Gait stability in older persons: Development of methods to assess structural instabilities in gait dynamics
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Gait instabilities in older persons are considered as a risk factor for falls during walking. Walking consists of both a single and a double support phase within each stride cycle and the age-related changes in both gait kinematics and weight transfer is phase-dependent. However, none of the gait stability measures suggested in the literature is able to indicate intra-stride changes in gait stability. One of the gait stability measures considered to be most valid is called local dynamical stability. Local dynamical stability is numerically defined by the reaction of the gait dynamics to a small perturbation. Local dynamical stability assumes that the structure of the gait dynamics does not change according to transitions between single and double support phase. However, models of the gait dynamics of the single and double support phases define structurally different gait dynamics for these phases. The aim of the present thesis is therefore to develop and assess the intra-stride changes in structure and local dynamical stability of the gait dynamics of young and healthy older adults for different gait speeds. The results indicated that both the structure and local dynamical stability had a characteristic change within the stride cycle for both young and healthy older adults and across different gait speeds. The gait dynamics of the older persons decoupled more in unloading of the stance leg during the double support phase making the gait kinematics more local dynamically unstable in this particular phase compared with the young persons. The suggested assessment of intra-stride changes in the structure and intrinsic stability properties of the gait dynamics introduces more detailed measures of gait stability able to identify changes in the gait stability in particular phases of the stride cycle. These measures might be of value for early fall risk detection and detection of gait impairments in older persons and patients with neurodegenerative diseases.