Low back pain is the number one cause of disability in the world. It is a well established problem in industry often caused by excessive repetition, awkward postures, and heavy lifting. Back support exoskeletons have increasingly been studied as a solution to this problem. In addition to evaluating exoskeletons, giving some focus to the various lifting styles themselves can also provide some insight into ameliorating this problem. Research evaluating warehouse workplace postures has found that workers switch between a variety of tasks and many different lifting styles, beyond the standard squat and stoop postures, on a daily basis. This dissertation is primarily a compilation of three papers. The first focuses on the VTLowe's exoskeleton and the kinematic differences found during Stoop, Squat, and Freestyle lifting. These lift styles were evaluated while the study participants lifted boxes weighing 0% or 20% of their body weight both With and Without the exoskeleton. Evaluating the kinematic results showed that wearing the exoskeleton resulted in a 1.5 degree increase in ankle dorsiflexion, a 2.6 degree decrease in knee flexion, and a 2.3 degree decrease in SHK angle. Subjects' shoulder, elbow, and wrist heights were slightly higher while wearing the exoskeleton, and they lifted slightly more slowly while wearing the exoskeleton. Subjects moved more quickly while bending down as compared to standing up, and with the 0% bodyweight box as compared to the 20% bodyweight box. The values for Freestyle lifts generally fell in between Squat and Stoop lift styles or were not significantly different from Squat. EMG data (analyzed in a different study) from the leg muscles had relationships with torso torque while the back and stomach muscles showed no significant relationships. Exoskeleton efficacy research has a strong focus on Stoop, Squat, and Freestyle lifting. However, asymmetric styles such as One Legged lifting and Kneeling were found to be frequently used lifting styles in a warehouse setting. The second paper in this dissertation focuses on variations of asymmetric lifts while lifting light objects including Split Legged, Heel Up, One Legged, Kneeling, Asymmetric Squat, Bent Over (a freestyle task) and Bend Walk (picking up bean bags from the ground while walking forward and maintaining a bent over posture). These lift styles can be found not only in industry, but in any individual's daily life such as when it comes to picking up a dropped pen or sorting toys in a bin on the floor. Evaluating Split Legged, Heel Up, and One Legged found that many of the significant differences in muscle activity are dependent on the lifting stance (whether the front foot is on the same side or opposite side as the hand used to pick up objects). Combining the results that same side lifts have greater muscle imbalance in the iliocostalis and overall back muscle activity is greater in Split Legged than in Heel Up or One Legged suggests that One Legged or Heel Up in an Opposite side stance are the best options in regards to minimizing back muscle activity. Although there is a trade-off with the biceps femoris for these lift styles, back injuries are far more prevalent and supporting the back takes priority over minimizing muscle activity in the legs. The analysis for Asymmetric Squat, Bend Walk, Bent Over, and Kneeling was divided into three portions: bending down, picking bags, and rising up. Relevant differences between the lift styles for these portions were seen in the biceps femoris, longissimus, and rectus abdominis, with Bend Walk generally being the most taxing activity. Overall, there were minimal differences while rising up from any of these postures with most changes seen in the biceps femoris. Rising Up also generally had a higher peak muscle activity compared to bending down or picking bags. The final paper in this dissertation evaluates the effect of a different back exoskeleton with the variety of lift styles studied in the second paper. It is important to see how exoskeleton use aids or harms many of the lift styles commonly used by industry workers. Lift side was once again a factor in the Split Legged, Heel Up, and One Legged tasks. Participants benefited more from the exoskeleton in same side lifts as opposed to opposite side. For Asymmetric Squat, Bend Walk, Bent Over, and Kneeling greater benefits were seen in the back and leg muscles while rising up as opposed to bending down. Focusing on the peak of the lift (taken at the peak of bending down for the more static postures) found that the exoskeleton had more significant differences for Split Legged, Heel Up, and One Legged compared to Asymmetric Squat, Bend Walk, Bent Over, and Kneeling. One highly important aspect in evaluating exoskeletons is determining the subject population