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Introduction: Anxiety is induced by a perceived threatening situation and can impair the decision-making ability and maintenance of attention on relevant stimuli. The pre-frontal cortex (PFC) has been implicated in anxiety through the multiple network theory however, the PFC’s role in anxiety is poorly understood. Implementing visual perturbations increases PFC activity due to increased attentional demands, which is observed in younger adults. Due to increased attentional processes produced from visual perturbations, cortical activity can be altered. Methods: Twenty healthy young adults performed three treadmill walking tasks, without visual cues, with visual cues and with perturbations. Cortical activity was recorded with a 22-channel, 18 optode fNIRS cap (Dual Brite MKII; Artinis Medical Systems, Netherlands). Anxiety measurements included the state-trait anxiety inventory (Spielberger et al., 1971) and heart rate variability (polar hear rate monitor). A Friedman rank sum test was performed to determine differences observed in heart rate variability RMSSD (HrvRMSSD) and mean oxyhemoglobin concentration change, among gait conditions. Mann-Whitney U tests were used to determine effects of trait anxiety on HrvRMSSD for gait conditions. Spearman rank correlations where ran between anxiety measures and PFC activity. Results: No significant condition effect on mean oxyhemoglobin concentration change (χ2 = 3.9, p = 0.14) was found. There was a significant condition effect for HrvRMSSD (χ2 = 17.2, p < 0.001). Post hoc analysis showed a significant decrease between baseline and stepping (p = 0.003, r = 0.17) and baseline and stepping varied (p = 0.02, r = 0.24). No significant trait anxiety effects found on HrvRMSSD during baseline (p = 0.15), stepping (p=0.20) and stepping varied (p=0.08), between low and moderate trait anxiety. No correlations were found between anxiety measures and PFC activity. Significance: The present experiment shows that PFC activity does not alter in young adults between a gait and visually perturbed gait. Further, we observed no significant change in PFC activity when anxiety, measured by HrvRMSSD, increased with gait condition difficulty. These results did not support our hypotheses, but the results will help inform protocol decisions of future investigations.

Gait is the method of human locomotion using limbs. Recently, the analysis of human motion, specifically human gait, has received a large amount of research attention. Human gait can contain a wide variety of information that can be used in biometrics, disease diagnosis, injury rehabilitation, and load determination. In this dissertation, the development of a model-based gait analysis technique to classify external loads is presented. Specifically, the effects of external loads on gait are quantified and these effects are then used to classify whether an individual gait pattern is the result of carrying an external load or not. First of all, the reliability of using continuous relative phase as a metric to determine loading condition is quantified by intra-class correlation coefficients (ICC) and the number of required trials is computed. The ICC(2, 1) values showed moderate reliability and 3 trials are sufficient to determine lower body kinematics under two external load conditions. Then, the work was conducted to provide the baseline separability of load carriage conditions into loaded and unloaded categories using several lower body kinematic parameters. Satisfactory classification of subjects into the correct loading condition was achieved by resorting to linear discriminant analysis (LDA). The baseline performance from 4 subjects who were not included in training data sets shows that the use of LDA provides an 88.9% correct classification over two loaded and unloaded walking conditions. Extra weights, however, can be in the form of an external load carried by an individual or excessive body weight carried by an overweight individual. The study now attempts to define the differences in lower body gait patterns caused by either external load carriage, excessive body weight, or a combination of both. It was found significant gait differences due to external load carriage and excessive body weight. Principal Component Analysis (PCA) was also used to analyze the lower body gait patterns for four loading conditions: normal weight unloaded, normal weight loaded, overweight unloaded and overweight loaded. PCA has been shown to be a powerful tool for analyzing complex gait data. In this analysis, it is shown that in order to quantify the effects of external loads for both normal weight and overweight subjects, only two principal components (PCs) are needed. The results in this dissertation suggest that there are gait pattern changes due to external loads, and LDA could be applied successfully to classify the gait patterns with an unknown load condition. Both load carriage and excessive body weight affect lower body kinematics, but it is proved that they are not the same loading conditions. Methods in the current work also give a potential for new medical and clinical ways of investigating gait effects in osteoarthritis patients and/or obese people. / Ph. D.

