Gait assessments can help identify individuals at an elevated risk of falling. Gait variability and local dynamic stability (LDS) are considered the most valid measures to assess gait stability and predict gait-related falls. Specifically, LDS of the trunk is most often used to assess gait stability given its important contribution to the centre of mass and the ability to discriminate between fallers and non-fallers using its kinematics. Reliable wearable sensors can be implemented in real-world gait assessments to actively screen for fall risk. Instrumented insoles are an example of unobtrusive wearable technology that can perform accurate gait assessments in real-world settings; however, they have not been validated for gait stability assessments, and cannot directly measure trunk LDS. The purpose of this thesis was to develop a framework to estimate gait stability using instrumented insoles. Fifteen participants were recruited to walk on a treadmill for seven minutes at their preferred walking speed while wearing instrumented insoles and a full-body inertial measurement unit suit. The reliability of foot LDS calculated from instrumented insole data was evaluated against the inertial measurement unit suit using intraclass correlation coefficients. Trunk LDS, measured via the IMU suit, was then predicted by applying linear regressions to the insole-derived metrics. A simple linear regression was used to establish the base amount of variance in trunk LDS that could be explained by foot LDS. Subsequently, a multiple linear regression model consisting of the standard deviation of stride time, standard deviation of double support time, mean single support time, mean yaw variability, and median absolute deviation of yaw variability was used to estimate trunk LDS. Results show that instrumented insoles can reliably measure foot LDS (ICC₃,₁ = 0.860). Moreover, the multiple linear regression explained 47.7% more variance than the simple linear regression (adjusted R² of 0.845 versus 0.368). This thesis demonstrates that instrumented insoles are an appropriate measurement tool for foot stability and that they can be used to predict trunk LDS with good accuracy during gait.

Les modifications de la marche liées à la peur de chuter sont généralement classées comme des troubles du contrôle de la marche supraspinaux, dits « de haut niveau » car rapportées à une déficience dans le contrôle cortical de la marche. Il est maintenant bien établi que l’étude de la variation des caractéristiques du pas, et notamment celles du temps du pas, est un moyen d’appréhender la désorganisation du caractère automatique de la marche. En effet, la variabilité du temps du cycle de marche qui semble être un marqueur du contrôle cortical de la marche est inversement reliée à la stabilité de la marche.Très peu d’études se sont intéressées à l’association entre la variabilité du temps du cycle de marche et la peur de chuter chez la personne âgée. Ces études ont montré des résultats divergents principalement en raison de la non-prise en compte de potentiels facteurs de confusion. Le travail de thèse que nous présentons a pour objectif principal d’étudier l’association entre la variabilité de la marche et la peur de chuter chez des personnes âgées en tenant compte des potentiels facteurs pouvant influencer la relation entre ces deux variables, afin d’appréhender la relation de causalité qui peut les unir. Nos résultats montrent que la peur de chuter est associée significativement à une augmentation de la variabilité de la marche. En effet, la combinaison peur de chuter et antécédent de chutes augmente la variabilité du temps du cycle de marche. Cependant, l’effet de cette combinaison dépend du niveau de la vitesse de la marche. / Changes in gait performance related to fear of falling (FOF) are usually classified as supraspinal gait control disorders called “higher-level gait disorders” due to impairment in cortical gait control. It is now well established that the study of the variability in stride characteristics and in particular the variability of stride time, provide information on the impairment of the automatic character of gait. In fact, gait variability, which is a biomarker of higher-level gait disorders, is inversely related to gait stability. A limited number of studies have examined the association between FOF and higher stride time variability (STV), and have showed mixed results mainly due to the non-consideration of potential factors that may influence the relationship between STV and FOF. Thus, the main objective of this thesis was to examine the association between STV and FOF in elder people taking into account the potential factors influencing the relationship between these two variables.Our results show that FOF is significantly associated with an increase in STV. Indeed, the combination of FOF and history of previous falls increases STV. The adverse gait effect of this combination depends on the level of the walking speed.

Motion capture technology and Magnetic Resonance Imaging with Diffusion Tensor Imaging (MRI-DTI) were used in this work to detect subtle abnormalities in patients with mild traumatic brain injury (MTBI). A new concept, termed dynamic variability, is introduced in this work to quantify and localize gait variability. Three chronic MTBI patients were recruited from the Veterans Affair Medical Center in Iowa City, IA, and three healthy controls with height, weight, and gender matched to the patients were recruited from the Reserve Officers' Training Corps in Iowa City, IA. Kinematic and kinetic data of the subjects were collected during the performance of three gait testing scenarios. The first test involved single-task walking and was used as a baseline. The second and third tests were dual tasks that involved walking while performing a cognitive or motor task and were designed to magnify gait abnormalities. The results showed that MTBI patients had reduced gait velocity, shortened stride length, and larger step width; findings that are consistent with those published in the literature. The new dynamic variability factor found that, as compared to controls, MTBI patients had more variability in their hip and ankle joint moments. MRI-DTI has been used to detect dysfunction of the major white matter tracts in chronic MTBI patients; although, the sample size of this study was too small to detect a difference between the MTBI and control subjects. The imaging and gait abnormalities are suggestive of frontal lobe-white matter tracts dysfunction.