that would most benefit from its use. Focusing on body mass, the longissimus saw decreased benefits as the body mass increased, with subjects under 75 kg benefiting the most from the exoskeleton, while the iliocostalis and biceps femoris typically saw the opposite effect when results were significant (i.e., heavier subjects benefited the most). / Doctor of Philosophy / Low back pain is the number one cause of disability in the world. It is a well established problem in industry often caused by excessive repetition, awkward postures, and heavy lifting. Back support exoskeletons have increasingly been studied as a solution to this problem. In addition to evaluating exoskeletons, giving some focus to the various lifting styles themselves can also provide some insight into ameliorating this problem. Research evaluating warehouse workplace postures has found that workers switch between a variety of tasks and many different lifting styles, beyond the standard squat and stoop postures, on a daily basis. This dissertation is primarily a compilation of three papers. The first focuses on the VTLowe's exoskeleton and the differences in how people move while wearing the exoskeleton during Stoop, Squat, and Freestyle lifting. These lift styles were evaluated while the study participants lifted boxes weighing 0% or 20% of their body weight both With and Without the exoskeleton. This resulted in small changes in the ankle, knee, and hip angles. Subjects' shoulder, elbow, and wrist heights were slightly higher while wearing the exoskeleton, and they lifted slightly more slowly while wearing the exoskeleton. Subjects moved more quickly while bending down as compared to standing up, and with the 0% bodyweight box as compared to the 20% bodyweight box. The values for Freestyle lifts generally fell in between Squat and Stoop lift styles or were not significantly different from Squat. Electromyography (muscle activity) data, analyzed in a different study, from the leg muscles had relationships with torso torque while the back and stomach muscles showed no significant relationships. Exoskeleton efficacy research has a strong focus on Stoop, Squat, and Freestyle lifting. However, asymmetric styles (i.e., where one side of the body is doing something different from the other side) such as One Legged lifting and Kneeling were found to be frequently used in a warehouse setting. The second paper in this dissertation focuses on variations of asymmetric lifts while lifting light objects including Split Legged, Heel Up, One Legged, Kneeling, Asymmetric Squat, Bent Over (a freestyle task) and Bend Walk (picking up bean bags from the ground while walking forward and maintaining a bent over posture). These lift styles can be found not only in industry, but in any individual's daily life such as when it comes to picking up a dropped pen or sorting toys in a bin on the floor. Evaluating Split Legged, Heel Up, and One Legged found many of the significant differences in muscle activity are dependent on the lifting stance (whether the front foot is on the same side or opposite side as the hand used to pick up objects). The results found that there were different imbalances between the sides of the body depending on the specific lift style examined. Overall, the muscle activity results suggest that One Legged or Heel Up in an Opposite side stance are the best options in regards to minimizing back muscle activity. While leg muscle activity does increase for these lift styles, back injuries are far more prevalent and supporting the back takes priority over minimizing muscle activity in the legs. The analysis for Asymmetric Squat, Bend Walk, Bent Over, and Kneeling was divided into three portions: bending down, picking bags, and rising up. Overall, Bend Walk was the most taxing of those activities. The final paper in this dissertation evaluates the effect of a second back exoskeleton with the variety of lift styles studied in the second paper. It is important to see how exoskeleton use aids or harms many of the lift styles commonly used by industry workers. Participants benefited more from the exoskeleton in same side lifts as opposed to opposite side. For Asymmetric Squat, Bend Walk, Bent Over, and Kneeling greater benefits were seen in the back and leg muscles while rising up as opposed to bending down. The exoskeleton helped Split Legged, Heel Up, and One Legged more than Asymmetric Squat, Bend Walk, Bent Over, and Kneeling. One highly important aspect in evaluating exoskeletons is determining the subject population that would most benefit from its use. One of the back muscles saw decreased benefits as the body mass increased, with subjects under 75 kg benefiting the most from the exoskeleton, while another back muscle and the legs typically saw the opposite effect.

