Browsing by Subject "Gait in humans"
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Item Analysis of potential muscular determinants of the preferred walk-run transition speed in human gait(2004) Sasaki, Kotaro; Neptune, Richard R.The spontaneous transition from walking to running as walking speed increases is an intriguing neuromotor phenomenon that consistently occurs near 2 m/s in humans. Despite investigations of various metabolic and biomechanical factors, the determinants of the transition have remained elusive. However, no study has investigated the potential influence of intrinsic muscle properties and fiber-tendon interactions as potential determinants. The overall objective of this research was to use a forward dynamical simulation framework in three studies to identify the potential influence of these muscular determinants on the preferred walk-run transition speed (PTS). In the first study, individual muscle force production was examined as walking speed increased to assess the influence of intrinsic muscle properties on the PTS. The simulation data showed that of all the major lower-extremity muscle groups examined, the ankle plantar flexors were the only muscles to show a decrease in force production, despite an increase in activation, as walking speed approached the PTS. The force reduction was attributed to adverse contractile conditions. Considering the importance of the plantar flexors to providing body support and forward progression, the impaired force generation was deemed an important determinant of the PTS. In the second study, individual muscle contributions to body support and forward progression in walking and running at the PTS were quantified to clarify differences in muscle function between the two gait modes. The most distinctive difference was the reduced soleus contribution to forward progression in running. All other muscle groups performed similarly between the two gait modes. In the third study, individual muscle fiber and tendon mechanical work was quantified to examine whether there existed an energetic advantage during walking and running above and below the PTS. The total muscle fiber work was found to be higher in running than walking below the PTS, and higher in walking than running above the PTS. In addition, tendon elasticity utilization was lower in running below the PTS than in running above the PTS. These results highlight the advantages of each gait mode and suggest why walking below the PTS and running above the PTS are the preferred gaits.Item Dynamic stability of human walking during perturbations and voluntary gait changes(2011-05) Young, Patricia Mary; Dingwell, Jonathan B.; Barr, Ronald; Grabiner, Mark; Markey, Mia; Neptune, RichardFalling during walking leads to millions of emergency room visits every year for all age groups and is a significant medical concern. While gait training has shown some promise for fall prevention, we know relatively little about how humans maintain stability, how we can quantify it and how we can use this knowledge to increase the success of fall prevention training. In this dissertation, I studied how human stability responds to continuous, small magnitude perturbations and to voluntary changes in gait characteristics by examining movement variability and long-term and instantaneous dynamic stability. In the first set of experiments, participants were exposed to continuous, pseudo-random external perturbations of the visual field and support surface in a Computer Assisted Rehabilitation ENvironment (CAREN). Participants exhibited increased step widths, shorter step lengths and increased step variability, orbital and short-term local instability. Despite this, mean instantaneous lateral stability remained approximately constant. In the second set of experiments, participants voluntarily adopted changes in their step widths and step lengths. Wider steps were associated with increased step width variability, decreased nonlinear stability, decreased anterior-posterior margins of stability and increased instantaneous lateral stability. Shorter steps were associated with decreased short-term and orbital stability but did not affect mean instantaneous stability. When instantaneous stability was examined between steps, as opposed to as an average over many steps, results from both studies indicated a relationship between each step’s stability and the stability of the immediately preceding step. From these studies, we now know that unpredictable, continuous perturbations during human walking applied in a given direction can be used to elicit predictable responses in motion variability and stability in that same direction. We know that the type of stability examined can influence the conclusions drawn about an individual’s stability during perturbed walking. For example, an individual’s variability may indicate increased risk of falling while he or she simultaneously demonstrates increased orbital stability and instantaneous lateral stability. A challenge faced in this area of research will be to understand how quantitative measures of stability relate to how we perceive our stability.Item Effects of limited foot placement on specific gait characteristics(Texas Tech University, 2004-08) Stephens, Leah SheaThe study of how people move in crowds must take into consideration two things: the movement of the crowd as a whole and the movement of the person as an individual. Egress and emergency evacuation studies produced results that showed crowd flow rates relative to density and the personal space preferred by most humans. From the other side, biomechanical studies have been performed on human gait to determine relationships between parameters such as velocity, step/stride length, stride frequency/cadence, time of swing and stance, etc. However, there is little information on how the spatial characteristics of the crowd affect the movement of the individual person within. The purpose of this study is to begin to link the two fields together by discovering the relationship between specific biomechanical characteristics of gait and the distance between people. The biomechanical characteristics taken into consideration for this study will be maximum velocity, stride length, and stride frequency. Each