Browsing by Author "Matrangola, Sara Louise"

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    An experimental and simulation based approach toward understanding the effects of obesity on balance recovery from a postural perturbation
    Matrangola, Sara Louise (Virginia Tech, 2011-09-08)
    Obesity is associated with an increased risk of falls and subsequent injury. Most falls result from some type of postural perturbation. As such, it is important to understand how obesity influences balance recovery from a postural perturbation. There is limited information on the effects of obesity on balance recovery, and the limited available information is ambiguous. Therefore, the purpose of the research within this dissertation was to investigate the effects of obesity on balance recovery after a postural perturbation in young adults to better understand how obesity contributes to fall risk. Four separate studies make up this dissertation. The purpose of the first study was to investigate the effects of obesity on balance recovery ability using an ankle strategy in young adults. Normal-weight and obese participants recovered balance using an ankle strategy after three types of postural perturbations: an initial angular displacement, an initial angular velocity from the natural stance, and an initial angular velocity from a prescribed position. Obese participants were unable to recover balance using an ankle strategy as well as normal-weight participants when perturbations involved an initial angular velocity. However, no differences between obese and normal-weight participants were found when perturbations only involved an initial angular displacement. The effect of obesity on balance recovery in young adults was dependent on the perturbation characteristics, and may be explained by a possible beneficial effect of increased inertia on balance recovery after perturbations with little or no initial angular velocity. The purpose of the second study was to examine the effects of obesity on balance recovery by stepping in young adults. The ankle strategy has the benefit of simplifying the mechanics of balance recovery, but limits generalizability to more realistic fall scenarios where stepping to extend the base of support and recover balance is desired. Similar to the first study, participants attempted to recover balance following two types of postural perturbations: an initial angular displacement from an upright stance (by releasing participants from a static forward lean), and an initial angular velocity while in an upright stance (using a translating platform). In contrast to the first study, the ability to recover balance with a single-step did not differ between young normal-weight and obese adults. These results suggest that the reported increase in fall risk in obese adults is not a result of impaired balance recovery ability (at least among young adults that were tested here). The third study examined the effects of obesity on body kinematics immediately following a trip-like perturbation in young adults. Obesity was found to increase body angular velocity the perturbation, and that increases in body angular velocity were associated with an increased probability of a failed recovery. These results suggest that when a young obese and young normal-weight individual trip while walking at similar speeds, the young obese individual may be at a greater risk of falling following a trip because the young obese individual will experience a greater body angular velocity. This detrimental effect of obesity on the difficulty of recovering from a trip-like perturbation in young adults is most likely due to how mass is distributed throughout the body and not the amount of mass itself. The final study examined the relationship between relative strength and functional capability in young adults, and how obesity influences this relationship. To compare relative strength used during a functional task (i.e. balance recovery from a forward fall), the obese and normal-weight individual should complete the task with identical kinematics. Forward dynamic simulations were used to address this research question, instead of human subjects testing, to achieve identical kinematics. Differences in peak relative torques were found between the normal-weight and obese model, with the largest differences seen at the hip. These findings suggest that young obese individuals use greater relative strength at some joints than young normal-weight individuals to perform the time-critical task of balance recovery, and that these differences in relative strength demands may limit functional capability in young individuals who are obese.
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    A Modeling Investigation of Obesity and Balance Recovery
    Matrangola, Sara Louise (Virginia Tech, 2008-07-15)
    Obesity is associated with an increased risk of falls and subsequent injury. Previous studies have shown weight loss and strength training to be beneficial to balance, but knowing which is more beneficial will allow researchers to design interventions to maximize the benefits in terms of balance and reducing risk of falls. Therefore, the purpose of the first study was to evaluate the effects of weight loss and strength training on balance recovery using a combination of laboratory experiments and mathematical modeling. Nine male subjects with BMI 30.1 to 36.9 kg/m² were released from a forward lean and attempted to recover balance using an ankle strategy. Lean angle was increased until subjects required a step or hip flexion to recover balance. The maximum lean angle, θmax, was used as the measure of balance recovery capability. Experimental data were used as inputs to an inverted pendulum model of balance recovery. Multiple simulations were used to determine the effects of strength (maximum ankle torque and ankle torque generation rate) and weight loss on θmax. Changes in weight and strength were linearly related to changes in θmax. A 6.6 ± 0.4% decrease in weight or 6.9 ± 0.9% increase in strength were estimated as required to improve (increase) θmax by 1 degree. Based on these results, balance recovery using an ankle strategy can improve with either reductions in weight or increases in strength. In addition, weight loss may be a more effective intervention than strength gain at improving balance recovery capability. The purpose of the second study was to quantify changes in body segment inertial parameters (BSIPs) with weight loss. These data were needed to alter BSIPs in the first study to mimic changes with weight loss. Both before and after weight loss, magnetic resonance imaging scans were acquired along the length of the body and were used to calculate segment masses, COM positions, and radii of gyration. A number of significant changes in BSIPs occurred with weight loss.