UBC Theses and Dissertations
Head acceleration during balance Roskell, Melanie
The overall purpose of this thesis was to study the angular and linear accelerations that occur at the head during quiet standing in healthy humans. To date, there were few descriptions of linear head accelerations in quiet standing, and no focus on angular head accelerations. The contribution of the vestibular system to standing balance can be better understood from recognizing these, the stimuli that the system experiences during the task. Head accelerations were measured under four manipulations of sensory condition, and RMS and median frequency values were reported for linear and angular head accelerations in Reid’s planes. Coherence was also calculated between force plate forces and head accelerations, and between lower leg EMG and angular head accelerations in the directions of the semi-circular canals. This study considered two factors in the manipulation of quiet standing sway: vision (eyes open/closed) and surface (hard/compliant foam). The results show that angular head accelerations are repeatable under full sensory conditions, and that angular head acceleration RMS is above known vestibular thresholds in all tested sensory conditions. Linear head acceleration absolute maximum and RMS values matched previous reports under similar conditions. Significant coherence was found below 7Hz in both coherence analyses, likely due to the mechanical linkage. This coherence also showed defined troughs in varying regions, which were attributed to the interference of active systems (visual, somatosensory and vestibular) on the mechanical propagation of forces. The results also reinforced that the inverted pendulum model is valid in quiet standing on a hard surface in the sagittal and frontal planes. This study shows that the vestibular system is able to detect sway at the head during quiet standing under all four sensory conditions tested. Consequently, the vestibular system may play a range of roles in quiet standing, which may change as its relative importance in balance increases. The measurement of head accelerations is confirmed as a useful technique in studying balance in quietly standing humans.
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