Human Physiology Theses and Dissertations

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Open Access
Assessing Inter-joint Coordination during Walking
(University of Oregon, 2012) Chiu, Shiu-Ling; Chiu, Shiu-Ling; Chou, Li-Shan
Coordination indicates the ability to assemble and maintain a series of proper relations between joints or segments during motions. In Dynamical Systems Theory (DST), movement patterns are results of a synergistic organization of the neuromuscular system based on the constraints of anatomical structures, environmental factors, and movement tasks. Human gait requires the high level of neuromuscular control to regulate the initiation, intensity and adaptability of movements. To better understand how the neuromuscular system organizes and coordinates movements during walking, examination of single joint kinematics and kinetics alone may not be sufficient. Studying inter-joint coordination will provide insights into the essential timing and sequencing of neuromuscular control over biomechanical degrees of freedom, and the variability of inter-joint coordination would reflect the adaptability of such control. Previous studies assessing inter-joint coordination were mainly focused on neurological deficiencies, such as stroke or cerebral palsy. However, information on how inter-joint coordination is modulated with different constraints, such as walking speeds, aging, brain injury or joint dysfunctions, are limited. This knowledge could help us in identifying the potential risks during walking and improve the performance of individuals with movement impairments. The purpose of the present study was to investigate the properties of inter-joint coordination pattern and variability during walking with different levels of neuromuscular system perturbations using a DST approach, including an overall neuromuscular systemic degeneration, a direct insult to the brain, and a joint disease. We found that aging seemed to reduce the pattern adaptability of neuromuscular control. Isolated brain injury and joint disease altered the coordination pattern and exaggerated the variability, indicating a poor neuromuscular control. To improve gait performances for different populations, clinical rehabilitation should be carefully designed as different levels of neuromuscular system constraints would lead to different needs for facilitating appropriate coordinative movement. This dissertation includes both previously published/unpublished and coauthored material.
Open Access
Clinical and Laboratory Balance Assessment in the Elderly
(University of Oregon, 2013-07-11) Chen, Tzurei; Chou, Li-Shan
Falls can have severe consequences for elderly adults. In 2000, nearly 10,300 people aged 65 years or older died as a result of falls, and 2.6 million individuals were treated for non-fatal fall-related injuries. In order to reduce fall incidences, it is important to identify possible causes of falls, such as muscle weakness and imbalance. In this study, we examined balance control in the elderly during task transitions while performing the Timed Up and Go test (TUG). The TUG is a commonly used clinical balance test that includes transition phases between three daily activity tasks: sit-to-stand, walking and turning. Our findings suggested that elderly adults, especially fallers, have reduced balance control ability while making transitions during TUG. During sit-to-walk (STW), when compared to young adults, elderly adults demonstrated a smaller forward center of mass (COM) velocity, a smaller anterior-posterior (A-P) COM-Ankle angle, and a larger upward kinetic energy ratio at seat-off. Additionally, the medial-lateral COM control in elderly fallers was also perturbed due to their significant reduction in forward COM velocity. The reduced initial hip extensor moment and increased ankle plantarflexor moment in elderly fallers was associated with their reduced generation of horizontal momentum during STW. Smaller A-P COM-Ankle angles and taking more steps when making a turn demonstrated a reduction in balance control ability in elderly adults. Our analyses suggest that balance control is an important factor contributing to longer STW and turning durations of TUG. Furthermore, lower extremity muscle strength at hip and knee joints demonstrated a stronger association with STW than turning duration. To enhance the early detection of fall risk, we also assessed the ability of balance tests to predict future risk of falling in elderly adults. Our results indicated that biomechanical balance parameters measured during TUG were associated with future fall status. Among all biomechanical parameters investigated, frontal plane balance control parameters appear to be the most significant predictors for future falls. This dissertation includes unpublished co-authored material.
