Accurately simulating human motions is a major function of and challenge to digital human models and integrating humans in computer-aided design systems. Numerous successful applications of human motion simulation have already demonstrated their ability to improve occupational efficiency, effectiveness, and safety. In this dissertation, a novel motion simulation model using fuzzy logic control is presented. This model was motivated by the fact that humans use linguistic terms to guide their behaviors while fuzzy logic provides mathematical representations of linguistic terms. Specifically in this model, fuzzy logic was used to specify a neural controller which was generally considered as the part in the postural control system that plans human motions. Fuzzy rules were generated according to certain trends observed from actual human motions. An optimization procedure was performed to specify the parameters of the membership functions by minimizing the differences between the simulated and actual final postures. This research contributed to the field of human movement science by providing a motion simulation model that can accurately predict novel human motions and provide interpretations of potential human motion planning strategies. Understanding balance control is another research focus in this dissertation. Investigating balance control may aid in preventing unnecessary fall-related incidents and understanding the postural control system. Since human behaviors are generally effective and efficient, balance control models (both two- and three-dimensional) based on an optimal control strategy were developed to aid in better understanding balance control. Specifically, the neural controller was considered as an optimal controller that minimizes a performance index defined by physical quantities relevant to sway. Free model parameters, such as weights of relevant physical quantities and sensory delay time, were determined by an optimization procedure whose objective was to minimize a scalar error between simulated and experimental center-of-pressure (COP) based measures. Many factors, such as aging, localized muscle fatigue, and external loads, have been found to adversely affect balance control. At the same time, behaviors during upright stance are commonly characterized by COP-based measures. Thus, changes in COP based measures with aging, LMF, and external loads were addressed by using the proposed models, and possible postural control mechanisms were identified by interpreting these changes. Findings from these studies demonstrated that the proposed models were able to accurately simulate human sway behaviors and provide plausible mechanisms regarding how the postural control system works when maintaining upright balance. / Ph. D.

Low back pain (LBP) is a substantial secondary disability among persons with lower-limb amputation (LLA). Abnormal mechanics of movement subsequent to LLA may increase the stability demands on the spinal column, and repetitive exposures to such abnormal movements may alter trunk passive properties and/or the coordination of surrounding trunk muscle responses. Further, preferential use of the sound limb may lead to asymmetries in these behaviors. Spine biomechanics (e.g., loading and stability) are substantially influenced by trunk passive properties and neuromuscular control, and alterations in these behaviors are associated with abnormal mechanics of the spinal column and an increased LBP risk. However, there is limited evidence regarding whether prolonged repeated exposures to abnormal gait and movement resulting from LLA and subsequent repeated use of a prosthetic device affect these trunk behaviors. Eight males with unilateral LLA and a matched sample of non-amputation controls completed three studies in which several measures of trunk passive properties, neuromuscular control, and spine biomechanics were quantified using laboratory experiments and biomechanical analyses. Each study involved a distinct task to investigate potential alterations and/or asymmetries in trunk passive properties and neuromuscular control. The first study used a seated balance task to assess trunk postural control and stability. The second study used multidirectional trunk perturbations to assess trunk mechanical and neuromuscular behaviors. Finally, the third study used controlled quasi-static trunk movements to assess load-sharing mechanisms between active and passive low back tissues. Significant alterations and asymmetries in trunk passive properties and trunk neuromuscular responses were present among participants with LLA, specifically reduced and asymmetric trunk stiffness and reflex response; decreased and asymmetric passive contributions to trunk movements; and increased trunk muscle activities. Significant increases in trunk postural sway and trunk muscle activities were also present during seated stability measures. Such alterations in these behaviors may be a result of repetitive exposures to abnormal gait and movement subsequent to LLA and the use of a prosthetic device, and could play a contributing role in the development of LBP in this population. Future work should investigate the temporal relationship between altered trunk behaviors and repeated exposure to abnormal gait and movement subsequent to LLA, to better identify critical years for rehabilitation and preventative care. / Ph. D.

