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Objectives: Determine the effect of contraction type and intensity, inertial loading, and visual feedback on various measures of hand tremor in subjects with essential tremor. Methods: Study 1. Twenty-three ET subjects and 22 controls held their hand in an outstretched position while supporting various submaximal loads (no-load, 5%, 15% and 25% 1-repetition maximum). Hand postural tremor and wrist extensor neuromuscular activity (EMG) were recorded. Study 2. Twenty-one ET subjects and 22 controls applied isometric wrist extension contractions with and without visual feedback. Various submaximal contraction intensities were evaluated (5%, 10%, 20% and 30% MVC). Force production and EMG were recorded. Study 3. Twenty-one ET subjects and 22 healthy controls performed slow wrist extension-flexion movements while supporting various submaximal loads (no-load, 5%, 15% and 25% 1-repetition maximum). Angular displacement and EMG were recorded. Results: Study 1. Inertial loading resulted in a reduction in postural tremor in ET subjects. The largest reduction in tremor amplitude occurred at the 15% load, which was associated with spectral separation of the mechanical reflex and central tremor component. Despite an increase in overall neuromuscular activity with inertial loading, EMG tremor power did not increase with loading. Study 2. Higher contraction intensities were associated with larger amplitude force fluctuations and greater EMG amplitudes. Tremor spectral power of force and EMG remained constant at all target intensities, resulting in a reduction in relative tremor power at higher contraction intensities. Visual feedback affected subjects in the control and ET groups similarly. Study 3. Subjects with more pronounced tremor spectral peaks had larger amplitude kinetic tremor, which was reduced with inertial loading. Despite an increase in overall neuromuscular activity with inertial loading, EMG tremor spectral power was only slightly increased with loading, which resulted in a large reduction in relative EMG tremor power. Conclusions: The effect of inertial loading on postural and kinetic tremor amplitude appears to be mediated in large part by its effect on the interaction between the mechanical reflex and central tremor components. The level of motor unit entrainment remains relatively constant in subjects with ET despite increasing contraction intensities. / Thesis (Ph.D, Rehabilitation Science) -- Queen's University, 2008-10-24 11:18:57.537

Körperlich aktiv zu sein ist Grundlage unseres täglichen Lebens. Für alle diese Aktivitäten ist das kontinuierliche Zusammenspiel des senso-motorischen System (SMS) erforderlich. Die Kontrolle der verschiedenen afferenten und efferenten Subsysteme innerhalb des SMS basiert auf Feedback-Mechanismen, die die Aufrechterhaltung des Gleichgewichts und der Stabilität während den verschiedensten statischen als auch dynamischen Aktivitäten ermöglichen. Trotz dieser Kontroll- und Stabilisierungssystems ist das kinematische und kinetische Resultat nicht konstant; stattdessen ist bei globalen „Ganzkörper-Bewegungen“, und lokaler Muskelanspannung ständig eine gewisse Variabilität vorhanden. Die Interpretation dieser Variabilität bei Bewegungshandlungen ist kontrovers. Wobei große Variabilität ist nicht zwangsläufig ein Indikator für Defizite des SMS darstellt. Das Ziel dieser Dissertation war, die Variabilität bei lokalen und globalen Bewegungshandlungen in statischen und dynamischen Ausgangstellungen zu quantifizieren. Darüberhinaus, wurde der Zusammenhang zwischen lokaler Variabilität der Muskelkraftproduktion und der Variabilität bei globalen Bewegungshandlungen. Die Ergebnisse zeigen, dass lokale und globale Variabilität von Bewegungshandlungen in Menge und Muster verändert sind, nach Störung des SMS durch: Ermüdung, Veränderungen der Umfeldbedingungen, Alterung und bei Personen mit Sturzerfahrung. Außerdem wurde gezeigt, dass sowohl zu große als auch zu kleine Variabilität, ein entscheidendes funktionelles Defizit bei älteren Personen darstellt. Dieser Dissertation hebt die Bedeutung der Variabilität während wiederholter Bewegungshandlungen hervor, welche einen funktionellen Biomarker für die Beurteilung von Bewegungsstörungen darstellt. In der klinische Praxis könnte dieser helfen bei der frühen Identifikation von Personen mit Bewegungsstörungen, zur Entwicklung von individual-spezifischen Rehabilitationsmaßnahmen, sowie der Beurteilung verschiedener Therapieansätze. / Undertaking activities is fundamental throughout daily living. In order to successfully perform these activities, continuous involvement of the human sensori-motor system (HSMS) is required. The HSMS involves feedback mechanisms to control numerous afferent and the efferent subsystems to ensure maintenance of balance and stability during both static and dynamic activities. Despite such control and stabilizing mechanisms, the kinematic and kinetic output of a task is not constant; instead variability occurs during continuous performance of both global tasks such as standing and walking, as well as local force production. The interpretation of variability during output task performance remains controversial, with larger levels of variability not always indicating deficits in human-motor performance. The aim of this dissertation was to assess variability during local as well as global task performance in static and dynamic settings. Furthermore, the association between the level of variability during local force production and variability during global tasks such as standing and walking was also investigated. The results within this dissertation showed that variability during task performance is modified in magnitude as well as in structure after perturbation due to fatigue, changes in environmental conditions, and aging, as well as in fall-prone elderly individuals. Furthermore, both high as well as low levels of variation constitute a key functional deficit among elderly individuals. This dissertation highlights the importance of considering trial-to-trial variations during continuous task performance as a key functional biomarker for motor-related pathologies. Effective assessment of such measures of variability in clinical settings could effectively complement current clinical practice for both early and effective identification of individuals with motor-related pathology, designing subject-specific rehabilitation programs, and evaluating therapy efficacy.