Open Access
Detecting Gait Imbalance Following Concussion Using an Inertial Measurement Unit
(University of Oregon, 2020-02-27) Pitt, William; Chou, Li-Shan
Concussion injury is shown to result in acutely impaired dynamic balance control. This impairment can last as long as two months post injury as evidenced by biomechanical metrics derived from data collected during dual-task (DT) gait using camera-based motion capture system. However, clinical application of such DT gait balance control with advanced kinematic analysis is yet limited. To advance the clinical translation of the laboratory findings to clinical practice, four studies were conducted to assess the utility of an inertial measurement unit (IMU) to detect gait imbalance following concussion. In the first study, a highly consistent and reliable DT assessment was developed using off the shelf hardware and software. Acceleration based kinematic markers collected from a single IMU placed over the fifth lumbar vertebra (L5) demonstrated potential for detecting subtle changes in gait balance control at a university sport medicine facility. In the second study the DT gait balance control of individuals sustaining an acute concussion was analyzed with the assessment and compared to that of healthy matched controls over a two month post injury period. Multiple-gait event specific accelerations and angular velocities collected from the L5 sensor were capable of detecting impaired gait balance control. In the third study, logistic regression models including groups of between three and six kinematic and neurocognitive metrics collected from both straight and turning gait were shown to have high sensitivity (Sn) and specificity (Sp) in distinguishing acutely concussed from healthy individuals. Furthermore, these models maintained moderate Sn and Sp throughout the two month post injury period suggesting they are capable of identifying individuals with lingering balance control deficits. In the fourth study, the utility of dual-task cost (DTC) metrics derived from the kinematic and neurocognitive measures was assessed for post-concussion gait imbalance detection. It was determined that due to high levels of variability inherent to the metrics in this application, their utility in gait imbalance detection is limited, and are similarly unable to be used to describe differences or changes in task prioritization. This dissertation includes co-authored work either previously published or unpublished.
Open Access
Dynamic Limits of Balance Control during Daily Functional Activities Associated with Falling
(University of Oregon, 2012) Fujimoto, Masahiro; Fujimoto, Masahiro; Chou, Li-Shan
Falls are one of the most serious problems among the elderly, resulting in fatal physical injuries. Early identification of people at a high risk of falling is needed to facilitate rehabilitation to reduce future fall risk. The overall goal of this dissertation was to develop biomechanical models that identify dynamic limits of balance control in daily functional activities associated with falling, including sit-to-stand (STS) movement, standing (stance perturbation), and walking. Poor performance of STS movement has been identified as one of the risk factors of falls among elderly individuals. We proposed a novel method to identify dynamic limits of balance control during STS movement using whole body center of mass (COM) acceleration and assessed its feasibility to differentiate individuals with difficulty in STS movement from healthy individuals. The results demonstrated that our model with COM acceleration could better differentiate individuals with difficulty in STS movement from healthy individuals than the traditional model with COM velocity. Poor postural control ability is also a risk factor of falls. Postural recovery responses to backward support surface translations during quiet standing were examined for healthy young and elderly adults. The results demonstrated that functional base of support (FBOS) and ankle dorsiflexor strength could be sensitive measures to detect elderly individuals with declined balance control. Our biomechanical model, which determines a set of balance stability boundaries, showed a better predictive capability than the statistical model for identifying unstable balance recovery trials, while the statistical model better predicted stable recovery trials. Lastly, walking requires a fine momentum control where COM acceleration could play an important role. Differences in control of dynamic stability during walking were examined with our proposed boundaries of dynamic stability. Elderly fallers adapted a more conservative gait strategy than healthy individuals, demonstrating significantly slower forward COM velocity and acceleration with their COM significantly closer to the base of support at toe-off, which could be indicative of a poor momentum control ability. Overall, this study demonstrated that COM acceleration would provide further information on momentum control, which could better reveal underlying mechanisms causing imbalance and provide an insightful evaluation of balance dysfunction. This dissertation includes unpublished co-authored material.