Patients returning to sport after anterior cruciate ligament (ACL) reconstruction surgery currently have a high risk for sustaining a second ACL injury and having early signs of knee osteoarthritis. Assessing lower extremity kinetics and kinematics during landing can provide information about a patient's risk for sustaining a second ACL injury and having further joint trauma. However, currently accepted methods to assess kinetics and kinematics are not feasible to use in most non-research settings as they are expensive, time consuming, and take up a lot of space. The goal of this project was to identify methods to assess landing mechanics which are reliable and feasible to use in non-research settings. First, we found that the loadsol®, a wireless force sensing shoe insole, is valid relative to embedded force plates and repeatable between days for assessing kinetics and kinetic symmetry during bilateral and unilateral landing tasks. Second, we developed a new method to collect continuous kinematic data using a low-cost videocamera, disposable markers, and an automated point tracking program. This method was validated against a 3D motion capture system for measuring a fixed angle and for measuring sagittal plane running kinematics. Third, we found that the new video analysis method is valid relative to 3D motion capture and is repeatable between days for assessing frontal and sagittal plane knee kinematics during landing. Finally, we used the loadsol® and automated 2D video analysis to assess landing mechanics in both patients following ACL reconstruction and healthy uninjured control participants in a non-research setting. We found that, relative to controls, patients following ACL reconstruction had reduced kinetic symmetry during bilateral landing, where they offloaded their surgical limb and relied more heavily on their non-surgical limb. Additionally, patients following ACL reconstruction had reduced knee flexion range of motion symmetry during unilateral landing, where they had reduced knee flexion when landing on their surgical limb. Collectively, these projects developed methods to quantitatively assess landing mechanics that are feasible to use in non-research settings, documented the validity and between-day repeatability of these methods, and demonstrated that they could be used to identify kinetic and kinematic deficits in patients following ACL reconstruction. This project is an important step toward being able to assess landing mechanics in patients recovering from an ACL reconstruction. / Doctor of Philosophy / The anterior cruciate ligament (ACL) is a bundle of connective tissue that helps stabilize the knee joint. ACL injuries are common in sport, and ACL reconstruction surgery is the most widely used treatment strategy for patients who wish to return to playing sports. Unfortunately, even after ACL surgery and rehabilitation, many patients who return to sport wind up getting hurt again and developing severe joint pain down the road. Previous research has identified movement and loading patterns which are associated with this increased risk for further injury in patients following ACL reconstruction. For example, patients who have increased asymmetry when landing from a jump, where they shift weight away from their surgical limb and towards their non-surgical limb, have an increased likelihood of sustaining a second ACL injury to either their surgical or non-surgical leg. Assessing movement during rehabilitation could help identify patients who exhibit poor movement mechanics and improve movement to reduce their risk for second injuries. However, there are not currently methods available to reliably assess movement that are feasible for widespread use in non-research settings (i.e. physical therapy clinics). The purpose of this project was to identify and develop methods to assess movement which are accurate and feasible to use in a clinical setting. In this dissertation, we first determined the accuracy of using wireless force sensing shoe insoles to measure how hard and how symmetrically people contact the ground when they land from a jump. Second, we developed a new method to measure knee motion using videos collected with low-cost cameras (e.g. iPad), and determined the accuracy of this method compared to a three-dimensional motion capture system. For the last part of this dissertation we demonstrated that the aforementioned methods could be used to identify deficits in landing mechanics in patients following ACL reconstruction in a non-research setting. When comparing ACL reconstruction patients with uninjured controls, we found movement and loading asymmetries which were expected and which are associated with the risk for second ACL injuries and early onset knee osteoarthritis. This project is an important step towards being able to assess landing mechanics in patients recovering from an ACL reconstruction, which could improve our ability to prevent subsequent injuries in this clinical population.