Every year, over 3.5 million women give birth in the United States, with about 67.9% delivering vaginally. Over 80% of postpartum (PP) women experience chronic pain in the pelvis, lower back, hip, and legs at 24 weeks after birth, and 20% continue to experience these issues 3 years later. PP women often face pelvic instability and weakness, which disturb balance and lead to asymmetric loading in the pelvis and legs. This imbalance makes daily tasks, such as lifting and carrying a car seat during childcare, more difficult, and increases the risk of chronic pain and injury. This study aimed to explore how different groups – PP and nulliparous (NP) women – and different ways of holding a car seat while standing – no holding, symmetrical holding with two hands in front, and asymmetrical holding with one arm by the side – affect balance and limb loading symmetry. Results showed that postpartum women struggled more with balance as the task became more challenging, with asymmetrical holding showing large differences between groups. PP women also exhibited greater asymmetric limb loading compared to NP women with asymmetrical holding creating the greatest level of asymmetric limb loading. The study also aimed to explore how the two groups – PP and NP – and the different ways of lifting a car seat – symmetrically and asymmetrically – affect balance and limb loading. Both groups had more asymmetric limb loading and worse balance with asymmetrical lifting, though NP women showed larger movements during asymmetrical lifting, likely reflecting the movement of the body during the condition. These results highlight the importance to further research balance and limb loading in PP compared to NP women. Understanding whether pelvic instability and weakness may contribute to differences in balance and limb loading is crucial as it may help explain how and why postpartum women face higher risk of injury and chronic pain. Ultimately, such work may find ways to improve postpartum health during daily activities. / VT Engineering Faculty Organization-Opportunity (EFO-O) Seed Investment / Master of Science / Every year, over 3.5 million women give birth in the United States, with about 67.9% delivering vaginally. Over 80% of postpartum (PP) women experience chronic pain in the pelvis, lower back, hip, and legs at 24 weeks after birth, and 20% continue to experience these issues 3 years later. PP women often face pelvic instability and weakness, which disturb balance and lead to asymmetric loading in the pelvis and legs. This imbalance makes daily tasks, such as lifting and carrying a car seat during childcare, more difficult, and increase the risk of chronic pain and injury. This study aimed to explore how different groups – PP and nulliparous (NP) women – and different ways of holding a car seat while standing – no holding, symmetrical holding with two hands in front, and asymmetrical holding with one arm by the side – affect balance and limb loading symmetry. Results showed that postpartum women struggled more with balance as the task became more challenging, with asymmetrical holding showing large differences between groups. PP women also exhibited greater asymmetric limb loading compared to NP women with asymmetrical holding creating the greatest level asymmetric limb loading. The study also aimed to explore how the two groups – PP and NP – and the different ways of lifting a car seat – symmetrically and asymmetrically – affect balance and limb loading. Both groups had more asymmetric limb loading and worse balance with asymmetrical lifting, though NP women showed larger movements during asymmetrical lifting, likely reflecting the movement of the body during the condition. These results highlight the importance to further research balance and limb loading in PP compared to NP women. Understanding whether pelvic instability and weakness may contribute to differences in balance and limb loading is crucial as it may help explain how and why postpartum women face higher risk of injury and chronic pain. Ultimately, such work may find ways to improve postpartum health during daily activities.

Yes / This article reviews the literature on how blurred vision contributes to falls, gait, and postural control and discusses how these are influenced by spectacle correction. Falls are common and represent a very serious health risk for older people. They are not random events as studies have shown that falls are linked to a range of intrinsic and extrinsic risk factors. Vision provides a significant input to postural control in addition to providing information about the size and position of hazards and obstacles in the travel pathway and allows us to safely negotiate steps and stairs. Many studies have shown that reduced vision is a significant risk factor for falls. However, randomized controlled trials of optometric interventions and cataract surgery have not shown the expected reduction in falls rate, which may be due to magnification changes (and thus vestibuloocular reflex gain) in those participants who have large changes in refractive correction. Epidemiological studies have also shown that progressive addition lens and bifocal wearers are twice as likely to fall as non-multifocal wearers, laboratorybased studies have shown safer adaptive gait with single-vision glasses than progressive addition lenses or bifocals, and a randomized controlled trial has shown that an additional pair of distance vision single-vision glasses for outdoor use can reduce falls rate. Clinical recommendations to help optometrists prevent their frail, older patients from falling are suggested. / Grant support: Atkinson Charitable Foundation, College of Optometrists, Dunhill Medical Trust, Essilor International R&D, Federation of Ophthalmic & Dispensing Opticians, Health & Welfare Canada, Health Foundation, National Institute for Health Research, PPP Foundation, and Vicon Motion Systems Ltd.

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.

