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 problèmes liés à l'équilibre sont diagnostiqués à l'aide de systèmes de cartographies des pressions plantaires ou de plateformes de force mesurant le déplacement du centre de pressions. Ces systèmes professionnels sont restreints à une utilisation en milieu médical, et on constate qu'aucun dispositif de surveillance de l'équilibre ne donne entière satisfaction en termes de mobilité et d'acceptabilité. Dans le contexte de la télémédecine et de l'e-santé, notre objectif a consisté à développer des outils pour la surveillance ambulatoire de l'équilibre postural, et contribuer à la compréhension du contrôle de l'équilibre. Nous avons d'abord entrepris une étude théorique de la faisabilité de la mesure des pressions plantaires et du déplacement dynamique du centre de pression, à partir d'un nombre très réduit de capteurs. Nous avons proposé pour cela un modèle mécanique simplifié du pied, ainsi que les hypothèses spécifiques à ces applications. Le modèle décrit la relation physique entre la posture du pied et la répartition des pressions plantaires suivant ses caractéristiques biomécaniques. Sur la base d'un prototype de semelle instrumentée à 3 capteurs uniquement, nous avons vérifié expérimentalement la capacité du système et des méthodes à générer le stabilogramme et les cartographies de pressions plantaires. Ceux-ci ont été comparés à un système matriciel de référence, et caractérisés en termes d'incertitude dans le cas du pied normal en position debout et durant la marche. Les stabilogrammes ainsi mesurés peuvent être analysés pour caractériser la signature de l'équilibre. Nous proposons un modèle spécifique à trois dimensions, décrivant la dynamique de l'équilibre et permettant d'identifier, par simulation, les principaux paramètres physiologiques qui assurent le maintien de l'équilibre postural. / Problems of balance are often diagnosed thanks to plantar pressure cartography systems or forces platform that measure the center of pressure displacement. These professional systems are restricted in use to medical environments, and until now, the balance monitoring systems do not offer complete satisfaction in terms of mobility and acceptability. In order to overcome these limitation and in the context of telemedicine and e-health, we aimed to develop tools for ambulatory monitoring of postural equilibrium and to understand the balance control. We have first undertaken a theoretical study on the feasibility of measuring plantar pressure and dynamic displacement of the center of pressure, from a very small number of sensors. For these applications, we have proposed a simplified mechanical foot model, as well as related assumptions. The model describes the physical relationship between foot posture and distribution of plantar pressures following its biomechanical characteristics. Based on a prototype of an instrumented insole with only 3 sensors, we have verified experimentally the ability of the system and the methods to generate both the stabilogram and the plantar pressure maps. Comparison is made with a matrix reference system, and characterization in terms of uncertainty in the case of normal foot in standing position and during walking is detailed. The measured stabilogram can be analyzed to characterize the signature of balance. We have also proposed a specific three-dimensional model describing the dynamics of balance. Based on simulation, it leads to identify the main physiological parameters related to balance control.