Concussions are diffuse injuries that affect areas of the brain responsible for a person's physical, cognitive, and emotional health. Although concussions were once thought only to present transient symptoms, mounting evidence suggests potential for long-term neurological impairments. The deleterious effects of concussion can be from a single, high severity impact event or the accumulation of lower severity impacts. Clinical changes that can result from concussion include an elevated symptom presentation and changes in gait, or an individual's walking pattern. It is not well understood if similar deficits result after an accumulation of subconcussive impacts. The majority of research on human tolerance to head injury has been based on American football, using helmet-mounted sensors in male athletes. Limited studies have attempted to quantify biomechanical tolerance in women, despite the sex-specific nature of presentation and outcome of concussion. Biomechanical, physiologic, and psychosocial factors differ between males and females, likely contributing to this difference. The research presented in this dissertation was aimed at describing sex-specific outcomes of subconcussion in a matched cohort of male and female athletes to gain a better sense of unhelmeted, sex-specific tolerance to head impacts. On-field data were collected from collegiate rugby players using instrumented mouthguards. Rugby involves high energy, frequent head impacts, does not require protective headgear, and is played the same for both men and women. The females in our study sustained fewer impacts per session than the males, but their impacts had similar linear acceleration magnitudes. The kinematics of the concussive male impacts were higher than the kinematics of the concussive female impacts. Both sexes reported concussion-like symptoms in the absence of diagnosed concussion during a season. Females reported more symptoms with a higher severity in-season compared to males after subconcussive and concussive impacts. Female athletes saw deficits in cadence, double support time, gait speed, and stride length post-concussion. The majority of athletes improved in their dual-task gait assessment by the end of the season, suggesting there may not be a negative effect on gait after an accumulation of subconcussive impacts. This work assessed the biomechanics of head impacts and concussions of this population, and evaluated changes in symptom presentation through weekly graded symptom surveys and dual-task gait assessments both after a concussion and as an effect of subconcussive impacts. Understanding the sex-specific clinical effects of head impacts is critical, and can provide insight into concussion diagnostic, management, and prevention tools that are appropriate and effective. / Doctor of Philosophy / Concussions are injuries that affect many areas of the brain, including those responsible for a person's physical, cognitive, and emotional health. Although concussions were once thought only to present transient symptoms, mounting evidence suggests potential for long-term neurological impairments. The harmful effects of concussion can be from a single, high intensity impact event or the build-up of lower intensity impacts. Clinical changes that can result from concussion include an elevated symptom presentation and changes in gait, or an individual's walking pattern. It is not well understood if similar side effects result after an accumulation of subconcussive impacts. The majority of research on human tolerance to head injury has been based on American football, using helmet-mounted sensors in male athletes. Limited studies have attempted to quantify concussion tolerance in women, despite the differences in men and women's symptoms and recovery time after a concussion. Female's neck strength, hormones, and increased honesty in reporting concussion differ from males, likely contributing to this difference. The research presented in this dissertation was aimed at describing how sex affects the results of subconcussion in a group of male and female athletes to gain a better sense of unhelmeted, sex-specific tolerance to head impacts. On-field data were collected from collegiate rugby players using sensor-embedded mouthguards. Rugby involves high energy, frequent head impacts, does not require protective headgear, and is played the same by both men and women. The females in our study sustained fewer impacts per session than the males, but their impacts were similar in magnitude. The impact energies of the concussive male impacts were higher than those of the concussive female impacts. Both sexes reported concussion-like symptoms in the absence of diagnosed concussion during a season. Females reported more symptoms with a higher severity in-season compared to males after subconcussive and concussive impacts. Female athletes had a slower walking pace and walking speed, a shorter stride length, and spent more time with both feet on the ground post-concussion. The majority of athletes improved in their dual-task gait assessment by the end of the season, suggesting there may not be a negative effect on gait after an accumulation of subconcussive impacts. This work assessed the biomechanics of head impacts and concussions of this population, and evaluated changes in symptom presentation through weekly graded symptom surveys and dual-task gait assessments both after a concussion and as an effect of subconcussive impacts. Understanding the sex-specific clinical effects of head impacts is critical, and can provide insight into concussion diagnostic, management, and prevention tools that are appropriate and effective.

