Includes bibliographical references (pages 95-117).

Copyright

Copyright 2014 Mark Christopher Schall

Share

COinS