• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 1427
  • 660
  • 168
  • 112
  • 41
  • 28
  • 21
  • 17
  • 16
  • 14
  • 14
  • 13
  • 12
  • 12
  • 12
  • Tagged with
  • 3106
  • 773
  • 648
  • 410
  • 392
  • 256
  • 226
  • 218
  • 216
  • 215
  • 210
  • 203
  • 187
  • 172
  • 163
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Gait kinematics and spinal loading in patients with lumbar spinal stenosis and healthy older adults

Lynch, Andrew Charles 30 May 2023 (has links)
BACKGROUND: Lumbar spinal stenosis (LSS) in older adults is a leading cause of pain and limitations to mobility. Compression of the spinal nerves can result in neurological symptoms that can decrease walking capacity and overall quality of life. It is clinically believed that patients with LSS alter their gait pattern to be able to increase their walking capacity but biomechanical assessment of spinal and pelvic motion during walking compared to healthy older adults is lacking. The purpose of this study was to gain further insight into how patients with LSS move and how their posture affects spinal loading compared to healthy older adults. METHODS: Whole body motion data was collected on 9 patients with LSS and 10 healthy older adults. Both cohorts completed a 3D opto-electronic motion analysis during standing and walking trials and patients with LSS were measured during both asymptomatic and symptomatic states. Pelvis, knee, and spine kinematics and spinal loading were obtained via subject-specific musculoskeletal models. RESULTS: In the LSS group, both asymptomatic and symptomatic trials, the average pelvic tilt was more posteriorly rotated than the healthy adults during standing and walking. Lumbar spine angles in the LSS group adopted a more flexed posture compared to the healthy group’s normal lordotic angle. This coincided with higher C7/S2 angles and distances compared to the healthy group. Lumbar spine loading doubled in both LSS groups compared to the healthy group’s standing trials, though little difference was seen during walking. Knee flexion angle increased greatly during both standing and walking. CONCLUSIONS: My results indicate that LSS patients both stand and walk with greater posterior pelvic tilt and lumbar flexion which greater knee flexion to counterbalance compared to healthy counterparts. While the provocation of symptoms did not affect their kinematics, both asymptomatic and symptomatic states showed significant modification from older healthy adults. The clear differences in gait and posture can aid in therapeutic interventions but additional work is needed to better understand the biomechanical differences between these two groups.
22

Knee joint kinematics before and after body weight change

Li, Jing-Sheng 06 July 2018 (has links)
Obesity is a well-defined mechanical factor for osteoarthritis (OA). More than one-third of adults in the United States are obese, and one in three obese adults has arthritis. In obese individuals, knee pain is highly prevalent and is often thought to be the first symptom of knee OA. In the pathomechanics of knee OA, altered kinematics and contact location in the knee joint are potent contributors to OA initiation and progression. However, such kinematics and cartilage contact location in obese individuals, and how the knee joint responses to excess load due to obesity are not clear and understudied, mainly limited by the instrumentations. Therefore, we conducted a series of dissertation studies to investigate the effect of weight on the knee joint kinematics in six degrees of freedom (6DOF) and cartilage contact location using a fluoroscopic imaging system with magnetic resonance-based morphological models. In Study 1, the 6DOF kinematic analysis showed that obese individuals with knee pain walked with a reduced range of flexion-extension motion and a reduced medial-lateral translation compared with non-obese controls. In Study 2, the cartilage contact analysis showed that obese individuals experienced different contact location on both the tibial and femoral cartilage surfaces during walking when compared with a healthy group, while pain had a minimal effect on the cartilage contact location. In Study 3, we followed up with the obese individuals in Study 1 and the kinematic analysis showed that the change in range of the flexion-extension and adduction-abduction motion during gait were associated with the change in body weight; however, knee pain was not associated with the kinematic change. In conclusion, this series of dissertation studies suggests that the kinematics of the knee in obese individuals with knee pain was modifiable through weight loss. Weight management should be addressed more than controlling for pain in obese individuals with pain, as pain management might not able to restore the contact locations. / 2020-07-06T00:00:00Z
23

Investigation of blood pressure waveform using harmonic distortion: implications for cardiovascular risk