This paper presents the design of an underactuated lower body exoskeleton to assist with walking. It reduces the amount of bodyweight going through the user's leg by providing a supporting force to the user that is engaged and disengaged depending on the stage of the gait cycle the user is in. It is engaged when the leg is in stance, effectively pushing between the ball of the foot and the hips, and is disengaged during leg swing. This support force is provided by a linear actuator on each leg that consists of a compression spring, ball screw, and motor. It works by having the motor turn the ball screw, which moves a metal plate to either compress or decompress the spring. The actuator is designed to always be able to extend, to avoid limiting the user's motion. The spring is disengaged while the leg is in swing in order to reduce any impedance to the user's natural stride. The exoskeleton is also designed to minimize any range of motion limitations to reduce its restrictiveness. The exoskeleton was found to be able to provide 19 lbs (85 N) of support to the user per leg. / Master of Science / Exoskeletons are external devices worn to assist the user's natural movement or strength. This paper outlines the design of an exoskeleton that assists the user in walking by providing a supporting force on any leg that the user's weight is on. This effectively reduces the load on the user's legs, which could help reduce leg strain and fatigue. The exoskeleton releases this force when weight is removed from the leg to allow the user to easily swing their leg forward to step. The exoskeleton was designed to minimize limitations to the range of motion of the leg joints while walking, squatting, or sitting to ensure that the exoskeleton did not feel restricting or uncomfortable. Testing revealed that the exoskeleton was able to provide a supporting force of approximately 19 lbs (85 N) to the user per leg and met all the joint range of motion requirements to avoid restrictiveness.

Study design is among the most fundamental factors influencing collection and interpretation of data. The purpose of this study is to understand the effect of design choices by evaluating gait mechanics in healthy control participants using three primary objectives: 1) determine the repeatability of marker placement, 2) determine the effect of set versus self-selected walking speed, and 3) examine the correlation between gait asymmetry and motor variability. Ten and fifty-one healthy control participants were recruited for aim 1 and aims 2/3, respectively. Reflective markers were placed on lower-extremity bony landmarks and participants walked on an instrumented treadmill while 3D motion capture data was collected. For aim 1, this procedure was repeated at two time points 30 minutes apart. For aims 2 and 3, participants completed set and self-selected speed trials. JMP Pro 13 was used to compare joint kinetics and gait kinematics for all aims. Marker placement was repeatable between time points. Participants walked slower in the self-selected walking speed trial, which resulted in both kinematic and kinetic gait mechanics alterations. Gait asymmetry was significantly correlated with motor variability for both spatial and temporal measures. Current study findings reiterated the importance of walking speed when evaluating gait symmetry, joint kinetics, and kinematics. The decision regarding whether to utilize a set or self-selected speed condition within a study design should be made based on whether the measures of interest are independent of walking speed. Gait asymmetry and motor variability are related and should not be treated as independent components of gait. / Master of Science / This study aims to evaluate gait mechanics in healthy young adults by evaluating the impact of multiple study design choices and relationships between different aspects of gait (walking). Loading and movement walking data was collected from a total of sixty-one participants. This data was then used to calculate several measures of gait including symmetry between limbs, joint ranges of motion, and variability of movement. The potential impact of study design choices including setting walking speed for all participants and evaluating loading asymmetry and movement variability independently are discussed based on the findings of the current study.

The union of electronics and textiles to form electronic textiles (e-textiles) provides a promising substrate upon which motion analysis applications can be developed and implemented. Familiarity with clothing allows sensors and computational elements to be naturally integrated into garments such that wearability and usability is preserved. The dynamics of the human body and the wide variety of sensor and processing choices render the typical prototype-based design methodology prohibitively difficult and expensive. Simulation of e-textile systems not only reduces these problems but allows for thorough exploration of the design space, faster design cycles, and more robust applications. Gait analysis, the measurement of various body motion parameters during walking for medical purposes, and context awareness, the recognition of user motions, are two immediate applications that e-textiles can impact and emphasize the feasibility of e-textiles as a medium for sensor deployment on the human body. This thesis presents the design of a simulation environment for wearable e-textile systems and demonstrates the use of the simulation via a prototype pair of e-textile pants. / Master of Science

