ORCID Identifier(s)


Graduation Semester and Year




Document Type


Degree Name

Doctor of Philosophy in Industrial Engineering


Industrial and Manufacturing Systems Engineering

First Advisor

Imrhan Sheik

Second Advisor

Mark D Ricard


Background: The most significant causes of lower back injuries at work are probably from manual lifting activities. Lifting unstable loads pose a significant strain to the lower back and can cause debilitating lumbar spine injuries. The primary function of the vertebral column is to support the upper body. The L5/S1 disc junction located between the lumbar and the sacral regions of the vertebral column is the most critical joint in spine with respect to lifting strain. Because of its position and the amount of upper body weight it handles, it is particularly vulnerable to misalignment, wear and tear, and injury.Lifting loads has several adverse effects on the back: spinal compression and excessive strain on the back’s tendons and ligaments may result in herniated or ruptured discs,disc degenerations, spinal stenosis, and other diseases. Biomechanical models have been developed to estimate the forces in the lumbar spine to determine the severity of lifting tasks, and NIOSH has developed an equation to determine a safe lifting load weight. However, neither covers all important types of lifting conditions adequately.The NIOSH equation does not include the lifting load type (stable versus unstable loads) as a variable due to insufficient research information, and the measurement of spinal force and body motion variables still need improvements to adequately measure and assess the severity of lifting unstable loads asymmetrically.Objective: The main objective of this study is to demonstrate a new method to measure compression, shear, and torque forces in L5/S1 disc when lifting unstable loads under different lifting conditions (load type, lifting style, and lifting speed). Methods: A total of 3 subjects volunteered for this study to lift a bin, partly filled with water, with various lifting conditions while standing on force plates. Each subject lifted the bin (stable and unstable load) at two different speeds (normal and fast), and along two different planes of the body (sagittal and frontal) – a total of 8 lifting conditions. The water induced the required instability in the load during lifting. For simulating stable loads (of the same weight – 30 lb) solids replaced water in the same bin. Body joint angles, velocities, accelerations (using a visual 3D Vicon camera system), and forces from force plates and load cells along with 12 electromyography (EMG) signals for detecting muscle contractions were used to determine compression, shear and lateral forces on the L5/S1 disc. To get a more precise force impact on the L5/S1 disc, a technical coordinate system was created to define the orientation of the L5/S1 disc. A bottom-up approach of Newton-Euler dynamics was used using visual 3D software to estimate compression, shear, and torque force on estimated virtual landmark of L5/S1disc. Results: This study has provided an alternative method to measure compression, shear,and torque forces at estimated location of L5/S1 disc proximal to the technical virtual landmarks. The results have shown to be consistent with other published research papers.


L5/S1 compression disc, Unstable loads, Asymmetrical lifting


Engineering | Operations Research, Systems Engineering and Industrial Engineering


Degree granted by The University of Texas at Arlington