Every year, more than 2.4 million eye injuries occur in the United States, with over 30,000 of those injured left blind in at least one eye as a result. Computer modeling is one of the most versatile ways to study ocular trauma, however, existing models lack accurate stress and strain properties for ocular globe rupture. A pressure system was built to examine static and dynamic globe rupture pressures for healthy postmortem human and porcine (pig) eyes. Maximum rupture stress for the quasi-static tests was found to be 11.17MPa for human tissue and 12.08MPa for porcine tissue, whereas stress for the dynamic tests was found to be 30.18MPa for human tissue and 26.01MPa for porcine tissue. Maximum rupture stress results correlate well with static material properties used in published research (9.4MPa), and dynamic properties of 23MPa found in published research. Healthy postmortem human eyes were ruptured statically and dynamically to determine the relationship between stress and strain for the ocular globe under intraocular pressure loading. Stress-strain relationships were investigated and values for the elastic modulus were found to be slightly lower than that previously published. This research shows that it is important to differentiate between tissue type, and static versus dynamic failure properties before drawing conclusions from computer models and other published research. Now that rupture can be accurately determined, safety systems designed to protect eyesight in automotive, sports, and military applications can also be applied to protect the quality of life for humans in these applications. / Master of Science

Psychophysics is defined as the scientific study of the relationship between stimuli and sensation. It has been used extensively over the last three decades for evaluation and design of manual materials handling tasks in many industries. Despite this, much is still not known about how subjective ratings, the core of the psychophysical methodology, relate to physical (biomechanical) loads. A fundamental assumption of this method is that humans are capable of estimating biomechanical and physiological loads that are placed on the body. Based on this assumption, estimates that are obtained through the methodology are used as an indicator of physical loads and stresses, and are assumed to be related to injury risk. An experiment was performed to achieve two primary goals:1) determine the correspondence between biomechanical loads (moments at the elbow, shoulder and torso) and subjective ratings of joint loads, as well as subjectively determined maximal loads and 2) determine whether any particular joint (i.e. low back, shoulder, elbow) is the limiting factor when a subject determines a maximally acceptable load. Participants were instructed to pose in four different postures, one serving as a baseline (neutral, or 'familiar') posture, while the remaining three varied moments at the elbow, shoulder and torso. While in each of these postures, participants determined a maximum acceptable static load (MASL). Ratings of perceived exertions for specific joints were also reported, as well as whole body ratings while supporting various fractions of the MASL. Experimental findings indicated that subject and posture effects neared significance as main effects on the magnitude of MASL. Strength was shown to be, at best, a weak predictor of MASL. Though no conclusive evidence was found to indicate that a specific joint is the limiting factor when determining maximum acceptability, trends in the data suggested that the low back and shoulder are possible candidates. Overall, the results of the study indicated that humans consider more than simple joint moments when forming perceptions of efforts and acceptability during static load handling. / Master of Science

A flexible and passive exoskeleton is presented in this paper. The exoskeleton uses carbon fiber beams to provide an energetic return to its wearer and relieve their lower back muscles. The design of the exoskeleton and potential elastic mechanisms are described, and the results of biomechanical testing are given. The exoskeleton decreased the erector spinae muscle activity by 21-39.7%. / MS / A flexible and passive wearable device, or exoskeleton, is presented in this paper. Utilizing carbon fiber beams, the un-powered exoskeleton provides assistance to the wearer during lifting. By storing energy as the wearer bends and returning it to the body as they straighten, the muscles have to work less. If muscles work less, then the risk of low back pain or low back disorders hopefully decreases. The design of the exoskeleton, tradeoffs between different types of springs to store energy, and the results of biomechanical testing are presented. The exoskeleton decreased the amount the low back muscles worked by 21-39.7%.

