The high incidence of falls and fall-related injuries among Canadians over the age of 65 continues to be a key public health issue. As the current proportion of individuals within this cohort of the population is predicted to double by the year 2031, the absolute number of individuals experiencing falls, fall-related injuries and subsequent hospitalization will increase dramatically. While a fall in any direction can lead to injury and reduced quality of life, lateral falls have been shown to be prevalent and can be particularly devastating because of the increased probability of hip fracture. Forward stepping tasks, whether initiated volitionally or by external perturbation, pose a challenge to stability, as they require the precise regulation of the spatial and temporal characteristics of the whole body centre of mass (COM) in relation to a changing base of support (BOS). Despite our understanding of both proactive and reactive mechanisms for balance control at movement initiation during such stepping tasks, there appears to be little understanding or consensus regarding the origins of age-related decline in mediolateral stability, which can manifest during the restabilisation phase, at movement termination. From this, the global objective of this thesis was to develop further understanding regarding such age-related differences in mediolateral dynamic stability control during the restabilisation phase of forward stepping. Notwithstanding the well documented differences between volitional and perturbation-evoked stepping until the time of foot-contact, we have proposed the control of the COM during the restabilisation phase of such stepping tasks to be a central determinant of age-related differences in mediolateral dynamic stability, common to both forms of stepping. We quantified the COM kinematics during the restabilisation phase and calculated the magnitude of incongruity between the peak and final, stable, COM position, in addition to the intertrial variability of this incongruity. Further, we analysed the orientation of the net ground reaction force (GRF) with respect to the COM, which allowed us to draw conclusions regarding the mechanisms that may be responsible for the age-related differences in the COM kinematics. To vary the challenge to control, we included conditions in which individuals were required to step with altered step width. In addition, we attempted to probe the extent and means by which individuals could alter the dynamics of stepping over time, with trial repetition. In general, we found that overshoots of the final COM position were common to all forms of stepping and may serve the functional role of simplifying reactive control during the restabilisation phase. The magnitude and intertrial variability of incongruity, however, were greater among the older adults during all forms of stepping. We believe such increased COM incongruity is likely indicative of greater instability within this group, which may be associated with the increased time required to reorient the net GRF in a manner necessary to oppose the total body angular momentum that developed during the swing phase. Particularly interesting was the use of proactive strategies by older adults, which may have the potential to offset instability that arises due to difficulty with reactive control during the restabilisation phase. The present work provides support for previous studies, which have suggested that the control of mediolateral stability may be particularly challenging for older adults. Further, our work provides evidence that the challenges associated with mediolateral stability control have important links to the restabilisation phase and are common to both volitional and reactive stepping. This work highlights the need to further explore the control of mediolateral stability and develop therapeutic interventions to reduce such incidence of instability among older adults.

The high incidence of falls and fall-related injuries among Canadians over the age of 65 continues to be a key public health issue. As the current proportion of individuals within this cohort of the population is predicted to double by the year 2031, the absolute number of individuals experiencing falls, fall-related injuries and subsequent hospitalization will increase dramatically. While a fall in any direction can lead to injury and reduced quality of life, lateral falls have been shown to be prevalent and can be particularly devastating because of the increased probability of hip fracture. Forward stepping tasks, whether initiated volitionally or by external perturbation, pose a challenge to stability, as they require the precise regulation of the spatial and temporal characteristics of the whole body centre of mass (COM) in relation to a changing base of support (BOS). Despite our understanding of both proactive and reactive mechanisms for balance control at movement initiation during such stepping tasks, there appears to be little understanding or consensus regarding the origins of age-related decline in mediolateral stability, which can manifest during the restabilisation phase, at movement termination. From this, the global objective of this thesis was to develop further understanding regarding such age-related differences in mediolateral dynamic stability control during the restabilisation phase of forward stepping. Notwithstanding the well documented differences between volitional and perturbation-evoked stepping until the time of foot-contact, we have proposed the control of the COM during the restabilisation phase of such stepping tasks to be a central determinant of age-related differences in mediolateral dynamic stability, common to both forms of stepping. We quantified the COM kinematics during the restabilisation phase and calculated the magnitude of incongruity between the peak and final, stable, COM position, in addition to the intertrial variability of this incongruity. Further, we analysed the orientation of the net ground reaction force (GRF) with respect to the COM, which allowed us to draw conclusions regarding the mechanisms that may be responsible for the age-related differences in the COM kinematics. To vary the challenge to control, we included conditions in which individuals were required to step with altered step width. In addition, we attempted to probe the extent and means by which individuals could alter the dynamics of stepping over time, with trial repetition. In general, we found that overshoots of the final COM position were common to all forms of stepping and may serve the functional role of simplifying reactive control during the restabilisation phase. The magnitude and intertrial variability of incongruity, however, were greater among the older adults during all forms of stepping. We believe such increased COM incongruity is likely indicative of greater instability within this group, which may be associated with the increased time required to reorient the net GRF in a manner necessary to oppose the total body angular momentum that developed during the swing phase. Particularly interesting was the use of proactive strategies by older adults, which may have the potential to offset instability that arises due to difficulty with reactive control during the restabilisation phase. The present work provides support for previous studies, which have suggested that the control of mediolateral stability may be particularly challenging for older adults. Further, our work provides evidence that the challenges associated with mediolateral stability control have important links to the restabilisation phase and are common to both volitional and reactive stepping. This work highlights the need to further explore the control of mediolateral stability and develop therapeutic interventions to reduce such incidence of instability among older adults.

