Our walking patterns must be adjusted continuously in everyday living, whether for maneuvering on slippery surfaces or stepping over cracks on the street. Walking becomes more challenging as it requires more energy to lift and accelerate the body due to additional loads on the body as we move through space. This dissertation investigates gait, stability, and adaptation in adults with range of adiposity. First, we studied how people with obesity adapt to spatial (obstacle crossing) and temporal (metronome walking) task constraints during walking over-ground. Results indicated that people prioritized a spatial over temporal constraint when attempting to meet both constraints at the same time. Second, we tested how massive weight loss affects gait and stability. We measured how bariatric surgery patients walked and crossed obstacles before and one year after surgery. Findings indicated that massive weight loss improved not only gait but also postural stability during gait. Third, we quantified whole-body rotational characteristics in adults with obesity through changes in angular momentum quantities during steady-state walking. I found that angular momentum (1) was greater in adults with higher BMI, (2) was highly regulated by foot placement, and (3) did not change with walking speed. Taken together these results suggest that gait and stability can be adapted. These findings may help to develop interventions to target specific walking deficits in patients with mobility limitations such as obesity.

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The development of postural stability in children with and without visual impairments (VI) was compared. Thirty eight subjects (4- 12 years old) without VI and 12 subjects with VI (5- 12 years) took part. Stability was measured in 4 quiet standing tasks (normal or foam surface, eyes open (EO) or eyes closed (EC)) and by measuring stability limits (SL) in the anterio-posterior (a-p) and lateral (lat) planes. Results for control subjects were compared using Pearson correlation coefficients, analysis of variance, and analysis of covariance (height as the covariate). For quiet standing tasks, outcome parameters were the standard deviation (SO) of the centre of pressure (CP) in the a-p and lat planes, and mean velocity (vel) of CP movements. For the leaning tasks, SL was measured (normalized to the base of support) in the a-p and lat planes, and SL was compared to CP. Individual results for subjects with VI were compared qualitatively to control subjects. For control subjects, stability increased with age. Subjects with VI were less _stable than controls on all outcome parameters. Differences between groups were more apparent as age increased, particularly for EO conditions. This could indicate a slower pattern of development for subjects with VI compared to controls. The groups were different both in the EO and EC conditions, indicating that postural control with EC is not the same as postural control with a VI, and that vision is important to the development of postural control in children. / Thesis / Master of Science (MSc)

Workload is defined as the cost incurred by an individual, given their capacities, while achieving a particular level of performance on a task with specific demands. Demands of a task or combination of tasks may include maintaining postural stability, executing physical actions, and/or performing cognitive tasks. While there have been attempts to establish a physiological measure of concurrent physical and mental workload, as yet there has been no work towards developing a single subjective method of evaluation. Select subjective assessment methodologies were evaluated quantitatively during laboratory-based experiments. Concurrent execution of mental and physical activity was required at various levels, since it was desired to be able to measure mental workload, physical workload, and also evaluate their interaction. Measurements of task performance were investigated to evaluate the effects of combined mental and physical demands and establish which subjective assessments were accurate and sensitive to changes in workload. The utility of existing subjective assessment tools created for one domain appeared to be limited when evaluating multi-task situations requiring substantial mental and physical activity. Further clarification of the impact of different types of physical demand on cognitive processing, performance and subjective workload assessment of a constant mental task was addressed in the second experiment. This experiment investigated the effect of several activity types, specifically global versus localized effort, changes in load, and different task frequencies. The results provided support that the type of activity, load and frequency of task influence subjective mental workload assessment scores and performance. Not all existing assessment tools accurately represented an individual's ability to perform a task when there was a combination of physical and mental demands. A unidimensional tool is suggested as a screening tool to identify situations requiring excessive or increased mental workload. Alternative methods, possibly a new multidimensional tool, should be developed to obtain more detailed information so ratings of workload for different tasks may be compared. Effectiveness of a subjective stability assessment tool was evaluated in situations demanding mental activity while maintaining an upright posture. Tests were performed over a wide range of conditions, including various mental loads, sensory conditions, and postural stances. The purpose was to determine the effects of each task variation on the perception of postural stability. Postural sway increased with task difficulty, regardless of the source (i.e. postural stance, visual condition, mental workload). The addition of mental workload did not alter the non-linear relationship between objective measures of postural sway and perceptions of postural stability. Since decrements in balance are well perceived, subjective assessment tools may be incorporated in control strategies to minimize falls. / Ph. D.

