京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第21251号 / 医博第4369号 / 新制||医||1029(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 佐藤 俊哉, 教授 川上 浩司, 教授 今中 雄一 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

According to the Public Health Agency of Canada, falls account for 95% of all hip fractures in Canada; 20% of fall-related injury cases end in death. This thesis evaluates the predictive power of many variables to predict fall-related injuries. The dataset chosen was CCHS which is high dimensional and diverse. The use of Principal Component Analysis (PCA) and random forest was employed to determine the highest priority risk factors to include in the predictive model. The results show that it is possible to predict fall-related injuries with a sensitivity of 80% or higher using four predictors (frequency of consultations with medical doctor, food and vegetable consumption, height and monthly physical activity level of over 15 minutes). Alternatively, the same sensitivity can be reached using age, frequency of walking for exercise per 3 months, alcohol consumption and personal income. None of the predictive models reached an accuracy of 70% or higher. Further work in studying nutritional diets that offer protection from incurring a fall related injury are also recommended. Since the predictors are behavioral determinants of health and have a high sensitivity but a low accuracy, population health interventions are recommended rather than individual-level interventions. Suggestions to improve accuracy of built models are also proposed. / Thesis / Master of Science (MSc)

Research Objectives The objective of this study was to evaluate if neuromusculoskeletal training (i.e., weight and balance training) for older adults could reduce the likelihood of slip-induced fall accidents. The study focused on evaluating biomechanics among the elderly at pre- and post-training stages during processes associated with slip-induced fall accidents. Motivations: Older adults are at a higher risk of falls due to deficient gait characteristics and postural control, especially when facing unexpected external perturbations such as slippery surfaces. The literature (Alexander et al., 1992; Englander 1996; Hausdorff, 2001; Rizzo 1998) indicates that falls among the elderly over 65 result in enormous economic and personal losses, therefore, the losses must be diminished. The results from this study can provide intervention strategies for researchers, health care individuals, and the elderly and their families in reducing the likelihood of slip-induced falls. Background: More than 25% of older adults fall every year (Sattin, 1992), and older adults and their family members fear their falls and fall-related injuries due to the associated high mortality rate (Jensen, 2003). The Center for Disease Control (CDC) reported in 2003 that emergency departments treated more than 1.6 million seniors due to fall-related injuries and, among them, 373,000 were admitted to the hospital. In 2002, The National Safety Council reported that 14,500 people died due to fall-related accidents, and 60 percent of them were 65 years of age and older. To minimize economic and personal losses, tribometric techniques for assessing shoe/floor interactions, the biomechanical responses in walking on slippery floor surfaces, and postural control were studied. Still, the elderly population is at a high risk of falling, severe enough that it is a major cause of hospitalization (CDC, 2003). Yet reasons for slip-induced fall accidents are not clear. Therefore, mechanisms involving fall accidents must be explored and, further, interventions to minimize fall accidents must be discovered and implemented. The occurrence of falls among the elderly are postulated to result from neuromusculoskeletal aging. The changes in neuromusculoskeletal components with advancing age are commonly accompanied with mobility problems and poor health status contributing to a decreased physical capability such as a reduction in lower extremity strength (Larsson et al., 1979; Lord et al., 1991 and 1994; Murray et al. 1985; Stalberg et al., 1989; Whipple et al. 1987) and insecure and unconfident balance (Manchester et al. 1989; Stelmach and Sirica, 1987; Teasdale et al. 1991; Thelen et al., 1998; Woolacott, 1986) leading to unstable dynamic postural control and poor gait dynamics (Alexander, 1994; Judge, 2003; Lockhart et al., 2003; Wolfson, 2001). Unstable dynamic postural control and poor gait dynamics influence the likelihood of falls among older adults (Guralnik et al.1994; Judge et al.1996; Lockhart et al., 2003; Tinetti et al. 1988). Therefore, in an effort to improve unstable dynamic postural control and poor gait dynamics, strength and balance training have been proposed and implemented. (Campbell et al., 1999; Day et al., 2002; Fiatarone et al., 1994; Neil, 1994; Shepard et al., 1993; Tinetti et al, 1994; Wolfson et al, 1993). Problem Statement: Although the significance of muscle strengthening and balance training in reducing falls for older adults has been addressed previously, most studies (Berg et al., 1992; Duncan et al., 1990; Guralnik et al.,1994; Hageman et al., 1995; Nashner, 1993; Nashner and McCollum, 1985; Nevitt et al., 1989; Overstall et al., 1977; Rikli and Jones, 1999; Tinetti, 1986) have focused on the effect of muscle strengthening and balance training on the static and dynamic postural control such as quite standing, one-leg stand, the sit-to-stand test, the test of precise movement, functional reaching, or the mobility test. Yet, research to evaluate the effectiveness of muscle strengthening and balance training on actual slip-induced fall events was lacking. This study were carried out to evaluate the likelihood of falls at pre- and post stages of training by incorporating and validating the effectiveness of training utilizing actual perturbations commonly associated with slips and falls. Method: 18 older adults participated in the study for 8 weeks: 6 individuals in balance group, 6 individuals in weight group, and 6 individuals in control group (social group). Each group met three times a week and each session lasted for 1 hour. Biomechanical dependent measures and psychosocial dependent measures were evaluated to the effects of training. Results: The results indicated that, overall, training resulted in improvements in biomechanical dependent measures. Further, regular social activities resulted in improvements in proprioception sensory sensitivity and in ankle dorsiflexion muscular strength. Conclusion: Balance training contributed to an improvement in ankle flexibility, whereas, weight training did not contribute to an improvement in ankle flexibility although either weight or balance training played a role in decreasing slip-propensity and the likelihood of slip-induced falls among older adults. An ability to integrate neuro-musculo-skeletal systems was improved by training and was a main contributor in reducing the likelihood of slip-induced falls. Proprioception sensitivity by itself did not play a role in decreasing the likelihood of slip-induced falls. In addition, the exercise training as well as social activities played a role in altering psychosocial behavior (i.e. fear of falling and independency) of older adults. The author concluded that an ability to integrate neuro-musculo-skeletal systems could be improved by either balance or weight training and could be a primary factor contributing to a reduction in the likelihood of slip-induced falls among older adults. In addition, the author concluded that the regular social activities also could contribute to an enhancement in the psychosocial characteristics of older adults. / Ph. D.