One 3D measurement method is laser scanning. By projecting and photographing a laser line, the centre line coordinates of the laser can be obtained with centre line detection methods and then be used to generate 3D model of the scanned object. This thesis compares three centre line detection algorithms with respect to their utility for the purpose of 3D reconstruction. The investigated algorithms were Steger’s method, Gaussian fitting and Centre of Mass. The algorithms were evaluated regarding noise sensitivity and their ability to detect jagged laser lines. It was concluded that Steger’s method was the most noise resistant, but less accurate than the others when the jagged line was at an acute angle. The performance of the Gaussian fitting and Centre of Mass algorithms was relatively equal for all investigated test cases.

Parkinson's disease (PD) is a neurological condition that can lead to changes to gait and postural stability of people with this condition. Tai Chi (TC) has been recommended for the management of PD by improving muscle strength, balance, and coordination. However, biomechanics research in TC for PD is lacking. This thesis investigated the effects of a biomechanical-based TC intervention program for people in the early-stage of PD by realizing three specific research objectives: 1) to develop a biomechanical-based TC intervention program for PD; 2) to examine the effects of a 12-week TC intervention on gait and postural stability in people with PD, by pre-test and post-test biomechanical analysis of obstacle crossing; 3) to explore the neuromuscular effects of TC intervention on gait and postural stability by analyzing the electromyography (EMG) activity of the lower limb muscles during obstacle crossing. Seven typical TC movements were selected, including Starting Form, Hero Touch Sky, Push Hand Back, Brush Knee and Twist Step, Repulse Monkey, Wave-hand in Cloud, and Lateral Forward Step to develop the TC intervention program. The joint angles, joint moment, and EMG signals of lower limbs muscles were analyzed during performance of the selected TC movements by an experienced TC master aged 38 years. Results showed that the selected TC movements are characterized by multidirectional movements, greater joint movement angles of the lower limb, and more active muscle activity than walking. The TC intervention program was formed based on the biomechanics analysis of the seven TC movements. The program consisted of 5-10 min warm up, 40 minutes of core activities, and 5 min cool down. To examine the effects of a biomechanical-based TC intervention program on gait and postural stability and to explore the neuromuscular effects of TC intervention on the lower limb muscles in people with PD, fifteen individuals in the early stage of PD (n = 15, Hoehn and Yahr stages 1 to 2; age 72.0 ± 6.9) participated in a 12-week online TC intervention, and 15 age- and sex-matched healthy participants (n = 15) served as control. The 3D motion data of the lower limb and EMG signals from the rectus femoris, adductor longus, tibialis anterior, semitendinosus, gluteus medius, tensor fasciae latae, and medial and lateral gastrocnemius muscles were collected during obstacle crossing from both groups using Vicon motion analysis system before intervention in both groups and after TC intervention in the TC group. Obstacle crossing was used to challenge the participants' gait and postural stability. Gait was assessed by measuring the temporospatial parameters such as crossing stride length, crossing step length, and crossing speed. Postural stability was assessed by measuring toe and clearance distance, pre- and post-horizontal distance, displacement and velocity of center of mass (COM), and COM-center of pressure (COP) separation. To examine the neuromuscular activity of the lower limbs following TC training, the ratio of the peak EMG, the integrated EMG (iEMG), and the ratio of the peak EMG and iEMG antagonistic pairs of the leading and trailing limb were examined during obstacle crossing and walking. In addition, the timed up-and-go test (TUG) and single-leg stance with eyes open and closed were tested. VICON Nexus, custom MATLAB scripts, and SPSS software (version 20) were used to analyze the data. Analysis of the PD participants' obstacle crossing performance revealed that they had significantly slower gait speed, smaller hip flexion angles, and larger knee adduction angles of the trailing limb, significantly larger mediolateral (ML) COM displacement and COM-COP separation distance, and significantly higher peak EMG ratios of the adductor longus, gluteus medius, and tensor fasciae latae (p < 0.05) than the healthy participants. Following the 12-week TC intervention, the PD participants had significantly increased crossing stride length, significantly decreased ML COM-COP separation (p < 0.05) and significantly increased AP COM displacement (p < 0.05), and increased EMG activity of the tibialis anterior in the leading and trailing limbs during obstacle crossing, whereas the activity of the gluteus medius and adductor longus in the leading limb decreased (p < 0.05). Moreover, the significant differences in the EMG of the gluteus medius and tensor fasciae latae muscles between PD and healthy participants found in pre-test were no longer present. After the TC intervention, the PD participants significantly improved their performance on the TUG test (p = 0.002). Therefore, people with early-stage PD presented changed gait and postural stability as well as changed neuromuscular activity of the lower limb. The 12-week online biomechanical-based TC intervention improved their gait and postural stability, particularly dynamic postural stability as measured by the COM-COP separation in people with early-stage PD. Compared to walking, performing the TC movements involved larger changes in the lower limb angles, range of motion, and higher muscle activity, particularly in the hip abductors and adductors. These characteristics of the TC movements could provide training to strengthen the muscles and improve the range of motion of the lower limbs. The gait and postural stability improvements following TC intervention are consistent with the neuromuscular activity changes in gluteus medius, tensor fasciae latae, and adductor longus muscles, indicating the mechanisms of TC training. The 12-week online biomechanical-based TC intervention program helped to decrease the ML COM-COP separation distance and could be used for the management of PD in the early stages of this condition.

