Browsing by Subject "Falls (Accidents)"
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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 Floor slipperiness and load carrying effects on the biomechanical study of slips and falls(Texas Tech University, 1993-05) Myung, RohaeBiomechanical and tribological studies have been the main approaches for investigating slips and falls. The commonly used dynamic coefficient of friction (DCOF), a tribological approach, is based on limited biomechanical studies. Therefore, a study was conducted to find the floor slipperiness effect, load carrying effect, and contaminant effect with slip distance, heel velocity, and stride length using a broader variety of floors and levels of slipperiness than has been used before. Slip distance was hypothesized as being a superior parameter over DCOF in differentiating floor slipperiness. Heel velocity was measured to find its significance m a biomechanical approach, since it is the most important factor in tribological DCOF measures. Stride length was measured to find the gait pattern changes for different levels of floor slipperiness and load carrying levels. Four different floor surfaces covering the full range of safety standards for slipperiness (with and without an oil contaminant) were prepared for ten subjects with each walking at a fixed velocity while carrying five different loads. A programmable slip resistance tester was used to measure DCOF with conventional setup values for heel velocity and vertical force. The results showed that the floor slipperiness effect and load carrying effect were very significant. The effect of the contaminant was highly significant and even overpowered the floor slipperiness and load carrying effects. Slip distance and heel velocity increased while stride length decreased as floor slipperiness and load carrying levels increased. The inconsistency of steel DCOF showed that slip distance was a comparatively stable measure because it was measured directly from human reactions and resulted in as good as DCOF in differentiating floor slipperiness. In measuring DCOF in the past, the selection range of heel velocities and load carrying levels were chosen at levels seen with a normal waDcing gait in non-slippery conditions. However, a normal gait could not be maintained on contaminated floors because stride length decreased so that a faster transfer of the body weight could be accomplished. Therefore, faster heel velocities and heavier load carrying levels should be applied for realistic DCOF measures on contaminated floors.Item Human posture control: preparation gait to avoid slips and falls(Texas Tech University, 2004-05) Park, Woo-HyungThe purpose of the present study was to identify preparation gait patterns for avoiding slips and falls. Six experimental conditions combining two walking speeds and three internal gait models were presented. In order to investigate the initiation time of the preparation gait, subject walking speed was manipulated by using two step frequencies. In order to investigate the effect of a subject's intention and future external condition, the internal gait model was manipulated by combining two adaptation gait styles and two target surface conditions. The hypotheses of this study were that (1) a preparation gait is observable and significantly different from a normal surface gait; (2) a preparation gait pattern is a function of an internal gait model; and (3) a preparation gait is initiated as a function of walking speed. To test the hypotheses, (1) kinetics and kinematics of gait were simulated using a two-link inverted pendulum model applying a system control theory; (2) the simulation results were used to derive specific hypotheses concerning how the preparation gait is generated by each of two adaptation gaits, that is, the walk-over adaptation gait and the slide-over adaptation gait; and (3) kinetic and kinematic data were collected from human subjects to identify the preparation gait. It was found that a preparation gait involves several levels of motor programming. At the level of segment control, the overall motion patterns of segments are consistent regardless of the internal gait model. At the level of coordination control, different coordination patterns were found, corresponding to different internal gait models. Subjects attempted certain initial postures to adapt to a slippery surface, minimizing the foot and shank forward angles and maximizing the thigh and trunk forward angles. To do this, subjects reduced the angular velocity of distal segments more than that of the proximal segments. Subjects also changed the coordination strength of adjacent segments from the distal segments to the proximal segments as balance control became critical. Finally, preparation gait is initiated in the middle of the step cycle prior to contact with a slippery surface: preparation gait was a part of the gait rather than a unique movement.Item The effect of postural changes on slip and fall accidents(Texas Tech University, 1990-05) Son, Dal Ho"Injury in U.S.A" identified the role of falls in producing injury throughout all segments of the nation. The economic and social costs arising from falls have been established in numerous sources, both nationally and from the international literature. "Injury in U.S.A." also indicated the potential role of epidemiology in identifying the significant features of falls, the need for a basic understanding of the energy exchange mechanism involved and the subsequent rehabilitation processes required. It appears unlikely that any other major cause of injury has an etiology so little researched and consequently, so little understood, which in turn has prevented the development of an intervention strategy or a scientifically based control technology of falls. Also, tribometric research on rubber-like materials confirms the need for dynamic data from human gait and slipping. So far, unfortunately, this problem has been underestimated by many investigators of slipping accidents, who did not consider slips and falls to be complicated phenomena from both tribological and biomechanical aspects. In most walking the heel slides upon heel strike. Usually, the sliding motions are unnoticed by the subject and occur even without lubricant. Under certain circumstances, these microslips develop into uncontrolled slides which in turn lead to the most common type of fall. However, a larger number of slips are clearly stopped at a distance of a few centimeters or less. This study reports on the relationship between foot attitude, two-dimensional slip patterns, body segment motion, the forces involved through the whole of the slip:stop cycle for a two walking speeds and two levels of slipperiness design.