Bakgrund: Befolkningen blir allt äldre och ökad ålder medför funktionsnedsättningar som minskad muskelmassa och balans. Det påverkar gången negativt, men genom att träna funktionellt eller träna upp muskelstyrkan och balansen kan äldres gångförmåga förbättras. Syfte: Syftet med studien är att undersöka hur äldres gångförmåga, self-efficacy och eventuell oro inför att gå påverkas av två olika åttaveckors interventioner med träning inom kommunal verksamhet, samt hur följsamhet till träning påverkas av self-efficacy och eventuell oro. Metod: Studiedesignen är en experimentell design i form av pretest-posttest control group som är en form av RCT. Nitton deltagare ≥65 år rekryterades via konsekutivt urval. Testresultat från TUG, självvald gånghastighet och skattningar på oro och self-efficacy inför att gå samlades in. Resultat: Ingen signifikant skillnad (p&gt;0,05) förekom mellan eller inom grupperna med avseende på testvariablerna. Korrelationsanalyserna visade på ingen, låga och moderata korrelationer, både positiva och negativa men inga signifikanta korrelationer observerades. Slutsats: Resultatet i studien kan inte generaliseras till en större population, men kan vara till grund för ytterligare studier med ett större stickprov som randomiseras utifrån populationen. Ytterligare studier krävs med syfte att undersöka om enbart gångträning är effektivt för att utveckla gångförmågan. / Background:  Since the population is aging the decrease in muscle function and balance impairments leads to increased disable. Which has a negative impact on walking ability, though through functional training, by training muscle strength and balance can enhance walking ability in elderly. Aim: The purpose of the study is to investigate how elderly people walking ability, self-efficacy and any anxiety about going, influenced by two different eight-week interventions within municipal operations, and how adherence to exercise is influenced by self-efficacy and anxiety. Method: The study design is an experimental variant of the pretest-posttest control group design. Nineteen participants’ ≥65 years recruited consecutively through selection. Test results from TUG, self-selected walking speed, and estimates on anxiety and self-efficacy before going was collected. Result: No significant difference (p&gt;0, 05) occurred between or within groups for the test variables. The correlation analysis showed none, low, moderate correlation, both positive and negative but no significant correlations was observed. Conclusion: The results of the study can’t be generalized to a larger population, but can be the basis for further studies with a larger sample to be randomized on the basis of population.  More studies are needed to investigate if only walking exercise is effective for developing the walking ability.

Les pertes d’équilibre représentent une cause importante de blessure et de mortalité, notamment sur le milieu du travail et chez les personnes âgées. Cette thèse explore les effets du manque de sommeil sur le contrôle postural en fonction de l’âge et s’intéresse à l’influence des ressources attentionnelles, perceptuelles et motrices sur la relation entre le sommeil et le contrôle postural. Des sujets jeunes et âgés ont effectué diverses tâches posturales statiques sur des plates-formes de force après une nuit de sommeil et après 25 heures de privation de sommeil. L’étendue et la vitesse des déplacements du centre de pression ont été mesurées en gardant les yeux ouverts et les yeux fermés sous trois niveaux de charge cognitive. Les résultats montrent que la privation de sommeil a augmenté l’étendue du centre de pression dans les deux groupes d’âge et a augmenté la vitesse du centre de pression chez les sujets âgés. De plus, les effets de la privation de sommeil sur le contrôle postural étaient davantage prononcés lorsque les sujets âgés gardent les yeux fermés. L’augmentation de la charge cognitive sous privation de sommeil a poussé la majorité des sujets jeunes à adopter un contrôle postural plus statique, alors que chez les sujets âgés, les effets de la charge cognitive ne se surajoutaient pas à ceux de la privation de sommeil. Ces observations suggèrent que la privation de sommeil ait des effets déstabilisateurs sur le contrôle postural qui sont plus marqués chez les personnes âgées, surtout lorsque les informations visuelles sont altérées. Il est donc proposé que le manque de sommeil soit un facteur de risque significatif pour les chutes. / Falls are an important cause of injuries and mortality, especially in the work force and in the elderly population. This thesis investigates the effects of sleep loss on postural control according to age and explores the influence of attentional, perceptual and motor resources on the relationship between sleep and postural control. Young and older participants completed various postural tasks on force plates after a night of sleep and after 25 hours of sleep deprivation. Center of pressure range and velocity were measured with eyes open and with eyes closed while participants performed an interference task, a control task, and no cognitive task. Sleep deprivation increased the range of center of pressure in both age groups and center of pressure speed in older participants only. Moreover, in elderly participants, the destabilizing effects of sleep deprivation were more pronounced with eyes closed. The interference task brought younger participants to adopt a more static postural strategy when sleep deprived. However, in older participant, the interference task did not alter postural control beyond the destabilization induced by sleep loss. These observations suggest that sleep loss has greater destabilizing effects on postural control in older than in younger adults, especially when vision is altered. It is therefore proposed that sleep debt may be a significant risk factor for falls.