Yes / To terminate gait, the mechanical work-done by the lower-limbs is likely to be predominantly negative but how such work is produced/completed has not previously been investigated. The aim of this study was to determine the amount of negative mechanical (external) work-done by the lower-limbs, along with the associated joints (muscle) work, to terminate gait and how these work contributions were affected by a change in surface angle. Eight males completed terminations on the level floor and a declined ramp. Negative mechanical limb-work (limbW(−ve)) was computed (each orthogonal direction) as the dot-product of the ground-reaction-force and centre-of-mass (CoM) velocity. Inverse dynamics was used to calculate ankle, knee and hip negative joints (muscle) work (Wj(−ve)). Measures were determined for each limb for the two-locomotor steps of gait termination. The trailing-limb did 67% (−0.386 J/kg) of the overall limbW(−ve) to terminate gait on the level; and this increased to 74% (−0.451 J/kg) for ramp trials. Wj(−ve) was greater for the trailing- (ankle −0.315; knee −0.357; hip −0.054 J/kg) compared to terminating- limb (ankle, −0.063; knee −0.051; hip −0.014 J/kg), with the increases in ankle Wj(−ve) being temporally associated with increases in perpendicular limbW(−ve). Wj(−ve) increased on both limbs for declined compared to level surface, particularly at the knee (declined −0.357, level −0.096 J/kg), with such increases being temporally associated with increases in parallel limbW(−ve). These findings provide new perspectives on how the limbs do work on the CoM to terminate gait, and may be helpful in designing prosthetic limbs to facilitate walking on ramps. / ZA was funded by the Higher Committee of Education Development in IRAQ (HCED).

No / Unilateral lower-limb amputees lead with their intact limb when stepping up and with their prosthesis when stepping down; the gait initiation process for the different stepping directions has not previously been investigated. Ten unilateral amputees (5 transfemoral and 5 transtibial) and 8 able-bodied controls performed single steps up and single steps down to a new level (73 and 219 mm). Duration, a-p and m-l centre of mass and centre of pressure peak displacements and centre of mass peak velocity of the anticipatory postural adjustment and step execution phase were evaluated for each stepping direction by analysing data collected using a Vicon 3D motion analysis system. There were significant differences (in the phase duration, peak a-p and m-l centre of pressure displacement and peak a-p and m-l centre of mass velocity at heel-off and at foot-contact) between both amputee sub-groups and controls (P<0.05), but not between amputee sub-groups. These group differences were mainly a result of amputees adopting a different gait initiation strategy for each stepping direction. Findings indicate the gait initiation process utilised by lower-limb amputees was dependent on the direction of stepping and more particularly by which limb the amputee led with; this suggests that the balance and postural control of gait initiation is not governed by a fixed motor program, and thus that becoming an amputee will require time and training to develop alternative neuromuscular control and coordination strategies. These findings should be considered when developing training/rehabilitation programs.

The theoretical part of the thesis includes introduction of Riemann integral and its qualities, introduction of function of more variables, introduction of double and triple Riemann integral and physical applications of integral. The practical part includes derivation of general area formulas for different shapes and volume formulas for different solids, in some examples there are shown different ways of solution. The practical part also includes the use of Riemann integral for the determination of centre of mass, of statical moments and moments of inertia of objects.

This MSc Thesis focuses on the collision detection between scene objects and consequent resolution of such collisions on the basis of physical model. The implementation of all the applications and algorithms is achieved in Win32 environment in Visual Studio using the programming language C++; it also employs the graphical library Open Inventor based on OpenGL. The work also includes additional application for the calculation of physical values. The demo applications involve algorithms for detection and resolution of explosive collision by the use of a simple and physical reflection on the basis of physical formulas and relationships. The main demo application called "tunnel transit" incorporates a simple game engine. The thesis also includes a discussion over the aroused problems with collision solving and some suggestions how to overcome them.