Fall prevention strategy for an active orthotic system

Dissertação de mestrado integrado em Engenharia Biomédica (especialização em Eletrónica Médica)Todos os anos, são reportadas cerca de 684,000 quedas fatais e 37.3 milhões de quedas não fatais que requerem atenção médica, afetando principalmente a população idosa. Assim, é necessário identificar eficientemente indivíduos com alto risco de queda, a partir da população alvo idosa, e prepará los para superar perturbações da marcha inesperadas. Uma estratégia de prevenção de queda capaz de eficientemente e atempadamente detetar e contrariar os eventos de perdas de equilíbrio (PDE) mais frequentes pode reduzir o risco de queda. Como slips foram identificados como a causa mais prevalente de quedas, estes eventos devem ser abordados como foco principal da estratégia. No entanto, há falta de estratégias de prevenção de quedas por slip. Esta dissertação tem como objetivo o design de uma estratégia de prevenção de quedas de slips baseada na conceção das etapas de atuação e deteção. A estratégia de atuação foi delineada com base na resposta biomecânica humana a slips, onde o joelho da perna perturbada (leading) apresenta um papel proeminente para contrariar LOBs induzidas por slips. Quando uma slip é detetada, a estratégia destaca uma ortótese de joelho que providencia um torque assisstivo para prevenir a queda. A estratégia de deteção considerou as propriedades atrativas dos controladores Central Pattern Generator (CPG) para prever parâmetros da marcha. Algoritmos baseados em threshold monitorizam o erro de previsão do CPG, que aumenta após uma perturbação inesperada na marcha, para a deteção de slips. O ângulo do joelho e a velocidade angular da canela foram selecionados como os parâmetros de monitorização da marcha. Um protocolo experimental concebido para provocar perturbações de slip a sujeitos humanos permitiu a recolha de dados destas variáveis para posteriormente validar o algoritmo de deteção de perturbações. Algoritmos CPG foram capazes de produzir aproximações aceitáveis dos sinais de marcha em estado estacionário do ângulo do joelho e da velocidade angular da canela com sucesso. Além disso, o algoritmo de threshold adaptativo detetou LOBs induzidas por slips eficientemente. A melhor performance global foi obtida usando este algoritmo para monitorizar o ângulo do joelho, que detetou quase 80% (78.261%) do total de perturbações com um tempo médio de deteção (TMD) de 250 ms. Além disso, uma média de 0.652 falsas perturbações foram detetadas por cada perturbação corretamente identificada. Estes resultados sugerem uma performance aceitável de deteção de perturbações do algoritmo, de acordo com os requisitos especificados para a deteção.Every year, an estimated 684,000 fatal falls and 37.3 million non-fatal falls requiring medical attention are reported, mostly affecting the older population. Thus, it is necessary to effectively screen high fall risk individuals from targeted elderly populations and prepare them to successfully overcome unexpected gait perturbations. A fall prevention strategy capable of effectively and timely detect and counteract the most frequent loss of balance (LOB) events may reduce the fall risk. Since slips were identified as the main contributors to falls, these events should be addressed as a main focus of the strategy. Nonetheless, there is a lack of slip-induced fall prevention strategies. This dissertation aims the design of a slip-related fall prevention strategy based on the conception of an actuation and a detection stage. The actuation strategy was delineated based on the human biomechanical reactions to slips, where the perturbed (leading) leg’s knee joint presents a prominent role to counteract slip-induced LOBs. Thereby, upon the detection of a slip, this strategy highlighted a knee orthotic device that provides an assistive torque to prevent the falls. The detection strategy considered the attractive properties of biological-inspired Central Pattern Generator (CPG) controllers to predict gait parameters. Threshold-based algorithms monitored the CPG’s prediction error produced, which increases upon an unexpected gait perturbation, to perform slip detection. The knee angle and shank angular velocity were selected as the monitoring gait parameters. An experimental protocol designed to provoke slip perturbations to human subjects allowed to collect data from these variables to further validate the perturbation detection algorithm. CPG algorithms were able to successfully produce acceptable estimations of the knee angle and shank angular velocity signals during steady-state walking. Furthermore, an adaptive threshold algorithm effectively detected slip-induced LOBs. The best overall performance was obtained using this algorithm to monitor the knee angle from the perturbed leg, which detected almost 80% (78.261%) of the total perturbations with a mean detection time (MDT) of 250 ms. In addition, a mean of 0.652 false perturbations were detected for each correct perturbation identified. These results suggest an acceptable perturbation detection performance of the algorithm implemented in light of the detection requirements specified

