Objective: Lifting-seat devices are designed to raise the seat height to reduce biomechanical and neuromuscular demands of a sit-to-stand (STS). The goal of this thesis was to understand how seat height and lifting-seat devices with different mechanisms affect trunk, hip, and knee biomechanics and neuromuscular activity of surrounding muscles, and determine whether the effects are altered by age. Four conditions were tested; 1) no device normal seat height (ND-normal), 2) Seat Assist™ (SA), 3) Power Seat™ (PS), 4) no device raised height (ND-raised). Using a cross-sectional design, two objectives were completed. Objective one compared ND-normal and ND-raised to determine the effects of seat height. Objective two compared ND-raised, PS, SA to determine the effects of lifting-seats. Design: 10 healthy older and 10 healthy younger adults performed five trials of each STS condition. Bilateral lower limb and trunk three-dimensional motion, ground reaction forces and electromyography (EMG) from five muscles were collected.

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This thesis puts forward a fuzzy logic-based control strategy for artificially reproducing the sit-to-stand movement. The aim of this work is to contribute to the machine intelligence being developed for advanced mobility support devices; and specifically, those which are able to assist the mobility impaired user with the sit-to-stand task. Three fuzzy logic controllers were designed. The first controller seeks to move the model into the “most stable” configuration. The second seeks to move the model toward the goal configuration (i.e., standing). And the third combines the output from the first two controllers to produce a unified control action. Each controller was implemented and tested in software using Mathwork’s Matlab(TM). The results of the software simulation were compared against motion capture data taken from a single healthy male test subject. The automated controller was shown to produce a movement very similar to the natural sit-to-stand movement.

Standing up from a seated position, known as sit-to-stand (STS) movement, is one of the most frequently performed activities of daily living (ADLs). However, the aging generation are often encountered with STS issues owning to their declined motor functions and sensory capacity for postural control. The motivated is rooted from the contemporary market available STS assistive devices that are lack of genuine interaction with elderly users. Prior to the software implementation, the robot chair platform with integrated sensing footmat is developed with STS biomechanical concerns for the elderly. The work has its main emphasis on recognising the personalised behavioural patterns from the elderly users’ STS movements, namely the STS intentions and personalised STS feature prediction. The former is known as intention recognition while the latter is defined as assistance prediction, both achieved by innovative machine learning techniques. The proposed intention recognition performs well in multiple subjects scenarios with different postures involved thanks to its competence of handling these uncertainties. To the provision of providing the assistance needed by the elderly user, a time series prediction model is presented, aiming to configure the personalised ground reaction force (GRF) curve over time which suggests successful movement. This enables the computation of deficits between the predicted oncoming GRF curve and the personalised one. A multiple steps ahead prediction into the future is also implemented so that the completion time of actuation in reality is taken into account.

Falls are one of the most serious problems among the elderly, resulting in fatal physical injuries. Early identification of people at a high risk of falling is needed to facilitate rehabilitation to reduce future fall risk. The overall goal of this dissertation was to develop biomechanical models that identify dynamic limits of balance control in daily functional activities associated with falling, including sit-to-stand (STS) movement, standing (stance perturbation), and walking. Poor performance of STS movement has been identified as one of the risk factors of falls among elderly individuals. We proposed a novel method to identify dynamic limits of balance control during STS movement using whole body center of mass (COM) acceleration and assessed its feasibility to differentiate individuals with difficulty in STS movement from healthy individuals. The results demonstrated that our model with COM acceleration could better differentiate individuals with difficulty in STS movement from healthy individuals than the traditional model with COM velocity. Poor postural control ability is also a risk factor of falls. Postural recovery responses to backward support surface translations during quiet standing were examined for healthy young and elderly adults. The results demonstrated that functional base of support (FBOS) and ankle dorsiflexor strength could be sensitive measures to detect elderly individuals with declined balance control. Our biomechanical model, which determines a set of balance stability boundaries, showed a better predictive capability than the statistical model for identifying unstable balance recovery trials, while the statistical model better predicted stable recovery trials. Lastly, walking requires a fine momentum control where COM acceleration could play an important role. Differences in control of dynamic stability during walking were examined with our proposed boundaries of dynamic stability. Elderly fallers adapted a more conservative gait strategy than healthy individuals, demonstrating significantly slower forward COM velocity and acceleration with their COM significantly closer to the base of support at toe-off, which could be indicative of a poor momentum control ability. Overall, this study demonstrated that COM acceleration would provide further information on momentum control, which could better reveal underlying mechanisms causing imbalance and provide an insightful evaluation of balance dysfunction. This dissertation includes unpublished co-authored material.

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Osteoarthritis (OA) of the knee is common in Western society. OA of the patellofemoral (PF) compartment of the knee is prevalent in adults greater than 55 years of age. Isolated radiographic PFOA is present in 13.6-24% of females and 11-15.4% of males with knee pain. Biomechanical factors such as tibiofemoral alignment and high joint stress are associated with the development and progression of PFOA. PF joint stress is high when the quadriceps contracts with the knee in a position of extreme flexion, such as rising from sitting. The purposes of this study were to determine 1) the triplanar biomechanics of the hips and knees during sit-to-stand (STS) for persons with PFOA versus age- and gender-matched control subjects, 2) the impact of PFOA on physical performance, perceived functional status, and pain, and 3) the relationship between knee kinematics during STS and physical performance. The biomechanics of STS was examined using a video-based motion analysis system and two force plates. Physical performance was measured with the Timed Up and Go (TUG) and Fifty-Foot Walk (FFW) tests. Perceived functional status, pain, and stiffness were measured using the Western Ontario and McMaster University Osteoarthritis Index (WOMAC) questionnaire. Knee pain was measured with a Visual Analog Scale (VAS) following STS, TUG, and FFW. Persons with PFOA required a significantly longer time to perform STS and the TUG as compared to healthy controls. The PFOA group demonstrated greater hip flexion and knee abduction versus the control group. The hip and knee moments were significantly different with the PFOA group demonstrating greater hip extension, hip abduction, hip external rotation, knee extension, and knee adduction moments. Persons with PFOA were found to have significantly less perceived physical function, greater stiffness, and greater pain. Pain following STS, TUG, and FFW were all greater in the PFOA group. No significant association was found between any knee angle and time to perform the TUG or the FFW. These results indicate that dynamic malalignment of the TF joint is present during STS in persons with PFOA. This may contribute to the increased pain and decreased function in persons with PFOA. / Physical Therapy