characteristic will be obtained by use of a motion analysis system and then compared against the buffer zone (the distance ahead of and behind the subject available for foot placement).Item Effects of musculoskeletal and sensory degradation due to aging on the biomechanics of slips and falls(Texas Tech University, 2000-05) Lockhart, Thurmon EInjuries associated with slip and fall accidents continue to pose a significant problem to industry, both in terms of human suffering and economic losses. Although much has been learned over the last few decades about the deterioration of muscular strength, gait adaptations and sensory degradation among older individuals, still little is known about how these intrinsic changes affect biomechanical parameters of slip and fall accidents among the aging workforce. The objective of this study was to closely investigate the process of initiation and recovery of inadvertent slips and falls. The specific aim of the proposed research was to investigate the changes in the biomechanical parameters of walking and ground reaction forces due to intrinsic deficits associated with increase in age. More specifically, how deterioration of muscular strength and sensory degradation among older individuals affect biomechanical parameters of slip and fall accidents under normal and abnormal conditions. The investigation compared biomechanical parameters of walking in three age groups; (18-30 years), (35-59 years), and (65 years or over). Biomechanical parameters included; step length, heel velocity, required coefficient of friction, slip distance, and position and velocity of center of gravity of the whole body during heel contact phase of the gait. These parameters were measured utilizing force platforms, a 3-D motion analysis system, and a fall arresting rig. To determine the position and velocity of center of gravity during heel contact phase of the gait, a 3-D link (14) segment model was utilized. Walking surfaces included oily vinyl tiles (DCOF-0.08) and outdoor carpet (DCOF-1.80). Subjects walked according to their natural cadences. A sensory organization test was also performed to obtain information concerning the subject's proprioceptive, visual, and vestibular systems. These sensory components were measured using an Equitest Posturography Platform. In addition, isometric strength test was performed (using a force transducer) to obtain information concerning the subject's over-all strength. The results indicated that younger subjects slipped as often as the elderly subjects, however, the recovery process of older individuals was much slower and less effective. The ability to successfully recover from a slip (thus preventing a fall) is believed to be affected by lower extremity muscle strength and sensory degradation of the elderly individuals.Item Kinematic and motor variability and stability during gait: effects of age, walking speed and segment height(2007-12) Kang, Hyun Gu, 1978-; Dingwell, Jonathan B.To understand how falls occur during walking in older adults, we need to understand how the nervous system maintains stability, and how aging affects walking. Four studies were conducted to better understand the effect of age on gait. Older adults display higher gait variability compared to young adults, possibly because of their slower walking. We compared gait stability at multiple controlled walking speeds. Greater gait variability in healthy elderly existed independent of slower walking. Their diminished strength and flexibility partly explained this difference. To explain slower walking in the elderly, some have suggested that muscle weakness and stiffness may force people to walk slower. Others have suggested that people choose to walk slower to be more stable. We compared dynamic stability of gait at multiple speeds. Healthy older adults also exhibited more stability at slower speeds, yet walked at speeds comparable to young adults despite the lower strength and flexibility. Therefore, weakness and stiffness may not force healthy older adults to walk slower. The goal of the nervous system during walking may be to maintain stability of superior segments. We tested whether superior segments are more stable than inferior segments during walking. Superior segments exhibited less orbital stability during preferred walking speed, in contrast to previous suggestions. This highlighted the importance of trunk control during gait. The effects of aging on the fluctuations in the muscle activity during gait are not well understood. We quantified the stride-to-stride fluctuations of EMG as a measure of muscle activation patterns in state-space. Variability increased with speed except in the gastrocnemius. Orbital stability was less in older adults, suggesting that deviations in the EMG amplitude pattern were not readily corrected. Less local stability was seen in older adults, suggesting that older adults were more sensitive to perturbations. Together, these findings suggest that trunk control is important during gait. Strength and flexibility deficits help explain higher variability and lower stability in older adults. Future work will need to address the effect of strength interventions, neurophysiological decline on gait stability and fall risk.Item The role of musculoskeletal dynamics and neuromuscular control in stress development in bone(Texas Tech University, 1998-05) DeWoody, YssaThe role of forces produced by the musculotendon units in the stress development of the long bones during gait has not been fully analyzed. It is well known that the musculotendons act as actuators producing the joint torques which drive the body. Although the joint torques required to perform certain motor tasks can be recovered through a kinematic analysis, it remains a difficult problem to determine the cictual forces produced by each muscle that resulted in these torques. As a consequence, few studies have focused on the role of individual muscles in the development of stress in the bone. This study takes a control theoretic approach to the problem. A seven-link, eight degrees of freedom model of the body is controlled by various muscle groups on each leg to simulate gait. The simulations incorporate HiQ-type models of muscles with activation and contra