Identifying Gait Deficits in Stroke Patients Using Inertial Sensors

Falls remain a significant problem for stroke patients. Tripping, the main cause of falls, occurs when there is insufficient clearance between the foot and ground. Based on an individual’s gait deficits, different joint angles and coordination patterns are necessary to achieve adequate foot clearance during walking. However, gait deficits are typically only quantified in a research or clinical setting, and it would be helpful to use wearable devices – such as accelerometers – to quantify gait disorders in real-world situations. Therefore, the objective of this project was to understand gait characteristics that influence the risk of tripping, and to detect these characteristics using accelerometers. Thirty-five participants with a range of walking abilities performed normal walking and attempted to avoid tripping on an unexpected object while gait characteristics were quantified using motion capture techniques and accelerometers. Multiple regression was used to identify the relationship between joint coordination and foot clearance, and multiple analysis of variance was used to determine characteristics of gait that differ between demographic groups, as well as those that enable obstacle avoidance. Machine learning techniques were employed to detect joint angles and the risk of tripping from patterns in accelerometer signals. Measures of foot clearance that represent toe height throughout swing instead of at a single time point are more sensitive to changes in joint coordination, with hip-knee coordination during midswing having the greatest effect. Participants with a history of falls or stroke perform worse than older non-fallers and young adults on many factors related to falls risk, however, there are no differences in the ability to avoid an unexpected obstacle between these groups. Individuals with an inability to avoid an obstacle have lower scores on functional evaluations, exhibit limited sagittal plane joint range of motion during swing, and adopt a conservative walking strategy. Machine learning processes can be used to predict knee range of motion and classify individuals at risk for tripping based on an ankle-worn accelerometer. This work is significant because a portable device that detects gait characteristics relevant to the risk of tripping without expensive motion capture technology may reduce the risk of falls for stroke patients

人のつま先制御能力を向上させる歩行訓練ロボットの適応的な介入手法の提案

早大学位記番号:新8439早稲田大

Contributions to successful trip recovery in younger and older adults

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Postural stability during standing and walking and the effects of ageing

The postural stability during quiet stance and during walking was investigated in 22 elderly and 20 young subjects. A motion analysis system was used to simultaneously record movements of 14 markers on the body while a force plate recorded movement of the centre of pressure (COP) during stance (but not during walking). The movements of the body during stance could be well described (> 90 % of the variance explained) as a simple inverted pendulum moving about the ankles in the anterior-posterior and medial-lateral directions. This model was applicable to both young and elderly subjects and also predicted the records of COP movement well (r > 0.90). When account was taken of the ground reaction forces the prediction was further improved. The greater COP movements commonly observed in the elderly are shown to be due to increased pendulum sway in the medial-lateral direction, compared to young subjects. The inverted pendulum model also gave an adequate description of the deviations from the mean path ("sway") during walking which are larger than those during stance. The static measurement that best predicts sway during walking is medial-lateral movements of the COP when standing on a compliant surface with the eyes closed. The relationship between muscle strength and COP displacement was examined in a larger group of elderly subjects (N = 56). Maximum voluntary force per cross-sectional area was found not to be correlated with COP movements during quiet stance. This suggests that muscle weakness and increased sway in the elderly have separate physiological causes. A method was developed for inducing a trip-like perturbation of gait as subjects walked on a treadmill. Muscle activation patterns and body kinematics were recorded in 9 young subjects to establish the normative response to such a perturbation with a view to investigating these responses in the elderly

Recovery from a trip in young and older adults : mechanics and control of the support limb

Falls and fall-related injuries are the cause of serious medical and social problems, especially in the growing elderly population. Tripping over an obstacle is one of the major causes for falls in the elderly. This thesis was aimed to obtain insight in the requirements for a successful recovery reaction after tripping and to understand why older people sometimes fail to meet these requirements and fall. Young and older subjects were tripped over an obstacle during walking over an experimental setup, while wearing a safety harness. The kinematics, dynamics and muscle activity during their balance recovery reactions were measured and compared. A rapid and strong push-off reaction by the support limb appeared to be important for successful balance recovery. Older adults, especially older fallers, were less able to recovery their balance due to a lower rate of change of moment generation in all support limb joints and a lower peak ankle moment. In addition to changes in muscle and tendon properties, a lower rate of muscle activation can reduce the rate of force generation, which can hamper the recovery mechanism and lead to a fall. These results suggest that muscle strength may be a limiting factor in preventing a fall. Strength training, combined with training on a functional level, is indicated in older people with low physical capacities to reduce the risk of falling after a trip.Dieen, J.H. van [Promotor]Bobbert, M.F. [Copromotor