No / PURPOSE. To determine the influence of refractive blur on postural stability during somatosensory and vestibular system perturbation and dual tasking. METHODS. Fifteen healthy, elderly subjects (mean age, 71 ± 5 years), who had no history of falls and had normal vision, were recruited. Postural stability during standing was assessed using a force platform, and was determined as the root mean square (RMS) of the center of pressure (COP) signal in the anterior-posterior (A-P) and medial-lateral directions collected over a 30-second period. Data were collected under normal standing conditions and with somatosensory and vestibular system perturbations. Measurements were repeated with an additional physical and/or cognitive task. Postural stability was measured under conditions of binocular refractive blur of 0, 1, 2, 4, and 8 D and with eyes closed. The data were analyzed with a population-averaged linear model. RESULTS. The greatest increases in postural instability were due to disruptions of the somatosensory and vestibular systems. Increasing refractive blur caused increasing postural instability, and its effect was greater when the input from the other sensory systems was disrupted. Performing an additional cognitive and physical task increased A-P RMS COP further. All these detrimental effects on postural stability were cumulative. CONCLUSIONS. The findings highlight the multifactorial nature of postural stability and indicate why the elderly, many of whom have poor vision and musculoskeletal and central nervous system degeneration, are at greater risk of falling. The findings also highlight that standing instability in both normal and perturbed conditions was significantly increased with refractive blur. Correcting visual impairment caused by uncorrected refractive error could be a useful intervention strategy to help prevent falls and fall-related injuries in the elderly.

No / The present study determined the effects of flexing and extending the head on the postural stability and mean anterior-posterior (A-P) center of mass (CM) position during upright stance in the elderly. To ensure visual input to stability was not a confounding variable, visual information was kept as constant as possible for all head positions. Twelve healthy elderly subjects (72.3±4.7 years) were asked to stand stationary on a single force-platform. Postural stability (assessed using the rms A-P excursion of the center of pressure (CP)) was determined for standing with the head erect, and with the head flexed and extended. The vestibular contribution to postural stability becomes increasingly important under challenging conditions, so to highlight the effects of vestibular system input, measurements of postural stability under conditions where visual and somatosensory inputs were disrupted were included. Changes in the mean A-P CM position when tilting the head were assessed by determining changes in the mean A-P location of the CP from standing with the head erect. Compared to standing with the head erect and looking straight ahead, postural stability was reduced when the head was flexed or extended (P<0.01). Changes in mean A-P CM position were only significant when standing with the head flexed (P<0.05). This suggests that increases in postural instability with the head tilted from the erect position may be in part due to mechanical perturbation rather than solely vestibular disruption.

No / PURPOSE. To determine the influence of cataractous and refractive blur on postural stability and limb-load asymmetry (LLA) and to establish how postural stability changes with the spatial frequency and contrast of the visual stimulus. METHODS. Thirteen elderly subjects (mean age, 70.76 ± 4.14 [SD] years) with no history of falls and normal vision were recruited. Postural stability was determined as the root mean square [RMS] of the center of pressure (COP) signal in the anterior¿posterior (A-P) and medial¿lateral directions and LLA was determined as the ratio of the average body weight placed on the more-loaded limb to the less-loaded limb, recorded during a 30-second period. Data were collected under normal standing conditions and with somatosensory system input disrupted. Measurements were repeated with four visual targets with high (8 cyc/deg) or low (2 cyc/deg) spatial frequency and high (Weber contrast, ¿95%) or low (Weber contrast, ¿25%) contrast. Postural stability was measured under conditions of binocular refractive blur of 0, 1, 2, 4, and 8 D and with cataract simulation. The data were analyzed in a population-averaged linear model. RESULTS. The cataract simulation caused significant increases in postural instability equivalent to that caused by 8-D blur conditions, and its effect was greater when the input from the somatosensory system was disrupted. High spatial frequency targets increased postural instability. Refractive blur, cataract simulation, or eye closure had no effect on LLA. CONCLUSIONS. Findings indicate that cataractous and refractive blur increase postural instability, and show why the elderly, many of whom have poor vision along with musculoskeletal and central nervous system degeneration, are at greater risk of falling. Findings also highlight that changes in contrast sensitivity rather than resolution changes are responsible for increasing postural instability. Providing low spatial frequency information in certain environments may be useful in maintaining postural stability. Correcting visual impairment caused by uncorrected refractive error and cataracts could be a useful intervention strategy to help prevent falls and fall-related injuries in the elderly.