Milkovich, Nicholas 18 January 2024 (has links)
Blood pressure waveform (BPW) can be used to characterize changes in the cardiovascular system due to diseases and aging. The BPW morphology is largely determined by both the total mechanical impedance of the vasculature and the flow waveform produced by the left ventricle. The BPW can be further decomposed into its two primary components: the forward and reflected waveforms. It is known that under several conditions, such as aging, arterial wall stiffening, and increased cardiovascular risk, the magnitudes and phases of these waves change and therefore distort the aggregate BPW. Previous studies of the BPW has yielded mixed results, largely due to the insensitivities of the primary wave morphology index, augmentation index (AI). To this end, a new method of morphology characterization was developed which takes into account the overall harmonic content of the BPW. Harmonic distortion (HD), derived from Fourier-transformed BPW, was first used to characterize changes in the aortic wall. Utilizing mice subjected to normal and high fat, high-sucrose diets, the results demonstrate that HD exhibits a linear relationship with both systolic blood pressure (SBP) and arterial stiffness. Next, a transmission line model of arterial impedance was developed to study physiologically realistic BPWs under various arterial tree sizes and stiffness. Comparison of HD and other indexes reveals that HD correlates strongly with arterial stiffness, surpassing AI in accuracy for higher stiffness values. Finally, HD analysis was applied to BPWs collected clinically on a diverse group of participants. HD emerges as a more sensitive indicator than AI, notably correlating with diabetes and demonstrating stability across heart rate variations. The superior statistical performance of HD over AI in hemodynamic variables underscores its potential as a robust measure for cardiovascular risk assessment. This research offers a comprehensive framework for assessing arterial health, highlighting the potential of HD as a stable, sensitive, and noninvasive measure. This integrated approach contributes to a nuanced understanding of the intricate factors influencing BPW morphology and its implications for cardiovascular health in the context of aging and disease.
24

An investigation into the mechanisms responsible for the successful completion of a ballistic elbow extension task

Wrbaskic, Nebojsa 11 1900 (has links)
<p>A dynamic ballistic elbow extension task was chosen to investigate the mechanisms responsible for achieving a high final velocity during this type of movement. After a screening process of one hundred male participants, thirty-two were chosen to be further investigated who fell into the extremes of the strength and speed continuums. The main investigation involved having participants ballistically extend their elbows against external relative loads of 0%, 20%, 40%, 60% and 80% of their maximum isometric force and two absolute loads of 1.1 kg and 2.2 kg. External torque and angular displacement measurements were recorded as well as triceps and biceps electrical activity. EMG modeling, which employed the characteristics of muscle mechanics, was used to determine the differences in performance. Isometric strength did not produce a 1:1 mapping with maximum velocity. Individuals existed that were relatively strong but not fast. Additionally, there were subjects that were quite strong but not appreciably fast. Peak instantaneous power, however, produced the best correlations with peak final velocity. To determine why certain individuals were capable of producing more power, each subject's triceps EMG was modeled in order to predict the actual muscle torque. The model predicted torques with a mean correlation of 0.957 and a mean RMSerror value of 5.8 Nm for the 224 trials. As a result of the good predictions, a forward-dynamics approach was used to manipulate weaknesses in one performance with another individual's superior attributes. Performance improvements were noted as a result. These findings demonstrate that peak instantaneous power best predicts peak terminal velocity. Furthermore, this study has developed a model capable of identifying neuro-muscular weaknesses in performance and suggesting how improvements in those areas would change the maximum velocity attained. The next stage is to determine the proper training stimuli that would make these specific neuro-muscular improvements possible.</p> / Doctor of Philosophy (PhD)
25

Development of an experimental method to identify structural properties of the intervertebral joint after spine staple implantation under simulated physiologic loads

Coombs, Matthew T. January 2011 (has links)
No description available.
26

AN INVESTIGATION OF LEANING BEHAVIOURS DURING ONE-HANDED SUBMAXIMAL EXERTIONS WITH EXTENDED REACHES

Fewster, Kayla M. 10 1900 (has links)
<p>The purpose of this study was to investigate leaning behaviours when completing tasks with constrained reaches. A logistic regression was developed, with the input of individual subject anthropometry and specific task characteristics, and the resulting model was able to provide a very accurate prediction of when an individual would lean. The inputs to this model give insight into what factors are important in the decision making process when a worker chooses whether lean. The task hand locations with the longest reaches resulted in the most frequent choice to lean. Leaning appears to be particularly common, and important, with long reaching and pulling tasks that can reduce task hand shoulder and trunk loads and improve balance, while allowing the worker to get closer to the task. Leaning hand forces were highest during pulling tasks. These findings are very important to document, as current ergonomic tools neglect to consider that different task characteristics may change how, and when, a worker leans. Even when only the direction of the task hand force was changed, leaning hand forces differed significantly. In this study, leaning hand height was slightly higher for the shoulder height, when compared to the umbilical height, task hand locations. The average height of the leaning hand did not vary considerably and ranged between 106.6cm to 116.3cm, depending on the condition. The leaning hand force magnitude changed as task hand location, force direction and force level changed. Leaning hand forces increased with increasing task hand load. Task hand forces in the push direction were higher compared to push and down exertions, regardless of task hand location or task hand load. The findings from this study are of particular use to industry as ergonomists now have representative forces and heights, to help guide leaning estimates during proactive risk assessments.</p> / Master of Science (MSc)
27

Focus of attention influences on Olympic weightlifting kinematics

Schutts, Kyle S. 09 February 2016 (has links)
<p> Recent motor control literature has demonstrated that using verbal cues to direct a performer&rsquo;s attention externally (i.e. toward movement outcome) enhances motor skill performance. The purpose of this study was to investigate how an athlete&rsquo;s focus of attention impacts kinematic performance of the snatch. 12 competitively trained athletes performed blocks of 3 snatch repetitions at 80% 1RM following internal and external instructions. The results indicated that athletes adopting an internal focus increased elbow velocity relative to an external, while an external focus increased horizontal barbell velocity. Internal cues resulted in larger BCH angles at the max height (MH), relative to external, indicating that the athletes are squatting under the barbell too soon. This information adds to the literature suggesting small changes in coaching cues can impact performance significantly. It is recommended that coaches use cues that direct an athlete&rsquo;s attention externally, toward the movement outcome, rather than the action itself. </p>
28