As computational power has increased, computational modeling has become a very promising tool to model the biomechanics of complex joint systems. Musculoskeletal computational models have become more complex when compared to original iterations which utilized a number of simplifications. This thesis utilized a three-dimensional computational model of the wrist joint structure to investigate scapholunate kinematics. The model accurately represented the bony anatomy of the wrist and hand and represented soft tissue structures such as ligaments, tendons, and other surrounding tissues. Creation of the model was done using commercially available computer-aided design and medical image processing software, and utilized the rigid body modeling methodology. It was validated for scapholunate kinematics against a cadaver study and then utilized to investigate further measures and surgical procedures. The simulations performed by the model demonstrated an accurate anatomical response of wrist function. As better understanding of the biomechanics of the wrist joint is achieved, this model could prove to be an important tool to further investigate wrist mechanics.

Intervertebral disc (IVD) degeneration is strongly associated with back pain, and affects approximately 60% of the population by age 70. Furthermore, it has been suggested that this degeneration may play an important role in the initiation or perpetuation of vertebral fractures. Given that the IVD is a primary load-bearing structure in the spine, the change of intradiscal pressure (IDP) over time that accompanies disc degeneration provides a functional measure of the disease pathology. Studies show that both an overall decrease in IDP magnitude and changes in the spatial distribution of IDP are found with increasing levels of degeneration. Thus, the overall goal of this study was to determine the correlation between the spatial distributions of IDP, as measured along both mid-sagittal and mid-coronal paths, and a clinically feasible assessment of disc health. Disc degeneration was assessed non-invasively using quantitative computed tomography (QCT). A custom, electro-mechanical device was designed, manufactured and assembled to measure IDP distributions. The results indicated that the spatial distribution of IDP was most homogenous for the nucleus pulposus (NP) region regardless of load type and disc health grade. Mean IDP tended to be lowest in severely degenerated discs, consistent with earlier findings that axial loads in spinal columns with degenerated IVDs shift from the disc to the neural arch in both flexural and erect postures.

While Lisfranc injuries in the mid foot are less common than other ankle and mid foot injuries, they pose challenges in both properly identifying them and treating them. When Lisfranc injuries are ligamentous and do not include obvious fractures, they are very challenging for clinicians to identify unless weight bearing radiographs are used. The result is that 20%-40% of Lisfranc injuries are missed in the initial evaluation. Even when injuries are correctly identified the outcomes of surgical procedures remain poor. Existing literature has compared the different surgical procedures but has not had a standard approach or procedures across studies. This study uses a computational biomechanical model validated on a cadaveric study to evaluate factors that impact injury presentation and to compare the different procedures ability to stabilize the Lisfranc joint after an injury. Using SolidWorks® a rigid body kinematic model of a healthy human foot was created whereby the 3D bony anatomy, articular contacts, and soft tissue restraints guided biomechanical function under the action of external perturbations and muscle forces. The model was validated on a cadaveric study to ensure it matched the behavior of a healthy Lisfranc joint and one with a ligamentous injury. The validated model was then extended to incorporate muscle forces and different foot orientations when simulating a weight bearing radiograph. The last section of work was to compare the stability of four different surgical repairs for Lisfranc injuries. These procedures were three open reduction and internal fixation (ORIF) procedures with different hardware (screws, screws and dorsal plates, and endobuttons) and primary arthrodesis with screws. They required use of finite element analysis which was performed in Ansys Workbench. For the presentation of injuries, both muscle forces and standing with inversion or eversion could reduce the diastasis (separation) observed for weight bearing radiographs and thus confuse the diagnosis. When comparing the different surgical procedures, the ORIF with screws and primary arthrodesis with screws showed the most stable post-operative Lisfranc joint. However, the use of cannulated screws for fixation showed regions of high stress that may be susceptible to breakage. A challenge in the literature has been the use of different experimental designs and metrics when comparing two of the possible procedures for a Lisfranc injury head to head. This study has been able to benchmark four procedures using the same model and set of metrics. Since none of the existing procedures showed consistently good to excellent patient outcomes, more procedures could be proposed in the future. If this were to occur, this study offers a standard procedure for benchmarking the new procedure’s post-operative mechanical stability versus those procedures currently in use.