Open Access
Effects of Fatigue on Balance Control During Dual-task Walking
(University of Oregon, 2020-02-27) Chen, Szu-Hua; Chou, Li-Shan
Fatigue is one of the most frequently mentioned symptoms among older adults. Although there were many studies examining effects of fatigue on walking and balance control, the findings were inconclusive due to methodology discrepancy. In addition, the cognitive component is often neglected. Therefore, four studies were conducted in this dissertation to investigate how fatigue affects balance control during dual-task locomotion in older adults using a laboratory fatiguing protocol, and further, how these findings could be applied in real-life settings. In the first study, we demonstrated the use of a repetitive sit-to-stand protocol by examining changes in inter-joint coordination variability along the course of the protocol. The findings suggested that the knee-ankle coordination variability was higher towards the end of protocol. In the second and the third experiments, such fatiguing protocol was applied. Results from the second study suggested that participants regardless of age walked faster after fatigue when concurrently responding to a working memory test. Moreover, young adults showed a greater and faster mediolateral center of mass sway after fatigue; whereas older adults demonstrated a shorter reaction time from pre- to post-fatigue while maintaining a similar body sway during walking. The results from the third study followed the same trend, in which significantly deteriorated balance control during obstacle-crossing was only found in young adults but not in older adults. Taken together, healthy older adults might have a better adaptation to a fatigued status induced by a repetitive sit-to-stand protocol. In the last study, the connection between findings from laboratory experiments and real-life scenarios was explored through examining the effect of fatigue in three older workers following a day-long of occupational activities. Our results showed that some changes observed after work were in line with that observed in the laboratory, but some were opposite or demonstrated unique fatigue adaptations, such as increased body sway, which was not identified when the results were pooled together. Although conclusive interpretation could not be made given the descriptive nature of the study, it highlights the necessity of subgroup analysis and targets the future recruitment on fatigue-prone population. This dissertation includes unpublished co-authored material.
Open Access
An Examination of Motor and Cognitive Recovery Following Concussion
(University of Oregon, 2014-09-29) Howell, David; Chou, Li-Shan
Cognitive and motor impairments have been identified as signs following a concussion which may compromise the performance of everyday tasks or physical activities. However, little work has been done in the adolescent population using laboratory based measurements of attention or balance control to identify recovery from concussion. Therefore, the purpose of this dissertation was to prospectively and longitudinally observe how individuals who have sustained a concussion recover on measures of attention and gait balance control in comparison to individually matched, healthy control subjects from within 72 hours of injury up to two months following injury. Individuals were identified as sustaining a concussion by healthcare professionals and began participation in the study within 72 hours of injury. They then returned to the laboratory at approximately 1 week, 2 weeks, 1 month, and 2 months post-injury. Control subjects were individually matched by sex, age, height, and weight and tested in similar time increments. Attentional abilities were measured via multiple computerized testing assessments, and gait balance control was measured with whole-body motion analysis. The results indicated that following concussion, adolescents display deficits in conflict resolution ability, task switching ability, and gait balance control during dual-task walking for a time period of up to two months following injury in comparison to a matched control group. During dual-task walking, the complexity of the cognitive task performed may affect adolescents with concussion to a greater degree than matched control subjects. Adolescents also displayed regressions to gait stability recovery following their return to physical activities. Finally, adolescents with concussion displayed greater gait balance control deficits than young adults with concussion throughout the two months of testing when each group was compared to a respective healthy control group. Results from this dissertation indicate that concussion affects cognitive and motor functions in adolescents, who display deficits throughout two months post-injury. Computerized attentional tests and dual-task dynamic balance control assessments represent a multifaceted approach to concussion management and may provide another assessment battery for healthcare professionals to utilize in order to identify recovery following concussion. This dissertation includes previously published/unpublished co-authored material.