No / The effect of refractive blur upon postural stability was investigated under three conditions: normal standing, standing with input from the somatosensory system disrupted and standing with input from the somatosensory and vestibular systems disrupted. Standing stability was assessed using the centre of pressure (COP) signal from force plate data in four young subjects (mean 23.9 ± 3.1 years) and five repeated sets of measurements were taken. The subjects looked straight ahead at a horizontal and vertical square wave pattern of 2.5 cycles (degree)¿1. Under each of the three test conditions, standing stability was measured with the optimal refractive correction and under binocular blur levels of 0, + 1, + 2, + 4, and + 8 D and with eyes closed. In the normal standing condition, dioptric blur had only a mild effect on postural stability. However refractive blur produced large increases in postural instability when input from one or both of the other two sensory systems were disrupted. We hypothesized that dioptric blur would have an even great effect on postural stability if the visual target used was of higher spatial frequency. This was confirmed by repeated measurements on one subject using a target of 8 cycles (degree)¿1. The study highlights the possible importance of an optimal correction to postural stability, particular in situations (or people) where input from the somatosensory and/or vestibular systems are disrupted, and where the visual surrounds are of high spatial frequency.

Title: Influence of pregnancy on static and dynamic postural stability Objectives: The aim of this thesis is to evaluate the influence of pregnancy on the static and dynamic postural stability using the dynamic computerized posturography. Another objective of this thesis is to determine which one of sensory inputs (visual, somatosensory, vestibular) plays the most important role in the control of postural stability during pregnancy with the help of various posturographic tests. Based on literature search to characterize changes in the organism of pregnant woman, which are responsible for postural instability in gravidity. Methods: One healthy pregnant woman was enrolled in this longitudinal study. She was evaluated in terms of static and dynamic postural stability using the dynamic computerized posturograph NeuroCom®. Posturographic tests were performed once every two or three weeks in the period from the 16th week of pregnancy until the 37th week of pregnancy and consisted of a battery of diagnostic tests of the module Smart EquiTest System. The data were processed in the program NeuroCom Data Analyzer. Results: The results demonstrate that there is an increased reliance on sensory inputs to maintain balance during pregnancy. Limitation of visual and proprioceptive components of stability...

Title: Influence of whole body vibration training on postural stability in selected sporting population Objectives: The aim of this study is to compare the influence of whole body vibration training on the stability of the human body and assessing the possibility of using this training method to improve postural stability in selected sporting population. Methods: 15 mainly beach volleyball players (athletes) were randomly assigned into two groups. Experimental group (n 8) in addition to their own training practiced twice a week on the Power Plate, while the control group (n 7) to continue the current practice of beach volleyball. The experimental group participated in a total of twelve units during the six-week exercise intervention. We reviewed the standard deviation and average values of COP displacements in the anteroposterior, mediolateral and overall direction of the COP path. For this purpose, we used pressure platform Footscan. Results: The results indicate a clear trend to improve postural stability at the beach volleyball player after a six-week intervention, whole body vibration training. Improvement was most noticeable in tests Flamengo (standing on one leg), in which the total COP path decreased for all probands at the right lower extremity and in six of the eight probands in the left...