The Effects of Age on Gait and Functional Movement Characteristics in an Older Adult Population

The maintenance of function in an ageing population is essential to ensure current and future health in older people. The ability to walk independently in a range of situations and environments is key to successful ageing. Age-related gait adaptations including spatial-temporal parameters, joint kinematics and kinetics have been identified to be a consequence of the ageing process. For example, reduced walking speed and increased pelvic tilt are suggestive of compensation strategies to minimise falls. The majority of research has compared young adults (20-40 yrs) to older adults (≥ 50 yrs), categorising older adults into a single group regardless of actual age. An alternative approach is to explore the effects of age on gait and functional movement characteristics within an older adult population. One-hundred and fifty-eight community-dwelling older adults, age range 55 to 86 years (65.7 ± 6.8 yrs) were recruited to create a new gait database. Three-dimensional motion analysis captured five walking tasks: normal walking (with and without force plate contact), manual dual task walking and walking with obstacle clearance (stepping onto, off and over an obstacle). Age-related adaptations to walking occurred from age 75 years by adopting a joint kinetic strategy (including reduced hip extension moment) and altering gait (including a reduced walking speed). Increasing the task complexity was associated with altered gait patterns for this older adult group including a reduction in toe-clearance during manual dual task walking (increasing the likelihood of tripping) and increased arm swing during obstacle clearance (potentially increasing stability). This work represents the creation of one of the largest databases of gait in older people including three-dimensional motion analysis for normal walking and three functional walking tasks for healthy high-functioning older adults. It has the potential to be used to identify factors that predispose older adults to falling or with previously unidentified pathological changes

Effects of triceps surae muscle strength and tendon stiffness on the reactive dynamic stability and adaptability of older female adults during perturbed walking

This study aimed to examine whether the triceps surae (TS) muscle-tendon unit (MTU) mechanical properties affect gait stability and its reactive adaptation potential to repeated perturbation exposure in older adults. Thirty-four older adults each experienced eight separate unexpected perturbations during treadmill walking, while a motion capture system was used to determine the margin of stability (MoS) and base of support (BoS). Ankle plantar flexor muscle strength and Achilles tendon (AT) stiffness were analyzed using ultrasonography and dynamometry. A median split and separation boundaries classified the subjects into two groups with GroupStrong (n = 10) showing higher ankle plantar flexor muscle strength (2.26 +/- 0.17 vs. 1.47 +/- 0.20 N center dot m/kg, means +/- SD: P < 0.001) and AT stiffness (544 +/- 75 vs. 429 +/- 86 N/mm; P = 0.004) than GroupWeak in = 12). The first perturbation caused a negative Delta MoS (MoS in relation to unperturbed baseline walking) at touchdown of perturbed step (Pert(R)), indicating an unstable position. GroupStrong required four recovery steps to return to Delta MoS zero level, whereas GroupWeak was unable to return to baseline within the analyzed steps. However, after repeated perturbations, both groups increased Delta MoS at touchdown of Pert(R) with a similar magnitude. Significant correlations between Delta BoS and Delta MoS at touchdown of the first recovery step and TS MTU capacities (0.41 < r < 0.57: 0.006 < P < 0.048) were found. We conclude that older adults with TS muscle weakness have a diminished ability to control gait stability during unexpected perturbations, increasing their fall risk, but that degeneration in muscle strength and tendon stiffness may not inhibit the ability of the locomotor system to adapt the reactive motor response to repeated perturbations. NEW & NOTEWORTHY Triceps surae muscle weakness and a more compliant Achilles tendon partly limit older adults' ability to effectively enlarge the base of support and recover dynamic stability after an unexpected perturbation during walking, increasing their fail risk. However, the degeneration in muscle strength and tendon stiffness may not inhibit the ability of the locomotor system to adapt the reactive motor response to repeated perturbations

New Trends in Neuromechanics and Motor Rehabilitation

Neuromechanics has been used to identify optimal rehabilitation protocols that successfully improve motor deficits in various populations, such as elderly people and individuals with neurological diseases (e.g., stroke, Parkinson’s disease, and essential tremor). By investigating structural and functional changes in the central and peripheral nervous systems based on neuromechanical theories and findings, we can expand our knowledge regarding underlying neurophysiological mechanisms and specific motor impairment patterns before and after therapies to further develop new training programs (e.g., non-invasive brain stimulation). Thus, the aim of this Special Issue is to present the main contributions of researchers and rehabilitation specialists in biomechanics, motor control, neurophysiology, neuroscience, and rehabilitation science. The current collection provides new neuromechanical approaches addressing theoretical, methodological, and practical topics for facilitating motor recovery progress