Thesis (M.Sc.)--University of British Columbia, 2005. / Includes bibliographical references.

Comme l'indiquent les divergences observées dans la littérature, la question de l'existence d'une modification du contrôle proprioceptif du mouvement au cours du vieillissement physiologique de l'adulte fait encore débat. Pour mieux comprendre ces divergences, trois études ont été réalisées afin de tester les effets de contraintes d'origines musculaire, attentionnelle et temporelle sur le contrôle proprioceptif du mouvement. La tâche commune à ces trois études était une tâche d'estimation active directe controlatérale de la position de la cheville. Les effets de contraintes musculaire, cognitive et temporelle sur les performances de contrôle proprioceptif ont été respectivement testés dans les conditions de fatigue et non fatigue, de simple et double tâche, et de vitesses libre et rapide. Pour évaluer la performance de contrôle proprioceptif, les erreurs totale, variable et constante ainsi que des variables temporelles et cinématiques ont été analysées. Chez les participants jeunes, les résultats de la première étude ont montré que la fatigue musculaire altère la performance d'estimation de position lorsque la cheville de référence est maintenue activement en position mais pas lorsqu'elle est maintenue passivement. Afin d’éviter de confondre un effet de la fatigue musculaire éventuellement induite par la répétition de la tâche d'estimation de position, les deuxième et troisième études ont été réalisées avec la référence maintenue passivement en position. Les résultats de ces deux études ont montré qu'en l'absence de contraintes cognitive et temporelle, la performance de positionnement final dans la tâche proprioceptive est comparable entre les adultes jeunes et âgés. Cependant, la stratégie utilisée pour atteindre cette position est différente selon l'âge. Les résultats ont également montré que l'adjonction d'une contrainte cognitive ou temporelle produit une dégradation de la performance de contrôle proprioceptif des adultes âgés par rapport aux adultes jeunes. Dans l’ensemble, ces résultats montrent que la capacité des adultes âgés à résoudre les problèmes posés par les contraintes environnementales est inférieure à celle des adultes jeunes et mettent en évidence la modification de contrôle proprioceptif du mouvement qui s'opère au cours du vieillissement physiologique. / As outlined by strong and unexplained discrepancies in the literature, whether proprioceptive control of movement is altered in physiological adult ageing is still under debate. In an attempt to unify these previous results, the three studies of the present thesis proposed to test the effects of muscle, attentional and temporal stresses on the proprioceptive control of movement, respectively. The common task of these three studies was an ankle contralateral concurrent matching task. To test the effects of muscle, cognitive and temporal stresses on the proprioceptive control performance of older and young adults, participants performed the matching task in fatigue and no-fatigue, single and dual task, and self-paced and fast speed conditions, respectively. To assess participants' proprioceptive performance, error, temporal and kinematic variables were analysed. The results of the first study showed that performance in the matching task was altered by muscle fatigue only when the reference was actively maintained. To avoid confounding fatigue effects with other effects, the second and third studies assessed the matching task with a reference passively maintained. The results of these studies first showed that end-point performance in the matching task was similar in young and older adults in the absence of cognitive and temporal stress. However, the strategies the participants used to reach the end-point position were different in young and older adults. Second, the addition of a cognitive or temporal stress degraded the proprioceptive control performance in older adults as compared to the young ones. Taken together, these results emphasize a decreased resilience to stressors in older adults as compared to young ones and highlight the age-related alteration in proprioceptive control of movement.

No description available.

No description available.

Thesis (PhDPhysiotherapy)--University of South Australia, 2002

Thesis (PhDPhysiotherapy)--University of South Australia, 2002

This thesis investigates the processes of human postural control. How do we keep still? In any action, the force required changes with limb position. This force-position relationship is elastic stiffness. Holding a desired posture requires muscle activation that accounts for this load property. The studies here examine the physiological processes of postural control as elastic stiffness changes. Psychophysical studies show that thresholds for detecting differences in load stiffness are large relative to those normally encountered. To discriminate stiffness, subjects made consistent movements and judged the force required and detection thresholds followed rules for force perception. For the purposes of postural control, stiffness per se is not a variable of primary interest. The effects of load stiffness on postural stability were investigated using a pendulum that allowed independent control of load force and stiffness. Postural stability varied with load stiffness and this effect was independent of load force. Performance deteriorated as load stiffness became more negative. Load-dependent changes were at low frequencies only, suggesting neural processes operating at long latency, and perhaps ???volitional??? tracking, are the key to postural control. Imposed perturbations evoke patterns of muscle activation reflecting the state of the neural pathways of postural control. Stretch responses obtained while subjects held different loads show that the short-latency spinal reflex and the long-latency functional reflex in the active flexor muscle are unaffected by load stiffness. However, a stereotyped response observed after stretch-reflex latency varied systematically with load stiffness, as did reciprocal activation of the antagonist extensor muscle. The long-latency reflex appears to be a part of a coordinated reciprocal response of antagonist muscle pairs. Adapting to load properties involves modulating these later neural responses. A method was developed, based on ultrasound, to track changes in muscle and tendon length associated with small postural movements. The relationship between wrist angle and muscle and tendon length in the active muscle changed with load stiffness. Particularly with negative-stiffness loads, the wrist moves on the end of a compliant tendon without corresponding changes in muscle length. Thus, compensation of postural performance by neural modulation is limited by the properties of muscle and tendon.