<p>Pediatric cervical spinal injuries are associated with high morbidity and mortality. Cervical injuries observed in the pediatric population appear to be age dependent with younger children experiencing more upper cervical level injuries compared to increased lower level cervical injury patterns to older children. The majority of pediatric cervical spinal injuries are motor vehicle crash related. Current progress in child occupant protection, including increased and proper restraint usage continues to reduce serious injury and fatalities to child occupants. However, improper restraint usage and incorrect child seating location, especially with children transitioning from rear-facing child restraints to forward-facing restraints is still a concern. Continued reductions in serious injury and fatalities to child occupants in survivable motor vehicle crashes will be based on continued education and improvements in child anthropometric test devices, child computational injury models and child restraint system design. Improvements in all of these categories are dependent on an improved understanding of the developmental biomechanics of the human cervical spine. Currently, limited data exist on human child neck biomechanics and none of the current cadaveric work has evaluated the biomechanical response over the entire age spectrum from birth to young adulthood. Numerous surrogate studies exist and have formed the basis of child injury criteria and developmental biomechanics, but have not been assessed in relation to the response of the pediatric human cervical spine. The current work investigates the biomechanics of the osteoligamentous human cervical spine from birth to young adulthood under tensile and bending loading environments. Tensile low-load and load-to-failure stiffness, load-to-failure, and flexion-extension bending stiffness increased with age. Tensile normalized displacement at failure and total bending low-load range of motion decreased with age. Viscoelastic rate effects are present in the pediatric cervical spine and are modeled with quasi-linear viscoelasticity. Peak load and loading energy increases with increased loading rate, while hysteresis energy is rate insensitive at lower loading rates, but increases at higher rates of loading. These data establish structural response behavior and injury thresholds for the osteoligamentous cervical spine by age. Additionally, they provide human data to assess the appropriateness of current surrogate models and current scaling techniques associated with these models. Finally, these data provide human response by age useful in progressing the biofidelity of computational and physical models for child occupant protection.</p> / Dissertation

Fishes are the most speciose group of living vertebrates, making up more than half of extant vertebrate diversity. They have evolved a wide array of swimming modes and body forms, including the batoid elasmobranchs, the dorsoventrally flattened skates and rays, which swim via oscillations or undulations of a broad pectoral fin disc. In this work I offer insights into locomotion by an undulatory batoid, freshwater stingray Potamotrygon orbignyi (Castelnau, 1855), combining studies of live animals, physical models, and preserved specimens. In Chapter 1, I quantify the three-dimensional kinematics of the P. orbignyi pectoral fin during undulatory locomotion, analyzing high-speed video to reconstruct three-dimensional pectoral fin motions. A relatively small portion (~25%) of the pectoral fin undulates with significant amplitude during swimming. To swim faster, stingrays increase the frequency, not the amplitude of propulsive motions, similar to the majority of studied fish species. Intermittently during swimming, a sharp, concave-down lateral curvature occurred at the fin margin; as the fin was cupped against the pressure of fluid flow this curvature is likely to be actively controlled. Chapter 2 employs a simple physical model of an undulating fin to examine the ground effects that stingrays may experience when swimming near a substrate. Previous research considering static air- and hydrofoils indicated that near-substrate locomotion offers a benefit to propulsion. Depending on small variations in swimming kinematics, undulating fins can swim faster near a solid boundary, but can also experience significant increases (~25%) in cost-of-transport. In Chapter 3, I determine how pectoral and pelvic fin locomotion are combined in P. orbignyi during augmented punting, a hybrid of pectoral and pelvic fin locomotion sometimes employed as stingrays move across a substrate. The timing of pectoral and pelvic fin motions is linked, indicating coordination of thrust production. Chapter 4 discusses pectoral fin structure and morphological variations within the fin, correlating morphology with the swimming kinematics observed in Chapter 1. Passive and active mechanisms may stiffen the anterior fin to create the stable leading edge seen during swimming; stingrays have converged on several structural features (fin ray segmentation and branching) shared by actinopterygian fishes.