Sit-to-stand performance in people with stroke and the effect of constraint-induced movement strategies on sit-to-stand performance

Gray, CHARLA 24 July 2013 (has links)
Asymmetry of weight-bearing and impaired ability to maintain centre of pressure in midline contribute to an increased fall risk during sit-to-stand in people with stroke. The main objective of this thesis was to investigate the effect of constraint-induced movement strategies on affected limb weight-bearing and measures of balance in people with stroke. Four studies were conducted to achieve this objective. Study one and two investigated the methodology for describing sit-to-stand performance in people with stroke and reliability of measures of sit-to-stand performance. Findings from study one demonstrated that methods for describing sit-to-stand performance in healthy adults are not feasible in people with stroke and established a method for describing sit-to-stand performance in subsequent studies. Findings from the second study demonstrated within and between day reliability of temporal, weight-bearing and displacement measures of sit-to-stand performance in both groups. The third study of this thesis described impairments of sit-to-stand performance in people with stroke when compared with healthy age and sex matched adults. The findings confirmed results from previous studies and further described sit-to-stand performance by demonstrating a shift in the frontal plane centre of pressure and centre of mass position toward the unaffected limb at seat-off in people with stroke. The final study investigated the effect of three constraint-induced movement strategies on sit-to-stand performance in people with stroke. The results demonstrated increased affected limb weight-bearing and a shift of the centre of pressure and centre of mass toward midline with all of the strategies. Only two of the strategies altered centre of pressure and centre of mass displacement in the sagittal plane. Findings from this body of research provide new information regarding the methodology of describing sit-to-stand performance in people with stroke and the reliability of measures of sit-to-stand performance. The results also provide an advanced understanding of sit-to-stand performance in people with stroke and the effect of constraint-induced movement strategies on sit-to-stand performance. Additional research using constraint-induced movement strategies in a randomized controlled trial will inform clinical practice and may reduce the fall risk in people with stroke. / Thesis (Ph.D, Rehabilitation Science) -- Queen's University, 2013-07-24 13:30:53.585
29

A cinematographic analysis of the parallel arm downswing from a handstand on the still rings

Kinoshita, Hiroshi January 1977 (has links)
The purpose of this study was to study the essential• factors involved in the execution of the parallel arm downswing in the sequence of the backward giant swing on the still rings. Comparisons were made among gymnasts who had had different amounts of experience in the use of the parallel arm downswing technique.The subjects were four male American collegiate gymnasts. Selected as the experienced performers were an Olympic gymnast from Indiana State University, Terre Haute, Indiana, and. a specialist on the still rings from Ball State University, Muncie, Indiana. Selected as the less experienced performers were two all around gymnasts from the Ball State University men's gymnastic team.The cinematographic method was used to collect the data. In order to identify the biomechanical differences between the subjects, seven categories were considered to be the essential factors possibly involved in the execution of the parallel arm downswing. The horizontal and linear velocities of the wrist, the body angles, the angular velocity of the body segments, and the total body's tangential forces were graphed and studied. Plots of the trajectory of the center of gravity and plots of the loci of the body joints were compared and interpreted. The performance times of the subjects were compared in terms of the time elapsed during the whole and a part of the downswing.It was concluded that for these subjects, the successful parallel arm downswing should be accomplished by using the following factors: a faster push of the rings, a lean of the shoulders, a straighter body, a stronger beat action of the trunk, a proper timing (after the bottom of the downswing) of the legs and. a closer trajectory of the center of gravity throughout the downswing. The total body's tangential force and the performance time, appeared to be essential factors for the successful parallel arm downswing. However, it was not determined whether a greater amount of force or a shorter execution time is necessary for the ideal execution of the reverse giant swing on the still rings.
30

Using an IMU for ground reaction force estimation during a vertical jump task

Berardo-Cates, Alexander T. 03 December 2016 (has links)
<p> The purpose of this study was to determine if a single inertial measurement unit (IMU) could be used to estimate the vertical ground reaction force (vGRF) of a vertical jump. To do this 16 college-age participants (8 female, 8 male) preformed three counter movement jumps, three drop jumps, and three squat jumps. All jumps were simultaneously recorded with a force plate (1250 Hz) and an IMU (128 Hz) placed on the sacral-L5 junction. The peak rate of force development, reactive strength index, jump impulse, jump height determined from impulse (h<sub>imp</sub>), jump height determined from flight time, and peak force were measured using both the force plate and IMU. There was a significant difference between measuring devices for all dependent variables (p &lt; 0.05) except the h<sub>imp</sub> (p = 0.341). In conclusion, this study does not provide a means of accurately estimating vGRF using an IMU.</p>

Page generated in 0.0598 seconds