This thesis investigates the processes of human postural control. How do we keep still? In any action, the force required changes with limb position. This force-position relationship is elastic stiffness. Holding a desired posture requires muscle activation that accounts for this load property. The studies here examine the physiological processes of postural control as elastic stiffness changes. Psychophysical studies show that thresholds for detecting differences in load stiffness are large relative to those normally encountered. To discriminate stiffness, subjects made consistent movements and judged the force required and detection thresholds followed rules for force perception. For the purposes of postural control, stiffness per se is not a variable of primary interest. The effects of load stiffness on postural stability were investigated using a pendulum that allowed independent control of load force and stiffness. Postural stability varied with load stiffness and this effect was independent of load force. Performance deteriorated as load stiffness became more negative. Load-dependent changes were at low frequencies only, suggesting neural processes operating at long latency, and perhaps ???volitional??? tracking, are the key to postural control. Imposed perturbations evoke patterns of muscle activation reflecting the state of the neural pathways of postural control. Stretch responses obtained while subjects held different loads show that the short-latency spinal reflex and the long-latency functional reflex in the active flexor muscle are unaffected by load stiffness. However, a stereotyped response observed after stretch-reflex latency varied systematically with load stiffness, as did reciprocal activation of the antagonist extensor muscle. The long-latency reflex appears to be a part of a coordinated reciprocal response of antagonist muscle pairs. Adapting to load properties involves modulating these later neural responses. A method was developed, based on ultrasound, to track changes in muscle and tendon length associated with small postural movements. The relationship between wrist angle and muscle and tendon length in the active muscle changed with load stiffness. Particularly with negative-stiffness loads, the wrist moves on the end of a compliant tendon without corresponding changes in muscle length. Thus, compensation of postural performance by neural modulation is limited by the properties of muscle and tendon.

This thesis investigates the processes of human postural control. How do we keep still? In any action, the force required changes with limb position. This force-position relationship is elastic stiffness. Holding a desired posture requires muscle activation that accounts for this load property. The studies here examine the physiological processes of postural control as elastic stiffness changes. Psychophysical studies show that thresholds for detecting differences in load stiffness are large relative to those normally encountered. To discriminate stiffness, subjects made consistent movements and judged the force required and detection thresholds followed rules for force perception. For the purposes of postural control, stiffness per se is not a variable of primary interest. The effects of load stiffness on postural stability were investigated using a pendulum that allowed independent control of load force and stiffness. Postural stability varied with load stiffness and this effect was independent of load force. Performance deteriorated as load stiffness became more negative. Load-dependent changes were at low frequencies only, suggesting neural processes operating at long latency, and perhaps ???volitional??? tracking, are the key to postural control. Imposed perturbations evoke patterns of muscle activation reflecting the state of the neural pathways of postural control. Stretch responses obtained while subjects held different loads show that the short-latency spinal reflex and the long-latency functional reflex in the active flexor muscle are unaffected by load stiffness. However, a stereotyped response observed after stretch-reflex latency varied systematically with load stiffness, as did reciprocal activation of the antagonist extensor muscle. The long-latency reflex appears to be a part of a coordinated reciprocal response of antagonist muscle pairs. Adapting to load properties involves modulating these later neural responses. A method was developed, based on ultrasound, to track changes in muscle and tendon length associated with small postural movements. The relationship between wrist angle and muscle and tendon length in the active muscle changed with load stiffness. Particularly with negative-stiffness loads, the wrist moves on the end of a compliant tendon without corresponding changes in muscle length. Thus, compensation of postural performance by neural modulation is limited by the properties of muscle and tendon.

Thesis (M.S.)--Indiana University, 2006. / Includes bibliographical references.