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Back to the Future of Ergonomics: Utilizing Inertial Motion Capture and Fatigue Failure Theory to Develop a Cumulative Damage Assessment Method for Estimating Risk of Low Back Injury in Industrial Settings




Nail Ulloa, Iván Enrique

Type of Degree

PhD Dissertation


Industrial and Systems Engineering

Restriction Status


Restriction Type

Auburn University Users

Date Available



The central objectives of this dissertation are to critically evaluate the efficacy of a wireless sensor Inertial Motion Capture (IMC) system in estimating lumbar kinematics and kinetics within a controlled laboratory setting and to apply the IMC system in a manufacturing facility for data acquisition. Furthermore, it focuses on formulating and assessing a model based on fatigue failure theory for estimating cumulative damage to the lower back using continuous exposure data in a live manufacturing environment. In the first study, "Assessing the Accuracy of a Wireless Sensor System for Estimating Lumbar Moments During Manual Lifting Tasks Considering the Effects of Load Weight, Asymmetry, and Height," the IMC system's accuracy is evaluated for estimating 3D moments at the L5/S1 joint during manual lifting tasks with load weight, asymmetry, and height variations. The analysis compares IMC-derived estimates to those obtained through bottom-up and top-down laboratory models using an Optical Motion Capture (OMC) and Force Plate (FP) system. This investigation establishes the benefits and limitations of the IMC system in terms of lumbar moment assessments. The second study, "Estimating Compressive and Shear Forces at L5-S1: Exploring the Effects of Load Weight, Asymmetry, and Height using Optical and Inertial Motion Capture Systems", extends the examination to compression and anteroposterior shear forces at the L5/S1 joint. The IMC estimates are compared against a top-down laboratory musculoskeletal model using an OMC system, and additional kinematic variables such as trunk rotation, flexion, and lateral bending are assessed to understand discrepancies in force estimations. Moreover, an analysis of the distance between the handled box and the L5/S1 joint center is included to estimate segment length differences comprehensively. In the third study, "Development of a Fatigue-Failure Based Continuous Risk Assessment Method for the Low Back Region Using Inertial Motion Capture Technology", the focus shifts to a real-world manufacturing environment, where a novel framework for processing IMC-collected data to estimate cumulative lumbar loading is developed and evaluated. Utilizing fatigue failure theory, cumulative damage is computed based on continuous low-back loading time-series data, offering an innovative approach to analyzing kinematic data and assessing cumulative loading exposure in complex real-world scenarios. Overall, this body of work showcases the promising capabilities of IMC technology in lumbar kinematics and kinetics assessments while also introducing a pioneering approach for cumulative damage estimation. It also emphasizes the necessity for ongoing advancements in sensor technology and data processing methodologies to enhance accuracy and applicability in laboratory and field environments.