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Tidigare forskning har funnit samband mellan gång och kognitiv funktion, men sambandet mellan lindrig kognitiv svikt (MCI) och gång är inte helt klarlagt. Syftet med den föreliggande examensuppsatsen var således att undersöka hur gångvariabler och gångvariabilitet är påverkat hos personer med MCI i relation till kognitivt friska individer. Studien genomfördes i det pågående projektet the Healthy Ageing Initiative vid Umeå Universitet. Totalt 1937 personer inkluderades i studien. Samtliga var 70 år gamla och bosatta i Umeå kommun. Totalt 112 personer bedömdes ha MCI utifrån instrumentet Mini-Mental State Examination (MMSE). Gånganalys genomfördes med den elektroniska gångmattan GAITRite® system och deltagarna utförde fyra gångförsök: egenvald hastighet, snabb hastighet, kognitiv dual task och motorisk dual task. Resultatet visade att det finns skillnader mellan grupper vad gäller både spatiala och temporala aspekter, främst i de tre första försöken. Exempelvis uppvisade gruppen MCI lägre gånghastighet, kortare steg och kliv samt längre double support och kortare swing. Gruppen MCI uppvisade högre variabilitet under kognitiv dual task. Ett flertal gång- och variabilitets-variabler under kognitiv dual task kunde, enligt logistisk regression, predicera sannolikheten att ha MCI. Resultaten indikerar att gången hos de med MCI kan ge ökad fallrisk. / Previous research has found a connection between gait and cognitive function. However, the relationship between mild cognitive impairment (MCI) and gait has not been fully explored. Thus, the aim of this study was to examine how spatiotemporal gait parameters, and gait variability, are affected in people with MCI compared to cognitively healthy individuals (CHI). The study was carried out in cooperation with the Healthy Ageing Initiative research project, Umeå University, Sweden. A total of 1937 participants were included in the study. All participants were 70-years old and residents of the municipality Umeå. A total of 112 participants were classified as having MCI, as measured with the Mini-Mental State Examination (MMSE). Gait analysis was performed with the GAITRite® system, and participants performed four trials: preferred pace, fast pace, cognitive dual task and motor dual task. Results showed group differences in both spatial and temporal aspects of gait, especially during the first three trials. For example, participants with MCI walked more slowly, had shorter steps and strides, as well as a longer duration of the double support phase and lower duration of the swing phase. Participants with MCI revealed higher gait variability during cognitive dual task. Several of these variability variables, as well as spatiotemporal variables, could predict probability of having MCI, as seen through logistic regression. Results indicate that the gait observed in MCI could be related to a higher risk of falling.

Friedreich's Ataxia (FA) is an autosomal-recessive, neurodegenerative disease characterized by progressive lower extremity muscle weakness and sensory loss, balance deficits, limb and gait ataxia, and dysarthria. FA is considered a sensory ataxia because the dorsal root ganglia and spinal cord dorsal columns are involved early in the disease, whereas the cerebellum is affected later. Balance deficits and gait ataxia are often evaluated clinically and in research using clinical rating scales. Recently, quantitative tools such as the Biodex Balance System SD and the GAITRite Walkway System have become available to objectively assess balance and gait, respectively. However, there are limited studies using instrumented measures to quantitatively assess and characterize balance and gait disturbances in FA, and longitudinal, quantitative analyses of both balance and gait have not been investigated in this patient cohort. The purpose of the present study was to characterize gait patterns of adults with FA and to identify changes in gait and balance over time using clinical rating scales and quantitative measures. Additionally, this study investigated the relationship between disease duration, clinical rating scale scores and objective measures of gait and balance. This study used a longitudinal research design to investigate changes in balance and gait in 8 adults with genetically confirmed FA and 8 healthy controls matched for gender, age, height, and weight. Subjects with FA were evaluated using the Berg Balance Scale (BBS), the Friedreich's Ataxia Rating Scale (FARS) and instrumented gait and balance measures at baseline, 6 months, 12 months and 24 months. Controls underwent the same tests at baseline and 12 months. Gait parameters were measured utilizing the GAITRite Walkway system with a focus on gait velocity, cadence, step and stride lengths, step and stride length variability and percent of the gait cycle in swing, stance and double limb support. Balance was assessed using the BBS and the Biodex Balance System; the latter included tests of postural stability and limits of stability. At baseline, there were significant differences in gait and balance parameters, BBS scores and FARS total scores between FA subjects and controls as determined using paired t-tests (p This is the first longitudinal study to demonstrate changes over time in gait and balance of adults with FA using both quantitative measures and clinical rating scales. This study provided a detailed characterization of the gait pattern and balance of adults with FA. The GAITRite Walkway system proved to be a sensitive measure, and able to detect subtle changes in gait parameters over time in adults with FA. In addition, the BBS was an appropriate and sensitive assessment to detect changes in static and dynamic balance in this patient cohort. Finally, results revealed a strong and consistent relationship between clinical rating scale scores, postural stability indices, limits of stability scores, and step and stride length variability in individuals with FA.

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.