Open Access
Neuromuscular Control of the Hip, Pelvis, and Trunk During Running
(University of Oregon, 2018-04-10) Hannigan, James; Chou, Li-Shan
Patellofemoral pain syndrome (PFPS) is the most common injury in runners and has a significant female sex bias. Current evidence suggests that several proximal factors, including hip muscle strength, hip muscle activation, and hip kinematics during running, play a large role in the development of PFPS, particularly in females. However, the relationships between these variables are unclear. A better understanding of these relationships in both males and females could help clinicians develop targeted interventions for this syndrome. Thus, this dissertation is comprised of four studies aimed to better understand the relationships between these risk factors. The first study investigated whether there are any relationships between hip muscle strength and hip muscle activation during running. Overall, hip muscle strength and hip muscle activity during running do not appear to be strongly related. The second study used a multiple regression approach to look for predictors of hip adduction and hip internal rotation during running. Sex was a significant predictor in both models, and running speed, static subtalar inversion range of motion, and gluteus maximus amplitude were significant predictors in the hip adduction model. The third study examined the effect of decreasing hip abduction strength on running kinematics and hip muscle EMG. After the fatigue protocol, there were no changes in gluteus medius amplitude or timing, and no changes in hip kinematics during running. However, there were some changes in kinematics, particularly at the trunk, as well as differences in gluteus maximus and tensor fascia latae activation. Finally, the fourth study used an alternative biomechanical method called continuous relative phase (CRP) to investigate the effect of sex and decreasing hip abduction strength on CRP variability at the hip. Decreasing hip abduction strength increased frontal plane CRP variability from 20-40% of stance phase, primarily in females, and females demonstrated less CRP variability than males in the frontal plane and transverse planes. Overall, the results from this study improve our understanding of the relationships between hip strength, hip muscle activation, and hip kinematics during running in both males and females, which may have implications for knee injury rehabilitation strategies. This dissertation includes unpublished co-authored material.
Open Access
Quantifying Segmental Spinal Motion during Activities of Daily Living
(University of Oregon, 2013-10-03) Breloff, Scott; Chou, Li-Shan
Back pain is a very common musculoskeletal impairment in most Americans. Average annual occurrence of back pain is reported around 30% of the population and is the most common cause of activity limitation in people younger than 45 years old. Eighty percent of the back pain presents in the lumbar spine. Although this ailment is very prevalent in the American population, there is a lack of empirical evidence supporting the common clinical diagnosis and intervention back pain strategies. The frequency of back pain and the lack of treatment methods were the motivation for this investigation. It is important to better understand spine dynamics during ambulatory tasks of daily activities to identify possible biomechanical mechanisms underlying back pain. Current biomechanical quantification methods for spine dynamics are either too invasive or not detailed enough to fully comprehend detailed spinal movement. Therefore, a non-invasive but detailed procedure to calculate spine dynamics was developed and tested. In this study, multi-segmented spine dynamics (kinematics and kinetics) were calculated during four activities of daily living (level walking (W), obstacle crossing (OC), stair ascent (SA) and stair descent (SD)). Our findings suggested an in-vivo multi-segmented spine surface marker set is able to detect different and repeatable motion patterns during walking among various spinal segments. The sacrum to lower lumbar (SLL) joint had the largest range of motion (ROM) when compared to the other more superior joints (lower lumbar to upper lumbar and upper lumbar to lower thoracic). Furthermore, SA task demonstrated more flexion ROM than both W and SD tasks. In addition to task influence, joints at different spine levels also demonstrated different ROMs, where SLL had a greater ROM than upper lumbar to lower thoracic (ULLT) in the transverse plane. Age was found to not significantly affect the segmental spinal ROM or peak angles. The vertical segmental joint reaction forces were different between tasks, where SD yielded larger vertical reaction forces than W. Overall, findings from this dissertation work were able to show that a multi-segment spine marker system could be an effective tool in determining different spinal dynamics during various activities of daily living. This dissertation includes unpublished co-authored material.
Open Access
The Relationship Between Hip Strength and Hip, Pelvis, and Trunk Kinematics in Healthy Runners
(University of Oregon, 2014-09-29) Hannigan, James; Chou, Li-Shan
This study examined the relationship between hip strength and hip, pelvis, and trunk kinematics in healthy runners. Whole body kinematic data were collected while subjects ran in the laboratory. Isometric hip abduction, flexion, external rotation, and internal rotation torques were measured bilaterally using a dynamometer. Subjects were divided into strong and weak groups for each muscle strength parameter. Differences in hip, pelvis, and trunk motion were then examined using independent sample t-tests. Pearson correlation coefficients were used to assess these relationships for all subjects. Most notably, runners with weak abductors displayed greater hip adduction and pelvic rotation compared to the strong abductor group, while runners with weak external rotators displayed greater trunk rotation compared to the strong external rotator group. Moderate, negative correlations were observed for the above relationships. While data from this study help clarify the relationship between hip strength and running kinematics, no causal conclusions can be made.