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. / Ph. D.

Falls from heights are a major concern in the occupational setting, and are often the result of a loss of balance. Lumbar extensor fatigue (LEF) increases postural sway which has been associated with degradations in balance. Study one focuses on the effects of fatiguing time and fatigue level on the duration of these increases in postural sway. Measures of postural sway were collected before fatigue and at 3 minute intervals for 30 minutes following fatigue. LEF had a significant effect on postural sway immediately following fatigue but this effect had only minor dependence on fatigue condition. During the 30 minutes following fatigue, the effects of fatiguing time and fatigue level became more apparent. Longer fatiguing time and higher fatigue levels resulted in significantly greater prolonged effects. While it is important to understand the immediate effect of LEF on sway, this study has demonstrated that the prolonged effect of such fatigue should be considered when addressing falls from heights. Study two attempts to explain the increases in postural sway associated with LEF. The ankle plays a major role in upright standing and degradations in proprioception could contribute to increases in sway, thus the effect of LEF on ankle proprioception was studied. Additionally, the effect of circumferential ankle pressure (CAP) on ankle proprioception was assessed to evaluate it as a potential intervention to improve proprioception. Results showed that both LEF and CAP impaired proprioception. These results may help to explain observed increases in postural sway subsequent to LEF. / Master of Science

No / Falls in the elderly are a major cause of serious injury and mortality. Impaired and absent stereopsis may be a significant risk factor for falls or hip fracture, although data from epidemiological studies are not consistent. Previous laboratory based studies, however, do suggest that stereoacuity is an important factor in adaptive gait. The present study investigates how acute impairment of stereopsis, through monocular blur of differing levels, ranging from 0.50 diopter (D) to a monovision correction affected gait when negotiating a raised surface in elderly subjects. Eleven elderly subjects (73.3 3.6 years) walked up to and negotiated a raised surface under nine visual conditions, binocular vision, one eye occluded and 0.50 D, 1.00 D and monovision correction (mean 2.50 D 0.20 D) with blur and occlusion either over the dominant or non-dominant eye. Analysis focused on foot positioning and toe clearance parameters. There was no effect of ocular dominance on any parameters. Monocular blur impaired stereopsis (p 0.01), with more minor effects on high and low contrast acuity. Vertical and horizontal lead limb toe clearance both increased under all levels of monocular blur including the lowest level of 0.50 DBlur (p 0.03) and monovision correction led to toe clearance levels similar to that found with occlusion of one eye. Findings demonstrated that even small amounts of monocular blur can lead to a change in gait when negotiating a raised surface, suggesting acute monocular blur affected the ability to accurately judge the height of a step in the travel path. Further work is required to investigate if similar adaptations are used by patients with chronic monocular blur.

Thesis (Ph.D.)--Memorial University of Newfoundland, 2001. / Bibliography: leaves [382]-405.

Thesis (Ph. D.)--Memorial University of Newfoundland, 2001. / Includes bibliographical references.

The purpose of this thesis was to compare the contributions of attentional resources relevant to postural control between fall-fearful and non-fearful older adults. Levels of postural challenge and instructions of task prioritization were manipulated to obtain this goal. Results indicated that fall-fearful subjects demonstrated a reorganization of attentional resources when challenge to upright standing was imposed. Additionally, only non-fearful subjects demonstrated flexibility in the prioritization of the cognitive task. However both fall-fearful and non-fearful subjects demonstrated flexibility in the prioritization of the postural task. Findings suggested that fall-fearful older adults reorganize the allocation of attentional resources differently than non-fearful counterparts, potentially placing them at greater risk for falling as their awareness of the external environment and threats to balance may be compromised. / xii, 80 leaves : ill. ; 29 cm

Thesis (Ph.D.)--University of Wollongong, 2005. / Typescript. Includes bibliographical references: leaf 251-287.