The extraction and analysis of human gait characteristics using image sequences and the subsequent classification of these characteristics are currently an intense area of research. Recently, the focus of this research area has turned to the realm of computer vision as an unobtrusive way of performing this analysis. With such systems becoming more common, a gait analysis system that will quickly and accurately determine if a subject is walking normally becomes more valuable. Such a system could be used as a preprocessing step in a more sophisticated gait analysis system or could be used for rehabilitation purposes. In this thesis a system is proposed which utilizes a novel fusion of spatial computer vision operations as well as motion in order to accurately and efficiently determine if a subject moving through a scene is walking normally or abnormally. Specifically this system will yield a classification of the type of motion being observed, whether it is a human walking normally or some other kind of motion taking place within the frame. Experimental results will show that the system provides accurate detection of normal walking and can distinguish abnormalities as subtle as limping or walking with a straight leg reliably. / Master of Science

An underactuated exoskeleton design for walking assistance is presented and evaluated. The exoskeleton uses one motor per leg and makes use of a pantograph to reduce the overall profile and allow the exoskeleton to closely follow the shape of the user's leg. Support is provided between the ball of the user's foot and their waist by compressing a spring in parallel with the user's leg during Stance Phase. The exoskeleton has a mass of 14.0 kg (30.8 lbs) and was tested up to a supplied spring force of 323.6 N (72.75 lbf) which equates to around 161.8 N (36.38 lbf) of assistive force at the waist. Range of motion tests showed minimal restriction at the knee and ankle, but some restriction of the hip. Human subject experiments using a simple gait detection method based on GRF at walking speeds from 0.45 m/s to 1.12 m/s (1.0 mph to 2.5 mph) were performed and showed an increase in the time between actual heel strike and predicted heel strike of approximately 0.05 seconds to 0.1 seconds. Lastly, calculations are presented examining the effect of exoskeleton assistance on the biological joint moments and optimizing the actuator design to reduce power consumption. The actual performance of the exoskeleton is compared with the calculations based on the joint angles during a typical walking cycle. / Master of Science / A design for an exoskeleton capable of providing walking assistance without requiring a motor for every joint is presented and evaluated. The exoskeleton uses one motor per leg and makes use of a pantograph to reduce the required size and allow the exoskeleton to closely follow the shape of the user's leg. Support is provided between the ball of the user's foot and their waist by compressing a spring attached beside the user's leg while the user's foot is on the ground. The exoskeleton weighs 14.0 kg (30.8 lbs) and was tested up to a supplied spring force of 323.6 N (72.75 lbf) which equates to around 161.8 N (36.38 lbf) of assistive force at the waist. Range of motion tests showed minimal restriction at the knee and ankle, but some at the hip. Testing with a human participant using a simple method for determining when to apply support and remove it based on the forces measured at the user's foot were performed at walking speeds of 0.45 m/s to 1.12 m/s (1.0 mph to 2.5 mph). These tests showed an increase in the time between when the heel of the foot initially hits the ground and when the exoskeleton code determined that it occurred of approximately 0.05 seconds to 0.1 seconds. Lastly, calculations are presented examining how exoskeleton assistance affects what is felt at the joints of the user and determining what spring stiffness would best reduce the power required from the motors. The actual performance of the exoskeleton is compared with the calculations based on the joint angles during normal human walking.

Electrical components constantly being scaled down in size allows for small, inexpensive sensors to be placed on or around the human body for motion sensing applications. In addition, the merging of textiles with electrical components, known as electronic textiles (e-textiles), allows for these sensors to be placed directly on a wearable fabric. Simulation allows for extensive application testing and verification before prototype development. This thesis presents a simulation environment for motion sensing E-textiles. Specifically, this environment incorporates motion capture position data to simulate a rate sensing gyroscope and a dual-axis accelerometer. In addition, this simulation environment is applied to the field of gait analysis, which is the process of quantification and interpretation of a person's stride, to calculate a subject's step length. / Master of Science