Open Access
Towards an Understanding of Prolonged Pronation: Implications for Medial Tibial Stress Syndrome and Achilles Tendinopathy
(University of Oregon, 2013-10-03) Becker, James N. M., 1979-; Chou, Li-Shan
Epidemiologic data suggest 25% to 75% of all runners experience an overuse injury each year. Commonly cited biomechanical factors related to overuse injuries such as Achilles tendinopathy or medial tibial stress syndrome include excessive amounts or velocities of foot pronation. However, there is conflicting evidence in the literature supporting this theory. An alternative hypothesis suggests it is not necessarily the amount or velocity of pronation which is important for injury development; rather it is the duration the foot remains in a pronated position throughout stance that is the important variable. This project examined this hypothesis by first identifying biomechanical markers of prolonged pronation. Second, it assessed whether individuals currently symptomatic with injuries typically attributed to excessive pronation instead demonstrate the biomechanical markers of prolonged pronation. Finally, musculoskeletal modeling techniques were used to examine musculotendinous kinematics in injured and healthy runners, as well as healthy runners with prolonged pronation. The results suggest the two most robust measures for identifying individuals with prolonged pronation are the period of pronation and the eversion of the rear foot at heel off. Individuals with prolonged pronation can also be identified with a set of clinically feasible measures including higher standing tibia varus angles, reduced static hip internal rotation range of motion, and increased hip internal rotation during stance phase. Finally, individuals with prolonged pronation display a more medially located center of pressure trajectory during stance. Compared to healthy controls, individuals currently symptomatic with Achilles tendinopathy or medial tibial stress syndrome did not differ in the amount or velocity of pronation. However, they did demonstrate the biomechanical markers of prolonged pronation. Injured individuals also demonstrated greater average musculotendinous percent elongation than healthy controls, especially through mid and late stance. Currently healthy individuals demonstrating prolonged pronation exhibited musculotendinous percent elongations intermediate to the healthy and injured groups. As a whole, the results from this study suggest prolonged pronation may play a role in the development of common overuse running injuries. It is suggested future studies on injury mechanisms consider pronation duration as an important variable to examine. This dissertation includes unpublished co-authored material.
Open Access
Visuospatial attention during locomotion
(University of Oregon, 2016-02-23) Lo, On-Yee; Chou, Li-Shan
Locomotion requires visuospatial attention. However, the role and cortical control of visuospatial attention during locomotion remain unclear. Four experiments were conducted in this study to examine the role and cortical control of visuospatial attention during locomotion in healthy young adults. In the first experiment, we employed a visuospatial attention task at different phases of obstacle crossing during gait. The results suggested that toe-obstacle clearance was significantly reduced for the trailing limb when distraction interfered with visuospatial attention during the approaching phase of obstacle crossing. In the second experiment, subjects performed a visual Stroop task while approaching and crossing an obstacle during gait. The results for the second experiment indicated toe-obstacle clearance was significantly increased for the leading and trailing limbs. Taken together, it was found that different visual attention tasks lead to distinct modifications on obstacle crossing behaviors. In the third and fourth experiments, anodal transcranial direct current stimulation (tDCS) was applied over the right posterior parietal cortex (PPC) to examine the aftereffects on attention function and locomotor behavior. The results suggested that the orienting attention was significantly improved after anodal tDCS. In addition, the aftereffects of anodal tDCS potentially enhanced cognitive and motor performance while interacting with a challenging obstacle-crossing task in young healthy adults, suggesting that the right PPC contributes to attending visuospatial information during locomotion. This study demonstrated that visuospatial attention is critical for planning during locomotion and the right PPC contributes to this interplay of the neural processing of visuospatial attention during locomotion. This dissertation includes previously published and unpublished co-authored material.

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