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<p>Few studies have shown the process of adaptation in muscle activity and joint angle during prolonged repetitive work. Fifteen healthy men performed 1 minute cycles of automotive-related tasks, which included a finger pull, knob turn, drill press and hose connector push. The experiment occurred on two days, separated by 24 hours. Day 1 required 61 cycles, with 5 cycles on day 2. Electromyography and kinematics of the upper extremity were analyzed at 12-minute intervals. Time to complete work cycle decreased by 6.3 s at the end of day 1 and 5.3 s on day 2. Peak EMG decreased for triceps brachii (TB), anterior deltoid (AD) and infraspinatus (IN) during work cycle, TB (finger pull), biceps brachii (BB), TB, AD, middle deltoid (MD) and IN during the hose insertion task. Peak EMG increased for MD and IN during the drill task. Mean EMG decreased for MD (work cycle), BB (hose insertion) and AD (finger pull), while MD and IN increased (drill task) and upper trapezius increased during the work cycle. EMG COV decreased for TB, AD, posterior deltoid and IN during the work cycle, TB during the finger pull task and AD during the hose insertion task. COV increased for BB during the work cycle, AD during the finger pull and for BB and lower trapezius during the drill press. Peak shoulder flexion decreased by 7.0° during the work cycle. Perceived discomfort increased by 1.2 units. This thesis found adaptations to highly repetitive but light work in only one hour, some of these changes persisted through the next day suggesting an adaptive process. This thesis is one of the first to examine adaptations to a highly repetitive simulated assembly work and has provided new insights into the evaluation of repetitive jobs as a whole and as isolated subtasks.</p> / Master of Science in Kinesiology

No-vision walking is supported in the central nervous system (CNS) by a spatial updating process. This process involves the iterative updating of a mental representation of the environment using estimates of distance traveled gleaned from locomotive kinematic activity. An effective means of examining the online regulation of this process is a continuous pointing task, which requires performers to walk along a straight-line forward trajectory while keeping their right arm straight and index finger fixated on a stationary ground-level target beside the walking path. In the current thesis, no-vision continuous pointing was examined in typically calibrated and recalibrated perceptual-motor states. Shoulder and trunk joint angles provided the basis for perceptual measures that reflected spatial updating performance and kinematic measures that reflected its underlying CNS online regulation. In the typically calibrated conditions, no-vision walking demonstrated a slight perceptual underestimation of distance traveled (Study 1). In the recalibrated conditions, no-vision walking demonstrated: a) perceptual underestimation and overestimation following adaptation periods involving walking with low and high visual gains, respectively (Study 2); and b) partial recalibration following exposures to vision and arm gains (Study 3). The latter was suggested as being impacted by task specific changes in CNS multisensory integration resulting from the development of a robust task prior and/or the altering of sensory cue weights. Importantly, this thesis used a novel trajectory parsing procedure to quantify discrete CNS perceptual updating units in the shoulder plane of elevation trajectory. The starts and ends of these updating units were consistently timed to the late left-to-early right foot swing phase of the step-cycle, regardless of perceptual-motor state. This was suggested to reflect perceptual units that were purposely timed, but indirectly mapped, to this kinematic event. The perceptual differences in Studies 1 and 2 were at least partially reflected in these units. / Thesis / Doctor of Philosophy (PhD) / It is well understood that humans can effectively walk without vision to environmental locations up to 15 metres away. However, less is known about how these walking movements are controlled during the course of forward progression. This thesis fills this knowledge gap using a task that requires participants to walk forward along a straight path while keeping their right index finger pointed toward a ground-level target beside the walking path. The patterns of arm movements performed during this task are indicative of the control strategies used by the performer to mentally update their positions in space. One of the key contributions of this work is showing that humans perform this mental updating in a repetitive manner, and that these repetitions are consistently linked to early forward movements of the right leg. This pattern is maintained when walking without vision is performed in a variety of different contexts.

Closer attention has been given to the acoustic noise performance of electric motors as electrified powertrains penetrate into the transportation system. Particularly, switched reluctance machines (SRMs) introduce a new challenge to the acoustic noise aspects given that the radial force harmonics can excite the natural frequencies of the main circumferential modes. A practical understanding of the radial force density decomposition is crucial in identifying the primary source of acoustic noise at different operating points, and it is one of the contributions of this thesis. An analytical expression is introduced to identify the temporal harmonic orders that excite different spatial mode shapes. The mode excitation is investigated along with the sound pressure level (SPL) produced by the primary vibrating mode shapes. Acoustic noise characteristics for each mode and the corresponding natural frequency at different speeds have been analyzed by using a waterfall plot. The acoustic noise generation by conventionally controlled SRMs prevents its use on applications where acoustic comfort is required. Acoustic noise is radiated by the stator frame when a vibration mode is excited by the respective spatial order at a forcing frequency that is close to the stator's modal natural frequency. The excitation surface wave is the radial force density waveform as a function of time and spatial position. From the harmonic content analysis, a phase radial force shaping method is for switched reluctance machines is proposed. A generic function for the radial force shape is identified, whose parameters are calculated by an optimization algorithm to minimize the torque ripple for a given average torque. From the phase radial force, a current reference is obtained. The proposed methodology is experimentally validated, with a four-phase 8/6 SRM, by acoustic noise measurements at different speeds and load torque conditions. / Thesis / Doctor of Philosophy (PhD)